Particle image velocimetry (PIV) was used for flow measurements in a motored single- cylinder engine fitted with various intake port geometries. In conjunction, engine performance measurements were made in a running engine using the same intake port geometries. The intent was to characterize observed flow structures in a physically significant way that provided a useful correlation between intake port geometry, in-cylinder flow and engine performance.
The implementation of PIV was discussed in detail, including the use of a low-resolution video camera, software-based image acquisition and analysis, microsphere flow seeding, and an optical engine capable of 3600 RPM.
Experimental hardware used for engine performance testing, including ion probes used for flame propagation measurements, was also described in depth.
In-cylinder measurements were made of horizontal velocity components on three horizontal planes at 90 degrees after BDC compression, with the engine motored at 1200 RPM. Fifty vector fields were collected and averaged at each location. The flows for the directed and helical port geometries were dominated by a single swirl structure (axis parallel to bore). The production port showed swirling flow on one plane, but strong cross-flow on the other two planes suggested significant out-of-plane (unmeasured) velocities.
Engine performance, measured over a range of equivalence ratios and spark timings, showed much more significant port-to-port variation. Flame propagation and IMEP measurements showed that the helical port typically produced the fastest combustion and lowest cyclic variability of all three ports, while the production port produced the slowest combustion and greatest variability. Corroboration of heat release data with flame propagation measurements indicated the influence of the strong swirling flow associated with the helical port.
Flows were characterized according to kinetic energy present at ignition (based on measured velocities). The scope of the flow measurements was not sufficient to provide a strong correlation between port geometry and engine performance. Several recommendations were made, including measurement of the third velocity component, which would likely provide a better estimate of kinetic energy. However, limited improvement in the correlation between in-cylinder flow and engine performance is expected, due to the complexity of the trends observed in the engine performance data.