The Determination of Thermal Properties of Engine Combustion Chamber Deposits

Thermal conductivity and thermal diffusivity of combustion chamber deposits in an s. i. engine and a diesel engine were determined by measuring thickness, response time to a radiation pulse, time-varying deposit surface temperature and deposit-wall interface temperature. The results show that, for the s. i. engine deposits formed with a stoichiometric mixture of unleaded gasoline, the thermal conductivity is hardly influenced by engine load, speed and equivalence ratio, and that thermal diffusivity depends on equivalence ratio, but hardly depends on engine load and speed. The test result with unleaded gasoline containing lubricating oil indicates that the thermal properties are sensitive to the lubricating oil content and depend considerably on engine load. The thermal properties of diesel deposit are the first data that have been presented. The result show that the thermal conductivity depends on engine load and is larger in general than that of s. i. engine and that the thermal diffusivity has no meaningful dependence on engine load and is larger than that of s. i. engine operated with stoichiometric mixture of unleaded gasoline.