Large-eddy simulations of a stratified-charge direct-injection spark-ignition engine: Comparison with experiment and analysis of cycle-to-cycle variations

Multiple-cycle large-eddy simulations (LES) have been performed for an optically accessible, single-cylinder, four-stroke-cycle, spray-guided direct-injection spark-ignition (SG-DISI) engine operating in a stratified globally fuel-lean mode. The combine standard Smagorinsky turbulence model, stochastic Lagrangian parcel method liquid fuel injection and spray modeling, simple energy-deposition modified thickened flame model turbulent propagation through highly reactant mixtures. Comparisons between experiments include individual-cycle ensemble-average pressure apparent-heat-release-rate traces, indicated mean effective pressures (IMEP), instantaneous two-dimensional vapor-equivalence-ratio contours. Although the number of LES cycles is small (35), results show that are able to capture global combustion behavior observed experiments, including cycle-to-cycle variations. simulation then analyzed further provide insight into conditions lead misfire versus robust combustion. As has reported earlier experimental studies homogeneous-charge SI engines, local vicinity spark gap at time ignition largely determine subsequent development. However, contrast no single or quantity correlates as strongly with eventual peak IMEP each cycle. Rather, it interplay among early kernel, velocity field experiences, distribution encounters ultimately determines fate event. Deeper analysis quantitative statistical comparisons will require larger numbers cycles.