Investigation of In-Cylinder Mixing Using Large Eddy Simulation Models for LTC Diesel Applications

Abstract

In-cylinder mixture preparation and early combustion heat release are studied using Large Eddy Simulation (LES) for direct injection (DI) diesel with high exhaust gas recirculation (EGR) and early injection timing. Both LES and traditional Reynolds Average Navier-Stokes (RANS) calculations are carried out using KIVA-3V release 2 and compared with experimental results of medium load LTC-diesel (Low Temperature Combustion) cases. Simulations presented in this paper are carried out using KH-RT (Kelvin Helmholtz – Rayleigh Taylor) breakup model for spray atomization and CHEMKIN n-heptane mechanism for combustion and both dynamic structure LES and RNG (re-normalized group) kε RANS for turbulence model. Although engine simulation using LES model poses significant challenges on practical engine grids, significant agreement with LTC-diesel experiments is observed by using an additional spray source term for modeling the effect of liquid sprays on sub-grid kinetic energy transport calculation in engines. Results when compared to RANS, demonstrate that LES is able to predict local spots of early heat release resulting in more accurate prediction of start of combustion timing and early heat release phasing. Mixing due to bulk fluid motion such as swirl is also observed more distinctively in LES calculations.