Experimental investigations on combustion acceleration behavior of methane/gasoline under partial load conditions of SI engines

Natural gas/gasoline dual-fuel combustion mode has been proposed to use respective advantages. Recent study showed that a combustion acceleration behavior may exist for methane/gasoline dual-fuel under partial load conditions of spark-ignition (SI) engines. As engine thermal efficiency is significantly affected by burning rate, it is necessary to further investigate the combustion characteristics of methane/gasoline dual-fuel. In this work, a port-injection of methane and direct-injection of gasoline strategy was employed in a SI engine, and variations of methane addition, intake pressure, intake temperature, compression ratio, excessive air coefficient and fuel injection timing were considered. Firstly, engine performance in combustion and emissions was explored to illustrate the advantage of methane/gasoline dual-fuel combustion. Then, the effect of various operation parameters on combustion characteristics of methane/gasoline dual-fuel, with addressing combustion acceleration behaviors, were further studied. It showed that obvious combustion acceleration was observed under low compression ratio, lean burning and fuel stratification conditions, characterizing slight increases in in-cylinder pressure and obvious improvement in initial combustion phasing with methane addition. Finally, combined with previous fundamental work, the underlying mechanism for combustion acceleration behaviors was analyzed and the role of diffusion and stretch effect on initial flame development was emphasized.