Microscopic characterization of spray impingement under flash boiling conditions

The microscopic characteristics and dynamics of real spray impingement were studied by employing long distance microscope and ultrahigh speed camera. The effects of flash boiling on the impact process were investigated, and the macroscopic impingement characteristics were also probed to find the development of fuel concentration and its distribution. It was found that the existence of fuel film weakened the impingement process and breakup of the secondary droplets, especially for the late stage of injection when the droplet velocities were low. The increase of flash boiling strength boosted the impact process and the breakup of the secondary droplets essentially by improving the primary breakup and secondary breakup before impact. The fuel film was also reduced by approximately 75% through better dispersion, quicker evaporation and less deposited fuel. In addition, strong flash boiling decreased the impinged fuel area and the propagation length. The proportion of high fuel concentration on the impact surface was also reduced by the increasing strength of flash boiling. The increase of flash boiling by increasing fuel temperature is believed to be an effective and practical way to alleviate the adverse effects of impingement.