Particle Image Velocimetry Measurements of In-Cylinder Flow in a Multi-Valve Internal Combustion Engine

Abstract

Particle image velocimetry (PIV) has been used here to characterize the formation and breakdown of barrel swirl or tumble in a production geometry, four-stroke, four-valve motored optical internal combustion (IC) engine. The engine was motored at 1000 r/min at wide open throttle. Double exposed images were recorded from a plane parallel to the cylinder axis which passed through the centre-lines of an inlet and exhaust valve. Particle image velocimetry images from a range of crank angles between inlet valve closure and the ignition point were interrogated by digital autocorrelation to give two-dimensional maps of instantaneous velocity. The in-cylinder flow is characterized by the formation of an ordered barrel swirl or tumbling vortex, which is shown to persist throughout the majority of the compression stroke with maximum velocities of the order of three times the mean piston speed and a high velocity bulk flow at the time of ignition near the spark plug. With respect to the PIV technique itself, image labelling and cross correlation are considered essential to improve measurement dynamic range, valid data rate and tolerance to velocity gradients in the turbulent flows encountered near top dead centre (TDC).