Effect of Fuel Vapor Concentration of an Ambient Gas on Flame Spread along a Fuel Droplet Array Combustion and Effects of Fuel Droplet Array on Gas-Phase Flame Propagation

Abstract

Combustion experiments of fuel droplet array in a fuel vapor-air mixture were performed at normal and microgravities to investigate growth mechanism of group combustion of fuel droplets. The purpose of this research is to examine the effect of fuel vapor concentration of an ambient gas on the flame spread and the effect of fuel droplet array on gas-phase flame propagation. The initial droplet diameter was 0.32, 0.8 or 1.0 mm, and the droplet spacing was varied from 1.6 to 15 mm. Behavior of flame spread along a fuel droplet array and gas-phase flame propagation were observed and flame speed was measured for various droplet spacing and fuel vapor concentrations of an ambient gas. As a low-volatile fuel, normal decane was used. As a high-volatile fuel, ethanol was employed. In the case of the gas equivalence rations below the flammability limit, the flame spread speed increases with the increase in the gas equivalence ratio. The flame spread speed of ethanol droplet array was about two times as large as that of decane droplet array when the droplet spacing was 1.6 mm. A decane droplet array did not influence the gas-phase flame propagation. On the other hand, an ethanol droplet array disturbed a flame propagation in the gas phase, and increased slightly flame propagation speed at the gas equivalence rations near the lower flammability limit.