Using Large Eddy Simulations to Study Mixing Effects in Early Injection Diesel Engine Combustion

Early direct injection with HCCI like properties is characterized by the presence of an ignition dwell - the interval between end of fuel injection and start of combustion, during which fuel-air mixing occurs. Previous work by Jhavar and Rutland (2005) has focused on investigating different methods to affect fuel-air mixing during the ignition dwell. That study helped to evaluate the relative influence of various mixing control strategies to achieve ignition control. In this study, we attempt to look into the mixture preparation process in more detail. Therefore, turbulence is studied using Large Eddy Simulation (LES) models in place of Reynolds Averaged Navier Stokes (RANS) models. While LES is computationally more expensive than RANS, it depicts the flow structure more accurately. Therefore, it can be applied to engines in order to gain a better representation of local mixing as well as accurately simulate unsteady flow behavior in engines. In this study, various LES models have been added to the KIVA-3V code. Early injection cases have been simulated on a CAT 3401 engine mesh and comparisons made with RANS results. LES results show more detailed flow structure and therefore enable a more accurate study of mixing. Multiple cycle cases have also been simulated and compared to identify cycle to cycle variations. A grid sensitivity study for LES has also been performed. In addition to this, LES has been added to KIVA-CHEMKIN for more accurate flow representation. Currently the DOLFA technique (Haworth et al. 2003) is being added with KIVA-CHEMKIN to speed up kinetics calculations.