Effect of fuel injection timing on performance and emissions with a dedicated direct injector in a hydrogen engine

In this study, hydrogen fuel was injected directly into a cylinder using a prototype of a dedicated hydrogen direct injector (HDI). The effects of fuel injection timing and amount of hydrogen fuel injected on engine output performance and emissions (e.g., nitrogen oxides and carbon dioxide) were investigated by varying the fuel injection timing from before top dead center (BTDC) 190 crank angle degree (CAD) toward BTDC 60 CAD. Strategies for maximizing the engine's output performance when an after-treatment system for nitrogen oxide removal catalysts is not used were assessed. When using the HDI, a torque improvement result (up to 35.9%) can be obtained even under the condition that the hydrogen supply pressure was half as low as compared to the case of using a gasoline direct injector for hydrogen fuel. Under the condition of retarded fuel injection timing, a locally rich mixture is formed to increase the emission of nitrogen oxides at a level of 50 ppm or higher. The engine oil is burned to affect the emission of carbon dioxide (CO2), which is proportional to the load.