通过废气再循环实现低温燃烧能有效降低氮氧化物排放.但大负荷工况下应用EGR将导致发动机性能下降和碳烟排放恶化.对此本文中采用CFD软件和自编程序,进行大负荷工况下低温燃烧的研究,分析不同EGR率下的燃油雾化、壁面油膜生成和燃烧过程.结果表明,随着EGR率的增大,燃油雾化效果变差,壁面油膜增加,燃烧过程滞后,热效率和经济性变差,碳烟排放增加；综合考虑排放和热效率与油耗,选定EGR率为10％,再通过喷油定时优化实现热效率和经济性的改善；最后通过后喷优化,在碳烟排放与原机相近的条件下使NOx排放大幅降低.%The low temperature combustion (LTC) through exhaust gas recirculation (EGR) can effectively reduce NOX emissions, however, it deteriorates engine performance and increases soot emissions at high load. In view of this, the LTC at high load is studied in this paper by using CFD software and self-developed program to analyze the fuel atomization, wallfilm formation and combustion process at different EGR rates. The results show that increasing EGR rate results in poor fuel atomization, increased wallfilm, delayed combustion and deteriorated thermal efficiency, fuel economy and soot emissions. With concurrent considerations of soot emission, thermal efficiency and fuel economy, an EGR rate of 10% is chosen and the improvement of thermal efficiency and fuel economy is a-chieved by injection timing optimization. Finally the emission of NOX is significantly reduced by post-injection optimization with a soot emission close to the level of original engine.
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