SOLID LUBRICANTS FOR AN ADIABATIC ENGINE

This paper presents a high temperature piston concept, whereby a conventional liquid lubricant in combination with a solid lubricant can potentially provide the total lubrication requirement at high temperatures. This concept utilizes a two-piece piston which consists of: 1) a low thermal conductivity piston crown which is lubricated by a solid lubricant piston ring and cylinder liner, and 2) a lower skirt section which is hydrodynamically lubricated by conventional liquid lubricant and conventional piston rings. This two-piece hybrid piston has been analyzed for functional operation using various solid liner materials. Analysis shows the combined effects of piston ring mass side angle groove relationship, location, face profile, tension, orifice area, and ring cross section on oil transport, blowby, and ring force between ring face and cylinder wall over the cycle. Solid lubricant cylinder and piston ring combinations investigated were NASA PS200 against Stellite 6B, chrome oxide against chrome oxide, and chrome oxide against Cu + LiF coating. The proposed hybrid design offers the potential of operation at over 427-degrees-C top ring reversal temperature without significant advances above conventional synthetic liquid lubrication. Moreover, it promotes an engine that operates with low fuel consumption and low emissions characteristics.