Effect of steam-assisted atomization on spray flame characteristics

Abstract

The use of steam for the atomization of liquid kerosene fuel in an commercially available twin-fluid atomizer (e.g. air-assist) is presented in this paper. Data on droplet size characteristics were recorded using a phase Doppler interferometer. Information on chemical composition downstream of the spray flames was obtained using FTIR. The enhanced vaporization of liquid fuel under combustion conditions in steam-assisted atomizers from the enthalpy of the steam as well as the decrease of fuel viscosity by the heating-up of the fuel nozzle is believed to result in smaller droplet size as compared to the same atomizer operated with air as the fluid. Higher viscosity associated with the steam as compared to air breaks the liquid conical sheet and provides finer atomization. The effect of enthalpy that is associated with steam is simulated by preheating the atomization air to higher temperatures. Near to the nozzle exit enhanced vaporization of the fuel with preheated air is found similar to steam. Steam is miscible with kerosene so that the combined two miscible liquid has widely different boiling points. It is conjectured that the presence of these widely different boiling point liquids may assist in the further break-up of the initial droplet size formed from the nozzle. However, due to the presence of negligible oxidant near to the nozzle exit on the centerline of the spray the process of combustion is somewhat retarded. The droplet size, vaporization and trajectory are different with steam than air as the atomization fluids. Furthermore, the flame plume size and configuration, as well as the flame radiation are much different under combustion conditions of steam-assisted atomization than air. The use of steam in place of or in conjunction with air or oxygen enables one to affect the droplet size and vapor distribution in sprays, and flame plume configuration. The steam-assist atomizers therefore provide finer atomization and enhanced droplet evaporation under combustion conditions. The flame stability limits were