EGR对直喷式柴油机冷起动过程着火燃烧的影响分析

通过在一台135单缸直喷柴油机上分别进行内部EGR（IEGR）、外部EGR（EEGR）条件下的冷起动试验，分析了内、外部EGR对柴油机冷起动过程着火燃烧性能及排放的影响。加入内、外部EGR后，由于EGR中含有大量的燃油蒸气、部分氧化产物等活性成分，初始着火循环的着火燃烧性能得到显著改善。在冷起动过程中，加入一定量的内部或外部EGR，有利于提高燃烧过程的稳定性。但过大的外部EGR量，将导致发动机燃烧极度不稳定甚至失火。由试验结果还可以看到，加入适当的内、外部EGR，均能有效地改善冷起动过程的烟度排放。对于NOx排放，当采用外部EGR方式时，有明显的改善作用；但当采用内部EGR方式时，由于残余废气的热效应，NOx排放随内部EGR量的增大而增大。

Effects of EGR on Combustion Process of DI Diesel Engine During Cold Start

Experiments on the effects of external and internal EGR on combustion and emission performance during cold start process were investigated in a 135 single cylinder DI diesel engine. Combustion was improved during the initial ignition cycles by introducing internal or external EGR. Addition of appropriate amount of internal or external EGR could promote the combustion stability significantly. However, overexcessive amount of external EGR could lead to an extremely unstable combustion or even misfiring. Ap- propriate amount of internal or external EGR decreased smoke opacity effectively during cold start. External EGR could also reduce NOx emissions effectively during cold start. However, internal EGR led to increase in NOx emissions due to the thermal effects.