PIV Measurements of In-Cylinder Flow in a Four-Stroke Utility Engine and Correlation With Combustion Measurements

Large-scale flows in internal combustion engines directly affect combustion duration and emissions production. The effect of intake port geometry on combustion performance was studied in a four-stroke spark-ignition utility engine. Three intake port geometries were investigated at three port orientations. In-cylinder flows in orthogonal planes were measured using particle image velocimetry (PIV). Combustion performance data were acquired at two load conditions and three equivalence ratios. The PIV data were processed to calculate the large-scale mean vorticity and mean high-pass filtered velocity. These flow parameters were used to characterize the in-cylinder flow in a measurement plane in a physically meaningful way and correlate the flow with combustion performance. The cumulative distribution functions of the flow parameters did not show significant port-to-port differences in either measurement plane. The mean vorticity and high-pass filtered velocity did exhibit differences due to port orientation in the horizontal plane, but not in the vertical plane. The 0-degree ports consistently produced the highest values of large-scale mean vorticity and mean high-pass filtered velocity in the horizontal plane. The kinetic energy present at ignition was also calculated to characterize the flow. The ensemble average values of the mean large-scale vorticity, high-pass filtered velocity and kinetic energy were compared to the combustion duration. The vertical plane vorticity and high-pass filtered velocity did not correlate with combustion performance. The horizontal plane vorticity and high-pass filtered velocity were found to exhibit modest correlation at the fixed torque condition, and somewhat lower correlation at the WOT condition. The correlation between kinetic energy and combustion duration was poor. The best correlation of flow field structure with engine performance was achieved for ports at the 0-degree port orientation. Ports at this orientation generated coherent, large-scale swirl.