Abstract
In-cylinder flow transition during a piston compression stroke was measured under motoring conditions using particle image velocimetry (PIV). A single-cylinder optical engine (bore diameter: 86 mm, stroke length: 86 mm, displacement volume: 500 cc) was used. This engine had quartz windows in the side of a pent roof, a quartz cylinder liner, and a quartz piston top. The two-dimensional velocity field along the center plane was measured. The temporal velocity change along the center plane and the size of the bulk flow were examined during the compression stroke. The turbulence intensity was calculated, and its distribution and temporal change were analyzed qualitatively. PIV measurements were conducted under four different engine speeds to investigate their effect on the in-cylinder turbulent flow field. The bulk flow velocity increased with the engine speed, but the flow pattern remained similar. The velocity of the bulk flow decreased and the turbulence intensity around the spark plug increased during the compression stroke. The turbulence intensity was a maximum around top dead center (TDC). These results describe the in-cylinder flow transition from large-scale bulk flow to small-scale turbulence.
