废气再循环对车用汽油机热功转换过程的影响

The Influences of EGR on Heat-Work Conversion Process of Automotive Gasoline Engines

为提高车用汽油机部分负荷下的燃油经济性,探讨了废气再循环(EGR)对汽油机热功转换过程的影响。基于某款汽油机的性能试验数据,搭建并标定其仿真模型,研究了多种部分负荷工况下EGR对汽油机性能的影响。结果表明:就换气循环而言,随着EGR率的增大,进气压力增大,泵气平均有效压力(PMEP)减小,未冷却的EGR对PMEP减小的幅度更大;就高压循环而言,燃烧温度下降导致传热损失下降,从而使高压循环热效率增加。由缸内热平衡分析可知,有效热效率的提高主要依赖于缸内传热损失的减小,其次才是泵气损失的减小。在1 300r/min、0.295MPa时,采用20%的EGR率可以使有效热效率提升4.5%。

In order to improve the fuel economy of automotive gasoline engines under partial load, the influences of exhaust gas recirculation （EGR） on the heat-work conversion process in a gasoline engine were discussed. Based on the performance test data of a gasoline engine, the simulation model was built and calibrated. And then the effects of EGR rate on the gasoline engine performances under various partial load operating conditions were studied. The results show that as for the low-pressure cycle, with the increase of EGR rate, the intake pressure will increase while the PMEP reduce; the PMEP can reduce more with the un-cooled EGR adopted. As for the highpressure cycle, the heat transfer loss as well as its proportion will decrease due to the falling of combustion temperature, which result in the increase of high-pressure cycle thermal efficiency. The analysis of in cylinder heat balance shows that the improvement of effective thermal efficiency mainly relies on the decrease of in-cylinder heat transfer loss, followed by the decrease of pumping loss. At the operating condition of 1 300 r/min and 0. 295 MPa, the effective thermal efficiency of the gasoline engine can be increased by 4.5 G with a 20 G of EGR rate.