Investigation on gas-coupled vibration damping modules in free-piston Stirling generator

Abstract

The free-piston Stirling generator (FPSG) is efficient and environmentally friendly. However, the inherent vibration limits FPSG’s application and shortens its life. This paper presents two novel vibration damping modules, which are placed inside the FPSG with the vibration damping piston (VDP) driven by the pressure fluctuation in the back space. One is a passive vibration damping module (PVDM), and the other is an active vibration damping module (AVDM). By adjusting the movement of VDP, the sum of the momentums of the moving parts can be zero, thus eliminating the shell’s vibration. For PVDM, the movement of VDP is adjusted by changing the opening of a needle valve. For AVDM, it is adjusted by changing the electric power of the linear alternator. The performances of these two modules are investigated based on SAGE software. Both PVDM and AVDM enable FPSG’s shell to work without vibration under the design condition with minimal reduction of thermal-acoustic-electric conversion efficiency. When the damping coefficient of vibration damping piston, external load, and heating block temperature deviate from the design value, PVDM can reduce the vibration to a certain extent. AVDM can eliminate the vibration completely under any operating conditions. For this module, the acoustic power in the back space and the input electric power are its two main energy sources, and the input electric power is relatively small. The efficiency of the whole system is reduced by no more than 1% to eliminate the vibration. Adopting these two vibration damping modules can facilitate the application of the free-piston Stirling generator.