Stirling engine design manual pdf


 

r.,_. DOE/NASA/I. NASA C,q Stirling Engine Design Manual. Second Edition. {NASA-CR 88). ST_LiNG.,,'-NGINEDESI_. Stirling engine design manual, 2nd edition. NTRS Full-Text: View Document [ PDF Size: MB]. Author and Affiliation: Martini, W. R., (Martini Engineering. Investigating the applicability of Stirling engines in a design analysis and synthesis tool capable of opti- Keywords: Heinrici Stirling engine, Schmidt, adia -.

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Stirling Engine Design Manual Pdf

a Stirling engine to function as an electric generator. design the engine components, and manufacturing was performed using Haas CNC. Download the Book:Stirling Engine Design Manual PDF For Free, Preface: For Stirling engines to enjoy widespread application and acceptance, not only must. Stirling engine is used to generate electrical power from the solar radiation, it results in . with greater detail in “Stirling Design Manual” [3]. Third order Analysis.

History[ edit ] The early Hot Air Engines[ edit ] Robert Stirling is considered as one of the fathers of hot air engines, notwithstanding some earlier predecessors, notably Amontons , [6] who succeeded in building, in , the first working hot air engine. He has been later followed by Cayley. Stirling came up with a first air engine in It was to it that the inventor devoted most of his attention. A two horse-power engine, built in for pumping water at an Ayrshire quarry, continued to work for some time, until a careless attendant allowed the heater to become overheated. This experiment proved to the inventor that, owing to the low working pressure obtainable, the engine could only be adapted to small powers for which there was at that time no demand. The Stirling patent [9] was also about an "Economiser", is the predecessor of the regenerator. In this patent he describes the "economiser" technology and several applications where such technology can be used. Out of them came a new arrangement for a hot air engine.

These usually limit the engine's heat throughput. In practice this additional power may not be fully realized as the additional "dead space" unswept volume and pumping loss inherent in practical regenerators reduces the potential efficiency gains from regeneration. The design challenge for a Stirling engine regenerator is to provide sufficient heat transfer capacity without introducing too much additional internal volume 'dead space' or flow resistance. These inherent design conflicts are one of many factors that limit the efficiency of practical Stirling engines.

A typical design is a stack of fine metal wire meshes , with low porosity to reduce dead space, and with the wire axes perpendicular to the gas flow to reduce conduction in that direction and to maximize convective heat transfer. The regenerator is the key component invented by Robert Stirling and its presence distinguishes a true Stirling engine from any other closed cycle hot air engine.

Many small 'toy' Stirling engines, particularly low-temperature difference LTD types, do not have a distinct regenerator component and might be considered hot air engines; however a small amount of regeneration is provided by the surface of the displacer itself and the nearby cylinder wall, or similarly the passage connecting the hot and cold cylinders of an alpha configuration engine.

In small, low power engines this may simply consist of the walls of the cold space s , but where larger powers are required a cooler using a liquid like water is needed to transfer sufficient heat. The larger the temperature difference between the hot and cold sections of a Stirling engine, the greater the engine's efficiency.

The heat sink is typically the environment the engine operates in, at ambient temperature. In the case of medium to high power engines, a radiator is required to transfer the heat from the engine to the ambient air.

Marine engines have the advantage of using cool ambient sea, lake, or river water, which is typically cooler than ambient air. In the case of combined heat and power systems, the engine's cooling water is used directly or indirectly for heating purposes, raising efficiency. Alternatively, heat may be supplied at ambient temperature and the heat sink maintained at a lower temperature by such means as cryogenic fluid see Liquid nitrogen economy or iced water. The displacer is a special-purpose piston , used in Beta and Gamma type Stirling engines, to move the working gas back and forth between the hot and cold heat exchangers.

Depending on the type of engine design, the displacer may or may not be sealed to the cylinder, i. There are three major types of Stirling engines, that are distinguished by the way they move the air between the hot and cold areas:. An alpha Stirling contains two power pistons in separate cylinders, one hot and one cold. The hot cylinder is situated inside the high temperature heat exchanger and the cold cylinder is situated inside the low temperature heat exchanger.

This type of engine has a high power-to-volume ratio but has technical problems because of the usually high temperature of the hot piston and the durability of its seals. The crank angle has a major effect on efficiency and the best angle frequently must be found experimentally.

The following diagrams do not show internal heat exchangers in the compression and expansion spaces, which are needed to produce power. A regenerator would be placed in the pipe connecting the two cylinders. A beta Stirling has a single power piston arranged within the same cylinder on the same shaft as a displacer piston. The displacer piston is a loose fit and does not extract any power from the expanding gas but only serves to shuttle the working gas between the hot and cold heat exchangers.

When the working gas is pushed to the hot end of the cylinder it expands and pushes the power piston. When it is pushed to the cold end of the cylinder it contracts and the momentum of the machine, usually enhanced by a flywheel , pushes the power piston the other way to compress the gas.

Unlike the alpha type, the beta type avoids the technical problems of hot moving seals, as the power piston is not in contact with the hot gas. Again, the following diagrams do not show any internal heat exchangers or a regenerator, which would be placed in the gas path around the displacer.

If a regenerator is used in a beta engine, it is usually in the position of the displacer and moving, often as a volume of wire mesh. A gamma Stirling is simply a beta Stirling with the power piston mounted in a separate cylinder alongside the displacer piston cylinder, but still connected to the same flywheel. The gas in the two cylinders can flow freely between them and remains a single body. This configuration produces a lower compression ratio because of the volume of the connection between the two but is mechanically simpler and often used in multi-cylinder Stirling engines.

The rotary Stirling engine seeks to convert power from the Stirling cycle directly into torque, similar to the rotary combustion engine. No practical engine has yet been built but a number of concepts, models and patents have been produced, such as the Quasiturbine engine.

A hybrid between piston and rotary configuration is a double acting engine. This design rotates the displacers on either side of the power piston. In addition to giving great design variability in the heat transfer area, this layout eliminates all but one external seal on the output shaft and one internal seal on the piston.

Also, both sides can be highly pressurized as they balance against each other. Another alternative is the Fluidyne engine Fluidyne heat pump , which uses hydraulic pistons to implement the Stirling cycle. The work produced by a Fluidyne engine goes into pumping the liquid. In its simplest form, the engine contains a working gas, a liquid, and two non-return valves. The Ringbom engine concept published in has no rotary mechanism or linkage for the displacer.

This is instead driven by a small auxiliary piston, usually a thick displacer rod, with the movement limited by stops. In a double acting engine, the pressure of the working fluid acts on both sides of the piston.

One of the simplest forms of a double acting machine, the Franchot engine consists of two pistons and two cylinders, and acts like two separate alpha machines. In the Franchot engine, each piston acts in two gas phases, which makes more efficient use of the mechanical components than a single acting alpha machine. However, a disadvantage of this machine is that one connecting rod must have a sliding seal at the hot side of the engine, which is difficult when dealing with high pressures and temperatures.

Free-piston Stirling engines include those with liquid pistons and those with diaphragms as pistons. In a free-piston device, energy may be added or removed by an electrical linear alternator , pump or other coaxial device.

This avoids the need for a linkage, and reduces the number of moving parts. In some designs, friction and wear are nearly eliminated by the use of non-contact gas bearings or very precise suspension through planar springs. In the early s, W. Beale invented a free piston version of the Stirling engine to overcome the difficulty of lubricating the crank mechanism.

Cooke-Yarborough and C. Benson also made important early contributions and patented many novel free-piston configurations. The first known mention of a Stirling cycle machine using freely moving components is a British patent disclosure in The first consumer product to utilize a free piston Stirling device was a portable refrigerator manufactured by Twinbird Corporation of Japan and offered in the US by Coleman in Design of the flat double-acting Stirling engine solves the drive of a displacer with the help of the fact that areas of the hot and cold pistons of the displacer are different.

The drive does so without any mechanical transmission. Using diaphragms eliminates friction and need for lubricants. When the displacer is in motion, the generator holds the working piston in the limit position, which brings the engine working cycle close to an ideal Stirling cycle.

The ratio of the area of the heat exchangers to the volume of the machine increases by the implementation of a flat design. Flat design of the working cylinder approximates thermal process of the expansion and compression closer to the isothermal one.

The disadvantage is a large area of the thermal insulation between the hot and cold space. Thermoacoustic devices are very different from Stirling devices, although the individual path travelled by each working gas molecule does follow a real Stirling cycle.

These devices include the thermoacoustic engine and thermoacoustic refrigerator. High-amplitude acoustic standing waves cause compression and expansion analogous to a Stirling power piston, while out-of-phase acoustic travelling waves cause displacement along a temperature gradient , analogous to a Stirling displacer piston.

Stirling engine

Thus a thermoacoustic device typically does not have a displacer, as found in a beta or gamma Stirling. Starting in , Infinia Corporation began developing both highly reliable pulsed free-piston Stirling engines, and thermoacoustic coolers using related technology. The published design uses flexural bearings and hermetically sealed Helium gas cycles, to achieve tested reliabilities exceeding 20 years.

As of , the corporation had amassed more than 30 patents, and developed a number of commercial products for both combined heat and power, and solar power. More recently, NASA has considered nuclear-decay heated Stirling Engines for extended missions to the outer solar system.

American Stirling Company

Kamen refers to it as a Stirling engine. The idealised Stirling cycle consists of four thermodynamic processes acting on the working fluid:. Theoretical thermal efficiency equals that of the hypothetical Carnot cycle — i. However, though it is useful for illustrating general principles, the ideal cycle deviates substantially from practical Stirling engines. Other real-world issues reduce the efficiency of actual engines, because of limits of convective heat transfer , and viscous flow friction.

There are also practical mechanical considerations, for instance a simple kinematic linkage may be favoured over a more complex mechanism needed to replicate the idealized cycle, and limitations imposed by available materials such as non-ideal properties of the working gas, thermal conductivity , tensile strength , creep , rupture strength , and melting point.

A question that often arises is whether the ideal cycle with isothermal expansion and compression is in fact the correct ideal cycle to apply to the Stirling engine.

Professor C. Rallis has pointed out that it is very difficult to imagine any condition where the expansion and compression spaces may approach isothermal behavior and it is far more realistic to imagine these spaces as adiabatic. He called this cycle the 'pseudo-Stirling cycle' or 'ideal adiabatic Stirling cycle'. An important consequence of this ideal cycle is that it does not predict Carnot efficiency. A further conclusion of this ideal cycle is that maximum efficiencies are found at lower compression ratios, a characteristic observed in real machines.

In an independent work, T. Finkelstein also assumed adiabatic expansion and compression spaces in his analysis of Stirling machinery [78]. Since the Stirling engine is a closed cycle, it contains a fixed mass of gas called the "working fluid", most commonly air , hydrogen or helium.

Hand Book Stirling Engine - Stirling Engine Manual | Internal Combustion Engine | Combustion

In normal operation the engine is sealed and no gas enters or leaves the engine. No valves are required, unlike other types of piston engines. The Stirling engine, like most heat engines, cycles through four main processes: This is accomplished by moving the gas back and forth between hot and cold heat exchangers , often with a regenerator between the heater and cooler.

The hot heat exchanger is in thermal contact with an external heat source, such as a fuel burner, and the cold heat exchanger is in thermal contact with an external heat sink, such as air fins. A change in gas temperature causes a corresponding change in gas pressure, while the motion of the piston makes the gas alternately expand and compress.

The gas follows the behaviour described by the gas laws , which describe how a gas's pressure , temperature and volume are related. When the gas is heated the pressure rises because it is in a sealed chamber and this pressure then acts on the power piston to produce a power stroke. When the gas is cooled the pressure drops and this drop means that the piston needs to do less work to compress the gas on the return stroke.

The difference in work between the strokes yields a net positive power output. As with other external combustion engines, Stirling engines can use heat sources other than from combustion of fuels. When one side of the piston is open to the atmosphere, the operation is slightly different.

As the sealed volume of working gas comes in contact with the hot side, it expands, doing work on both the piston and on the atmosphere. When the working gas contacts the cold side, its pressure drops below atmospheric pressure and the atmosphere pushes on the piston and does work on the gas.

To summarize, the Stirling engine uses the temperature difference between its hot end and cold end to establish a cycle of a fixed mass of gas, heated and expanded, and cooled and compressed, thus converting thermal energy into mechanical energy.

The greater the temperature difference between the hot and cold sources, the greater the thermal efficiency. The maximum theoretical efficiency is equivalent to that of the Carnot cycle , but the efficiency of real engines is less than this value because of friction and other losses.

Very low-power engines have been built that run on a temperature difference of as little as 0. A temperature difference is required between the top and bottom of the large cylinder to run the engine. In the case of the low-temperature difference LTD stirling engine, the temperature difference between one's hand and the surrounding air can be enough to run the engine.

The power piston in the displacer type stirling engine is tightly sealed and is controlled to move up and down as the gas inside expands. The displacer, on the other hand, is very loosely fitted so that air can move freely between the hot and cold sections of the engine as the piston moves up and down. The displacer moves up and down to cause most of the gas in the displacer cylinder to be either heated, or cooled. Note that in the following description of the cycle the heat source at the bottom the engine would run equally well with the heat source at the top:.

In most high power Stirling engines, both the minimum pressure and mean pressure of the working fluid are above atmospheric pressure. This initial engine pressurization can be realized by a pump, or by filling the engine from a compressed gas tank, or even just by sealing the engine when the mean temperature is lower than the mean operating temperature.

All of these methods increase the mass of working fluid in the thermodynamic cycle. All of the heat exchangers must be sized appropriately to supply the necessary heat transfer rates. If the heat exchangers are well designed and can supply the heat flux needed for convective heat transfer , then the engine, in a first approximation, produces power in proportion to the mean pressure, as predicted by the West number , and Beale number.

In practice, the maximum pressure is also limited to the safe pressure of the pressure vessel. Like most aspects of Stirling engine design, optimization is multivariate , and often has conflicting requirements. This heat transfer is made increasingly difficult with pressurization since increased pressure also demands increased thicknesses of the walls of the engine, which, in turn, increase the resistance to heat transfer.

At high temperatures and pressures, the oxygen in air-pressurized crankcases, or in the working gas of hot air engines , can combine with the engine's lubricating oil and explode.

At least one person has died in such an explosion. Lubricants can also clog heat exchangers, especially the regenerator. For these reasons, designers prefer non-lubricated, low- coefficient of friction materials such as rulon or graphite , with low normal forces on the moving parts, especially for sliding seals.

Some designs avoid sliding surfaces altogether by using diaphragms for sealed pistons. These are some of the factors that allow Stirling engines to have lower maintenance requirements and longer life than internal-combustion engines.

In contrast to internal combustion engines, Stirling engines have the potential to use renewable heat sources more easily, and to be quieter and more reliable with lower maintenance.

By maintaining a hot and cold temperature difference the engine is able to run and produce mechanical power. It is different from the Internal Combustion Engine ICE in that it is a closed cycle; that is, the working gas is enclosed sealed inside the engine.

This is in contrast to the ICE in which the working gas air is drawn in from the environment, combusted with fuel, and expelled as exhaust. In such an engine valves and timing mechanisms are necessary. But in a Stirling engine, no such components are required. In addition, the Stirling engine is not restricted to the type of fuel used.

It is indifferent to the source of heat, which opens up many possibilities, including non-polluting solar energy, or the burning of biomass wood, husks, ethanol, etc , which are carbon-neutral. Carbon-neutral means they absorb as much carbon dioxide during their growth - due to photosynthesis as they emit when burned. This is unlike fossil fuels, which add a net amount of carbon dioxide to the atmosphere when burned.

The basic principle of the Stirling engine is this. The engine is filled under pressure , with a gas such as air, helium, or hydrogen.

This is called the working gas. Inside the engine the gas is heated. This increases its pressure and moves pistons as a result. The gas is then cooled, lowering its pressure. It is then heated again, and the cycle repeats. In a real engine this typically happens very fast, on the same order of speed as an ICE.

The working gas is shuttled back and forth very quickly inside the engine, between the hot and cold ends, continuously gaining and losing heat and producing power as a result. The working gas inside the engine is heated with a heater, and cooled with a cooler.

The heater and cooler are typically compact heat exchangers consisting of narrow tubes or passageways in which the working gas flows.

It is through these passageways that the working gas either gains heat becoming hotter , or loses heat becoming cooler. The outside surface of the heater is exposed to a source of high temperature, such as the flame of a burner, or concentrated solar energy. The outside surface of the cooler is exposed to a source of cold temperature such as ambient air, or water. In between the heater and cooler is a regenerator.

A regenerator increases the efficiency of a Stirling engine by lowering the heat input requirement of the heater and the heat removal requirement of the cooler. It is not necessary to have a regenerator for the engine to run but in the interest of cost-reduction, especially where the cost of heater fuel is concerned, it is wise to have one. The way the regenerator works is by storing some of the heat energy of the working gas as it moves from the heater to the cooler, thereby reducing the cooling demand on the cooler.

And on the return path, as the working gas moves from the cooler to the heater, it gains back some of that heat energy, thereby reducing the heating requirement of the heater. A regenerator basically pre-heats the working gas before it enters the heater, and pre-cools the working gas before it enters the cooler.

The regenerator is usually made of an intricate matrix material, made of stacked metal screens or metal felt, woven from fine wire. This provides the large surface area necessary for efficient heat exchange with the working gas. In general, when designing Stirling engines for high power and efficiency there are several main factors, which must be addressed: 1 Keep dead volume to a minimum.

Dead volume decreases engine power. Dead volume is the volume that is unswept by the motions of the pistons. This is the volume contained in the heater, cooler, regenerator, and all the clearance spaces. This volume is constant at all times.

This can be accomplished by using a sufficiently dense matrix material with large surface area. Now, points 2 - 5 can all be satisfied at the same time. There's a problem with your browser or settings. Primary menu Skip to content. Start a New Search: Record 1 of 1. Martini, W. This manual is intended to serve as an introduction to Stirling cycle heat engines, as a key to the available literature on Stirling engines and to identify nonproprietary Stirling engine design methodologies.

Two different fully described Stirling engines are discussed. Engine design methods are categorized as first order, second order, and third order with increased order number indicating increased complexity.

FORTRAN programs are listed for both an isothermal second order design program and an adiabatic second order design program.

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