Modeling evaporation of Jet A, JP-7, and RP-1 drops at 1 to 15 bars

Abstract

A model describing the evaporation of an isolated drop of a multicomponent fuel containing hundreds of species has been developed. The model is based on continuous thermodynamics concepts wherein the composition of a fuel is statistically described using a probability distribution function (PDF). Following previous studies, this PDF is parametrized on the species molar weight. However, unlike in previous studies, a unified formulation is developed wherein the same PDF holds for three major homologous hydrocarbon classes. The new PDF is a double-Gamma-PDF that is parametrized on the square root of the molar weight. The additional advantage of the formulation is that it is valid in the subcritical region from 1 to 15 bars. Discrete species distributions for Jet A, JP-7, and RP-1 are fitted using this novel PDF and extensive calculations for isolated drops of these kerosenes are performed. The results show that under the quasi-steady gas phase assumption, the D^2 law is recovered after an initial transient. The evaporation constant is an increasing function of the far field temperature and pressure and a complex function of far field composition according to the values of the far field temperature and pressure. The difference between the surface and the far field vapor molar fraction is nearly independent of the far field pressure. The composition of the vapor at the drop surface is kerosene-fuel specific. A comparison between results obtained with a model assuming the drop interior to be well mixed and a model wherein the drop may evaporate either in a well-mixed mode or at unchanging composition shows that the percentage difference between the evaporation constant predicted by the two models is within the range of uncertainty in the transport properties.

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