LDV measurements of axial distributions of in-cylinder gas velocities

Characteristics of in-cylinder gas flow in a two-cycle uniflow-type engine were investigated by using laser doppler velocimetry (LDV). Through swirl velocity measurements at several sections along the cylinder axis, it was found that in the early compression stroke, axial distribution of angular momentum is uneven and swirl velocity at each measuring section fluctuates periodically. Mean angular momentum in the whole of the combustion chamber, however, decays monotonously and analysis showed that its decaying process after a late compression stroke is similar to the swirl-decaying process in a cylindrical constant-volume bomb. A secondary airflow in the upper part of the combustion chamber is inferred from the measured radial and axial velocities in an early compression stroke.