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Valve wear has been identified as a major durability problem in natural gas fueled reciprocating engines. Over the years, progress has been made to alleviate this problem through improved valve design and materials development. Recently high performance ceramics have shown promise for wear component applications. This paper presents the results of a valve train component materials investigation supported by the Gas Research institute. Testing tools and methods are described. The testing program culminated in a 300 hour component test in a full size turbocharged natural gas engine. Results of the engine test appeared to confirm preceding laboratory tests. Sintered silicon nitride valve seat inserts and Stellite 6 coated 21-12 stainless steel valves appeared to be the most promising material combination evaluated.

A new generation of Wankel rotary engines that can offer multifuel capability, increased fuel economy, and improved performance and reliability could have a profound influence on the design of future power plants for aircraft, automotive and other applications. The recent advances in adiabatic diesel engine technology have potential to improve the Wankel rotary engine. In this paper, the potential benefits of adiabatic Wankel engine and advanced concepts like- advanced turbochargers, high compression ratio, faster combustion, and reduced leakage have been assessed. A Wankel simulation model was used to predict performance of the adiabatic Wankel engine with these advanced concepts- predicting an overall improvement of 25.5% in ISFC and 34.5% in power output. Also, excellent multifuel capability of adiabatic Wankel engine is expected.

Cummins Engine Company, Inc. and the U.S. Army have been jointly developing an adiabatic turbocompound engine during the last nine years. Although progress in the early years was slow, recent developments in the field of advanced ceramics have made it possible to make steady progress. It is now possible to reconsider the temperature limitation imposed on current heat engines and its subsequent influence on higher engine efficiency when using an exhaust energy utilization system. This paper presents an adiabatic turbocompound diesel engine concept in which high performance ceramics are used in its design. The adiabatic turbocompound engine will enable higher operating temperatures, reduced heat loss, and higher exhaust energy recovery, resulting in higher thermal engine efficiency. This paper indicates that the careful selection of ceramics in engine design is essential.

This paper presents the results of an analytical study to identify the essential features of a futuristic engine for cars. A combination of several advanced features in one engine package results in a dramatic increase in the fuel economy of the car while maintaining all other essential features at comparable levels to current cars on the market. This advanced adiabatic diesel (AAD) engine is expected to give 78.8 mpg in the Federal Combined Driving cycle in a 3,000-pound vehicle. This compares to 37.7 mpg and 30.0 mpg obtained in current diesel and gasoline engine powered cars, respectively. The study identified the research and development efforts needed to bring this concept to fruition and concluded that an aggressive 10-year program will result in production availability of these cars.

Recent developments of high performance ceramics have given a new impetus for the advancement of heat engines. The thermal efficiencies of the Otto, Diesel, Brayton and the Stirling cycle can now be improved by higher operating temperatures, reduced heat loss, and exhaust energy recovery. Although physical and chemical properties of the high performance ceramics have been improved significantly, they still fall short of meeting the requirements necessary for application and commercialization of advanced heat engine concepts. Aside from the need for greater strength, the problems of consistency, quality, design, material inspection, insulative properties, oxidation and other important features must be solved before high performance ceramics can be considered a viable material for advanced heat engines. Several approaches in developing an adiabatic engine design in the laboratory are shown.