中文摘要：

在1台CA6DL2-35E3重型高压共轨柴油机上建立原理性低压EGR系统，并进行了EGR性能试验。试验结果表明：在欧Ⅲ高压共轨柴油机平台下，小EGR率即可大幅度降低NOx排放；从性能及排放折中考虑，在中小负荷可适当增大废气回流量以实现低温燃烧；根据优化策略优化EGR率后，仅在13％EGR率范围内气体排放即可达到欧Ⅳ法规水平，而通过对大负荷最佳EGR率的修正，在满足排放要求的同时，可降低EGR散热损失；NOx比排放量随燃烧放热率峰值变化存在拐点（EGR率最优点），可作为改善尾气排放的有效判据。

英文摘要：

The external low-pressure EGR system was built and tested on a CA6DL2-35E3 common rail diesel engine. The results show that, for a Euro Ⅲ high-pressure common rail engine, the NOx emission can be greatly decreased with low EGR ratio. Considering the compromise between engine performance and emission, the EGR ratio should be increased in order to realize low temperature combustion （LTC） at low and middle loads. According to the optimization of EGR ratio, the engine exhaust pollutants can arrive to Euro Ⅳ standard within 13 percent EGR ratio. Through correcting the optimum EGR rate at high loads, the emission requirement is satisfied, and the EGR heat loss is simultaneously decreased. The inflexion, which is the point of optimal ECR ratio, lie in the curve of heat release peak with NOx emission, which can be considered as the reference of improving the emission.