A Study of Velocities and Turbulence Intensities Measured in Firing and Motored Engines

Laser Doppler velocimetry was used to make cycle-resolved velocity and turbulence measurements under motoring and firing conditions in a ported homogeneous charge S.I. engine. The engine had a flat pancake chamber with a compression ratio of 7.5. In one study, the effect of the intake velocity on TDC turbulence intensity was measured at 600, 1200, and 1800 rpm with three different intake flow rates at each speed. The TDC swirl ratio ranged from 2 to 6. The TDC turbulence intensities were found to be relatively insensitive to the intake velocity, and tended to scale more strongly with engine speed. For the combustion measurements, the engine was operated at 600, 1200, and 2400 rpm on stoichiometric and lean propane-air mixtures. Velocity measurements were made in swirling and non-swirling flows at several spatial locations on the midplane of the clearance height. The TDC swirl ratio was about 4. The measurements were made ahead, through, and behind the flame. The turbulence intensities and swirl velocities were found to scale approximately linearly with engine speed. In general, the turbulence intensity ahead of the flame was found to be little different from that measured in non-firing cycles and under motored conditions, but increased across the flame. The turbulence intensity in the burned gas was found to be homogeneous and showed a rapid rate of decay. Velocities and turbulence intensities were also measured in regions close to the cylinder and piston surfaces. The tangential component was measured as close as 0.5mm from the cylinder wall, and the radial component as close as 1.5mm from the wall. A very thin boundary layer was found both with and without combustion. The turbulence intensity increased sharply near the cylinder wall, but not near the piston surface.