Conversion of a Small Size Passenger Car to Hydrogen Fueling: Focus on Rated Power and Injection Phasing Effects

In the context of increasing efforts towards zero emissions transport, hydrogen represents a valid alternative to electric powertrains. Spark ignition (SI) engines are well suited for this alternative fuel and its specific application requires relatively minor changes with respect to added components. Limited range is one of the main issues with hydrogen as an energy source for transportation, due to its low energy density. The present study looked at the possibility of converting a small size passenger car powered by a turbocharged SI unit to hydrogen fueling. Taking the electric version of the vehicle as benchmark, the initial evaluation of the hydrogen SI alternative appears feasible with an additional gas container comparable in size to the gasoline tank. As a result, further investigation was aimed at actual engine operation in port fuel injection mode, with a focus on rated power and injection phasing effects. The first parameter is essential for ensuring acceptable vehicle dynamics; the second one becomes paramount when considering the requirement of avoiding closed valves injection so as to minimize the possibility of abnormal combustion phenomena. 0D/1D simulation was applied for investigating the effects of hydrogen fueling and injection phasing. Flow requirements were identified for correct operation of the engine and full load stoichiometric output was found to be completely compatible with rated power requirements. No significant changes of turbine/compressor unit operation were predicted by the model, even if higher pressure ratio is needed when using hydrogen. One issue identified by the numerical results is that cylinder imbalance tended to be much more prominent with respect to gasoline fueling and heavily dependent on injection timing. The knock sub-model predicted more intense effects of abnormal combustion phenomena, which could be mitigated when cylinder imbalance was eliminated.