The ability to accurately predict the outcome of the drop/wall interaction is essential to engine spray combustion modeling. In this paper, the process of fuel drop impact on a wet wall was simulated using a numerical method based on smoothed particle hydrodynamics (SPH). The present numerical method was first validated using experimental data on the crown height and crown diameter resulting from water drop impact on a liquid film. Then, the impact process of iso-octane drops on wet walls under engine relevant conditions were studied. The presence of a wall film will affect not only the splash threshold but also the crown evolution and the secondary droplets ejected from the rim of the crown. Numerical results show that the splash threshold increases with the film thickness; the splashed mass ratio increases as the kinetic energy of the incident drop increases. The effect of film thickness on the splashed mass ratio is determined by two competing mechanisms. On the one hand, as the film thickness increases, more incident energy will be absorbed and transferred into the crown, thus producing more secondary droplets. On the other hand, more impinging energy will be dissipated during the spreading as the film thickness increases, thus generating fewer secondary droplets. The properties of the secondary droplets are very different as the film thickness increases. Instead of moving outward, the secondary droplets will move upward and even congregate to the center when the film becomes thicker. The impact angle will affect not only the distributions of the secondary droplets but also the splashed mass. The locations and velocities of the secondary droplets were analyzed. These outcomes were incorporated into formulas that can be further developed into a model for simulating engine spray/wall interactions.

准确预测滴/壁相互作用结果的能力对于发动机喷雾燃烧建模至关重要。在本文中，基于基于光滑粒子流体动力学（SPH）的数值方法，模拟了燃料滴撞击湿壁的过程。首先使用关于水滴对液膜的冲击产生的胎冠高度和胎冠直径的实验数据来验证本数值方法。然后，研究了在发动机相关条件下，异辛烷滴在湿壁上的撞击过程。壁膜的存在不仅会影响飞溅阈值，而且会影响胎冠的演变以及从胎冠边缘喷出的次要液滴。数值结果表明，飞溅阈值随膜厚的增加而增大；飞溅质量比随入射液滴动能的增加而增加。膜厚对飞溅质量比的影响由两种竞争机制决定。一方面，随着膜厚度的增加，更多的入射能量将被吸收并转移到冠部，从而产生更多的次级液滴。另一方面，随着膜厚度的增加，在铺展过程中会消耗更多的撞击能量，从而产生更少的次级液滴。随着膜厚度的增加，次要液滴的性质非常不同。当薄膜变厚时，次要液滴将不向上移动，而是向上移动，甚至聚集到中心。冲击角不仅会影响次级液滴的分布，还会影响飞溅的质量。分析了次级液滴的位置和速度。这些结果被合并到公式中，可以进一步发展为模拟发动机喷雾/壁相互作用的模型。