Advanced Stirling Regenerator and Heat Exchanger Assembly for Stirling Generator of Radioisotope Space Power Systems

DOE NE-75 is seeking advanced radioisotope space power conversion systems in the 10-500 watt electric range to support NASA science missions. Current radioisotope thermoelectric generators (RTGs) for these applications are very reliable, but extremely inefficient. Due to the cost and limited availability of radioisotope fuel, robust and reliable dynamic power conversion systems are needed that can convert 25% or more of the radioisotope heat into useful electricity. PI for the proposed project and ITC/Qnergy developed free-piston Stirling engine based Technology Demonstration Convertors (TDC) which demonstrated outstanding robustness and reliability. Two TDC units have continued in operation at NASA Glenn Research Center for over 11 years and two others are approaching 10 years of operation with no maintenance and no performance degradation. In the proposed effort, the team that developed the TDC will retain the proven basic topology, but will develop an integrated foil regenerator/heat exchanger assembly, and upgrade the TDC with the new regenerator/heat exchanger assembly to increase the efficiency to near 30% without increasing the operating temperature or pressure, while further enhance the regenerator reliability. In Phase I, an integrated regenerator/heat exchanger assembly will be designed to upgrade the original Stirling convertor. A complete regenerator/heat exchanger assembly design and analysis, including full performance projections over the potential operating envelope, will also be conducted. Additive manufacturing will be applied to the fabrication of the regenerator/heat exchanger assembly. Additive manufacturing methods will be explored and identified. In Phase II, this design will be expanded to a final design that includes all manufacturing drawings and specifications. Additive manufacturing of the assembly, integration of the assembly with TDC heater head, testing and evaluation of upgraded TDC over its operating envelope will also be completed. The primary benefit of the proposed effort will be to demonstrate a practical approach to significantly increase the efficiency and reliability of free-piston Stirling convertor with state-of-art regenerator/heat exchanger assembly technology. This improved Stirling convertor can subsequently be refined into a high confidence flight system that can replace RTGs in many space science applications. The manufacturing methods and the regenerator/heat exchanger assembly with additive manufacturing can be adapted to other power levels of Stirling convertor for many applications, such as remote power, combined heating and power, portable power. Key Words: Stirling, space power, radioisotope power system, remote power, portable power, high efficiency, high reliability, regenerator/heat exchanger assembly.