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Free-Piston Stirling Power Conversion Unit for Fission Power System, Phase II Final ReportIn Phase II, the manufacture and testing of two 6-kW(sub e)Stirling engines was completed. The engines were delivered in an opposed 12-kW(sub e) arrangement with a common expansion space heater head. As described in the Phase I report, the engines were designed to be sealed both hermetically and with a bolted O-ring seal. The completed Phase II convertor is in the bolted configuration to allow future disassembly. By the end of Phase II, the convertor had passed all of the final testing requirements in preparation for delivery to the NASA Glenn Research Center. The electronic controller also was fabricated and tested during Phase II. The controller sets both piston amplitudes and maintains the phasing between them. It also sets the operating frequency of the machine. Details of the controller are described in the Phase I final report. Fabrication of the direct-current to direct-current (DC-DC) output stage, which would have stepped down the main controller output voltage from ~700 to 120 V(sub DC), was omitted from this phase of the project for budgetary reasons. However, the main controller was successfully built, tested with the engines, and delivered. We experienced very few development issues with this high-power controller. The project extended significantly longer than originally planned because of yearly funding delays. The team also experienced several hardware difficulties along the development path. Most of these were related to the different thermal expansions of adjacent parts constructed of different materials. This issue was made worse by the large size of the machine. Thermal expansion problems also caused difficulties in the brazing of the opposed stainless steel sodium-potassium (NaK) heater head. Despite repeated attempts Sunpower was not able to successfully braze the opposed head under this project. Near the end of the project, Glenn fabricated an opposed Inconel NaK head, which was installed prior to delivery for testing at Glenn. Engine development prior to this was performed using both single- and dual-opposed (common expansion space) Inconel heads with clamp-on electric heaters.
Document ID
20160010605
Acquisition Source
Glenn Research Center
Document Type
Contractor Report (CR)
Authors
Wood, J. Gary
(SunPower, Inc. Athens, OH, United States)
Stanley, John
(SunPower, Inc. Athens, OH, United States)
Date Acquired
August 29, 2016
Publication Date
August 1, 2016
Subject Category
Spacecraft Propulsion And Power
Report/Patent Number
GRC-E-DAA-TN29210
E-19217
NASA/CR-2016-219088
Funding Number(s)
WBS: WBS 887359.02.03.06.01
CONTRACT_GRANT: NNC09CA23C
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
Free-piston Stirling Power Conversion Unit
NaK heating circuit
Fission Surface Power
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