Micro particle image velocimetry investigation of near-wall behaviors of tumble enhanced flow in an internal combustion engine

A micro particle image velocimetry has been performed to investigate tumble enhanced flow characteristics near piston top surface of a motored internal combustion engine for three inlet valve open timing (−30, −15, 0 crank angle degrees). Particle image velocimetry was conducted at 340, 350 and 360 crank angle degrees of the end of the compression stroke at the constant motored speed of 2000 r/min. The measurement region was 3.2 mm × 1.5 mm on the piston top including central axis of the cylinder. The spatial resolution of particle image velocimetry in the wall-normal direction was 75 µm and the vector spacing was 37.5 µm. The first velocity vector is located about 60 µm from the piston top surface. The micro particle image velocimetry measurements revealed that the ensemble-averaged flow near the piston top is not close to the turbulent boundary layer and rather has tendency of the Blasius theorem, whereas fluctuation root-mean-square velocity near the wall is not low. This result shows that revision of a wall heat transfer model based on an assumption of the proper characteristics of flow field near the piston top is required for more accurate prediction of heat flux in gasoline engines.