A simple calculation method based on an evaporation analysis proposed previously [1] [2] is used to predict the variation of JP-5 fuel spray characteristics (median drop diameter, Dm, and drop-size distribution parameter, n) with time during evaporation in stagnant hot air. The method takes full account of transient effects occurring during the heat-up period. The results show that Dm increases with time, and so also does n, indicating that the drop-size distribution narrows with passage of time. The time to vaporize any given fraction of the spray mass is found to be proportional to D2mo. The effect of the initial value of n, no, is that a spray having a large value of no will reach its 90% evaporation point faster, but a smaller value of no will give a shorter 20% evaporation time. Based on these calculations, a general method for estimating the time required for any liquid fuel to attain any given percentage of spray mass evaporation in stagnant air is proposed.

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