Momentum Near-wall Region Characterization in a Reciprocating Internal-combustion Engine

Abstract

Accurately modeling the transfer of mass, momentum, and energy through engine near-wall regions is critical to achieving the long-standing goal of predictive engine simulations. This work presents the first planar near-wall velocimetry measurements to be recorded in a fired engine, the first near-wall velocimetry measurements to be recorded at the piston surface, the first planar near-wall velocimetry measurements to be recorded at multiple surfaces in the same engine, and expands the engine speed envelope of planar near-wall velocimetry measurements to higher engine speeds. These measurements were performed in an engine with well-characterized boundary conditions that serves as a reference and validation platform for researchers around the world. The velocimetry measurements were accompanied by head surface temperature and heat flux measurements. A unique particle image velocimetry (PIV) system was developed that both overcomes inherent experimental challenges in the engine used in this work, but also teaches general techniques broadly applicable to near-wall imaging in internal-combustion engines. The utility of an imaging system inclined towards the surface, specific selection of PIV processing parameters, and careful alignment of the vector grid to the surface are all shown to be important contributions to improve near-wall vector quality. High-resolution PIV measurements were taken in a 5- x 6 mm field of view at the head and piston surfaces. Measurements were recorded at engine speeds of 500- and 1300 rpm under both motored and fired conditions. High crank-angle resolution tests permit visualization of the variety of flow types imposed upon engine in-cylinder surfaces including wall-parallel flow, impinging jet-like flows, wall jet-like flows, and shear flows. The influence of the wall is observed to have an effect on the wall-normal velocity component farther from the wall than for the wall-parallel velocity component. Velocity magnitudes are found to be similar at the head and piston surfaces when the piston is stationary, but significant differences develop at high piston speed even after normalizing for the piston speed. The effects of inviscid compression are found to account for a significant portion of the observed wall-normal flow at the head and piston surfaces. These investigations are an essential effort towards the development of improved models for wall heat transfer in reciprocating internal-combustion engines.