Design, simulation, manufacture and testing of a free-piston Stirling engine

[摘要] ENGLISH ABSTRACT: The aim of this study was to design and manufacture an experimentally testablefree-piston Stirling engine (FPSE), including a linear electric generator; to developand validate a theoretical simulation model; to identify problem areas pertainingto its manufacture; andfinally to assess the work undertaken, to lay out thegroundwork for the future development of a 3 kWe FPSE suitable for incorporationin a solar Stirling dish power generator. A redesigned version of the Beale B-10B demonstrator engine was manufactured to overcome design diffculties andto simplify testing. The design made use of an electric generator designed at theDepartment of Electrical and Electronic Engineering at Stellenbosch University.Experimental measurements included piston and displacer motions, hot side andcold side temperatures, working space pressure, electric generator output, as wellas heat rejection via a water jacket. Experimental measurements were taken priorto and subsequent to the addition of the electric generator. Indicated power wascalculated as 0,659 W at a frequency of 10,99 Hz prior to the addition of theelectric generator. The addition of the electric generator was unsuccessful sinceit was not well matched with the engine. The indicated power calculated wasbetween 0,138 W and 0,144 W for different loads on the electric generator, whilethe electrical output power ranged from 1,23 mWe to 1,79 mWe. The addition ofthe electric generator produced non-continuous motion caused by magnetic forcesinstead of engine pressure variations. The major manufacturing diffculty was theattachment of magnets for the electric generator, but this was overcome with themanufacture of a special assembly jig. The theoretical simulation model was acombination of a third-order and dynamic analysis. Working space values weresolved by the application of the conservation of mass, momentum and energyequations for a one-dimensional discretised model of the engine, while the motionof the piston and displacer was determined by applying the equations of motion.The majority of experimental measurements were predicted more accurately whenhigher heat transfer coeficients were used between the working space and wall temperatures. The theoretical simulation model was used to gain insight into theeffect of input parameters on engine operation. The displacer rod diameter wasshown to have implications on output power and stability, while it was shown thatthere is a natural tendency to deliver constant output power at a near-constantfrequency over a range of piston loads for an FPSE. It was also shown that thedesign of an FPSE is complex and that the design of all components should bedone in parallel. The control of an FPSE was seen to be both a necessity and canbe used to exploit the advantages of the uncoupled nature of an FPSE.

[发布机构] Stellenbosch University