A RNG k-epsilon model with application to diesel combustion modeling

摘要

A modified RNG k-epsilon turbulence model has been implemented in the KIVA-II computer code and applied to diesel combustion computations. The modifications account for effects of non-zero velocity dilatation on turbulence dissipation for density-variable engine flows. Computations were made of the in-cylinder processes in a Caterpillar engine and a Tacom engine with the use of both the modified RNG k-epsilon model and a traditional k-epsilon model. The RNG approach produces smaller turbulent voscosity than the traditional k-epsilon model does, which was found to be important for accurate predictions of spray combustion. Large scale flow structures with higher local gas temperatures were predicted with the use of the present turbulence model. With the improvement of flow modeling, better rates and soot and NOx emissions were obtained over the range of injection timings and load considered. Quantitatively improved predictions of NOx formation in both the engines were also achieved due to the extreme sensitivity of NOx to the local gas temperatures.