Heat Transfer into Ceramic Combustion Wall of Internal Combustion Engines

An Investigation of Metal and Ceramic Thermal Barrier Coatings in a Spark-Ignition Engine

“…In addition to surface roughness, there are at least two other possible explanations for why the TBCs did not reduce overall heat transfer. First, as suggested by Furuhama and Enomoto [4] and Woschni et al [6], higher temperatures at the coating surface may increase the convective heat transfer coefficient because of thinning of the thermal boundary layer. A higher coefficient could increase heat transfer despite a smaller temperature difference between the gas and wall.…”

“…The copper performs the same function as it did with the Furuhama and Enomoto thermocouple [4], that being to conduct heat away from the tip of the constantan wire to the aluminum substrate. Thus, the copper helps to equalize the temperature of the constantan and the aluminum substrate, allowing the thermocouple to measure true temperatures much more accurately.…”

“…Furuhama and Enomoto covered the piston crown with a 4.5 mm SN disk over an air gap to raise the average surface temperature by several hundred degrees K [4]. Surface temperature measurements found that heat flux into the insulated piston crown was higher during the expansion stroke compared to an aluminum alloy piston.…”

“…Furuhama and Enomoto developed a different coaxial thermocouple which their analysis found to be very accurate at measuring temperature swings [4]. The design featured a 3 mm aluminum cylinder with a 0.17 mm hole drilled through to house an insulated constantan wire.…”

“…Thermal conductivities (k) have ranged from less than 0.5 W/m·K [2] to 10 W/m·K [3], and thicknesses have ranged from 0.1 mm [2] to 4.5 mm [4]. Ceramic coatings can be applied by a variety of methods, although thermal spraying techniques such as plasma spray are the most common [5].…”