Coatings for Increased Efficiency in Compression Ignition Engines

The use of thermal barrier coatings (TBCs) in reciprocating engines has been pursued for more than 40 years. While their introduction can be traced to reducing cooling in military vehicles, contemporary research focuses on improving fuel economy, reducing emissions, and enabling alternative fuels. Despite these benefits TBCs have seen little implementation due to the lack of consensus taken in the literature regarding their efficacy. Associated literature reveals a disconnect between the role of thermal transience, the necessary materials selection and processing controls, and the tuning of engine parameters for optimal performance. This is reflected in increased TBC surface temperature during intake causing heating of incoming gasses and reducing volumetric efficiency. Further, uncontrolled coating surface topography dramatically changes combustion characteristics which manifest as increased smoke, particulate, and NO_x emissions, particularly at high loads. In this collaborative study between Stony Brook University and US Army TARDEC material and architecture variations were studied in relation to thermal response and toughness. A laboratory designed thermal impulse test was used to simulate diesel engine transience and rapidly screen promising coatings. This integrated approach allowed for down selection of coatings and fabrication onto complex piston geometries with the most promising candidates finally subjected to engine testing.