柴油机喷油嘴喷射过程空化效应数值分析

Numerical Analysis of Cavitation Effect of Injection Process in Diesel Injector Nozzles

以某型机械式喷油器为对象,采用CFD软件STAR-CCM+,基于不可压缩流体体积函数(VOF)多相流模型,研究分析了在怠速、50%负荷、100%负荷工况下,完整喷射期内喷油嘴处的内流场及空化效应。结果表明:喷射过程中针阀升程的变化对于流动和空化特性影响显著,针阀升程较小时,在针阀的拐角处形成局部低压区,空化现象开始发生,形成大量的燃油蒸气,并在囊室内形成显著的二次涡漩流动,在喷孔底部产生二次空化;在相同的针阀升程下,压强越大,空化效应越显著。

Taking a mechanical injector as the research object,based on the multiphase flow model of incompressible fluid volume function(VOF),the internal flow field and cavitation effect at the injector nozzle during the complete injection period of a diesel engine at idle speed,50%load and 100%load were studied and analyzed by using a CFD software STAR-CCM+.The results show that the change of needle valve lift has a significant effect on the flow and cavitation characteristics during injection.When the needle valve lift is small,a local low pressure zone is formed at the corner of the needle valve,cavitation occurs,a large amount of fuel vapor is formed,and a significant secondary swirl flow is formed in the chamber,then a secondary cavitation occurs at the bottom of the nozzle.With the same needle valve lift,the higher the pressure goes,the more significant the cavitation effect could be.