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INTRODUCTION
In trying to keep up with emissions and fuel efficiency laws, the fuel system used in moderncars has changed a lot over the years. The 1990 Subaru Justy was the last car sold in the
United States to have a carburetor; the following model year, the Justy had fuel injection.
But fuel injection has been around since the 1950s, and electronic fuel injection was used
widely on European cars starting around 1980. Now, all cars sold in the United States have
fuel injection systems.
Air pollution has been the main reason due to which all the developed countries have
switched over to Electronic Fuel Injection system. Not only air pollution but keeping in
mind rise in fuel prices day by day, fuel economy is also one of the reasons leading to the
transformation from carburetors to injection system. Electronic control over the injection
system has made it much easier to control the engine functioning. Earlier cold starting was
achieved by heating the intake manifold with the help of a glow plug. But now EFI has
introduced a separate injector called cold start injector which makes the charge rich by
injecting an extra amount of fuel in the intake manifold.
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HISTORY OF FUEL INJECTION
(1) Fuel Injection: Diesel engines from the very beginning have been using fuel
injection system. But the year 1903 is a memorable year in the history of IC engine
development. It was in this year that the Wright brothers made the maiden SI engine
powdered flight which had a gear pump that injected fuel into the intake port. Thus
fuel injection in case of SI engine is not a recent development.
(2) Air injection : Developed in around 1895. Fuel oil was metered and delivered by a
pump to the atomizer, which was in communication with a high pressure air storagetank supplied by an air compressor, and injection occurred when the injector valve
was opened by a cam actuated mechanism. High pressure air then flowed into the
engine cylinder carrying along with it the metered fuel as a finely atomized spray.
The use of bulky compressors led to its obsolete use.
(3) Solid injection:(a) Mechanical injectors: The first satisfactory airless injection system was
James McKechnie of Vickers in 1910. Here the fuel was injected without
the use of any high pressure air from the compressor. Oil was delivered
by a metering pump to a spring loaded plunger, which was raised by a
cam. Tripping of the cam allowed the fuel to be injected into the engine
cylinder as the spring returned the plunger t o its bottom position.
(b) Automatic or differential valve injectors: The inwardly opening
differential valve type nozzle , which is most commonly used today was
first used by Thornycroft of England in 1908. It consists of a spring
loaded needle valve which was operated hydraulically by the pressure of
the fuel. Differential areas were used on the valve stem to augment the
fuel pressure to lift the needle valve.
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(4) Electro-magnetically operated valves: The idea of lifting nozzles by solenoids was
first introduced by an American named Thomas T Gaff in 1913 but was finally
experimented and brought up by another American in 1933. This was the beginning
of the Electronic Fuel injection System. It was commercially used by AMC in its
model Rambler Rebel in 1956 . But due to cold starting defects it couldnt be
successful.
(5) Gasoline injection: The first ever IC engine to use gasoline injection was Chevrolet
Corvette of the General Motors in 1957. It was a mechanical fuel injection system.
(6) ECU: In 1980, Motorola introduced the first electronic engine
control unit. Its integrated control of engine functions (such as fuel
injection and spark timing) is now the standard approach for fuel
injection systems. [1]
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WHY EFI ?
The fuel injection from the very beginning in 1903 has undergone vast transformations.
Electronic Fuel Injection system is going to be the sole injection system in the near future.
All the vehicles running in developed countries have already been restricted to fuel injection
systems be it for diesel or gasoline. E.g. USA, Canada, Germany etc. [1]
For developing countries carburetors are still prevailing but they too are undergoing
this transformation to EFI.
EFI is used because of :
(1) Pollution control:
In the present era the environmental air pollution is mainly caused due to vehicular
emissions. Various gases emitted are carbon dioxide, carbon dioxide, nitrogen dioxide, etc.
In EFI systems various sensors are employed like the exhaust gas oxygen sensors. It senses
the amount of oxygen in the exhaust emissions and the ECU adjusts the thereafter fuel
requirements. If more oxygen is detected then rich fuel is injected and if less oxygen is
detected then rich fuel is injected.
(2) Fuel economy:
Rise in fuel price is a matter of concern today. Therefore we either have to find an
alternative source to such fuels or utilize the present fuel in an economical and efficient
manner. The alternatives should be much cheaper and be abundantly available. EFI system
plays an important role in using the fuel economically. The ECU along with the feedback
available from various sensors meter the fuel in a very precise manner and fuel wastage is
negligible.
(3) Decreasing cost of electronic components:
The day to day decrease in the prices of electronic components is a good sign in this field.
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FUEL DELIVERY SYSTEM IN EFI
The fuel supply from the fuel tank to the injector valves for all electronic systems follows
the same basic layout. The delivery of fuel at the injector valves is also based on a similar
function for all systems. It basically consists of fuel tank, electrical fuel pump, fuel pressure
regulator, fuel injector, fuel return pipe and fuel filter.
(a) Fuel tank:
It is used for the storage purpose of the fuel. The fuel tank is the obvious place to start in
any full system explanation. Unlike the tanks on early carburetor cars, it is a sealed unit that
allows the natural gassing of the fuel to aid delivery to the pump by slightly pressursing the
system. It may be noted that when the filler cap is removed, that pressure is heard to escape
(b) Electrical fuel pump:
It draws fuel from tank and forces it into the regulator. Fuel injected engines often use
electric fuel pumps that are mounted inside the fuel tank (and some fuel injected engines
have two fuel pumps: one low pressure/high volume supply pump in the tank and one high
pressure/low volume pump on or near the engine.) . Placing the pump in the tank puts the
component least likely to handle fuel vapour well (the pump itself) farthest from the engine,
submerged in cool liquid. Another benefit to placing the pump inside the tank is that it is
less likely to start a fire. Though electrical components (such as a fuel pump) can spark and
ignite fuel vapors, liquid fuel will not explode and therefore submerging the pump in the
tank is one of the safest places to put it. In most cars, the fuel pump delivers a constant flow
of gasoline to the engine; fuel not used is returned to the tank. This further reduces the
chance of the fuel boiling, since it is never kept close to the hot engine for too long.
(c) Fuel pressure regulator:
It controls the amount of pressure that enters the injector and any extra fuel is returned to
the fuel tank. The fuel pressure regulator is fitted to maintain a precise pressure at the fuel
injector valve nozzles. On port fuel-injection systems, a fuel rail is used to hold the pressure
regulator and the fuel feed to the injector valves. The injector valves usually fit directly onto
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or into the fuel rail. The fuel rail holds sufficient fuel to dampen fuel pressure fluctuations
and keep the pressure applied at all injector nozzles at a similar level.
Fuel pressure regulators are sealed units with a spring-loaded diaphragm and valve
on the return outlet to the fuel tank. Fuel is pumped into the regulator, and when the pressure
is high enough it acts against the diaphragm and compression spring to open the valve.
Surplus pressure and fuel is allowed to return to the fuel tank. Once the pressure in the fuel
regulator is reduced, the valve closes and the pressure builds up again. Throttle-body
injection systems operate in the region of 1 bar, and port fuel injection systems in the region
of 2.5 bars.
(d) Electrical fuel injectors:
The injector valves spray finely atomized fuel into the throttle body or inlet ports,
depending on the system. The electromagnetic injection valves are actuated by signals from
the ECU. These are an electromagnetic solenoid, a spring-loaded plunger, a jet needle and
the injector-valve nozzle. The electrical supply to the solenoid is made from the system relay
or ECU. Grounding the other connection energizes the solenoid. This lifts the plunger and
jet needle so that fuel is injected for the duration that the electrical current remains live. As
soon as the electrical supply is switched off in the ECU, a compression spring in the injector
valve acts on the solenoid plunger to close the nozzle.
Figure 1: Solenoid fuel injectors [2]
(e) Fuel return pipe:
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The return pipe run from the fuel pressure regulator to the fuel tank. . Surplus pressure
and fuel in the fuel pressure regulator is allowed to return to the fuel tank.
(f) Fuel filter:
The fuel filter is an in-line paper element type that is replaced at scheduled service intervals.
The filter uses micro-porous paper that is directional for filtration. Filters are marked for fuel
flow with an arrow on the casing. Correct fitting is essential. The fuel filter is the fuelsystem's primary line of defense against dirt, debris and small particles of rust that flake off
the inside of the fuel tank. [2]
(g) Accumulator:
It is used to maintain the fuel pressure. When the engine is in off positon it maintains the
fuel pressure so that it can be restarted.
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AIR INDUCTION SYSTEM
The air-supply components consist of ducting and silencing components between the air
intake and the inlet manifolds. This also includes an air filter, a throttle body, throttle plate
assembly and idle control components. The air-supply components must provide sufficient
clean air for all operating conditions.
(a) Air filter:
Air filters on most modern gasoline-engined vehicles consist of a plastic casing with a paper
filter element. Airflow into the filter is upwards so that dust and dirt particles drop into the
dust chamber, or is rotary so that dust and dirt is thrown out before the air enters the engine.
Crankcase ventilation and the air supply or pulse air exhaust emission systems are also
connected to the filter assembly.
(b) Throttle body:
A throttle is the mechanism by which the flow of a fluid is managed by constriction orobstruction. An engine's power can be increased or decreased by the restriction of inlet
gases. The throttle is a conventional circular plate in an air tube. For fast idle and warm-up,
an auxiliary air valve is fitted to bypass the throttle plate, or an electromechanical link is
made to the throttle plate spindle
When you step on the gas pedal, the throttle valve opens up more, letting in more air.
The engine control unit (ECU, the computer that controls all of the electronic components
on your engine) "sees" the throttle valve open and increases the fuel rate in anticipation of
more air entering the engine. It is important to increase the fuel rate as soon as the throttle
valve opens; otherwise, when the gas pedal is first pressed, there may be a hesitation as
some air reaches the cylinders without enough fuel in it.
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Figure2 : Engine throttle valve [3]
(c) Idle speed control components:
An idle air control valve, also called an idle air sensor control motor, is an electrically
operated valve that controls the amount of air that bypasses the throttle plate in an engine
with a fuel injection system. This causes the idling speed of the engine to change as needed.
The computer in the vehicle that governs this function receives information from the air
sensor and determines the amount of air that the idle air valve allows to pass through it and
bypass the throttle plate.
Idle speed control can also be provided by direct action onto the throttle spindle.
Electrical solenoids or stepper motors are used for this method of control. The solenoids can
be single position or multi-position types and can be used for not only cold start and warm-
up control but also to open the throttle when high load systems, such as the air conditioner,
are switched on. [2]
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SENSORS USED IN EFI
ENGINE SPEED SENSORS :
The engine speed is measured by the use of Inductive Pulse Generators Most of the latest
systems have inductive pulse generators mounted close to, and responding to, a toothed
wheel attached to the crankshaft pulley or flywheel. There is an air gap between the toothed
wheel and the inductive generator. As the teeth pass the inductive generator, an alternating
electrical current is produced. The waves of the alternating current are used to measure
engine speed.
Figure4: Inductive Pulse Generator [2]
AIR FLOW METER:
This is required so as to determine the volume of the air entering the engine. A Vane Air
Flow Meter (VAF) is used for this purpose. The vane type air flow meter consists of an air
passage and damping chamber into which is fitted a fixed pair of flaps (or vanes). These
rotate on a spring-loaded spindle. The spindle connects to and operates a potentiometer
which is further connected to the ECU.
TEMPERATURE SENSORS:
Two temperature sensors are used mainly measure the air intake temperature and coolant
temperature.
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Figure5 : Coolant thermistor [2]
(a) Engine coolant temperature sensor
The engine coolant temperature sensor is a negative temperature coefficient (NTC)
thermistor. It is of a similar type to the air-temperature sensor. It is fitted into the water
jacket close to the thermostat or to the bypass coolant-circuit passages. The sensor measures
the engine coolant temperature and provides a signal voltage to the ECU. This is used for
cold start and warm-up enrichment as well as fast idle speed control through the idle-speed
control valve.
(b) Air intake temperature sensorIn order for the ECU to correctly calculate the required fuel for a correct mixture ratio, an
accurate figure for air mass is necessary. However, air volume and density are affected by
changes in temperature. As the temperature rises, the air density falls. The airflow, or
manifold absolute pressure measurement, therefore, must be corrected for temperature. The
sensor is a temperature-dependent resistor with a negative temperature coefficient (NTC).
EXHAUST GAS OXYGEN SENSORS:
The overall purpose of oxygen sensor is to maintain a close tolerance of the stoichiometric
ratio (14.7:1). The Greek letter () lambda is used as the symbol for a chemically correct air-
to-fuel ratio. This is the stoichiometric ratio of 14.7 parts of air to 1 part of fuel by mass.
This is why the sensor used to measure the oxygen content is called as Lamda Sensor. It is
fitted in the lower part of the exhaust stream and measures the oxygen content in it. More
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fuel is delivered when oxygen content is detected and less fuel when it is not. In this way, an
accurate fuel mixture close to the stoichiometric ratio is maintained.
Types are:
(a) Zirconia sensors
The zirconium dioxide, or zirconia, lambda sensor is based on a solid-state electrochemical
fuel cell called the Nernst cell. Its two electrodes provide an output voltage corresponding to
the quantity of oxygen in the exhaust relative to that in the atmosphere. An output voltage of
0.2 V (200 mV) DC represents a "lean mixture" of fuel and oxygen, where the amount of
oxygen entering the cylinder is sufficient to fully oxidize the carbon monoxide (CO),
produced in burning the air and fuel, into carbon dioxide (CO2). An output voltage of 0.8 V
(800 mV) DC represents a "rich mixture", one which is high in unburned fuel and low in
remaining oxygen.
Figure6 : Zirconia sensor [5]
(b) Titania sensor
A less common type of narrow-band lambda sensor has a ceramic element made of titania
(titanium dioxide). This type does not generate its own voltage, but changes its electrical
resistance in response to the oxygen concentration. The resistance of the titania is a function
of the oxygen partial pressure and the temperature
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THROTTLE POSITION SENSOR:
Two types of throttle-position sensor are used. Both are fitted to the throttle body and
operated by the throttle plate spindle. The two types are a throttle switch assembly and a
throttle potentiometer.
(a) Throttle switch assembly
A throttle switch assembly has two switches, one to indicate the closed throttle or idle
position and the other for the wide-open throttle position.
(b) Throttle potentiometer
A throttle potentiometer is a variable resistor with a rotary sliding contact. The sliding
contact is moved along the rotary resistance track to provide changes in voltage proportional
to the position of the throttle i.e the angle of the throttle plate. As the throttle opens, this
potentiometer circuit converts the mechanical movement of the throttle valve into a variable
voltage signal. The throttle potentiometer signals are used in the ECU for a number of
functions. At the closed throttle position, idle speed and deceleration fuel cut-off are
controlled. In the part-open throttle position (about 5 percent to 70 percent open) there is
normal operation with close control of fuel delivery and exhaust emissions. In the
wide-open throttle position (70 percent to 100 percent), full-load enrichment is provided.
MANIFOLD AIR PRESSURE SENSOR:
These sensors are used to monitor the vacuum in the intake manifold so that the mixture
strength can be adjusted according to the engine load. It can be said that it indirectly
measures the intake air volume i.e why those engines engines equipped with MAP sensors
do not have an Air Flow Meter. The MAP sensor is a pressure-sensitive component
consisting of a diaphragm and piezoelectric circuit. It can be a component fitted in
the engine compartment .It is connected by a rubber hose to the inlet manifold. The ECU
supplies a stabilized reference voltage, usually 5 V, to the sensor. This voltage is adjusted by
the MAP sensor electronics to provide an output signal proportional to the sensed absolute
atmospheric pressure. [2]
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ELECTRONIC CONTROL UNIT
At the heart of electronic fuel-injection (EFI) systems is the fuel control or electronic-controlunit (ECU) with a stored map of operating conditions. Electronic sensors provide data to the
microprocessor in the ECU, which calculates and sends the output signals to the system
actuators, which are the fuel pump, fuel injectors and idle air-control units. The ECU will
also switch some of the exhaust emission and auxiliary system components.
The electronic-control unit is an electronic microcomputer with a central processing
unit (CPU) or microprocessor. Inside the CPU are software programs that compare all
sensor-input data with a fixed map of operating conditions. It then calculates the required
output signal values for the injection valves and other actuators. Also called as Engine
Control Module (ECM).
Working of ECU
(i) Control of fuel injection: ECU will determine the quantity of fuel to inject
based on a number of parameters. If the throttle pedal is pressed further
down, this will open the throttle body and allow more air to be pulled into the
engine. The ECU will inject more fuel according to how much air is passing
into the engine. If the engine has not warmed up yet, more fuel will be
injected .
(ii) Control of ignition timing : A spark ignition engine requires a spark to initiate
combustion in the combustion chamber. An ECU can adjust the exact timing
of the spark (called ignition timing) to provide better power and economy.
(iii) Control of idle speed : Most engine systems have idle speed control built into
the ECU. The engine RPM is monitored by the crankshaft position sensor
which plays a primary role in the engine timing functions for fuel injection,
spark events, and valve timing. Idle speed is controlled by a programmable
throttle stop or an idle air bypass control stepper motor.
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WORKING OF EFI SYSTEM
Taking example forpetrol injection:
. Air enters through the air induction system where it is measured by the air flow meter. As
the air flows into the cylinder fuel is mixed into the air by the fuel injector.
. Fuel injectors are arranged in the intake manifold behind each intake valve. The injectors
are electrical solenoids which are operated by the ECU.
. The ECU pulses the injector by switching it on and off.
. When the injector is switched on, it opens spraying the atomized fuel at the back side of theintake valve.
. As the fuel is sprayed into the intake air stream, it mixes with the incoming air and
vaporizes due to the low pressure in the intake manifold. The ECU signals the injector to
deliver just enough fuel to achieve an ideal air/fuel ratio of 14.7:1.
. The precise amount of fuel delivered is a function of ECU control.
. This charge is introduced into the combustion during the suction stoke.
. The ECU determines the basic injection quantity based upon measured intake air volume
and engine rpm.
. Depending upon the engine operating conditions injection quantity will vary. The ECU
monitors variables such as coolant temperature, engine speed, throttle angle, and exhaust
oxygen content and makes injection corrections which determine final injection quantity.
DIESEL INJECTION:
Diesel being a less volatile fuel requires greater pressure for its atomization.The functioning
of a diesel EFI system is similar to that of petrol EFI system except the fact that air is
separately introduced into the combustion chamber during the suction stroke and diesel is
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introduced into the combustion chamber at around 15 to 25 before TDC during
compression stroke. [11]
Figure7 : Gasoline EFI system [11]
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Figure8: micro computer used in EFI system [11]
ADVANTAGES OF EFI
(1) Improvement in volumetric efficiency due to comparatively less resistance in the intake
manifolds which will cause less pressure losses. It eliminates majority of carburetor
losses and almost eliminates the requirement of manifold heating.
(2) Manifold wetting is eliminated due to fuel being injected into or close to the cylinder and
need not flow through the manifold.
(3) Atomization is independent of cranking speed and therefore starting will be easier.
(4) Highly accurate air/fuel ratio control throughout all engine operating conditions is
achieved.
(5) Excellent fuel economy , with improved emission controls.
(6) Improved cold engine startability and operation.
(7) Elimination of large number of mechanical components leads to reduction in
maintenance and provides a increased reliability.
(8) Superior throttle response and power. [3]
DISADVANTAGES OF EFI
(1) High maintenance cost.
(2) Difficulty in servicing and requires well skilled and professional workers who have
good knowledge of Electronic, Computers and Mechanical components.
(3) Possibility of malfunction of some sensors. [3]
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RECENT ADVANCEMENTS
(1) RDSO LUCKNOW:
It was the collaborative effort RDSO Lucknow and IIT
KANPUR that the first diesel locomotive equipped with
electronic fuel injection system (EFI) was flagged of from
RDSO lucknow on 14th September 2011. This retrofitment
is estimated to save 2% of fuel used as compared to the
conventional injection system.
Indian Railways consumes upto 2.5 billion litres of
fuel annually spending Rs 10,000 crores. This is going to
be a saving of Rs 200 Crores yearly. It involves a one time
investment. In the first phase RDSO has decided to equip
100 ALCO diesel engines with EFI system. [6]
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APPLICATIONS
(1)Royal Enfield Thunderbird 500
Figure9: Royal enfield [10]
It is a 499cc single-cylinder 4-stroke air-cooled Twin spark engine Fed by an advanced
Keihin electronic fuel injection system.
(2) Honda City ZX:
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Figure10: A 1497cc and EFI equipped car [7]
(3) Rolls Royce Phantom Series II
Figure11: Rolls Royce [8]
(4) F1 racing cars
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Figure12 : Racing car [9]
(5) All jet fighter planes
(6) Passenger planes
REFERENCES
[1] History of Fuel Injection by Frank Deluca.
[2] Automotive Technician Training - Tom Denton
[3] IC Engine by V Ganeshan.
[4]https://reader009.{domain}/reader009/html5/0421/5adb0f531b50d/5adb0f5f7bef0
[5] http://en.wikipedia.org/wiki/File:ZirconiaSensor.svg
[6] http://www.rdso.gov.in/
[7] http://www.autoinfoz.com/Honda/cars/Honda_City/Honda_City_Newspecification.html
[8] https://reader009.{domain}/reader009/html5/0421/5adb0f531b50d/5adb0f601e702.jpg
[9] http://www.autoblog.com/media/2012/13/F-1-racing-car.jpg
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[10] http://static.zigwheels.com/media/content/2012/Sep/rethunderbird500_1_560x420_560
420.jpg
[11] http://www.toyota.com/toyotaSearch/search?keyword=working+of+efi&locale=en
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