喷油定时和涡流比对低温燃烧影响的模拟研究

基于计算流体动力学(CFD)软件和耦合自行编写的程序,对一台柴油机进行低温燃烧模拟研究,对比分析不同废气再循环(EGR)率、喷油定时和涡流比对燃烧和排放的影响.结果表明,随着EGR率增大,燃烧放热过程滞后,缸内压力、温度和放热率峰值和累计放热量降低,壁面油膜生成增加,氮氧化物(NO_x)排放大幅降低的同时,碳烟(soot)、未燃碳氢化物(UHC)和CO排放增加;固定EGR率为40%的同时将喷油定时曲轴转角从353°提前至345°,可使燃烧放热过程适当提前,并有利于提高热效率和改善燃油经济性;保持EGR率为40%,喷油定时曲轴转角为345°时,随着涡流比的增大,soot和UHC排放减少,而CO排放出现先减少后增大的趋势,涡流比为3.0时,综合效果较好.

A Simulation Study on the Effect of Start-of-Injection and Swirl Rate on the Low Temperature Combustion

Based on the CFD simulation software and coupled with the written codes, a study on the effect of the exhaust gas recirculation(EGR), start of injection and swirl rate on the low temperature combustion is conducted. The results show that the combustion and heat release lag, the cylinder pressure, temperature, peak of heat release rate and the accumulated heat release decrease, nevertheless the wall film increase with the increased EGR rate. Besides, NOx emissions decrease drastically with the increased EGR rate, meanwhile soot, unburned hydro carbons(UHC) and CO emissions increase. When the EGR rate is kept constant at 40%, and the start of injection is advanced from 353°CA to 345°CA, the combustion and heat release are advanced, the efficiency and fuel economy are improved. When the EGR rate and start of injection are kept constant at 40% and 345°CA, with the increased swirl rate, the soot and UHC emissions is decreased, meanwhile CO emissions has a trend that first decreased than increased. There is the better effect when the swirl rate is 3.0.