生物柴油发动机燃烧和排放的数值模拟

Numerical Simulation for Combustion and Emission of an Engine Fueled with Biodiesel

针对一款轻卡用立式、直列、水冷、四冲程、电控直喷、高压共轨、带废气旁通阀的涡轮增压中冷柴油机,采用计算流体动力学(Computational Fluid Dynamics,CFD)软件AVL-FIRE和试验相结合的方法,建立发动机缸内燃烧的三维仿真模型,对生物柴油发动机缸内燃烧、排放物形成以及废气再循环(Exhaust Gas Recirculation,EGR)率对其排放的影响进行仿真分析。结果表明:相比于纯柴油,生物柴油滞燃期缩短,燃烧始点提前,缸内爆发压力曲线整体前移,燃烧持续期略延长;相比于纯柴油发动机,生物柴油发动机碳烟(soot)排放量明显降低,氮氧化物(NO_x)排放略有上升;在不明显影响soot排放量的条件下EGR能显著降低生物柴油发动机NO_x排放,表明生物柴油发动机对EGR的容忍度增强。

For a vertical, straight,water cooled, four stroke, electronically controlled direct injection, high pressurecommon rail, high pressure common rail, and high pressure diesel engine with exhaust gas hypass valve, threedimensionalcombustion process simulation models were established with the method of combining computationalfluid dynamics （CFD） software AVL-FIRE and experiment. Effects of combustion process, emission formationand exhaust gas recirculation （EGR） rate on the emission of biodiesel engine were simulated.The results show thatcompared with pure diesel oil, biodiesel combustion has a shorter ignition delay and earlier ignition, cylinderpressure curve ahead, and the combustion duration is slightly longer; compared with the pure diesel engine, thebiodiesel engine soot emissions are significantly lower, and the nitrogen oxides （NOx） emissions increase slightly;EGR can significantly reduce NOx emissions of biodiesel engine under the condition of no significant impact onsoot emission, which indicates that the biodiesel engine can enhance the tolerance of EGR.