Research on the piston dynamics and energy distribution characteristics of a free-piston Stirling generator: Numerical model and experimental results

The Free-piston Stirling generator (FPSG) is an advanced energy-conversion device known for its high thermal efficiency and compatibility with various heat sources. Understanding the piston dynamics and energy distribution characteristics in FPSGs is essential for improving their efficiency and output performance. Moreover, developing an accurate numerical model is crucial for precisely analysing the piston dynamics and energy distribution characteristics in FPSGs. Therefore, this study proposes a comprehensive numerical model integrating nonlinear dynamics, electromagnetism, and thermodynamics to investigate the piston dynamics and energy distribution characteristics in the FPSG. The simulation results showed good agreement with experimental data, with a maximum deviation of only 5.3 %. At a temperature difference of 500 K and an initial charge pressure of 3.5 MPa, heat loss accounted for 37.6 %, mechanical loss for 20.8 %, hysteresis loss for 3.0 %, leakage loss for 7.3 %, and generator loss for 3.6 %. When the hot-end temperature increased from 764 K to 864 K, the overall efficiency of the FPSG increased from 24.5 % to 34.3 %. In contrast, the overall efficiency decreased from 30.1 % to 26.4 % as the initial charge pressure increased from 2.5 MPa to 4.5 MPa. Additionally, a higher damping coefficient of the power piston led to reduced overall efficiency.