阶跃EGR对重型柴油机燃烧过程的影响

Effect of Stepped EGR on Combustion Process of a Heavy-Duty Diesel Engine

研究了阶跃过程中废气再循环(EGR)流量在管路中的变化及其对重型柴油机燃烧过程的影响.证实可利用一系列相互之间有延迟的阶跃函数对EGR流量的变化过程进行描述,而进气流量等的变化可用一阶或二阶惯性系统的阶跃响应函数来描述.研究发现,随着EGR的加入引起的进入气缸总充量的减少是燃烧初始边界条件发生变化的主要原因之一.对放热率的研究表明,在空燃比较低的工况,EGR的加入并没有使主喷燃烧向后推迟,且EGR对燃烧的抑制作用并不表现在燃烧的初期和末期放热率较小、燃烧速度不快的时候,而对燃烧快速、放热率大的燃烧部分抑制作用明显.

Experimental study on variation of EGR flow in the tube and its effects on working process of a heavy-duty diesel engine were conducted.The study shows that controlling on EGR flow is feasible by using series of delayed step functions.Variation in intake flow rate can be described using the step response function of first-order or second-order inertia system.Study shows that the decrease in charge amount due to EGR introduction is the major reason to change initial combustion boundary condition.Heat release rate shows that,at low air-fuel ratio,EGR introduction does not delay the main combustion and the suppres-sion effect of EGR on combustion becomes important for the phase of rapid combustion and high heat re-lease rate.