On the Assumptions Underlying Droplet Vaporization and Combustion Theories

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Abstract
A study is undertaken to determine the range of validity of the assumptions that (a) the liquid temperature is constant and equal to the boiling temperature for a burning droplet, (b) the instantaneous vaporization rate of a droplet at a given size is the same as that of a constant-diameter sphere of the same size, and (c) the duration of the initial unsteady period is much less than the total vaporization time of a droplet. It is shown that assumption (a) may lead to observable differences between the theoretical and experimental burning rates for low-energy fuels, that for practical purposes assumption (b) is probably always valid, and that approximation (c), which is most accurate for large values of the temperature at infinity, may lead to a 20% error in the computed value of the total vaporization time. The calculated duration of the initial unsteady period compares favorably with experiments on droplet ignition delay times.

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