Abstract
Measurements of the integral length scale in a motored gasoline engine using different techniques and methods are described. An attempt is made to compare the length scales with and without contributions from cycle to cycle variations of the in-cylinder flow. A special evaluation technique developed for this purpose was applied using two-point LDV, Laser Doppler Velocimetry, and PIV, Particle Imaging Velocimetry. Length scales were obtained using both longitudinal and transversal correlation coefficients. Of particular interest was to investigate whether PIV could be used to generate similar results as the more established but rather elaborate two-point LDV technique. Also turbulence intensities obtained from the two techniques were compared. The LDV and PIV measurements were performed in the top of a motored 4-valve optical gasoline engine with pentroof design. It was shown that velocity fluctuations are substantially lower if cyclic variations of the cylinder flow are excluded and that results obtained for the turbulence intensity are similar using PIV and LDV. Using the special evaluation technique also measured length scales are very similar using PTV and LDV indicating that the less elaborate PFV technique is a useful tool for length scale measurements.
