Nghv Notes

SRIRAM Engineering College, Chennai – 602 024. Department of Automobile Engineering

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AU2029 NEW GENERATION AND HYBRID VEHICLES L T P C 3 0 0 3 OBJECTVE To illustrate the new generation vehicles and their operation and controls UNIT I INTRODUCTION 7 Electric and hybrid vehicles, flexible fuel vehicles (FFV), solar powered vehicles, magnetic track vehicles, fuel cells vehicles. UNIT II POWER SYSTRM AND NEW GENERATION VEHICLES 12 Hybrid Vehicle engines, Stratified charge engines, learn burn engines, low heat rejection engines, hydrogen engines, HCCI engine, VCR engine, surface ignition engines, VVTI engines. High energy and power density batteries, fuel cells, solar panels, flexible fuel systems. UNIT III VEHICLE OPERATION AND CONTROL 9 Computer Control for pollution and noise control and for fuel economy – Transducers and actuators - Information technology for receiving proper information and operation of the vehicle like optimum speed and direction. UNIT IV VEHICLE AUTOMATED TRACKS 9 Preparation and maintenance of proper road network - National highway network with automated roads and vehicles - Satellite control of vehicle operation for safe and fast travel, GPS. UNIT V SUSPENSION, BRAKES, AERODYNAMICS AND SAFETY 8 Air suspension – Closed loop suspension, compensated suspension, anti skid braking system, retarders, regenerative braking, safety gauge air backs- crash resistance. Aerodynamics for modern vehicles, safety systems, materials and standards. TOTAL: 45 PERIODS TEXT BOOKS 1. Modern Vehicle Technology by Heinz. 2. Bosch Hand Book, SAE Publication,, 2000 REFERENCES 1. Light weight electric for hybrid vehicle design. 2. Advance hybrid vehicle power transmission, SAE. 3. Noise reduction, Branek L.L., McGraw Hill Book company, New York, 1993.


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CHAPTER I

INTRODUCTION

1.1 ELECTRIC VEHICLE

An electric vehicle (EV), also referred to as an electric drive vehicle, uses one or more electric motors or traction motors for propulsion. Three main types of electric vehicles exist, those that are directly powered from an external power station, those that are powered by stored electricity originally from an external power source, and those that are powered by an on-board electrical generator, such as an engine (a hybrid electric vehicle), or a hydrogen fuel cell.[1]Electric vehicles include electric cars, electric trains, electric lorries, electric aeroplanes, electric boats, electric motorcycles and scooters and electric spacecraft.

Electric vehicles first came into existence in the mid-19th century, when electricity was among the preferred methods for motor vehicle propulsion, providing a level of comfort and ease of operation that could not be achieved by the gasoline cars of the time. The internal combustion engine (ICE) is the dominant propulsion method for motor vehicles but electric power has remained commonplace in other vehicle types, such as trains and smaller vehicles of all types.

During the last few decades, environmental impact of the petroleum-based transportation infrastructure, along with the peak oil, has led to renewed interest in an electric transportation infrastructure. Electric vehicles differ from fossil fuel-powered vehicles in that the electricity they consume can be generated from a wide range of sources, including fossil fuels, nuclear power, and renewable sources such as tidal power, solar power, and wind power or any combination of those. Currently though there are more than 400 coal power plants in the U.S. alone. However it is generated, this energy is then transmitted to the vehicle through use of overhead lines, wireless energy transfer such as inductive charging, or a direct connection through an electrical cable. The electricity may then be stored on board the vehicle using a battery, flywheel, or super capacitors. Vehicles making use of engines working on the principle of combustion can usually only derive their energy from a single or a few sources, usually non-renewable fossil fuels. A key advantage of electric or hybrid electric vehicles is regenerative braking and suspension; their ability to recover energy normally lost during braking as electricity to be restored to the on-board battery.


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Schematic shows the difference between conventional internal combustion engines, hybrid electric vehicle

A ground vehicle propelled by a motor that is powered by electrical energy from rechargeable batteries or other source onboard the vehicle, or from an external source in, on, or above the roadway. Examples are the golf cart, industrial truck and tractor, automobile, delivery van and other on-highway truck, and trolley bus. In common usage, electric vehicle refers to an automotive vehicle in which the propulsion system converts electrical energy stored chemically in a battery into mechanical energy to move the vehicle. This is classed as a battery-only-powered electric vehicle. The other major class is the hybrid-electric vehicle, which has more than one power source. See also: Automobile; Bus; Truck

Construction of the first electric vehicle is credited to the French inventor and electrical engineer M. Gustave Trouvé, who demonstrated a motorized tricycle powered by lead-acid batteries in 1881. In the United States, Andrew L. Riker is credited with building the first electric vehicle (also a tricycle) in 1890, and by 1891 William Morrison had built the first electric four-wheeler. In France in 1899, a four-wheel electric vehicle driven by Camille Jenatzy became the first car to break 60 mi/h (96 km/h). By then, production of battery-powered vehicles for use as personal transportation, commercial trucks, and buses had already begun.

Electric vehicles, with their instant starting, quiet running, and ease of operation, peaked in their challenge to steam- and gasoline-powered cars in 1912. The limited performance, range, and speed of electric vehicles, plus the need for frequent battery


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charging, restricted their usefulness and dampened their popularity. By the 1920s, the piston-type internal combustion engine had prevailed as the dominant automotive power plant. Most production and development work on electric vehicles ended during the 1930s.

In the 1960s, interest revived in electric vehicles as a result of concern with diminishing petroleum reserves, rising cost of crude oil production, and air pollution from the automotive engine that burned gasoline which was refined from crude oil. Over the years, a few electric vehicles had been constructed, usually by converting small light cars and trucks into electric vehicles by removing the engine and fuel tank and installing an electric motor, controls, and batteries. However, during that time no major automotive manufacturer brought out an electric vehicle. See also: Air pollution; Gasoline; Petroleum

The Clean Air Act of 1963 and its amendments established limits on emissions from new vehicles sold in the United States. In 1990, the California Air Resources Board decided to further reduce air pollution by mandating ( but later rescinding) that 2% of each automaker's sales must have zero emissions in the 1998 model year. This demand for a zero-emission vehicle (ZEV) could be met only by the electric vehicle, which typically was powered by lead-acid batteries. Used in an electric vehicle, lead-acid batteries have two major weaknesses: relatively high weight for the amount of energy stored, and reduced capacity in cold weather.

To help develop a better battery for electric vehicles, the U.S. Advanced Battery Consortium was formed in 1991. The purpose of this partnership among United States automakers and the electric utility industry was to develop advanced batteries capable of providing future generations of electric vehicles with significantly increased range and performance.

In 1996 General Motors began limited marketing of the electric vehicle EV1 (Fig. 1). The EV1 was the first specifically designed electric car produced by a major automaker since before World War II. Other automakers also have developed and tested electric vehicles and vehicle conversions powered by lead-acid or advanced batteries.


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Figure EV1, a two-seat electric vehicle powered by lead-acid batteries.

(General Motors Corp.)

Battery only power

The General Motors EV1 is a battery-only-powered vehicle containing 26 lead-acid batteries which are assembled into a T-shaped pack that provides a nominal voltage of 312 volts (Fig. 2). These batteries differ from 12-V automotive batteries primarily in duty cycle. In the electric vehicle, the batteries must supply all the energy needs. Except for regenerative braking, there is no onboard charging. The batteries provide the power to propel the vehicle, and to power the lights and all accessories such as air conditioning and radio. As a result, electric-vehicle batteries go through much deeper discharge cycles than an automotive battery, which seldom is discharged more than 5% of its rated capacity.


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Figure Power flows through a hybrid vehicle which uses a gasoline engine to propel the vehicle and drive a generator that cans opera te the electric motor directly or charge the

batteries, as necessary. (Toyota Motor Sales, U.S.A., Inc.)

Because of the increased duty cycle, electric-vehicle batteries can deliver 85% of their charge without damaging the batteries or shortening their useful life. Ideally, this could provide the EV1 and similar electric vehicles with a useful range of 70 mi (113 km) of city driving or 90 mi (145 km) of highway driving. A top speed of 80 mi/h (130 km/h) may be possible, but at a sacrifice in range, which also is shortened by hilly terrain and use of any electrical equipment on the vehicle.

In addition to lead-acid batteries, other batteries are used in electric vehicles. These include the newer nickel-metal hydride battery and the lithium-ion battery. Hybrid power

A hybrid electric vehicle has more than one source of power. These sources can be different types of energy storage devices, power converters, and inverters. The first hybrid vehicle is credited to an Italian, Count Felix Carli. In 1894, Carli constructed an electric-powered tricycle that had a system of rubber springs which could release a short burst of additional power when needed.


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Although power losses occur each time that energy is converted from one form to another, hybrid drive can be more efficient than a conventional automotive engine. However, having two or more power sources can increase the complexity, cost, and weight of a hybrid vehicle, as well as its manufacturing, safety, emissions, maintenance, and service problems. See also: Automotive engine Internal combustion engine

Since the 1890s, major hybrid-vehicle research and development work has focused on adding a small internal combustion engine to an electric vehicle. Typically, the battery-powered motor drives the wheels, while the engine, usually running at constant speed, drives a generator that charges the batteries. Operating the engine at constant speed reduces fuel consumption and produces cleaner exhaust gas than if the engine were larger, operating at variable speed, and providing the sole source of vehicle power.

In some hybrid vehicles, engine power is split (Fig. 2). Part of the engine power propels the vehicle, while part drives the generator which can operate the motor directly or charge the batteries, as necessary. Reportedly, engine exhaust emissions of hydrocarbons, carbon monoxide, and oxides of nitrogen are about 10% that of a conventional gasoline-engine vehicle. In addition, fuel efficiency is doubled.

In this electrochemical device, the reaction between a fuel, such as hydrogen, and an oxidant, such as oxygen or air, converts the chemical energy of the fuel directly into electrical energy. The fuel cell is not a battery and does not store energy, although the fuel cell also has two electrodes separated by an electrolyte. As long as fuel is supplied to one electrode of the fuel cell and oxygen or air to the other, a voltage is produced between the electrodes. When an external circuit connects the electrodes, electrons will flow through the external circuit. Since fuel-cell voltage is less than 1 V, stacks of fuel cells are connected together to provide the needed electrical energy.

When fuel cells are the primary power source in a hybrid vehicle, batteries provide secondary power. Fuel cells do not provide immediate output during a cold start. Until the fuel cells reach operating temperature, which may take about 5 min, a battery pack supplies the power for initial startup and vehicle movement. See also: Fuel cell; Hydrogen

Three types of fuel cell under development for electric vehicles are the hydrogen-fueled, the methanol-fueled, and the gasoline-fueled. (1) A hydrogen-fueled cell runs on


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hydrogen gas stored in pressure tanks carried by the vehicle. Range of the vehicle is determined by the amount of compressed hydrogen that the tanks can hold. When hydrogen is used as the fuel, fuel cell operation produces no significant amounts of unwanted emissions. Water vapor and electricity are the only products. However, widespread use of hydrogen as a near-term vehicle fuel is unlikely because there exists no infrastructure of hydrogen refueling stations which are in place and accessible to the public. (2) To provide the fuel cell with hydrogen gas while avoiding the problems of hydrogen refueling, a methanol-to-hydrogen reformer onboard the vehicle can produce hydrogen as from liquid methanol. Installed on production models, this would allow motorists to refuel vehicles in the conventional manner at existing service stations through any pump which dispensed methanol. However, use of a reformer to obtain hydrogen lowers vehicle efficiency and creates some emissions of carbon dioxide. A gasoline-to-hydrogen reformer on the vehicle can extract hydrogen gas from gasoline. The hydrogen is then delivered to the fuel cell stack (Fig. 3). Use of gasoline could move fuel cell technology years closer to production in automotive vehicles, while reportedly improving fuel efficiency by 50% and emissions by 90%.

Figure Layout and five-step process that produces electricity from gasoline, which

powers the fuel cells.


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1.2 HYBRID VEHICLES

Hybrid Electric Vehicles (HEV) are primarily propelled by an internal combustion engine, just like conventional vehicles. However, they also convert energy normally wasted during coasting and braking into electricity, which is stored in a battery until needed by the electric motor. The electric motor is used to assist the engine when accelerating or hill climbing and in low-speed driving conditions where internal combustion engines are least efficient. Unlike all-electric vehicles, HEVs now being offered do not need to be plugged into an external source of electricity to be recharged; conventional gasoline and regenerative braking provide all the energy the vehicle needs.

They combine the best features of the internal combustion engine with an electric

motor and can significantly improve fuel economy without sacrificing performance or driving range. HEVs may also be configured to provide electrical power to auxiliary loads such as power tools.

Modern HEVs make use of efficiency-improving technologies such

as regenerative braking, which converts the vehicle's kinetic energy into electric energy to charge the battery, rather than wasting it as heat energy in a conventional braking system. Many HEVs reduce idle emissions by shutting down the ICE at idle and restarting it when needed; this is known as a start-stop system.

Hybrids are classified by the division of power between sources; both sources may operate in parallel to simultaneously provide acceleration, or they may operate in series with one source exclusively providing the acceleration and the second being used to augment the first's power reserve. The sources can also be used in both series and parallel as needed, the vehicle being primarily driven by one source but the second capable of providing direct additional acceleration if required. Current hybrids use both an internal combustion (IC) engine and a battery/electric drive system (using ultra capacitors) to improve fuel consumption, emission, and performance. Electrically assisted pedal bicycles are a form of hybrid drive. Other combinations of energy storage and conversion are possible, although not yet in commercial production.

Combustion-electric hybrids have larger battery sets than what a normal combustion engine only vehicle would have. Battery and super capacitor technology is advancing.[1] A potential advantage is that when these battery sets require renewing in the future, the newer battery sets will be potentially superior having higher energy storage giving greater ranges enhancing a vehicle.


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Parallel Hybrid Electric Vehicle

Parallel hybrid systems, which are most commonly produced at present, have both an internal combustion engine (ICE) and an electric motor connected to a mechanical transmission. Most designs combine a large electrical generator and a motor into one unit, often located between the combustion engine and the transmission, replacing both the conventional starter motor and the alternator. To store power, a hybrid uses a large battery pack with a higher voltage than the normal automotive 12 volts. Accessories such as power steering and air conditioning are powered by electric motors instead of being attached to the combustion engine. This allows efficiency gains as the accessories can run at a constant speed, regardless of how fast the combustion engine is running.

Parallel hybrids can be categorized by the way the two sources of power are mechanically coupled. If they are joined at some axis truly in parallel, the speeds at this axis must be identical and the supplied torques adds together. Most electric bicycles are in effect of this type. When only one of the two sources is being used, the other must either also rotate in an idling manner or be connected by a one-way clutch or freewheel. With cars it is more usual to join the two sources through a differential gear. Thus the torques supplied must be the same and the speeds add up, the exact ratio depending on the differential characteristics. When only one of the two sources is being used, the other must still supply a large part of the torque or be fitted with a reverse one-way clutch or automatic clamp.

Parallel hybrids can be further categorized depending upon how balanced the different portions are at providing motive power. In some cases, the combustion engine is the dominant portion (the electric motor turns on only when a boost is needed) and vice versa. Others can run with just the electric system operating. But because current parallel hybrids are unable to provide all-electric (ICE=OFF) propulsion, they are often categorized as mild hybrids. Because parallel hybrids can use a smaller battery pack as they rely more on braking and the internal combustion engine can also act as a generator


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for supplemental recharging, they are more efficient on highway driving compared to urban stop-and-go conditions or city driving.

Vehicles incorporated with the Parallel Hybrid System

Honda's Insight, Civic, and Accord hybrids are examples of production parallel hybrids.[2] General Motors Parallel Hybrid Truck (PHT) and BAS Hybrids such as the Saturn VUE and Aura Green line and Chevrolet Malibu hybrids are also considered as utilizing a parallel architecture.

Series Hybrid Electric Vehicle

Series hybrids have also been referred to as range-extended electric vehicles (REEV) where they are designed to be run mostly by the battery, but have a petrol or diesel generator to recharge the battery when going on a long drive. However, range extension can be accomplished with either series or parallel hybrid layouts.

Series-hybrid vehicles are driven only by electric traction. Unlike piston internal combustion engines, electric motors are efficient with exceptionally high power to weight ratios providing adequate torque over a wide speed range. Unlike combustion engines electric motors matched to the vehicle do not require a transmission between the engine and wheels shifting torque ratios. Transmissions add weight, bulk and sap power from the engine. Mechanical automatic shifting transmissions can be very complex. In a series-hybrid system, the combustion engine drives an electric generator instead of directly driving the wheels. The generator provides power for the driving electric motors. In short, a series-hybrid is simple; the vehicle is driven by electric motors with a generator set providing the electric power.

A wheel hub motor arrangement, with a motor in each of the two front wheels was used, setting speed records. This arrangement was sometimes referred to as an electric transmission, as the electric generator and driving motor replaced a mechanical transmission. The vehicle could not move unless the internal combustion engine was running. The setup was difficult for production cars being unable to


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synchronize the electric driving motors with the generator set power, resulting in higher fuel consumption. No longer has an issue with modern computer engined optimizing when the generator runs to match the power needed. Electric motors have become substantially smaller, lighter and efficient over the years. These advances have given the advantage to the electric transmission in normal operating conditions, over a conventional internal combustion engine and mechanical automatic transmission. One of the advantages is the smoother progressive ride with no stepped gear ratio changes.

The electric transmission is currently viable in replacing the mechanical transmission. However, the modern series-hybrid vehicles take the electric transmission to a higher plane adding greater value.

There is a difference to an electric transmission. Modern series-hybrids contain:

• Electric traction only - using only one or more electric motors to turn the wheels.

• Combustion engine - that turns only a generator. • A generator - turned by the combustion engine to make up a generator set that

also acts as an engine starter. • A battery bank - which acts as an energy buffer. • Regenerative braking - Driving motor becomes a generator and recovers

potential and kinetic (inertial) energies through its conversion to electrical energy, a process which in turn is able to slow the vehicle and thus preventing wasteful transfer of this energy as thermal losses within the friction brakes.

• May be plugged into the electric mains system to recharge the battery bank. • May have supercapacitors to assist the battery bank and claw back most energy

from braking - only fitted in proven prototypes currently.

The electric driving motor may run entirely fed by electricity from a large battery bank or via the generator turned by the internal combustion engine, or both. The battery bank may be charged by mains electricity reducing running costs as the range running under the electric motors only is extended. The vehicle conceptually resembles a Diesel-electric locomotive with the addition of large battery bank that may power the vehicle without the internal combustion engine running. The generator may simultaneously charge the battery bank and power the driving electric motor that moves the vehicle. The battery bank acts as an energy buffer. An advantage is that when the vehicle is stopped the combustion engine is switched off. When the vehicle moves it does so using the energy in the batteries. This reduces kerbside emissions greatly in cities and towns. Vehicles at traffic lights or in slow moving stop start traffic need not be polluting when stationary.


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In some arrangements when high levels of power are required, such as in vehicle acceleration, the electric driving motor draws electricity from both the batteries and the generator. Because a series-hybrid omits a mechanical link between the combustion engine and the wheels, the engine can be run at a constant and efficient rate even as the vehicle changes speed. The vehicle speed and engine speed are not necessarily in synchronization. The engine can thus maintain efficiency closer to the theoretical limit of 37%, rather than the current average of 20%. At low or mixed speeds this could result in ~50% increase in overall efficiency.

There are stages of operation: power from the combustion engine to the generator and then to the electric motor and, depending on the design, may also run through the generator and into the battery pack then to the electric motor further reducing efficiency (see illustration). Each transformation through each stage results in a loss of energy. However in normal vehicle operating conditions the energy buffer of the battery bank, which stores clawed back energy from braking and the optimum running of the combustion engine may raise overall operating efficiency, despite each stage being an energy loss. The engine to mechanical automatic shifting transmission efficiency is approximately 70%-80%. A conventional mechanical clutch transmission has an engine to transmission efficiency of 98%. In a series-hybrid vehicle, during long-distance high speed highway driving, the combustion engine will need to supply the majority of the energy, in which case a series-hybrid may be 20%-30% less efficient than a parallel hybrid.

The use of a motor driving a wheel directly eliminates the conventional mechanical transmission elements: gearbox, transmission shafts and differential, and can sometimes eliminate flexible couplings. This offers great simplicity. If the motors are integrated into the wheels a disadvantage is that the unsprung mass increases and suspension responsiveness decreases which impacts ride performance and potentially safety. However the impact should be minimal if at all as electric motors in wheel hubs such as Hi-Pa Drive, may be very small and light having exceptionally high power to weight ratios. The braking mechanisms can be lighter as the wheel motors brake the vehicle. Light aluminum wheels may be used reducing the unsprung mass of the wheel assembly. Vehicle designs may be optimized to lower the center of gravity having the heavy mechanics and battery banks at floor level. If the motors are attached to the vehicle body, flexible couplings are still required. Advantages of individual wheel motors include simplified traction control and all wheel drive if required, allowing lower floors, which is useful for buses. Some 8x8 all-wheel drive military vehicles use individual wheel motors. Diesel-electric locomotives have used this concept (albeit with the individual motors driving axles connecting pairs of wheels) for 70 years.


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In a typical road vehicle the whole series-hybrid power-transmission setup may be smaller and lighter than the equivalent conventional mechanical power-transmission setup which liberates space. As the combustion generator set only requires cables to the driving electric motors, there is greater flexibility in major component layout spread across the vehicle giving superior weight distribution and maximizing vehicle cabin space. This flexibility may lead to superior vehicle designs.

Power-split or series-parallel hybrid +

Power-split hybrid or series-parallel hybrids are parallel hybrids. They incorporate power-split devices allowing for power paths from the engine to the wheels that can be either mechanical or electrical. The main principle behind this system is the decoupling of the power supplied by the engine (or other primary source) from the power demanded by the driver.

1.3 FLEXIBLE-FUEL VEHICLE (FFV)

Flexible-fuel vehicle (FFV) or dual-fuel vehicle (colloquially called a flex-fuel vehicle) is an alternative fuel vehicle with an internal combustion engine designed to run on more than one fuel, usually gasoline blended with either ethanol or methanol fuel, and both fuels are stored in the same common tank. Flex-fuel engines are capable of burning any proportion of the resulting blend in the combustion chamber as fuel injection and spark timing are adjusted automatically according to the actual blend detected by electronic sensors. Flex-fuel vehicles are distinguished from bi-fuel vehicles, where two fuels are stored in separate tanks and the engine runs on one fuel at a time, for example, compressed natural gas (CNG), liquefied petroleum gas (LPG), or hydrogen.

The most common commercially available FFV in the world market is the ethanol flexible-fuel vehicle, with 22.6 million automobiles, motorcycles and light duty trucks sold worldwide by 2010, and concentrated in four markets, Brazil (12.5 million), the United States (9.3 million), Canada (more than 600,000), and Europe, led by Sweden


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(216,975). The Brazilian flex fuel fleet includes 515,726 flexible-fuel motorcycles sold since 2009. In addition to flex-fuel vehicles running with ethanol, in Europe and the US, mainly in California, there have been successful test programs with methanol flex-fuel vehicles, known as M85 flex-fuel vehicles. There have been also successful tests using P-series fuels with E85 flex fuel vehicles, but as of June 2008, this fuel is not yet available to the general public.[10][11] These successful tests with P-series fuels were conducted on Ford Taurus and Dodge Caravan flexible-fuel vehicles.

Though technology exists to allow ethanol FFVs to run on any mixture of gasoline and ethanol, from pure gasoline up to 100% ethanol (E100), North American and European flex-fuel vehicles are optimized to run on a maximum blend of 15% gasoline with 85% anhydrous ethanol (called E85 fuel). This limit in the ethanol content is set to reduce ethanol emissions at low temperatures and to avoid cold starting problems during cold weather, at temperatures lower than 11 °C (52 °F). The alcohol content is reduced during the winter in regions where temperatures fall below 0 °C (32 °F) to a winter blend of E70 in the U.S. or to E75 in Sweden from November until March. Brazilian flex fuel vehicles are optimized to run on any mix of E20-E25 gasoline and up to 100% hydrous ethanol fuel (E100). The Brazilian flex vehicles are built-in with a small gasoline reservoir for cold starting the engine when temperatures drop below 15 °C (59 °F). An improved flex motor generation was launched in 2009 which eliminated the need for the secondary gas tank Affordability

FFVs are priced the same as gasoline-only vehicles, offering drivers the opportunity to buy an E85 capable vehicle at no additional cost. In general, E85 reduces fuel economy and range by about 20-30 percent, meaning an FFV will travel fewer miles on a tank of E85 than on a tank of gasoline. This is because ethanol contains less energy than gasoline. Vehicles can be designed to be optimized for E85—which would reduce or eliminate this tendency. However, no such vehicles are currently on the market. The pump price for E85 is often lower than regular gasoline; however, prices vary depending on supply and market conditions. Benefits

Much of the increased interest in ethanol as a vehicle fuel is due to its ability to replace gasoline from imported oil. The United States is currently the world’s largest ethanol producer, and most of the ethanol we use is produced domestically from corn grown by American farmers.


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E85 also provides important reductions in greenhouse gas (GHG) emissions. When made from corn, E85 reduces lifecycle GHG emissions (which include the energy required to grow and process corn into ethanol) by 15-20 percent as compared to gasoline. E85 made from cellulose can reduce emissions by around 70 percent as compared to gasoline.

EPA’s stringent Tier II vehicle emission standards require that FFVs achieve the same low emissions level regardless of whether E85 or gasoline is used. However, E85 can further reduce emissions of certain pollutants as compared to conventional gasoline or lower volume ethanol blends. For example, E85 is less volatile than gasoline or low volume ethanol blends, which results in fewer evaporative emissions. Using E85 also reduces carbon monoxide emissions and provides significant reductions in emissions of many harmful toxics, including benzene, a known human carcinogen. However, E85 also increases emissions of acetaldehyde—a toxic pollutant. EPA is conducting additional analysis to expand our understanding of the emissions impacts of E85. 1.4 SOLAR POWERED CARS/ VEHICLE

Solar power is energy from the sun and without its presence all life on earth would end. Solar energy has been looked upon as a serious source of energy for many years because of the vast amounts of energy that are made freely available, if harnessed by modern technology. A simple example of the power of the sun can be seen by using a magnifying glass to focus the suns rays on a piece of paper. Before long the paper ignites into flames.

This is one way of using the suns energy, but flames are dangerous and difficult to control. A much safer and practical way of harnessing the suns energy is to use the suns power to heat up water

A magnifying glass can be used to heat up a small amount of water. A short piece of copper tube is sealed at one end and filled with water. A magnifying glass is then used to warm up the pipe. Using more than one magnifying glass will increase the temperature more rapidly. After a relatively short time the temperature of the water increases. Continuing to heat the water will cause water vapour to appear at the top of the tube. In theory, with enough patience, several magnifying glasses and very strong sun light enough heat should be generated to boil the water, producing steam. This is one way of harnessing solar power.


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The principle of heating water to boiling point was used by the French in 1888. They developed a solar powered printing press. It used the energy of the sun to boil water, producing steam. The steam was used to drive a steam engine which provided the power to drive the mechanical printing press. The machine was unreliable and very expensive to manufacture Modern solar panels are a combination of magnifying glasses and fluid filled pipes. The solar panel seen opposite has a glass front which is specially made to focus the power of the sun on pipes behind it. The pipes carry a special fluid that heats up rapidly. They are painted black to absorb the heat from the sun. The silver reflective surface behind the pipes reflects sun light back, further heating the pipes and the fluid they contain. The reflective surface also protects anything behind the solar panel (such as a roof). The heat produced in the pipes is then used to heat a tank of water. This saves using electricity or gas to heat up the water tank.


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Parabolic Solar Collectors Solar power is energy from the sun. Although the sun is 150 million kilometres

away it is still extremely powerful. The amount of energy it provides for the earth in one minute is large enough to meet the earth’s energy needs for one year. The problem is in the development of technology that can harness this ‘free’ energy source. Solar collectors are one way of focussing the suns rays to heat up fluids. A typical array of solar collectors is seen opposite. They are basically unusually shaped mirrors (parabolic in shape) that focus the heat of the sun on a pipe carrying a special fluid. The temperature of the fluid in the pipe increases as it flows down the pipe, along the solar collectors. The pipe extends the entire length of the mirrors.

This type of set up works at its best in desert areas where there is no shortage of sunlight and very little cloud. The hot fluid in the pipe can be used, through a system of heat exchangers, to produce electricity or hot water.


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Photovoltaic cells Photovoltaic cells look similar to solar panels but they work in a different way.

Solar panels are use to produce hot water or even steam. Photovoltaic panels convert the sunlight directly into electricity. A typical example of a device powered by photovoltaic cells is a solar powered calculator. This type of device only needs a small amount of electrical power to work and can even be used in a room with artificial light (bulbs / fluorescent light).

Although we see photovoltaic cells powering small devices such as calculators they have a more practical application especially in the third world. Photovoltaic cells have been developed that will provide electrical power to pump drinking water from wells in remote villages. British Telecom have developed a system that can be used to power a radio telephone system. During the day the cells power the phone and also charge batteries. The batteries power the phone during the night. Often photovoltaic cells are used as a backup to conventional energy. If conventional fails the cells are used to produce electricity. Silicon is a material known as a ‘semiconductor’ as it conducts electricity and it is the main material for photovoltaic cells. Impurities such as boron or phosphorus are added to this base material. These impurities create the environment for electrons to be freed when sunlight hits the photovoltaic panel. The freeing of electrons leads to the production of electricity.

The diagram above shows a basic photovoltaic cell. The blue represents the main material, silicon. The black round and irregular shapes represent the impurities of boron or phosphorous. As the sun/light strikes the cell the impurities free up electrons which ‘bounce’ around at incredible speeds. This creates an electrical charge.


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Advantages

• Solar energy is free although there is a cost in the building of ‘collectors’ and other equipment required to convert solar energy into electricity or hot water.

• Solar energy does not cause pollution. However, solar collectors and other associated equipment / machines are manufactured in factories that in turn cause some pollution.

• Solar energy can be used in remote areas where it is too expensive to extend the electricity power grid.

• Many everyday items such as calculators and other low power consuming devices can be powered by solar energy effectively.

• It is estimated that the worlds oil reserves will last for 30 to 40 years. On the other hand, solar energy is infinite (forever).

Disadvantages • Solar energy can only be harnessed when it is daytime and sunny. • Solar collectors, panels and cells are relatively expensive to manufacture although

prices are falling rapidly. • Solar power stations can be built but they do not match the power output of

similar sized conventional power stations. They are also very expensive. • In countries such as the UK, the unreliable climate means that solar energy is also

unreliable as a source of energy. Cloudy skies reduce its effectiveness. • Large areas of land are required to capture the suns energy. Collectors are usually

arranged together especially when electricity is to be produced and used in the same location.

• Solar power is used to charge batteries so that solar powered devices can be used at night. However, the batteries are large and heavy and need storage space. They also need replacing from time to time.

Solar Powered Car Solar cars have been developed in the last twenty years and are powered by energy from the sun. Although they are not a practical or economic form of transportation at present, in the future they may play a part in reducing our reliance on burning fossil fuels such as petrol and diesel


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A solar powered racing car is shown above. These are expensive to produce and usually seat only one or two people. The main cost is due to the large number of expensive and delicate photovoltaic solar panels that are needed to power the vehicle. Also, many of the solar powered cars used in races today are composed of expensive, lightweight materials such as titanium composites. These materials are normally used to manufacture fighter jets. Carbon fibre and fibre glass are also used for much of the bodywork. Most of the cars used in races are hand made by specialist teams and this adds to the expense. A solar powered vehicle can only run efficiently when the sun shines, although most vehicles of this type have a battery backup. Electricity is stored in the batteries when the sun is shining and this power can be used when sun light is restricted (cloudy). The batteries are normally nickel-metal hydride batteries (NiMH), Nickel-Cadmium batteries (NiCd), Lithium ion batteries or Lithium polymer batteries. Common lead acid batteries of the type used in the average family car are too heavy. Solar powered cars normally operate in a range of 80 to 170 volts. To reduce friction with the ground the wheels are extremely narrow and there are usually only three. Some solar powered cars are practical and one is shown below. This is a solar powered golf cart and it can be used in sunny climates to carry golfers from one hole to the next. When it is standing still the solar panels charge up the batteries and it is the batteries that power the electric motors, directly. As the vehicle is not in continuous use the batteries have time to charge up before they are needed.


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One of the more realistic ways in which that solar powered cars could become practical is to charge up their batteries when they are parked, during the day. Imagine driving the short distance to work and plugging the car into a set of photovoltaic solar panels. Whilst you are working the batteries charge up ready for use for the journey home. The same procedure could be carried out when the car is parked at home. A combination of solar power and wind power may prove to be a method of charging the batteries of ‘electric cars’.

A model solar powered racing car can the manufactured from some basic materials and components. These include cheap low powered electric 'solar' motors, straws, card and insulation tape. The most expensive component will be the solar panel, costing approximately ten British Pounds (sixteen US Dollars). A sample model is seen below.The photovoltaic solar panel produces approximately 2 to 3 volts, easily enough to drive round the 1.5 to 3 volt electric motors. The voltage produced depends on the intensity of sunlight.


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Photovoltaic panels convert the sunlight directly into electricity. A typical example of a device powered by photovoltaic cells is a solar powered calculator. This type of device only needs a small amount of electrical power to work and can even be used in a room with artificial light (bulbs / fluorescent light). The panels required for a powered model vehicle are much larger but can be purchases cheaply as solar power kits, for children to use

The completed model racing car is shown below. The ‘underneath’ view shows the motors fixed top a polystyrene base, held to it by insulation tape. The front plastic wheel has a 2mm axle which is taped to the card base. The sequence / stages involved in the construction of the model car are shown on the pages to follow.


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1.5 MAGNETIC TRACK VEHICLES

Maglev (derived from magnetic levitation), is a system of transportation that suspends, guides and propels vehicles, predominantly trains, using magnetic levitation from a very large number of magnets for lift and propulsion. This method has the potential to be faster, quieter and smoother than wheeled mass transit systems. The power needed for levitation is usually not a particularly large percentage of the overall consumption; most of the power used is needed to overcome air drag, as with any other high speed train.


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The highest recorded speed of a Maglev train is 581 kilometres per hour, achieved in Japan in 2003, 6 kilometres per hour faster than the conventional TGV wheel-rail speed record.

The first commercial maglev people mover was simply called "MAGLEV" and officially opened in 1984 near Birmingham, England. It operated on an elevated 600-metre section of monorail track between Birmingham International Airport and Birmingham International railway station, running at speeds up to 42 km/h; the system was eventually closed in 1995 due to reliability problems.

Perhaps the most well known implementation of high-speed maglev technology currently operating commercially is the Shanghai Maglev Train, an IOS (initial operating segment) demonstration line of the German-built Transrapid train in Shanghai, China that transports people 30 km to the airport in just 7 minutes 20 seconds, achieving a top speed of 431 km/h, averaging 250 km/h.

Several favourable conditions existed when the link was built:

• The British Rail Research vehicle was 3 tonnes and extension to the 8 tonne vehicle was easy.

• Electrical power was easily available. • The airport and rail buildings were suitable for terminal platforms. • Only one crossing over a public road was required and no steep gradients were

involved. • Land was owned by the railway or airport. • Local industries and councils were supportive. • Some government finance was provided and because of sharing work, the cost per

organization was not high.

Technology

The term "maglev" refers not only to the vehicles, but to the railway system as well, specifically designed for magnetic levitation and propulsion. All operational implementations of maglev technology have had minimal overlap with wheeled train technology and have not been compatible with conventional rail tracks. Because they cannot share existing infrastructure, these maglev systems must be designed as complete transportation systems. The Applied Levitation SPM Maglev system is inter-operable with steel rail tracks and would permit maglev vehicles and conventional trains to operate at the same time on the same right of way. MAN in Germany also designed a maglev system that worked with conventional rails, but it was never fully developed.


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There are two particularly notable types of maglev technology:

• For electromagnetic suspension (EMS), electromagnets in the train attract it to a magnetically conductive (usually steel) track.

• Electrodynamic suspension (EDS) uses electromagnets on both track and train to push the train away from the rail.

Another experimental technology, which was designed, proven mathematically, peer reviewed, and patented, but is yet to be built, is the magnetodynamic suspension (MDS), which uses the attractive magnetic force of a permanent magnet array near a steel track to lift the train and hold it in place. Other technologies such as repulsive permanent magnets and superconducting magnets have seen some research.

Electromagnetic suspension

In current electromagnetic suspension (EMS) systems, the train levitates above a steel rail while electromagnets, attached to the train, are oriented toward the rail from below. The system is typically arranged on a series of C-shaped arms, with the upper portion of the arm attached to the vehicle, and the lower inside edge containing the magnets. The rail is situated between the upper and lower edges.

Magnetic attraction varies inversely with the cube of distance, so minor changes in distance between the magnets and the rail produce greatly varying forces. These changes in force are dynamically unstable - if there is a slight divergence from the optimum position, the tendency will be to exacerbate this, and complex systems of feedback control are required to maintain a train at a constant distance from the track, (approximately 15 millimeters).

The major advantage to suspended maglev systems is that they work at all speeds, unlike electrodynamic systems which only work at a minimum speed of about 30 km/h. This eliminates the need for a separate low-speed suspension system, and can simplify the track layout as a result. On the downside, the dynamic instability of the system demands high tolerances of the track, which can offset, or eliminate this advantage. Laithwaite, highly skeptical of the concept, was concerned that in order to make a track with the required tolerances, the gap between the magnets and rail would have to be increased to the point where the magnets would be unreasonably large. In practice, this problem was addressed through increased performance of the feedback systems, which allow the system to run with close tolerances.


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Electrodynamic suspension

JR-Maglev EDS suspension is due to the magnetic fields induced either side of the vehicle by the passage of the vehicles superconducting magnets.

EDS Maglev Propulsion via propulsion coils

In electrodynamic suspension (EDS), both the rail and the train exert a magnetic field, and the train is levitated by the repulsive force between these magnetic fields. The magnetic field in the train is produced by either superconducting magnets (as in JR-Maglev) or by an array of permanent magnets (as in Induct rack). The repulsive force in the track is created by an induced magnetic field in wires or other conducting strips in the track. A major advantage of the repulsive maglev systems is that they are naturally stable—minor narrowing in distance between the track and the magnets creates strong forces to repel the magnets back to their original position, while a slight increase in distance greatly reduces the force and again returns the vehicle to the right separation. No feedback control is needed.

Repulsive systems have a major downside as well. At slow speeds, the current induced in these coils and the resultant magnetic flux is not large enough to support the weight of the train. For this reason the train must have wheels or some other form of landing gear to support the train until it reaches a speed that can sustain levitation. Since a train may stop at any location, due to equipment problems for instance, the entire track must be able to support both low-speed and high-speed operation. Another downside is that the repulsive system naturally creates a field in the track in front and to the rear of the lift magnets, which act against the magnets and create a form of drag. This is generally only a concern at low speeds, at higher speeds the effect does not have time to build to its full potential and other forms of drag dominate.


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The drag force can be used to the electrodynamic system's advantage, however, as it creates a varying force in the rails that can be used as a reactionary system to drive the train, without the need for a separate reaction plate, as in most linear motor systems. Laithwaite led development of such "traverse-flux" systems at his Imperial College laboratory. Alternatively, propulsion coils on the guideway are used to exert a force on the magnets in the train and make the train move forward. The propulsion coils that exert a force on the train are effectively a linear motor: an alternating current flowing through the coils generates a continuously varying magnetic field that moves forward along the track. The frequency of the alternating current is synchronized to match the speed of the train. The offset between the field exerted by magnets on the train and the applied field creates a force moving the train forward.

Pros and cons of different technologies

Each implementation of the magnetic levitation principle for train-type travel involves advantages and disadvantages.

Technology Pros Cons EMS (Electromagnetic suspension)

Magnetic fields inside and outside the vehicle are less than EDS; proven, commercially available technology that can attain very high speeds (500 km/h); no wheels or secondary propulsion system needed.

The separation between the vehicle and the guideway must be constantly monitored and corrected by computer systems to avoid collision due to the unstable nature of electromagnetic attraction; due to the system's inherent instability and the required constant corrections by outside systems, vibration issues may occur.

EDS (Electrodynamic suspension)

Onboard magnets and large margin between rail and train enable highest recorded train speeds (581 km/h) and heavy load capacity; has demonstrated (December 2005) successful operations using high-

Strong magnetic fields onboard the train would make the train inaccessible to passengers with pacemakers or magnetic data storage media such as hard drives and credit cards, necessitating the use of


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temperature superconductors in its onboard magnets, cooled with inexpensive liquid nitrogen.

magnetic shielding; limitations on guideway inductivity limit the maximum speed of the vehicle; vehicle must be wheeled for travel at low speeds.

Inductrack System(Permanent Magnet EDS)

Failsafe Suspension—no power required to activate magnets; Magnetic field is localized below the car; can generate enough force at low speeds (around 5 km/h) to levitate maglev train; in case of power failure cars slow down on their own safely; Halbach arrays of permanent magnets may prove more cost-effective than electromagnets.

Requires either wheels or track segments that move for when the vehicle is stopped. New technology that is still under development (as of 2008) and as yet has no commercial version or full scale system prototype.

Neither Inductrack nor the Superconducting EDS are able to levitate vehicles at a standstill, although Inductrack provides levitation down to a much lower speed; wheels are required for these systems. EMS systems are wheel-less.

The German Transrapid, Japanese HSST (Linimo), and Korean Rotem EMS maglevs levitate at a standstill, with electricity extracted from guideway using power rails for the latter two, and wirelessly for Transrapid. If guideway power is lost on the move, the Transrapid is still able to generate levitation down to 10 km/h speed, using the power from onboard batteries. This is not the case with the HSST and Rotem systems.

Propulsion

An EDS system can provide both levitation and propulsion using an onboard linear motor. EMS systems can only levitate the train using the magnets onboard, not propel it forward. As such, vehicles need some other technology for propulsion. A linear motor (propulsion coils) mounted in the track is one solution. Over long distances where the cost of propulsion coils could be prohibitive, a propeller or jet engine could be used.


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Stability

Earnshaw's theorem shows that any combination of static magnets cannot be in a stable equilibrium. However, the various levitation systems achieve stable levitation by violating the assumptions of Earnshaw's theorem. Earnshaw's theorem assumes that the magnets are static and unchanging in field strength and that the relative permeability is constant and greater than unity everywhere. EMS systems rely on active electronic stabilization. Such systems constantly measure the bearing distance and adjust the electromagnet current accordingly. All EDS systems are moving systems (no EDS system can levitate the train unless it is in motion).

Because Maglev vehicles essentially fly, stabilisation of pitch, roll and yaw is required by magnetic technology. In addition to rotation, surge (forward and backward motions), sway (sideways motion) or heave (up and down motions) can be problematic with some technologies.

If superconducting magnets are used on a train above a track made out of a permanent magnet, then the train would be locked in to its lateral position on the track. It can move linearly along the track, but not off the track. This is due to the Meissner Effect.

Guidance

Some systems use Null Current systems (also sometimes called Null Flux systems); these use a coil which is wound so that it enters two opposing, alternating fields, so that the average flux in the loop is zero. When the vehicle is in the straight ahead position, no current flows, but if it moves off-line this creates a changing flux that generates a field that pushes it back into line. However, some systems use coils that try to remain as much as possible in the null flux point between repulsive magnets, as this reduces eddy current losses.

Evacuated tubes

Some systems (notably the swissmetro system) propose the use of vactrains—maglev train technology used in evacuated (airless) tubes, which removes air drag. This has the potential to increase speed and efficiency greatly, as most of the energy for conventional Maglev trains is lost in air drag.

One potential risk for passengers of trains operating in evacuated tubes is that they could be exposed to the risk of cabin depressurization unless tunnel safety


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monitoring systems can repressurize the tube in the event of a train malfunction or accident. The Rand Corporation has designed a vacuum tube train that could, in theory, cross the Atlantic or the USA in 20 minutes.

Power and energy usage

Energy for maglev trains is used to accelerate the train, and may be regained when the train slows down ("regenerative braking"). It is also used to make the train levitate and to stabilise the movement of the train. The main part of the energy is needed to force the train through the air ("air drag"). Also some energy is used for air conditioning, heating, lighting and other miscellaneous systems.The maglev trains are powered on electromagnetism.

At very low speeds the percentage of power (energy per time) used for levitation can be significant. Also for very short distances the energy used for acceleration might be considerable. But the power used to overcome air drag increases with the cube of the velocity, and hence dominates at high speed (note: the energy needed per mile increases by the square of the velocity and the time decreases linearly.).

Advantages and disadvantages Compared to conventional trains

Major comparative differences exist between the two technologies. First of all, maglevs are not trains, they are non-contact electronic transport systems, not mechanical friction-reliant rail systems. Their differences lie in maintenance requirements and the reliability of electronic versus mechanically based systems, all-weather operations, backward-compatibility, rolling resistance, weight, noise, design constraints, and control systems.

• Maintenance Requirements Of Electronic Versus Mechanical Systems: Maglev trains currently in operation have demonstrated the need for nearly insignificant guideway maintenance. Their electronic vehicle maintenance is minimal and more closely aligned with aircraft maintenance schedules based on hours of operation, rather than on speed or distance traveled. Traditional rail is subject to the wear and tear of miles of friction on mechanical systems and increases exponentially with speed, unlike maglev systems. This basic difference is the huge cost difference between the two modes and also directly affects system reliability, availability and sustainability.

• All-Weather Operations: Maglev trains currently in operation are not stopped, slowed, or have their schedules affected by snow, ice, severe cold, rain or high winds. This cannot be said for traditional friction-based rail systems. Also,


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maglev vehicles accelerate and decelerate faster than mechanical systems regardless of the slickness of the guideway or the slope of the grade because they are non-contact systems.

• Backwards Compatibility: Maglev trains currently in operation are not compatible with conventional track, and therefore require all new infrastructure for their entire route, but this is not a negative if high levels of reliability and low operational costs are the goal. By contrast conventional high speed trains such as the TGV are able to run at reduced speeds on existing rail infrastructure, thus reducing expenditure where new infrastructure would be particularly expensive (such as the final approaches to city terminals), or on extensions where traffic does not justify new infrastructure. However, this "shared track approach" ignores mechanical rail's high maintenance requirements, costs and disruptions to travel from periodic maintenance on these existing lines. The use of a completely separate maglev infrastructure more than pays for itself with dramatically higher levels of all-weather operational reliability and almost insignificant maintenance costs. So, maglev advocates would argue against rail backward compatibility and its concomitant high maintenance needs and costs.

• Efficiency: Due to the lack of physical contact between the track and the vehicle, maglev trains experience no rolling resistance, leaving only air resistance and electromagnetic drag, potentially improving power efficiency.

• Weight: The weight of the electromagnets in many EMS and EDS designs seems like a major design issue to the uninitiated. A strong magnetic field is required to levitate a maglev vehicle. For the Transrapid, this is about 56 watts per ton. Another path for levitation is the use of superconductor magnets to reduce the energy consumption of the electromagnets, and the cost of maintaining the field. However, a 50-ton Transrapid maglev vehicle can lift an additional 20 tons, for a total of 70 tones, which surprisingly does not consume an exorbitant amount of energy. Most energy use for the TRI is for propulsion and overcoming the friction of air resistance. At speeds over 100 mph, which is the point of a high-speed maglev, maglevs use less energy than traditional fast trains.

• Noise: Because the major source of noise of a maglev train comes from displaced air, maglev trains produce less noise than a conventional train at equivalent speeds. However, the psychoacoustic profile of the maglev may reduce this benefit: a study concluded that maglev noise should be rated like road traffic


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while conventional trains have a 5-10 dB "bonus" as they are found less annoying at the same loudness level.

• Design Comparisons: Braking and overhead wire wear have caused problems for the Fastech 360 railed Shinkansen. Maglev would eliminate these issues. Magnet reliability at higher temperatures is a countervailing comparative disadvantage (see suspension types), but new alloys and manufacturing techniques have resulted in magnets that maintain their levitational force at higher temperatures.

As with many technologies, advances in linear motor design have addressed the limitations noted in early maglev systems. As linear motors must fit within or straddle their track over the full length of the train, track design for some EDS and EMS maglev systems is challenging for anything other than point-to-point services. Curves must be gentle, while switches are very long and need care to avoid breaks in current. An SPM maglev system, in which the vehicle is permanently levitated over the tracks, can instantaneously switch tracks using electronic controls, with no moving parts in the track. A prototype SPM maglev train has also navigated curves with radius equal to the length of the train itself, which indciates that a full-scale train should be able to navigate curves with the same or narrower radius as a conventional train.

• Control Systems: EMS Maglev needs very fast-responding control systems to maintain a stable height above the track; multiple redundancy is built into these systems in the event of component failure and the Transrapid system has still levitated and operated with fully 1/2 of its magnet control systems shut down. Other maglev systems not using EMS active control are still in the experimental stage, except for the Central Japan Railway's MLX-01 superconducting EDS repulsive maglev system that levitates 11 centimeters above its guideway.

Compared to aircraft

For many systems, it is possible to define a lift-to-drag ratio. For maglev systems these ratios can exceed that of aircraft (for example Inductrack can approach 200:1 at high speed, far higher than any aircraft). This can make maglev more efficient per kilometre. However, at high cruising speeds, aerodynamic drag is much larger than lift-induced drag. Jet transport aircraft take advantage of low air density at high altitudes to significantly reduce drag during cruise, hence despite their lift-to-drag ratio disadvantage, they can travel more efficiently at high speeds than maglev trains that operate at sea level (this has been proposed to be fixed by the vactrain concept). Aircraft are also more flexible and can service more destinations with provision of suitable airport facilities.


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Unlike airplanes, maglev trains are powered by electricity and thus need not carry fuel. Aircraft fuel is a significant danger during takeoff and landing accidents. Also, electric trains emit little direct carbon dioxide emissions, especially when powered by nuclear or renewable sources, but more than aircraft if powered by fossil fuels.

1.6 FUEL CELL AND ITS TYPES Hydrogen Fuel Cells – Basic Principles The basic operation of the hydrogen fuel cell is extremely simple. The first demonstration of a fuel cell was by lawyer and scientist William Grove in 1839, using an experiment along the lines of that shown in Figures 1.1a and 1.1b. In Figure 1.1a, water is being electrolyzed into hydrogen and oxygen by passing an electric current through it. In Figure 1.1b, the power supply has been replaced with an ammeter, and a small current is flowing. The electrolysis is being reversed – the hydrogen and oxygen are recombining, and an electric current is being produced. Another way of looking at the fuel cell is to say that the hydrogen fuel is being ‘burnt’ or combusted in the simple reaction

(a) The electrolysis of water. The water is separated into hydrogen and oxygen by the passage of an electric current. (b) A small current flows. The oxygen and hydrogen are recombining.

However, instead of heat energy being liberated, electrical energy is produced.

The experiment shown in Figures 1.1a and 1.1b makes a reasonable demonstration of the basic principle of the fuel cell, but the currents produced are very small. The main reasons for the small current are

• the low ‘contact area’ between the gas, the electrode, and the electrolyte – basically just a small ring where the electrode emerges from the electrolyte.


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• the large distance between the electrodes – the electrolyte resists the flow of electric current. To overcome these problems, the electrodes are usually made flat, with a thin

layer of electrolyte as in Figure 1.2. The structure of the electrode is porous so that both the electrolyte from one side and the gas from the other can penetrate it. This is to give the maximum possible contact between the electrode, the electrolyte, and the gas. However, to understand how the reaction between hydrogen and oxygen produces an electric current, and where the electrons come from, we need to consider the separate reactions taking place at each electrode. These important details vary for different types of fuel cells, but if we start with a cell based around an acid electrolyte, as used by Grove, we shall start with the simplest and still the most common type.

At the anode of an acid electrolyte fuel cell, the hydrogen gas ionises, releasing electrons and creating H+ ions (or protons).

This reaction releases energy. At the cathode, oxygen reacts with electrons taken

from the electrode, and H+ ions from the electrolyte, to form water.


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Clearly, for both these reactions to proceed continuously, electrons produced at the anode must pass through an electrical circuit to the cathode. Also, H+ ions must pass through the electrolyte. An acid is a fluid with free H+ ions, and so serves this purpose very well. Certain polymers can also be made to contain mobile H+ ions. These materials are called proton exchange membranes, as an H+ ion is also a proton. Comparing equations 1.2 and 1.3 we can see that two hydrogen molecules will be needed for each oxygen molecule if the system is to be kept in balance. This is shown in Figure 1.3. It should be noted that the electrolyte must only allow H+ ions to pass through it, and not electrons. Otherwise, the electrons would go through the electrolyte, not a round the external circuit, and all would be lost.

Positive Cathodes and Negative Anodes

Looking at Figures 1.3 and 1.4, the reader will see that the electrons are flowing from the anode to the cathode. The cathode is thus the electrically positive terminal, since electrons flow from • to +. Many newcomers to fuel cells find this confusing. This is hardly surprising. The Concise Oxford English Dictionary defines cathode as “1. the negative electrode in an electrolyte cell or electron valve or tube, 2. the positive terminal of a primary cell such as a battery.”

Having two such opposite definitions is bound to cause confusion, but we note that the cathode is the correct name for the positive terminal of all primary batteries. It also helps to remember that cations are positive ions, for example, H+ is a cation. Anions are negative ions, for example, OH• is an anion. It is also true that the cathode is always


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the electrode into which electrons flow, and similarly the anode is always the electrode from which electrons flow. This holds true for electrolysis, cells, valves, forward biased diodes, and fuel cells.

A further possible confusion is that while negative electrons flow from minus to plus, the ‘conventional positive current’ flows the other way, from the positive to the negative terminal.

In an alkaline electrolyte fuel cell the overall reaction is the same, but the reactions at each electrode are different. In an alkali, hydroxyl (OH•) ions are available and mobile.

At the anode, these react with hydrogen, releasing energy and electrons, and

producing water. At the cathode, oxygen reacts with electrons taken from the electrode, and water in the electrolyte, forming new OH• ions.

For these reactions to proceed continuously, the OH• ions must be able to pass

through the electrolyte, and there must be an electrical circuit for the electrons to go from the anode to the cathode. Also, comparing equations 1.4 and 1.5 we see that, as with the acid electrolyte, twice as much hydrogen is needed as oxygen. This is shown in Figure 1.4. Note that although water is consumed at the cathode, it is created twice as fast at the anode.

There are many different fuel cell types, with different electrolytes. The details of the anode and cathode reactions are different in each case. However, it is not appropriate to go over every example here.


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Basic Structure Unit cells form the core of a fuel cell. These devices convert the chemical energy

contained in a fuel electrochemically into electrical energy. The basic physical structure, or building block, of a fuel cell consists of an electrolyte layer in contact with an anode and a cathode on either side. A schematic representation of a unit cell with the reactant/product gases and the ion conduction flow directions through the cell is shown in Figure 1-1.

Figure 1-1 Schematic of an Individual Fuel Cell In a typical fuel cell, fuel is fed continuously to the anode (negative electrode) and

an oxidant (often oxygen from air) is fed continuously to the cathode (positive electrode). The electrochemical reactions take place at the electrodes to produce an electric current through the electrolyte, while driving a complementary electric current that performs work on the load. Although a fuel cell is similar to a typical battery in many ways, it differs in several respects. The battery is an energy storage device in which all the energy available is stored within the battery itself (at least the reductant). The battery will cease to produce electrical energy when the chemical reactants are consumed (i.e., discharged). A fuel cell, on the other hand, is an energy conversion device to which fuel and oxidant are supplied continuously. In principle, the fuel cell produces power for as long as fuel is supplied.

Fuel cells are classified according to the choice of electrolyte and fuel, which in turn determine the electrode reactions and the type of ions that carry the current across the electrolyte


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Critical Functions of Cell Components A critical portion of most unit cells is often referred to as the three-phase interface. These mostly microscopic regions, in which the actual electrochemical reactions take place, are found where either electrode meets the electrolyte. For a site or area to be active, it must be exposed to the reactant, be in electrical contact with the electrode, be in ionic contact with the electrolyte, and contain sufficient electro-catalyst for the reaction to proceed at the desired rate. The density of these regions and the nature of these interfaces play a critical role in the electrochemical performance of both liquid and solid electrolyte fuel cells:

• In liquid electrolyte fuel cells, the reactant gases diffuse through a thin electrolyte film that wets portions of the porous electrode and react electrochemically on their respective electrode surface. If the porous electrode contains an excessive amount of electrolyte, the electrode may "flood" and restrict the transport of gaseous species in the electrolyte phase to the reaction sites. The consequence is a reduction in electrochemical performance of the porous electrode. Thus, a delicate balance must be maintained among the electrode, electrolyte, and gaseous phases in the porous electrode structure.

• In solid electrolyte fuel cells, the challenge is to engineer a large number of

catalyst sites into the interface that are electrically and ionically connected to the electrode and the electrolyte, respectively, and that is efficiently exposed to the reactant gases. In most successful solid electrolyte fuel cells, a high-performance interface requires the use of an electrode which, in the zone near the catalyst, has mixed conductivity (i.e. it conducts both electrons and ions).

Fuel Cell Types A variety of fuel cells are in different stages of development. The most common classification of fuel cells is by the type of electrolyte used in the cells and includes 1) Polymer electrolyte fuel cell (PEFC) 2) Alkaline fuel cell (AFC) 3) Phosphoric acid fuel cell (PAFC) 4) Molten carbonate fuel cell (MCFC) 5) Solid oxide fuel cell (SOFC)


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Polymer Electrolyte Fuel Cell (PEFC)

The electrolyte in this fuel cell is an ion exchange membrane (fluorinated sulfuric acid polymer or other similar polymer) that is an excellent proton conductor. The only liquid in this fuel cell is water; thus, corrosion problems are minimal. Typically, carbon electrodes with platinum electro catalyst are used for both anode and cathode, and with either carbon or metal interconnects.

Water management in the membrane is critical for efficient performance; the fuel cell must operate under conditions where the by-product water does not evaporate faster


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than it is produced because the membrane must be hydrated. Because of the limitation on the operating temperature imposed by the polymer, usually less than 100 C, but more typically around 60 to 80 °C. , and because of problems with water balance, a H2-rich gas with minimal or no CO (a poison at low temperature) is used. Higher catalyst loading (Pt in most cases) than that used in PAFCs is required for both the anode and cathode. Extensive fuel processing is required with other fuels, as the anode is easily poisoned by even trace levels of CO, sulfur species, and halogens.

PEFCs are being pursued for a wide variety of applications, especially for prime power for fuel cell vehicles (FCVs). As a consequence of the high interest in FCVs and hydrogen, the investment in PEFC over the past decade easily surpasses all other types of fuel cells combined. Although significant development of PEFC for stationary applications has taken place, many developers now focus on automotive and portable applications. Advantages

The PEFC has a solid electrolyte which provides excellent resistance to gas crossover. The PEFC’s low operating temperature allows rapid start-up and, with the absence of corrosive cell constituents, the use of the exotic materials required in other fuel cell types, both in stack construction and in the BoP is not required. Test results have demonstrated that PEFCs are capable of high current densities of over 2 kW/l and 2 W/cm2. The PEFC lends itself particularly to situations where pure hydrogen can be used as a fuel. Disadvantages

The low and narrow operating temperature range makes thermal management difficult, especially at very high current densities, and makes it difficult to use the rejected heat for cogeneration or in bottoming cycles. Water management is another significant challenge in PEFC design, as engineers must balance ensuring sufficient hydration of the electrolyte against flooding the electrolyte. In addition, PEFCs are quite sensitive to poisoning by trace levels of contaminants including CO, sulfur species, and ammonia. To some extent, some of these disadvantages can be counteracted by lowering operating current density and increasing electrode catalyst loading, but both increase cost of the system. If hydrocarbon fuels are used, the extensive fuel processing required negatively impacts system size, complexity, efficiency (typically in the mid thirties), and system cost. Finally, for hydrogen PEFC the need for a hydrogen infrastructure to be developed poses a barrier to commercialization.


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Alkaline Fuel Cell (AFC)

The electrolyte in this fuel cell is concentrated (85 wt percent) KOH in fuel cells operated at high temperature (~250 C), or less concentrated (35 to 50 wt percent) KOH for lower temperature (<120 C) operation. The electrolyte is retained in a matrix (usually asbestos), and a wide range of electro-catalysts can be used (e.g., Ni, Ag, metal oxides, spinels, and noble metals). The fuel supply is limited to non-reactive constituents except for hydrogen. CO is a poison, and CO2 will react with the KOH to form K2CO3, thus altering the electrolyte. Even the small amount of CO2 in air must be considered a potential poison for the alkaline cell. Generally, hydrogen is considered as the preferred fuel for AFC, although some direct carbon fuel cells use (different) alkaline electrolytes.

The AFC was one of the first modern fuel cells to be developed, beginning in 1960. The application at that time was to provide on-board electric power for the Apollo space vehicle. The AFC has enjoyed considerable success in space applications, but its terrestrial application has been challenged by its sensitivity to CO2. Still, some developers in the U.S. and Europe pursue AFC for mobile and closed-system (reversible fuel cell) applications. Advantages

Desirable attributes of the AFC include its excellent performance on hydrogen (H2) and oxygen (O2) compared to other candidate fuel cells due to its active O2 electrode kinetics and its flexibility to use a wide range of electro-catalysts. Disadvantages

The sensitivity of the electrolyte to CO2 requires the use of highly pure H2 as a fuel. As a consequence, the use of a reformer would require a highly effective CO and CO2 removal system. In addition, if ambient air is used as the oxidant, the CO2 in the air must be removed. While this is technically not challenging, it has a significant impact on the size and cost of the system. Phosphoric Acid Fuel Cell (PAFC)

Phosphoric acid, concentrated to 100 percent, is used as the electrolyte in this fuel cell, which typically operates at 150 to 220 C. At lower temperatures, phosphoric acid is a poor ionic conductor, and CO poisoning of the Pt electro-catalyst in the anode becomes severe. The relative stability of concentrated phosphoric acid is high compared


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to other common acids; consequently the PAFC is capable of operating at the high end of the acid temperature range (100 to 220 C). In addition, the use of concentrated acid (100 percent) minimizes the water vapor pressure so water management in the cell is not difficult. The matrix most commonly used to retain the acid is silicon carbide (1), and the electro-catalyst in both the anode and cathode is Pt.

PAFCs are mostly developed for stationary applications. Both in the U.S. and Japan, hundreds of PAFC systems were produced, sold, and used in field tests and demonstrations. It is still one of the few fuel cell systems that are available for purchase. Development of PAFC had slowed down in the past ten years, in favor of PEFCs that were thought to have better cost potential. However, PAFC development continues. Advantages

PAFCs are much less sensitive to CO than PEFCs and AFCs: PAFCs tolerate about one percent of CO as a diluent. The operating temperature is still low enough to allow the use of common construction materials, at least in the BoP components. The operating temperature also provides considerable design flexibility for thermal management. PAFCs have demonstrated system efficiencies of 37 to 42 percent (based on LHV of natural gas fuel), which is higher than most PEFC systems could achieve (but lower than many of the SOFC and MCFC systems). In addition, the waste heat from PAFC can be readily used in most commercial and industrial cogeneration applications, and would technically allow the use of a bottoming cycle. Disadvantages

Cathode-side oxygen reduction is slower than in AFC, and requires the use of a Platinum catalyst. Although less complex than for PEFC, PAFCs still require extensive fuel processing, including typically a water gas shift reactor to achieve good performance. Finally, the highly corrosive nature of phosphoric acid requires the use of expensive materials in the stack (especially the graphite separator plates). Molten Carbonate Fuel Cell (MCFC)

The electrolyte in this fuel cell is usually a combination of alkali carbonates, which is retained in a ceramic matrix of LiAlO2. The fuel cell operates at 600 to 700 C where the alkali carbonates form a highly conductive molten salt, with carbonate ions providing ionic conduction. At the high operating temperatures in MCFCs, Ni (anode)


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and nickel oxide (cathode) are adequate to promote reaction. Noble metals are not required for operation, and many common hydrocarbon fuels can be reformed internally.

The focus of MCFC development has been larger stationary and marine applications, where the relatively large size and weight of MCFC and slow start-up time are not an issue. MCFCs are under development for use with a wide range of conventional and renewable fuels. MCFC-like technology is also considered for DCFC. After the PAFC, MCFCs have been demonstrated most extensively in stationary applications, with dozens of demonstration projects either under way or completed. While the number of MCFC developers and the investment level are reduced compared to a decade ago, development and demonstrations continue. Advantages

The relatively high operating temperature of the MCFC (650 °C) results in several benefits: no expensive electro-catalysts are needed as the nickel electrodes provide sufficient activity, and both CO and certain hydrocarbons are fuels for the MCFC, as they are converted to hydrogen within the stack (on special reformer plates) simplifying the BoP and improving system efficiency to the high forties to low fifties. In addition, the high temperature waste heat allows the use of a bottoming cycle to further boost the system efficiency to the high fifties to low sixties. Disadvantages

The main challenge for MCFC developers stems from the very corrosive and mobile electrolyte, which requires use of nickel and high-grade stainless steel as the cell hardware (cheaper than graphite, but more expensive than ferritic steels). The higher temperatures promote material problems, impacting mechanical stability and stack life. Also, a source of CO2 is required at the cathode (usually recycled from anode exhaust) to form the carbonate ion, representing additional BoP components. High contact esistances and cathode resistance limit power densities to around 100 – 200 mW/cm2 at practical operating voltages. Solid Oxide Fuel Cell (SOFC)

The electrolyte in this fuel cell is a solid, nonporous metal oxide, usually Y2O3-stabilized ZrO2. The cell operates at 600-1000 C where ionic conduction by oxygen ions takes place. Typically, the anode is Co-ZrO2 or Ni-ZrO2 cermet, and the cathode is Sr-doped LaMnO3.


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Early on, the limited conductivity of solid electrolytes required cell operation at around 1000 °C, but more recently thin-electrolyte cells with improved cathodes have allowed a reduction in operating temperature to 650 – 850 °C. Some developers are attempting to push SOFC operating temperatures even lower. Over the past decade, this has allowed the development of compact and high-performance SOFC which utilized relatively low-cost construction materials.

Concerted stack development efforts, especially through the U.S. DOE’s SECA program, have considerably advanced the knowledge and development of thin-electrolyte planar SOFC. As a consequence of the performance improvements, SOFCs are now considered for a wide range of applications, including stationary power generation, mobile power, auxiliary power for vehicles, and specialty applications. Advantages

The SOFC is the fuel cell with the longest continuous development period, starting in the late 1950s, several years before the AFC. Because the electrolyte is solid, the cell can be cast into various shapes, such as tubular, planar, or monolithic. The solid ceramic construction of the unit cell alleviates any corrosion problems in the cell. The solid electrolyte also allows precise engineering of the three-phase boundary and avoids electrolyte movement or flooding in the electrodes. The kinetics of the cell are relatively fast, and CO is a directly useable fuel as it is in the MCFC. There is no requirement for CO2 at the cathode as with the MCFC. The materials used in SOFC are modest in cost. Thin-electrolyte planar SOFC unit cells have been demonstrated to be cable of power densities close to those achieved with PEFC. As with the MCFC, the high operating temperature allows use of most of the waste heat for cogeneration or in bottoming cycles. Efficiencies ranging from around 40 percent (simple cycle small systems) to over 50 percent (hybrid systems) have been demonstrated, and the potential for 60 percent+ efficiency exists as it does for MCFC. Disadvantages

The high temperature of the SOFC has its drawbacks. There are thermal expansion mismatches among materials, and sealing between cells is difficult in the flat plate configurations. The high operating temperature places severe constraints on materials selection and results in difficult fabrication processes. Corrosion of metal stack components (such as the interconnects in some designs) is a challenge. These factors


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limit stack-level power density (though significantly higher than in PAFC and MCFC), and thermal cycling and stack life (though the latter is better than for MCFC and PEFC). Characteristics

The interest in terrestrial applications of fuel cells is driven primarily by their potential for high efficiency and very low environmental impact (virtually no acid gas or solid emissions).

Efficiencies of present fuel cell plants are in the range of 30 to 55 percent based on the lower heating value (LHV) of the fuel. Hybrid fuel cell/reheat gas turbine cycles that offer efficiencies greater than 70 percent LHV, using demonstrated cell performance, have been proposed. Figure 1-4 illustrates demonstrated low emissions of installed PAFC units compared to the Los Angeles Basin (South Coast Air Quality Management District) requirements, the strictest requirements in the U.S. Measured emissions from the PAFC unit are < 1 ppm of NOX, 4 ppm of CO, and <1 ppm of reactive organic gases (non-methane) (5). In addition, fuel cells operate at a constant temperature, and the heat from the electrochemical reaction is available for cogeneration applications. Table summarizes the impact of the major constituents within fuel gases on the various fuel cells. The reader is referred to Sections 3 through 7 for detail on trace contaminants.

Another key feature of fuel cells is that their performance and cost are less dependent on scale than other power technologies. Small fuel cell plants operate nearly as efficiently as large ones, with equally low emissions, and comparable cost.1 This opens up applications for fuel cells where conventional power technologies are not practical. In addition, fuel cell systems can be relatively quiet generators.

To date, the major impediments to fuel cell commercialization have been insufficient longevity and reliability, unacceptably high cost, and lack of familiarity of markets with fuel cells. For fuel cells that require special fuels (such as hydrogen) the lack of a fuel infrastructure also limits commercialization.

Other characteristics that fuel cells and fuel cell plants offer are:

• Direct energy conversion (no combustion) • No moving parts in the energy converter • Quiet • Demonstrated high availability of lower temperature units • Siting ability


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• Fuel flexibility • Demonstrated endurance/reliability of lower temperature units • Good performance at off-design load operation • Modular installations to match load and increase reliability • Remote/unattended operation • Size flexibility • Rapid load following capability

General negative features of fuel cells include

• Market entry cost high; Nth cost goals not demonstrated. • Endurance/reliability of higher temperature units not demonstrated. • Unfamiliar technology to the power industry. • No infrastructure.


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CHAPTER II

POWER SYSTRM AND NEW GENERATION VEHICLES 2.1 LEAN BURN ENGINE Introduction

Internal combustion (IC) engines are used in a variety of stationary applications ranging from power generation to inert gas production. Both spark ignition and compression ignition engines can be found. Depending on the application, stationary IC engines range in size from relatively small (~50 hp) for agricultural irrigation purposes to thousands of horsepower for power generation. Often when used for power generation, several large engines will be used in parallel to meet the load requirements. A variety of fuels can be used for IC engines including diesel and gasoline among others. The actual fuel used depends on the owners/operators preference but can be application dependent as well.

The operation of IC engines results in the emission of hydrocarbons (NMHC or VOC), carbon monoxide (CO), nitrogen oxides (NOx), and particulate matter (PM). The actual concentration of these criteria pollutants varies from engine to engine, mode of operation, and is strongly related to the type of fuel used.

Various emission control technologies exist for IC engines which can afford substantial reductions in all four criteria pollutants listed above. However depending on whether the engine is being run rich, lean, or stoichiometrically and the emission control technology used, the targeted emissions vary as do the levels of control. For example, an oxidation catalyst can be used to control NMHC, CO, and PM emissions from diesel engines which inherently operate in a lean environment, whereas selective catalytic reduction (SCR) could be used to additionally control NOx emissions. More recently, lean-NOx catalysts have been demonstrated to provide greater than a 80 percent reduction in NOx emissions from a stationary diesel engine, while providing significant CO, NMHC, and PM control as well.

PM emissions from stationary diesel engines are more of a concern than those for IC engines using other fuels. Several emission control technologies exist for diesel engine PM control. Oxidation or lean-NOx catalyst can be used to not only reduce the gaseous emissions associated with the use of diesel engines but further provide significant PM control. Likewise, diesel particulate filter systems can be used to achieve up to and


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greater than 90 percent PM control while in some instances, also providing reductions in the gaseous emissions.

IC engines use a variety of fuels and run rich, lean, or stoichiometrically as outlined in Table 1. The engines used in these applications range in size from fifty horsepower to thousands of horsepower.

Table Engine Types and Fuels Rich Burn Natural Gas, Propane, Gasoline Stoichiometric Natural Gas, Propane, Gasoline Lean Burn Diesel, Natural Gas, Dual Fuel

A lean burn mode is a way to reduce throttling losses. An engine in a typical vehicle is sized for providing the power desired for acceleration, but must operate well below that point in normal steady-speed operation. Ordinarily, the power is cut by partially closing a throttle. However, the extra work done in pumping air through the throttle reduces efficiency. If the fuel/air ratio is reduced, then lower power can be achieved with the throttle closer to fully open, and the efficiency during normal driving (below the maximum torque capability of the engine) can be higher.

The engines designed for lean burning can employ higher compression ratios and thus provide better performance, efficient fuel use and low exhaust hydrocarbon emissions than those found in conventional petrol engines. Ultra lean mixtures with very high air-fuel ratios can only be achieved by direct engines.

Disadvantages

The main drawback of lean burning is that a complex catalytic converter system is required to reduce NOx emissions. Lean burn engines do not work well with modern 3- way catalytic converter—which require a pollutant balance at the exhaust port so they can carry out oxidation and reduction reactions—so most modern engines run at or near the stoichiometric point. Alternatively, ultra-lean ratios can reduce NOx emissions. Lean burn technology

Internal combustion engine-powered generator sets fueled by natural gas are commanding more attention these days as interest grows in on-site power production equipment that is both efficient and environmentally friendly.


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In response to this interest, manufacturers have introduced natural gas engine-powered generator sets that feature “lean-burn” technology. The combustion is considered "lean" when excess air is introduced into the engine along with the fuel. This produces two positive effects. First, the excess air reduces the temperature of the combustion process and this reduces the amount of oxides of nitrogen (NOx) produced by nearly half, compared to a conventional natural gas engine. Second, since there is also excess oxygen available, the combustion process is more efficient and more power is produced from the same amount of fuel.

Combustion Process

Any air/fuel reaction requires an energy source to initiate combustion. In natural gas engines, the spark plug performs this function. In lean-burn engines, the combustion process is enhanced by pre-mixing the air and fuel upstream of the turbocharger before introduction into the cylinder. This creates a more homogenous mixture in the combustion chamber and reduces the occurrence of “knocking” or detonation. To prevent either knocking or misfiring, the combustion process must be controlled within a narrow operating window. Charge air temperatures and volume, together with air to fuel ratio, are constantly monitored. The microprocessor-based engine controller regulates the fuel flow and air/gas mixture and ignition timing.


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New lean-burn engines from Cummins are designed to operate at a lean air/gas ratio of Lambda = 1.7. (Traditional stoichiometric natural gas engines have an air/gas ratio of Lambda = 1.0). In the chart (at left) that plots Break Mean Effective Pressure (BMEP) against Air Excess (Lambda), the operating window is a very narrow band where efficiency peaks and where NOx is near its minimum. A richer mixture (stoichiometric) can potentially produce knocking and higher NOx emissions; a leaner mixture than Lambda 1.7 may not combust reliably and cause misfiring, which raises HC emissions. Full-authority electronic engines, sensors and microprocessors in the new lean-burn engines are critical for maintaining combustion within these boundaries.

The design of the lean-burn engine incorporates a simple open combustion chamber housed in the piston crown. The shape of the piston crown introduces turbulence in the incoming air/fuel mixture that promotes more complete combustion by thoroughly exposing it to the advancing flame front. The flame plate of the cylinder head is regular (flat) and the spark plug is centrally located. The air and gas fuel are correctly mixed under the control of the engine management system. Reduced Emissions

One of the results of this technology is significantly reduced emissions in the exhaust. Cummins’ new lean-burn gas engine generators have NOx emissions as low as .85 grams/BHP-hr, and produce low amounts of hydrocarbons (HC), carbon monoxide (CO) and particulate matter (PM). This allows the generator sets to meet the most stringent air quality regulations without after treatment devices in the exhaust stream. For even lower emissions, lean-burn gas engine generator sets are also available with factory-integrated after treatment options such as Selective Catalytic Reduction (SCR) and Oxidation Catalysts, resulting in NOx levels at or below 0.15 grams/BHP-hr. With these after treatment options, the gas engine generators have been shown to meet the most stringent prime power emissions regulations anywhere in the world. Fuel Flexibility

Another advantage of the lean-burn technology with full-authority electronic engine controls is the ability to operate on gas with a wide range of quality. A measurement called the Methane Number (MN) is used to determine fuel gas suitability as an engine fuel. Most natural gas has an MN from 70 to 97, and pipeline quality gas typically has an MN of about 75. Resource recovery gas from landfills or sewage treatment facilities is typically of lower quality, but is often suitable for use in lean-burn engines. Cummins’ lean-burn gas engine generators will operate on gas with an MN of


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50 or greater, providing excellent fuel flexibility. However, gas with a MN below 70 may require derating of the generator output.

Lean-burn gas engine generator sets are setting a new standard for fuel efficiency, high power output for their size, and for low emissions. In regions with supplies of natural gas, these generator sets are providing highly reliable electric power for utility peaking, distributed generation, prime power and for combined heat and power systems.

2.2 LOW HEAT REJECTION ENGINE Introduction

The compression ignition system of diesel engine has now a day become the most preferred prime mover in medium and medium large unit application (truck, ship etc,) owing to its reliability and excellent fuel efficiency. However, its transient operation is often linked with an off design (turbo charger lag) and consequent non optimum performance. Over the last three decades, a tremendous increase of interest amongst researchers on low heat rejection (LHR) diesel engine is noteworthy. A large number of studies based on performance, structure and durability of the LHR engines have been carried out and this was because of the initiative by the researchers, presented a new concept of LHR engine combined with turbo compound system . Although, the end results seem to be promising, some mixed have been obtained. Some researchers say that insulation reduces heat transfer, but improves thermal efficiency and increases energy availability in the exhaust. However, on the contrary to the above mentioned expectations, some experimental studies have indicated that almost no improvement in thermal efficiency is obtained and claim that exhaust emissions are deteriorated as compared to those of the conventional water cooled engines.

The heat lost to the in-cylinder and heat transfer in internal combustion engines made a significant amount of increase in input fuel efficiency. Typically, about one-third of the input energy is converted into mechanical work, another one-third is lost as heat in the exhaust gases, and remaining is lost as heat to the cooling system through mechanical friction and heat transfer losses within the engine. Also, some amount of fuel is lost to in cylinder during heat transfer, (i.e.) heat transfer from the hot gas to the combustion chamber surface area. Clearly, this shows that there is a possibility for improving engine fuel efficiency, if the heat losses can be reduced and utilized either directly as piston work or via increased exhaust gas enthalpies in a bottom cycle.


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Conventional engine energy balance LHR engine energy balance

The concept of thermal barrier coatings for diesel engine was initiated in the mid

1970’s by Kvernes at The Central Institute for Industrial Research, Oslo, Norway (Fair banks, 1995). In the 1980’s, the concept of using thermal barrier coating (TBC) to insulate the combustion chamber of the diesel engine was investigated. The idea was to insulate the combustion chamber of an engine with a TBC to reduce heat energy transfer from the engine coolant. The recovered energy from the engine may be used to promote a slight increase at the fly wheel and turbocharger with higher boost and higher efficiency. In the early 1990’s, several drawbacks of low heat rejection engines were determined, the first was the issue of elevated combustion chamber temperatures resulting in unwanted high NOx emission levels. Today’s emission standards, the focuses on zero emissions from engines, but has neglected the use of thermal barrier coatings (TBC) in diesel engines. This fact was brought out by Dorsaf Saad , Philipe Saad and Lloyd Kamo. The Shortcomings of LHR Research

The LHR are mainly the result of the improvisation of conventional engines to LHR designs. The mere substitution of ceramic components or the addition of insulating coatings fails to account for increased combustion temperatures and an altered combustion process. There is no inherent utilization of the resulting retained heat energy. Consequently, complex turbo compounding devices or bottoming cycles must be employed to capture some portion of the retained heat energy from the exhaust stream.

In addition, conventional piston-crank designs produce piston side-wall stresses which make the direct substitution of ceramic for metallic materials troublesome. New designs which reduce piston side forces, or slapping forces, would be more compatible with ceramics. In a LHR review done by West Virginia University it was concluded that, “It may be helpful to return to the basics of engine design in formulating models of LHR engines.” This is the fundamental principle which this paper will address.


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While “returning to the basics” of engine design for the purpose of

accommodating LHR concepts, this paper will next suggest factors which further optimize this power plant with regard to its compatibility with its intended application, the passenger vehicle. Design Criteria

Below are several sets of design criteria which are the framework for the design process producing the engine described in this paper. While any engineering endeavor is fraught with compromises and undesirable practicalities, no individual criterion has been completely eliminated at the expense of another in this design. Criteria Satisfying to the Vehicle operator which will produce a marketable product:

• Quiet operation. • Smooth operation, lacking in vibration. • Quick response to control input. • Ample torque and power. • High reliability and durability. • Ease of operation and maintenance.

Economic criteria pertaining to cost effective production and maintenance while in service:

• Simple in design. • Manufactured from the minimum amount of materials by economical methods. • Modular and/or compact in construction for ease of repair and ease of placement

in compact engine compartments. • Long service life.

Passenger vehicle compatibility criteria relating to typical automotive power requirements and driving cycles:

• High torque at low speeds and less at high speeds. • Efficient part load operation. • Operable at temperatures between -30°C to 50°C, and unaffected by altitude.

Efficiency criteria pertaining to fuel consumption and to the challenges we face with our environment:

• Multi-fuel capable. • Highly fuel efficient. • Low in emissions of incomplete combustion products.


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These criteria bear upon the basic design of any automotive power plant. However, the wealth of practical knowledge contained in the above cited references identifies several key pitfalls. These can be utilized as additional, invaluable criteria which must be avoided, or accounted for in the design process.

• Low tolerance of ceramic materials to mechanical stress and thermal shock. • Failure of liquid lubricants at high temperatures. • Degraded combustion process due to high temperatures. • Reduced volumetric efficiency due to increased component temperatures

encountered during induction. Ceramic Materials

Two major obstacles of the LHR engine are component strength and tribology at high temperatures. Where conventional metals and lubricants fail to perform at elevated temperatures, advanced ceramic materials provide an alternative. These materials have provided the major impetus to LHR research and development in recent decades. High hardness, high elastic moduli, resistance to corrosion and wear, strength at high temperatures, and often low thermal conductivity are physical properties of ceramics. Principal substances of interest include nitrides and carbides of silicon (Si3N4 and SiC); oxides of chromium, aluminum, and iron (Cr2O3, Al2O3, and Fe2O3); and partially stabilized oxide of zirconium, (ZrO2, or PSZ).

Low ductility, low tensile strength, and low bending strength have impeded the direct replacement of metals with ceramics in conventional engine designs. Conventional piston and cylinder stresses make the application of ceramics extremely challenging. Large piston ring loading forces produce large stresses and large friction forces. To reduce these forces, modifications to piston and connecting rod mechanics would decrease the demands which are currently placed upon tribological research.

Both monolithic ceramic components and ceramic coatings have been used by various LHR engine researchers. The work done by Adiabatic and the U.S. Army makes extensive use of titanium and ceramic coated steel components. Compared to monolithic ceramics, coatings “can be attributed to lower cost, better reliability and durability, and the ease in design of the ceramic coated diesel engine.” [17] A 100 hour endurance test of a partially cooled prototype was successfully completed. Liquid lubricant and a “self-cleaning” top piston ring were utilized. Subsequent to this test, solid lubricant top piston rings are under development.


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Most experimental LHR diesel engines to date employ liquid lubricants. Although the performance of liquid lubricants in the above studies has been improved, their continued use will severely limit further increases in combustion temperatures. The design developed in this paper will utilize expander temperatures of 1200°C to 1500°C, precluding the use of any known liquid lubricant. In fact, one of the design goals is to develop a structure that could operate with ceramic tribolical surfaces in the absence of liquid lubrication. Therefore, an investigation into other means of lubrication is essential.

M. Vittal, J.A. Borek, D.A. Marks and A.L. Boehman, made a detailed study on materials suitable for thermal barrier coatings. They were very much impressed with the properties and characteristics of Zirconia. It is a ceramic material that has very low thermal conductivity values, good strength and good thermal expansion coefficients similar to that of metals and can be able to withstand higher temperatures than metals. However, one of the disadvantages to be noted is its characteristic of changing phases as its temperature is gradually increased. Phase changes occur on the molecular level and involve the altering of molecular bonding and structure. On eliminating this phase change, it would be possible to ease the burden of construction and the use of this material in an engine that would often go through a lot of variation in temperature. Partially stabilized zirconia (PSZ) has been developed, that decreases the magnitudes of these changes and is now considered as a very good product for engine use. E.G. Giakoumis [5] had conducted experiments on coating materials that have good insulating property, along with various other properties. Zirconia and HTP (High Temperature Polymer) seemed to be the most apt materials for testing purpose and they were tested for various factors. The thermal conductivity of HTP is generally very low and is a good insulator for LHR engines. One of the basic ways to reduce heat rejection and losses in engines is to insulate the combustion chamber. The primary advantage of low heat rejection (LHR) engines is that, increased gas temperatures are possible and can maintained throughout the operation. This corresponds to an increased enthalpy in exhaust gases. The progress in raising combustion temperatures in the early days of engine design was restricted by cast iron and other construction materials that were available then. Thick walled combustion chambers were built to conduct heat away from burning gases in the cylinder. The other materials that were examined at that time, included glass derivatives that seemed to possess low thermal conductivities. Glass generally has excellent insulating qualities, low expansion ratios, low cost but, unfortunately lacks sufficient strength for its use in engines. The desirable material characteristics are

• Low thermal conductivity • Low specific heat, high flexure strength


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• High fracture toughness • High thermal shock resistance • Good wear and tear resistance • Chemical inertness • Thermal expansion ratios, equal to iron and steel.

First and Second Law Of Thermodynamics

The analysis of first and second laws of thermodynamics of a turbocharged diesel engine with cylinder wall insulation effects was done by E.G. Giakoumision of first law of thermodynamics is seen in the engine modeling processes and the second law of thermodynamics with the engine performance to evaluate the inefficiencies associated with the various processes. For second-law analysis, the key concept was the availability of energy. The availability of the material represents its potential to do useful work. Unlike energy, availability can be destroyed a result of which is the phenomenon of combustion, friction, mixing or throttling. The destruction of availability of material, which is usually termed as irreversibility is the source for the defective exploitation of fuel into useful mechanical work in an internal combustion engine.

Volumetric Efficiency

Volumetric efficiency reduces in heat rejection with the addition of ceramic insulation causes an increase in the temperature of the combustion chamber walls of an LHR engine. The volumetric efficiency should drop, as the hotter walls and residuals gas decrease the density of the inducted air. As expected all the investigations on LHR engine show poor volumetric efficiency. The deterioration in volumetric efficiency of the LHR engine can be prevented by turbo charging and then there can be more effective utilization of the exhaust gas energy.


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Thermal Efficiency

Thermal efficiency is the true indication of the efficiency with which the chemical energy input in the form of fuel is converted into useful work. Improvement in engine thermal efficiency by reduction of in-cylinder heat transfer is the key objective of LHR engine research. A lot of work has been done at many research institutes to examine the potential of LHR engines for reducing heat rejection and achieving high thermal efficiency. Researchers attribute this to in-cylinder heat transfer reduction and lower heat flux. However their report proposes that thermal efficiency reduces with insulation. They all attribute this to an increase in the convective heat transfer coefficient, higher heat flux (increase in-cylinder heat transfer) and deteriorated combustion. The in-cylinder heat transfer characteristics of LHR engine are still not clearly understood. Thus, the effect of combustion chamber insulation on reducing heat rejection and thermal efficiency is not clearly is unable to be understood till date. Fuel Consumption

Numerous investigators have modeled and analyzed the effects of in-cylinder thermal insulation on fuel consumption. In general, it has been reported that fuel consumption of, naturally aspirated LHR engine is in range of 0 to 10% higher, turbocharged LHR engine in the order of 0 to 15% lower, when compared with the conventionally cooled engine. R.H. Thring indicates reduction in fuel consumption, and attributes this to reduced friction due to increased wall temperature. He also states that there is no measurable improvement in fuel consumption based on the thermodynamics involved.


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Effect of Insulation on Emissions Unburned Hydrocarbon

The emissions of unburned hydrocarbon from the LHR engines are more likely to be reduced because of the decreased quenching distance and the increased lean flammability limit. The higher temperatures both in the gases and at the combustion chamber walls of the LHR engine assist in permitting the oxidation reactions to proceed close to completion. Most of the investigations show reduction in HC level. Carbon monoxide

It is expected that LHR engines would produce less carbon monoxide for reasons similar to those for unburned hydrocarbon. The reduced level of pre-mixed combustion in the insulated engine decreases the initial production of CO and the higher temperatures during diffusion combustion accelerate the oxidation of CO.


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Nitrogen Oxides

NOx reactions are highly temperature dependent. NOx is formed by chain reactions involving nitrogen and oxygen in the air. Since diesel engines always operate with the excess air, NOx emissions are mainly a function of gas temperature and residence time. Most of the earlier investigations show that NOx emission from LHR engines is generally higher than that in water-cooled engines. Particulates Emission

The particulates in exhaust gas are collected in such a way that the particulates may be solid or liquid that collects in the filter and the particulate is analyzed and the graph is drawn .were in ceramic coated engine the particulate emission is reduced by applying the high loads. This is because at light loads a greater fraction of the fuel energy is lost in coolant. thus the decrease in energy rejection to the coolant due to ceramic coating is lighter loads, and a larger decrease in particulate emission is realized .The soot particulates are more granular in the ceramic coated engine in which it shows that particulates appear to be a very less in the ceramic coated engine .

2.2 HYDROGEN ENGINE Introduction

Diesel engines are the main prime movers for public transportation vehicles, stationary power generation units and for agricultural applications. But diesel engines are found to emit more NOx and smoke emissions in addition to its rapid depletion. Hence it is very important to find a best alternate fuel, which can fully or partially replace diesel


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which emits fewer pollutants to the atmosphere from diesel engines. In this regard hydrogen is receiving considerable attention as an alternative source of energy to replace the rapidly depleting petroleum resources. Its clean burning characteristics provide a strong incentive to study its utilization as a possible alternate fuel. While electrochemically reacting hydrogen in fuel cell was considered to be the cleanest and most efficient means of using hydrogen, it was believed by many to be a technology of the distant future. Currently fuel cell technology is expensive and bulky. In the near term, the use of hydrogen in internal combustion engine may be feasible as a low cost technology to reduce emissions. Usage of hydrogen

Hydrogen can be adapted in both SI and CI engines. In SI engine hydrogen can be used as a sole fuel, but in the case of CI engine dual fuelling technique is used.

The concept of using hydrogen as an alternative to diesel fuel in C.I engines was a recent one. As the self ignition temperature of hydrogen (858 K) is higher than diesel (453 K), hydrogen cannot be ignited by compression. Hence it requires the use of external ignition source like a spark plug or a glow plug.

One of the alternative methods is to use diesel as a pilot fuel for ignition purpose or by using ignition improvers like DEE. The methods of using hydrogen in C.I. engines are; 1. Hydrogen enrichment in air 2. Hydrogen injection in the intake system 3. In cylinder injection

Hydrogen substitution by 10-20 % of energy share in diesel reduces substantially the smoke, particulate and soot emissions. Hydrogen powered I.C. engines produces more or similar power compared to diesel. The problems of preignition and backfire are less severe and knock can be eliminated compared to spark ignited engines that make the hydrogen usage to be safer in CI mode rather than SI mode. Recent developments in India

The Ministry of Non-conventional Energy Sources with an annual operating budget of US $ 100 million has been extensively supporting hydrogen and fuel cell research at many of India’s top universities and public research laboratories. Researchers have been successful in the biological production of hydrogen from organic effluents and


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a large-scale bioreactor of 12.5 m3 capacity is being developed in India. Efforts are also underway to utilize significant amounts of hydrogen produced as a byproduct in many industries such as the chlor-alkali industry, which currently has no applications. In 2003 India joined the International partnership for the hydrogen economy a move that will provide impetus to collaborative research and funding opportunities. The US Department of Energy and US based ECD Ovonics, Inc have already launched a collaborative effort with Indian auto manufacturer to launch a hydrogen powered three wheeler with a grant of US $ 5,00,000 from the US agency for international development. The Ministry of Non-Conventional Energy sources have set up a National Hydrogen Energy Board (NHEB) under the chairmanship of Mr. Ratan Tata for the development of national hydrogen energy road map. NHEB has also proposed to launch 1000 hydrogen vehicles by 2009 including 500 small three wheelers, 300 heavy vehicles and 200 buses [8].

Several works have been done earlier on hydrogen. Hydrogen engine develops lesser power mainly due to its low volumetric energy density. Various fuel induction techniques such as carburetion, continuous manifold injection, timed manifold injection (TMI) and direct cylinder injection were investigated and TMI was adopted by the author since it gave higher thermal efficiency and eliminated undesirable combustion. It was observed that under stoichiometric condition, hydrogen occupies 29.6 % by volume whereas gasoline-air mixture occupies only about 2 % by volume. The results indicated that the thermal efficiency of the intake port injection was higher than in-cylinder injection at all equivalence ratios. In order to minimize the possibility of flashback occurrence, the injection timing of the hydrogen injection was fixed in coordination with the intake valve opening timing. Advantage of hydrogen fueled engine

• The most important advantage of hydrogen fueled engine is that they emit fewer pollutants than comparable diesel fueled engine.

• In hydrogen fueled engine, the principal exhaust products are water vapor and NOx. Emissions such as HC, CO, CO2, SOx and smoke are either not observed or are very much lower than those of diesel engine.

• Unburnt hydrogen may also come out of the engine, but this is not a problem since hydrogen is non-toxic and does not involve in any smog producing reaction.

• NOx are the most significant emission of concern from a hydrogen engine. NOx have an adverse effect on air quality through the formation of ozone or acid rain.


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Technique to reduce NOx

In order to reduce the NOx, in the present work exhaust gas recirculation (EGR) technique was adopted. Exhaust gases from the engine were by-passed, regulated and cooled by using a counter flow type heat exchanger in the EGR unit. The flow rate of EGR cooling water was varied in such a way that the cooled exhaust gas temperature was maintained around 30°C. The cooled exhaust gas was allowed to pass through a filtering device to remove the soot and particulate matter from the exhaust gas. The EGR flow rate was determined by measuring the CO2 concentration in the exhaust gas. The EGR percentage was calculated from the ratio of CO2 concentration present in the intake manifold to the CO2 concentration present in the exhaust gas. The flow rate of EGR was increased until the necessary CO2 concentration in the intake manifold was attained. The schematic view of the EGR unit is shown in Figure 1.

Safety arrangements

Hydrogen fuel is often associated with either the Hindenburg or Challenger disasters or even the hydrogen bomb. However other fuels such as gasoline and natural gas pose similar dangers. Hydrogen actually has a good overall safety record due to strict adherence to regulations and procedures, good training for the persons who handle hydrogen. In order to have the overall safety the safety devices given below and some safety measures have been taken for hydrogen operation.

• A special, effective hydrogen sensor was used to monitor the hydrogen gas in the operating environment and also used to sense any leak of hydrogen through the


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pipeline during the operation of the engine. The sensor works on the principle of electrochemical reaction. Hydrogen has the highest diffusivity characteristics, of about 3-8 times faster in air. Any hydrogen leakage will result in quicker dispersion in air compared to that of hydrocarbon dispersion. Hence it will not form any cloud of hydrogen vapour in the working space. Blowers were also made available to disperse the hydrogen gas if present in the environment and proper ventilation was provided during engine operation. The hydrogen cylinders were also stored away from the working environment. The crankcase for the hydrogen-operated engine was properly ventilated to avoid ignition from taking place inside due to blow by gases. The clouds of gases collected in the crankcase were removed from the rocker arm holes and were vented into the atmosphere.

• Flame arrestor was used to suppress explosion inside the hydrogen cylinder. The

flame arrestor consists of a tank partly filled with water with a fine wire mesh to prevent the flame propagation beyond the wire mesh. The flame also gets quenched while reaching the water surface in case of any backfire.

• A non-return line was provided to prevent the reverse flow of hydrogen into the

system. Such a possibility of reverse flow can occur sometimes in hydrogen – injected engine, particularly in the later part of injection duration.

• Flow indicator was used to visualize the flow of hydrogen during engine

operations. As the hydrogen was allowed to pass through a glass tube containing water, bubbles were formed during hydrogen flow, which clearly showed the flow of hydrogen.

Figure Methodology of hydrogen enrichment in air


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Engine Operation

Figure Schematic view of the experimental setup

• The hydrogen from the flame trap was passed to the 2-way valve. One end of the two-way valve was connected to the pipeline and it was kept away from the working area.

• This was done to remove the excess hydrogen in the fuel line during the engine

shutoff time. The other end of the two-way valve was connected to a selector switch, which will permit the supply of hydrogen to either the port fuel injector or the manifold injector.

• The port injector was placed in the engine head 13 mm above the intake valve and

the manifold injector was placed at a distance of 100 mm away from the engine head in the intake manifold.

• A Quantum make gas injector was used. An electronic control unit (ECU)

controlled the injector opening timing and duration.

• An infrared detector was used to give the signal to the ECU for the injector opening.


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• Based on the preset timing and duration the injector was opened for injection and closed after injection. The injection timing and injection duration was varied within the specified range by using a knob.

• The power supply for opening the injector was 4A and for holding the armature to

inject the fuel was 1A.

• Based on the preset timing the hydrogen flow was taking place and the flow was controlled by using the pressure regulator and also by using the digital mass flow controller.

Brake thermal efficiency

Variation of brake thermal efficiency with load for optimized EGR flow rate of 20 %

The increase in efficiency with EGR at part loads compared to diesel is due to the recirculation of active radicals that enhances the combustion process by providing hotter environment in the combustion chamber. In general the brake thermal efficiency increases with increase in EGR percentage compared to diesel. This is because at no load lean mixture is admitted into the engine cylinder during suction stroke and increasing the quantity of exhaust gases results in the reduction of air-fuel ratio and increases the inlet charge temperature thus enhancing the thermal efficiency of the engine.

The reduction in efficiency at full load is due to the high EGR flow rates resulting in deficiency in oxygen concentration in addition to the replacement of air hydrogen.


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At full load the thermal efficiency in manifold injection drops by 6 % compared to that in port injection with 20 % EGR and the reduction in efficiency is due to smaller replacement of air by hydrogen compared to port injection.

The higher specific heat capacity of both CO2 and H2O and high flow rates of EGR also reduces the average combustion temperature inside the combustion chamber thus reducing the brake thermal efficiency at full load. Specific energy consumption

Specific energy consumption is defined as the amount of energy needed to produce unit kilowatt power. It is observed that the SEC decreases with increase in EGR flow rates at low load conditions. At part loads due to the recycling of exhaust gases the inlet charge temperature increases which leads to accelerated combustion resulting in the reduction of SEC compared to diesel. With increase in EGR flow percentages at part loads the SEC drops due to the replacement of air by inert gases which improve the over all charge temperature at part loads resulting in SEC reduction. At full load less air is admitted due to replacement of air by hydrogen and EGR. Hence more fuel is admitted to attain the rated power, which results in an increase in SEC. Table 9 gives the energy share ratio of hydrogen to diesel in port injection.

Generally the NOX emission tends to reduce significantly with increase in EGR percentages at all the load conditions due to the rise in total heat capacity of the working gases, which lowers the elevated temperature. At full load the NOx emission reduces with increase in EGR flow percentage, due to the presence of inert gas (CO2 and H2O) inside the combustion chamber, which reduces the peak combustion temperature, in addition to the replacement of oxygen. As a result of reduction in both the parameters the


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NOX percentage reduces with the use of EGR. Compared to that of port injection, manifold injection shows a reduction in NOX.

Smoke

The smoke emission reduces with both increase in hydrogen and with increase in EGR percentage. Even with EGR, the smoke concentration is lesser than diesel upto 75 % load but it increases in full load condition due to richening of gas-air mixture, promoting the combustion. At higher loads with high EGR flow rates, the intensity of smoke is higher which may be due to the reason that, some of the oxygen in the inlet charge is replaced by recycled exhaust gases results in improper combustion.

Carbon Monoxide

Based on the oxygen availability the CO formed during the combustion is oxidized further to form CO2. In general in hydrogen diesel dual fuel operation at full


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load condition combustion takes place in a slightly richer mixture than normal diesel combustion due to the air replacement by hydrogen in the intake manifold that causes a marginal increase in CO concentration. The CO emission at no load and full load is higher in manifold injection. An increase in EGR percentage at no load does not show a dramatic effect on CO variation.

Hydrocarbon emission

The reason for the increase in HC emission is due to extremely lean mixture (mixture becomes too lean to auto ignite) and the longer ignition delay period. A small increase in ignition delay by 2º CA causes an increase in HC emission by 60-70 %.

For hydrogen diesel dual fuel operation the delay period is lower, due to the rapid

combustion of hydrogen that assists diesel combustion resulting in a reduction in delay period. The decrease in HC in manifold injection compared to port injection is due to


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more time available for mixing hydrogen with air. The increase in HC is due to the flame quenching at part load condition and reduction in oxygen in the inlet charge by the EGR admitted into the cylinder. Compared to port injection an increase in HC in the order of 25 % is noticed in manifold injection at full load with 20 % EGR. The increase may be due to the large replacement of oxygen in the inlet charge. 2.4 HOMOGENEOUS CHARGE COMPRESSION IGNITION (HCCI) Introduction

The internal combustion engine is the key to the modern society. Without the transportation performed by the millions of vehicles on road and at sea we would not have reached the living standard of today. We have two types of internal combustion engines, the spark ignition, SI, and the compression ignition, CI. Both have their merits. The SI engine is a rather simple product and hence has a lower first cost. This engine type can also be made very clean as the three-way catalyst, TWC, is effective for exhaust aftertreatment. The problem with the SI engine is the poor part load efficiency due to large losses during gas exchange and low combustion and thermodynamic efficiency. The CI engine is much more fuel efficient and hence the natural choice in applications where fuel cost is more important than first cost. The problem with the CI engine is the emissions of nitrogen oxides, NOx, and particulates; PM. Aftertreatment to reduce NOx and particulates is expensive and still not generally available on the market. The obvious ideal combination would be to find an engine type with the high efficiency of the CI engine and the very low emissions of the SI engine with TWC. One such candidate is named Homogeneous Charge Compression Ignition, HCCI.

HCCI is an alternative piston-engine combustion process that can provide efficiencies as high as compression-ignition, direct-injection (CIDI) engines (an advanced version of the commonly known diesel engine) while, unlike CIDI engines, producing ultra-low oxides of nitrogen (NOx) and particulate matter (PM) emissions. HCCI engines operate on the principle of having a dilute, premixed charge that reacts and burns volumetrically throughout the cylinder as it is compressed by the piston. In some regards, HCCI incorporates the best features of both spark ignition (SI) and compression ignition (CI), as shown in Figure 1. As in an SI engine, the charge is well mixed, which minimizes particulate emissions, and as in a CIDI engine, the charge is compression ignited and has no throttling losses, which leads to high efficiency. However, unlike either of these conventional engines, the combustion occurs simultaneously throughout the volume rather than in a flame front. This important attribute of HCCI allows combustion to occur at much lower temperatures, dramatically reducing engine-out


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emissions of NOx. Most engines employing HCCI to date have dual mode combustion systems in which traditional SI or CI combustion is used for operating conditions where HCCI operation is more difficult. Typically, the engine is cold-started as an SI or CIDI engine, then switched to HCCI mode for idle and low- to mid-load operation to obtain the benefits of HCCI in this regime, which comprises a large portion of typical automotive driving cycles. For high-load operation, the engine would again be switched to SI or CIDI operation. Research efforts are underway to extend the range of HCCI operation, as discussed in the body of this report.

Figure HCCI (as most-typically envisioned) would use low-pressure fuel injection outside the cylinder, and no ignition system. If charge stratification is desired, it may be

necessary to use in cylinder injection. HCCI fundamentals

THE HCCI PRINCIPLE – HCCI means that the fuel and air should be mixed before combustion starts and that the mixture is autoignited due to the increase in temperature from the compression stroke. Thus HCCI is similar to SI in the sense that both engines use a premixed charge and HCCI is similar to CI as both rely on autoignition for combustion initiation. However, the combustion process is totally different for the three types.


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Figure The difference between SI and HCCI combustion process. Q= total amount of heat, q=heat per mass unit, w=mass [3]

Figure shows the difference between (a) SI combustion and (b) HCCI. In the SI

engine we have three zones, a burnt zone, an unburned zone and between them a thin reaction zone where the chemistry takes place. This reaction zone propagates through the combustion chamber and thus we have flame propagation. Even though the reactions are fast in the reaction zone, the combustion process will take some time as the zone must propagate from spark plug (zero mass) to the far liner wall. With the HCCI process the entire mass in the cylinder will react at once. We see that the entire mass is active but the reaction rate is low both locally and globally. This means that the combustion process will take some time even if all the charge is active. The total amount of heat released, Q, will be the same for both processes. It could be noted that the combustion process can have the same duration even though HCCI normally has a faster burn rate. Initial tests in Lund on a two stroke engine revealed the fundamental difference between these two types of engines.

Figure shows normal flame propagation from two spark plugs at the rated speed of 9000 rpm. We see two well defined flames and a sharp border between burned and unburned zones. Figure shows the same engine when HCCI combustion was triggered by using regular gasoline (RON 95) instead of iso-octane. The engine speed was increased up to 17000 rpm and a more distributed chemiluminescense image resulted.


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Figure SI flame propagation in 2-Stroke

engine at 9000 rpm. Figure HCCI combustion in 2-Stroke

engine at 17000 rpm. Requirements for HCCI The HCCI combustion process puts two major requirements on the conditions in the cylinder: (a) The temperature after compression stroke should equal the autoignition temperature of the fuel/air mixture. (b) The mixture should be diluted enough to give reasonable burn rate.

Figure Ignition temperature for a few fuels as a function of dilution (••).

Figure shows the autoignition temperature for a few fuel as a function of •. The

autoignition temperature has some correlation with the fuels’ resistance of knock in SI engines and thus the octane number. For iso-octane, the autoignition temperature is roughly 1000 K. This means that the temperature in the cylinder should be 1000 K at the end of the compression stroke where the reactions should start. This temperature can be reached in two ways, either the temperature in the cylinder at the start of compression is controlled or the increase in temperature due to compression i.e. compression ratio is


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controlled. It could be interesting to note that the autoignition temperature is a very weak function of air/fuel ratio.

The change in autoignition temperature for iso-octane is only 50 K with a factor 2 changes in •. Figure also shows the normal rich and lean limits found with HCCI. With a too rich mixture the reactivity of the charge is too high. This means that the burn rate becomes extremely high with richer mixtures. If an HCCI engine is run too rich the entire charge can be consumed within a fraction of a crank angle. This gives rise to extreme pressure rise rates and hence mechanical stress and noise. With a high autoignition temperature like that of natural gas, it is also possible that formation of NOx can be the load limiting factor. Figure 8 shows the NO formation as a function of maximum temperature. Very low emission levels are measured with ethanol. If the combustion starts at a higher temperature like with natural gas, the temperature after combustion will also be higher for a given amount of heat released.

On the lean side, the temperature increase from the combustion is too low to have complete combustion. Partial oxidation of fuel to CO can occur at extremely lean mixtures; •above 14 has been tested. However, the oxidation of CO to CO2 requires a temperature of 1400-1500 K. As a summary, HCCI is governed by three temperatures. We need to reach the auto ignition temperature to get things started; the combustion should then increase the temperature to at least 1400 K to have good combustion efficiency but it should not be increased to more that 1800 K to prevent NO formation. Benefits of HCCI


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The fuel efficiency of HCCI has been compared to that of normal SI operation. Noted that an improvement of fuel efficiency from 15% to 30% at 1.5 bar BMEP. This is an improvement of 100% equivalent to a reduction of fuel consumption with 50%. Also found that much higher fuel consumption benefit for HCCI than for DISI concepts.

The major benefit of HCCI compared to CI is the low emissions of NOx and PM. The CI engine normally has a trade-off between particulates and NOx. If the engine operates at conditions with higher in-cylinder peak temperature, the oxidization of soot will be good but the thermal production of NO will increase. If on the other hand the engine is operated with lower temperature NO can be suppressed but PM will be high due to bad oxidation.

In the CI engine, NO is formed in the very hot zones with close to stoichiometric conditions and the soot is formed in the fuel rich spray core. The incylinder average air/fuel ratio is always lean but the combustion process is not. This means that we have a large potential to reduce emissions of NOx and PM by simply mixing fuel and air before combustion. The NOx is normally less than 1/500 of the CI level and no PM is generated by combustion. Advantages of HCCI

The advantages of HCCI are numerous and depend on the combustion system to which it is compared. Relative to SI gasoline engines, HCCI engines are more efficient, approaching the efficiency of a CIDI engine. This improved efficiency results from three sources: the elimination of throttling losses, the use of high compression ratios (similar to a CIDI engine), and a shorter combustion duration (since it is not necessary for a flame to propagate across the cylinder). HCCI engines also have lower engine-out NOx than SI engines. Although three-way catalysts are adequate for removing NOx from current-technology SI engine exhaust, low NOx is an important advantage relative to spark-ignition, direct-injection (SIDI) technology, which is being considered for future SI engines.

Relative to CIDI engines, HCCI engines have substantially lower emissions of PM and NOx. (Emissions of PM and NOx are the major impediments to CIDI engines meeting future emissions standards and are the focus of extensive current research.) The low emissions of PM and NOx in HCCI engines are a result of the dilute homogeneous air and fuel mixture in addition to low combustion temperatures. The charge in an HCCI engine may be made dilute by being very lean, by stratification, by using exhaust gas recirculation (EGR), or some combination of these. Because flame propagation is not


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required, dilution levels can be much higher than the levels tolerated by either SI or CIDI engines. Combustion is induced throughout the charge volume by compression heating due to the piston motion, and it will occur in almost any fuel/air/exhaust-gas mixture once the 800 to 1100 K ignition temperature (depending on the type of fuel) is reached. In contrast, in typical CI engines, minimum flame temperatures are 1900 to 2100 K, high enough to make unacceptable levels of NOx. Additionally, the combustion duration in HCCI engines is much shorter than in CIDI engines since it is not limited by the rate of fuel/air mixing. This shorter combustion duration gives the HCCI engine an efficiency advantage. Finally, HCCI engines may be lower cost than CIDI engines since they would likely use lower-pressure fuel-injection equipment.

Another advantage of HCCI combustion is its fuel-flexibility. HCCI operation has been shown using a wide range of fuels. Gasoline is particularly well suited for HCCI operation. Highly efficient CIDI engines, on the other hand, cannot run on gasoline due to its low cetane number. With successful R&D, HCCI engines might be commercialized in light-duty passenger vehicles by 2010, and by 2015 as much as a half-million barrels of oil per day may be saved.

Tests have also shown that under optimized conditions HCCI combustion can be very repeatable, resulting in smooth engine operation. The emission control systems for HCCI engines have the potential to be less costly and less dependent on scarce precious metals than either SI or CIDI engines.

HCCI is potentially applicable to both automobile and heavy truck engines. In fact, it could be scaled to virtually every size-class of transportation engines from small motorcycle to large ship engines. HCCI is also applicable to piston engines used outside the transportation sector such as those used for electrical power generation and pipeline pumping. Challenges for the HCCCI engine operation

HCCI combustion is achieved by controlling the temperature, pressure and composition of the air/fuel mixture so that it auto ignites near top dead center (TDC) as it is compressed by the piston. This mode of ignition is fundamentally more challenging than using a direct control mechanism such as a spark plug or fuel injector to dictate ignition timing as in SI and CIDI engines, respectively. While HCCI has been known for some twenty years, it is only with the recent advent of electronic engine controls that HCCI combustion can be considered for application to commercial engines. Even so, several technical barriers must be overcome before HCCI engines will be viable for high-


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volume production and application to a wide range of vehicles. The following describes the more significant challenges for developing practical HCCI engines for transportation. Greater detail regarding these technical barriers, potential solutions, and the R&D needed to overcome them are provided in Section V. Some of these issues could be mitigated or eliminated if the HCCI engine was used in a series hybrid-electric application, as discussed above.

1. Controlling Ignition Timing over a Range of Speeds and Loads

Expanding the controlled operation of an HCCI engine over a wide range of speeds and loads is probably the most difficult hurdle facing HCCI engines. HCCI ignition is determined by the charge mixture composition and its temperature history (and to a lesser extent, its pressure history). Changing the power output of an HCCI engine requires a change in the fueling rate and, hence, the charge mixture. As a result, the temperature history must be adjusted to maintain proper combustion timing. Similarly, changing the engine speed changes the amount of time for the autoignition chemistry to occur relative to the piston motion. Again, the temperature history of the mixture must be adjusted to compensate. These control issues become particularly challenging during rapid transients.

Several potential control methods have been proposed to provide the

compensation required for changes in speed and load. Some of the most promising include varying the amount of hot EGR introduced into the incoming charge, using a VCR mechanism to alter TDC temperatures, and using VVT to change the effective compression ratio and/or the amount of hot residual retained in the cylinder. VCR and VVT are particularly attractive because their time response could be made sufficiently fast to handle rapid transients. Although these techniques have shown strong potential (see Section III B), they are not yet fully proven, and cost and reliability issues must be addressed. 2. Extending the Operating Range to High Loads

Although HCCI engines have been demonstrated to operate well at low-to-medium loads, difficulties have been encountered at high-loads. Combustion can become very rapid and intense, causing unacceptable noise, potential engine damage, and eventually unacceptable levels of NOx emissions. Preliminary research indicates the operating range can be extended significantly by partially stratifying the charge (temperature and mixture stratification) at high loads to stretch out the heat-release event.


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Several potential mechanisms exist for achieving partial charge stratification, including varying in-cylinder fuel injection, injecting water, varying the intake and in-cylinder mixing processes to obtain non-uniform fuel/air/residual mixtures, and altering cylinder flows to vary heat transfer. The extent to which these techniques can extend the operating range is currently unknown, and R&D will be required. Because of the difficulty of high-load operation, most initial concepts involve switching to traditional SI or CI combustion for operating conditions where HCCI operation is more difficult. This dual mode operation provides the benefits of HCCI over a significant portion of the driving cycle but adds to the complexity by switching the engine between operating modes. 3. Cold-Start Capability

At cold start, the compressed-gas temperature in an HCCI engine will be reduced because the charge receives no preheating from the intake manifold and the compressed charge is rapidly cooled by heat transferred to the cold combustion chamber walls. Without some compensating mechanism, the low compressed-charge temperatures could prevent an HCCI engine f rom firing. Various mechanisms for cold-starting in HCCI mode have been proposed, such as using glow plugs, using a different fuel or fuel additive, and increasing the compression ratio using VCR or VVT. Perhaps the most practical approach would be to start the engine in spark-ignition mode and transition to HCCI mode after warm-up. For engines equipped with VVT, it may be possible to make this warm-up period as short as a few fired cycles, since high levels of hot residual gases could be retained from previous spark-ignited cycles to induce HCCI combustion. Although solutions appear feasible, significant R&D will be required to advance these concepts and prepare them for production engines. 4. Hydrocarbon and Carbon Monoxide Emissions

HCCI engines have inherently low emissions of NOx and PM, but relatively high

emissions of hydrocarbons (HC) and carbon monoxide (CO). Some potential exists to mitigate these emissions at light load by using direct in-cylinder fuel injection to achieve appropriate partial-charge stratification. However, in most cases, controlling HC and CO emissions from HCCI engines will require exhaust emission control devices. Catalyst technology for HC and CO removal is well understood and has been standard equipment on automobiles for many years. However, the cooler exhaust temperatures of HCCI engines may increase catalyst light-off time and decrease average effectiveness. As a result, meeting future emission standards for HC and CO will likely require further development of oxidation catalysts for low-temperature exhaust streams. However, HC and CO emission control devices are simpler, more durable, and less dependent on


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scarce, expensive precious metals than are NOx and PM emission control devices. Thus, simultaneous chemical oxidation of HC and CO (in an HCCI engine) is much easier than simultaneous chemical reduction of NOx and oxidation of PM (in a CIDI engine). In addition, HC and CO emission control devices are simpler, more durable, and less dependent on scarce, expensive precious metals. 2.5 VARIABLE COMPRESSION RATIO ENGINE

Conventional gasoline engines operate at a fixed compression ratio, which is set low enough to prevent premature ignition of the fuel, or “knock,” at high power levels under fast acceleration, high speeds, or heavy loads. Most of the time, however, gasoline engines operate at relatively low power levels under slow acceleration, lower speed, or light loads. If the compression ratio were increased at low-power operation, gasoline engines could achieve higher fuel efficiency.

A variable compression ratio (VCR) engine is able to operate at different compression ratios, depending on the particular vehicle performance needs. The VCR engine is optimized for the full range of driving conditions, such as acceleration, speed, and load. At low power levels, the VCR engine operates at high compression to capture fuel efficiency benefits, while at high power levels, it operates at low compression levels to prevent knock.

To further improve fuel economy, the VCR engine is small, with about one third the displacement volume of a conventional gasoline engine. A supercharger boosts engine peak power when needed for occasional hard acceleration or hill climbing.

Computer modeling showed that the projected efficiencies for the VCR engine should meet the propulsion system requirements needed to reach the goal of 80 miles per gallon set by the Partnership for a New Generation of Vehicles (PNGV). AVL Power train conducted dynamometer tests on an engine in which the compression ratios were varied. Findings from these tests include the following:

• The test results validated the efficiencies predicted by the computer model. • The test engine exhibited a very favorable burn rate and coefficient of variance,

which allows the application of lean-burn technology that, will further improve efficiency.


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• A preliminary evaluation of hydrocarbon and nitrogen oxide emission levels yielded results that were favorable and consistent with expectations for a gasoline engine of similar power output.

Benefits of VCR

At the low power levels (0-20 kW), typical of most vehicle operating conditions, the VCR engine could achieve efficiency comparable to that of a diesel engine – about 25% higher than that of a conventional gasoline engine (see graph on page 1). At the same time, because it is a gasoline engine, the VCR engine should be able to achieve federal Tier 2 and California LEV 2 emission standards. Development in future

• Develop an optimized cylinder head for the VCR engine that is capable of realizing the full potential of this technology.

• Conduct an optimization assessment and determine the best engine configuration

and develop optimized components for a second-generation engine.

• Develop a second-generation engine by using assessment results and optimized components.


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2.6 HOT BULB ENGINE

The hot bulb engine, or hot bulb or heavy oil engine is a type of internal combustion engine. It is an engine in which fuel is ignited by being brought into contact with a red hot metal surface inside a bulb. Most hot bulb engines were produced as one-cylinder low-speed two-stroke crankcase scavenging units.

The concept of this engine was established by Herbert Akroyd Stuart at the end of the 19th century. The first prototypes were built in 1886 and production started in 1891 by Richard Hornsby & Sons of Grantham, Lincolnshire, England under the title Hornsby Akroyd Patent Oil Engine under licence. It was later developed in the USA by the German emigrants Mietz and Weiss by combining it with thetwo-stroke engine developed by Joseph Day. Similar engines, for agricultural and marine use, were built by Bolinder and Pythagoras engine factory in Sweden. Bolinder is now part of the Volvo group. A Hornsby-Akroyd hot bulb engine, built to the original horizontal cylinder, four-stroke design. This particular engine has been adapted to run on lamp oil. Akroyd-Stuart's heavy oil engine (compared to spark-ignition) is distinctly different from Rudolf Diesel's better-known engine where ignition is initiated through the heat of compression. An oil engine will have a compression ratio of about 3:1, where a typical Diesel engine will have a compression ratio ranging between 15:1 and 20:1. Furthermore fuel is injected during the intake stroke and not at the end of the compression stroke as in a diesel.


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Working principle

The hot-bulb engine shares its basic layout with nearly all other internal combustion engines, in that it has a piston, inside a cylinder, connected to a flywheel via a connecting rod and crankshaft. Akroyd-Stuart's original engine operated on the four-stroke cycle (Induction, Compression, Power, Exhaust) and Hornsby continued to build engines to this design, as did several other British manufacturers such as Blackstone and Crossley. Manufacturers in Europe, Scandinaviaand in the USA built engines working on the two-stroke cycle with crankcase scavenging. The latter type formed the majority of hot-bulb engine production. The flow of gases through the engine is controlled by valves in four-stroke engines, and by the piston covering and uncovering ports in the cylinder wall in two-strokes.

In the hot-bulb engine combustion takes place in a separated combustion chamber, the "vaporizer" (also called the "hot bulb"), usually mounted on the cylinder head, into which fuel is sprayed. It is connected to the cylinder by a narrow passage and is heated by the combustion while running; an external flame such as a blow-lamp or slow-burning wick is used for starting (on later models sometimes electric heating or pyrotechnics was used). Another method is the inclusion of a spark plug and vibrator coil ignition. The engine could be started on petrol and switched over to oil after it had warmed to running temperature.

The pre-heating time depends on the engine design, the type of heating used and the ambient temperature, but generally ranges from 2–5 minutes (for most engines in a temperate climate) to as much as half an hour (if operating in extreme cold or the engine is especially large). The engine is then turned over, usually by hand but sometimes by compressed air or an electric motor.

Once the engine is running, the heat of compression and ignition maintains the hot-bulb at the necessary temperature and the blow-lamp or other heat source can be removed. From this point the engine requires no external heat and requires only a supply of air, fuel oil and lubricating oil to run. However, under low power the bulb could cool off too much, and a throttle can cut down the cold fresh air supply. Also, as the engine's load increased, so does the temperature of the bulb, causing the ignition period to advance; to counteract pre-ignition, water is dripped into the air intake.[5] Equally, if the load on the engine is low, combustion temperatures may not be sufficient to maintain the temperature of the hot-bulb. Many hot-bulb engines cannot be run off-load without auxiliary heating for this reason.


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Four-stroke engines

Air is drawn into the cylinder through the intake valve as the piston descends (the induction stroke). During the same stroke, fuel is sprayed into the vaporizer by a mechanical (jerk-type) fuel pump through a nozzle. The air in the cylinder is then forced through the top of the cylinder as the piston rises (the compression stroke), through the opening into the vaporizer, where it is compressed and its temperature rises. The vaporized fuel mixes with the compressed air and ignites primarily due to the heat of the hot bulb generated while running or heat applied to the hot-bulb prior to starting. By contracting the bulb to a very narrow neck where it attaches to the cylinder, a high degree of turbulence is set up as the ignited gases flash through the neck into the cylinder, where combustion is completed. The resulting pressure drives the piston down (the power stroke). The piston's action is converted to a rotary motion by the crankshaft-flywheel assembly, to which equipment can be attached for work to be performed. The flywheel stores momentum, some of which is used to turn the engine when power is not being produced. The piston rises, expelling exhaust gases through the exhaust valve (the exhaust stroke). The cycle then starts again.

Two-stroke engines

The cycle starts with the piston at the bottom of its stroke. As it rises, it draws air into the crankcase through the Inlet Port. At the same time fuel is sprayed into the vaporizer. The charge of air on top of the piston is compressed into the vaporizer where it is mixed with the atomized fuel and ignites. The piston is driven down the cylinder. As it descends the piston first uncovers the Exhaust Port. The pressurized exhaust gases flow out of the cylinder. A fraction after the Exhaust Port is uncovered; the descending piston uncovers the Transfer Port. The piston is now pressurizing the air in the crankcase, which is forced through the Transfer Port and into the space above the piston. Part of the incoming air charge is lost out of the still-open Exhaust Port to ensure all the exhaust gases are cleared from the cylinder (a process known as 'scavenging'). The piston then reaches the bottom of its stroke and begins to rise again, drawing a fresh charge of air into the crankcase and completing the cycle. Induction and Compression are carried out on the upward stroke and Power and Exhaust on the downward stroke.

A supply of lubricating oil must be fed to the crankcase to supply the crankshaft bearings. Since the crankcase is also used to supply air to the engine, the engine's lubricating oil is carried into the cylinder with the air charge, burnt during


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combustion and carried out of the exhaust. The oil carried from the crankcase to the cylinder is used to lubricate the piston. This means that a two-stroke hot-bulb engine will gradually burn its supply of lubricating oil – a design known as a 'total loss' lubricating system. There were also designs that employed a scavenge pump or similar to remove oil from the crankcase and return it to the lubricating oil reservoir. Lanz hot-bulb tractors and their many imitators had this feature. This reduces oil consumption considerably.

In addition, if excess crankcase oil is present on start up, there is a danger of the engine starting and accelerating uncontrollably to well past the RPM limits of the rotating and reciprocating components. This can result in destruction of the engine. There is normally a bung or stopcock that allows draining of the crankcase before starting.

The lack of valves and the doubled-up working cycle also means that a two-stroke hot bulb engine can run equally well in both directions. A common starting technique for smaller two-stroke engines is to turn the engine over against the normal direction of rotation. The piston will 'bounce' off the compression phase with sufficient force to spin the engine the correct way and start it. This bi-directional running was an advantage in marine applications as the engine could, like the steam engine, drive a vessel forward or backwards without the need for a gearbox. The direction could be reversed either by stopping the engine and starting it again in the other direction or, with sufficient skill and timing on the part of the operator, slowing the engine until it carried just enough momentum to bounce against its own compression and run the other way. This was an undesirable quality in hot-bulb powered tractors equipped with gearboxes. At very low engine speeds the engine could reverse itself almost without any change in sound or running quality and without the driver noticing until the tractor drove in the opposite direction to that intended. Lanz Bulldog tractors featured a dial, mechanically driven by the engine that showed a spinning arrow. The arrow pointed in the direction of normal engine rotation – if the dial spun the other way the engine had reversed itself.

Advantages

At the time the hot-bulb engine was invented, its great attractions were its economy, simplicity, and ease of operation in comparison to the steam engine, which was then the dominant source of power in industry. Steam engines achieved an average thermal efficiency (the percent of heat generated that is actually turned into useful work) of around 6%. Hot-bulb engines could easily achieve 12% thermal efficiency. During the


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1910s–1950s, hot-bulb engines were more economical to manufacture with their low pressure crude fuel injection and lower compression ratio than diesel engines.

The hot-bulb engine is much simpler to construct and operate than the steam engine. Boilers require at least one person to add water and fuel as needed and monitor pressure to prevent overpressure and a resulting explosion. If fitted with automatic lubrication systems and a governor to control engine speed, a hot-bulb engine could be left running, unattended for hours at a time.

Another attraction was their safety. A steam engine, with its exposed fire and hot boiler, steam pipes and working cylinder could not be used in flammable conditions such as munitions factories or fuel refineries. Hot-bulb engines also produced cleaner exhaust fumes. A big danger with the steam engine was that if the boiler pressure grew too high and the safety valve failed, a highly dangerous explosion could occur (although this was a relatively rare occurrence by the time the hot-bulb engine was invented). A more common problem was that if the water level in the boiler of a steam engine dropped too low the lead plug in the crown of the furnace would melt, extinguishing the fire. If a hot bulb engine ran out of fuel, it would simply stop and could be immediately restarted with more fuel. The cooling water was usually a closed circuit, so no water loss would occur unless there was a leak. If the cooling water ran low, the engine would seize through overheating – a major problem, but it carried no danger of explosion.

Compared with steam, gasoline (petrol), and diesel engines, hot-bulb engines are simpler and therefore have fewer potential problems. There is no electrical system as found on a petrol engine, and no external boiler and steam system as on a steam engine.

A big attraction with the hot-bulb engine was its ability to run on a wide range of fuels. Even poor-burning fuels could be used since a combination of vaporizer- and compression-ignition meant that such fuels could be made to combust. The usual fuel used was fuel oil, similar to modern-day diesel, but natural gas, kerosene, paraffin, crude oil, vegetable oil or creosote could also be used. This made the hot-bulb engine very cheap to run, since it could be run on cheaply available fuels. Some operators even ran engines on used engine oil, thus providing almost free power. Recently, this multi-fuel ability has led to an interest in using hot bulb engines in developing nations where they can be run on locally produced biofuel.


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Due to the lengthy pre-heating time, hot-bulb engines were nearly always guaranteed to start quickly, even in extremely cold conditions. This made them popular choices in cold regions such as Canadaand Scandinavia, where steam engines were not viable and early gasoline and diesel engines could not be relied on to operate.

Uses

The reliability of the hot-bulb engine, their ability to run on many fuels and the fact that they can be left running for hours or days at a time made them extremely popular with agricultural, forestry and marine users, where they were used for pumping and for powering milling, sawing and threshing machinery. Hot-bulb engines were also used onroad rollers and tractors.

2.7 VARIABLE VALVE TIMING

Variable Valve Timing, often abbreviated to VVT, is a type of piston engine technology that deliberately delivers inconsistent timing of the intake and/or exhaust valves. The benefit of this is improved gas mileage and flexibility for an engine to deliver peak performance over a variety of driving conditions. For example, traditional piston engines often are required to sacrifice low-end torque for high-end power (or vice versa). A VVT engine more easily accommodates both of these preferred performance conditions.

There are several proprietary VVT engine technologies that work slightly differently to prolong exhaust and intake cycles at high speeds and reduce cycles at slow speeds. The three major solutions to varying the valve timing of an engine are as follows:

§ The actual timing of the intake or exhaust valves are slowed or sped up as needed § Two sets of cam lobes are utilized and switched between as needed § Timing and lift is continuously altered for maximum efficiency (called continuous

variable valve timing)

The VVT-i system is designed to control the intake camshaft within a range of 50° (of Crankshaft angle) to provide valve timing that is optimally suited to the engine condition. This improves torque in all the speed ranges as well as increasing fuel economy, and reducing exhaust emissions.


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Using the engine speed, intake air volume, throttle position and engine coolant temperature, the ECM can calculate optimal valve timing for each driving condition and controls the camshaft timing oil control valve. In addition, the ECM uses signals from the camshaft position sensor and the crankshaft position sensor to detect the actual valve timing, thus providing feedback control to achieve the target valve timing.


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Effectiveness of the VVT-i System


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Construction 1) VVT-i Controller

This controller consists of the housing driven from the timing chain and the vane coupled with the intake camshaft.

The oil pressure sent from the advance or retard side path at the intake camshaft causes rotation in the VVT-i controller vane circumferential direction to vary the intake valve timing continuously. When the engine is stopped, the intake camshaft will be in the most retarded state to ensure startability. When hydraulic pressure is not applied to the VVT-i controller immediately after the engine has been started, the lock pin locks the movement of the VVT-i controller to prevent a knocking noise.

2) Camshaft Timing Oil Control Valve

This camshaft timing oil control valve controls the spool valve position in accordance with the duty-cycle control from the ECM. This allows hydraulic pressure to be applied to the VVT-i controller advance or retard side. When the engine is stopped, the camshaft timing oil control valve is in the most retarded state.


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Operation 1) Advance When the camshaft timing oil control valve is positioned as illustrated below by the advance signals from the ECM, the resultant oil pressure is applied to the vane chamber of advance side to rotate the camshaft in the timing advance direction.

2) Retard When the camshaft timing oil control valve is positioned as illustrated below by the retard signals from the ECM, the resultant oil pressure is applied to the vane chamber of retard side to rotate the camshaft in the timing retard direction.

3) Hold After reaching the target timing, the valve timing is held by keeping the camshaft timing oil control valve in the neutral position unless the traveling state changes. This adjusts the valve timing at the desired target position and prevents the engine oil from running out when it is unnecessary.


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CHAPTER III VEHICLE OPERATION AND CONTROL

3.1 ELECTRONIC CONTROL UNIT (ECU)

An automotive electronics, electronic control unit (ECU) is a generic term for any embedded system that controls one or more of the electrical systems or subsystems in a motor vehicle.

Other terms for ECU include Electronic/Engine Control Module (ECM), Power train Control Module (PCM), Transmission Control Module (TCM), Brake Control Module (BCM or EBCM), Central Control Module (CCM), Central Timing Module (CTM), General Electronic Module (GEM), Body Control Module (BCM), Suspension Control Module (SCM), control unit, or control module. Taken together, these systems are sometimes referred to as the car's computer. (Technically there is no single computer but multiple ones.) Sometimes one assembly incorporates several of the individual control modules (PCM is often both engine and transmission)

Some modern motor vehicles have up to 80 ECUs. Embedded software in ECUs continue to increase in line count, complexity, and sophistication.[1] Managing the increasing complexity and number of ECUs in a vehicle has become a key challenge for original equipment manufacturers (OEMs).

Types of electronic control unit

• Airbag Control Unit (ACU) • Body Control Module controls door locks, electric windows, courtesy lights, etc. • Convenience Control Unit (CCU) • Door Control Unit • Engine Control Unit (ECU)—not to be confused with electronic control unit, the

generic term for all these devices • Electric Power Steering Control Unit (PSCU)— Generally this will be integrated

into the EPSpowerpack. • Man Machine Interface (MMI)


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• Powertrain Control Module (PCM): Sometimes the functions of the Engine Control Unit andTransmission Control Unit are combined into a single unit called the Powertrain Control Module.

• Seat Control Unit • Speed Control Unit • Telephone Control Unit (TCU) • Transmission Control Unit (TCU) • Brake Control Module (ABS or ESC)

The following clearly describe the control strategy for the combustion, emission

and noise control. The ECU for the above said control included the following sensors. 1 Coolant temperature sensor 2 Mass Air Flow sensor 3 Manifold absolute pressure sensor 4 Throttle position sensor 5 Crank shaft speed sensor 6 Exhaust gas oxygen sensor

Temperature Sensors

The ECM needs to adjust a variety of systems based on temperatures. It is critical for proper operation of these systems that the engine reach operating temperature and the temperature is accurately signaled to the ECM. For example, for the proper amount of fuel to be injected the ECM must know the correct engine temperature. Temperature sensors measure Engine Coolant Temperature (ECT), Intake Air Temperature (IAT) and Exhaust Recirculation Gases (EGR), etc.


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Engine Coolant Temperature (ECT) Sensor

The ECT responds to change in Engine Coolant Temperature. By measuring engine coolant temperature, the ECM knows the average temperature of the engine. The ECT is usually located in a coolant passage just before the thermostat. The ECT is connected to the THW terminal on the ECM. The ECT sensor is critical to many ECM functions such as fuel injection, ignition timing, variable valve timing, transmission shifting, etc. Always check to see if the engine is at operating temperature and that the ECT is accurately reporting the temperature to the ECM.


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Intake Air Temperature (IAT) Sensor

The IAT detects the temperature of the incoming air stream. On vehicles equipped with a MAP sensor, the IAT is located in an intake air passage. On Mass Air Flow sensor equipped vehicles, the IAT is part of the MAF sensor. The IAT is connected to the THA terminal on the ECM. The IAT is used for detecting ambient temperature on a cold start and intake air temperature as the engine heats up the incoming air.


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NOTE: One strategy the ECM uses to determine a cold engine start is by comparing the ECT and IAT signals. If both are within 8'C (15'F) of each other, the ECM assumes it is a cold start. This strategy is important because some diagnostic monitors, such as the EVAP monitor, are based on a cold start.

Exhaust Gas Recirculation (EGR) Temperature Sensor

The EGR Temperature Sensor is located in the EGR passage and measures the temperature of the exhaust gases. The EGR Temp sensor is connected to the THG terminal on the ECM. When the EGR valve opens, temperature increases. From the increase in temperature, the ECM knows the EGR valve is open and that exhaust gases are flowing. ECT, IAT, & EGR Temperature Sensor Operation

Though these sensors are measuring different things, they all operate in the same way. From the voltage signal of the temperature sensor, the ECM knows the temperature. As the temperature of the sensor heats up, the voltage signal decreases. The decrease in the voltage signal is caused by the decrease in resistance. The change in resistance causes the voltage signal to drop.

The temperature sensor is connected in series to a fixed value resistor. The ECM supplies 5 volts to the circuit and measures the change in voltage between the fixed value resistor and the temperature sensor.


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When the sensor is cold, the resistance of the sensor is high, and the voltage signal is high. As the sensor warms up, the resistance drops and voltage signal decreases. From the voltage signal, the ECM can determine the temperature of the coolant, intake air, or exhaust gas temperature.

The ground wire of the temperature sensors is always at the ECU usually terminal E2. These sensors are classified as thermistors. Temperature Sensor Diagnostics Temperature sensor circuits are tested for:

• Opens. • Shorts. • Available voltage. • Sensor resistance.

The Diagnostic Tester data list can reveal the type of problem. An open circuit

(high resistance) will read the coldest temperature possible. A shorted circuit (low resistance) will read the highest temperature possible. The diagnostic procedure purpose is to isolate and identify the temperature sensor from the circuit and ECM.

High resistance in the temperature circuit will cause the ECM to think that the temperature is colder than it really is. For example, as the engine warms up, ECT resistance decreases, but unwanted extra resistance in the circuit will produce a higher voltage drop signal. This will most likely be noticed when the engine has reached operating temperatures. Note that at the upper end of the temperature/resistance scale, ECT resistance changes very little. Extra resistance in the higher temperature can cause the ECM to think the engine is approximately 20'F = 30’F colder than actual temperature. This will cause poor engine performance, fuel economy, and possibly engine overheating. AIR FLOW SENSORS


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Mass Air Flow (MAF) Sensors

The Mass Air Flow Sensors converts the amount of air drawn into the engine into a voltage signal. The ECM needs to know intake air volume to calculate engine load. This is necessary to determine how much fuel to inject, when to ignite the cylinder, and when to shift the transmission. The air flow sensor is located directly in the intake air stream, between the air cleaner and throttle body where it can measure incoming air.

There are different types of Mass Air Flow sensors. The vane air flow meter and Karmen vortex are two older styles of air flow sensors and they can be identified by their shape. The newer and more common is the Mass Air Flow (MAF) sensor.

Mass Air Flow Sensor: Hot Wire Type

The primary components of the MAF sensor are a thermistor, a platinum hot wire, and an electronic control circuit.

The thermistor measures the temperature of the incoming air. The hot wire is maintained at a constant temperature in relation to the thermistor by the electronic control circuit. An increase in air flow will cause the hot wire to lose heat faster and the electronic control circuitry will compensate by sending more current through the wire. The electronic control circuit simultaneously measures the current flow and puts out a voltage signal (VG) in proportion to current flow.


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This type of MAF sensor also has an Intake Air Temperature (IAT) sensor as part of the housing assembly. Its operation is described in the IAT section of Temperature Sensors. When looking at the EWD, there is a ground for the MAF sensor and a ground (E2) for the IAT sensor.


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AIR FLOW SENSORS

Vane Air Flow Meter

The Vane Air Flow Meter provides the ECM with an accurate measure of the load placed on the engine. The ECM uses it to calculate basic injection duration and basic ignition advance angle.

Vane Air Flow Meters consist of the following components:

• Measuring Plate. • Compensation Plate. • Return Spring. • Potentiometer. • Bypass Air Passage. • Idle Adjusting Screw (factory adjusted). • Fuel Pump Switch. • Intake Air Temperature (IAT) Sensor.


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During engine operation, intake air flow reacts against the measuring plate (and return spring) and deflects the plate in proportion to the volume of air flow passing the plate. A compensation plate (which is attached to the measuring plate) is located inside a damping chamber and acts as a "shock absorber" to prevent rapid movement or vibration of the measuring plate. Movement of the measuring plate is transferred through a shaft to a slider (movable arm) on the potentiometer. Movement of the slider against the potentiometer resistor causes a variable voltage signal back to the VS terminal at the ECM. Because of the relationship of the measuring plate and potentiometer, changes in the VS signal will be proportional to the air intake volume.

The r2 resistor (connected in parallel with r1) allows the meter to continue to provide a VS signal in the event that an open occurs in the main potentiometer (r1). The


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Vane Air Flow Meter also has a fuel pump switch built into the meter that closes to maintain fuel pump operation once the engine has started and air flow has begun. The meter also contains a factory adjusted idle adjusting screw that is covered by a tamper resistant plug. The repair manual does not provide procedures on resetting this screw in cases where it has been tampered with. Types of VAF Meters

There were two major types of VAF meters. The first design is the oldest type. It uses battery voltage for supply voltage. With this type of VAF meter, as the measuring plate opens signal voltage increases.


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Karmen Vortex Air Flow Meter

This air flow meter provides the same type of information (intake air volume) as the Vane Air flow Meter. It consists of the following components: Vortex Generator.

• Mirror (metal foil). • Photo Coupler (LED and photo transistor).

Karman Vortex Air Flow Meter Operation

Intake air flow reacting against the vortex generator creates a swirling effect to the air downstream, very similar to the wake created in the water after a boat passes. This wake or flutter is referred to as a "Karman Vortex." The frequencies of the vortices vary in proportion to the intake air velocity (engine load).


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The vortices are metered into a pressure directing hole from which they act upon the metal foil mirror. The air flow against the mirror causes it to oscillate in proportion to the vortex frequency. This causes the illumination from the photo coupler's LED to be alternately applied to and diverted away from a photo transistor. As a result, the photo transistor alternately grounds or opens the 5-volt KS signal to the ECM.

This creates a 5 volt square wave signal that increases frequency in proportion to the increase in intake air flow. Because of the rapid, high frequency nature of this signal, accurate signal inspection at various engine operating ranges requires using a high quality digital multimeter (with frequency capabilities) or oscilloscope. PRESSURE SENSORS Pressure sensors are used to measure intake manifold pressure, atmospheric pressure, vapor pressure in the fuel tank, etc. Though the location is different, and the pressures being measured vary, the operating principles are similar.


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Manifold Absolute Pressure (MAP) Sensor

In the Manifold Absolute Pressure (MAP) sensor there is a silicon chip mounted inside a reference chamber. On one side of the chip is a reference pressure. This reference pressure is either a perfect vacuum or a calibrated pressure, depending on the application. On the other side is the pressure to be measured. The silicon chip changes its resistance with the changes in pressure. When the silicon chip flexes with the change in pressure, the electrical resistance of the chip changes. This change in resistance alters the voltage signal. The ECM interprets the voltage signal as pressure and any change in the voltage signal means there was a change in pressure.

Intake manifold pressure is a directly related to engine load. The ECM needs to know intake manifold pressure to calculate how much fuel to inject, when to ignite the cylinder, and other functions. The MAP sensor is located either directly on the intake manifold or it is mounted high in the engine compartment and connected to the intake manifold with vacuum hose. It is critical the vacuum hose not have any kinks for proper operation.


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The MAP sensor uses a perfect vacuum as a reference pressure. The difference in pressure between the vacuum pressure and intake manifold pressure changes the voltage signal. The MAP sensor converts the intake manifold pressure into a voltage signal (PIM).

The MAP sensor voltage signal is highest when intake manifold pressure is highest (ignition key ON, engine off or when the throttle is suddenly opened). The MAP sensor voltage signal is lowest when intake manifold pressure is lowest on deceleration with throttle closed.


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POSITION SENSORS

In many applications, the ECM needs to know the position of mechanical components. The Throttle Position Sensor (TPS) indicates position of the throttle valve. Accelerator Pedal Position (APP) sensor indicates position of the accelerator pedal. Exhaust Gas Valve (EGR) Valve Position Sensor indicates position of the EGR Valve. The vane air flow meter uses this principle.

Electrically, these sensors operate the same way. A wiper arm inside the sensor is mechanically connected to a moving part, such as a valve or vane. As the part moves, the wiper arm also moves. The wiper arm is also in contact with a resistor. As the wiper arm moves on the resistor, the signal voltage output changes. At the point of contact the available voltage is the signal voltage and this indicates position. The closer the wiper arm gets to VC voltage, the higher the signal voltage output. From this voltage, the ECM is able to determine the position of a component.


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Throttle Position Sensor

The TPS is mounted on the throttle body and converts the throttle valve angle into an electrical signal. As the throttle opens, the signal voltage increases. The ECM uses throttle valve position information to know:

• Engine mode: idle, part throttle, wide open throttle. • Switch off AC and emission controls at Wide Open Throttle (WOT). • Air-fuel ratio correction. • Power increase correction. • fuel cut control

The basic TPS requires three wires. Five volts are supplied to the TPS from the

VC terminal of the ECM. The TPS voltage signal is supplied to the VTA terminal. A ground wire from the TPS to the E2 terminal of the ECM completes the circuit.

At idle, voltage is approximately 0.6 - 0.9 volts on the signal wire. From this voltage, the ECM knows the throttle plate is closed. At wide open throttle, signal voltage is approximately 3.5 - 4.7 volts.

Inside the TPS is a resistor and a wiper arm. The arm is always contacting the resistor. At the point of contact, the available voltage is the signal voltage and this indicates throttle valve position. At idle, the resistance between the VC (or VCC terminal and VTA terminal is high, therefore, the available voltage is approximately 0.6 - 0.9 volts. As the contact arm moves closer the VC terminal (the 5 volt power voltage), resistance decreases and the voltage signal increases.


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Some TPS incorporate a Closed Throttle Position switch (also called an idle contact switch). This switch is closed when the throttle valve is closed. At this point, the ECM measures 0 volts and there is 0 volts at the IDL terminal. When the throttle is opened, the switch ope006E s and the ECM reads +B voltage at the IDL circuit.


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The TPS on the ETCS-i system has two contact arms and to resistors in one housing. The first signal line is VTA1 and the second signal line is VTA2.

VTA2 works the same, but starts at a higher voltage output and the voltage change rate is different from VTA1 As the throttle opens the two voltage signals increase at a different rate. The ECM uses both signals to detect the change in throttle valve position. By having two sensors, ECM can compare the voltages and detect problems.


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Accelerator Pedal Position (APP) Sensor

The APP sensor is mounted on the throttle body of the ETCS-i. The APP sensor converts the accelerator pedal movement and position into two electrical signals. Electrically, the APP is identical in operation to the TPS.

EGR Valve Position Sensor

The EGR Valve Position Sensor is mounted on the EGR valve and detects the

height of the EGR valve. The ECM uses this signal to control EGR valve height. The EGR Valve Position Sensor converts the movement and position of the EGR valve into an electrical signal. Operation is identical to the TPS except that the signal arm is moved by the EGR valve. Position Sensor Diagnostics

The following explanations are to help you with the diagnostic procedures in the Repair Manual. The explanations below are representative to the order listed in the RM. You may find different orders in the RM.


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POSITION / SPEED SENSORS Position / Speed Sensors

Position/speed sensors provide information to the ECM about the position of a component, the speed of a component, and the change in speed of a component. The following sensors provide this data:

• Camshaft Position Sensor (also called G sensor). • Crankshaft Position Sensor (also called NE sensor). • Vehicle Speed Sensor.

The Camshaft Position Sensor, Crankshaft Position Sensor, and one type of

vehicle speed sensor are of the pick-up coil type sensor. This type of sensor consists of a permanent magnet, yoke, and coil. This sensor is mounted close to a toothed gear. As each tooth moves by the sensor, an AC voltage pulse is induced in the coil. Each tooth produces a pulse. As the gear rotates faster there more pulses are produced. The ECM determines the speed the component is revolving based on the number of pulses. The number of pulses in one second is the signal frequency.


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Pick-Up Coil (Variable Reluctance) Type Sensors

The distance between the rotor and pickup coil is critical. The further apart they

are, the weaker the signal.

Not all rotors use teeth. Sometimes the rotor is notched, which will produce the same effect.

These sensors generate AC voltage, and do not need an external power supply. Another common characteristic is that they have two wires to carry the AC voltage.

The wires are twisted and shielded to prevent electrical interference from disrupting the signal. The EWD will indicate if the wires are shielded.

By knowing the position of the camshaft, the ECM can determine when cylinder No. I is on the compression stroke. The ECM uses this information for fuel injection timing, for direct ignition systems and for variable valve timing systems.

This sensor is located near one of the camshafts. With variable timing V-type engines, there is one sensor for each cylinder bank. On distributor ignition systems, it is often called the G sensor and is located in the distributor. An AC signal is generated that is directly proportional to camshaft speed. That is, as the camshaft revolves faster the frequency increases.


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Camshaft Position Sensor (G Sensor)

The terminal on the ECM is designated with a letter G, and on some models a G and a number, such as G22 is used.

Variable Valve Position Sensor

Some variable valve timing systems call the Camshaft Position Sensor the

Variable Valve Position Sensor. See section on variable valve timing systems for more information.


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Crankshaft Position Sensor (NE Sensor)

The ECM uses crankshaft position signal to determine engine RPM, crankshaft position, and engine misfire. This signal is referred to as the NE signal. The NE signal combined with the G signal indicates the cylinder that is on compression and the ECM can determine from its programming the engine firing order. See Section 3 on ignition systems for more information. Vehicle Speed Sensor (VSS)

The ECM uses the Vehicle Speed Sensor (VSS) signal to modify engine functions and initiate diagnostic routines. The VSS signal originates from a sensor measuring transmission/ transaxle output speed or wheel speed. Different types of sensors have been used depending on models and applications.

On some vehicles, the vehicle speed sensor signal is processed in the combination meter and then sent to the ECM.

On some anti-lock brake system (ABS) equipped vehicles, the ABS computer processes the wheel speed sensor signals and sends a speed sensor signal to the combination meter and then to the ECM. You will need to consult the EWD to confirm the type of system you are working on. Pick-Up Coil (Variable Reluctance) Type

This type of VSS operates on the variable reluctance principle discussed earlier and it is used to measure transmission/ transaxle output speed or wheel speed depending on type of system.

On some anti-lock brake system (ABS) equipped vehicles, the ABS computer processes the wheel speed sensor signals and sends a speed sensor signal to the combination meter and then to the ECM. You will need to consult the EWD to confirm the type of system you are working On some anti-lock brake system (ABS) equipped vehicles, the ABS computer processes the wheel speed sensor signals and sends a speed sensor signal to the combination meter and then to the ECM. You will need to consult the EWD to confirm the type of system you are working


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Magnetic Resistance Element (MRE) Type

The MIRE is driven by the output shaft on a transmission or output gear on a transaxle. This sensor uses a magnetic ring that revolves when the output shaft is turning.


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The MIRE senses the changing magnetic field. This signal is conditioned inside the VSS to a digital wave. This digital wave signal is received by the Combination meter, and then sent to the ECM. The MIRE requires an external power supply to operate.

Reed Switch Type

The reed switch type is driven by the speedometer cable. The main components are a magnet, reed switch, and the speedometer cable. As the magnet revolves the reed switch contacts open and close four times per revolution. This action produces 4 pulses per revolution. From the number of pulses put out by the VSS, the combination meter/ECM is able to determine vehicle speed. Benefits

• Enables electronic fuel injection to help manufacturers meet emissions standards, increase fuel economy and improve performance

• Small package size uses a standard FR4 circuit board enabling mounting flexibility and manufacturing flexibility

• Optimized connection system design • high-speed processing • Electronic fuel control for 1-cylinder and 2-cylinder fuel injection applications • Electronic spark control with 1-cylinder and 2-cylinder spark applications, with or

without high current coil drivers in the ECM • Digital signal processing provides knock control • Advanced feature functions include closed loop control with Idle Air Control

(IAC) and heated oxygen sensor.


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Exhaust Gas Oxygen Sensor

Description

The EGO1 is a precision, heated, 4-wire exhaust gas oxygen sensor. It produces an output voltage that varies from 0 V to 1V as the residual oxygen level in the exhaust gas stream ranges from lean to rich. The operation of the sensor is based on a zirconium dioxide cell which provides a precise indication of the stoichiometric air/fuel ratio of 14.7:1. At the stoichiometric point, the EGO1 produces an output voltage of 0.45 V.

The transfer function of the sensor is less abrupt than other oxygen sensors which makes it possible to make valid readings over a wide range of air/fuel ratio. The output characteristics of the EGO1 are predictable, repeatable and well characterized. Coupled with a precise air/fuel ratio meter such as the Split Second ARM1, the EGO1 generates accurate readings ranging from 17.0:1 to 12.5:1. Tables and graphs showing output voltage vs. air /fuel ratio are contained in this data sheet.

Due to its internal heater and wide operating temperature range, the EGO1 provides valid readings quickly after engine start and over a wide range of engine operating conditions including idle. Features: • Generates calibrated outputs for air/fuel ratios ranging from 17.0:1 to 12.5:1 • 0V to 1.0 V output range • Signal ground lead allows precise output voltage measurements • Internal heater for stable, predictable readings • Consistent output over 800°F to 1400° F temperature range


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CHAPTER V SUSPENSION, BRAKES, AERODYNAMICS AND SAFETY

5.1 AIR SUSPENSION SYSTEM

Air suspension is a type of vehicle suspension powered by an engine driven or electric air pump or compressor. This pump pressurizes the air, using compressed air as a spring. Air suspension replaces conventional steel springs. If the engine is left off for an extended period, the car will settle to the ground. The purpose of air suspension is to provide a smooth ride quality and in some cases self-leveling.

Vehicles that use air suspension today include models from Maybach, Rolls-Royce, Lexus, Jeep Grand Cherokee, Cadillac (GM), Mercedes-Benz, Land Rover/Range Rover, SsangYong, Audi, Subaru,Volkswagen, and Lincoln and Ford, among others. Citroën now feature Hydractive suspension, a computer controlled version of their Hydropneumatic system, which features sport and comfort modes, lowers the height of the car at high speeds and continues to maintain ride height when the engine is not running. Air Strut Assembly

The McPherson Strut Spring is replaced with an Air Spring. The height and

firmness of the front struts is then determined by the air pressure applied to the bags.


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This system provides 3 pressure levels: Air System Controls System

Ride Height Pressure

Ride Height Pressure is set by Regulator 1. This is the default pressure applied to the front struts. This pressure should be set to allow proper ground clearance and suspension firmness according to driving style. Stage 1 Pressure

Stage 1 Pressure is set by Regulator 2. This increased pressure is adjusted to provide a 1 inch lift above Ride Height pressure. Stage 1 Pressure is applied either by pressing the Stage 1 Button, or by applying the brake pedal. Once applied the pressure is held for a preset length of time after the brake or button is released. After the release time, the suspension is returned to Right Height Pressure. Stage 2 Pressure

Stage 2 Pressure is set by adjusting the maximum air tank pressure at the compressor pressure switch. This setting MUST NOT exceed 100 PSI or damage to the


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front air suspension may occur. Stage 2 Pressure dumps the maximum air pressure from the tank to the front suspension when the Stage 2 button is pressed. Pressure is held for a preset length of time after the button is released, and then returns to Ride Height Pressure. Controls

An air pressure gauge is installed in the A-Piller to indicate pressure at the front suspension. A second pod is provided in the A-Piller with pushbuttons and switches for the Stage 1 and Stage 2 air systems. Pressing the momentary buttons will boost the air pressure to the regulator setting. Once released, the system will hold the boost air pressure for a preset amount of time. The air system LED Lights will illuminate any time the air solenoid valves are powered (by the pushbutton, hold timer, or brake pedal). AIR SYSTEM

A 12V Compressor provides the compressed air for the suspension system. The Tank Drain and Water Separator drain should be bled monthly to keep contaminants out of the air suspension system.

Regulator 1 (Ride Height Pressure) and Regulator 2 (Stage 1 Pressure) should be set with the car sitting on a level paved surface. Ride Height Pressure should be set so the car sits level and has a suitable amount of firmness in the suspension for cornering. Stage 1 Pressure should be set so that it causes approximately a 1 inch lift of the air dam to improve clearance for driveways, and reduce front end dive during heavy braking.

Main System Air Pressure, used during Stage 2 applications, is adjusted at the compressor pressure switch. This pressure should be verified at the tank with a known good gauge and must not exceed 100 psi. CONTROL SYSTEM

A 12V Compressor is powered by the air management system, which is automatically activated when the engine is running. The control system will not allow the compressor to run while the rake pedal is pressed, so as not to cause a sound similar to ABS braking.


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C1 and C2 capacitors are installed to hold the system on for a predetermined length of time after the pushbutton (or brake pedal for Stage 1) is released. This allows the driver to apply lift and drive over an obstacle without having to hold the button/pedal.

LED 1 and LED 2 light any time power is applied to the air solenoid valves. A monthly check should be made that when the buttons for Stage 1 and Stage 2 are pressed, the LED lights and the pressure gauge indicates the correct pressure at the suspension. After the timer is completed, the LED light should go out and the pressure should release to Ride Height Pressure. Suspension system in AUDI

Designing a vehicle this perfect for on and off-road use sounds like squaring the

circle. Usually the strengths of an off-road vehicle are decided weaknesses when it comes to road use. A high ground clearance, crucial for rough terrain, gives the vehicle a correspondingly high centre of gravity. When it comes to fast cornering, however, this is as disadvantageous as it is for driving stability at higher speeds. In addition, the air


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resistance is increased, which significantly affects fuel consumption. In contrast, the shorter spring travel and the firmer running gear matching of an “on-road running gear” offer inadequate driving comfort off-road. A variable ground clearance is the solution for all road use and it’s called air suspension Air supply from the compressor

The construction and function of the compressor corresponds largely to the unit

described in the self-levelling suspension of the A6. The following is a description only of the differences in the 4-level air suspension system.

• The fitting location is outside the vehicle and without noise insulation (in front of spare wheel well).

• The operating pressure is increased to 16 bar owing to the pressure accumulator system. Lower speed for reduced noise.


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• Suction and discharge of the air is performed from the spare wheel well via an air filter/noise damper (passenger compartment).

• An additional noise damper in the suction/ discharge line ensures minimal through flow noise, particularly during discharge.

• Temperature monitoring is performed via a temperature sensor at the cylinder head and a simulation formula in the control unit (temperature model) (more information, see Temperature sensor G290).

Common air suspension problems

Air bag or air strut failure is usually caused by wet rot, due to old age, or moisture within the air system that damages it from the inside. Air ride suspension parts may fail because rubber dries out. Punctures to the air bag may be caused from debris on the road. With custom applications, improper installation may cause the air bags to rub against the vehicle's frame or other surrounding parts, damaging it. The over-extension of an airspring which is not sufficiently constrained by other suspension components, such as a shock absorber, may also lead to the premature failure of an airspring through the tearing of the flexible layers. Failure of an airspring may also result in complete immobilization of the vehicle, since the vehicle will rub against the ground or be too high to move.

Air line failure is a failure of the tubing which connects the air bags or struts to the rest of the air system, and is typically DOT-approved nylon air brake line. This usually occurs when the air lines, which must be routed to the air bags through the chassis of the vehicle, rub against a sharp edge of a chassis member or a moving suspension component, causing a hole to form. This mode of failure will typically take some time to occur after the initial installation of the system, as the integrity of a section of air line is compromised to the point of failure due to the rubbing and resultant abrasion of the material. An air-line failure may also occur if a piece of road debris hits an air line and punctures or tears it.

Compressor failure is primarily due to leaking air springs or air struts. The compressor will burn out trying to maintain the correct air pressure in a leaking air system. Compressor burnout may also be caused by moisture from within the air system coming into contact with its electronic parts.


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In Dryer failure the dryer, which functions to remove moisture from the air system, eventually becomes saturated and unable to perform that function. This causes moisture to build up in the system and can result in damaged air springs and/or a burned out compressor

5.2 ANTI-LOCK BRAKING SYSTEM (ABS)

An anti-lock braking system (ABS) is a safety system that allows the wheels on a motor vehicle to continue interacting tractively with the road surface as directed by driver steering inputs while braking, preventing the wheels from locking up (that is, ceasing rotation) and therefore avoiding skidding.

An ABS generally offers improved vehicle control and decreases stopping distances on dry and slippery surfaces for many drivers; however, on loose surfaces like gravel or snow-covered pavement, an ABS can significantly increase braking distance, although still improving vehicle control.

Antilock Brake Systems address two conditions related to brake application;

wheel lockup and vehicle directional control. The brakes slow the rotation of the wheels, but it is actually the friction between the tire and road surface that stops the vehicle. Without ABS when brakes are applied with enough force to lock the wheels, the vehicle slides uncontrollably because there is no traction between the tires and the road surface. While the wheels are skidding, steering control is lost as well.

An antilock brake system provides a high level of safety to the driver by preventing the wheels from locking, which maintains directional stability. A professional driver may be capable of maintaining control during braking by pumping the brake pedal which allows a locked wheel to turn momentarily. Whereas a professional driver may be capable of modulating the brakes approximately once per second, ABS is capable of modulating the brake pressure at a given wheel up to fifteen times per second. An ABS system does something else that no driver can do, it controls each front brake separately and the rear brakes as a pair whenever one of the wheels starts to lock. ABS helps stop a car in the shortest possible distance without wheel lockup while maintaining directional control on most types of road surface or conditions. If a Toyota ABS system malfunctions, normal braking will not be affected.


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Figure ABS is combined with the conventional braking system and located between the

master cylinder and the wheel cylinders

Four Wheel ABS Systems use a speed sensor at each front wheel and either a single speed sensor for both rear wheels or individual speed sensors at each rear wheel. The speed sensors are monitored by a dedicated ECU. The system controls the front brakes individually and rear brakes as a pair.

In a panic braking situation, the wheel speed sensors detect any sudden changes in wheel speed. The ABS ECU calculates the rotational speed of the wheels and the change in their speed, then calculates the vehicle speed. The ECU then judges the slip ratio of each wheel and instructs the actuator to provide the optimum braking pressure to each wheel. For example, the pressure to the brakes will be less on slippery pavement to reduce brake lockup. As a result, braking distance may increase but directional control will be maintained. It is also important to understand that ABS is not active during all stops.

Operation of ABS

A typical ABS includes a central electronic control unit (ECU), four wheel speed sensors, and at least two hydraulic valves within the brake hydraulics. The ECU constantly monitors the rotational speed of each wheel; if it detects a wheel rotating significantly slower than the others, a condition indicative of impending wheel lock, it actuates the valves to reduce hydraulic pressure to the brake at the affected wheel, thus reducing the braking force on that wheel; the wheel then turns faster. Conversely, if the ECU detects a wheel turning significantly faster than the others, brake hydraulic pressure


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to the wheel is increased so the braking force is reapplied, slowing down the wheel. This process is repeated continuously and can be detected by the driver via brake pedal pulsation. Some anti-lock system can apply or release braking pressure 16 times per second.

The ECU is programmed to disregard differences in wheel rotative speed below a critical threshold, because when the car is turning, the two wheels towards the center of the curve turn slower than the outer two. For this same reason, a differential is used in virtually all road going vehicles.

If a fault develops in any part of the ABS, a warning light will usually be illuminated on the vehicle instrument panel, and the ABS will be disabled until the fault is rectified.

The modern ABS applies individual brake pressure to all four wheels through a control system of hub-mounted sensors and a dedicated micro-controller. ABS is offered or comes standard on most road vehicles produced today and is the foundation for ESC systems, which are rapidly increasing in popularity due to the vast reduction in price of vehicle electronics over the years.

Modern electronic stability control (ESC or ESP) systems are an evolution of the ABS concept. Here, a minimum of two additional sensors are added to help the system work: these are a steering wheelangle sensor, and a gyroscopic sensor. The theory of operation is simple: when the gyroscopic sensor detects that the direction taken by the car does not coincide with what the steering wheel sensor reports, the ESC software will brake the necessary individual wheel(s) (up to three with the most sophisticated systems), so that the vehicle goes the way the driver intends. The steering wheel sensor also helps in the operation of Cornering Brake Control (CBC), since this will tell the ABS that wheels on the inside of the curve should brake more than wheels on the outside, and by how much.

The ABS equipment may also be used to implement a traction control system (TCS) on acceleration of the vehicle. If, when accelerating, the tire loses traction, the ABS controller can detect the situation and take suitable action so that traction is


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regained. More sophisticated versions of this can also control throttle levels and brakes simultaneously.

The hydraulic brake actuator operates on signals from the ABS ECU to hold, reduce or increase the brake fluid pressure as necessary, to maintain the optimum slip ratio of 10 to 30% and avoid wheel lockup.

System of components

There are four main components to an ABS: speed sensors, valves, a pump, and a controller.

Speed sensors The anti-lock braking system needs some way of knowing when a wheel is about

to lock up. The speed sensors, which are located at each wheel, or in some cases in the differential, provide this information. Valves

There is a valve in the brake line of each brake controlled by the ABS. On some systems, the valve has three positions:

§ In position one, the valve is open; pressure from the master cylinder is passed right through to the brake.


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§ In position two, the valve blocks the line, isolating that brake from the master cylinder. This prevents the pressure from rising further should the driver push the brake pedal harder.

§ In position three, the valve releases some of the pressure from the brake. Pump

Since the valve is able to release pressure from the brakes, there has to be some way to put that pressure back. That is what the pump does; when a valve reduces the pressure in a line, the pump is there to get the pressure back up. Controller

The controller is an ECU type unit in the car which receives information from each individual wheel speed sensor, in turn if a wheel loses traction the signal is sent to the controller, the controller will then limit the brake force (EBD) and activate the ABS modulator which actuates the braking valves on and off. Advantages of ABS

There are many different variations and control algorithms for use in an ABS. One of the simpler systems works as follows

• The controller monitors the speed sensors at all times. It is looking for decelerations in the wheel that are out of the ordinary. Right before wheel locks up, it will experience a rapid deceleration. If left unchecked, the wheel would stop much more quickly than any car could. It might take a car five seconds to stop from 60 mph (96.6 km/h) under ideal conditions, but a wheel that locks up could stop spinning in less than a second.

• The ABS controller knows that such a rapid deceleration is impossible, so it reduces the pressure to that brake until it sees acceleration, then it increases the pressure until it sees the deceleration again. It can do this very quickly, before the tire can actually significantly change speed. The result is that the tire slows down at the same rate as the car, with the brakes keeping the tires very near the point at which they will start to lock up. This gives the system maximum braking power.

• When the ABS system is in operation the driver will feel a pulsing in the brake pedal; this comes from the rapid opening and closing of the valves. This pulsing also tells the driver that the ABS has been triggered. Some ABS systems can cycle up to 16 times per second.

There are four types of ABS systems used in current Toyota models distinguished by the actuator. The four actuator types include:

• 2-position solenoid valves.


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• 3-position solenoid valves with mechanical valve (Bosch). • 3-position solenoid valves (Nippondenso). • 2-position solenoid controlling power steering hydraulic pressure which controls

brake hydraulic pressure.

• 2-Position Solenoid


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2-position solenoid actuators come in configurations of six or eight solenoids. The eight solenoid configuration uses two solenoids per brake assembly. The six solenoid configuration uses two solenoids to control the rear brake assemblies while the front brake assemblies are controlled independently by two solenoids each. 3-Position Solenoid and Mechanical Valve This actuator uses three, 3-position solenoid valves. Two solenoids control the front wheels independently while the third solenoid controls the right rear and the mechanical valve translates controls to the left rear.

3-Position Solenoids


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The 3-position solenoid valve actuator comes in three solenoid or four solenoid configurations. The four-solenoid system controls hydraulic pressure to all four wheels. In the 3-solenoid system, each front wheel is controlled independently while the rear wheels are controlled in tandem.

5.3 A REGENERATIVE BRAKING

A regenerative brake is an energy recovery mechanism which slows a vehicle by converting its kinetic energy into another form, which can be either used immediately or stored until needed. This contrasts with conventional braking systems, where the excess kinetic energy is converted to heat by friction in the brake linings and therefore wasted.

The most common form of regenerative brake involves using an electric motor as an electric generator. In electric railways the generated electricity is fed back into the supply system, whereas in battery electric and hybrid electric vehicles, the energy is stored in a battery or bank of capacitors for later use. Energy may also be stored via pneumatics, hydraulics or the kinetic energy of a rotating flywheel.

The motor as a generator

Vehicles driven by electric motors use the motor as a generator when using regenerative braking: it is operated as a generator during braking and its output is supplied to an electrical load; the transfer of energy to the load provides the braking effect.

Regenerative braking is used on hybrid gas/electric automobiles to recoup some of the energy lost during stopping. This energy is saved in a storage battery and used later to power the motor whenever the car is in electric mode.

Early examples of this system were the front-wheel drive conversions of horse-drawn cabs by Louis Antoine Krieger (1868–1951). The Krieger electric landaulet had a drive motor in each front wheel with a second set of parallel windings (bifilar coil) for regenerative braking. In England, the Raworth system of "regenerative control" was introduced by tramway operators in the early 1900s, since it offered them economic and operational benefits as explained by A. Raworth of Leeds in some detail. These included tramway systems at Devonport (1903), Rawtenstall, Birmingham, Crystal Palace-Croydon (1906) and many others. Slowing down the speed of the cars or keeping it in hand on descending gradients, the motors worked as generators and braked the vehicles. The tram cars also had wheel brakes and track slipper brakes which could stop the tram


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should the electric braking systems fail. In several cases the tram car motors were shunt wound instead of series wound, and the systems on the Crystal Palace line utilized series-parallel controllers. Following a serious accident at Rawtenstall, an embargo was placed on this form of traction in 1911. Twenty years later, the regenerative braking system was reintroduced.

Regenerative braking has been in extensive use on railways for many decades. The Baku-Tbilisi-Batumi railway (Transcaucasian railway or Georgian railway) started utilizing regenerative braking in the early 1930s. This was especially effective on the steep and dangerous Surami Pass. In Scandinavia the Kiruna to Narvik railway carries iron ore from the mines in Kiruna in the north of Sweden down to the port of Narvik in Norway to this day. The rail cars are full of thousands of tons of iron ore on the way down to Narvik, and these trains generate large amounts of electricity by their regenerative braking. From Riksgränsen on the national border to the Port of Narvik, the trains use only a fifth of the power they regenerate. The regenerated energy is sufficient to power the empty trains back up to the national border. Any excess energy from the railway is pumped into the power grid to supply homes and businesses in the region, and the railway is a net generator of electricity.

An Energy Regeneration Brake was developed in 1967 for the AMC Amitron. This was a completely battery powered urban concept car whose batteries were recharged by regenerative braking, thus increasing the range of the automobile.

Many modern hybrid and electric vehicles use this technique to extend the range of the battery pack. Examples include the Toyota Prius, Honda Insight, the Vectrix electric maxi-scooter, and the Chevrolet Volt.

Limitations

Traditional friction-based braking is used in conjunction with mechanical regenerative braking for the following reasons:

• The regenerative braking effect drops off at lower speeds; therefore the friction brake is still required in order to bring the vehicle to a complete halt. Physical locking of the rotor is also required to prevent vehicles from rolling down hills.

• The friction brake is a necessary back-up in the event of failure of the regenerative brake.

• Most road vehicles with regenerative braking only have power on some wheels (as in a two-wheel drive car) and regenerative braking power only applies to such wheels because they are the only wheels linked to the drive motor, so in order to


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provide controlled braking under difficult conditions (such as in wet roads) friction based braking is necessary on the other wheels.

• The amount of electrical energy capable of dissipation is limited by either the capacity of the supply system to absorb this energy or on the state of charge of the battery or capacitors. No regenerative braking effect can occur if another electrical component on the same supply system is not currently drawing power and if the battery or capacitors are already charged. For this reason, it is normal to also incorporate dynamic braking to absorb the excess energy.

• Under emergency braking it is desirable that the braking force exerted be the maximum allowed by the friction between the wheels and the surface without slipping, over the entire speed range from the vehicle's maximum speed down to zero. The maximum force available for acceleration is typically much less than this except in the case of extreme high-performance vehicles. Therefore, the power required to be dissipated by the braking system under emergency braking conditions may be many times the maximum power which is delivered under acceleration. Traction motors sized to handle the drive power may not be able to cope with the extra load and the battery may not be able to accept charge at a sufficiently high rate. Friction braking is required to dissipate the surplus energy in order to allow an acceptable emergency braking performance.

For these reasons there is typically the need to control the regenerative braking and match the friction and regenerative braking to produce the desired total braking output. The GM EV-1 was the first commercial car to do this. Engineers Abraham Farag and Loren Majersik were issued two patents for this brake-by-wire technology.

Electric railway vehicle operation

During braking, the traction motor connections are altered to turn them into electrical generators. The motor fields are connected across the main traction generator (MG) and the motor armatures are connected across the load. The MG now excites the motor fields. The rolling locomotive or multiple unit wheels turn the motor armatures, and the motors act as generators, either sending the generated current through onboard resistors (dynamic braking) or back into the supply (regenerative braking).

For a given direction of travel, current flow through the motor armatures during braking will be opposite to that during motoring. Therefore, the motor exerts torque in a direction that is opposite from the rolling direction.

Braking effort is proportional to the product of the magnetic strength of the field windings, times that of the armature windings.


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Savings of 17% are claimed for Virgin Trains Pendolinos. There is also less wear on friction braking components. The Delhi Metro saved around 90,000 tons of carbon dioxide (CO2) from being released into the atmosphere by regenerating 112,500 megawatt hours of electricity through the use of regenerative braking systems between 2004 and 2007. It is expected that the Delhi Metro will save over 100,000 tons of CO2 from being emitted per year once its phase II is complete through the use of regenerative braking.

Another form of simple, yet effective regenerative braking is used on the London Underground which is achieved by having small slopes leading up and down from stations. The train is slowed by the climb, and then leaves down a slope, so kinetic energy is converted to gravitational potential energy in the station.

Electricity generated by regenerative braking may be fed back into the traction power supply; either offset against other electrical demand on the network at that instant, or stored in lineside storage systems for later use.

Comparison of dynamic and regenerative brakes

Dynamic brakes ("rheostatic brakes" in the UK), unlike regenerative brakes, dissipate the electric energy as heat by passing the current through large banks of variable resistors. Vehicles that use dynamic brakes include forklifts, Diesel-electric locomotives, and streetcars. This heat can be used to warm the vehicle interior, or dissipated externally by large radiator-like cowls to house the resistor banks.

The main disadvantage of regenerative brakes when compared with dynamic brakes is the need to closely match the generated current with the supply characteristics and increased maintenance cost of the lines. With DC supplies, this requires that the voltage be closely controlled. Only with the development of power electronics has this been possible with AC supplies, where the supply frequency must also be matched (this mainly applies to locomotives where an AC supply is rectified for DC motors).

A small number of mountain railways have used 3-phase power supplies and 3-phase induction motors. This results in a near constant speed for all trains as the motors rotate with the supply frequency both when motoring and braking.

Kinetic Energy Recovery Systems

Kinetic Energy Recovery Systems (KERS) were used for the motor sport Formula One's 2009 season, and are under development for road vehicles. KERS was abandoned


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for the 2010 Formula One season, but re-introduced for the 2011 season. As of the 2011 season, 9 teams are using KERS, with 3 teams having not used it so far in a race. One of the main reasons that not all cars use KERS is because it adds an extra 25 kilograms of weight, while not adding to the total car weight, it does incur a penalty particularly seen in the qualifying rounds, as it raises the car's center of gravity, and reduces the amount of ballast that is available to balance the car so that it is more predictable when turning. FIA rules also limit the exploitation of the system. The concept of transferring the vehicle’s kinetic energy using flywheel energy storage was postulated by physicist Richard Feynman in the 1950sand is exemplified in complex high end systems such as the Zytek, Flybrid. Torotrak and Xtrac used in F1 and simple, easily manufactured and integrated differential based systems such as the Cambridge Passenger/Commercial Vehicle Kinetic Energy Recovery System (CPC-KERS).

Xtrac and Flybrid are both licensees of Torotrak's technologies, which employ a small and sophisticated ancillary gearbox incorporating a continuously variable transmission (CVT). The CPC-KERS is similar as it also forms part of the driveline assembly. However, the whole mechanism including the flywheel sits entirely in the vehicle’s hub (looking like a drum brake). In the CPC-KERS, a differential replaces the CVT and transfers torque between the flywheel, drive wheel and road wheel.

A case study for Toyota Brake System Overview

The hybrid vehicle brake system includes both standard hydraulic brakes and a unique regenerative braking system that uses the vehicle’s momentum to recharge the battery. As soon as the accelerator pedal is released, the HV ECU initiates regenerative braking. MG2 is turned by the wheels and used as a generator to recharge the batteries. During this phase of braking, the hydraulic brakes are not used. When more rapid deceleration is required, the hydraulic brakes are activated to provide additional stopping power. To increase energy efficiency the system uses the regenerative brakes whenever possible. Selecting B" on the shift lever will maximize regenerative efficiency and is useful for controlling speeds downhill. In ‘B’ mode about 30% of the energy is recovered.

If either the regenerative or hydraulic braking system fails, the remaining system will still work. However, the brake pedal will be harder to press and the stopping distance will be longer. In this situation, the brake system warning light will illuminate.


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The battery will accept charge up to an instantaneous rate of 20 to 21 KWH. Much of the energy from light braking at high speeds and harder braking at lower speeds can be recovered. Excess energy over the charging limits is wasted as heat in the brakes just as in other cars. At this time there is no way for the customer to know the limit of regenerative energy recovery.

Regenerative braking cooperative control Regenerative brake cooperative control balances the brake force of the regenerative and hydraulic brakes to minimize the amount of kinetic energy lost to heat and friction. It recovers the energy by converting it into electrical energy.

To convert kinetic energy to electrical energy the system uses MG2 as a generator. The drive axle and MG2 are joined mechanically. When the drive wheels rotate MG2 it tends to resist the rotation of the wheels, providing both electrical energy and the brake force needed to slow the vehicle. The greater the battery charging amperage, the greater the resistance.

On the ’04 & later Prius, the increased power output of MG2 provides increased regenerative brake force. In addition, the distribution of the brake force has been improved through the adoption of the Electronically Controlled Brake (ECB) system, effectively increasing the range of the regenerative brake. These attributes enhance the system’s ability to recover electrical energy which contributes to fuel economy.


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5.4 AIR BAGS

When a car is speeding along at 50 Km per hour it has a tendency ('Inertia') to keep moving at the same speed and in the same direction unless some force acts on it. The car accelerates its occupants to its own speed so that they seem to be moving as a single unit. The inertia of the occupants is, however, independent of the inertia of the car. If the car were to crash into a tree, the force of the tree would bring the car to an abrupt halt. The speed of the occupants, however, would remain the same because of their independent inertia and they would bang into the steering wheel, the dashboard or the windshield. The force exerted by the steering wheel or the windshield would then bring the occupants to a stop but may in the process cause injury to vulnerable body parts such as the head and the face. Car manufacturers use 2 different restraint systems to help stop the occupants while doing as little damage to him or her as possible. The oldest and till now the most trusted device for restraining the passengers has been the seatbelt that spreads this stopping force across sturdier parts of the body over a longer period of time to minimize damage. The air bag is the second and a more recently developed system that is used to supplement the slowing down by the seat belt by deploying a rapidly inflating cushion in the space between the passenger and the steering wheel or dash board to prevent crash injuries. The Air Bag typically consists of the following 3 parts:

• The bag itself is made of a thin, nylon fabric, which is folded into the steering wheel or dashboard or, more recently, the seat or door.


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• The sensor is the device that tells the bag to inflate. Inflation happens when there is a collision force equal to running into a brick wall at 10 to 15 miles per hour (16 to 24 km per hour). Sensors detect the crash using a mechanical switch that closes when a mass shifts and an electrical contact is made. Electronic sensors use a tiny accelerometer that has been etched on a silicon chip.

• The air bag's inflation system uses the rapid pulse of hot nitrogen gas from the chemical reaction of sodium azide (nan3) and potassium nitrate (kno3) to inflate the bag.

The inflation system is not unlike a solid rocket booster. The air bag system ignites a

solid propellant, which burns extremely rapidly to create a large volume of gas to inflate the bag. The bag then literally bursts from its storage site at up to 200 mph (322 kph) -- faster than the blink of an eye! A second later, the gas quickly dissipates through tiny holes in the bag, thus deflating the bag so you can move. Even though the whole process happens in only one-twenty-fifth of a second, the additional time is enough to help prevent serious injury.


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Safety Concerns: It is important to note that the force of an air bag can hurt those who are too close to it. Researchers have determined that the risk zone for driver air bags is the first 2 to 3 inches (5 to 8 cm) of inflation. So, placing yourself 10 inches (25 cm) from your driver air bag gives you a clear margin of safety. Measure this distance from the center of the steering wheel to your breastbone. If you currently sit less than 10 inches away, you can adjust your driving position in the following ways:

• Move your seat to the rear as far as possible while still reaching the pedals comfortably.

• Slightly recline the back of your seat. • Point the air bag toward your chest, instead of your head and neck, by tilting your

steering wheel down (if your steering wheel is adjustable).

The rules are different for children. An air bag can seriously injure or even kill an unbuckled child who is sitting too close it or is thrown toward the dash during emergency braking. Experts agree that the following safety points are important:

• Children 12 and under should ride buckled up in a properly installed, age-appropriate rear car seat.

• Infants in rear-facing child seats (under one year old and weighing less than 20 pounds / 9 kg) should never ride in the front seat of a car that has a passenger-side air bag.

• If a child over one year old must ride in the front seat with a passenger-side air bag, he or she should be in a front-facing child safety seat, a booster seat or a properly fitting lap/shoulder belt, and the seat should be moved as far back as possible.

It is important to remember that air bags are effective only when used in tandem with a lap/shoulder seat belt. An air bag can actually cause serious injury if used improperly and without the seat belt. The Future of Air Bags: Until recently, most of the strides made in auto safety were in front and rear impacts, even though 40 percent of all serious injuries from accidents are the result of side impacts, and 30 percent of all accidents are side-impact collisions. Many carmakers have responded to these statistics by beefing up doors, door frames and floor and roof sections. Engineers say that designing effective side air bags is much more difficult than designing front air bags. This is because much of the energy from a front-impact collision is absorbed by the bumper, hood and engine, and it takes almost 30 to 40 milliseconds before it reaches the car's occupant. In a side impact, only a relatively thin


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door and a few inches separate the occupant from another vehicle. This means that door-mounted side air bags must begin deploying in mere 5 or 6 milliseconds! Also under development is the head air bag that looks a little like a big sausage and, unlike other air bags, is designed to stay inflated for about 5 seconds to offer protection against second or third impacts.

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