Novel Thermal Barrier Coatings for Gasoline Spark Ignition Engines

Currently spark ignition (SI) engines dominate the light vehicle market, with over 80 million light vehicle engines made worldwide. These SI engines experience exceptionally poor efficiency at low to medium loads and speeds, making it difficult to meet new fuel efficiency standards expected to be imposed in many countries. Low wall temperatures at the end of the combustion process leads to emissions of unburned hydrocarbons (UBHC), and carbon monoxide (CO) in the engine exhaust, raising environmental concerns. Therefore, there is a significant push by vehicle manufacturers to find effective solutions to improved IC engine efficiency, while simultaneously reducing emissions. A promising way to address the economic and environmental challenge of SI engines is to adopt thermal barrier coatings (TBCs). With the application of TBCs, the heat loss to the piston and the cylinder head can be substantially reduced, leading to higher temperatures in the combustion chamber, which will increase the thermal efficiency of the engine work cycle. The increased coating surface temperatures will also improve oxidation of the charge emanating from the top-land crevices, thereby reducing emission of UBHC and, CO. The hotter exhaust also aids NOx reduction after treatment. The SST/CUICAR team identified and demonstrated a novel TBC with ultra-low thermal conductivity(<1/3rd of state of the art yttria stabilized zirconia) and a high coefficient of thermal expansion that better matches that of the aluminum engine components. This TBC was applied to engine pistons, road tested in a BMW motorcycle, and showed excellent durability. Pistons with a complex geometry were coated and tested in a highly instrumented Buick Regal. This testing demonstrated up to a 2% thermodynamic efficiency improvement and over a 20% reduction in UBHC emissions, when compared to the same engine run with uncoated pistons. The SST/CUICAR team will further develop the ultra low thermal conductivity TBC material demonstrated in Phase I to increase its commercial potential by 1. By replacing the solution precursor plasma spray process used in Phase I with the commercial air plasma spray to markedly increase process robustness and reduce coating cost. 2. By conducting modeling studies to determine the performance benefits of coating additional engine components, such as valves and cylinder heads. and selecting the ones with the highest additional benefit for coating and testing. 3. Validating the technology by coating at least three different engine components and conducting both highly instrumented single cylinder and four-cylinder engine tests to demonstrate performance and emission improvements, including during cold starts. SI engines dominate the 230-million unit internal combustion engine market worldwide, and the projected engine efficiency achieved by this TBC technology will bring significant economic benefits to US consumers, US manufacturers and positive environmental impact. The technological advantage of more efficient IC engines also strengthens the competitiveness of US engine manufacturers in the global market, which will result in new high-paying domestic jobs.