LDV Measurements of Axial Distributions of In-Cylinder Gas Velocities

Velocity distributions of in-cylinder gas flow in a two cycle uni-flow type engine were measured under motoring conditions by a forward scattered LDV. Measurements were conducted in several planes along the cylinder axis so that the axial distribution and decaying process of swirl velocity in the whole combustion chamber could be investigated. The obtained results are as follows. (1) The initial profile of swirl velocity distribution like solid-body-rotation changes into a flat-top trapezoidal one during the course of the compression and the expansion stroke. (2) A complicated three dimensional flow structure exists in the early compression stroke. (3) The volume mean angular momentum of swirl velocity decays monotonously and maintains about 65% of the initial value when TDC is reached. It shows a similar decaying process in a pancake shaped constant volume bomb after the midway in the compression stroke.