PARTICLE IMAGE VELOCIMETRY MEASUREMENTS OF IN-CYLINDER FLOW IN A MULTI-VALVE INTERNAL-COMBUSTION ENGINE

Particle image velocimetry (PIV) has been used here to characterize th e formation and breakdown of barrel swirl or tumble in a production ge ometry, four-stroke, four-valve motored optical internal combustion (I C) engine. The engine was motored at 1000 r/min at wide open throttle. Double exposed images were recorded from a plane parallel to the cyli nder axis which passed through the centre-lines of an inlet and exhaus t valve. Particle image velocimetry images from a range of crank angle s between inlet valve closure and the ignition point were interrogated by digital autocorrelation to give two-dimensional maps of instantane ous velocity. The in-cylinder flow is characterized by the formation o f an ordered barrel swirl or tumbling vortex, which is shown to persis t throughout the majority of the compression stroke with maximum veloc ities of the order of three times the mean piston speed and a high vel ocity bulk flow at the time of ignition near the spark plug. With resp ect 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 e ncountered near top dead centre (TDC).