Test results on a free-cylinder Stirling engine

In the early 1980s Sunpower Incorporated of Athens, Ohio designed and built some prototype free-cylinder Stirling engine powered water pumps for use in rural areas. In 1988, one of the products of this development was donated to the University of Witwatersrand. This engine has been comprehensively instrumented and is in the process of being tested. A net output power of 40 W has been obtained from the engine, using helium at an absolute pressure of 1600 kPa as the working fluid and an external heater temperature of 624°C. The frequency of the engine was 33 Hz, and the case stroke was 6.8 mm. The piston and displacer motion, as well as the energy flow paths through the gas spaces, are discussed. This program has not been successful in producing an efficient stand-alone free-cylinder engine to date. A positive output power of 40 W for a helium-charged engine of this size is disappointing, especially since similar engines have produced approximately 100 W when charged with air