Heat Transfer in Engines: Comparison of Cars Thermal Boundary Layer Measurements and Heat Flux Measurements†

We have used broadband coherent anti-Stokes Raman scattering (CARS) to measure the gas temperatures near the cylinder head surface in an operating single-cylinder research engine. The CARS measurements were performed in both motored and fired engines at the bore half-radius position. A toroidal contoured head was used to allow laser probing to within 25-50 μm of the surface, and the spatial resolution of the measurements was approximately 50 μm. Two different shrouded intake valves were used to produce high and low swirl conditions which resulted in much different velocity boundary layers at me measurement location. The measured CARS profiles are quite different for the low and high swirl cases in the motored engine, but surprisingly similar for the two cases in the fired engine. The results indicate a distinct thickening of the boundary layer during the expansion stroke of the fired engine. The heat flux as a function of crank angle was also measured for the high and low swirl cases in the motored and fired engine at the CARS measurement location.