The Impact of a Non-Linear Turbulent Stress Relationship on Simulations of Flow and Combustion in an HSDI Diesel Engine

In-cylinder flow and combustion processes simulated with the standard k -ε turbulence model and with an alternative model—employing a non-linear, quadratic equation for the turbulent stresses—are contrasted for both motored and fired engine operation at two loads. For motored operation, the differences observed in the predictions of mean flow development are small and do not emerge until expansion. Larger differences are found in the spatial distribution and magnitude of turbulent kinetic energy. The non-linear model generally predicts lower energy levels and larger turbulent time scales. With fuel injection and combustion, significant differences in flow structure and in the spatial distribution of soot are predicted by the two models. The models also predict considerably different combustion efficiencies and NO x emissions. The turbulence model impacts entrainment and jet velocity; this is believed to be the major factor influencing the flow structure development and the formation of NO x emissions. Like the motored simulations, major differences in the distribution and magnitude of turbulent kinetic energy and time scale are seen—differences which are likely to impact the modeled combustion behavior.