高压喷射条件下非常态燃油喷嘴内部空化流动特性

Nozzle Inner Cavitation Flow Characteristics of Non-normal Fuel Based on High Pressure Injection Condition

为了改善柴油机喷嘴出口处燃油液滴的破碎状态并增加初始湍动能,采用了180 MPa的高压燃油喷射。推导了受高压喷射影响时非常态燃油各个物性参数与压力之间的关系。搭建了高压定容器喷雾闪光摄影试验台架,在AVL FIRE软件平台上建立了喷油嘴喷孔内部流场的三维CFD模型,通过喷雾测试结果对仿真模型进行了修正。分析了喷孔内部气液两相流场的三维流态以及空化流动特性。结果表明,非常态燃油物性参数的变化有利于增强空化效应;增大燃油喷射背压对孔内的空化效应具有抑制作用;随着喷孔直径增加,燃油高速区域扩大,空化效应增强;增大喷射夹角也有利于增强空化效应,但效果不明显。

In order to improve the breakup condition of oil beams and increase their initial turbulent kinetic energy at the exit of the nozzle,the high injection pressure of 180 MPa was used. The changing relationship between the physical properties of the non-normal fuel and the pressure under the influence of the high pressure injection was derived. The spraying flash photography test bench based on the high pressure constant vessel was set up. The three-dimensional CFD model of nozzle inner flow field was established on software AVL FIRE. The simulation model was modified according to the spraying test results. The three-dimensional flow state and cavitation flow characteristics of nozzle inner gas-liquid twophase flow field were analyzed. The results show that when the temperature is constant,the density,the speed of sound and the bulk modulus of fuel increase with the ascent of pressure,the change of these physical parameters of non normal fuel is beneficial to the production of cavitation gas and enhance the cavitation effect; increasing the fuel injection back pressure restrains the flow of cavitation gas and fuel,so the cavitation effect is weakened; with the increase of nozzle diameter,the high speed region of fuel becomes more extensive and the cavitation effect becomes more prominent. The increase of the injection angle also helps to enhance the cavitation effect,but the effect is not obvious due to the limitation of the structure form. So the reasonable matching relationship between the nozzle diameter and injection angle is helpful to improve the initial turbulent kinetic energy intensity at the outlet of the nozzle,and obtain a better jet state.