Gas property effects on droplet atomiation and combustion in an air-assist atomier

Abstract

Nitrogen, Ar, and CO 2 were used as the atomizing gas in an “air-assist” fuel nozzle to determine the effect of these gases on droplet size, number density, and velocity in kerosene spray flames using a two-dimensional phase Doppler interferometer. Data were obtained with these atomizing gases and compared to the reference, air-assist case, since air is the most commonly used atomizing fluid. Comparisons were made between the gases on a mass and momentum flux basis. Both burning and nonburning sprays were investigated. The results show that under burning conditions, the presence of O 2 in the air-atomized sprays influences the combustion process, reducing droplet size and increasing droplet velocity, especially in the region near the nozzle exit. Differences in droplet characteristics (size, velocity, and number density) are minimized in the momentum flux controlled cases, indicating the relevance of momentum flux over mass flux to control atomization. In both the nonburning and burning sprays, lighter gases more effectively atomized the fuel in comparison to the denser gases. Ar and CO 2 produced larger, slower moving droplets than the air and N 2 assisted cases under mass flux controlled conditions. The Ar and CO 2 atomized flames were also observed to be significantly more luminous than air-atomized flames. These results suggest that the presence of O 2 in the atomizing gas and gas density have significant effect on the atomization, mixing, and combustion processes, which, in turn, influence droplet lifetimes, flame structure, and emission levels.