废气再循环对二甲醚/天然气双燃料均质压燃燃烧过程和排放特性的影响

在一台单缸直喷式柴油机上研究了冷却废气再循环(EGR)对二甲醚(DME)／天然气(CNG)双燃料均质压燃(HCCI)燃烧过程和排放的影响．结果表明，EGR率加大，着火时刻滞后，放热速率降低，燃烧持续期延长，DME比例加大，着火始点提前，放热率峰值上升，燃烧持续期缩短，EGR率增大，发动机“失火”和爆震燃烧的DME比例增大，但“失火”和爆震燃烧之间的DME比例区间变宽，EGR可以拓宽HCCI发动机的工况范围．对应不同比例的EGR，有一个热效率最佳的DME比例区域．HC排放和CO排放随EGR率的增高而增加，随DME比例的增大而降低．NO。排放在不发生爆震的情况下保持在极低的水平．因此，控制DME比例和EGR率是控制DME／CNG双燃料HCCI发动机燃烧过程、性能和排放的关键。

Experimental Study on the Effects of EGR on HCCI Combustion Process and Emissions of DME/CNG Dual Fuel

Experimental study of effects of cooled exhaust gas recirculation(EGR) on homogenous charge compression ignition(HCCI) combustion process and emission characteristics was carried out on a single-cylinder direct injection diesel engine fueled with dimethyl ether(DME)/compressed natural gas(CNG) dual fuel. The results indicate that with the increased EGR rate, the ignition time delayed, the heat release rate decreased, and the combustion duration extended. While the proportion of DME increased, the ignition time advanced, the peak heat release rate increased, and the combustion duration decreased. Although the proportions of DME of misfire and knock both increased with EGR rate increased, the proportion range of DME between misfire and knocking was enlarged. So EGR can extend the operating range of HCCI engine. For each EGR rate, there is a proportion range of DME in which higher thermal efficiency can be obtained. HC and CO (emissions) both ascended with the increased EGR rate, and decreased with the proportion of DME increased. NO_x emission remained at a very low level except that knocking occurred. The control of the proportion of DME and EGR rate is the key technique to control the combustion process, performance and emissions of HCCI engine fueled with DME/CNG dual fuel.