甲醇多次喷射对直喷射流点火发动机燃烧特性的影响

To address the problem of poor lean-burn capacity for passive pre-chamber engines,an investigation was conducted on a methanol direct-injection engine equipped with pre-chamber jet ignition (PCJI)system.Specifically,tests were carried out under varied operating conditions with the excess air coefficient ranging from 1.0 to 1.4 to explore the influence of single,double, and triple injection strategies on combustion and emission characteristics of the engine.The findings reveal that the multiple injection strategies significantly enhanced the mixture concentration within the pre-chamber, increased the jet ignition energy, and thereby improved the combustion stability.Under stoichiometric combustion conditions,the multiple injection strategy slightly extended the combustion duration and led to a marginal increase in HC and CO brake specific emissions.However,obvious benefits were observed under lean-burn conditions.When the excess air coefficient was 1.4,the coefficient of variation of the indicated mean effective pressure for the single injection,double injection,and triple injection strategies was 4.9 6%,4.36%,and 3.7 9%,respectively.Compared with the single injection strategy,the double injection and triple injection strategies resulted in reductions in HC brake specific emissions by 0.26 g•(kW•h)^-1and 0.35 g•(kW•h)^-1,reductions in CO brake specific emissions by 0.44 g•(kW•h)^-1and 0.93 g•(kW•h)^-1,and increases in indicated thermal efficiency by 0.5% and 1.1%,respectively. These research findings offer valuable references for enhancing the lean-burn performance of passive pre-chamber engines through the optimization of injection strategies.