Electrical Design and Operating Characteristics Study of a Dual-Opposed Free-Piston Stirling Generator

Abstract

In recent years, free-piston Stirling generators (FPSG) have drawn significant attention in the field of space nuclear power generation and distributed energy systems. A FPSG with a dual-opposed configuration enables reduced vibration and increased overall power density. So far, the electrical connection of the two linear alternators in dual-opposed FPSGs has not been specifically studied. Moreover, the operating characteristics of dual-opposed FPSGs remain poorly understood due to the complex heat transfer and flow interaction within it. In this work, a 3 kW dual-opposed FPSG prototype which is capable of integrating heat pipes was designed, fabricated and tested with the aid of computational fluid dynamics and thermoacoustics. To gain a deep understanding of the linear alternators’ electrical connection on the operation of the dual-opposed FPSG, the effect of two electrical connection methods of liner alternators on the system performance was compared numerically and experimentally. The obtained experimental results well validate the numerical model, with the maximum deviation of heat-to-electricity efficiency within 5% under different electrical connection modes. The dual-opposed FPSG operates consistently and reaches its rated power of 3 kW in both series and parallel connection modes, achieving a thermal-to-electric efficiency of 25.2%. While the series connection mode outperforms the parallel connection mode in terms of sensitivity and inconsistency. Based on the series connection mode, effect of key operating parameters, including charge pressure, load resistance and external capacitance on the system performance was investigated through experiments, which lays the groundwork for further comprehensive study of the inconsistency. The results reveal that when the external electric circuit of the alternators resonate, both the wall temperature of the hot end and the heat-to-electricity efficiency culminate, while the displacement of the power piston and damping temperature reach their minimum values. This work preliminarily unravels the complex characteristics of dual-opposed FPSGs and contributes to the understanding of high-performance dual-opposed FPSGs.

Keywords: dual-opposed, free-piston Stirling generator, electrical connection mode, operating characteristics