Simultaneous High-speed and High-resolution PIV and Heat Flux Measurements near Piston Top under Tumble Enhanced Condition

Simultaneous measurements of high-speed high-resolution particle image velocimetry near the piston top with spatial resolution of 152 × 76 μm at 24 kHz and a micro-electro-mechanical-systems (MEMS) heat flux sensor on the piston surface was conducted in a motored optical gasoline engine with enhanced tumble flow for 2000 rpm. Characteristics of mean velocity profiles are discussed based on fitting to the turbulent and laminar boundary layers with conditioning by momentum. It has been found that the velocity profile of high momentum tends to be close to that of turbulent boundary layer, while its probability is not large. Cross correlation between maximum heat flux in each cycle and velocity in the piston-surface normal direction shows that heat flux is 3 CAD behind the velocity, which corresponds to about 0.25 ms. Also it is found that the correlation coefficient shows higher value at 0.50 mm from the piston wall rather than that at 0.27 and 0.12 mm with the delay of 3 CADs for heat flux. Furthermore, cross correlation coefficient of fluctuating components of heat flux and velocity shows also the similar tendency.