基于CFD的柴油机渐扩形喷孔喷嘴空穴流动特性研究

Study on Cavitation Flow Characteristics in Diesel Nozzle with Divergent Hole Based on CFD

柴油机喷嘴的内部流动特性直接影响到燃油的喷射和雾化,进而影响到随后的蒸发、混合和燃烧。基于喷孔形状对其内部流动特性的重要影响,将混合多相流模型与空穴模型相结合,对渐扩形喷孔喷嘴的内部流动特性进行了三维数值模拟。研究结果显示:随着喷油压力或针阀升程的增加,渐扩形喷孔喷嘴内的空化效应和液流紊乱均是逐渐增强的,喷孔的质量流量和出口平均流速均是逐渐提高的,喷油背压的增加对上述参量均具有一定的抑制作用;但与圆柱形喷孔喷嘴相比,相同喷射条件或针阀升程下,渐扩形喷孔喷嘴的质量流量和空化效应均是较高的,流量系数和出口平均流速均是较低的。

The internal flow characteristics of diesel nozzle have direct effects on the fuel injection and atomization, and then on the subsequent spray evaporation, mixing and combustion. Based on the important influence of nozzle hole shape on the internal flow characteristics of diesel nozzle, three-dimensional numerical simulation of the internal flow characteristics in diesel nozzle with divergent hole was carried out by using the mixed multiphase flow model coupled with cavitation model. The results show that： for the diesel nozzle with divergent hole, the cavitation effect and the flow disturbance are enhanced gradually, and the mean flow velocity at outlet and the mass flow are improved little by little with the improvement of the injection pressure or the needle lift, but the increasing injection back pressure will inhibit all of the above parameters, which are consistent with those of the diesel nozzle with cylindrical orifice. However, the cavitation effect and the mass flow rate of the diesel nozzle with divergent hole are higher than those of the diesel nozzle with cylindrical hole, the mean flow velocity at outlet and the discharge coefficient of the diesel nozzle with divergent hole are lower than those of diesel nozzle with cylindrical hole.