Proposed Otto Cycle/Stirling Cycle Hybrid Engine Based Power Generation System

The generation of electrical and thermal power is a matter of critical importance to the modern world. Considerable quantities of both power types are required in all sectors of society; industrial, domestic and leisure, with the future prosperity of both developed and developing societies being dependant on generation of both a sufficient quantity and quality of power. Central to this discussion on the international front is the topic of fossil fuel usage. Despite considerable advances in renewable energy conversion technologies, the human race remains dependant on fossil fuels as a primary energy source. With increasing demand for these finite resources giving rise to strained international relations and economic uncertainty, emphasis has fallen on optimization of usage patterns. The area of power plant efficiency is essential to this optimization. This paper proposes a method for increasing the efficiency of an Otto cycle engine based plant as is typically used in CHP and other Distributed Generation scenarios. The method proposed is to utilise a Stirling cycle engine as a heat recovery device on the exhaust stream of the Otto engine. Thermal energy that may otherwise be lost would thereby be recovered and used to generate additional electrical power. In this manner energy is effectively diverted from the exhaust flow of the engine and converted to mechanical work by way of the Stirling cycle engine. It is postulated that this combined cycle will yield higher plant efficiency than the Otto engine alone. This paper introduces work completed to date and an experimental plan for the project. The project was initiated at undergraduate level as a feasibility study for application of the hybrid engine in automotive circumstances. The study suggested that the combination of the engines in the proposed manner was indeed feasible, with significant power gains possible. However, it proved unlikely that automotive application was the best use of the system unless certain constraints were addressed. Therefore, it was decided to pursue the concept in terms of a stationary generation system. The advantages of the stationary system over the automotive system are addressed briefly, with the constraints of the automotive scenario analysed and their relevance to the stationary generation situation examined. The central areas under investigation are detailed, including thermodynamic theory pertaining to the Otto cycle and Stirling cycle engines, and the combined cycles. Possible limiting factors to the design are discussed also.