Study on the effect of low carbon alcohol gasoline stratified injection strategy on engine knock combustion under lean burn conditions

This paper focuses on the "oxygenated fuel concentration stratified lean burn to improve combustion and thermal efficiency" as a starting point and investigates the effects of combustion of high-octane oxygenated fuels in gasoline engines under overall lean burn conditions by using different injection strategies on the performance and knock combustion. The study shows that: the flame during the knock shows the characteristics of spontaneous combustion flame and normal flame collision along the cylinder wall propagation alternately, followed by local deflagration and auto-ignition point to the center of the cylinder, and then turned to the center of the surrounding flow of disordered stacked high-speed fluctuations. Combustion under concentration stratification manifests phase lag, with heat release characterized by either a single-peak continuous pattern or a double-peak staged pattern, which interchange dynamically. The single-variable method was used to obtain the optimal working condition for concentration stratification: n-butanol volume ratio of 15 %, secondary injection moment of 150°CA BTDC and injection ratio of 15 %, which improves the thermal efficiency by about 3.2 % and reduces the intensity of knock by about 20.7 %. When the proportion of ethanol replacement increases, the thermal efficiency maximum increase is about 5.2 %, but the knock situation tends to be serious. •Mixture concentration stratified combustion.•Optimal operating point for concentration stratification.•Comparison of the effect of stratified combustion of different alcohols.•Knock suppression and overall optimization of combustion.