Droplet sie distribution effects in spray combustion

Abstract

The effect of the initial droplet-size distribution (DSD) on spray combustion processes has been studied experimentally. Suitable flames were produced by igniting ethanol sprays issuing from a pipe into a coannular air stream. Three different DSDs were examined for their effect on spray combustion processes, while the initial Sauter mean diameter (SMD or D 32 ), mixture ratio, and gas/liquid velocities were held constant. Variations in spray/flame structure resulting from changes in the DSD were determined by measuring droplet sizes and velocities, and gas temperature and composition, within the reacting spray field. The results show that more complete combustion occurs in sprays possessing narrower DSDs, even with the SMD held constant. Reductions in the burning efficiency of sprays with wider DSDs is attributed primarily to their greater relative population of large fuel droplets and to droplete-size-segregating effects occurring at the spray periphery, which affect mixing rates. The results establish the DSD as an important indicator of atomization quality and an independent parameter regarding spray combustion processes.