In-cylinder gas flow characteristics study of CI engine under motoring and pre-ignition firing conditions using a high-speed PIV

Engine properties such as engine speed and fuel injection quantity may affect the swirl flow of diesel engines. In this paper, experiments are conducted at two engine rpm and various operation conditions. For instance, motoring with no fuel injected, pre-ignition firing conditions, in addition to different fuel quantities. In this experimental analysis, PIV technique is performed to observe the flow patterns of the charging gas. The obtained results indicate that the swirls behavior is similar under all operation conditions during the intake and compression strokes regardless of the engine speed. In comparison to pre-ignition firing process, generation of more swirl centers has been observed for both engine speeds i.e., 1000 rpm and 1500 rpm under motoring conditions. Additionally, at CA of 610 deg., the swirls centers were maintained for all configurations except for motoring conditions and lowest fuel quantity of 2 mg. Moreover, during expansion strokes for both engine speeds the least magnitude of velocity-vectors was observed under motoring condition. Nevertheless, the higher mean velocity-vectors among that of expansion stroke was observed under pre-ignition firing configuration. The obtained results suggest that, the movement of the induced swirl centers across the piston cavity during expansion to exhaust strokes and increasing the engine speed corresponded to an increase in the mean-velocity, swirl ratios, and TKE