Slide 1

Hydrogen - Properties - Use in CI Engines - Use in SI Engines - Storage methods - Safety precautions. Producergas and biogas - Raw materials - Gasification - Properties - Cleaning up the gas - Use in SI and CI engines, LPG& Natural gas - Properties - Use in SI and CI Engines.UNIT 3

GASEOUS FUELS

1HydrogenHYDROGEN - Cleanest of the Clean Fuels

. I believe that water will one day be employed as fuel, that hydrogen and oxygen which constitute it, used singly or together will furnish an inexhaustible source of heat and light of an intensity of which coal is not capablewater will be coal of the future

JULES VERNE - Mysterious Island (1876)

Properties of some gaseous fuelPropertyLPGNatural gasHydrogenBiogasProducer gasCompositionC3H8-62%C4H10-37%C2H6-1.08%CH4-86.4-90%C2H6-3.0-6.0%C3H8-0.35-2.0%H2CH4-60-70%CO2-30-40%CO-0.18%H2-0.18%CO-24.3%H2-22.6%CH4-2.2%CO2-9.3%N2-41.28%LCV at 1atm&15oc(kJ/kg)46000500001200005000 kJ/m33500-6000 kJ/m3Density at 1 atm&15oc(kg/m3)2.240.790.091.11.05Flame speed (cm/s)38.2534265-3252520-30Stoichiometric A/F 15.517.334.360.95-1.2Flammability limits (vol.% in air)2.15-9.65.3-154-757.5-147-21.6Octane number103-105130130120100-105Auto-ignition temperature (C)493-549 (propane)730585700625LHV of stoich mixture kJ/m33000 kJ/kg2900 kJ/kg3400 kJ/kg28002500Hydrogen gas properties

The properties that contribute to Hydrogens use as a combustible fuel are :

Wide range of flammabilityLow ignition energySmall quenching distanceHigh auto ignition temperatureHigh flame speed at stoichiometric ratiosHigh diffusivityVery low density

Wide Range of FlammabilityHas a wide flammability range (4 ~ 75 % in Vol.) in comparison with all other fuels.Lean mixture

Greater fuel economy

Complete combustion reaction.

Final combustion temperature is lower leading to reduction in the amount of pollutants such as NOx.

Affects power output due to volumetric heating value of the air/fuel mixture.

Low Ignition Energy

Has very low ignition energy (0.02 MJ) which ensures prompt ignition.

Amount of energy needed to ignite hydrogen is less than that required for gasoline.

Disadvantage of the low ignition energy is that hot gases and hot spots on the cylinder can serve as sources of ignition, creating problems of premature ignition and flashback.

Smaller Quenching Distance

Has a small quenching distance (0.64mm), smaller than gasoline (2mm).

Hydrogen flames travel closer to the cylinder wall than other fuels before they extinguish.

This can also increase the tendency for backfire since the flame from a hydrogen-air mixture more readily passes a nearly closed intake valve, than a hydrocarbon-air flame.

High Auto ignition TemperatureHas a relatively high auto ignition temperature (858K).

This decides what compression ratio we can use, since the temperature rise during compression is related to compression ratio.

High auto ignition temperature allows larger compression ratios to be used in a hydrogen engine than in a hydrocarbon engine which leads to better thermal efficiency.High Flame SpeedHas high flame speed (278 cm /sec) at stoichiometric ratios.

Under these conditions, the hydrogen flame speed is higher (faster) than that of gasoline.

This means that hydrogen engines can more closely approach the thermodynamically ideal engine cycle.

At leaner mixtures, the flame velocity decreases significantly.

High DiffusivityHas very high diffusivity (Velocity ~ 2 cm / sec).

High diffusivity in air, greater than gasoline and is advantageous for two main reasons.

It facilitates the formation of a uniform mixture of fuel and air.

If a hydrogen leak develops, the hydrogen disperses rapidly. Thus, unsafe conditions can either be avoided or minimized.

Low DensityHydrogen has very low density.

This results in two problems when used in an internal combustion engine.

Firstly, a very large volume is necessary to store enough hydrogen to give a vehicle an adequate driving range.

Secondly, the energy density of a hydrogen-air mixture, and hence the power output, is reduced.

Volume based storage densities ofdifferent fuels

Production of HydrogenElectrolysis of WaterThermal Cracking of MethaneEthanol ReformingCoal GasificationSteam ReformingNuclear FissionDecomposition of Biomass

HYDROGEN INFRASTRUCTURE

HYDROGEN FOR AUTO APPLICATIONSAs combustion fuel directly in IC engines.

In ad-mixture with CNG and LPG.

Combustion improver.

As a fuel for fuel cell.

In hybrid electric vehicles (H2 to run small generator for on-board charging of batteries).HYDROGEN FOR IC ENGINE APPLICATIONSFuel cell is a costly technology - about10 times than IC enginesIt will take at least 10 years to become affordable.

H2 can be used in existing I.C EnginesIC engine is a 100 years established technology and will require some modifications in tooling to make it adaptable for using hydrogen as a fuel

H2 is a clean burning fuel in IC enginesIt gives only NOx emission which can be minimized to negligible. No after treatment needed, hence no deterioration of emissions

Hydrogen can be competitive with CNGWith the infrastructure existing for CNG usage, H2 can replace CNGexcept of additional cost for reforming facility

HYDROGEN STORAGE

Storage as gas under pressureCryogenic storage as liquid hydrogen

Storage as metallic hydrides

Storage as ammonia, methanol and hydrocarbon fuels

ON BOARD STORAGE OF HYDROGEN The biggest issue is how to provide fuelThe space needed to store the fuel on board the vehicleEfficient ways for processing fossil fuels on board must be developedEven though reforming is a gentler process than combustion, it still introduces trace emissions, which will drag down the overall efficiencyThree methods are available for on board storage of hydrogen

ON BOARD STORAGE OF HYDROGENLIQUID H2

The conditions required are 20 K temperature and 2 Bar pressure.To maintain these conditions, LH2 is stored in a double-walled, super insulating cryogenic vessel. Hydrogen can be drawn either in liquid or gas phase from these containersAn amount of energy equivalent to 40% of the heating value of H2 is lost during the liquefaction process.Liquid Hydrogen

ON BOARD STORAGE OF HYDROGENMETAL HYDRIDES

They are based on the fact that gaseous H2 readily absorbs in metals, forming a weak chemical bondThey are in granular or powder form thus having larger surface area and large capacityTo release the gases, the hydride is heated to a certain temperatureThe biggest disadvantage is that they have low mass energy density and thus tend to be heavy

Metal Hydrides

ON BOARD STORAGE OF HYDROGENCOMPRESSED HYDROGEN GAS This is the most straightforward way to store H2 (aluminum cylinders wrapped in fiberglass)

Pressurized to 20MPa, H2 gas weighs approximately 3 times the liquid storage system and occupies more than twice the volume

Possibility of leakage is higher

COMPARISON OF ON BOARD STORAGE SYTEMS FOR HYDROGEN

Gasoline referenceLiquid Hydrogen (20K)Hydride (1.2% of Hydride weight)Compressed H2 (20.7 to 69MPa)Energy, Btu629,500629,500629,500629,500Fuel weight (kg)13.94.74.74.7Tank wt (kg)6.318.6547.563.3-86Total fuel system wt (kg)20.42355267.9-90.5Volume (liter)18.9177.9189.3408-227Safety PrecautionsPressure regulatorFlow control valveWater trapFlame arrestorWater Trap

Hydrogen inHydrogen outWaterFlame Arrestor

Challenges - Pre-Ignition

Due to hydrogens lower ignition energy, wider flammability range and shorter quenching distance

Premature ignition occurs before ignition by the spark plug, and results in an inefficient, rough running engine.

Backfire conditions can also develop if the premature ignition occurs near the fuel intake valve and the resultant flame travels back into the induction system.

Possiblecauses for Pre-Ignition

Can be caused by hot spots in the combustion chamber, such as on a spark plug or exhaust valve, or on carbon deposits.Backfire can occur when there is overlap between the opening of the intake and exhaust valves.

Pyrolysis of oil suspended in the combustion chamber or in the crevices just above the top piston ring can contribute to pre-ignition.

Delivery Systems

Adapting or re-designing the fuel delivery system can be effective in reducing or eliminating pre- ignition.Hydrogen fuel delivery system can be broken down into three main types:

Central injection (or carbureted)

Port injection

Direct injection.

Delivery System (Contd)

Central and port fuel delivery systems injection form the fuel-air mixture during the intake stroke. In the case of central injection or a carburetor, the injection is at the inlet of the air intake manifold. In the case of port injection, it is injected at the inlet port.

Direct cylinder injection is more technologically sophisticated and involves forming the fuel-air mixture inside the combustion cylinder after the air intake valve has closed.

Central Injection or Carbureted Systems

Simplest method of delivering fuel.

Firstly, central injection does not require the hydrogen supply pressure to be as high as for other methods.

Secondly, central injection or carburetors are used on gasoline or diesel engines, making it easy to convert a standard gasoline or diesel engine to a hydrogen or a gasoline-diesel/hydrogen engine.

Central Injection or Carbureted Systems

Disadvantage of central injection is that it is more susceptible to irregular combustiondue to pre- ignition and backfire.

The greater amountof hydrogen/airmixture within the intake manifold compounds the effects of pre-ignition

34Port Injection Systems

Hydrogen is injected into the manifold after the beginning of the intake stroke which reduces the probability for premature ignition.

Air sent separately at the beginning of the intake stroke to dilute the hot residual gases andcool any hot spots.

The inlet supply pressure for port injection tends to be higher than for carbureted or central injectionsystems, but lessthan for direct injection systems.

Electronic Fuel Injection

The electronic fuel injection (EFI) system meters the hydrogen to each cylinder.

This system uses individual electronic fuel injectors (solenoid valves) for each cylinder and are plumbed to a common fuel rail located down the center of the intake manifold.

EFIsystem uses variable injection timing and constant fuel rail pressure.

InjectorforHydrogen

Direct Injection System

More sophisticated hydrogen engines use direct injection into the combustion cylinder during the compression stroke.

In direct injection, the intake valve is closed when the fuel is injected, completely avoiding premature ignition during intake stroke. Consequently the engine cannot backfire into the intake manifold.

The power output of a direct injected hydrogen engine is 20% more than for a gasoline engine and 42% more than a hydrogen engine using a carburetor.Direct Injection Systems (Contd)

While direct injection solves the problem of pre-ignition in the intake manifold, it does not necessarily prevent pre- ignition within the combustion chamber.

In addition, due to the reduced mixing time of the air and fuel in a direct injection engine, the air/fuel mixture can be non-homogenous.

Direct injection systems require a higher fuel rail pressure than the other methods.

Ignition Systems

Due to hydrogens low ignition energy limit, igniting hydrogen is easy and gasoline ignition systems can be used.

At very lean air/fuel ratios (130:1 to 180:1) the flame velocity is reduced considerably and the use of a dual spark plug system is preferred.

Emissions

The combustion of hydrogen with oxygen produces water as its only product:2H2 + O2 = 2H2O

The combustion of hydrogen with air however can also pro-duce oxides of nitrogen (NOx):H2 + O2 + N2 = H2O + N2 + NOx + CO + CO2

In addition to oxides of nitrogen, traces of carbon monoxide and carbon dioxide can be present in the exhaust gas.

Emissions from IC Engine

Power OutputThe theoretical maximum power output from a hydrogen engine depends on the air/fuel ratio and fuel injection method used. As mentioned the stoichiometric air/fuel ratio for hydrogen is 34:1.

At this air/fuel ratio, hydrogen will displace 29% of the combustion chamber leaving only 71% for the air.

Brake thermal efficiency increases due to high heating value of hydrogen.

Use of Hydrogen in CI Engines

Dual fuel engineDiesel/vegetable oil fuelled engine

Neat Fuel EngineHCCI EngineSpark assisted engine

Dual fuel engine

Conclusions

Hydrogen has the potential to be the fuel for the future with carbon free emission.

Use of appropriate technology to compensate for the power loss could benefit its usage over a long term.

Development of lighter cylinders (material wise) for storing Hydrogen.

Challenges of safety in handling need to be carefully considered while using it as a fuel.