The Multi-Cylinder Free-Piston Stirling Engine:A Breakthrough for High-Power Space Applications

摘要

Free-piston Stirling engines (FPSE) have been shown to be viable, dynamicrngenerators for space power systems. Extensive Stirling development over a decade ago for thernSP-100 space power reactor system resulted in the 25-kWe Component Test Power Convertorrn(CTPC) that demonstrated greater than 20% efficiency with a specific weight of 7 kg/kW at heatrnsource and sink temperatures of 1050 K and 525 K, respectively. A flight configuration designrnwas projected to provide 27% efficiency at 6 kg/kW under the same operating conditions. Free-pistonrnStirling and related pulse tube cryocoolers have become the standard for dynamicrncryocooling requirements in space. Smaller radioisotope-fueled, free-piston Stirling convertorsrnfor space and terrestrial applications are being aggressively pursued. Highlights include: arncontinuing endurance test exceeding 91,000 hours (10.4 years) with no maintenance orrndegradation; six currently operating hermetically sealed convertors; efficiency up to 29% (grossrnelectric power out relative to heat delivered to engine); and plans to deliver 40 units, includingrnflight configurations, over the next 3 years. Augmented with the key support of a recent SmallrnBusiness Innovation Research (SBIR) contract from the NASA Glenn Research Center (GRC),rnStirling Technology Company (STC) is pursuing an internally funded effort to develop anrninnovative FPSE configuration with numerous advantages over all prior Stirling engines andrncoolers. A successful feasibility demonstration was recently completed. A preliminary conceptualrndesign based on the CTPC system interface specifications projects a 50-kWe module with arnspecific weight of 4.5 kg/kW in essentially the same envelope as the CTPC 25-kWe module. Thernapproach maintains a direct legacy to the existing long-life, high-reliability, high-efficiencyrnStirling convertors, but greatly simplifies the dynamic tuning and balancing issues typical of arnFPSE. The presentation fully describes the concept, shows the feasibility test hardware andrnresults, and illustrates representative configurations and projected performance for space powerrnsystems. This new topology offers a low-risk approach for fast-track development of convertorrnmodules from under 1 kilowatt to at least 100 kilowatt capacity.