农用柴油—二甲醚发动机喷雾、燃烧与排放性能数值研究

Numerical Study on Spray Combustion and NOx Emission Characteristics of Agricultural Engine with Dual Fuels of Diesel/DME

为研究二甲醚作为替代燃料的可行性,本文利用CFD软件对农用柴油机和二甲醚发动机在标定点的缸内燃料喷射雾化、燃烧过程与NOx排放进行了数值模拟研究。结果表明,计算所得的缸内平均压力和放热率曲线与试验值吻合良好。研究发现,柴油的喷雾贯穿距接近于二甲醚的2倍,而二甲醚的喷雾蒸发延迟角比柴油约小2°CA,且二甲醚的蒸发持续期比柴油约短10°CA。同时还发现,与柴油相比,二甲醚燃烧温度分布较均匀,且最高温度比柴油要低,决定了二甲醚发动机燃烧产生的NOx排放比柴油机降低了50%。

In this paper,the spray atomization,combustion process and NOx emission in cylinder of engine with diesel fuel and DME were numerically simulated by CFD software separately,in order to study on the characteristics of DME as an alternative fuel.The results show that,there were good agreements between simulation and experimental data of mean pressure in-cylinder and heat release rate.It was found that the spray tip penetration of diesel fuel was about two times of DME＇s penetration.However,the atomization delay angle of DME was 2°CA less than that of diesel fuel,and the atomization duration of DME was 10°CA less than that of diesel fuel.It was also concluded that distribution of DME combustion temperature was better than that of diesel fuel,and the peak temperature of DME combustion was lower than that of diesel engine,which resulted in the NOx emission of DME engine 50% lower than diesel engine.