Improving the efficiency of engine performance will require the design of systems with higher operating temperatures and pressures. These conditions will stress traditional lubricants beyond their current performance capabilities, and require the development of improved methods for friction and wear reduction. The most revolutionary approach to high-temperature lubrication is the concept of vapor phase delivery. An ashless organic compound can be vaporized by the heat of the operating engine or a carrier gas, and introduced into the ring zone of the cylinder. The vapor condenses or chemically binds with the piston ring or cylinder wall, and provides boundary lubrication. A minute amount of lubricant is constantly introduced in order to maintain a lubricating film. Each stroke of the piston shears off a portion of the lubricant layer, but condensing vapor continually replaces the surface film. Lubricant contributions to exhaust emissions are expected to be lower than those currently resulting from liquid lubricants. Vapor phase lubrication is an emerging concept that may be the key to the development of a commercial low heat rejection engine with improved energy efficiency and reduced emissions. The Department of Energy continues to fund research at a variety of industrial and academic institutions. Basic concepts and recent developments in the field of vapor phase lubrication will be reviewed.

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