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Knowledge of the relevant cause-effect relationships for the combustion process, such as the interaction between the in-cylinder flow and the combustion behavior, are becoming essential for future combustion engines. Apart from the general interdependencies between the combustion rate and the turbulence intensity, specific combustion concepts, known from lean-burn engines, also strongly depend on the global flow structure which for example controls the mixing processes. Particle tracking velocimetry (PTV) was used to analyse the bulk in-cylinder flow of multi-valve production engines. The PTV results gave rise to well-aimed modifications of the intake ports and thus of the in-cylinder flow in order to achieve an optimized mixing of the charge or to affect the turbulence production during the compression stroke.

Flame propagation as well as the special role of detonation waves during knocking combustion are still unsolved questions. In order to examine these phenomena during cyclic resolved knocking combustion, high-speed schlieren photography and multi optical fiber technique were applied simultaneously. The pictures were taken at a rate of 200 000 frames per second, whereas the flame radiation signals of the knocking combustion, detected with the multi optical fiber technique at 49 measuring points, were recorded with a sampling frequency of 500 kHz. The exact correlation between schlieren photography and optical fiber technique shows that knocking combustion is initiated by self ignitions in the unburned regions, clearly separated from the spark ignited flame. The complete autoignition (i.e. knocking combustion) proceeds in two stages thus showing distinct prereactions.