Innovative 20-kW Delta Stirling Generator for Fission Surface Power

Stirling Innovations, LLC (SI) has introduced innovative delta Stirling machines. Delta engines and coolers are a subset of double-acting alpha free-piston Stirling machines. They are characterized by having a piston on each end of a linear alternator/motor and by optimal heat exchanger interfaces and manifolds. This leads to the potential for the highest efficiency, lightest weight and lowest cost possible for Stirling machines. Development of a 20-kW delta Stirling engine is proposed to directly address NASA needs for high efficiency and high reliability fission surface power convertors. SI uses the flexure bearings with clearance seals technology developed by Infinia and Qnergy to enable unparalleled life and reliability for Stirling machines. These are exemplified by three Infinia engines that have operated at NASA GRC for over 17 years with no maintenance or degradation and thousands of Qnergy remote power generators in the field with no issues for up to 60,000 hours. The proposed Phase I project will expand the existing 20-kW delta engine conceptual design to a fully resolved preliminary design that will be ready for final design at the beginning of Phase II. The anticipated Phase II prototype will be much closer to a pre-production engine than a typical lab prototype because it uses critical components directly from the Qnergy production line.

Proposed Innovation Relevance to NASA SBIR Subtopic Z.Enable.01: This Subtopic Scope Title of “Kilowatt-Class Thermal Energy Conversion Technologies” includes in its Scope Description “… NASA is currently funding the Fission Surface Power (FSP) project to deliver 40 kW of continuous, sun-independent power on the surface of the Moon and Mars. Fission power systems are likely to generate AC power, either single-phase AC at relatively low frequency with Stirling conversion (50 to 100 Hz) or three-phase AC at higher frequency with Brayton conversion (500 to 2000 Hz).” Needed Technologies objectives include “Capable of long-life (>10 years), and high efficiency (>30%).” and “… Free-Piston Stirling cycle convertors and Closed Brayton Cycle convertors supporting the 40 kW FSP target and scalable to support future 50 kW-100 kW for larger surface power and NEP systems. There is an interest in higher power convertors, and it is anticipated all systems will contain more than one convertor for the purpose of redundancy. Balancing fault tolerance and complexity, past concepts have explored two to four convertors.” The proposed delta Stirling converter system is a perfect fit with this Subtopic that meets or exceeds all of these objectives. Two 20-kW convertors meet the 40-kW system objective with redundancy, the delta configuration provides direct 3-phase power in contrast to conventional single-phase Stirling engines, proven life with the Infinia flexure bearing/clearance seal technology is significantly greater than 10 years, and efficiency is projected to be closer to 40% than 30%. Future capacity growth can be accommodated either by using additional 20-25 kW units or by scaling up to use Qnergy 8-kW alternators rather than the proposed 4-kW alternators, leading to 40-50 kW output at 50-60 Hz. Additional NASA applications specifically include nuclear electric power, which can use the same delta power convertor. The most successful current commercial Stirling engine products are the one to six kW free-piston Stirling remote power generators manufactured and marketed by Qnergy. The proposed FSP engine uses linear alternators and flexure bearings directly from the Qnergy assembly line, together with slightly modified pistons and piston housings. Current Qnergy markets do not support engines with the larger delta capacity, but they are exploring the market for power generation from landfill gas. If that market materializes delta engines would be a strong candidate for serving it. A direct comparison between the cost of an AMSC commercial cryocooler that uses the same Qnergy linear alternator/motor, flexure bearings, and piston assembly as a conceptualized delta cryocooler showed that the delta configuration would reduce cost per cooling watt by more than a factor of two. This resulted from the elimination of the displacer assembly, complex housings, and closed end pressure vessels. Similar cost benefits will apply to delta engines in general and will be a strong driver in opening up new markets for Stirling engines. Given the above, the first commercial application derived from the proposed SBIR development is likely to be for Qnergy to serve the landfill gas methane abatement market. Other candidate markets include higher power remote power needs and emerging nation community power systems using locally available biogas or biomass fuel. At this point we anticipate Qnergy will manufacture and market delta engines for these and/or other applications under license from SI. The collective advantages of delta engines will expedite Stirling commercialization.

This is a mature technology (TRL 7+) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

None of these are guaranteed paths for this specific project — TechPort itself doesn't have an "apply" button. Reaching out to the contact(s) above with a specific question is usually the fastest way to find out what's actually open.