High-speed high-resolution vector field measurements and analysis of boundary layer flows in an internal combustion engine.

摘要

Heat transfer properties vary locally and temporally in internal combustion engines due to variations in the boundary layer flow. In order to characterize the dynamics in the boundary layer, crank-angle resolved high-speed Micro Particle Image Velocimetry (muPIV) and Particle Tracking Velocimetry (PTV) have been used for near-wall velocity measurements in a spark-ignition direct-injection single cylinder engine. A 527 nm dual cavity green Nd:YLF laser was used for velocity measurements near the cylinder head wall between the intake and exhaust valves in the tumble mean flow plane parallel to the cylinder axis. A long distance microscope was used to obtain a spatial resolution of 45 mum. Flow fields were determined from 180 to 490 CAD in the compression and expansion strokes. The accomplished experiment represents first-time two-dimensional and a time history velocity measurements in a boundary layer flow in internal combustion engine. The data shows significant variation in the flow during the compression and expansion strokes and from cycle to cycle. Flow deceleration was observed during the end of the compression which continued during the expansion stroke until 400 CAD when the flow direction reverses. Submillimeter sized vortical structures were observed within the boundary layer over extended periods of time. Inner length and velocity scales were determined from the experimental results and were used to construct the law of the wall velocity distribution in the viscous sublayer and in the log law region. Experimental velocity profiles show agreement with the law of the wall in the viscous sublayer but they exhibit an early departure in the log law region due to the unique nature of the tumbling free stream flow in internal combustion engines. Reynolds stresses in the plane flow along with turbulent kinetic energy production and dissipation were determined.