柴油机喷油嘴内部喷嘴流量和空化现象直接影响到燃油的喷射和雾化，进而影响柴油机的性能和排放。以两种非对称柴油机喷油嘴——小压力室喷油嘴（minisac）和无压力室喷油嘴（VCO）为例，通过Fluent软件对其进行空化和流量数值仿真，研究入口压力和背压参数对质量流量变化的影响。研究结果表明：在相同进出口压力下，minisac型喷油嘴各孔的流量均比VCO型的大；在较低和中等进口压力下VCO型喷油嘴各孔比minisac型更容易产生空化，而在较高的进口压力下这两种类型喷油嘴各孔产生空化难易程度基本一致；当进口压力不变时，随着出口压力的降低，在无空化产生时其质量流量与压力差呈线性关系；当空化出现时其质量流量继续增加，当出现超空化现象时该孔的质量流量不再变化；随着各孔的轴向夹角的增大，流量越小，空化越容易；对于这两种喷油嘴来说，只有minisac型孔3和孔4的空化出现在喷孔的上端和下端，其余孔的空化都只产生在上端。

The nozzle flow and cavitation of diesel engine nozzle directly affected the fuel injection and atomization, which affected the performance and emissions of diesel engine. Taking two asymmetric nozzles of minisac and VCO as examples, the influences of entrance pressure and back pressure on mass flow rate were researched through the simulation of cavitation and flow with Fluent software. The results show that the flow of each orifice for minisac nozzle is larger than that for VCO nozzle. VCO nozzle is easier to produce cavitation at low and medium pressure，but the probability to generate cavitation for both types of nozzles is nearly the same at high pressure. The mass flow is linear to pressure difference with the decrease of outlet pressure at constant inlet pressure when the cavitation doesnot occur, increases continually when the cavitation happens and keeps unchanged when the super cavitation happens. In addition, the mass flow becomes small and the cavitation becomes sensitive with the increase of axial included angle. For the two types of nozzles, the cavitation of orifice happens mainly at upper part except that that the cavitation of third and fourth orifice for minisac nozzle happens at upper and lower part.