Abstract
Direct numerical simulation (DNS) of ignition/propagation and auto-ignition of turbulent premixed flames has been conducted to investigate turbulent combustion mechanism in PCCI and HCCI engines. DNS are conducted for hydrogen/air, methane/air and n-heptane/air mixtures by considering detailed or reduced kinetic mechanism. From DNS of ignition/propagation of homogeneous and inhomogeneous mixtures, effects of turbulence characteristics, fuel species and pressure on the ignition and propagation processes are clarified. The ignition delay of the premixed mixture is correlated with mean strain rate near the ignition kernel. For high intensity and fine scale turbulent field, multiple-point ignition is observed even for a single initial ignition kernel, which is caused by the local suppression of radical production by turbulence. From DNS of auto-ignition of turbulent premixed flames, effects of turbulence and inhomogeneity of mixture on the auto-ignition process are investigated. Even for the homogeneous mixture, temperature in the auto-ignition process fluctuates in space, while this fluctuation slightly affects on global combustion process of the mixture. As for the hydrogen, inhomogeneity effects are not significant due to molecular diffusion of hydrogen. For hydrocarbons, however, inhomogeneity of the mixture changes auto-ignition process. Form these DNS with different combustion field, turbulent combustion mechanism in PCCI and HCCI engines is discussed.
