喷孔形状对柴油喷雾燃烧及碳烟特性的影响

Effects of Nozzle Shape on Characteristics of Diesel Spray Combustion and Soot Formation

基于定压燃烧弹系统,通过纹影法和碳烟辐射光法的同步光学诊断技术,针对圆柱形和渐缩形两种形状的单孔喷油器,对比分析了两种喷孔在不同环境温度、喷射压力的工况下喷雾燃烧及碳烟生成特性.结果表明:两种喷孔形状在不同环境温度和喷射压力下,喷孔形状对喷雾贯穿距和喷雾锥角的影响较为微弱,由于圆柱形喷孔内部的空化作用,在喷嘴出口处湍流动能增加,致使圆柱形喷孔喷雾锥角较大,喷雾贯穿距较小;由于相对较低的喷油速率,圆柱形喷孔的火焰浮起长度略短;通过碳烟辐射强度分析可以看出,喷孔形状对碳烟的生成产生显著影响,圆柱形喷孔的碳烟初始位置距离喷嘴更远,其由于易产生空化效应,能改善燃油与空气混合,降低火焰中碳烟的生成.

In order to study the effects of nozzle cavitation on characteristics of diesel spray combustion and soot formation,two types of nozzle with cylindrical and convergent shapes were measured with high-speed Schlieren imaging and soot natural luminosity techniques simultaneously within a high-pressure high-temperature constant pressure vessel.It is found that the effects of nozzle shape on spray morphology are not remarkable under different operating conditions.The spray tip penetration is a little more slow and the spray cone angle is a little larger for the cylindrical nozzle compared with the convergent one.This is because the cavitation effect within the nozzle brings an increase in turbulence energy at the nozzle orifice.The flame lift-off length of the cylindrical nozzle is slightly shorter than that of the convergent one due to the relatively lower injection velocity.Based on the analysis of soot radiation intensity,it can be found that the nozzle shape has a significant effect on the formation of soot.The soot initial position of the cylindrical nozzle is far downstream away from the nozzle tip.Furthermore,thanks to the cavitation effect,the mixing between fuel and air of the cylindrical nozzle is better than that of the convergent one,which is in favor of reducing the in-flame soot formation.