Efficiency and Emissions-Optimized Operating Strategy of a High-pressure Direct Injection Hydrogen Engine for Heavy-duty Trucks

Hydrogen engines are required to provide high thermal efficiency and low nitrogen oxide (NOx) emissions. There are many possible combinations of injection pressure, injection timing, ignition timing, lambda and EGR rate that can be used in a direct-injection system for achieving such performance. In this study, several different combinations of injection and ignition timings were classified as possible combustion regimes, and experiments were conducted to make clear the differences in combustion conditions attributable to these timings. Lambda and the EGR rate were also evaluated for achieving the desired performance, and indicated thermal efficiency of over 45% was obtained at IMEP of 0.95 MPa. It was found that a hydrogen engine with a high-pressure direct-injection system has a high potential for improving thermal efficiency and reducing NOx emissions. Different engine management strategies involving the injection pressure, injection timing, ignition timing, lambda and the EGR rate were also evaluated under a Japanese emissions test cycle. Based on the experimental results, NOx emissions and fuel economy were estimated by simulation for a heavy-duty vehicle fitted with a 6-cylinder DI hydrogen engine. An original simulation program has been developed and a simulation database has been created based on experiments conducted with a single-cylinder engine. Finally, the paper projects the potential of an engine management strategy for obtaining high output power and energy efficiency equal to the baseline diesel vehicle while also attaining low NOx emissions of 0.5 g/kWh under the emissions test cycle.