| A comprehensive axisymmetric numerical model has been developed to study evaporation of a droplet translating within a high pressure and high temperature nitrogen environment. Using this model, predictions are in very good agreement with the extensive experimental data of Nomura et al. [Proceedings of the Combustion Institute, vol. 26, pp. 1267--1273, 1996]. Predictions are also in very good agreement with the experimental data of Gokalp et al. [Proceedings of the Combustion Institute, vol. 22, pp. 2027--2035, 1988].; For stagnant droplets, the droplet average evaporation constant (defined as the average value for (d/do) 2 < 0.5) decreases with pressure for subcritical ambient temperatures. It increases with pressure for supercritical ambient temperatures and becomes insensitive to pressure at ambient temperatures around the critical temperature of the fuel. The effect of the droplet initial temperature on the average droplet evaporation constant is insignificant for the ambient conditions considered. However, the effect on the droplet swelling during the initial heat-up period can still have a significant impact on the droplet lifetime.; For droplets moving within an environment at supercritical temperatures, it is predicted that the average evaporation constant increases almost linearly with ambient pressure. However, at an ambient pressure which is a few times the thermodynamic critical pressure of the fuel, the slope of the average evaporation constant changes sharply, leading to a weaker linear variation with further increase in the ambient pressure. With increasing initial droplet velocity, the above change in slope occurs at higher ambient pressures. The numerical model predictions show that the droplet lifetime decreases with increasing ambient pressure or increasing initial droplet velocity. It is also shown that the droplet penetration distance decreases exponentially with ambient Pressure, and that droplet deformation due to the decrease in surface tension at elevated ambient pressures can not be neglected. |
