LDV measurement and analysis of tumble formation and decay in a four-valve engine

Tumbling motion is very effective for turbulence enhancement during the compression process inside the cylinder of a four-valve engine. The tumble formation and decay mechanisms in a transparent four-valve engine were investigated by laser-Doppler velocimetry and analyzed by means of the tumble angular momentum and two nondimensional parameters, the tumble eccentricity and the shape factor in the tumble velocity profile. Three intake port configurations are compared and discussed. The results show that in the engine in which tumble decays rapidly during the compression process, the center of the tumble vortex is located above the instantaneous cylinder center and the tumble velocity profile tends more closely to a linear pattern.