缸内直喷CNG发动机燃烧过程及NO生成率的仿真分析

Simulation Analysis of the Combustion Process and NO Generation Rate of DI CNG Engine

基于缸内直喷CNG试验样机,在前期燃烧过程可视化试验研究结果的基础上,利用三维仿真软件FIRE建立了燃烧过程的仿真计算模型。在验证模型的基础上,计算分析了不同喷气量对缸内速度场、浓度场、火焰传播速度、温度场和NO生成率的影响。结果表明,当缸内温度大于2 000 K且喷气量当量比为0.8～1范围内时先生成NO,且最大NO生成率出现在放热率峰值之后;当喷气量减小时,放热率峰值降低,NO生成率降低。

Based on the research results of visualization test of DI CNG sample engine in the earlier combustion process,a simulative computation model for the combustion process has been established using 3D simulation software FIRE.Influences of different gas spray volumes on velocity field,concentration field,flame propagation temperature,temperature field and NO generation rate inside the cylinder have been calculated and analyzed on the basis of the verification model.The results show that NO is generated first when temperature inside the cylinder goes above 2 000 K and the equivalence ratio of gas spray volume is within the range of 0.8～1.Besides,the maximum NO generation rate occurs after the heat release rate reaches its peak value.The peak value of the heat release rate falls as the gas spray volume decreases and so does the NO generation rate.