Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: The aim of this study was to design and manufacture an experimentally testable
free-piston Stirling engine (FPSE), including a linear electric generator; to develop
and validate a theoretical simulation model; to identify problem areas pertaining
to its manufacture; and finally to assess the work undertaken, to lay out the
groundwork for the future development of a 3 kWe FPSE suitable for incorporation
in a solar Stirling dish power generator. A redesigned version of the Beale B-
10B demonstrator engine was manufactured to overcome design diffculties and
to simplify testing. The design made use of an electric generator designed at the
Department of Electrical and Electronic Engineering at Stellenbosch University.
Experimental measurements included piston and displacer motions, hot side and
cold side temperatures, working space pressure, electric generator output, as well
as heat rejection via a water jacket. Experimental measurements were taken prior
to and subsequent to the addition of the electric generator. Indicated power was
calculated as 0,659 W at a frequency of 10,99 Hz prior to the addition of the
electric generator. The addition of the electric generator was unsuccessful since
it was not well matched with the engine. The indicated power calculated was
between 0,138 W and 0,144 W for different loads on the electric generator, while
the electrical output power ranged from 1,23 mWe to 1,79 mWe. The addition of
the electric generator produced non-continuous motion caused by magnetic forces
instead of engine pressure variations. The major manufacturing diffculty was the
attachment of magnets for the electric generator, but this was overcome with the
manufacture of a special assembly jig. The theoretical simulation model was a
combination of a third-order and dynamic analysis. Working space values were
solved by the application of the conservation of mass, momentum and energy
equations for a one-dimensional discretised model of the engine, while the motion
of the piston and displacer was determined by applying the equations of motion.
The majority of experimental measurements were predicted more accurately when
higher heat transfer coeficients were used between the working space and wall temperatures. The theoretical simulation model was used to gain insight into the
effect of input parameters on engine operation. The displacer rod diameter was
shown to have implications on output power and stability, while it was shown that
there is a natural tendency to deliver constant output power at a near-constant
frequency over a range of piston loads for an FPSE. It was also shown that the
design of an FPSE is complex and that the design of all components should be
done in parallel. The control of an FPSE was seen to be both a necessity and can
be used to exploit the advantages of the uncoupled nature of an FPSE. / AFRIKKANSE OPSOMMING: Die doel van hierdie studie was om 'n eksperimentele toetsbare vrye-werksuier
Stirling enjin te vervaardiging, wat 'n lineêre elektriese kragopwekker insluit; om
'n teoretiese simulasie model te ontwikkel en te yk; om vervaardiging probleme
te identi seer; en om die ondernemende werk te assesseer om 'n fondasie te lê vir
die toekomstige ontwikkeling van 'n 3 kWe vrye-werksuier Stirling enjin wat by
'n Stirling sonskottel ingelyf kan word. 'n Herontwerpte weergawe van die Beale
B-10B demonstrasie enjin was vervaardig om ontwerp probleme te bowe te kom
en om die toets daarvan te vereenvoudig. Die ontwerp het gebruik gemaak van 'n
elektriese kragopwekker wat by die Departement Elektriese en Elektroniese Ingenieurswese
aan die Universiteit van Stellenbosch ontwerp is. Eksperimentele metings
het die werksuier en verplaser bewegings ingesluit, sowel as die warm kant en
koue kant temperature, die werkruimte druk, die elektriese uitset van die kragopwekker,
sowel as die hitteuitruiling wat met 'n water verkoelingskringloop gepaard
gaan. Eksperimentele metings was geneem voor en na die byvoeging van die elektriese
kragopwekker. Kraglewering was bereken op 0,659 W teen 'n frekwensie
van 10,99 Hz voordat die elektriese kragopwekker bygevoeg is. Die byvoeging van
die elektriese kragopwekker was onsuksesvol omdat die nie gepas was vir die enjin
nie. Die kraglewering is bereken op vlakke wat gewissel het tussen 0,138 W en
0,144 W vir die verskillende belastings op die elektriese kragopwekker, terwyl die
elektriese uitset gewissel het tussen 1,23 mWe en 1,79 mWe. Die byvoeging van
die elektriese kragopwekker het 'n nie-aaneenlopende beweging veroorsaak weens
die magnetiese kragte wat dit beinvloed het in plaas van enjindruk variasies. Die
belangrikste ontwerpuitdagings was die ontwerp van 'n werksuier en verplaser wat
'n klein toleransie passing kon handhaaf om sodoende 'n seël te verseker terwyl
dit aan temperatuur variasies blootgestel was. Die grootste vervaardigingsprobleem
was die aanheg van magnete vir die elektriese kragopwekker, maar dit is te
bowe gekom deur 'n spesiale voeg te vervaardig. Die teoretiese simulasie model
was 'n kombinasie van 'n derde-orde en 'n dinamiese analise. Werkruimte waardes was opgelos deur die toepassing van die behoud van massa, momentum en energie
vergelykings vir 'n een-dimensionele gediskretiseerde model van die enjin, terwyl
die beweging van die werksuier en verplaser bepaal was deur die toepassing van die
bewegingvergelykings. Die meerderheid van die eksperimentele metings was meer
akkuraat voorspel wanneer hoër warmteoordrag koë siënte tussen die werkruimte
en muurtemperature gebruik was. Die teoretiese simulasie model was gebruik om
insig in terme van die e ek van invoer veranderlikes op die enjin gedrag te toon.
Daar was getoon dat die verplaserstaaf diameter implikasies het op kragoplewering
en stabiliteit, terwyl die natuurlike tendens van 'n vrye-werksuier Stirling enjin
gewys was om 'n konstante kraguitvoer te lewer op 'n naby-konstante frekwensie
oor 'n reeks werksuier laste. Daar was ook gewys dat die ontwerp van 'n vryewerksuier
Stirling enjin kompleks is en dat die ontwerp van alle komponente in
parallel gedoen moet word. Die beheer van 'n vrye-werksuier Stirling enjin was
gewys om beide noodsaaklik te wees, sowel as gebruik kan word om die unieke
voordele van 'n vrye-werksuier Stirling enjin se ongekoppelde natuur te ontgin.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/95922 |
| Date | 12 1900 |
| Creators | Deetlefs, Ivan Niell |
| Contributors | Dobson, R. T., Stellenbosch University. Faculty of Engineering. Department of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xvi, 78, [43] p. : ill. |
| Rights | Stellenbosch University |
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