Browse Topic: Stirling engines

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Quantification of Windage and Vibrational Losses in Flexure Springs of a One kW Two-Stroke Free Piston Linear Engine Alternator2019-01-08164/2/2019
Methods to quantify the energy losses within linear motion devices that included flexural springs as the main suspension component were investigated. The methods were applied to a two-stroke free-piston linear engine alternator (LEA) as a case study that incorporated flexure springs to add stiffness to the mass-spring system. Use of flexure springs is an enabling mechanism for improving the efficiency and lifespan in linear applications e.g. linear engines and generators, cryocoolers, and linear Stirling engines. The energy loss due to vibrations and windage effects of flexure springs in a free piston LEA was investigated to quantify possible energy losses. A transient finite element solver was used to determine the effects of higher modes of vibration frequencies of the flexure arms at an operational frequency of 65 Hz. Also, a computational fluid dynamics (CFD) solver was used to determine the effects of drag force on the moving surfaces of flexures at high frequencies. A parametric study was performed to understand the effects of geometrical and operational parameters including the diameter of flexures, gap width between flexure arms, stroke length, and frequency of oscillation on the drag force coefficient on the flexure surfaces. The numerical results were compared to experimental results obtained from damping tests and steady-state tests in a vacuum chamber. Modeled results were in good agreement with experiments and showed between 30 to 40 Watts of mechanical energy loss at 65 Hz in the 1 kW LEA design including windage and vibrational losses. It was also found that windage losses contributed to between 10-15% of the total mechanical losses. Also, damping tests in a vacuum chamber showed that in the absence of windage and acoustic losses between 30-35% of total input energy was lost due to structural and frictional damping. Measuring the amplitude of damped vibrations the damping ratio was calculated to be ζ=0.003.
Zamani Meymian, Nima, Clark, Nigel, Subramanian, Jayaram, Heiskell, Gregory, Johnson, Derek, Mahmudzadeh, Fereshteh, Darzi, Mahdi, Musho, Terence, Famouri, Parviz
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.
Experimental and Numerical Study of Porosity Gradient in a Stirling Engine Regenerator2017-01-01483/28/2017
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. The results show that in the second model with a small increase in pressure drop during recovery, the amount of energy recovery increase dramatically compared to the conventional model.
Arab, Majid, Majidi, Majid
Automobile Exhaust Gas Heat Energy Recovery Using Stirling Engine: Thermodynamic Model2017-26-00291/10/2017
Higher fuel economy of the vehicle is a critical concern in automobile industry. Traditional internal combustion (IC) engines waste a large portion of the available fuel energy as heat loss via exhaust gas. This proposal aims at recovering the available exhaust heat of the IC engines using stirling engine (SE) as an add-on device. SE is a type of cyclic heat engine which operates by compression and expansion of the working fluid, at different temperature levels resulting in a conversion of the heat energy into mechanical work. A thermodynamic analysis is performed on the chosen beta SE rhombic drive configuration with different combinations of design parameters like working fluid mass, total dead volume, thermal resistance, and hot side and cold side temperatures. A regenerator temperature model is developed to account for first law consistency in the regenerator section of SE, along with heat transfer in accordance with mass flow within the regenerator. In conclusion, the results indicate that a device based upon the typical tube fin type compact heat exchanger and Hydrogen as working fluid will have a working fluid volume of about 7.8 liters with 1016 W power at 12.65% thermal efficiency. For similar power output (1028 W), a smaller heat exchanger like the printed circuit heat exchanger (PCHE) requires 3.25 liters of working fluid volume at 10.85% thermal efficiency.
Saxena, Shubham, Ahmed, Mudassir
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.
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.
Double-acting Extremely Light Thermo-Acoustic (DELTA) ConverterTBMG-249487/1/2016
Power generation from an external or internal heat source using thermal energy conversion technologies such as solid-state thermionics and thermoelectrics or dynamic conversion with Otto, Stirling, Brayton, or Rankine technologies is fundamentally limited in maximum specific power due to either low efficiency and/or operating frequency. These solid-state technologies are low voltage and hence produce a high DC current that restricts their minimum geometry to approximately 4 A/mm2 to avoid overheating. High-power implementations of this technology class are inefficient, large, and heavy.
Honda R&D Technical Review April 2016B-HON-0194/1/2016
Honda's April 2016 R&D Technical Review features cutting-edge developments and new ways of solving engineering problems from Honda's worldwide R&D teams. This edition brings 23 technical papers and provides featured topics that include: • Development of New Fuel Cell Vehicle CLARITY FUEL CELL • Development of RC213V-S • Introduction of Heat Exchanger Production Technique for Stirling Engine Using Additive Manufacturing
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
High Efficiency Internal Combustion Stirling Engine Development2011-01-04104/12/2011
A unique engine, based on the regenerative principle, is being developed with the goal of achieving high brake efficiency over a wide power range. It can be characterized as an internal combustion Stirling engine (ICSE). The engine is a split-cycle configuration with a regenerator between the intake/compression cylinder and the power/exhaust cylinder. The regenerator acts as a counter-flow heat exchanger. During exhaust, the hot gases are cooled by the regenerator. The regenerator stores this heat. On the next cycle, compressed gases flow in the opposite direction and are heated by the regenerator. The gases coming from the regenerator into the power cylinder are very hot (~900°C), which provides the necessary gas temperature for auto-ignition of diesel and other fuels. A simplified Air Cycle analysis of the ICS engine is presented to validate the concept thermodynamics and to show the inherent difference between the ICS and conventional internal combustion engine (ICE) indicated efficiency. The ICE engine indicated efficiency increases with increasing compression ratio and is insensitive to peak temperatures, whereas in the ICS engine indicated efficiency increases with decreasing compression ratio and increasing peak temperature. This engine concept is a candidate for application of adiabatic engine technology which has been explored for many years. With materials that can withstand high temperatures, brake efficiencies of 60-70% are possible. Low heat transfer is important to the proper operation of the engine. A multi-step cycle computer indicated thermodynamic and fluid flow model of the ICS engine of increasing detail was used during the engine development. Finally, detailed perturbation studies were conducted to fully understand the ICS design sensitivities. An engine friction model was added to the computer model to be able to compare estimates of ICSE BSFC and BMEP with ICE engines. Important ICS engine innovations include elimination of throttling losses, low friction due to low compression ratio, and very high air cycle efficiencies (~80%) combined with low compression ratio. The engine is designed for the highest possible efficiencies. In addition to these advantages, the engine has nearly constant pressure combustion, which should help reduce NOx formation. The major findings were: the ICS engine is more efficient than either gasoline or diesel engines over the entire operating range especially at part power. At wide open throttle, an ICS engine is more efficient than either a gasoline or a diesel engine. This advantage increases at part power. On the negative side, the ICS engine has inherent low power density (volumetric efficiency) because of low compression ratio, late air intake and late combustion. A prototype engine and a modest engine test dynamometer and instrumentation are nearing completion to demonstrate the P&B Enterprises, Inc. (PBEI), ICSE concept. The prototype is a retrofitted two-cylinder diesel engine. The prototype uses the existing engine block, and the crankshaft and camshaft fit into existing spaces in the block. Anticipated problems to be addressed with the prototype engine are starting, combustion characteristics, regenerator temperature control and high turbocharging ratios to achieve reasonable power density.
Patton, Richard, Bennett, George
Heading back to the future10AEMD0519_015/19/2010
As the buzz about space grows, and with the potential for government resurrection of funding, materials for space travel-and materials creation in space-are taking on new life. New materials for space applications can be exceptionally expensive to develop, and expensive has not been a positive concept in the space community for many years. Never mind the technology spin-offs from space exploration; give no consideration to the advances in metals, composites, electronics, you name it-all of which have moved ahead since the 1950s thanks to rocket and space research. The national dismay and envy around Sputnik translated into government dollars. Not surprisingly, project numbers rose when funding was the most free and the romance of space travel caught the fancy of the public. Today, time has dimmed the romance, national pride has taken a back seat to international projects, and there have been high-profile reminders that life in space is precarious. The result: relatively low research funding.
Gayman, David
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.
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.
Ford turns 100AUTOJUN03_036/1/2003
Pausing to celebrate its many technical achievements of the past century, Ford maintains its focus on being an innovation leader for the next 100 years. One hundred years of existence is quite an accomplishment for any company, particularly for one in an industry that's as globally competitive as the automotive industry. Weathering two World Wars, the Great Depression, the challenges of constantly evolving to suit consumer demands of the time, not to mention some personal rough spots such as the tire-recall incident in 2000, Ford Motor Co. has managed to not merely survive throughout the past century, but to succeed.
Gehm, Ryan, Ludvigsen, Karl
Performance of Stirling Engine Hybrid Electric Vehicles: A Simulation Approach2001-01-25138/20/2001
Hybrid Vehicles have gained momentum in the automotive industry. The joint action of power sources and energy storage systems for energizing the vehicle improves the vehicle's fuel economy while reducing its pollutant emissions and noise levels, challenging automotive designers to optimize vehicle's cost, weight and control. The marketing success of hybrid vehicles significantly depends on the selection, integration and cost of the energy systems. The internal combustion engine, dominant of the vehicle market, has been the “option of choice” for auxiliary power unit of the hybrid vehicle, although other power sources as fuel cells, Stirling engines and gas turbines have been employed as well [1]. This document is focused in the application of Stirling engines as the power source for automobile propulsion. In order to optimize this process, a simulation tool for Stirling vehicle was developed based in ADVISOR, a proven hybrid electric vehicle simulation software, and MARWEISS, a Stirling engine simulator. [2] The simulation tool allows the study of Stirling-powered vehicles in conventional or hybrid electric (series, parallel or split) configurations, determining parameters of the vehicle like fuel consumption, power output, emissions, energy flow and the engine's temperature profile. The analysis of the simulation results can be employed to identify the critical features of the Stirling-powered vehicle.
Figueroa, Luis, Fauvel, Owen R., Reader, Graham T.
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.
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.
Study on Design and Performance Prediction Methods for Miniaturized Stirling Engine1999-01-33089/28/1999
This paper shows a design and performance prediction methods for a miniaturized Stirling engine, in order to develop a small portable generator set. First, a 100 W class Stirling engine is designed and manufactured. In order to miniaturize the engine, unique type heat exchangers were applied. A regenerator was located in a displacer piston. For a piston drive mechanism, a Scotch-yoke mechanism which was useful to realize the small-size engine without any lubricating device, was adopted. Next, an analysis model for the miniaturized engine is developed to improve the engine performance efficiently. The pressure in the working space is analyzed by an isothermal analysis which takes into account a gas leakage through a piston ring and pressure loss in the heat exchangers. To estimate a shaft power, the mechanical loss and the buffer loss, which is caused by a pressure change in a crank case are considered on the analysis model. The calculated results were compared with the experimental data carefully. Then we suggest how to develop practical Stirling engines as a next step.
Hirata, Koichi, Iwamoto, Shoichi
Afterburning Ericsson Cycle Engine1999-01-28808/17/1999
Initial development of an afterburning Ericsson cycle engine is described. The recently developed engine integrates the Ericsson cycle power producing processes (compression, heating, expansion, and cooling) with the combustion process. This cycle is capable of high thermodynamic efficiency and provides complete, continuous, combustion. The cycle offers the opportunity to achieve the high efficiencies that are promised by Stirling engines but have not been achieved in practice. Unlike Stirling engines, there is no efficiency lost in an external burner by having to heat the combustion air from ambient temperature. Instead, combustion is initiated at the high temperature of the isothermal expander exhaust. The flame temperature combustion products then transfer heat to the expander while cooling back to the expander temperature. In this manner, all the heat of combustion is available to the cycle. The afterburning Ericsson cycle engine can potentially use mostly conventional internal-combustion engine components to provide reduced fuel consumption and minimized emissions. Such powerplants may become a viable alternative to diesel engines or a candidate for use in hybrid vehicles. The cycle also has the environmental advantage of being adaptable to a wide range of both liquid and gaseous fuels.
Proeschel, Richard A.
Performance Modeling of 5th Generation Heat-Assisted Stirling Heat Pump (E-3)1999-01-27008/2/1999
This paper describes recent results in a project at KUBOTA to develop a multi-fuel gas engine driven Stirling heat pump. It is mainly driven by engine shaft power and is partially assisted by thermal power from the engine exhaust heat source. We have previously developed the D-3 machine, the fourth generation prototype of the heat-assisted Stirling heat pump. Performance simulations of the next (E-3) machine are presented in conjunction with driving engine characteristics. System matching and optimization criteria and constraints are discussed with implications for performance. This machine uses helium gas as a working gas and is constructed as two 3-cylinder sets, each a combination of two Stirling sub-systems (one a power producer and one a heat pump). Utilizing both shaft power and thermal power, performance is controlled by phase shifting of the hot-side pistons to adjust the absorbing of thermal power. This heat pump system is expected to produce cooling and heating water at high COP. Developing this machine will provide a CFC-free thermal utilization system technology that satisfies both wide heat demands and various fuel systems.
Yagyu, Sumio, Fujishima, Ichiro, Fukuyama, Yuji, Morikawa, Tomoyuki, Corey, John, Isshiki, Naotsugu, Satoh, Isao
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
Design and Analysis Code for Radiators of Stirling Power Systems With General Purpose (GPHS) Heat Sources1999-01-26748/2/1999
An efficient finite difference (FD) computational code has been developed for the analysis and design of circular sector radiators for linear alternator output “Free Piston Stirling Engine” space power systems utilizing a radioisotope Pu-238 General Purpose (GPHS) heat source. The code calls on a subroutine developed by the author to solve the second order, fourth degree, ordinary differential equation (ODE) of a fin (extended heat transfer surface) radiating to the space environment. Although the code was originally written for a rectangular coordinates system, it was transcribed into polar (cylindrical) coordinates for the present application. The circular sector radiator panel analyzed has an embedded heat pipe at an arbitrary radial location conducting cycle reject heat from the Stirling engine cold end to the radiator. For a required radiator heat load and a given set of geometrical and thermo-physical properties of the radiator sector, the code will compute the required radiator surface area and mass, surface temperature and heat flux profiles and also the optimum radial location for the heat pipe. A novel second subroutine is also used to determine equilibrium space sink temperatures anywhere within the Solar System. Since this non-zero sink temperature is included in the FD iterative solution of the non-linear ODE, the code has been useful in analyzing radiator temperatures of spacecraft with a perihelion well inside the orbit of Venus, as planned for some deep space missions.
Juhasz, Albert J., Thieme, Lanny G.
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
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
Basic Research on Solar Stirling Power Technology for Future Space Applications1999-01-26818/2/1999
A semi free-piston Stirling engine alternator, called NALSEM500, has been experimentally studied since April 1994, as part of a space solar power technology program in NAL (National Aerospace Laboratory). The Stirling alternator is one of candidates for future space power applications, and will be integrated with the solar cavity receiver subsystem, having both Na heat pipes and thermal energy storage. Through a series of preliminary bench tests, it was found that the efficiency of the linear alternator was significantly low as compared to our initial design. To improve the alternator performance, some design modifications of the magnet assembly and stator core have been made. As a result, the thermodynamic efficiency of 33% and system efficiency of 20% was obtained.
Hoshino, Takeshi, Fujihara, Tsutomu, Eguchi, Kunihisa
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, Ohtomo, Michihiro, Isshiki, Naotsugu
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
New Energy Management Technology Gives Hybrid Cars Long Battery Life1999-01-24688/2/1999
New energy-and-power management technology makes low-pollution hybrid electric vehicles practical and competitive in performance with gasoline powered cars. The fuel-burning engine can now run at its most efficient speed and load, with the propulsion motor supplying acceleration power and the generator capturing deceleration power. Battery depth of discharge can be monitored and controlled to get long battery life. A heavy battery is not needed for long travel distance. For example, the new Toyota Prius hybrid car delivers 66 miles per gallon in city driving and has a range of 600 miles on a tankful of gasoline. When acceleration power is supplied from a battery, then the engine can be a high-efficiency type, such as the 43-percent efficient Meijer version of the Stirling-cycle engine. Hydrogen, a previously impractical engine fuel, can be burned in external-combustion Stirling engines. Hydrogen can now be compactly stored in carbon nano-tubes or lithium aluminum tetrahydride. A new electrolyzer can produce hydrogen with 93.2 percent efficiency. The energy in hydrogen made with 6-cents-per kWh electricity costs one-half the price of energy in gasoline.
Oman, Henry
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.
History of the Electric AutomobileR-18710/1/1998
For more than a century, people have attempted to harness electricity, the clean and versatile fuel, for personal transportation. With impressive technical clarity and historical insight, author Ernest Wakefield reviews these attempts in History of the Electric Automobile: Hybrid Electric Vehicles. He focuses exclusively on electric vehicles that harness the potential of electricity when combined with another energy source - hybrid electric vehicles (HEV). The book details the historical development of capacitors, engines, flywheels, fuel cells, inductive charging, and solar cells - and the application of each to hybrid electric vehicles.
Wakefield, Ernest H.
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.
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.
Effective Energy Utilization and Emission Reduction of Exhaust Gas in a Two-Stroke Cycle Engine — Part II9323949/1/1993
This paper deals with a research project concerning an effective utilization of exhaust gas heat. Exhaust gas from a exhaust gas-separate type two-stroke cycle engine containing a high concentration of unburned gas was temporarily stored in a floating-bell type tank as an form of heat energy conservation, while in the previous report [1]* exhaust heat was recovered with continuous operation. A Stirling engine with a hot-water supply system was then used to oxidize or burn again the exhaust gas in a catalyzer and an after-burner unit in order to recover the unspent heat energy from the exhaust gas. A three-way catalyzer was employed to remove pollutants both from the combustion gas in this process and the high-concentration burned gas from the two-stroke cycle engine. The results of the research in the present paper are intended as a follow-up of the previous report [1] to clarify a method for the more effective use of exhaust gas heat. Similarly to the results presented in the previous paper the present follow-up report establishes a method for the nearly complete removal of the pollutants CO and HC from emission gas at a fuel lean range of air-fuel ratio. The method significantly reduces the NO content of the gas at the same air-fuel ratio. It should also be noted that utilizing the Zeldovich reaction mechanism increases the ability to verify NO formation characteristics in the emission gas for measured results. The previous paper had reported that the bimolecular reaction mechanism also served to study the formation characteristics of NO in the process.
Sato, Kazuo, Nakano, Masamitsu, Ukawa, Haruo
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.
Dynamic Behavior and Load Matching Analysis of the Mark II Free-Piston Stirling Engine Heat Pump9290348/3/1992
The Mark II free-piston heat actuated heat pump (HAHP) utilizes a linear magnetic coupling to transfer engine power across a hermetic shell, thereby driving the refrigerant compressor piston. Compliance in the coupling affects the dynamic behavior of the system. This paper presents the results of dynamic/thermodynamic analyses performed on a baseline Mark II design that is intended for the residential heat pump market. The machine has 3 ton cooling capacity at 95°F ambient conditions. Load matching behavior is evaluated using the HFAST Stirling cycle thermodynamics code, coupled to harmonic equations representing the 5 degree-of-freedom free-piston dynamic system. Behavior at outdoor ambients from 115°F to 0°F is presented, along with the results of nonlinear transient simulations done to verify stability.
Vincent, Ronald J.
Comparison of GLIMPS and HFAST Stirling Engine Code Predictions with Experimental Data9290298/3/1992
Predictions from GLIMPS and HFAST design codes are compared with experimental data for the RE-1000 and SPRE free-piston Stifling engines. Engine performance and available power loss predictions are compared. Differences exist between GLIMPS and HFAST loss predictions. Both codes require engine-specific calibration to bring predictions and experimental data into agreement.
Geng, Steven M., Tew, Roy C.
Dynamic Analysis of Free-Piston Stirling Engine/Linear Alternator-Load System - Experimentally Validated9292658/3/1992
This paper discusses the effects of variations in system parameters on the dynamic behavior of a Free-Piston Stirling Engine/Linear Alternator (FPSE/LA)-load system. The mathematical formulations incorporate both the mechanical and thermodynamic properties of the FPSE, as well as the electrical equations of the connected load. State-space technique in the frequency domain is applied to the resulting system of equations to facilitate the evaluation of parametric impacts on the system dynamic stability. Also included is a discussion on the system transient stability as affected by sudden changes in some key operating conditions. Some representative results are correlated with experimental data to verify the model and analytic formulation accuracies. Guidelines are given for ranges of the system parameters which will ensure an overall stable operation.
Kankam, M. David, Rauch, Jeffrey S., Santiago, Walter
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.
Rauch, Jeffrey S., Madi, Frank J., Kankam, M. David, Santiago, Walter
M-H Characteristics and Demagnetization Resistance of Samarium-Cobalt Permanent Magnets to 300 C9292638/3/1992
The influence of temperature on the M-H demagnetization characteristics of permanent magnets is important information for the full utilization of the capabilities of samarium-cobalt magnets at high temperatures in demagnetization-resistant permanent magnet devices. In high temperature space power converters, such as free-piston Stirling engine driven linear alternators, magnet demagnetization can occur as a long-term consequence of thermal agitation of domains and of metallurgical change, and also as an immediate consequence of too large an applied field. This paper investigates the short-term demagnetization resistance to applied fields derived from basic M-H data. This quasistatic demagnetization data was obtained for commercial, high-intrinsic-coercivity, Sm2Co17-type magnets, from 5 sources, in the temperature range 23 to 300 C. An electromagnet driven, electronic hysteresigraph was used to test the 1-cm cubic samples. The observed variation of the 2nd quadrant M-H characteristics was a typical rapid loss of M-coercivity and a relatively lesser loss of remanence with increasing temperature. The 2nd quadrant M-H curve knee point is used to define the limits of operation safe against irreversible demagnetization due to an excessive bucking field for a given flux density swing at temperature. Such safe operating area plots are shown to differentiate the high temperature capabilities of the samples from different sources. For most of the samples their 2nd quadrant M-H loop squareness increased with temperature, reaching a peak or a plateau above 250 C.
Niedra, J. M.
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., Rosswurm, Mark
HOTS to WATTS: The FPSE Linear Alternator System Re-Invented9292618/3/1992
Functional cost analyses of recent free-piston Stirling engines with linear alternators (FPSE/LA's) show that the majority of the manufacturing cost is in the mechanical to electrical conversion, not in the Stirling cycle. This paper introduces the first fruits of a systems-based redesign; the STAR™ alternator and Commuter™ suspension, which replace conventional linear alternator and bearings for less than half the mass and cost. Descriptions are given of the mechanisms, analyses, prototypes and initial test results, including those from a NASA-Lewis Phase I SBIR into this promising new technology.
Corey, John A., Yarr, George A.
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.
Kolin, Ivo, 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
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.
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