The use of hydrogen as an energy carrier for the transport sector is an interesting option with the potential of lowering CO2 emissions. Hydrogen-fueled internal combustion engines equipped with port fuel injection (PFI) offer a cheap alternative to fuel cells and can be run in bi-fuel operation. Thus, one is able to alleviate fuel station density and vehicle autonomy requirements.
Here, details are given on the conversion of a passenger car gasoline engine to bi-fuel operation (hydrogen/gasoline). The engine is equipped with a continuously variable intake valve timing (CVVT). The effects of this timing were investigated, first for gasoline to determine a base set to compare the hydrogen results with. Then, tests were done on hydrogen, looking at power output, brake thermal efficiency and emissions of oxides of nitrogen (NOx).
The effects of the CVVT system on the occurrence of backfire, an abnormal combustion phenomenon typical of port fuel injected hydrogen engines, were also examined. A PFI hydrogen engine operating stoichiometric at WOT, has a theoretical power deficit of about 15% compared to a gasoline engine, due to the lower volumetric energy density. In practice, the power deficit can be even higher if the equivalence ratio has to be limited to avoid abnormal combustion. Variable valve timing is a means to enable hydrogen engines to run stoichiometric without backfire, through better scavenging of hot exhaust gases.