Browse Publications Technical Papers 2019-01-0228
2019-04-02

LOW HEAT CAPACITANCE THERMAL BARRIER COATINGS FOR INTERNAL COMBUSTION ENGINES 2019-01-0228

A new generation of TBCs has been developed under U.S. Dept. of Energy / ARPA-E sponsored research with the Wisconsin Engine Research Consultants, University of Wisconsin, Briggs & Stratton and Adiabatics, Inc. 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 gm/cm3. These improved properties resulted in 1.4% improved thermal efficiency on a small natural gas engine through reduced heat rejection without loss of volumetric efficiency or increased engine knock. The coatings were also found to reduce base metal temperatures by an average of > 10 °C and have been validated with 400 hours of engine durability testing.Thermal barrier coatings (TBCs) have long been studied as a means of more efficient Internal Combustion (IC) engines by minimizing thermal energy loss in the combustion chamber. TBCs can also raise exhaust gas temperatures which benefit aftertreatment systems from the additional exhaust energy. Early TBCs were thick and made from high heat capacitance materials which resulted in high entropy combustion energy being absorbed into the chamber wall and carried over into the exhaust and intake strokes. The high wall temperatures would result in poor combustion due to volumetric efficiency loss and changes in the fuel autoignition. Computer simulations in 1987 (SAE-870156) were used to show that lower heat capacitance and thin TBCs were more beneficial to engine performance. Only plasma sprayed zirconia coatings were available until the development of the Toyota SIRPA® coating in 2013 (SAE 2013-01-0274).

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