A Study of Cyclic Variations in Gas Velocities in an Engine Cylinder

Measurements of the magnitude of the instantaneous velocity components were taken within the combustion chamber of a four-valve head using a triaxial hot-wire probe. Cyclic variation in the “mean” flow was studied for operation with only the large inlet valve. Several groups of “similar” cycles having a time-averaged mean velocity within a specified range were obtained. The mean and rms velocities were estimated for each group using an ensemble averaging technique. The overall “corrected” turbulence intensity and the overall power spectral density function were also determined. The overall power spectra for different engine speeds were normalized by the engine speed and the overall “corrected” turbulence intensity.

Large cyclic variations in the levels of mean velocity and turbulence intensity were clearly demonstrated by the results. The turbulence intensity was found to be overestimated significantly by the ensemble analysis due to cyclic variations in the mean velocity. The normalized power spectra collapsed into one unique curve with negligible deviation.