Visualization of spatial distribution of the droplet size and velocity in flash boiling spray with extended glare-point imaging technique

摘要

Flash boiling is an effective way to improve the atomization quality. Droplet diameter and velocity distribution of the flash boiling spray extremely impact the mixture formation of direct injection engines. We visualize and measure the spatial distribution of the droplet size and velocity of flash boiling spray with extended glare-point imaging technique in this paper. An improved correlation-based processing algorithm for droplet identification is proposed. The algorithm is capable of identifying the droplet positions and sizes as well as tracking and matching of the droplet displacement vectors. The employed template matching algorithm using serial particle mask and the centroid method provide higher accuracy for estimating the droplet displacement, and the cross correlation matching algorithm and the two-frame particle tracking algorithm further ensure higher matching rates for the droplet pairs. The performance of the algorithm is well validated by simulations. Furthermore, the method is applied for the experimental study of flash boiling spray with extended glare-point imaging technique in combination with particle tracking velocimetry for measuring the particle size and velocity with higher accuracy, the results of which provides improved understanding of the flash boiling spray formation mechanism.