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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.

A better understanding of turbulent kinetic energy is important for improvement of fuel-air mixing, which can lead to lower emissions and reduced fuel consumption. An in-cylinder flow study was conducted using 1548 Laser Doppler Velocimetry (LDV) measurements inside one cylinder of a 3.5L four-valve engine. The measurement method, which simultaneously collects three-dimensional velocity data through a quartz cylinder, allowed a volumetric evaluation of turbulent kinetic energy (TKE) inside an automotive engine. The results were animated on a UNIX workstation, using a 3D wireframe model. The data visualization software allowed the computation of TKE isosurfaces, and identified regions of higher turbulence within the cylinder. The mean velocity fields created complex flow patterns with symmetries about the center plane between the two intake valves. High levels of TKE were found in regions of high shear flow, attributed to the collisions of intake flows.

The flow field contained within ten planes inside a cylinder of a 3.5 liter, 24-valve, V-6 engine was mapped using a three-dimensional Laser Doppler Velocimetry (3-D LDV) system. A total of 1,548 LDV measurement locations were used to construct the time history of the in-cylinder flow fields during the intake and compression strokes. The measurements began during the intake stroke at a crank angle of 60° ATDC and continued until approximately 280° ATDC. The ensemble averaged LDV measurements allowed for a quantitative analysis of the dynamic in-cylinder flow process in terms of tumble and swirl motions. Both of these quantities were calculated at every 1.8 crank degrees during the described measurement interval. Tumble calculations were performed about axes in multiple planes in both the Cartesian directions perpendicular to the plane of the piston top. Swirl calculations were also accomplished in multiple planes that lie parallel to the plane of the piston top.