Effects of Droplet Spacing on Evaporation of a Cluster of 13 Fuel Droplets

Abstract

The evaporation behavior of the central droplet in droplet clusters was observed in microgravity without combustion, and the effects of the droplet spacing were examined. The solidified-fuel fiber-suspension technique was utilized for preparing the monodispersed suspended-droplet cluster (MSDC) model. Most of the experiments were conducted with the HCP (hexagonal closest packing) structure cluster models of thirteen n-eicosane droplets at the atmospheric pressure, and some were conducted with the BCC (body-centered cubic) structure cluster models of nine 1-octadecanol droplets at an elevated pressure. The droplet images suggested that critical thermodynamic state was not attained at the ambient pressure above the critical pressure of the fuel, and the results at the elevated pressure were not largely different from those at the atmospheric pressure. The whole evaporation process was unsteady and the unsteadiness was enhanced with decreasing the droplet spacing. The initial heat-up time increased monotonically with decreasing the droplet spacing. The evaporation rate defined after the initial heat-up time was almost constant or showed an increasing trend with decreasing the droplet spacing.