Simulation of Temperature Fluctuations in Stirling Engine Regenerator Matrices

The objective of this study has been to create a model for studying the effects of fluctuations in regenerator matrix temperatures on Stirling engine performance. A one-dimensional model with axial discretisation of engine components has been formulated using the balance equations for mass, energy, and momentum and the ideal gas equation of state. ODEs that govern the dynamic behaviour of the regenerator matrix temperatures are included in the model. Known loss mechanisms are coupled directly into the governing equations instead of applying the losses as corrections to simulation results from an idealised model. Steady state periodic solutions to the model are found using a custom built shooting method that finds solutions that simultaneously satisfy cyclic boundary conditions and integral conditions. It has been found that true steady state periodic solutions to the model can be reliably and accurately calculated. Simulation results have been compared to experimental data for a 9 kW Stirling engine and reasonable agreement has been found over a wide range of operating conditions using Helium or Nitrogen as working gas. Simulation results indicate that fluctuations in the regenerator matrix temperatures have significant impact on the regenerator loss, the engine power output, and the cycle efficiency.