Infrared nondestructive measurement of thermal resistance between liner and engine block: design of experiment

Thermal resistances between liners and engine blocks are nondestructively studied by photothermal infrared thermography. Under controlled sinusoidal light irradiation, the thermal response of the sample is measured by means of an infrared camera. A numerical lock-in procedure yields amplitude and absolute phase maps of the thermal field periodic component. Then, apart from classical qualitative detection of air layers, a quantitative characterization of thermal resistance becomes available. An analytical modeling, associated with an inverse procedure using the Gauss-Newton parameter estimation method, allows to identify the thermal resistance on academic samples representative of the liner-engine block interface. Simply joined cast iron and aluminum plates present thermal resistances about 2×10−3Km2W−1. The implementation of a numerical modeling allows to study two-dimensional defects. When the samples are pressed on their periphery, thus straightened, contact resistances ranging from 2×10−4 to 7×10−4Km2W−1 have been measured. Then, the method is applied to liner-engine block interfaces where the thermal resistances fall to about 2×10−5Km2W−1, matching the values obtained when a cast iron plate is locally pressed against an aluminum plate.