Combustion of monodisperse droplet clouds in a reactive environment

Abstract

In practical spray combustion, the behavior of an individual droplet can be significantly affected by the presence of neighboring droplets and by a reactive environment within the spray. Recently, several theoretical approaches to the problem have been presented. These results suggest that droplet spacing affects the combustion rate of the spray, and in some models a dependence of droplet lifetime and mode of burning on ambient oxygen content is predicted. In the present work, the combustion of monodisperse clouds of droplets in a hot reactive environment is studied experimentally with an emphasis on examining the role of the ambient oxidizer mass fraction, Y0∞, and droplet spacing on the droplet combustion rate. The experiments are conducted in a two-phase flow facility that produces an atmospheric-pressure, laminar, one-dimensional monodisperse hydrocarbon aerosol air flame. The droplet burning rates appear to be correlated by a D2 burning law, but the observed dependence on ambient oxidizer mass fraction is not predicted by a quasi-steady isolated droplet model. In addition, a significant reduction in the burning rate is observed with decreasing droplet spacing. The experimental results suggest that for low ambient oxidizer mass fractions fuel vapor accumulation occurs within the droplet cloud.