The evaporation and combustion of single, spherical fuel droplets in a high pressure, high temperature environment has been studied numerically. The model is fully transient in both the liquid and the vapor phases. Transport properties are functions of temperature, pressure and composition, and vary throughout the liquid droplet and the vapor boundary layer. Equilibrium at the liquid-vapor interface is calculated using the Peng-Robinson equation of state, and accounts for diffusion of the gas into the liquid droplet. The Peng-Robinson equation of state is also used to calculate the enthalpy of vaporization of the fuel species as well as the liquid and vapor mixture densities.;Transient effects in both the liquid and vapor phases are found to have a large effect on the droplet heat up and vaporization process. At very high temperature and pressure conditions the droplets were found to reach their thermodynamic critical mixing point in a totally transient process. Coupled diffusion processes were studied and found to be an important factor in high pressure droplet vaporization and combustion. Anomalies in the transport properties of a fluid near its critical mixing point were studied and found to be insignificant in droplet vaporization and combustion under conditions similar to those in a diesel engine. The use of an ideal solution assumption along with the assumption of a pure liquid droplet was found to increase the predicted vaporization time by up to 60% in diesel engine conditions. The assumption of a constant liquid density was found to increase the initial heat up time of a vaporizing droplet, and decrease the vaporization rate in diesel engine conditions.
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