EFFECTS OF INTAKE FLOW ON IN-CYLINDER SWIRL FLOW UNDER MOTORING AND FIRING CONDITIONS FOR CI ENGINES USING PIV MEASUREMENTS

The in-cylinder flow during intake and compression strokes in engines significantly affects the fuel-air mixing, combustion, and emissions. In this study, the in-cylinder swirl flow velocities in an optical single-cylinder combustion ignition (CI) engine were measured using particle image velocimetry (PIV) under various driving conditions. As a result, comparing motoring and firing, the flow structures for expansion and exhaust strokes differed but almost resembled for intake and compression strokes. To evaluate the intake and compression strokes, the flow velocities under motoring conditions were used. Comparing the maximum velocity under different engine speeds, it was found that the flow structure did not change significantly, but the flow velocity increased as the engine speed increased. The swirl centre position varied at each crank angle and showed a counter-clockwise trajectory, and the centre positions differed at each plane. These results indicate that different flow structures could be confirmed by changing the measurement plane. Furthermore, comparing the swirl ratio at a different helical port opening ratio, the swirl ratio increased as the opening ratio decreased. It suggested that the intake air from the helical port disturbed the large vortex structure and caused the swirl ratio to decrease. Additionally, comparing the swirl ratio when the measurement plane and intake port opening ratio were changed simultaneously, the order of in-cylinder average variance was Tan., 1/3 Heli., 1/2 Heli., and Double. When comparing the distance between the swirl centre and cylinder centre, and turbulent kinetic energy, it showed the same tendency as the swirl ratio