Accounting for real gas effects in CFD simulations of high density combustion

Advanced combustion systems characterized by high efficiencies and low emissions can be achieved by organizing combustion processes at high densities (high pressures and low temperatures). Under these conditions, the ideal gas model widely used in CFD simulations fails to properly capture the relation among pressure, density, and temperature as well as variation of the mixture internal energy. As such, discrepancies between experimental observations and CFD simulations cannot only be traced to experimental or turbulent combustion model uncertainties. This paper investigates differences in the mixing and combustion of a high-pressure n-heptane jet into a quiescent chamber of air based on ideal and real gas models. Since the results reveal substantial differences, and the real gas model is more physically sound, there is therefore a strong motivation to resolve the problem. A method is then suggested for incorporating real gas models in CFD simulations based on available transport and thermodynamic data. This attempt also brings out an often-ignored problem in existing chemical kinetic models in the literature, namely, the non-systematic assignment of transport properties for various species.