Design and performance of a 25-kWe free-piston Stirling space power demonstrator engine

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Design and performance of a 25-kWe free-piston Stirling space power demonstrator engine

Dhar, M. / Jones, D. / Huang, S. / Rauch, J.

The U.S. Government, under the NASA/OSAT SP-100 Advanced Technology Program, awarded a contract to Mechanical Technology Incorporated (MTI) in February 1984 to demonstrate the feasibility of key concepts of a Stirling space power demonstrator engine (SPDE). The objective of the SPDE program was to design, fabricate, and test a dynamically balanced, free-piston Stirling engine that operated at a heat exchanger temperature ratio of 2.0 and produced 25-kWe output at 25 % system efficiency, with a maximum specific weight of 8 Kg/kW. The SPDE power module has been tested over the entire operating range, demonstrating indicated power of 25 kW at 22 % indicated efficiency with very low casing vibrations. The net electrical power achieved has been 17 kW. Alternator bench tests and finite-element analysis indicate that the power deficiency is due primarily to eddy current losses in the alternator support structure. By substitution of nonmagnetic materials for components surrounding the alternator, an alternator design point efficiency as high as 90 % is anticipated. This paper summarizes the major design aspects of the SPDE and details the SPDE performance evaluation and the alternator loss evaluation.