Toward a unified high-pressure drop model for spray simulations

This research focuses on the development of a unified drop vaporization model for use in simulations of high-pressure spray combustion processes. Emphasis is placed on the analysis of supercritical and transcritical processes. These processes occur when a liquid drop that is initially at a subcritical temperature is injected into a high-pressure gaseous environment that exceeds the thermodynamic critical pressure of the interfacial mixture. For this situation the gas-liquid interface undergoes what is commonly referred to as a transcritical heating process. This process is dominated by thermodynamic nonidealities and transport anomalies. Classical models derived using the quasi-steady approximation fail in this limit because of the fundamental assumption that drop vaporization rates are dominated by quasi-steady convective processes. In the transcritical limit, drop vaporization rates are dominated by unsteady diffusion processes. These rate-limiting modes represent two extremes. Here we investigate these extremes by presenting the results from a series of direct numerical simulations. Emphasis is placed on the existence of two ratelimiting parameters and on obtaining a unified approach for modeling the transitional behavior of vaporizing drops over a range of pressures from atmospheric to supercritical.