Abstract
Thermal conductivity and thermal diffusivity of combustion chamber deposits in an SI engine and a diesel engine have been measured to provide the data for analyzing heat transfer which is greatly reduced by the deposits. The deposits were built-up on surface thermocouples under different engine operating conditions. After removing the sooted surface thermocouples from the engines, the thermal properties were determined by the combination of several techniques. The results for the SI engine deposits show that the thermal conductivity is almost unchanged with engine speeds, loads and equivalence ratios, while the thermal diffusivity is influenced by the equivalence ratio. The thermal properties of the diesel engine deposits are shown to be nearly the same as those of the SI engine deposits formed in rich mixture operations.