Numerical simulation of the effect of combustion characteristics in a high-compression-ratio lean-burn gasoline engine utilizing a two-stage water injection strategy

Abstract

High compression ratios and lean burning were recognized as effective strategies to enhance the thermal efficiency of engines. However, knocking phenomena often impose constraints on further efficiency improvements in engines with high compression ratios. In this paper, computational fluid dynamics (CFD) was employed to simulate the combustion characteristics of an ultra-high compression ratio (CR = 17) gasoline engine with an Atkinson cycle. Meanwhile, single and two-stage water injection strategies were proposed to address the knocking of lean burn engines. Knocking could apparently be suppressed by direct water injection; specifically, the two-stage water injection strategy depicted a better cooling influence caused by evenly distributed water vapor. The two-stage injection strategy resulted in a 105 K reduction in cylinder temperature compared to no water injection. Moreover, this strategy effectively mitigates the deleterious effects of water injection on the initial flame kernel formation and flame propagation, thereby reducing ignition delay time and duration of combustion. Notably, the water injection efficiency of the two-stage water injection strategy is about four times higher than that of the single water injection strategy.