Cycle-Resolved Velocity and Turbulence Measurements Near the Cylinder Wall of a Firing S.I. Engine 861530
Laser Doppler velocimetry has been used to make cycle-resolved velocity and turbulence measurements in a homogeneous-charge, spark-ignition engine. The engine had a ported intake and disc-shaped chamber with a compression ratio of 7.5 to 1. It was operated at a speed of 1200 rpm and with a TDC swirl number of 4. A stoichiometric propane-air mixture was used, and ignition was near the wall. Measurements of the tangential velocity component were made in both firing and non-firing cycles at nine spatial locations along a radius 180 degrees downstream of the spark. The radial velocity component was also measured at four of the locations. All measurements were made in the center of the clearance height. Tangential component measurements were made as close as 0.5mm from the cylinder wall, and the radial component was measured as close as 1.5mm from the wall. It was found that a very thin boundary layer exists both with and without combustion; the tangential velocity at a location 0.5mm from the wall was greater than 90 percent of the maximum value reached across the chamber. Turbulence intensity was found to increase little immediately ahead of the flame, but to increase significantly across the flame; it was higher in the burned gas than in the unburned gas at all radial positions examined. The near-wall turbulence intensity was isotropic to within 20 percent (as near as 1.5mm from the wall). The measured tubulence intensity increased sharply near the wall indicating a significant amount of wall generated turbulence.