利用废气滞留改善缸内直喷汽油机部分负荷性能的研究

Study on Improvement of Part-Load Performance in a GDI Engine Using Exhaust Gas Trap

废气滞留比传统的废气再循环具有更好的稀释和加热混合气作用，有利于减小汽油机中小负荷泵气损失，降低油耗。在一台缸内直喷汽油机（GDI）上对比研究了部分负荷下利用负阀重叠（NVO）产生废气滞留对于发动机性能的影响。结果表明，利用废气滞留方法可使发动机油耗降低5％～16％，并且随着负荷减小节油效果明显。分析表明，废气滞留可以提高进气歧管压力，明显降低泵气损失；混合气温度提高促进燃烧更完全，使燃烧效率得以提高；但燃烧速度会有一定程度降低，循环波动有所增大；综合作用下使得有效热效率提高。同时．废气滞留作用可降低缸内盲喷汽油机HC、CO排放．尤其可显著降低NOx排放达70％以上。

Exhaust gas trap （EGT） is more effective strategy for mixture dilution and heating, and it is beneficial to reduce pumping loss and fuel consumption than exhaust gas recirculation （ EGR ）. In this paper, fuel economy, combustion and emission performance were studied in a GI）I engine at part-load and using EGT strategy. The experimental results indicate that fuel consumption benefit can be obtained by 5% - 16% by using EGT strategy as load decreases. With EGT strategy, the pumping loss is reduced due to the increase of intake manifold pressure, and the increase of intake temperature leads to the complete combustion and high combustion efficiency. However, EGT decreases the combustion rate with prolonged ignition delay and increases cycle-to-cycle variation. The comprehensive result increases the effective thermal efficiency. In addition, EGT can effectively reduce HC, CO and NOx emissions, especially in NOx with 70% reduction.