John E. Augenblick

Developing a Free-Piston Stirling Convertor for advanced radioisotope space power systems

The Department of Energy (DOE) has selected Free-Piston Stirling Convertors as a technology for future advanced radioisotope space power systems. In August 2000, DOE awarded competitive Phase I, Stirling Radioisotope Generator (SRG) power system integration contracts to three major aerospace contractors, resulting in SRG conceptual designs in February 2001. All three contractors based their designs on the Technology Demonstration Convertor (TDC) developed by Stirling Technology Company (STC) for DOE. The contract award to a single system integration contractor for Phases II and III of the SRG program is anticipated in late 2001. The first potential SRG mission is targeted for a Mars rover. This paper provides a description of the Flight Prototype (FP) Stirling convertor design as compared to the previous TDC design. The initial flight prototype units are already undergoing performance tuning at STC. The new design will be hermetically scaled and will provide a weight reduction from approximately 4.8 kg to...

The New Generation Infinia Free-Piston Stirling Engine for Micro-CHP and Remote Power Applications

The advancement of free-piston Stirling engines in the last decade has made them attractive for use in the micro-CHP (combined heat and power) and remote power markets. Infinia Corporation, the leader in free-piston Stirling engine technology development, is the primary provider of high-efficiency, long-life Stirling engines and cryocoolers to U.S. government and commercial companies. This paper reviews Infinia’s free-piston Stirling technology development and latest technology advancements as they relate to the next generation Infinia 3.1-kW free-piston engine for micro-CHP and remote power applications. This new generation 3.1-kW Stirling engine inherits the key features of all Infinia free-piston engines – prodigious durability, low noise, and multi-fuels compatibility – while substantially reducing costs and increasing specific power. Many new technologies and features have been implemented to further improve the reliability and some design issues have been addressed to simplify system integration.

Conceptual Design Update for an Improved Stirling Convertor

The Department of Energy, Lockheed Martin Astronautics, Stirling Technology Company (STC), and NASA Glenn Research Center are developing a high-efficiency Stirling Radioisotope Generator (SRG) prototype design for potential NASA Space Science Missions. This first generation SRG will represent a substantial improvement in efficiency relative to the current state of the art thermoelectric space power systems. Early demonstration versions of the STC Stirling convertor used in the SRG prototype have proven it to be very robust during more than 2 years of testing and evaluation. In order to achieve higher power density and efficiency for 2 and 3 generation SRG systems, STC and others have focused additional design efforts on improving the current hardware. This paper details STC’s progress to date on this evolution of an improved Stirling convertor design. Through several modifications to STC’s existing hardware, weight reductions of approximately 74% are possible and will improve power density to nearly 50 W / kg. Additional future efforts to develop a more advanced Stirling convertor could increase the power density even further.

Preliminary Computational Fluid Dynamics Modeling of STC Stirling Engines

*† ‡ § Stirling Technology Company (STC) has developed a 55W-class Stirling Convertor technology-demonstration machine (RG-55), with capabilities suitable to meet existing specifications for a potential space-borne Stirling Radioisotope Generator. The RG-55 has proven to be very successful and robust, and has met ever changing performance targets designated by various potential customers. The RG-55 is the current baseline for a firstgeneration generator system, but there are also parallel efforts by STC and others to improve on the design with smaller, lighter, better performing machines. A recent STC conceptual design study is focused on improving power density and reducing size relative to the RG-55, with the introduction of a 70W-class Stirling Convertor. This new machine will incorporate low-mass packaging and has several improvements, including improved performance and simplified system interfaces. Computational fluid dynamics has been used as part of this new design, in an effort to improve thermodynamic modeling capabilities and to improve internal flow geometries for the new heater head. The fluid modeling described in this paper is very preliminary and no attempts were made to evaluate regenerator performance or heat exchanger performance. The current modeling effort specifically focused on developing simple models to help visualize entrance and exit losses and flow recirculation in variable-volume regions, in manifolds, and in gas ports.

Structural and Thermal Analysis of Infinia Corporation Stirling Convertors

Free-piston Stirling machines offer high efficiency, long life, quiet operation and long durability. They are the primary candidates for micro-CHP (combined heat and power) and remote power markets. They are also potential candidates for future deep space missions. To ensure the long durability of the Stirling engines, Infinia has worked with NASA Glenn Research Center and Allied Signal to develop a comprehensive set of FEA design criteria and standards. The design standard Infinia is using is ASME pressure vessel design-code compliant. It also combines the material testing results, as well as other aerospace companies’ past practical experiences. This paper describes the detailed FEA analysis process at Infinia for Stirling pressure vessel and component design. This paper also illustrates the path to achieving long durability without sacrificing the system efficiency.

Structural Analysis for an Innovative Stirling Engine Design

Stirling machines offer high efficiency and decreased fuel-usage relative to traditional long life space power systems. In order to improve power density and efficiency relative to current machines, Stirling Technology Company (STC) has focused a conceptual design effort on reducing mass of its first generation Stirling Radioisotope Generator (SRG) hardware. STC has proposed several innovations during this effort, including a new Stirling engine architecture that is inherently lower mass than existing STC designs. This new architecture shares some features in common with previous cryocooler hardware and is useful for both commercial-terrestrial and space-borne applications. Several advantages of this new architecture include a compact and light weight package, maximized heat exchanger efficiency, and improved system integration potential. This paper specifically discusses the structural analysis and some of the design challenges associated with the new low-mass STC design. Conceptual design and analysis results are presented, along with a discussion of the survivability of the hardware over long mission lifetimes. STC reliability will not be compromised, and could be improved, by this new engine configuration.

Stirling Convertor Performance Mapping Test Results for Future Radioisotope Power Systems

Long‐life radioisotope‐fueled generators based on free‐piston Stirling convertors are an energy‐conversion solution for future space applications. The high efficiency of Stirling machines makes them more attractive than the thermoelectric generators currently used in space. Stirling Technology Company (STC) has been performance‐testing its Stirling generators to provide data for potential system integration contractors. This paper describes the most recent test results from the STC RemoteGen™ 55 W‐class Stirling generators (RG‐55). Comparisons are made between the new data and previous Stirling thermodynamic simulation models. Performance‐mapping tests are presented including variations in: internal charge pressure, cold end temperature, hot end temperature, alternator temperature, input power, and variation of control voltage.

Continuing Development for Free‐Piston Stirling Space Power Systems

Long‐life radioisotope power generators based on free‐piston Stirling engines are an energy‐conversion solution for future space applications. The high efficiency of Stirling machines makes them more attractive than the thermoelectric generators currently used in space. Stirling Technology Company (STC) has been developing free‐piston Stirling machines for over 30 years, and its family of Stirling generators is ideally suited for reliable, maintenance‐free operation. This paper describes recent progress and status of the STC RemoteGen™ 55 W‐class Stirling generator (RG‐55), presents an overview of recent testing, and discusses how the technology demonstration design has evolved toward space‐qualified hardware.

Low -Mass Stirling Convertor Assembly Progress Update

Infinia is developing the next generation of space‐ready Stirling Convertor Assemblies. Infinia has previously proposed a Low‐Mass Stirling Convertor Assembly (SCA) design employing a flux‐concentrating, moving‐iron linear alternator. This paper describes further development of that proposed machine, including additional improvements and advancements. One significant change is a new, lighter‐weight moving‐magnet alternator design. Infinia has shown progress in the low mass design’s development and testing: namely in the area of flexure spring rates, welding techniques on the flange, and a change to the alternator configuration. Progress has been made with the flat‐top heater head design and its capabilities, as well. The changes described in this paper will significantly reduce the mass and increase the power density of the low‐mass design.

Stirling Convertor and System Configuration Concepts for Reduced Vibration and a Balanced System

Infinia Corporatio ns free -piston Stirling machines offer high efficiency, prodigious durability, and low noise. They are the primary candidates for micro -CHP and remote power markets, as well as potential candidates for future deep space missions. This paper presents a few concepts to provide insight into future Stirling engine design and power system integration. Some of the self -balancing design concepts can be used to further reduce the vibration without the need for balancers. Some of the system concepts can be employed to greatly reduce the complexity of the system integration. REE -PISTON Stirling engines (FPSE) are a t the core of Infinia Corporations business. Infinia products are currently in the field or undergoing qualification testing for micro -CHP (combined heat and power) and remote power markets, as well as future deep -space missions. Over 30 years of product development have allowed Infinia to hone computational and design methods related to their FPSE products, with the current Stirling Convertor Assembly (SCA) designs reflecting Infinias expertise. The key features of FPSEs - high efficiency, low noise, an d prodigious durability - are inherent in Infinias designs. However, many of the existing and potential applications are also dependent on the ability of the SCA to integrate into a system. As a result, recent technology developments at Infinia have focus ed not only on improving the specific power of the SCA, but also on system integration characteristics. The main focus areas include: SCA volume and mass; SCA heat source interface(s); and system vibration reduction. Several of the SCA improvements have be en achieved through work funded under a NASA Glenn Research Center (GRC) task order 1 . Other modifications and system improvements have been developed internally at Infinia to support commercialization of the technology 2 . Several of the concepts that have b een developed are presented in this paper, with the main focus on system vibration reduction.