A PDF method for multidimensional modeling of HCCI engine combustion: Effects of turbulence/chemistry interactions on ignition timing and emissions

In the limit of homogeneous reactants and adiabatic combustion, ignition timing and pollutant emissions in homogeneous-charge compression-ignition (HCCI) engines would be governed solely by chemical kinetics. The influence of turbulence/chemistry interactions (TCI) on auto-ignition and emissions of CO and unburned hydrocarbon (UHC) was examined using a three-dimensional time-dependent computational fluid dynamics (CFD) model that includes detailed chemical kinetics. For low-swirl nearly homogeneous conditions and no top-ring-land crevice (TRLC), TCI had little effect on ignition timing; however, even in that case the influence of TCI on emissions was not negligible. With increasing swirl, higher degrees of mixture in-homogeneity, and for cases that include a TRLC, TCI effects became increasingly important and resulted in significant changes in ignition timing and emissions. Unburned fuel was a non-negligible contribution to UHC for high swirl and in cases where a TRLC was considered. The work also demonstrated the feasibility of bring transported probability density function methods to bear in modeling a geometrically complex three-dimensional time-dependent turbulent combustion system. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).