Browse Topic: Stirling engines

Items (87)

EDITORIAL: The world's most capable hybrid vehicle

20AUTP08_0407/01/2020

What does the future hold for hybrid-electric vehicle technology? In recent years battery EVs have captured the mobility industry's focus, Hybrids, of course, continue to offer efficiency and practicality for millions of customers - ask the owner of any Prius taxicab. The technology is robust and proven, even making its way recently into Jeeps and soon, Ford's F-150 (see p. 11). But when the BEVs finally take over the world's roads and even its airspace, as some predict, what then for hybrids? The answer may reside in what is reputed to be the world's most capable HEV. Can you guess what it is?

Brooke, Lindsay

Detecting Chemical Weapons Using Fourier Transform Infrared Spectroscopy

TBMG-3516509/01/2019

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.

Alpha-STREAM Convertor

TBMG-2719807/01/2017

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

Experimental and Numerical Study of Porosity Gradient in a Stirling Engine Regenerator

2017-01-014803/28/2017

The approaching the ideal efficiency assumption is possible in Stirling engine. Regenerator is the main component in improving the efficiency of the engine. Besides the Geometry and materials of the regenerator, amount and quality of porosity have significant impacts on the regenerator performance which is focused on this research. The main idea of this study is to evaluate the effect of porosity, or unsymmetrical porosity gradient in pressure drop and the thermodynamic performance of regenerator, so three models of regenerator are developed and analyzed: First, a model in which the porosity is constant and do not change (Common mode). In the Second model, the length of regenerator porosity is changed from high to low and in the third model, the length of regenerator porosity is changed from low to high. All versions of models have the same global porosity. Each of these models is separately simulated in Ansys software and validated with experimental results from a laboratory sample

Arab, Majid, Majidi, Majid

Mechanisms for Achieving Non-Sinusoidal Waveforms on Stirling Engines

TBMG-2614901/01/2017

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

Improving Stirling Engine Performance Through Optimized Piston and Displacer Motion

TBMG-2615201/01/2017

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 Engine

2014-36-028209/30/2014

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

de Paula Brito, Gelcino, Borges, José Antônio Ferreira

Magnetostrictive Alternator

TBMG-1767411/01/2013

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 Bearings

TBMG-1484810/01/2012

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.

Microfabricated Segmented-Involute-Foil Regenerator for Stirling Engines

TBMG-870511/01/2010

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.

Dynamic Balancing of Multiple Independent Stirling Engines

TBMG-TB-00730702/05/2010

Vibrations are minimized without sacrificing redundancy. 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

Development of a Single-Fluid Consumable Infrastructure for Life Support Systems

2007-01-324607/09/2007

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.

Thermoelectric Air/Soil Energy-Harvesting Device

TBMG-TB-00052212/19/2006

Small amounts of power would be extracted from natural temperature differences. 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.

Microscale Regenerative Heat Exchanger

TBMG-6108/01/2006

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 Device

TBMG-52210/01/2005

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 Engines

TBMG-730804/01/2001

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 Engines

TBMG-730704/01/2001

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.

Evaluation of 6 Different Correlations for the Flow Friction Factor of Stirling Engine Regenerators

1999-01-245608/02/1999

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

Thomas, Bernd

Hydrogen Permeation Issue for Gas Fired AMTEC Systems

1999-01-255708/02/1999

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

Mital, R., Butkiewicz, D. A., Childs, K. F., Hayes, D. D., Svedberg, R. C., Hunt, T. K.

A Study on Temperature Distribution of Stirling Engine Regenerator

1999-01-250608/02/1999

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 System

1999-01-245308/02/1999

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

THE SECOND STIRLING TECHNO RALLY CONTEST OF MODEL AND MANNED STIRLING ENGINE CARS

1999-01-250308/02/1999

“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

PROPOSAL AND BASIC EXPERIMENTS OF SUPER STIRLING ENGINES

1999-01-250208/02/1999

“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

Composite-Matrix Regenerators for Stirling Engines

TBMG-211301/01/1999

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 Rig

TBMG-222302/01/1998

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 Systems

97238507/01/1997

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 Cryocooler

95172007/01/1995

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 Aid

95009702/01/1995

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.

Development of Lightweight Radiators for Lunar Based Power Systems

94132706/01/1994

This report discusses application of a new lightweight carbon-carbon (C-C) space radiator technology developed under the NASA Civil Space Technology Initiative (CSTI) High Capacity Power Program to a 20 kWe lunar based power system. This system comprises a nuclear (SP-100 derivative) heat source, a Closed Brayton Cycle (CBC) power conversion unit with heat rejection by means of a plane radiator. The new radiator concept is based on a C-C composite heat pipe with integrally woven fins and a thin walled metallic liner for containment of the working fluid. Using measured areal specific mass values (1.5 kg/m2) for flat plate radiators, comparative CBC power system mass and performance calculations show significant advantages if conventional heat pipes for space radiators are replaced by the new C-C heat pipe technology.

Juhasz, Albert J., Bloomfield, Harvey S.

Free-Piston Stirling Convertor Dynamic Gas Bearings

92938408/03/1992

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

Dimofte, Florin, Liebler, Kenneth A.

Regenerator Elements for Internal Combustion Stirling Engine

92938708/03/1992

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

Moriya, Shinji, Isshiki, Naotsugu

Further Evaluations of Low-Temperature Difference Stirling Engine Characteristics

92902208/03/1992

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.

Visualization of Entry Flow Separation for Oscillating Flow in Tubes

92946608/03/1992

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

Qiu, Songgang, Simon, Terrence W.

Energy Source Selection for Stirling Engine Driven AUV's

92940408/03/1992

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

Potter, I. J., Reader, G. T., Walker, G.

Pulsed Single-Blow Regenerator Testing

92938608/03/1992

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.

HFAST - A Harmonic Analysis Program for Stirling Cycles

92902808/03/1992

HFAST is a general-purpose third-order harmonic analysis and design program for predicting the cyclic-steady state thermodynamic performance of Stirling cycles. It represents the state-of-the-art results of years of research efforts at Mechanical Technology Inc. (MTI) in the development of Stirling cycle machines. The code has been extensively used at MTI to support the development of both free-piston and kinematic Stirling cycle machines. Lately, HFAST has undergone many major improvements, both in the analysis method and in the user's interface. This paper presents a brief description of the current analysis method used in HFAST.

Huang, S. C.

Stability Analysis of Free Piston Stirling Engine Power Generation System

92902508/03/1992

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.

The Thermodynamics of Stirling Engines Revisited: The Relative Merits of Hot Zone or Cold Zone Work Extraction

92902608/03/1992

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

Kentfield, J. A. C.

The Power Formula for Atmospheric Stirling Engines

92902708/03/1992

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

A Linear Model of a Free-Piston Vuilleumier Machine Compared to Experimental Results of a Prototype

92903208/03/1992

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.

Mechanical Efficiency Considerations in the Design of an Ultra Low Temperature Differential Stirling Engine

92902408/03/1992

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

Senft, J. R.

Computer Analysis of an Adiabatic Stirling Cryocooler Using a Two-Phase Two-Component Working Fluid

92917508/03/1992

This paper describes the performance and behavior of a Stirling cyrocooler incorporating a working fluid composed of helium and nitrogen. At the operating temperature of the cryocooler (80 K), the nitrogen component will condense in the freezer section. It is shown that the phase change in the working fluid increased the heat lifted for a given size and weight of machine and the coefficient of performance. The magnitude of these effects was dependent on the mass ratio of nitrogen to helium, phase angle between the compression and expansion processes, and the ratio of the compression space volume to the expansion space volume. The optimum heat lifted performance was obtained for a mass ratio of four parts of nitrogen to one part of helium, a phase angle of approximately 100 degrees, and a volume ratio of two which resulted in a heat lifted increase of 75% over the single phase, 90 degree phase angle configuration. The coefficient of performance showed a 20% improvement.

Renfroe, David A., Cheung, Che Man

An Adiabatic Approach for the Design and the Response-to-Load Evaluation of Free-Piston Stirling Engines

92906608/03/1992

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

Heat Transfer in Oscillating Flows with Sudden Change in Cross Section

92946408/03/1992

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

Tew, Roy C., Dudenhoefer, James E., Ibrahim, Mounir, Hashim, Waqar

Stirling Engine - Approach for Long-Term Durability Assessment

92917908/03/1992

This paper summarizes the approach being used by the NASA Lewis Research Center for the long-term durability assessment of the Stirling engine hot-section components. The approach consists of: (1) preliminary Structural assessment; (2) development of a viscoplastic constitutive model to accurately determine material behavior under high-temperature thermomechanical loads, such as creep and plasticity interaction, and creep-ratcheting; (3) an experimental program to characterize material constants for the viscoplastic constitutive model, and for the short-time verification of specific materials of interest; (4) finite-element thermal analysis, and structural analysis using a viscoplastic constitutive model to obtain stress/strain/temperature at the critical location of the hot-section components for life assessment; and (5) development of a life prediction model applicable for long-term durability assessment at high temperatures.

Bartolotta, Paul A., Halford, Gary R., Freed, Alan D.

100-kWe Lunar/Mars Surface Power Utilizing the SP-100 Reactor with Dynamic Conversion

92944608/03/1992

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

Harty, Richard B., Mason, Lee S.

Investigation of a New Heat-Pipe/Latent-Heat-Storage Receiver Element for Solar Dynamic Space Power Systems

92945008/03/1992

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

Study on Atmospheric Stirling Engine NAS-1

92939008/03/1992

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

Watanabe, Hiroichi, lsshiki, Naotsugu, Ohtomo, Mitsuhiro, Watanabe, Kuniya

Stirling Bottoming Cycle for the Gas Turbine Exhaust Streams of Pipeline Compressor Stations

92939308/03/1992

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

Walker, G., Kremer, J., Fauvel, R., Reader, G., Bingham, E. R.

Magnetic Bearings for Free-Piston Stirling Engines

92938308/03/1992

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

Rao, D. K., Wilson, D. S.

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