Abstract
Unlike internal combustion engines, Stirling engines can be designed to work with many drive mechanisms based on the three primary configurations, alpha, beta and gamma. Hundreds of different combinations of configuration and mechanical drives have been proposed. Few succeed beyond prototypes. A reason for poor success is the use of inappropriate configuration and drive mechanisms, which leads to low power to weight ratio and reduced economic viability. The large number of options, the lack of an objective comparison method, and the absence of a selection criteria force designers to make random choices. In this article, the pressure—volume diagrams and compression ratios of machines of equal dimensions, using the main (alpha, beta and gamma) crank based configurations as well as rhombic drive and Ross yoke mechanisms, are obtained. The existence of a direct relation between the optimum compression ratio and the temperature ratio is derived from the ideal Stirling cycle, and the usability of an empirical low temperature difference compression ratio equation for high temperature difference applications is tested using experimental data. It is shown that each machine has a different compression ratio, making it more or less suitable for a specific application, depending on the temperature difference reachable.
Highlights
The environmental and social issues derived from the link between energy consumption, currently satisfied mostly by fossil fuels, and ethnographic and economic growth [1], can only be addressed by a growing share and diversification of renewable energy sources (RES) [2]
A bigger share of RES has the potential of promoting sustainable economic growth, and biomass and geothermal energy usage has been identified as primary contributors [3]
The main parameter considered in the current study, the compression ratio calculated from the machine’s kinematics, is first shown, along with the ideal compression ratio as given by Equation (36) and the compression ratio calculated with Ivo Kolin’s formula (Equation (37))
Summary
The environmental and social issues derived from the link between energy consumption, currently satisfied mostly by fossil fuels, and ethnographic and economic growth [1], can only be addressed by a growing share and diversification of renewable energy sources (RES) [2]. A bigger share of RES has the potential of promoting sustainable economic growth, and biomass and geothermal energy usage has been identified as primary contributors [3]. In order to increase the share of RES in the global energy production, it is necessary to explore all the technologies available. Stirling machines have had a wide range of application attempts since their appearance. Electric generation and co-generation [4], waste heat and wasted fuel recovery [5], high temperature difference (∆T) [6] and low ∆T [7] solar power, solar energy storage [8], biomass and geothermal, to refrigeration and cryogenics. Due to several factors few of these attempts have succeeded and reached a commercial stage, of these factors the main are their inherent low power to weight ratio if compared with internal combustion machines, their poor empirical performance compared with their theoretical performance [11], and the lack of policies
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