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A theoretical model of radiation heat transfer has been developed. A computation of radiation heat flux at a particular location in the combustion chamber by using the present model requires in-cylinder time- and space-resolved species data and cylinder pressure. From the species data, the burned fuel/air ratio distribution is inferred to compute space-resolved adiabatic flame temperature. For the computation of the spectral emissivity of an isothermal volume of adiabatic temperature containing soot, the Rayleigh-limit expression is used. The refraction indices in the expression are obtained by using the dispersion equations based on the electronic theory encompassing both free and bound electrons. For the spectral emissivity from the gaseous component in the volume, the semi-empirical band model is used.

The instantaneous heat transfer through the piston was measured in a motored direct injection-type diesel engine. The engine piston was equipped with a fast-response thermocouple on the surface and at a specified distance below the surface thermocouple at a number of locations. In order to record and process the measurement of temperature and cylinder pressure, a personal computer (PC)-based data acquisition system was connected to the probes, A special linkage device was designed and implemented to connect the thermocouple wires between the bottom of the connecting rod and a stationary point on the oil pan. The surface heat flux was calculated using a one-dimensional conduction model with the measured temperature boundary conditions. The in-cylinder pressure data was used to calculate the cylinder air temperature and the instantaneous film heat transfer coefficient was calculated by using those in-cylinder measurements.