喷孔几何特征对变截面喷油孔空穴流动状态的影响

Effect of Geometry Characteristics on Internal Cavitation Flow of Injection Nozzle with Varying Hole Cross-Section

采用混合多相流模型及空穴模型相结合的方法,对喷油嘴激光打孔过程形成的变截面喷油孔内空穴流动现象进行数值模拟,重点分析喷孔几何特征对空穴流动状态的影响规律.结果表明,变截面喷孔内喷孔截面收缩或者扩张的程度及位置对孔内燃油空穴流动状态具有重要影响.截面收缩型的喷孔可在出口形成更大的空穴强度分布,利于促进燃油的初次分裂及雾化.截面扩张型喷孔可使得出口燃油速度分布更均匀,出口平均速度增大,从而提高流量系数;研究还发现,相对于直喷孔,变截面喷油孔内空穴流动状态对孔入口倒角变化的敏感性减小,这将有利于提高多孔喷嘴各孔流量及雾化的均匀性.

Injection Nozzles with Varying Hole Cross-section （NVHC）accomplished by laser drilling may influence the internal flow. The phenomena of cavitation flow in two types of NVHC （elliptic-shaped and hyperbolic-shaped） were simulated using mixed multiphase flow model coupled with cavitation model. The main objective is to analyze the effect of nozzle shape with different types on the distribution of cavitation and the outlet velocity. Simulation results show that the outlet velocity of elliptic-shaped nozzles is higher than that of cylindrical-shaped nozzles, and the outlet velocity distribution gives more uniform profile. Stronger outlet cavitation intensity is found in hyperbolic-shaped nozzles, which enhances the fluctuation of outlet flow and eventually improves the fuel break-up and atomization. The study also shows that, the inner flow state in NVHC is less sensitive to the fluctuation of inlet rounded radius than that in cylindrical- shaped nozzle, and this improves the uniformity of flow discharge and spray in the process of multi-holes injection.