Document Type

Theses, Ph.D


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An exploratory study of the combined Otto and Stirling cycle prime mover is presented. The Stirling cycle acts as the bottoming cycle on the Otto cycle
exhaust, the aim being the generation of additional mechanical power which may subsequently be converted to electrical power. It is postulated that the
increases in brake power and efficiency afforded by the addition of the Stirling cycle are of sufficient magnitude to offset the inherent increase in plant cost and
complexity. The analysis necessitated the development of thermodynamic models for both the Otto cycle and Stirling cycle engines and relationships to link the two together through the Stirling cycle hot-side heat exchanger. The models are derived using the principles of Finite Time Thermodynamics (FTT), a field which is considered to offer reasonably good simulation capability for a comparably low level of model complexity. The Otto cycle FTT model is
developed from an existing model available in the literature. The Stirling cycle FTT model represents a new contribution to the literature. Both models are
validated as part of the present work. They are subsequently combined using expressions derived for the Stirling cycle hot-end heat exchanger and the
combined performance is simulated. Finally a techno-economic analysis is performed to compare the economic performance of the combined system with
a base-case single cycle system; this is done for mono-generation and polygeneration
scenarios. It is seen from the analysis that the combined cycle system offers an economically attractive investment when analysed for Net
Present Value, Internal Rate of Return and Simple Payback Period.