Validation of an LES Multi Mode Combustion Model for Diesel Combustion 2010-01-0361

Diesel engine combustion is simulated using Large Eddy Simulation (LES) with a multi-mode combustion (MMC) model. The MMC model is based on the combination of chemical kinetics, chemical equilibrium, and quasi-steady flamelet calculations in different local combustion regimes. The local combustion regime is identified by two combustion indices based on the local temperature and the extent of mixture homogeneity. The LES turbulence model uses the dynamic structure model (DSM) for sub-grid stresses. A new spray model in the LES context is used, and the Reynolds-averaged Navier-Stokes (RANS) based wall model is retained with the LES derived scales. These models are incorporated in the KIVA3V-ERC-Release 2 code for engine combustion simulations.

A wide range of diesel engine operating conditions were chosen to validate the combustion model. The engine operating conditions include both the Low Temperature Combustion (LTC)-diesel and the conventional diesel combustion with a variety of injection timing, boost pressure, and Exhaust Gas Recirculation (EGR). Diesel engine combustion typically exhibits both partially premixed and non-premixed characteristics. In the low temperature premixed combustion regimes, combustion is calculated by chemical kinetics. At higher temperatures, combustion is calculated by the quasi steady flamelet time scale combustion model supplemented with the chemical equilibrium calculations. The MMC model is able to predict a wide range of diesel combustion regimes. The simulation results of pressure and heat release compared well with the experimental measurements of the ignition delay, heat release phasing, peak pressure, and engine exhaust emissions. The MMC model required lower CPU cost than using the CHEMKIN in these simulations.