大缸径二冲程天然气发动机燃烧及排放特性仿真

Simulation of combustion and emission characteristics of large bore two-stroke natural gas engine

针对点燃式大缸径二冲程天然气发动机燃烧速率慢、动力性低及排放较高的问题,采用GT-Power与AVL-Fire分别构建其一维热力学模型和三维计算流体动力学(computational fluid dynamics,CFD)模型,通过数值模拟,研究空燃比、点火时刻及压缩比对发动机性能、燃烧及排放的影响。结果表明:在理论空燃比为17.24时,发动机的性能、燃烧及排放均表现较好;空燃比过低(13.00)或过高(27.50)都会导致燃烧恶化,性能大幅降低;当空燃比一定时,适当提前点火时刻,有效热效率增加,动力性与经济性提高,NO排放量升高,CO排放量降低;空燃比与点火提前角匹配后,将压缩比从6.1提升至11,发动机燃烧得以改善,动力性与经济性分别提升了45%与31%。

In view of the problems of slow combustion speed,low power performance and high emission of the spark-ignited large-bore two-stroke natural gas engine,one dimensional thermodynamic model and three dimensional computational fluid dynamics(CFD)model of the engine were constructed by GT-Power and AVL-Fire respectively.The effects of air-fuel ratio,ignition timing and compression ratio on engine performance,combustion and emission were studied by numerical simulation.Results show that the performance,combustion and emissions of the engine are better at the theoretical air-fuel ratio of 17.24;the air-fuel ratio is too low(13.00)or too high(27.50)will lead to combustion deterioration,and performance is reduced;When the air-fuel ratio is constant,advance the ignition timing appropriately,the effective thermal efficiency increases,the power and economy are improved,the NO emission is increased,and the CO emission is reduced.When the air-fuel ratio and ignition advance angle are matched,the compression ratio is increased from 6.1 to 11,and the engine combustion can be improved,and the power and economy are improved by 45%and 31%respectively.