Comparison of Computed and Measured Air Motion in Circular and Square Piston Cups

A multi-dimensional flow code was used to predict the motoring air motion in an engine with both circular and square piston cups. The program solved the Navier-Stokes equations, supplemented with a k-e turbulence model. The computational results were compared to recently published cycle-resolved LDV measurements for the same engine geometry. It was found that the predicted mean radial and tangential velocity distributions agreed well with the measurements. The predicted and measured turbulence intensities were also in good agreement prior to TDC. However, during the expansion stroke the computed turbulence intensities were much higher than the experimental values. These differences were related to reverse squish effects shortly after TDC. The response of the model to the change from circular to square piston geometries was also in agreement with the experimental data.