Low Heat Capacitance Thermal Barrier Coatings for Internal Combustion Engines

A new generation of low heat capacitance Thermal Barrier Coatings (TBCs) has been developed under U.S. Dept. of Energy / Advanced Research Projects Agency - Energy (ARPA-E) sponsored research. The TBCs developed under this project have significantly lower thermal conductivity of < 0.35 W/m-K, thermal heat capacitance of < 500 kJ/m³-K, and density of <0.35 g/cm³. Two different binder types were used for thermal barrier coatings applied by High Velocity Low Pressure (HVLP) spraying to the piston, cylinder head, and valve combustion surfaces of a small natural gas engine. The effects of thermal barrier coatings on engine efficiency and knock characteristics were studied in a small, high compression ratio, spark-ignition, internal combustion engine operating on methane number fuels from 60 to 100. The new TBCs with low thermal conductivity and low thermal heat capacities have been shown to increase overall engine efficiency through reduced heat transfer to the piston and cylinder head. These improved TBC properties resulted in 1.3% improved thermal efficiency or a 4.6% reduction in fuel consumption on the natural gas engine through reduced heat rejection without loss of volumetric efficiency or increased engine knock. The coatings were also found to reduce all base metal temperatures by an average of > 10 °C and have been validated with 400 hours of engine durability testing.