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In recent years, many attempts have been made to modify conventional thermal spray technologies to produce low cost alternatives to LPPS (Low Pressure Plasma System) and EBPVD (Electron Beam Physical Vapor Depostion). Gas shrouded plasma as developed by General Plasma and Praxair has had reasonable success. Gas shrouded plasma MCrAlYs, for instance have demonstrated capabilities in meeting certain turbine OEM LPPS specifications in terms of oxide content. However, there still remains concerns of gas shrouded plasma's reproducibility especially on complex geometric shapes like airfoils where turbulence can disturb the gas shroud and induce unacceptable levels of oxides. Studies at General Plasma in conjunction with several turbine OEMs suggest that HVOF may provide the solution. The highly stable and collimated HVOF flame, when coupled with a fuel-rich flame chemistry, is capable of producing low oxide MCrAlYs of high density and bond strength.

Ceramic thermal barrier coatings (TBCs), applied to diesel pistons, beads and valves, provide higher operating temperatures to improve thermal efficiency and control temperatures within the combustion chamber and exhaust systems. The results are advanced emission control of particulate matter, soot and smoke (opacity) and reduction of the damaging effects of heat to engine components. Management of the temperatures within the cylinder and exhaust systems is achieved by the ability of diesel ceramic coatings to reduce the amount of heat transferred from the combustion process into the engine components - an adjustment which improves the conditions for heat utilization, or removal, from the exhaust gases. Additionally, since engine components run cooler (under the ceramic coatings), the operating thermal stresses are reduced and engine operating life is increased.

Diesel ceramic coatings are now being applied to automotive engine components such as valves, pistons and heads to eliminate visible smoke, inhibit the formation of NOx, reduce CO and particulate emissions and improve combustion efficiency. Recently, specially designed software has been installed by trucking and transit companies to monitor the performance of the diesel ceramic coatings under actual operating conditions, with subsequent testing on EPA-certified dynamometers. The coatings are being evaluated for their ability to control particulate emissions (with and without particulate traps), for emissions in exhaust gases, for smoke, horsepower, speed in miles per hour, exhaust temperature and fuel rate in miles per gallon. These results, as well as the properties of the diesel ceramic coatings which effect these changes in diesel combustion, will be discussed.

Thermal barrier coatings (TBCs) have been employed for ten years in all types of diesel engines. TBCs have been used to reduce corrosion of pistons and valves, improve fuel efficiency, reduce pollution, allow use of lower quality fuels, improve cost start capability, reduce maintenance costs, improve power and improve lube oil life. Recently much interest has been demonstrated by transit operators in TBCs for pollution control and fuel economy results. A summary of the experience to date, current bus-related activities and advancements in thermal barrier coatings will be discussed. Diesel TBCs (thermal barrier coatings) are plasma-applied ceramic coatings which insulate combustion components such as pistons, valves and fire decks from thermal transmission and shock. Similar coatings have been effectively used in the aerospace industry for many decades.