Browse Topic: Stirling engines

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Detecting Chemical Weapons Using Fourier Transform Infrared SpectroscopyTBMG-351659/1/2019
Chemical Warfare Agents (CWA) are a class of Weapons of Mass Destruction (WMD) designed to kill and injure humans through exposure to extremely toxic chemicals. In addition to CWA many chemicals used by industry, often referred to as Toxic Industrial Chemicals (TICS) can potentially be used by terrorists as weapons.
Fuel Consumption Saving Potential of Stirling Machine on Series Parallel Hybrid Electric Vehicle: Case of the Toyota Prius2018-01-04214/3/2018
Investigations on alternative fuels and new hybrid powertrain architectures have recently undergone significant efforts in the automotive industry, in attempt to reduce carbon emissions from passenger cars. The use of these fuels presents a potential for re-emerging the deployment of external combustion non-conventional engines in automotive applications, such as the Stirling engines, especially under the current development context of powertrain electrification. This paper investigates the potential of fuel consumption savings of a series-parallel hybrid electric vehicle (SPHEV) using a Stirling machine as fuel converter. An exergo-technological explicit analysis is conducted to identify the Stirling system configuration presenting the best compromise between high efficiency and automotive implementation constraints. The Stirling engine with combustion chamber preheater is prioritized. A SPHEV model is developed based on the Prius power-split hybrid electric architecture. Energy consumption simulations are performed on the worldwide-harmonized light vehicles test cycle (WLTC) using dynamic programing as global optimal energy management strategy. Results show improved fuel consumption performance of the Stirling machine compared to the ICE. In addition, the Stirling offers other intrinsic advantages such as low noise and vibration operation and mainly multi-fuel use capability. Consequently, the studied Stirling presents a potential for implementation on SPHEVs.
Bou Nader, Wissam, Mansour, Charbel, Nemer, Maroun, Dumand, Clement
Alpha-STREAM ConvertorTBMG-271987/1/2017
Innovators at NASA’s Glenn Research Center have developed two novel technologies that make Stirling engines more efficient and less costly. First, Glenn’s thermoacoustic power converter uses sound to turn heat into electric power. Utilizing heat-driven pressures and volume oscillations from thermoacoustic sources to power piezoelectric alternators or other power-converter technologies, this device can generate electricity with unprecedented efficiencies. Unlike conventional Stirling-based devices, this thermoacoustic engine achieves high thermal-to-electrical efficiencies with no moving parts. Glenn’s second advancement for Stirling engines replaces the conventional linear alternator with a magnetostrictive alternator that converts the oscillating pressure wave into electric power (see figure). These innovations offer a reliable and efficient way to generate power from any heat source, benefiting applications such as combined heat and power (CHP) systems, distributed generation, solar power generation, and heating and cooling systems.
Mechanisms for Achieving Non-Sinusoidal Waveforms on Stirling EnginesTBMG-261491/1/2017
The current state-of-the-art Stirling engines use sinusoidal piston and displacer motion to drive the thermodynamic cycle and produce power. Research performed at NASA Glenn has shown that non-sinusoidal waveforms have the potential to increase Stirling engine power density, and could possibly be used to tailor engine performance to the needs of a specific application. However, the state-of-the-art Stirling engine design uses gas springs or planar springs that are very nearly linear, resulting in a system that resonates at a single frequency. This means that imposing non-sinusoidal waveforms, consisting of multiple frequencies, requires large forces from the drive mechanism (either the alternator or the crank shaft). These large forces increase losses, and increase the size and requirements of the control system. This innovation aims to reduce the external forcing requirements by introducing internal mechanical components that provide the forces necessary to achieve the desired waveforms.
Improving Stirling Engine Performance Through Optimized Piston and Displacer MotionTBMG-261521/1/2017
Stirling engines typically achieve high efficiency, but lack power density. Low power density prevents them from being used in many applications where internal combustion engines are viable competitors, and increases system costs in applications that require Stirling engines. This limits their operating envelope in both terrestrial and space applications. Sinusoidal piston and displacer motion is one of the causes of low power density. Previous work proposed solving this problem by replacing sinusoidal waveforms with waveforms that more closely approximate those of the ideal Stirling cycle. However, when working with real engines, imposing ideal waveforms has been shown to reduce power density and efficiency due to increased pressure drop through the regenerator and heat exchangers.
Numerical Computational Optimization Applied To The Dynamic Behavior of an Articulated Cursor, Connecting Rod and Crank Mechanism - Case Studies for Implementing a Beta Stirling Engine2014-36-02829/30/2014
The Stirling engine is a device that has great potential for being used in applications where energy (heat) is available in the system. As an example, a Stirling motor can use the energy available in the gases from the combustion process of an automotive engine by using exhaust manifold as hot source. The Stirling motor consists of a piston that can move along a cylinder that is fulfilled by a working fluid and a displacer installed between the hot and cold chambers. Due to the large temperature difference between the chambers, it becomes feasible to use the corresponding energy to drive the Stirling engine. For design purposes, a multi-objective problem is formulated so that the maximization of thermodynamic efficiency, the minimization of energetic loss associated with the movement of the displacer set, and the minimization of energetic loss related to the fluid displacement between the two chambers is obtained for the optimal configuration of the system. To solve this optimal design problem, the Non- dominated Sorting Genetic Algorithm is used. The preliminary results demonstrated that the methodology proposed represents a promising approach for the design of Stirling engines. The theoretical results were used to construct a prototype of a Stirling engine for evaluating the whole design process.
de Paula Brito, Gelcino, Borges, José Antônio Ferreira
Magnetostrictive AlternatorTBMG-1767411/1/2013
This innovation replaces the linear alternator presently used in Stirling engines with a continuous-gradient, impedance-matched, oscillating magnetostrictive transducer that eliminates all moving parts via compression, maintains high efficiency, costs less to manufacture, reduces mass, and eliminates the need for a bearing system.
Cascading Tesla Oscillating Flow Diode for Stirling Engine Gas BearingsTBMG-1484810/1/2012
Replacing the mechanical check-valve in a Stirling engine with a micromachined, non-moving-part flow diode eliminates moving parts and reduces the risk of microparticle clogging.
Temperature Controlled Exhaust Heat Thermoelectric Generation2012-01-12144/16/2012
The amount of energy wasted through the exhaust of an Internal Combustion Engine (ICE) vehicle is roughly the same as the mechanical power output of the engine. The high temperature of these gases (up to 1000°C) makes them intrinsically apt for energy recovery. The gains in efficiency for the vehicle could be relevant, even if a small percentage of this waste energy could be regenerated into electric power and used to charge the battery pack of a Hybrid or Extended Range Electric Vehicle, or prevent the actuation of a conventional vehicle's alternator. This may be achieved by the use of thermodynamic cycles, such as Stirling engines or Organic Rankine Cycles (ORC). However, these systems are difficult to downsize to the power levels typical of light-vehicle exhaust systems and are usually bulky. The direct conversion of thermal energy into electricity, using Thermoelectric Generators (TEG) is very attractive in terms of minimal complexity. However, current commercial thermoelectric modules based on Seebeck effect are temperature-limited, so they are unable to be in direct contact with the exhaust gases. A way to downgrade the temperature levels without significantly reducing the regeneration potential is to interpose Heat Pipes (HP) between the exhaust gas and the Seebeck modules in a controlled way. This control of maximum permissible temperature at the modules is achieved by regulating the pressure of phase change of the service fluid of the HP. In this way the system will be failsafe against overheating and will be able to operate efficiently under both low and high thermal loads. Such is the case of the range extender unit being developed by the team, which has a low (15 kW) and a high (40 kW) power mode of operation. Various designs concepts were evaluated by simulation, design and test. Although efficiencies were still moderate, it was possible to demonstrate the potential of this system for optimizing the output of commercially available temperature-limited TEGs.
P. Brito, Francisco, Martins, Jorge, Goncalves, L.M., Sousa, Rui
Microfabricated Segmented-Involute-Foil Regenerator for Stirling EnginesTBMG-870511/1/2010
An involute-foil regenerator was designed, microfabricated, and tested in an oscillating-flow test rig. The concept consists of stacked involute-foil nickel disks (see figure) microfabricated via a lithographic process. Test results yielded a performance of about twice that of the 90-percent random-fiber currently used in small Stirling converters.
Development of a Single-Fluid Consumable Infrastructure for Life Support Systems2007-01-32467/9/2007
Decomposition of high-grade hydrogen peroxide (H2O2) generates water vapor, oxygen, and heat. By converting heat to electrical energy with a Stirling engine, a spacesuit portable life support system can be maintained exclusively with H2O2; however, incorporation of additional cooling water may reduce the overall system mass. System components comprising the hydrogen peroxide portable life support system (HyPerPLSS) are discussed and analyzed. Component considerations and thermodynamic relations indicate an optimal hydrogen peroxide concentration of 95%. Life support requirements for eight hours of extravehicular activity are satisfied with 10.9 kg of liquid H2O2.
Lewandowski, Craig M., Akin, David L.
Design Concept for a Nuclear Reactor-Powered Mars RoverTBMG-17965/1/2007
A report presents a design concept for an instrumented robotic vehicle (rover) to be used on a future mission of exploration of the planet Mars. The design incorporates a nuclear fission power system to provide long range, long life, and high power capabilities unachievable through the use of alternative solar or radioisotope power systems. The concept described in the report draws on previous rover designs developed for the 2009 Mars Science laboratory (MSL) mission to minimize the need for new technology developments.
Microscale Regenerative Heat ExchangerTBMG-618/1/2006
The device illustrated in Figure 1 is designed primarily for use as a regenerative heat exchanger in a miniature Stirling engine or Stirling-cycle heat pump. A regenerative heat exchanger (sometimes called, simply, a “regenerator” in the Stirling-engine art) is basically a thermal capacitor: Its role in the Stirling cycle is to alternately accept heat from, then deliver heat to, an oscillating flow of a working fluid between compression and expansion volumes, without introducing an excessive pressure drop. These volumes are at different temperatures, and conduction of heat between these volumes is undesirable because it reduces the energy-conversion efficiency of the Stirling cycle. Hence, among the desired characteristics of a regenerative heat exchanger are low pressure drop and low thermal conductivity along the flow axis.
Thermoelectric Air/Soil Energy-Harvesting DeviceTBMG-52210/1/2005
A proposed thermoelectric device would exploit natural temperature differences between air and soil to harvest small amounts of electric energy. Because the air/soil temperature difference fluctuates between nighttime and daytime, it is almost never zero, and so there is almost always some energy available for harvesting. Unlike photovoltaic cells, the proposed device could operate in the absence of sunlight. Unlike a Stirling engine, which could be designed to extract energy from the air/soil temperature difference, the proposed device would contain no moving parts. The main attractive feature of the proposed device would be high reliability. In a typical application, this device would be used for low-power charging of a battery that would, in turn, supply high power at brief, infrequent intervals for operating an instrumentation package containing sensors and communication circuits.
Using Artificial Neural Networks To Monitor Stirling EnginesTBMG-73084/1/2001
An important secondary topic addressed in the research and development effort described in the preceding article is the use of artificial neural networks to improve the monitoring and thus the control and safety of multiple free-piston Stirling engines. Information collected by monitoring subsystems constitutes essential feedback for use by control and safety subsystems. This information includes such externally measurable quantities as heater-head temperatures, motions of engine housings, and output currents and voltages.
Dynamic Balancing of Multiple Independent Stirling EnginesTBMG-73074/1/2001
Experiments have shown that an assembly of multiple free-piston Stirling engines can be designed and constructed in such a way as to both (1) make the vibrations of the engines balance each other to minimize the overall level of vibration, and (2) enable the engines to operate independently of each other, so that if one fails, the other(s) can continue to provide power. Prior to these experiments and to the research and development effort that preceded them, it was not possible to achieve both redundancy and suppression of vibrations: The only previously demonstrated method to balance out vibrations of multiple Stirling engines was by use of counter-oscillating pistons coupled to each other via a common thermodynamic hot space, with the engines driving linear alternators connected electrically in series. This older scheme precludes redundancy because the common thermodynamic interaction and the series electrical connection causes both engines to fail when one fails.
A Study on Temperature Distribution of Stirling Engine Regenerator1999-01-25068/2/1999
The performance of Stirling engines depends on the performance of regenerators. Regenerators are primarily expected to have good temperature efficiency. In addition, the flow losses and dead space must be minimized. These factors, however, are in opposition to each other. Although a considerable amount of research has focused on these three factors, few studies have analyzed them in actual reciprocating flows. Moreover, it has not been possible to measure the temperature efficiency by using a working gas due to the rapid change of the gas temperature. Therefore, in this study, we measured the transition of the temperature in the reciprocating flows in a regenerator by using water instead of a gas and then examined the characteristics of the regenerator. Here, we report the observed transition of temperature, which almost coincided with results previously obtained by computer simulation.
Watanabe, Hiroichi, Fujisawa, Yuichi, Yoshida, Munenobu, Moriya, Shinji
Optimized Design of Stirling-Driven Vapor-Compression System1999-01-24538/2/1999
Stirling engines have many unique advantages including higher thermal efficiencies, preferable exhaust gas characteristics, multi-fuel usage, and low noise and vibration. On the other hand, heat pump systems are very attractive for space heating and cooling and industrial usage. There are several environmental merits of Stirling-driven vapor-compression (SDVC) systems. A design method for the SDVC, which is based on mathematical methods for Stirling and Rankine cycles, has been developed. The model treats a kinematic Stirling engine and a scroll compressor which are coupled by a belt. The measured performance of an actual system well agreed with the calculated results. The attractive SDVC performance using conventional and alternative refrigerants was shown. From the calculated Total Equivalent Warming Impact, TEWI and operating costs, it became clear that the SDVC system with the alternative refrigerant has a higher potential as the future air-conditioning system.
Kagawa, Noboru
Hydrogen Permeation Issue for Gas Fired AMTEC Systems1999-01-25578/2/1999
Diffusion of hydrogen in solids is an intriguing intellectual problem. Permeation of hydrogen generated in combustion into gas fired Alkali Metal Thermal to Electric Converter (AMTEC) systems can be detrimental to AMTEC performance for various reasons. Potential effects include depriming of the AMTEC cell arteries, blockage of the condenser and hydride formation. Numerous papers and reports have been published concerning hydrogen diffusion in solids (Birnbaum and Wert, 1972; Garber, 1975; Strehlow and Savage, 1974). Many of these papers concern the embrittling effects of hydrogen and many concern the diffusion process itself. Hydrogen permeation and permeation resisting strategies have been examined extensively in connection with other energy conversion technologies such as Stirling engines (Alger, 1988; Khalili etal., 1989) and high temperature heat pipes (Anderson et al., 1995; North and Anderson, 1997). Due to the different boundary conditions and materials involved, it was necessary to conduct experiments specifically designed for AMTEC to evaluate hydrogen permeation rates into AMTEC cells, to understand the effect of this permeation on AMTEC performance and finally, if hydrogen permeation turns out to be a cause for concern, to identify strategies to reduce permeation, and to design an AMTEC cell which will perform with adequate lifetime. This paper describes experiments and their results for AMTEC cells operated in a partial pressure of hydrogen. Experiments in which the hydrogen permeation rate across different thickness cell walls were measured with and without barrier coatings are also described. Due to greater sensitivity, the change in pressure on the vacuum side of the specimen was observed as hydrogen permeated the metal. Depending on the operating conditions and the operating life requirements of specific AMTEC systems, hydrogen permeation barriers may need to be included in the cell design. Some of the solution approaches that were implemented and their effectiveness in minimizing AMTEC degradation are also elucidated.
Mital, R., Butkiewicz, D. A., Childs, K. F., Hayes, D. D., Svedberg, R. C., Hunt, T. K.
PROPOSAL AND BASIC EXPERIMENTS OF SUPER STIRLING ENGINES1999-01-25028/2/1999
“Super Stirling Engine” is a Stirling engine assisted by saturated low pressure steam or compressed air of 0.2 ∼ 0.8 Mpa pressure range, which is injected into the cold side of the displacer cylinder at the top dead center of the power piston, and the steam or air expands into power cylinder at constant high temperature after passing regenerator and heater. Near the bottom dead center of the power piston, the steam or air is ejected to outside in low temperature after passing the regenerator again as same as Stirling engine. So, this engine works in the combination of Stirling cycle and steam Rankine cycle when steam is used.
ISSHIKI, Naotsugu, KOJIMA, Hiroshi, USHIYAMA, Izumi, ISSHIKI, Seita
Evaluation of 6 Different Correlations for the Flow Friction Factor of Stirling Engine Regenerators1999-01-24568/2/1999
The topic of this paper is to compare six well known and often used correlations for the flow friction factor of Stirling engine regenerators /1-5/. Therefore, the experimental methods and the geometric constraints in terms of the ranges of wire diameter and porosity investigated are summarized for each correlation. Additionally, the different equations for Reynolds number and flow friction factor are discussed in order to derive one general applicable set of equations for the Reynolds number and the friction factor. Using these general equations, it is possible to show all data in one plot, which gives a good impression of the characteristics of each set of data and the deviations among them. Additionally, the correlations are applied to a 2nd order computer model (PROSA), which was used to recalculate the performance of the well known GPU-3 engine. The results of these calculations in terms of regenerator pressure drop, mechanical power output and efficiency are also presented in the paper. This clearly indicates the impact of the different correlations on the simulation results.
Thomas, Bernd
THE SECOND STIRLING TECHNO RALLY CONTEST OF MODEL AND MANNED STIRLING ENGINE CARS1999-01-25038/2/1999
“The Second Stirling Techno Rally” is held at Nov. 1998 near Tokyo. This time about 100 normal size cars (N-class) and 30 mini cars (M-class) came to the contest and got better records than last year. Moreover, for this second rally, race of manned big cars and bikes (L-class) with self made Stirling engines are taken place also, and, about ten cars came to the race. The preparation and wonderful results of this second techno rally are reported here in details. By those rallies, it is hoped that understanding and progress of Stirling engine itself will be stimulated very much towards glorious 21st century.
ISSHIKI, Naotsugu, FUJII, Iwane, MATSUO, Masahiro, ISSHIKI, Seita
Composite-Matrix Regenerators for Stirling EnginesTBMG-21131/1/1999
A prototype Stirling-engine regenerator containing a matrix made of carbon-fiber-based composite materials has been developed. The concept underlying this development effort is one of exploiting the properties of composite materials (e.g., the anisotropy of thermal conductivity of carbon fibers and the tailorability of composite materials and structures) to reduce thermal and flow losses below those of previously developed regenerators containing metal matrices.
Oscillating-Flow Heat-Transfer and Pressure-Drop Test RigTBMG-22232/1/1998
The figure illustrates an apparatus for measuring heat-transfer and pressure-drop characteristics of porous plug specimens in oscillating flows. The apparatus is built around an oscillating-flow test rig that was originally designed for pressure-drop (but not heat-transfer) measurements and has since been modified and refined. The flows and specimens are chosen to be representative of those encountered in the regenerators of Stirling engines.
Low Temperature Stirling Cycle Refrigerator for Spacecraft Refrigeration Systems9723857/1/1997
This paper describes a Stirling Cycle Refrigerator that has been built and tested by Stirling Technology Company (STC) for the NASA Marshall Space Flight Center (MSFC). Its intended application is the space station food refrigerator freezer. The Stirling Cycle Refrigerator described herein has few moving parts, is nontoxic to both humans and the environment, is insensitive to gravity, and has a moderate efficiency. Its temperature setpoint is adjustable, making it adaptable to other space station applications including a -70 °C freezer and freeze drier, a -183 °C freezer, and a -196 °C snap freezer. Test results have been very promising, with a Coefficient of Performance (COP) of 1.1 at -26 °C (-15 °F) and a heat load of 130 watts. Reliability tests on individual components and the entire Stirling Cycle Refrigerator system show a 10-year life is possible. In addition, the benefits of using this technology for the space station refrigerator freezer will be described.
Penswick, L. Barry, Olan, Ronald W.
Computer Analysis of Stirling Cycle Cryocooler9517207/1/1995
This paper discusses about the software ‘ISCP’ developed for thermodynamic design and analysis of Stirling cycle cryocooler. The model is based on second order analysis method which assumes the various parasitic losses as independent of each other. The specifications of the cooler are arrived at using the Design Module of the software after performing various optimizations. The analysis module performs both dynamic and thermodynamic analyses.
Pande, G. V., Narayanamurthy, H.
Using a Stirling Engine Simulation Program as a Regenerator Design Aid9500972/1/1995
The regenerator in Stirling engines has long been recognized as a critical component as far as engine performance is concerned. Yet there are little or no formal Stirling engine regenerator design procedures to be found in the literature. A design procedure is proposed that makes use of a third order Stirling engine simulation program to predict the optimum regenerator configuration for the respective requirements of maximum engine power and efficiency. Tests were conducted to determine the heat transfer coefficient and pressure drop characteristic of a popular regenerator material.
Smook, W. G., Naude, A. F.
Magnetic Bearings for Free-Piston Stirling Engines9293838/3/1992
This paper assesses the feasibility and efficacy of applying magnetic bearings to free-piston Stirling-cycle power conversion machinery currently being developed for long-term space missions. The study was performed for a 50-kWe Reference Stirling Space Power Converter (RSSPC) which currently uses hydrostatic gas bearings to support the reciprocating displacer and power piston assemblies. Active magnetic bearings of the attractive electromagnetic type are feasible for the RSSPC power piston. Magnetic support of the displacer assembly would require unacceptable changes to the design of the current RSSPC. However, magnetic suspension of both displacer and power piston is feasible for a relative-displacer version of the RSSPC. Magnetic suspension of the RSSPC power piston can potentially increase overall efficiency by 0.5 to 1 % (0.1 to 0.3 efficiency points). Magnetic bearings will also overcome several operational concerns associated with hydrostatic gas bearing systems. These advantages, however, are accompanied by a 5 % increase in specific mass of the RSSPC.
Rao, D. K., Wilson, D. S.
Regenerator Elements for Internal Combustion Stirling Engine9293878/3/1992
Internal Combustion Stirling Engine is a kind of internal combustion engine with a heat regenerator and combustion room inside the cylinder head, so that it can be said “Regenerative internal combustion engine”. The engine under test here, is a one cylinder two cycles internal combustion engine with two pistons in tandem, the one is the displacer, the other the power piston. They are controlled by a rhombic mechanism to regulate their phase relation, similar to the conventional Stirling engine, and fuel is injected at the top space. Here in this paper, the temperature efficiency, flow resistance of materials and their endurability against corrosion and erosion of heat regenerator elements are studied and described. For the materials of heat regenerator (RG), stainless wire mesh, compressed foam metals, silicone carbide, stuffed wire mesh, and there combined materials, etc., are picked up and tested, and their temperature efficiencies are measured by another two cycle experimental engine model for simulation, and their performances are compared to each other. Also, recent status of various experiments on the main internal combustion Stirling engines in the author's laboratory are reported here.
Moriya, Shinji, Isshiki, Naotsugu
Free-Piston Stirling Convertor Dynamic Gas Bearings9293848/3/1992
Using a dynamic gas journal bearing in a free-piston Stirling convertor requires an analysis of the bearing which takes into account the actual working conditions of the bearing with high surrounding pressure, different boundary pressures on the bearing edges and axial movement of the “shaft”. Such an analysis has been developed and provides the steady state and dynamic characteristics of the gas bearing. Based upon this analysis a FORTRAN code has been written which, in addition, may be used to determine the influence of thermal, mechanical and manufacturing distortion. A generic bearing typical of one used in a 25 kW Stirling convertor was analyzed. The reported steady-state performance includes the load capacity, the power lost in friction and the axial flow. The dynamic analysis establishes the stability criteria of the gas lubricant film. The bearing radial clearance has a strong influence on the load capacity and axial flow past of the bearing. This influence can be used to optimize the bearing clearance with respect to the bearing efficiency and manufacturing possibilities. The pressure difference at the bearing edges and the axial movement of the shaft have negligible influence on the bearing performance. A perfect cylindrical bearing runs with whirl motion but could be accept. Any distortion, in the bearing radial clearance, can improve the bearing performance. A waved bearing concept has been shown to improve both the steady-state and the dynamic performance.
Dimofte, Florin, Liebler, Kenneth A.
Energy Source Selection for Stirling Engine Driven AUV's9294048/3/1992
Many non-renewable land-based resources are becoming depleted and the search for alternative sources of raw materials is intensifying. This situation has lead to the involvement of a number of countries, especially those of the European Community, in heavily funded ‘Wealth from the Oceans’ projects. A significant element of the research being conducted under the auspices of these projects is concerned with the development of small unmanned and untethered autonomous underwater vehicles (AUVs). To carry out their intended autonomous missions these vehicles will need reliable power systems which have high energy densities. However, although research into navigation, control and command systems has progressed considerably under this development effort, only limited headway has been made in the development of power systems which could be readily integrated into these vessels. Electrochemical power systems have been used in underwater applications for a number of years but those presently available cannot meet the rigorous specifications demanded by AUV missions. Consequently high performance fuel cells and advanced battery systems are being developed which should be generally available within the next ten years. Until then, power systems based on the utilisation of the more mature heat engine technologies appear to offer the possibility of a quicker solution to the energy density problem. Of the heat engine types available the Stirling Engine, already proven in larger submarines, shows considerable promise. One of the main reasons for the selection of the Stirling engine is it's ability to utilise any heat source, such as radioisotopes, thermal energy storage and metallic fuels. In this paper a project is described in which the design requirements for a Stirling engine driven AUV have been examined together with the identification of the most suitable primary energy source for a specific mission. As part of this project a user-friendly PC-based computer program has been developed which allows rapid assessments of the use of different energy sources with a double-acting Stirling for user defined missions. The structure and use of this code is discussed.
Potter, I. J., Reader, G. T., Walker, G.
The Power Formula for Atmospheric Stirling Engines9290278/3/1992
A new proposed formula allows the evaluation of the indicated power of an atmospheric Stirling engine by means of minimum working fluid volume, mean arithmetical pressure difference and correction factors for dead space and compression ratio, grounded on the simplest geometrical and design characteristics. The practical example given in this paper presents the comparison among the Beale formula and other similar equations, developed by other authors, showing various accuracy. Closer approximation has been reached by the proposed formula in comparison with other expressions.
Lista, Paolo, Naso, Vincenzo
Simple Vector Analysis of Stirling Machine's Performance9290308/3/1992
For more than eighteen years, the author has been engaged in the development of Stirling engines and coolers. The author has developed a very simple harmonic graphic vector analysis for the first estimation of performance of various Stirling machines including engine, cooler, and VM. (Vuilleumier) machines. This has been shown to be very useful for early estimation and understanding of each machine. So at this time, the author want to report this method. This method uses the Schmidt assumption at its base, and harmonic approximation, that was called the ellipsoidal assumption by the author previously ( 1 ). This method is applied to α, β, γ type Stirling machines and generalized three temperature machine including VM. machines. It provides very easy graphic way to show which cylinder generates power or coldness and how much power, or heat is generated, utilizing volume variation vectors (for each cylinder and the total volume) and a pressure variation vector. The author hopes this method is very helpful for the understanding, basic improvements, and development of new Stirling machines.
lsshiki, Naotsugu
Further Evaluations of Low-Temperature Difference Stirling Engine Characteristics9290228/3/1992
Low temperature-difference Stirling engines, while of limited perceived applicability, offer excellent opportunities to challenge the existing state of theoretical knowledge with low-cost yet revealing experimentation. The general availability of a well-performing low-cost Ringbom-Stirling engine provides an excellent basis for widespread experimentation based upon a common platform. Whereas some broad characteristics of this engine have already been presented this paper addresses in particular a number of aspects in regard to displacer springing. Most particularly, the gravitational effects on a vertically-oriented free displacer may be inferred with reference to a spring-suspended displacer. At the same time, theoretical predictions regarding sprung-displacer performance can be tested.
Fauvel, O. R., Reader, G. T., Walker, G.
Proof of Concept of a Magnetically Coupled Stirling Engine-Driven Heat Pump9293958/3/1992
A prototype magnetically-coupled Stirling engine-driven heat pump module has been designed and fabricated by Sunpower, Inc. under sponsorship of the U.S. Department of Energy and the Oak Ridge National Laboratory (ORNL). Preliminary testing indicates that the magnetic coupling is an effective means for transmitting power from a free-piston Stirling engine to a refrigerant compressor. Compared with other power transmission concepts, the magnetic coupling has relatively low cost, and will help make commercial development of Stirling-driven heat pumps more likely in the future.
Chen, Gong, McEntee, Jarlath
100-kWe Lunar/Mars Surface Power Utilizing the SP-100 Reactor with Dynamic Conversion9294468/3/1992
An integration study was performed coupling an SP-100 reactor with either a Brayton or Stirling power conversion subsystem. A power level of 100 kWe was selected for the study. The power system was to be compatible with both the lunar and Mars surface environment and require no site preparation. In addition, the reactor was to have integral shielding and be completely self-contained, including its own auxiliary power for start-up. Initial reliability studies were performed to determine power conversion redundancy and engine module size. Previous studies were used to select the power conversion optimum operating conditions (ratio of hot-side temperature to cold-side temperature). Results of the study indicated that either the Brayton or Stirling power conversion subsystems could be integrated with the SP-100 reactor for either a lunar or Mars surface power application. For the lunar environment, the reactor and primary coolant loop would be contained in a guard vessel to protect from a loss of primary loop containment. For the Mars environment, all refractory components including the reactor, primary coolant, and power conversion components would be contained in a vacuum vessel for protection against the CO2 environment. The vacuum would be maintained by an active ion pumping system. These active ion vacuum systems have no moving parts and have a long history of reliable operation.
Harty, Richard B., Mason, Lee S.
Visualization of Entry Flow Separation for Oscillating Flow in Tubes9294668/3/1992
Results of visualization experiments are presented for the entry flow to circular tubes under oscillatory flow conditions. Geometries and conditions have been chosen to simulate the flow in a Stirling engine with straight heat exchanger tubes. Since oscillating flow in Stirling engines is unavoidably strongly influenced by the entry conditions, such documentation is useful when engine designs are being considered and is needed when test results are being interpreted. Two entry geometries are explored, one with unrestricted entry to a squared-edged tube and another with entry from one side. The visualization technique is by illumination of neutrally-buoyant, helium-filled soap bubbles with laser light, capturing with still photography. Each picture is an ensemble of exposures from 150 cycles. Each entry to the ensemble is taken at the same range in crank position, typically five degrees. Thus, one picture may visualize the flow from 75 to 80 degrees of crank rotation, for instance. Such documentation is done for representive points throughout the cycle. The figures show that, upon entry, there is separation of streamlines from the wall with a separation bubble length of few diameters. During the acceleration phase of the cycle, this separation zone becomes larger with increasing velocity and Reynolds number. During the deceleration phase of the cycle, the scale of the separation region is roughly constant. It does not grow as might be expected. Circuitous bubble trajectories in photos taken during later portions of the deceleration phase hint that eddy circulation is intense. Such circulation may be curtailing the separation bubble growth. When the entry flow is restricted to one side, the recirculation zone on the side from which the flow enters becomes considerably larger than when the flow entry is unrestricted. In this case, the separation bubble does grow somewhat during the period of strong decelaration.
Qiu, Songgang, Simon, Terrence W.
Heat Transfer in Oscillating Flows with Sudden Change in Cross Section9294648/3/1992
Oscillating fluid flow (zero mean) with heat transfer, between two parallel plates with a sudden change in cross section, was examined computationally. The flow was assumed to be laminar and incompressible with inflow velocity uniform over the channel cross section but varying sinusoidally with time. Over 30 different cases were examined; these cases cover wide ranges of Remax (187.5 to 30 000), Va (1 to 350), expansion ratio (1:2, 1:4, 1:8, and 1:12) and Ar (0.68 to 4). Three different geometric cases were considered (asymmetric expansion/contraction, symmetric expansion/contraction, and symmetric blunt body). The heat transfer cases were based on constant wall temperature at higher (heating) or lower (cooling) value than the inflow fluid temperature. As a result of the oscillating flow, the fluid undergoes sudden expansion in one-half of the cycle and sudden contraction in the other half. In this paper, one heating case is examined in detail, and conclusions are drawn from all the cases (documented in detail elsewhere). Instantaneous friction factors and heat transfer coefficients, for some ranges of Remax and Va, deviated substantially from those predicted with steady-state correlations.
Tew, Roy C., Dudenhoefer, James E., Ibrahim, Mounir, Hashim, Waqar
Investigation of a New Heat-Pipe/Latent-Heat-Storage Receiver Element for Solar Dynamic Space Power Systems9294508/3/1992
A new latent heat storage technique for space applications developed by the DLR-ITT uses LiF as the storage medium in graphite capsules with internal capillary notches to accomodate the volume change upon melting. The receivers of solar dynamic power systems (SDPS) may contain a large number of heat pipes carrying annular such storage capsules for very effective heat transfer and thermal storage. The thermal behavior of one of these heat-pipe/latent-heat-storage elements was investigated theoretically and shall be verified experimentally, both in a geometrically and energetically 1:1 scale with respect to a 25 kWe SDPS. This paper summarizes the most important theoretical predictions and describes the planned experiment. The theoretical results show that the required heat flows are essentially achievable but subject to variation with the state of charge of the heat storage units. The relevant temperatures vary in a similar manner.
Krause, Siegfried
Stability Analysis of Free Piston Stirling Engine Power Generation System9290258/3/1992
This paper presents a stability analysis of the free-piston Stirling engine and linear alternator power generation system. Since such a system operates under sustained mechanical oscillations, stability of the system is important for proper operation, and as a criterion in selecting the tuning capacitor. The stability criterion of the system is that the rate of change in power dissipation and electric power output is always faster than the rate of the power generated by the engine. The dynamic equations and model of the system are developed in this paper. Frequency domain analysis and Bode plot techniques are utilized in the study. The stable operating frequency region corresponding to different levels of power output are then determined.
Fu, Z. X., Nasar, S. A.
Mechanical Efficiency Considerations in the Design of an Ultra Low Temperature Differential Stirling Engine9290248/3/1992
A recently developed general theory of mechanical efficiency has yielded some new and interesting theoretical insights into the intrinsic performance limits of reciprocating heat engines. Various aspects of this theory have been presented in a series of papers at the last six IECEC meetings. This paper shows how the theory can be put to practical use in guiding the design of a particular engine. The subject engine is a Stirling intended to operate on a very small temperature difference across the warm and cool sides. The project afforded an extreme case to which the new theoretical results could be applied. The end product of the project is a small kinematic Stirling engine capable of operating down to a temperature differential of only 1/2 degree Celsius, or less than 1 degree Fahrenheit. The engine easily runs from heat absorbed while resting on the palm of a human hand. It begins running within about 15 seconds of being picked up, and after a few minutes reaches steady state operation at about 80 rpm. The engine is extremely entertaining and invaluable for teaching and demonstration.
Senft, J. R.
The Thermodynamics of Stirling Engines Revisited: The Relative Merits of Hot Zone or Cold Zone Work Extraction9290268/3/1992
It was demonstrated by analytical means, that the specific work obtainable from a Stirling type engine, with separate power and displacer cylinders, having the power cylinder connected to the hot zone of the displacer cylinder is, for typical operating conditions, about twice that obtainable when the power cylinder is connected to the cold zone. The analysis, which does not reveal any differences in ideal thermal efficiency between cold-zone and hot-zone power cylinder connections, is based on conventional thermodynamic concepts applied in a manner which differentiates explicitly between the conditions applicable to hot-zone versus cold-zone interconnection of the power and displacer cylinders. A new feature of the analysis is the introduction of what have been termed bithermal processes. These involve two regions of different, but constant, temperatures with mass exchange between the regions which communicate freely via the engine regenerator. At any instant the pressure is equal in the communicating regions of a bithermal process.
Kentfield, J. A. C.
A Free-Piston Stirling Engine/Linear Alternator Controls and Load Interaction Test Facility9292648/3/1992
A test facility at NASA Lewis has been assembled for evaluating: free-piston Stirling engine/linear alternator control options, and interaction with various electrical loads. This facility is based on a “SPIKE” engine/alternator. The paper describes the engine/alternator, a multi-purpose load system, a digital computer based load and facility control, and a data acquisition system with both steady-periodic and transient capability. Preliminary steady-periodic results are included for several operating modes of a digital AC parasitic load control. Preliminary results on the transient response to switching a resistive AC user load are discussed.
Kankam, M. David, Santiago, Walter, Rauch, Jeffrey S., Madi, Frank J.
Tradeoff Between Magnet Volume and Tuning Capacitor in a Free Piston Stirling Engine Power Generation System9292628/3/1992
This paper presents the criteria in selecting the size of the tuning capacitor, and the cost tradeoff between magnet volume and tuning capacitor in a free piston Stirling engine power generation system. The permissible range of capacitor size corresponding to different magnet volume, in order to prevent magnet demagnetization and stabilize the operation of the system, is determined. Within the permissible range suitable capacitor size may be selected to compensate the inductive load of the system to improve the overall power factor. If the capacitor size is not in the permissible range, there would exists a danger of losing magnet strength, or unstable operation of the engine that would destroy the engine due to unbounded amplitude of piston oscillations. The theory developed is then applied to a practical system, and the cost tradeoff between magnet volume and capacitor is studied.
Fu, Z. X., Nasar, S. A.
A Linear Model of a Free-Piston Vuilleumier Machine Compared to Experimental Results of a Prototype9290328/3/1992
A linear model to predict the dynamics of a free-piston Vuilleumier machine will be presented. The model is based on the linear analysis of free-piston Stirling engines by Berchowitz /4/, where both the motion of the casing and the viscous coupling between the displacers are considered. Closed-form solutions are derived for the frequency, the phase angle and the amplitude ratio. In order to determine the accuracy of the results, they will be compared to the experimental data of a prototype.
Schulz, S., Thomas, B.
Application of the Fluidyne in Developing Countries9293898/3/1992
The Fluidyne, or liquid piston stirling engine, has many characteristics which make its use in developing nations particularly attractive. Besides being compatible with the use of lowgrade heat sources, the machine is simple to manufacture using a variety of low cost materials and is exceedingly reliable. This paper uses a summary of fluidyne experience to evaluate applications of the fluidyne to water pumping requirements in developing countries for purposes including domestic, livestock, and irrigating uses for water pumping. Possible sources of energy are evaluated in the light of availability and needs. Environmental, economic, and social benefits are also examined. Particular applications of the fluidyne to existing situations in China are evaluated in detail.
Yu, L., Fauvel, R., Reader, G., Walker, G.
An Adiabatic Approach for the Design and the Response-to-Load Evaluation of Free-Piston Stirling Engines9290668/3/1992
In past studies, the authors presented a dynamic analysis for the design and the performance evaluation of free-piston Stirling engines both at nominal and at off-design conditions. In this paper, the analysis is applied in conjunction with an adiabatic reference model, which, as compared with the classical isothermal assumption, can give a better representation of the engine thermodynamic behavior. This new approach involves some mathematical difficulties whose overcoming is discussed in the paper, as well as the influence of the thermodynamic modelization on the engine dynamic stability.
Benvenuto, Giovanni, De Monte, Filippo
Study on Atmospheric Stirling Engine NAS-19293908/3/1992
To get a simple and low cost Stirling engine that would be manufactured and used in any district of the world, a unique atmospheric Stirling engine named NAS-1 is under study at NIHON University. NAS-1 was originally planned to be used for the solar field, so the cylinder head was designed to have a glass head at its top with the concentrated solar beam penetrating the glass. NAS-1 uses a rubber diaphragm for the power piston, and it has proved to be very reliable and successful. It has James Watt's approximate linear motion link mechanisms (Watt link) for the main crank shaft, instead of the usual crossed head to eliminate liquid oil lubrication. This kind of engine has been thought to furnish very simple, low cost and efficient power for future clean energy fields. This engine design is simple, low in cost, and doses not involve problems of high pressure, and does not produce any pollutants whatsoever such as carbonic acid gas, NOx and others' pollution. We succeeded in low temperature operations of the new design atmospheric Stirling engine NAS-1 and 2 engine has shown very well indicated output power in our testing. By the experiments heated with electric heater, NAS-1 and 2 engine have shown very well indicated efficiency about 10 % at even a very low temperature difference of 200 °C.
Watanabe, Hiroichi, lsshiki, Naotsugu, Ohtomo, Mitsuhiro, Watanabe, Kuniya
Stirling Bottoming Cycle for the Gas Turbine Exhaust Streams of Pipeline Compressor Stations9293938/3/1992
In pipeline compressor stations natural gas fuelled aircraft derivative gas turbines are frequently used in conjunction with a power turbine to drive the large centrifugal compressors for ‘boosting’ the pipeline pressure. Typically two thirds of the energy provided to drive the turbine is carried off as heat in the exhaust stream. These hot exhaust streams, typically at temperatures around 500 K contain very substantial energies, 50 MW being not uncommon. This paper summarises recent studies carried out to assess the feasibility and worth of applying Stirling power systems to generate electric power from these ‘waste’ streams. Both ‘bottoming’ and topping cycles are of interest and are briefly considered in this paper. An elementary, but realistic, performance analysis indicates the possibility of recovering as much as 9 MW power from the exhaust of a gas compressor equipped with a Rolls-Royce RB 211 aircraft derivative gas turbine. There are approximately 6000 gas turbine/compressor units in 2750 gas pipeline compressor stations distributed throughout North America. On this basis it appears feasible that as much as 54,000 MW electric power may be generated from the existing turbine exhaust. It is anticipated the cost of the Stirling engine system would be about half the cost of the alternative Rankine cycle system.
Walker, G., Kremer, J., Fauvel, R., Reader, G., Bingham, E. R.
Pulsed Single-Blow Regenerator Testing9293868/3/1992
A pulsed single-blow method has been developed for testing of Stirling regenerator materials performance. The method uses a tubular flow arrangement with a steady gas flow passing through a regenerator matrix sample that packs the flow channel for a short distance. A wire grid heater spanning the gas flow channel is used to heat a plug of gas by approximately 2 K for approximately 350 ms. Foil thermocouples monitor the gas temperature entering and leaving the sample. Data analysis based on a 1-D incompressible-flow thermal model allows the extraction of Stanton number. A figure of merit involving heat transfer and pressure drop is used to present results for steel screens and steel felt. The observations show a lower figure of merit for the materials tested than is expected based on correlations obtained by other methods.
Oldson, J. C., Knowles, T. R.
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