Particle image velocimetry measurement of in-cylinder flow in internal combustion engines : Experiment and flow structure analysis

A cross-correlation digital particle image velocimetry (PIV) system has been developed and applied to study the in-cylinder flow in a single-cylinder engine with a production-type cylinder head. The PIV system set-up and its optimization are described in the first part of the paper. Two-dimensional velocity distributions measured over 100 cycles are analysed to obtain ensemble-averaged mean and fluctuating velocities, the turbulent length scale, vorticity and strain rate distribution in the measurement plane. In particular, a spatial filtering scheme is developed in order to obtain the cycle-resolved velocity measurements. The cycle-resolved analysis shows that the low-frequency velocity fluctuation component (i.e. cyclic variation) is mainly responsible for the spatial variation in velocity and turbulent kinetic energy distributions. The integral length scale calculated from the PIV data is between 6 and 10 mm and the strain rate is estimated to be within 1000 s in most areas of the measurement plane.