Effect of radiation absorption on fuel droplet evaporation

Fuel droplet evaporation is relevant to spray combustion in technologically important devices and must be understood to develop reliable combustion methods for hydrocarbon fuels. Motivated by this observation, this paper presents an analysis to examine the importance of radiation on unsteady evaporation of a single isolated fuel droplet. The droplet is considered to be spherical and semitransparent to radiation. A model based on radiative transfer theory is used to calculate the local volumetric rate of radiation absorption. Published spectral absorption coefficient data for hydrocarbon fuels is used to perform the calculations. The effects of thermal expansion and temperature-department thermophysical properties on the evaporation process are accounted for. The internal circulation in the droplet due to the external flow is accounted for through an effective thermal conductivity of the fuel droplet. The model predictions are compared with available theoretical results and experimental data. The results reveal that, depending on the relative importance of radiation and convection heat transfer, the neglect of radiation absorption by a droplet cannot be ignored in predicting the rate of fuel evaporation and the droplet lifetime.