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In this study two different simulation approaches to large eddy simulation of spark-ignition engines are compared. Additionally, some of the simulation results are compared to experimentally obtained in-cylinder velocity measurements. The first approach applies unstructured grids with an automated meshing procedure, using OpenFoam and Lib-ICE with a mapping approach. The second approach applies the efficient in-house code PsiPhi on equidistant, Cartesian grids, representing walls by immersed boundaries, where the moving piston and valves are described as topologically connected groups of Lagrangian particles. In the experiments, two-dimensional two-component particle image velocimetry is applied in the central tumble plane of the cylinder of an optically accessible engine. Good agreement between numerical results and experiment are obtained by both approaches.

Flame penetration into the top-land crevice of a combustion engine's cylinder is investigated by large-eddy simulation (LES) and high-speed visualization experiments. This penetration is of practical relevance as it leads to the formation of unburned hydrocarbons (UHC) wherever the flame is quenched inside the crevice. In optically accessible engines, the crevice is particularly large, so that it must be considered in simulations, which also creates an opportunity to study flame penetration in detail. The high-speed imaging shows a luminous front, subject to cyclical variation, penetrating into the top-land crevice, but cannot distinguish between a flame burning into the crevice or just being pushed into it by increasing pressure in the cylinder. The LES of the process permits to turn off the reaction source term, so that the effect of convection and free flame propagation can be separated.

Flame penetration into the top-land crevice of a combustion engine's cylinder is investigated by large-eddy simulation (LES) and high-speed visualization experiments. This penetration is of practical relevance as it leads to the formation of unburned hydrocarbons (UHC) wherever the flame is quenched inside the crevice. In optically accessible engines, the crevice is particularly large, so that it must be considered in simulations, which also creates an opportunity to study flame penetration in detail. The high-speed imaging shows a luminous front, subject to cyclical variation, penetrating into the top-land crevice, but cannot distinguish between a flame burning into the crevice or just being pushed into it by increasing pressure in the cylinder. The LES of the process permits to turn off the reaction source term, so that the effect of convection and free flame propagation can be separated.