Design and optimization of combustion chamber geometry and fuel spray targeting of a natural gas/biodiesel dual direct injection engine

In pilot fuel-ignited stratified premixed natural gas (NG) engines, the combustion chamber geometry significantly influences the distribution of NG. Meanwhile, the fuel spray targeting affects the dynamic distribution of the pilot fuel and NG mixture, thereby exerting a crucial impact on subsequent combustion. This study numerically investigated the coupling effects of combustion chamber geometry and fuel spray targeting on the performance of a NG/biodiesel dual direct injection engine, aiming to optimize these parameters. Three combustion chambers (double-lip, reentrant, and hemispherical) were constructed for comparison with the original open crater design. Based on the spray targeting of NG, the NG injection was categorized into three cases (A, B, and C) corresponding to NG injection into the squish region, the piston throat, and the piston bowl, respectively. The results indicate that the effect of combustion chamber geometry on NG distribution varies depending on the NG injection situation, with the impact being more pronounced in Cases B and C than in Case A. The spray targeting of biodiesel not only affects the biodiesel-NG mixing but also changes the ignition position. It is found that the variation of biodiesel ignition angle (BIA) in Case C has a much smaller impact on engine performance compared to Cases A and B. The double-lip combustion chamber with a large BIA is more favorable for Cases A and B, whereas the hemispherical combustion chamber with a small BIA achieves the best performance in Case C.