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This work investigates the image quality achievable with a large-aperture endoscope system and high-speed cameras in terms of detecting the premixed flame boundary in spark-ignited engines by chemiluminescence imaging. The study is an extension of our previous work on endoscopic flame imaging [SAE 2014-01-1178]. In the present work, two different high-speed camera systems were used together with the endoscope system in two production engines to quantify the time-resolved flame propagation. The systems were cinematography with a CMOS-camera, both with and without an intensifier, the latter variation being used in a four-cylinder automotive engine as well as in a single-cylinder motorcycle engine. An algorithm with automatic dynamic thresholding was developed to detect the line-of-sight projected flame boundary despite artifacts caused by the spark and the large dynamic range in image brightness across each time series.

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.