Experimental and numerical investigation of high-flow-rate injection focusing on improved thermal efficiency and output performance in low-pressure direct-injection hydrogen engines

Direct hydrogen injectors are actively being developed today to enable high-flow-rate injection of hydrogen into the engine cylinders at low pressure to promote opportunities for hydrogen application to internal combustion engines. In this study, the effect of high-flow-rate injection by direct hydrogen injectors on engine performance was evaluated under low hydrogen supply pressure. Combustion tests of a spark-ignition hydrogen engine were combined with a computational fluid dynamics analysis of jet and mixture formation behavior using large eddy simulation (LES). The results of this study revealed that a reduction of cooling losses accompanying attenuation of in-cylinder gas flow and changes in mixture location due to high-flow-rate injection contributed to a large improvement of thermal efficiency by 2-3%. This indicates that high-flow-rate injection in low-pressure direct-injection hydrogen engines is not only essential for achieving high power output through supercharging, but it is also effective in improving thermal efficiency by optimizing the injection timing.