Transient Evaporation and Combustion of a Fuel Droplet Near Its Critical Temperature

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Abstract
Recently obtained exact solutions for the transport-controlled lifetime of an isolated sphere of arbitrary density and “solubility” in a quiescent, constant-property fluid are exploited to predict the corresponding behavior of a fuel droplet evaporating (with or without vapor phase combustion) into a surrounding dense gas. Emphasis is placed on (i) systematic errors associated with the familiar quasi-steady (QS) approximation when applied to the vaporization of droplets which are not much denser than their surroundings, (ii) the chamber pressure-droplet temperature conditions under which the droplet will be driven to a subcritical (wet-bulb) temperature, or to its thermodynamic critical temperature, and (iii) the effects of gas/liquid solubility on the predicted lifetime of a fuel droplet. Illustrative calculations are included for the case of a kerosene-like (x-dodecane) droplet evaporating into compression-heated air, as encountered in diesel engine cylinders.