The Interdependence of Spray Characteristics and Evaporation History of Fuel Sprays in Stagnant Air

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, D_m, 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 D_m 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 D²_mo. The effect of the initial value of n, n_o, is that a spray having a large value of n_o will reach its 90% evaporation point faster, but a smaller value of n_o 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.