涡流对船用柴油机喷雾燃烧及排放影响的数值研究

Numerical Study of Effect of Swirl Flow on Combustion and Emission Spray of Marine Diesel Engines

涡流对船用柴油机的喷雾燃烧及排放过程起着至关重要的作用.基于雷诺平均模拟方法(RANS)结合KHRT液滴破碎模型和CTC/Shell燃烧模型研究了涡流对船用柴油机喷雾燃烧及排放的影响.首先对重油喷雾进行标定,标定后模拟贯穿距与实验数据吻合较好;然后基于验证的喷雾模型,通过对比环境涡流下不同喷射角的喷雾形态、贯穿距、燃油蒸发质量和液滴平均粒径(SMD),研究了涡流对重油喷雾的影响.结果表明,涡流方向与喷雾方向相反或垂直时,涡流作用力可抑制喷雾轴向贯穿距的发展,增加了液滴与环境气体的相互作用进而促进喷雾雾化和蒸发;涡流与喷雾相切时,涡流可以促进喷雾轴向贯穿,但喷雾蒸发较差.进一步对CTC/Shell燃烧模型进行标定,标定后模拟放热率与实验数据吻合良好.最后基于验证的喷雾燃烧模型,研究了涡流比对船用柴油机喷雾燃烧和排放的影响.结果表明:一定范围内随着涡流比增大,喷雾液滴更加分散,喷雾气相蒸发加强,导致缸内燃烧更加剧烈,缸内最高爆发压力和最高温度升高,氮氧化物(NO_x)排放增多.

The swirl flow is of vital importance to the spray combustion and emission of marine diesel engines.This paper investigated the effect of swirl flow on the spray combustion and emission of marine diesel engines based on Reynolds-averaged navier-stokes（RANS）simulation method combined with Kelvin-Helmholtz Rayleigh-Taylor（KHRT）droplet breakup model and CTC/Shell combustion model.First of all,the spray model was calibrated,and the numerical penetration length showed good agreement with the experimental data.Based on the calibrated spray model,the effects of swirl flow on spray were investigated by comparing the spray configuration,spray penetration length,fuel evaporated mass and Sauter mean diameter（SMD）of droplets at different spray angles.Results show that when the swirl flow is opposite or perpendicular to spray orientation,it can promote spray evaporation but suppress spray penetration.When the swirl flow is tangent to spray orientation,it can promote spray penetration while the fuel evaporation becomes worse.Then CTC/Shell model was further calibrated,and the numerical heat release rate matched well with the experimental data.Lastly,based on the calibrated spray combustion model,this paper studied the influence of swirl ratio on spray combustion and emission of marine diesel engines.Results show that within certain limits,as the swirl ratio increases,spray droplets becomes scattered and the evaporation of spray grows,flame moves to diffusion flame zone,which leads to more vigorous combustion higher maximum amplitude pressure and temperature and more NO_x emission.