1990-02-01

Motored and Steady Flow Boundary Conditions Applied to the Prediction of Scavenging Flow in a Loop Scavenged Two-Stroke Cycle Engine 900800

The application of in-cylinder multi-dimensional modelling to the scavenging process within the cylinder of a two-stroke cycle engine requires a prior knowledge of the flow entering that cylinder. Without this information, assumptions must be made which limit the accuracy of the theoretical simulation.
This paper describes laser doppler anemometry measurements of transfer port efflux flow for a two-port loop scavenged test cylinder motored at 200 rev/min. The cylinder was externally blown to ensure scavenge flow into the cylinder over the entire transfer port open period. The test results indicate that the flow does not enter the cylinder in the port design direction, but varies as a function of port height during both port opening and closing.
Comparison of motoring results with those obtained under steady flow testing of the same cylinder, shows adequate correlation, thereby justifying the use of steady flow information for dynamic simulation.
Incorporation of the measured LDA results as boundary conditions to the multi-dimensional modelling of isothermal scavenging produces very good correlation with experimental data. The predictions, obtained with the use of experimentally measured boundary conditions, are compared with those obtained using a assumption that flow enters the cylinder in the port design direction. Contour plots of the predicted in-cylinder fresh charge concentration are presented, which highlight the sensitivity of the scavenge process to the application of differing boundary conditions at cylinder entry.

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