废气再循环对二甲基醚均质压燃燃烧过程影响的试验研究

在一台单缸发动机上进行了废气再循环(EGR)对二甲基醚(DME)均质压燃(HCCI)燃烧过程影响的试验研究。结果表明，EGR比例小于20％对运行最大负荷工况范围影响不大；采用高比例EGR可以拓宽DME均质压燃运行工况范围，随着EGR率增大，HCCI运行的最大负荷工况增大，着火燃烧时刻推迟，燃烧放热率降低，缸内最大爆发压力降低，发动机热效率增大；EGR率小于75％，HC排放略有降低或相当，EGR率为75％时，HC排放显著增加；EGR率大于25％，随着EGR率增加，CO排放增大，小负荷工况尤其明显，在中高负荷工况，EGR率对CO排放影响较小。

Experimental Study on the Effects of Exhaust Gas Recirculation (EGR) on the HCCI Combustion of Dimethyl Ether (DME)

The effects of exhaust gas recirculation (EGR) ratios on homogeneous charge compression ignition (HCCI) combustion of Dimethyl Ether (DME) were experimentally investigated. The experiments were carried out in a single-cylinder, 4-stroke engine with a port fuel injection. Results showed that there had little influence on the operating range of HCCI when the EGR ratio was less than 20%. Increasing of EGR ratio would increase the ignition delay, decreasing the peak value of heat release ratio, increasing the combustion duration and the indicated thermal efficiency. Moreover, the engine operating range could be extended to the large load area. For EGR ratio less than 75%, HC emission decreased slightly with the increase of EGR ratio, whereas it increased largely in the case of 75% EGR ratio. For EGR ratio over than 25%, CO emission increased with the increase of EGR ratio, and this behavior was obvious under the small load. However, under the intermediate load, EGR ratio gave small effect on CO emissions.