loss understanding efforts are being performed at MTI, Sunpower, the University of Minnesota (two grants), Case Western Reserve University in Cleveland, Ohio, and Gedeon Associates of Athens, Ohio. A more thorough treatment of the above mentioned loss understanding mechanisms is given in Ref. [8], Concluding Remarks Although Stirling technology is an emerging technology, there is considerable justified interest as to its potential candidacy for space power missions whether in the tens of kilowatt range or the multimegawatt range. In less than five years, under limited funding, the free-piston Stirling accomplishments have been significant. An opposed- piston engine has generated 25 kW of engine power while the engine efficiency was greater than 22% at a temperature ratio of 2.0. Engine vibration is exceedingly low. The integrated concept uses a linear alternator and provides a compact power conversion system. Gas bearings were successfully demonstrated on an engine power piston at design conditions. Results of a scaling study show that single-cylinder engines are feasible at power levels as high as 500 kW. There appears to be no technological breakthrough needed—only verification of system reliability and life and the timely solution of engineering problems in the areas of high efficiency linear alternators; gas bearings for the reciprocating components; heat-pipe heater heads for either nuclear- or solar-powered systems; and validation of design and performance codes over the complete range of desired power. A 1050 K engine design is underway and the design—with the exception of materials substitution—should be applicable for 1300 K application. The 1050 K engine should be subjected to an endurance test which will go a long way toward establishing credibility for Stirling space power. The codes for design and performance prediction are constantly being upgraded through fundamental understanding of engine losses. REFERENCES [1] Shaltens, R.K. (1987) Comparison of Stirling Engines for Use with a 25 kW Dish-Electric Conversion System, NASA TM-100111, DOE/NASA/33408-2. [2] Dochat, G.R. (1984) Free-Piston Stirling Engine for Space Power, Proceedings of the Twenty-Second Automotive Technology Development Contractors' Coordination Meeting, Society of Automotive Engineers, Warrendale, PA, pp. 209-213. [3] Slaby, J.G. (1986) Overview of Free-Piston Stirling SP-100 Activities at the NASA Lewis Research Center, NASA TM-87224, D0E/NASA/1OO5-8. [4] Slaby, J.G. (1987) Overview of Free-Piston Stirling Engine Technology for Space Power Application, NASA TM-88886, DOE/NASA/1005-12. [5] Slaby, J.G. & Alger, D.L. (1987) Overview of Free-Piston Stirling Technology for Space Power Application, NASA TM-89832. [6] Slaby, J.G. (1988) 1988 Overview of Free-Piston Stirling Technology for Space Power at the NASA Lewis Research Center, NASA TM-100795. [7] Schreiber, J.G. (1988) The Design and Fabrication of a Stirling Engine Heat Exchanger Module with an Integral Heat Pipe, NASA TM-101296. [8] Tew, R.C., Jr. (1988) Overview of Heat Transfer and Fluid Flow Problem Areas Encountered in Stirling Engine Modeling, NASA TM-100131.
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