A Nonequilibrium Turbulence Dissipation Correction and Its Influence on Pollution Predictions for DI Diesel Engines

Abstract

A correction for the turbulence dissipation rate, based on nonequilibrium turbulence considerations from rapid distortion theory, has been derived and implemented in combination with the RNG k-ε model in a KIVA-based code. This correction reflects the time delay between changes in the turbulent kinetic energy due to changes in the mean flow and its turbulence dissipation rate, and it is shown that this time delay is controlled by the turbulence Reynolds number. The model correction has been validated with experimental data in the compression and expansion phase of a small diesel engine operated in motored mode. Combustion simulations of two heavy-duty DI diesel engines have been performed with the RNG k-ε model and the dissipation rate correction. The focus of these computations has been on the nitric oxide formation and the net soot production. These simulations have been compared with experimental data and their preditions are explained in terms of the turbulence dissipation effect on the transport coefficients for mass and heat diffusion. It has been found, that the dissipation correction yields consistent results with observations reported in previous studies.