柴油机渐缩形喷孔喷嘴流动特性研究

Flow Characteristics in Diesel Nozzle with Convergent Conical Orifice

利用混合多相流空穴模型,对柴油机渐缩形喷孔喷嘴进行了三维气液两相流数值模拟,分析了喷油压力、喷油背压及针阀运动对其内部空穴分布、湍动能分布、喷孔出口平均流速及流量系数的影响规律,并与圆柱形喷孔喷嘴进行了对比分析。结果表明:对于渐缩形喷孔喷嘴,喷油压力的提高或针阀开启速度的加快,均可增强喷孔内的空化效应,强化喷孔内的液流紊乱,提高喷孔出口平均流速及循环喷油量,这对于燃油喷射及雾化的改善、柴油机性能的提高都是有利的;随着喷油背压的增加,喷嘴的流量系数虽略有提高,但喷孔内的空化效应、液流紊乱及喷孔出口平均流速均逐渐降低;相同喷射条件或针阀升程下,喷嘴内的空化效应弱于圆柱形喷孔喷嘴,喷孔出口平均流速及流量系数高于圆柱形喷孔喷嘴。

The three-dimensional numerical simulation of gas-liquid two-phase flow in diesel nozzle with convergent conical orifice （CDN）was carried out by using the mixed muhiphase cavitation flow model, and the effects of injection pressure, injection back pressure and needle valve movement on the cavitating distribution, the turbulent kinetic energy distribution, the mean flow velocity at outlet（MFVO） and the discharge coefficient were analysed. The results show that the increasing in the injection pressure or the needle valve＇s open velocity will enhance the cavitation effect, strengthen the flow disturbance, improve MFVO and the cycle fuel injection quantity, which are beneficial to the performance of diesel engine, the fuel injection and atomization; with the increase of the injection back pressure, the discharge coefficient of CDN is increased slightly, but the cavitation effect, the flow disturbance and MFVO are decreased gradually; under the same injection condition or needle valve lift, the cavitation effect of CDN is weaker than that of diesel nozzle with cylindrical orifice, MFVO and the discharge coefficient of CDN are higher than those of diesel nozzle with cylindrical orifice.