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.