Combustion Performance of Hydrogen Direct Injection under Lean-burn Conditions for Power Generation

This paper studies the combustion phenomenon of hydrogen (H2) direct injection (DI) in a modified spark ignition (SI) engine. As we known, ignition timing strongly correlates with combustion performance, especially for power output and efficiency. Therefore, different ignition timing varying among -20, -15, -10, -5, 0, 5, 10, 15, and 20 deg top dead center (TDC) are tested in this research. Besides, different H2 injection timings and injection pressures are also compared in this study. Moreover, as H2 usually favors lean-burn combustion, λ at 3, 3.5, and 4 are tested to find the lean-burn limitation. In order to obtain the engine speed influences on power output, finally 1500, 2000, and 2500 revolutions per minute (rpm) are evaluated in this study. Finally, thermal brake efficiency (BTE) and power output are analyzed. Results showed that power output and efficiency increase with the delay of ignition timing from -20 to 5 deg TDC and then decrease with delaying timing from 5 to 20 deg TDC. However, injection timing has less effect on the H2 combustion phenomenon. H2 lean-burn limitation is found that when λ is larger than 3, the efficiency decreases sharply. Moreover, both power output and efficiency firstly increase then decrease with higher engine speed and 2000 rpm is the best option for this small engine. Finally, by evaluating the contribution index, ignition timing and engine speed should be optimized first to achieve higher efficiency.