撞击式喷雾特性的拉格朗日数值模拟

Numerical Study on the Impinging Spray Characteristics Using Lagrangian Simulation

采用数值模拟的方法对自由喷雾和撞击式喷雾特性展开研究.在开源CFD程序KIVA-3V的基础上,嵌入改良的环境压力表征的液滴碰撞模型,对1MPa和6MPa下自由喷雾与撞击式喷雾喷射过程中的液滴碰撞频率、索特平均直径(SMD)等微观特性进行研究.结果表明:低压环境(1MPa)下撞击式喷雾的液滴碰撞后融合频率较高,其SMD较自由喷雾偏大;随着压力升高,液滴碰撞后表现出以“弹开”为主的结果,高压环境(6MPa)下撞击式喷雾相比自由喷雾会有更小的SMD,更有利于随后的雾化与燃烧过程.在此基础上继续研究喷油量对撞击式喷雾雾化特性的影响,进一步发现了高压环境下空气阻力和环境压力诱导的液滴弹开行为主导了撞击式喷雾的微观特性,为今后直喷式内燃机供油系统的改进提供了参考.

Spray characteristics of free spray and impinging spray were investigated numerically.An open source code KIVA-3V was adopted to simulate the previous experiments.To account for the droplet collision within the spray,a recent proposed pressure dependent droplet collision model was employed to simulate the droplet collision frequency and Sauter mean diameter(SMD)for different spray layouts under different ambient pressures(1MPa and 6MPa).The results show that collision dynamic for either the free spray or the impinging spray is dominated by droplet coalescence under relatively lower ambient pressure(1MPa),and the higher collision frequency for impinging spray results in the larger droplet size.However,for higher ambient pressure condition(6MPa),droplet bouncing dominates collision dynamic therefore the impinging spray possesses smaller droplet size than the free spray does,which is more conductive to the subsequent atomization and combustion.With the increasing of ambient pressure,the increasing aerodynamic residence and droplet bouncing dominate the impinging spray characteristics.It is believed that the research results can be used to improve fuel supply system in the future direct injection internal combustion engines.