Internal Combustion Engine
Experimental results [10] with an IC engine fueled with a H2-air charge, revealed the lowest equivalence ratio to assure steady running without much misfire occurred at a equivalence ratio of 0.218, but reliable function occurred at f of 0.28 and above. Several papers report vast reduction of NO formation through direct fuel injection into the cylinder head or water injection [8, 10, 11] to keep the flame temperature down, yet the experimental setups vary considerably from gasoline converted to hydrogen engines, to exotic timed spark and manifold designs, yielding NOx concentration twice as high to fourteen times less [11] than gasoline. One undisputed repeatable results is the lean oxidation of hydrogen, with equivalence ratios bound between 0.3 and 0.6 values. Luckily, the maximum thermal efficiency under numerous observations occurred at f = 0.4 and has been reported as high at 55% [11], compared to a methane engine at 30% (gasoline).

Greater efficiency and power control of the engine is maintained through the use of the wide lean flammability limits, and use of fuel injection over a throttled carburated system. With the low LFL, quality regulation under unthrottled air intake can vary power output over the quantity regulation necessary for a hydrocarbon fuel [11]. Aspects of safety are no more stringent than those for gasoline, just different. Storage either as a compressed gas or liquid may pose difficult, but solvable. Consideration into managing other problems of backfire, flashback, and knock each has resolvable solutions slightly different to strategies association with carbon fuels. With all the combined efforts taken to perfect and refine the Otto-cycle petroleum based engine, the hydrogen engine has the opportunity to become the next chemical transportation fuel of choice.