A CFD analysis of the regenerator influence on the performance of alpha-type Stirling engine

The Stirling engine was invented and patented in 1816 by Scottish minister Robert Stirling. Basically, Stirling engine can be considered as an external combustion engine, which commonly can be powered by waste heat or solar energy. Combining this with high theoretical efficiency makes Stirling engine very interesting renewable source of energy. The paper presents Computational Fluid Dynamics (CFD) model of the alpha-type Stirling engine. Developed mathematical model comprises of Unsteady Reynolds Averaged Navier-Stokes (URANS) set of equations i.e. continuity, momentum and energy equations, turbulence was modelled using standard - model and was built in the framework of commercial CFD software ANSYS Fluent. Pistons walls movements were modelled using dynamic mesh capability in ANSYS Fluent, their movement kinematics was described based on the geometry of the crankshaft geometry and it was implemented in the model using user defined functions (UDF) written in C programming language and compiled with core of the ANSYS Fluent software. Moreover, developed mathematical model comprises non-equilibrium description of the regenerator, by introduction of the energy conservation equation for the regenerator matrix. Developed mathematical model was used to analyse influence of the regenerator on the performance of the Stirling engine. Specifically, heat transfer conditions between regenerator matrix and working fluid, pressure drop in the regenerator were investigated. Some results regarding covering internal structure of the regenerator filling and external regenerator geometry are also presented.