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The flow inside a combustion engine is highly complex and varies significantly with small changes in the engine configuration. For a long time IC-engine researchers have tried to predict the major mean flow patterns inside close-to-production engine setups. During the last decades computational fluid dynamics (CFD) has significantly contributed to the engine development process. Hence, significant research has focussed on the comparison of modeled and measured flows in IC engines. However, according to the knowledge of the authors, this study is the first fully three-dimensional (3-D), modeling and measurement effort that has evaluated the vast majority of the displacement volume by using an identical engine geometry. With improved, non-intrusive, 3-D velocity measurement technology, the vast majority of the cylinder displacement was explored and compared with Star-CD modeling results at the same locations.

Improvements in engine combustion depend on a thorough understanding of the actual in-cylinder flows. This study is thought to be the first fully three-dimensional (3-D) LDV measurement effort that evaluated the vast majority of the displacement volume under a variation of speed, load, and stroke during the intake and compression strokes. The intake port geometry was not changed during the course of the study. Most of the engine setups studied showed similar in-cylinder velocity patterns. The well developed tumble motion exhibited only marginal changes under the different speed, load, and throttle conditions with one exception: at idle condition, the tumble motion broke down into two equally strong downward flows along the cylinder liner. For all the other setups a robust tumble motion, which was distributed throughout the displacement volume prevailed until the end of measurement, sustaining significant amounts of ttumble motion until late in compression.