Tumble Flow and Turbulence Characteristics in a Small Four-Valve Engine

An experimental study on the tumble flow and turbulence characteristics in a small four-valve engine has been performed to provide better understanding of the formation and decay mechanisms of tumble and its effects on turbulence. The detailed comparison of the decay mechanisms of tumble during compression by means of two newly defined non-dimensional parameters, in addition to the tumble moment, has been effectively performed. The turbulence was analyzed in terms of turbulence intensity, integral time scales, and integral length scale. With tumble flow, the turbulence intensity at the end of compression was found to increase twice and the turbulence field became more homogeneous. The turbulence integral time scale during the compression was found to be inversely proportional to the engine speed, regardless of existence of tumble flow. However, the integral length scale is strongly affected and increased by tumble flow.