EVALUATION OF TURBULENCE-CHEMISTRY INTERACTION UNDER DIESEL ENGINE CONDITIONS WITH MULTI-FLAMELET RIF MODEL

摘要

The multi-fhmelet representative interactive flamelet (RIF) model is used to account for the effects of turbulence-chemistry interaction (TCI) to model spray combustion under typical diesel engine conditions. The RIF model calculates the species mass fraction based on the mixture fraction fields and scalar dissipation rates provided by the computational fluid dynamics solver. A time-dependent renormalization group turbulence model is used in conjunction with a grid-converged discrete phase model for the liquid phase. The minimum number offlamelets required is determined to sufficiently represent the large variation of stoichiometric scalar dissipation rates in the domain. Different forms of the presumed scalar probability density functions (PDFs) were also examined. The modeling results are then compared with the experimental data at different ambient temperatures, ambient O2 concentrations, ambient densities, and injection pressures. The effects of different chemical kinetic mechanisms (103-species and 106-species skeletal mechanisms) are also studied to further understand the performance of the model. Overall, the RIF model is observed to capture the measured ignition delay and flame lift-off length very well, especially under certain conditions characterized by low ambient temperatures, densities, and oxygen concentrations. The need for initializing multiple flamelets is highlighted in order to obtain simulation results devoid of modeling artifacts. Overall, the efficacy of using an advanced turbulence combustion model is demonstrated.