A STUDY OF VELOCITIES AND TURBULENCE INTENSITIES MEASURED IN FIRING AND MOTORED ENGINES (LASER, COMBUSTION)

Laser Doppler velocimetry has been used to make cycle-resolved velocity and turbulence measurements under motoring and firing conditions in a ported two-stroke homogeneous charge S.I. engine, and motoring measurements in a valved engine. Turbulence intensities in the valved engine were found to be less than in the ported engine due to lower intake velocities and longer decay times. The effect of the intake velocity on TDC turbulence intensity was measured. Velocity and turbulence measurements were made at three engine speeds for three different intake flow rates in the ported engine. The goal was to determine whether intake velocity or engine speed plays a greater role in determining the magnitude of the TDC turbulence intensity. The TDC turbulence intensities were found to be relatively insensitive to the intake velocity at constant engine speed, and tended to scale more strongly with engine speed for a given mass flow rate. For the combustion measurements, the engine was operated at Speeds of 600, 1200, and 2400 rpm on stoichiometric and lean propane-air mixtures. Velocity measurements were made in swirling and non-swirling flows. The measurements were made ahead, through, and behind the flame in an effort to determine the effect on the combustion on engine turbulence. The turbulence intensities and swirl velocities were found to scale approximately linearly with engine speed. The turbulence intensity ahead of the flame was found to be little different from that measured in non-firing cycles and under motored condition. The turbulence intensity was found to increase 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 as close as 0.5mm from the cylinder wall in both firing and non-firing cycles. It was found that a very thin boundary layer exists both with and without combustion. The turbulence intensity increased sharply near the wall indicating a significant amount of wall generated turbulence.