Thermal Barrier Coatings for Reciprocating Engines: Engine Tests of Various Materials and Coating Architectures

A comprehensive investigation was performed probing the impact of piston thermal barrier coatings (TBCs) on the performance of a single-cylinder diesel engine at high-output operating conditions. A total of nineteen piston crown coating variants were tested in a single-cylinder research engine. Coatings were tailored to probe the role of specific attributes thought to affect engine performance, including coating thermal and mechanical properties, thickness, surface patterning, surface finish, combustion interactions with open pores in the coating, and radiative heat transfer. Further insights are drawn from coating characterization before and after engine testing. Global and in-cylinder thermodynamic measurements reveal no significant change that could be attributed to the presence of a coating. Conversely, tests of two TBC variants utilizing a piston instrumented with subsurface thermocouples revealed a 15 to 30°C reduction in piston temperatures. Temperature reductions were proportional to the coating thermal resistance, suggesting that the coatings may have some small impact on in engine heat transfer. While a limited impact on global engine parameters was observed, numerous insights ranging from the manufacturability and durability of coatings to possible benefits for alternative engine platforms are given that may help guide future engine designs and the integration of coatings.