A NUMERICAL STUDY OF HIGH-PRESSURE DROPLET VAPORIZATION

The evaporation 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. The proposed model is compared with data obtained for a variety of liquids. The comparisons include the predictions of the critical mixing state, droplet vaporization rate, and droplet temperature. Transient effects in both the liquid and vapor phases are found to have a large effect on the droplet heatup 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. Anomalies in the transport properties of a fluid near its critical mixing point were studied and found to be insignificant in droplet vaporization under conditions similar to those in a diesel engine.