Design of a New Medium-temperature Stirling Engine for Distributed Cogeneration Applications

This paper presents and discusses the design and first prototype realization for a brand new generation of Stirling engines. This unit is realized within the DiGeSPo Project, in which it is coupled with a small-size parabolic trough concentration solar field. The engine is conceived for working with low-temperature heat sources (200-300 ̊C), in order to match the typical temperatures for the solar field itself.The first part presents the thermodynamic design, which is realized by using models and simulations, and give the specifications for each component, including pistons dimensions; the number, length, diameter for the heat exchangers tubes; regenerators porosity, length and diameter. Four independent and equally working spaces were chosen, as a compromise between the compactness of the overall system, limits imposed by the maximum charging pressure, and the target electrical power (3 kW). The parameters of the overall system were optimized during this phase with an iterative procedure, taking into account different concurrent constraints, such as the heat exchange requirements, mechanical friction power losses, and small dead spaces. The engine has been subsequently arranged in a double-acting mechanical configuration, in which the cylinders are opposed as in a boxer engine. This configuration gives the advantages of reducing leaking losses and can work with four pistons. The heat exchangers, which are the most crucial and complex components, have been realized by the Selective Laser Melting (SLM) manufacturing technique.The specific scientific and technical details related to a low-temperature Stirling engine, and the solutions adopted, are discussed and presented trough the paper, and finals recommendations are provided.