Theory of droplet vaporization and combustion

Abstract

The classical theory of vaporízation and combustión of fuel droplets is examined for low Reynolds numbers, when the effects of the motion of the droplet relative to the ambient atmosphere can be neglected, and the process can be considered spherico-symmetrical.
The large valué of the ratio of the liquid density the ty-pical gas density justifies the quasi-steady approximation in the analysis of the gas phase process.
The large valué of the ratio of the heat of vaporízation per unit mass of fuel to the typical specific thermal energy of the liquid results in the existence of a first stage of droplet heat-ing without vaporization, and a second stage when vaporizarion occurs at a nearly constant web-bulb temperature, close to the boiling temperature.
The large valúes of typical activation energies of the gas phase reactions, leads to the possibility of múltiple solutions of the quasi-steady conservation equations for the gas phase. These include solutions corresponding to a nearly frozen mode of vaporízation, that can not exist above an "ignition" valué of the ambient temperature, and a mode of vaporízation with diffusion controlled combustión that can not exist for ambient temperatures below an "extinction" valué.