Turbulence Intensity and Spatial Integral Scale During Compression and Expansion Strokes in a Four-Cycle Reciprocating Engine

A laser homodyne technique is applied to measure turbulence intensities and spatial scales during compression and expansion strokes in a non-fired engine. By using this techinique, relative fluid motion in a turbulent flow is detected directly without cyclic variation biases caused by fluctuation in the main flow. Experiments are performed at different engine speeds, compression ratios, and induction swirl ratios. In no-swirl cases the turbulence field near the compression end is almost uniform, whereas in swirled cases both the turbulence intensity and the scale near the cylinder axis are higher than those in the periphery. In addition, based on the measured results, the k-ε two-equation turbulence model under the influence of compression is discussed.