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In support of development efforts for advanced heat engines, self-lubricating materials were evaluated for their friction and wear characteristics above 260 C. The work focused on the ring/cylinder interface and tested self-lubricating ring or cylinder specimens against plasma-sprayed chromia or other ceramic materials. Three materials were chosen for the evaluation. Two of them were solid lubricant compacts, and one was a self-lubricating coating. The compacts were the Westinghouse (Boes) compact and a commercially available molybdenum disulfide-based composite. The coating consisted of a wear-resistant matrix filled with solid lubricating materials to reduce friction. The Boes compact resulted in high temperature friction and wear results that were in some cases equal to or better than those of earlier tests run with liquid lubrication. The other compact and the coating both had much higher wear and coefficients of friction than the Boes compact.

A Minimum Cooled Engine (MCE) has been successfully run for 250 hours at rated condition of 298 kW and 1900 rpm. This engine was all metallic without any coolant in the block and lower part of the heads. Ring/liner/lubricant system and thermal loading on the liner at top ring reversal (TRR) as well as on the piston are presented and discussed. Ring/liner wear is given as well as oil consumption and blow-by data during the endurance run. Another engine build with a different top ring coating and several lubricants suggested that a 1500 hours endurance run of MCE is achievable. Rig test data for screening ring materials and synthetic lubricants necessary for a successful operation of a so-called Adiabatic Engine with the ring/ceramic liner (SiN) interface temperature up to 650°C are presented and discussed.

In support of efforts to apply ceramics to advanced heat engines, a study was performed of the wear mechanisms of ceramics at the ring/cylinder interface. A laboratory apparatus was constructed to reproduce most of the conditions of an actual engine, but used easily prepared ring and cylinder specimens to facilitate their fabrication. Plasma-sprayed coatings of Cr2O3 and hypersonic flame-sprayed coatings of cobalt-bonded WC performed particularly well as ring coatings. Similar performance was obtained with these coatings operating against SiC, Si3N4, SiC whisker-reinforced Al2O3, and Cr2O3 coatings. The study demonstrated the critical need for lubrication and evaluated the performance of two available lubricants. SIGNIFICANT EFFICIENCY IMPROVEMENTS have been predicted resulting from the practical application of low-heat-rejection engines (1,2).