12-01-2012, 04:40 PM
Hydrogen use in internal combustion Engines
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OBJECTIVES
At the completion of this module, the technician will understand:
• the combustive properties of hydrogen that relate to its use as a combustive fuel
• the air/fuel ratio of hydrogen fuel mixtures and how it compares to other fuels
• the types of pre-ignition problems encountered in a hydrogen internal combustion engine and their solutions
• the type of ignition systems that may be used with hydrogen internal combustion engines
• crankcase ventilation issues that pertain to hydrogen use in an internal combustion engine
• the thermal efficiency of hydrogen internal combustion engines
• the type of emissions associated with hydrogen internal combustion engines
• the power output of hydrogen internal combustion engines
• the effect of mixing hydrogen with other hydrocarbon fuels
Hydrogen Engines
The small number of vehicles using hydrogen internal combustion engines (HICE) makes it difficult to explain how to repair them. Therefore, this section does not serve as a repair manual, but as an outline describing the operation of a hydrogen engine and its major components, its benefits, drawbacks and how components can be modified or re-designed to reduce the drawbacks.
Combustive Properties of Hydrogen
The properties of hydrogen are detailed in Section 1. The properties that contribute to its use as a combustible fuel are its:
• wide range of flammability
• low ignition energy
Small Quenching Distance
Hydrogen has a small quenching distance, smaller than gasoline. Consequently, hydrogen flames travel closer to the cylinder wall than other fuels before they extinguish. Thus, it is more difficult to quench a hydrogen flame than a gasoline flame. The smaller quenching distance 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.
• small quenching distance
• high autoignition temperature
• high flame speed at stoichiometric ratios
• high diffusivity
• very low density
