Velocity Field Characteristics in Motored Two-Stroke Ported Engines

Particle image velocimetry (PIV) was used to study the velocity field characteristics in motored two-stroke ported engines. Measurements of the two-dimensional velocity field were made at the midplane of the clearance volume for bowl-in-head and disk combustion chamber geometries. Measurements were also obtained for two scavenging port geometries, i.e. a loop-scavenged engine and a loop-scavenged engine with a boost port.

Results from this study show that in-cylinder geometry had a dominant effect on the flow structure observed at TDC. For example, with the boost-port scavenging crankcase, the disk-shaped chamber showed a turbulent flow-field at TDC with little large scale motion. In contrast, addition of a squish flow from the bowl-in-head geometry produced an organized cross-chamber flow.

The addition of a boost port also changed the flow structure markedly. A large-scale swirl flow was observed in the engine that did not contain a boost port. In contrast, the boost port apparently breaks down the tendency to swirl.