EGR柴油机瞬态性能优化研究

以降低瞬态过程烟度和NO_x排放为目标,在一台高压共轨电控重型柴油机上进行了EGR对柴油机恒转速增扭矩5s典型瞬态过程燃烧和排放性能影响的优化研究。结果表明:瞬态过程中固定EGR阀开度造成EGR率"超调"、烟度剧增;与"全程轨压"策略相比,"分段轨压"有利于改善小负荷工况的燃烧热氛围,提高瞬态起始负荷并耦合"分段轨压"可以有效降低瞬态过程烟度峰值;EGR阀的开闭对瞬态性能影响最大,瞬态过程1.5s关阀、4s开阀的策略可以实现较好的烟度和NO_x排放折中,消光烟度峰值为9.2%,NO_x峰值稍有增加但增幅不大。

Optimization of Transient Performance for Diesel Engine with EGR

In order to reduce the NOx and smoke emissions during the transient process,the influences of EGR on combustion and emission were studied though the test of 5 s torque increase at constant speed on a high pressure common rail electronically-controlled heavy duty diesel engine.The results show that the EGR rate will overshoot so that the soot emission drastically increases if the EGR opening keeps constant during the transient process.Compared with the full-stage rail pressure strategy,the multi-stage fuel injection strategy helps to form the better thermo-atmosphere,which can reduce the peak soot emission effectively combined with higher initial loads.In addition,the opening and closing behavior of EGR valve have a great influence on engine transient performance.The 1.5 s opening and 4.0 s closing strategy can realize the compromise between soot and NOx emissions,while the peak smoke opacity is 9.2％ and the peak NOx emission has little increase.