后喷技术与两级增压系统的优化匹配对燃烧过程的影响

Effect of Optimization Matching Between Post Injection Technology and Two-Stage Turbocharging System on Combustion Process

根据"高密度-低温燃烧"方案匹配的两级增压系统,使重型柴油机在中低速能实现低排放和高有效热效率.然而,在高速中高负荷工况,增压系统不经过必要的调压手段,会存在排气背压过高的问题,从而使柴油机油耗和烟度均较高,有效热效率较低.为此,本文采用后喷技术和涡端放气技术,通过分析后喷定时、主后喷油量比例和进气压力等参数对排放和有效热效率的影响,得到油路参数与气路参数的协同优化控制方法.研究表明,在高涡前压力工况,相比单次喷射模式,采用"主喷+后喷"的喷油模式,能实现更低排放,但有效热效率会下降.进一步研究发现,随着后喷定时和主后喷油量比例的变化,存在一个适当的后喷定时和后喷油量区间,使缸内碳烟易于降低.同时,随着涡端旁通阀开度增加,NOx排放会不断减小,碳烟排放会出现一个拐点,呈现先减小后增加的趋势,而有效热效率则逐渐增加.这充分说明,在高涡前压力工况,适时放气,能同时改善排放和有效热效率.

Low emissions and high brake thermal efficiency could be achieved in medium and low speed condition by the heavy-duty diesel engine with two-stage turbocharging system based on the high-density low temperature combus- tion theory. However, if the turbocharging system had none pressure regulation means, the exhaust backpressure would be so high that the fuel consumption and smoke intensity of the diesel engine would be relatively high and the brake thermal efficiency would be relatively low in high speed, medium and high load conditions. So post injection and turbo-side deflating technology was used in this paper, and the control method of collaborative optimization of oil and gas parameters could be achieved by analyzing the parameters of post injection timing, fuel quantity propor- tion of main and post injection and intake pressure. The study showed that compared to single injection mode, the main and post injection mode could achieve lower emissions, but worse brake thermal efficiency in high backpres- sure conditions. Further studies showed that it would be easier to reduce soot emission in an appropriate interval of post injection timing and post injection quantity. At the same time, the NOx emission would continue to decrease, the soot emission would have an inflection point showing a trend of first increase and then decrease, and the brake ther- mal efficiency would increase gradually. This fully showed that emissions and brake thermal efficiency could be im- proved by opportunely turbo-side deflating in high backpressure conditions.