High-Speed Particle Image Velocimetry Study of In-Cylinder Flows with Improved Dynamic Range 2013-01-0542

Engine in-cylinder velocity measurements are necessary for the study of cycle-to-cycle variations and the effect of turbulence and air-fuel mixing on combustion. High-speed particle image velocimetry (PIV) can provide measurements through the entire cycle, for multiple contiguous cycles. However, the PIV dynamic range, using a single spatial resolution and image separation, is insufficient to resolve the wide range of in-cylinder velocity and spatial scales encountered throughout the engine cycle. This paper discusses in-cylinder PIV data acquired with cycle resolution from the central tumble plane of a motored spark ignition optical engine using PIV image frame time separations (dts) that were dynamically varied as a function of crank angle. Also, two cameras with different magnifications were used to simultaneously acquire PIV images at high and low spatial resolution.

An assessment of the measurement errors revealed that the high spatial resolution data captured the lower velocity magnitudes with greater resolution while the low spatial resolution data better captured velocity vectors of higher magnitude, especially during early intake and exhaust valve opening. The low spatial resolution data was also compared with data acquired at a constant time separation optimized for the intake jet flow. Results showed that the noise in the Reynolds decomposed turbulent kinetic energy was about 50% for the constant dt data, while remaining below 5% for the variable dt data, for most of the compression stroke.