Fuel spray impingement on engine wall and piston in the spark-ignition direct-injection (SIDI) setting has been considered a major concern in the aspect of engine emission and combustion efficiency. Excess wall film will result in deterioration of engine friction, incomplete combustion, and substantial cycle-to-cycle variations. These effects are more pronounced during engine cold-start process. Therefore, the formation of wall film on engine wall/piston and the dynamic process of the wall film interacting with impinging spray and spray-induced gas flow are of great significance for reducing wall film mass. However, the dynamic process of wall film was not investigated thoroughly in existing literatures. This work will present a high-speed, simultaneous measurement of a single-hole spray structure, as well as wall film geometry and thickness, via Mie scattering and volumetric laser-induced fluorescence, respectively. Quantitative film thickness measurement was achieved via fluorescence intensity signal calibration with a known, wedge-shape liquid film apparatus. Remarkable wall film droplet entrainment at the leading edge of the liquid film waves was revealed in the measurement, which has not been adequately depicted or analyzed in existing spray impingement studies. A considerable amount of liquid droplets detaches from the liquid film via liquid film fingering, during which process the quantity of liquid mass on the wall is decreased. Quantitative analysis of such phenomenon is performed and we estimated that a liquid mass equivalent to 30–40% of the residual liquid film mass is detached from the liquid film via wave entrainment. Furthermore, through the comparative study of the side view of the spray and the liquid film caused by spray impingement, it is shown that non-uniform spray structure is likely the cause of liquid film wavy motions. These observations suggest that wave entrainment should be considered by numerical models and experimental designs to accurately predict spray impingement phenomenon.

在火花点火直接喷射（SIDI）设置中，燃油喷雾撞击发动机壁和活塞已被认为是发动机排放和燃烧效率方面的主要问题。过多的壁膜将导致发动机摩擦力恶化，燃烧不完全以及各个周期之间存在较大差异。这些影响在发动机冷启动过程中更为明显。因此，发动机壁/活塞上壁膜的形成以及壁膜与冲击喷雾和喷雾诱导的气流相互作用的动态过程对于降低壁膜质量具有重要意义。然而，在现有文献中尚未对壁膜的动态过程进行深入研究。这项工作将提供高速，同时测量单孔喷涂结构以及壁膜的几何形状和厚度的方法，分别通过米氏散射和体积激光诱导的荧光。定量的膜厚测量是通过使用已知的楔形液体膜装置的荧光强度信号校准来实现的。在测量中揭示了在液膜波前缘处明显的壁膜液滴夹带，在现有的喷雾冲击研究中尚未充分描述或分析。大量液滴通过液膜指状从液膜分离，在此过程中，减少了壁上的液量。对这种现象进行了定量分析，我们估计通过波夹带将相当于残余液膜质量的30–40％的液质量从液膜中分离出来。此外，通过对喷雾和由喷雾撞击引起的液膜的侧视图的比较研究，表明不均匀的喷雾结构很可能是引起液膜波动的原因。这些观察结果表明，数值模型和实验设计应考虑夹带波浪，以准确预测喷雾撞击现象。