Relating Integral Length Scale to Turbulent Time Scale and Comparing k-ε and RNG k-ε Turbulence Models in Diesel Combustion Simulation 2002-01-1117

A modified version of the Laminar and Turbulent Characteristic Time combustion model and the Hiroyasu-Magnussen soot model have been implemented in the flow solver Star-CD. Combustion simulations of three DI diesel engines, utilizing the standard k-ε turbulence model and a modified version of the RNG k-ε turbulence model, have been performed and evaluated with respect to combustion performance and emissions. Adjustments of the turbulent characteristic combustion time coefficient, which were necessary to match the experimental cylinder peak pressures of the different engines, have been justified in terms of non-equilibrium turbulence considerations. The results confirm the existence of a correlation between the integral length scale and the turbulent time scale. This correlation can be used to predict the combustion time scale in different engines. It was found that, although the standard k-ε turbulence model produced adequate results for the larger engines, the RNG turbulence model gave better agreement with the experimental data for all engines.