Plasma Electrolytic Oxidation (PEO) Coatings as Superior Thermal Barriers for Engine Pistons

Automobiles (cars and trucks for instance) are the predominant mode of transportation in the United States. These vehicles are powered by internal combustion engines that consume fossil fuels such as gasoline. Improving the efficiency of internal combustion engines is an ongoing challenge of enormous impact to energy consumption in the world. In order to improve engine efficiency and thus fuel economy of vehicles, advanced thermal barrier materials are needed to improve thermal management of the engine. The primary objective of this project is to improve fuel economy by 2.0% or more by reducing thermal losses in engines. Plasma electrolytic oxidation will be used to form an extremely durable, thermal barrier coating on engine piston crowns. This thermal barrier on the engine pistons will drastically reduce the thermal losses of the engine, in turn substantially improving engine efficiency and fuel economy. In the Phase I effort, plasma electrolytic oxidation coatings will be developed on samples of relevant aluminum alloys (such as aluminum 4032) that match piston materials. These coatings will be evaluated for low thermal conductivity and high resistance to thermal cycling. After thorough testing, the most promising candidate coatings will be applied to piston crowns in a commercial production engine. An engine with unmodified pistons and the engine with coated pistons will both be tested, monitored, and compared for engine efficiency and fuel economy. The compared results will demonstrate the superior performance of the engine with coated pistons (greater than 2.0% improvement in fuel economy), indicating the effectiveness of the plasma electrolytic oxidation coating as a durable thermal barrier coating.After successful completion of the proposed project and subsequent industry-wide adoption of plasma electrolytic oxidation as the piston thermal barrier coating, engines will be manufactured with fuel efficiencies significantly improved over the current state-of-the-art. The benefits of such an achievement to society include reducing greenhouse gas emissions and increasing capital available for spending and investment. The adoption of these coating methods will also potentially increase the market share for domestic automotive manufacturers, which would increase job opportunities and increase the United States’ competitiveness. The passenger vehicle market alone accounts for the manufacture of about 10 million internal combustion engines in the United States each year. With reduced fuel consumption, early adopters of this technology can increase their market share by advertising this benefit to their customers. Durable plasma electrolytic oxidation coatings will also likely lead to reduced frequency of costly warranty issues due to inferior coating spalling/cracking, thermal fatigue and carbon buildup on piston surfaces. Even a small fractional increase in the average time-to-failure of piston coatings will translate into substantial savings to the manufacturer. The product of this program is likely of significant benefit to the Department of Energy’s Vehicle Technologies Office and supports its stated goal to achieve passenger car efficiency of 54.5 miles per gallon by 2025. Also, this technology is very likely to be of value to all branches of the military. Fuel efficiency and engine durability in military vehicles are both of great strategic value to sustaining defense operations.