Size and velocity characteristics of spray droplets in near-region of liquid film breakup in a swirl atomizer

Abstract

The characteristics of spray droplets resulting from the breakup of liquid film are crucial for the description of the primary atomization process in engine atomizers. The size and velocity characteristics of droplets resulted from the liquid film breakup in a hollow cone swirl atomizer, measured within millimetre distance from the actual location of the liquid film breakup, are analyzed. The radial profiles of the Sauter Mean Diameter (SMD) nondimensionalized with the liquid film thickness for different spray conditions collapse into a single variation trend, and a similar result is obtained for the mean droplet axial velocity nondimensionalized with the streamwise liquid film velocity. The mean axial velocity of the spray droplets measured at the film breakup point is independent of droplet size, which is different from the correlation characteristics of the spray droplets observed in other regions of the spray. The linear film breakup theory overpredicts the SMD of the spray measured at the breakup point significantly, and a scaling law proposed recently for the determination of volume median diameter of the spray captures the experimental trend of the droplet size recorded at the breakup point. The droplet size distribution measured at the breakup point is well described by a Gamma distribution with index parameter n governing the corrugation features of ligaments formed in the film breakup. The chosen value of n = 6.12 is determined experimentally for the sprays from the hollow cone swirl atomizer.