Experimental studies on atmospheric Stirling engine NAS-2

Atmospheric hot air Stirling engines NAS-1 and 2 have a simple flat rubber sheet diaphragm as their power piston, and have been experimentally studied at Nihon University, Japan, for several years continuously, with the target of obtaining more than 100 watts shaft power by atmospheric air with simple construction and cheap materials. The first NAS-1 was intended to be a solar heated engine using television glass and wood for cheap cost, but it failed by thermal breaking of glass, so the improved NAS-2 has changed to be heated by a gas burner, using metallic materials in all parts except for the rubber power piston. Other than this rubber sheet diaphragm, NAS-2 has many features such as using the James Watt crank mechanism, highly finned copper tubes for conventional commercial heat exchangers and two kinds of hot gas heaters. The thickness of the power piston rubber sheet was gradually changed from 2 mm to 6 mm in order to determine which thickness was best; it was found that about 5 mm is best for this engine. After trying many improvements on this engine, NAS-2 has produced about 130 watt shaft power an with indicated power of 350 watt at 1994. In this paper, details of many features, history, results and experiments carried out these NAS Stirling engines are reported.