Effects of hydrogen injection timing,pressure and duration on the combustion and emission of hydrogen engines

Abstract

The hydrogen injection strategy plays a crucial role in the performance of hydrogen engines. However, optimizing these strategies to achieve efficient combustion and low emissions remains a significant challenge. In this study, experimental and numerical investigations were conducted on a heavy-duty hydrogen engine to examine the effects of hydrogen injection timing, pressure, and duration on combustion and emission characteristics at different engine speeds. The results showed that optimizing hydrogen injection timing, pressure, and duration can improve both combustion and emission performance. The best combustion performance, power, and thermal efficiency were obtained in the 120°CA BTDC to 130°CA BTDC range, while NOx emissions were minimized in the 140°CA BTDC to 150°CA BTDC range. However, excessively advancing injection timing increased the risk of knock and was accompanied by higher NOx emissions. As injection pressure increased from 15 to 30 bar, in-cylinder pressure, heat release rate, peak temperature, and indicated mean effective pressure rose accordingly. In addition, with increasing hydrogen injection pressure, the ignition delay and rapid combustion period became shorter, while the post combustion was prolonged. Notably, when injection pressure exceeded 20 bar, the risk of knock and emissions also increased. Unlike at other engine speeds, at 800 rpm, increasing injection pressure reduced power, torque, and thermal efficiency. Extending the injection duration enhanced in-cylinder pressure, heat release rate, and temperature, but when the duration exceeded 25°CA, peak temperatures surpassed 1800 K, which may promote NOx formation. These findings offer significant insights for the optimization of hydrogen injection strategies in heavy-duty hydrogen engines.