Abstract
Keywords: hydrogen, fuel, internal combustion engine
The article describes various aspects of internal combustion engines running on hydrogen. Properties of hydrogen are displayed with special regard to application in internal combustion engines. Physical properties, flammability limits, ignition energy, energy density and value are listed. Modes of on-board storage, such as high pressure gas bottles, storage in liquefied form, absorption, adsorption and storage in form of chemical compounds are dealt with. Combustion properties are analyzed in deeper details, their effect on engine operation is pointed out. Contributors are the broad range of flammability of hydrogen-air mixture, low minimum ignition energy, high spontaneous ignition temperature, low extinction distance (that makes it difficult to extinguish its flame), high combustion velocity, high diffusion velocity and extremely low density. Ignition problems such as spontaneous ignition mostly appearing at low rpm at large spark advance and engines of external carburetion; backfire and end-gas detonation (knock) are analyzed. Emissions, nitrogen-oxide formation issues are described. Mitigation of ignition problems such as change in spark advance, mixture dilution, water injection and exhaust gas recirculation are showcased. Alternatives of fuel supply systems such as continuous drag from near to atmospheric pressure, sequential multi port injection and direct injection are detailed, together with their advantages and disadvantages.