Non-combustion non-solar deployment characterization of a free-piston Stirling engine to integrate with an exothermic reactor

Background: A small 1 kW free-piston β type Stirling engine was tested for its feasibility of integration with an exothermic reactor under the EU funded research project SOCRATCES (GA 727348). The engine’s heat receptor was minimally modified to adapt it to the reactor’s integration needs, introducing, instead of a combustion chamber, a CFD-optimized hooded enclosure. The open-loop configuration also included a small plate heat exchanger acting as a recuperator. The study attempted to investigate the performance of the Stirling engine under these non-combustion non-solar deployment conditions, focusing on conversion efficiency and thermal loss. Methods: A number of tests were run under different temperatures and flowrates to assess the engine’s response. Temperature, power, pressure and flowrate were measured at points of interest. Results: It was found that the engine is able to operate at efficiencies comparable to that of gasoline engines at much lower working fluid temperatures. It was possible to demonstrate, with the aid of a downstream recuperator, that the system in an open-loop configuration can minimize thermal loss significantly, virtually eliminating it in some cases. Conclusions: The Stirling engine appears to be a sound choice, in terms of conversion efficiency, at comparatively low temperatures, to be integrated with an exothermic reactor, at least at small-scale applications.

Thermodynamic modeling and controlling of a combined Free Piston Stirling Engine System (FPSE) with a Permanent Magnet Linear Synchronous Machine (PMLSM)

Converting thermal energy to electricity is one of the most common energy conversions in the field of electricity production. This transformation of energy is essential for both renewable and non-renewable heat sources. One of the main parameters of such a system that is responsible for this conversion is its efficiency. To have an efficient transformation, many improvements have been made to the old methods, and also new techniques were developed. One of these new methods that will be discussed here is a combined system of a Free Piston Stirling Engine (FPSE) with a Permanent Magnet Linear Synchronous Machine (PMLSM). The two purposes of presenting such a system are that firstly, the theoretical efficiency of a Stirling engine is high. Secondly, by eliminating crank-shaft from this system compared to the standard Stirling engine system, some of the losses will be removed. To study this system, a thermodynamic model of a RE-1000 FPSE was presented and validated. Then it was coupled with a PMLSM, and the combined system was controlled. The total efficiency of this system in steady-state is 14.4%.

A method for evaluating the heat rejection efficiency in a Lunar power plant consisting of a free-piston Stirling engine (FPSE)

A method for evaluating the heat rejection efficiency in a Lunar power plant consisting of a free-piston Stirling engine FPSE is proposed. The waste heat from the FPSE is absorbed by the refrigerant circulating in a closed pumped loop and then rejected through a radiator into space. The magnitude of the heat flux rejected through the radiator is determined by the temperature difference between the radiator fins and surrounding environment, as well as the surface areas of the radiator and the emissivity coefficient. The method developed is used to qualitatively evaluate the refrigerant efficiency based on calculating the average temperature of the radiator fin which is established during the heat exchange process in the radiator. The method allowed us to determine the most efficient refrigerant in terms of maximum heat rejection at a given operating temperature range without the need of detailed calculations like in the previous works of the authors. Computational studies in a two-dimensional formulation of the radiator, using helium or liquid ammonia as a refrigerant, to determine the quantitative characteristics of the heat rejection process and overall dimensions of the radiator were performed, and a comparative analysis of the results is presented.