LDV Measurements of Axial Distributions of In-Cylinder Gas Velocities: (A Case of an Engine with a Bowl-in Type Piston)

Swirling flow in a motored engine with a bowl-in type piston was measured by Laser Doppler Velocimetry (LDV). Through the detailed measurements at several sections along the cylinder axis, flow characteristics in the piston bowl and squish area were revealed. Rising of swirl level occurs from the upper section near the bowl rim and propagates to the lower part decreasing its rising level. At the rising peak, swirl profile in the bowl shows the solid-body-rotation pattern. On the other hand, swirl in the squish area near TDC decreases rapidly to have a free-vortex-like profile. The analysis on the cycle-resolved velocity data shows that the turbulence intensity in the piston bowl increases slowly before TDC and decays monotonously after a piston passes TDC. Although the periodic oscillation and uneven axial distribution of swirl are detected in the early compression stroke, the angular momentum average over measuring planes decays monotonously and its decaying nature is qualitatively similar to that of an engine with a pancake-type combustion chamber.