Experimental study on the collision behaviors of micron-sized aluminum droplets with solid wall in high temperature burned gas

The collision and deposition behaviors of aluminum/alumina droplets on a solid wall play a crucial role in improving the engine performance of a solid rocket motor (SRM). This study employed a high temperature oxy-methane flame and a solid wall to simulate the environment of SRM. Micron-sized aluminum particles were axially added into the flame and they were melted and ignited before collision with the wall. The velocities of the particles were varied by adjusting the flow rates of gaseous reactant and the collision angle was adjusted by arranging the solid wall layout. The dynamic deforming process of micron-sized droplets colliding on a hot wall was observed by high speed photography. And thousands of droplets were tracked to examine the deposition probability on the hot wall. The results show that the collision velocity, angle and particle size codetermine the post-collision behaviors, which typically include rebound, deposition and splashing. The heat transfer between the droplet and wall plays an important role in the deposition process. By further considering the component of the condensed droplet, the dimensionless parameter of normal Weber number has been proposed to quantify the deposition rate. And an empirical formula has been obtained by employing the Weber number and collision angle.