ABSTRACT

In this paper, the cavitation and gas ingestion in a custom-made transparent nozzle were observed using a visual experimental platform of a transparent nozzle. Based on the Two-Fluid Model and dynamic grid overlapping, the evolution mechanism of the cavitation and gas ingestion in a diesel engine nozzle was analyzed at the end of injection, and the influence of three different velocities of the needle valve motion was analyzed. The results demonstrated that cavitation in the orifice preceded that in the sac, and the cavitation was mainly concentrated in the sac. As the needle valve seating velocity increased, the amount of cavitation and gas ingestion in the nozzle increased. Furthermore, as the amount of gas ingestion increased, the time of gas ingestion inception was delayed, and the value varied nonlinearly from 0.48 ms (0.2 m/s) to 0.13 ms (1.0 m/s). A dimensionless parameter $C_N$ was deduced by theoretical analysis to describe the cavitation extent in the orifice at the end of injection. This study provides a theoretical basis for further analysis of the mechanisms of cavitation and gas ingestion as well as the effect of the needle valve velocity on cavitation and gas ingestion.

摘要

在本文中，使用透明喷嘴的视觉实验平台观察了定制透明喷嘴中的空化和气体吸入。基于双流体模型和动态网格重叠，分析了柴油机喷油末喷气腔和进气的演化机理，分析了三种不同速度对针阀运动的影响。结果表明，孔口空化先于囊内，空化主要集中在囊内。随着针阀落座速度的增加，喷嘴中的气穴和气体吸入量增加。此外，随着气体摄入量的增加，气体摄入开始的时间被延迟，数值从0.48 ms（0.2 m/s）到0.13 ms（1. 0 米/秒）。无量纲参数$C_N$由理论分析推导出来描述注射结束时孔口中的空化程度。该研究为进一步分析空化和吸气机理以及针阀速度对空化和吸气的影响提供了理论依据。