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 solely governed by chemical kinetics. As one moves away from this idealization, turbulence and turbulence/chemistry interactions (TCI) play increasingly important roles. The influence of TCI on autoignition and emissions of CO and unburned hydrocarbon (UHC) is studied using a three-dimensional time-dependent computational fluid dynamics (CFD) model that includes detailed chemical kinetics. Heptane is used as fuel. For nearly homogeneous reactants with low to moderate swirl and no top-ring-land crevice (TRLC), TCI has little effect on ignition timing. With increasing levels of swirl, higher degrees of mixture inhomogeneity, and for cases that include a TRLC, TCI effects become increasingly important and result in significant changes in ignition timing, global in-cylinder temperature and pressure, and emissions. The combination of consistent hybrid particle/finite-volume algorithms, detailed chemical kinetics, and chemistry acceleration strategies makes probability density function methods practicable for three-dimensional time-dependent modeling of HCCI autoignition and emissions. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).