Size-scaling effect on the velocity field of an internal combustion engine, part I: Bulk motion

In-cylinder velocity measurements were acquired to study the bulk fluid motion in two geometrically scaled, two-valve, optically accessible, and single-cylinder research engines. Different port geometries (two), different port orientations (two), and both shrouded and nonshrouded intake valves were tested to vary the intake-generated flow. The engines were motored at speeds ranging from 300 to 1200 r/min for the larger engine and from 600 to 1800 r/min for the smaller engine. Prior to testing on the engines, the different head configurations were tested on a steady flow bench. Particle image velocimetry data were taken on a single plane, parallel to the piston surface, in the engines to characterize the large-scale flow phenomena. The mean location of the swirl center and the mean angular velocity were determined by fitting a solid-body profile to the flow. The results showed that the swirl center location was relatively insensitive to engine speed for both engines, but did change position throughout the cycle. The swirl center locations, scaled by the cylinder radii, were found to be in nearly the same location for the two-scaled engines in the same nominal configuration, indicating that the swirl center motion was deterministic in nature. Normalizing the best-fit solid-body angular velocity by the engine rotation rate was found to collapse the data from the multiple engine speeds nearly onto a single curve for a given engine configuration. The angular velocity was found to decrease with crank angle due to wall friction, which was higher for the small engine because of the higher surface-to-volume ratio.

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