Water Fueled Engine Patent

Stirling Engine

Name and definition
Robert Stirling invented the first practical example of an air cycle engine shut down in 1816 and has suggested by Jenkin Fleeming already in 1884 that all engines of this type should be called Stirling engine generator. This naming proposal found little support, and various types market continued to be known by the name of their creators or manufacturers, for example, Rider, Robinson or Heinrici (hot) air from the engine. In the early 1940, Philips was looking for a suitable name for their own version of air motor, which by then had already been tested with other gases, settling about "Stirling Engine" in April 1945. However, almost thirty years later, Graham Walker was deploring the fact that terms such as "motor hot air "continued to be used interchangeably with" Stirling engine "which in turn has been applied widely and indiscriminately. Now the situation has improved somewhat, at least in the academic literature, and is now generally accepted that "Stirling engine" must refer exclusively to a closed cycle heat engine regenerative with a permanent working fluid gas, which is defined as a closed loop thermodynamic system which is constantly working fluid contained within system and describes the regenerative use of a specific type of internal heat exchanger and thermal reservoir, known as the regenerator. An engine working in the same principle but with a liquid instead of gaseous fluid existed in 1931 and was called the heat engine Malone.
It follows from the closed-loop operation the Stirling engine is an external combustion engine that isolates its working fluid from the energy input supplied by an external heat source. There are many possible implementations Stirling engine most of whom belong to the category of reciprocating piston engines.
Functional description
The engine is designed for the working gas is usually compressed in the coldest part of the engine and expanded in the hottest part resulting in a net conversion of heat into work. An internal regenerative heat exchanger increases the thermal efficiency of Stirling engine is easier in comparison with hot air engines do not have this trait.
Key components
cross-sectional diagram of a diamond drive beta configuration Stirling engine design:
Hot pink cylinder wall
dark gray and cold cylinder wall (with coolant inlet and outlet pipe in yellow)
Dark green insulation that separates the two ends Cylinder
Displacer piston green light
dark blue power piston
Light blue handle and fly Link
Not shown: the heat source and heat sinks. In this design the piston is constructed without a regenerator designed for it.
As a result of the closed-loop operation heat that powers a Stirling engine must be transmitted from a heat source to working fluid heat exchanger and finally to a heat sink. A Stirling engine system has at least one source of heat, a heat sink and a maximum of five heat exchangers. Some types can be combined or waive some of them.
A heat source
Point focus parabolic mirror with a Stirling engine in the center and solar tracker at Plataforma Solar de Almera (PSA) in Spain
The source of combustion heat can be of a fuel and, since the products of combustion mix with the working fluid (ie, external combustion) and contact with moving internal parts engine, a Stirling engine can run on fuels other than other damages (that is, internal combustion) engines internally, such as landfill gas containing siloxane.
Some other appropriate sources of heat is concentrated solar energy, geothermal energy, nuclear energy, waste heat, or even biological. If the heat source is solar energy, regular solar dishes and solar mirrors can be used. Also, Fresnel lenses have been recommended to be used (eg to explore the planet's surface). Solar Stirling engines are becoming increasingly popular because they are a very good choice for the environment to produce energy. In addition, some designs are economically attractive development projects.
Recuperator
An optional heat exchanger is the recovery used where high efficiency of combustion of input to output mechanical power. As the heater of a diesel engine must operate high efficiency a nearly uniform high temperature, there is a considerable loss of heat from the combustion gases exit the burner unless it can be cooled by air preheating for combustion. The engines used in combined heat and power systems in place can cool the exhaust gases on the "cold" the engine.
Heater
In small engines, low-power this may simply consist of the walls of the hot space (s), but where the great powers requires a larger surface area is required to transfer enough heat. Typical deployments are internal and external fins or multiple small-diameter tubes
The design of heat exchanger of the Stirling engine is a balance between the heat transfer from low to high viscosity pumping losses and low dead space. With engines operating at high volumes and pressures, the heat exchangers on the hot side should be made of alloys retaining considerable strength in the temperature and will not corrode or crawl.
Regenerator
Main article: regenerative heat exchanger
In a Stirling engine, the regenerator is a heat exchanger internal heat and store temporary heat located between hot and cold areas so that the working fluid passes through it first in one direction after the other. Its function is to keep within the system that the heat that otherwise would be exchanged with the environment at temperatures intermediate between maximum and minimum temperatures cycle, thus allowing the thermal cycle efficiency approaching limiting Carnot efficiency defined by the maximum and minimum.
The main feedback effect in a Stirling engine is significantly increase the thermal efficiency heat internally in a "recycling" that would otherwise pass through irreversible engine. As a side effect, increased thermal efficiency promises an output power higher from a given set of heat exchangers extreme hot and cold (as it is these that often limit the performance of heat engine), although in practice this additional power can not be fully realized as additional "dead space" (unswept volume) and the loss of inherent regenerative pumping practice tends to have the opposite effect.
Regenerator acts as a thermal capacitor. The ideal regenerator has a high thermal capacity, low thermal conductivity parallel to fluid flow, thermal conductivity very high perpendicular to fluid flow, almost no volume, and introduces no friction in the working fluid. In the regenerator approaches these ideal limits, increases efficiency Stirling engine.
The challenge of designing a Stirling engine regenerator is to provide sufficient heat transfer capability without introducing too much additional volume interior (dead space) or resistance to flow, which tend to reduce power and efficiency. These inherent design conflicts are one of the many factors that limit the efficiency of Stirling engine practices. A typical design is a stack of metal wire mesh of thin, low porosity to reduce dead space, and the wire axis perpendicular to the flow of gas to reduce driving in that direction and to maximize heat transfer by convection.
The regenerator is a key component invented by Robert Stirling and his presence that distinguishes a true Stirling engine of any motor closed loop hot air. However, many engines no apparent regenerative yet can be correctly described as displacer Stirling engines as in the beta and gamma simple configurations with a "loose", the surfaces of the displacer and the cylinder will cyclically exchange heat with the working fluid regenerative providing a significant effect particularly in small engines, low pressure. The same applies to the passageway that connects the hot and cold cylinder engine configuration alfa.
Cooler
In small engines, the low power may simply consist of the walls of the cold space (s), but where the great powers requires a refrigerator with a liquid such as water needed in order to transfer sufficient heat.
Heatsink
The heat sink is usually the environment at room temperature. In the case of medium to high power motors, radiator is required to transfer heat from the engine to the ambient air. Marine engines can use water from the environment. In the case of combined heat and power, water cooling engine is used directly or indirectly, for heating purposes.
Moreover, the heat can be supplied at ambient and heat sink keeps a lower temperature, for example by cryogenic liquid (see the liquid nitrogen economy) or ice water.
Settings
There Two main types of Stirling engines are distinguished by how they move air between hot and cold sides of the cylinder:
The two piston design alpha has independent pistons in cylinders, and gas is conducted between hot and cold spaces.
The displacement type Stirling engines, known as beta and gamma types isolated using a mechanical slider to push the working gas between hot and cold sides of the bottle. Shifter is large enough to insulate hot and cold sides of the cylinder and displace a large amount of gas. There must be enough of a gap between the displacer and the cylinder wall to allow gas to flow easily around the shifter.
Alpha Stirling
An alpha Stirling has two pistons in the cylinders of independent power, a hot and cold. The hot cylinder is located inside the heat exchanger high temperature and cold cylinder is located inside the heat exchanger temperature. This type of motor has a high power / volume, but has technical problems due to the usually high temperature of the hot piston and the durability of the stamps. In practice, This piston usually carries a large head to move insulating boards outside the hot zone at the expense of some additional dead space.
Action of an engine type Alpha Stirling
The following diagrams show no internal heat exchangers in the compression and expansion spaces, which are needed to produce energy. A regenerator would be placed in the tubes connecting the two cylinders. The crankshaft has also been omitted.
1. Most of the working gas is in contact with the walls of heated cylinder has been heated and the expansion has driven the piston cold to the bottom of its stroke in the cylinder. The expansion continues in the hot cylinder, which is 90 behind the piston cold in the cycle, extracting more work from the hot gas.
2. The gas is at its maximum volume. The plunger hot cylinder is set in motion most of the cold gas in the cylinder, where it cools and the pressure decreases.
3. Almost all gas is now in the cylinder cold and continue cooling. The cold piston, powered by the momentum of the wheel (or other piston pairs on the same axis) compresses the remaining part of the gas.
4. The gas reaches its minimum volume, and now will expand in the hot cylinder where it is heated again to drive the hot piston in its stroke.
The full type Stirling cycle Alpha
Stirling Beta
A beta Stirling has a single power piston arranged in the same cylinder on the same axis as a displacer piston. The piston is a bad connection and not drawing any power from the expanding gas but only serves to move the working gas exchanger hot heat cold heat exchanger. When the working gas is pushed to the hot end of the cylinder expands and pushes the power piston. When inserted into the end bottle cold contracts and the momentum of the machine, usually improves by a flywheel, pushes the piston the other way to compress the gas. Unlike the type alpha, beta type avoids the technical problems of hot moving seals.
Action of a beta type Stirling Engine
Again, these diagrams do not shows the internal heat exchanger or a regenerator, which is placed in the passage of gas around the shifter.
1. Power piston (dark gray) has compressed the gas, the piston shifter (light gray) has been moved so that most of the gas is close to the heat exchanger.
2. The heated gas increases in pressure and pushes the power piston to the last limit of the stroke.
3. The displacer piston now moves, the derivation of gas to the cold end of the bottle.
4. The cooled gas is now compressed by the momentum of the wheel. This requires less energy because it cools the pressure drops.
The full beta cycle type Stirling
Gamma Stirling
A gamma Stirling is simply a beta Stirling, which is mounted the piston in a cylinder separately with the cylinder displacer piston, but still connected to the wheel itself. The gas in the two cylinders can flow freely between them and remains a single body. This configuration produces a lower compression ratio but is mechanically simple and often used in multi-cylinder Stirling engine.
Other
Other settings Stirling continue to interest engineers and inventors. Peat Tom designed a configuration that likes to call a "Delta" type, although at present this name is not widely recognized, with a slider and two power pistons, a hot and cold.
There is also a Stirling engine rotation seeking to convert energy Stirling cycle directly into torque, similar to the rotary combustion engine. No practice is to build engine, but a series of concepts, models and patents have been produced, such as the Quasiturbine.
Another alternative is the Fluidyne motor (heat pump Fluidyne), which uses hydraulic pistons to implement the cycle of Stirling. The work produced by a Fluidyne engine enters the pumping liquid. In its simplest form, the engine contains a working gas, a liquid and two valves retention.
The Ringbom engine concept published in 1907 has no mechanism for rotating or link displacer. This time it's powered by a small auxiliary piston, usually a thick slider bar with the restriction of mobility through buffers.
Free piston engines
Several free-piston configurations Stirling … F. "Free cylinder, G. Fluidyne, H. "Double effect" Stirling (typically 4-cylinder)
"Free Piston" engine Stirling are those with liquid pistons and those with diaphragms as pistons. In a piston "free" device, the energy that can be added or removed by a linear electric generator, pump or other actuator. This leaves aside the need for a link, and reduces the number of moving parts. In some designs are almost eliminated friction and wear by the use of non-contact gas bearings or suspension very accurately through leaf springs.
In early 1960, WT Beale invented a free version of the Stirling engine piston in order to overcome the difficulty of lubricating the gears. While the invention of the free piston base Stirling motor is generally attributed to Beale, independent inventions of similar types of engines were made by EH Cooke-Yarborough, C. West of the Harwell laboratory in the UKAERE. Benson GM also made significant contributions early and patented many novel free-piston configurations.
What appears to be the first mention of a Stirling cycle machine freely moving components using patent disclosure is a British in 1876. This machine was designed as a bar (ie inverted Stirling cycle). The first consumer product using a free piston Stirling device was a portable refrigerator manufactured by Twinbird Corporation of Japan and are offered in the U.S. by Coleman in 2004.
Thermoacoustic cycle
Thermoacoustic devices are very different from Stirling devices, although the path traveled per person each gas molecule is a true work of Stirling cycle. These devices include thermoacoustic engine and thermoacoustic refrigerator. acoustic waves high amplitude standing cause compression and expansion similar to a piston Stirling power while out of phase sound waves traveling cause displacement along a temperature gradient, like a displacer piston Stirling. Thus, a thermoacoustic device usually does not have a slider, as found in a beta or gamma Stirling.
History
Illustration of the patent application 1816 Robert Stirling air engine design that later became known as the Stirling engine
The Stirling engine (Stirling engine or the air, as he was known then) was invented and patented by Robert Stirling in 1816. He followed first attempts to make an air motor, but it was probably the first to be put into practice when in 1818 he built a Stirling engine was used in a water pumping quarry. The main theme of Stirling's original patent was a heat exchanger which he called an economizer "for improved fuel economy in a variety of applications. The patent also describes in detail the use of an economizer in a single air motor closed-loop design in which the application now generally known as a "regenerator". Subsequent development by Robert Stirling and his brother James, an engineer, resulted in several patents for improving configurations original engine, including the pressurization production in 1843 was enough to push more power all the machinery in an iron foundry Dundee.
Although it has been disputed is generally assumed that in addition to fuel savings of inventors were motivated to create a safer alternative to steam engines of the time, whose boilers often exploded, causing many injuries and deaths. The Stirling engines need to operate at very high temperatures to maximize power and efficiency exposed limitations in the materials of the day and few engines that were built in those early years he suffered from unacceptably frequent failures (although with far less disastrous consequences of an explosion of the boiler) – for example, the Dundee foundry motor was replaced by a steam engine after three failures hot cylinder in four years.
late nineteenth century
A typical late nineteenth-water pumping from the early twentieth century by the Rider-Ericsson Engine Company Engine
After the failure of the casting machine of Dundee there is no record of having any brothers Stirling greater participation in the development of air Stirling engine and the engine never again competed with water vapor as a source of energy on an industrial scale (steam boilers were becoming safer and more steam engines efficient, therefore less of a target for his rival the prime movers). However, around 1860 from the smaller engines of the Stirling / type of air heat is produced in large numbers seeking applications where a reliable source of low to medium power is required, such as climbing or water supply air for the bodies of the church. These generally operated at lower temperatures so as not to tax the available materials, so they were relatively ineffective. But its selling point was that, unlike a steam engine that could be handled safely by someone capable of managing a fire. Several types remained in production beyond the end of the century, but apart from some minor mechanical improvements to the Stirling engine design in general stagnated during this period.
Reactivation of the twentieth century
During the first part of the twentieth century the role of the Stirling engine as "internal engine" was gradually taken over by the electric motor and small internal combustion engines. At the end of 1930 was largely forgotten, only occurs for toys and some small ventilation fans. In this Philips is currently seeking to expand sales of its radios in areas where electricity was not available and uncertain supply of batteries. Philips' management decided a low-power portable generator to provide such sales and commissioned a group of engineers in the research laboratory of the company in Eindhoven to assess alternatives.
After a systematic comparison of different driving forces, quiet operation of the Stirling engine (both audibly and in terms radio interference) and the ability to work in a variety of heat sources (common lamp oil "cheap and available everywhere" was favored) Stirling picked team. They were also aware that, unlike internal combustion engines and steam, virtually no serious development work was held in the Stirling engine for many years and said that modern materials and knowledge must allow large improvements.
Philips generator MP1002CA 1951 Stirling
Encouraged by his first experimental engine, which produced 16 W of power in the axis of a 30mm bore and stroke of 25mm, Philips initiated a development program. This work continued throughout the Second World War and the 1940s gave the Type 10 to the subsidiary of Philips, Johan de Witt in Dordrecht to be "productionised" and incorporated into a set. The result, 200 W nominal diameter and stroke of 55 mm x 27 mm, was appointed MP1002CA (known as the Bungalow "set"). The production of an initial batch of 250 was launched in 1951, but was clear that there could be at a competitive price and the emergence of the transistor radio with much lower power requirements means that the original justification for the set was disappearing. Approximately 150 of these groups occurred over time. Some found their way in college and university engineering departments around the world giving generations of students a valuable introduction to the Stirling engine.
Philips Stirling went on to develop experimental engines for a wide variety of applications and continued working in the field until the 1970s, but only managed trade success with the 'reversed Stirling cryocooler motor. They did however take a large number of patents and accumulate a large amount of information which is licensed to other companies and which formed the basis of much of the development work in the modern era.
Towards the end of the century, several companies developed research prototypes average power engine and in some cases small series. A mass market will never be achieved because the unit costs were very high, and some technical problems still unresolved. Now in the twenty-first century, some commercial success began to be viable, particularly in combined heat and power units.
In the field of low-power engines, many plans, kits and finished engines are commercially available. Apart from the traditional models of small and some larger machines for actual use, a new type was introduced in the 1980s: the type of low-temperature flat plate.
Theory
Main article: Stirling cycle
A pressure / volume graph of the idealized Stirling cycle
The idealized Stirling cycle consists of four thermodynamic processes acting on the working fluid:
Isothermal Expansion. The expansion of space and heat exchanger maintained at a constant temperature high, and the gas undergoes an isothermal expansion almost absorbing heat from the hot pan.
A constant volume (known as isovolumetric or isochoric) heat removal. The gas passes through the regenerator, where cools the heat transfer to the regenerator for use in the next cycle.
Isothermal compression. The area of compression and associated heat exchanger are maintained at a constant low temperature so that the gas undergoes nearly isothermal compression to deliver heat to the cold sink
A constant volume (known as isovolumetric or isochoric) heat addition. The gas passes back through the regenerator, where he is recovering much of the heat transferred at 2-3, warming on its way to the expansion space.
Theoretical thermal efficiency is equal to the hypothetical Carnot cycle – ie the greatest possible efficiency of any heat engine. However, although useful to illustrate general principles, the text book cycle is a long way to represent what is really happening inside a Stirling engine practice and should not be regarded as a basis for analysis. In fact it has been argued that their indiscriminate use in many standard books on engineering thermodynamics has done a disservice to the study Stirling engines in general.
Other real-world issues reduce the efficiency of real engines, due to the limits of convection heat transfer and flow viscous (friction). There are also practical aspects of mechanics, for example, a simple kinematic link may be favored by a more complex mechanism to get playing the idealized cycle, and the limitations of available materials such as non-ideal gas properties of work, the thermal conductivity resistance traction, creep, tensile strength and melting point.
Operation
Since the Stirling engine is a closed loop, which contains a fixed mass of gas is called the "working fluid, most commonly air, hydrogen or helium. In normal operation, the engine is sealed and no gas enters or leaves the engine. Not required valves, unlike other types of piston engines. The Stirling engine, like most heat engines, cycles through four main processes: cooling, compressing, heating and expansion. This is accomplished by moving the gas back and forth between the hot heat exchangers and cold, often with a regenerator between the heater and cooler. The hot heat exchanger is in thermal contact with a heat source such as a fuel burner and heat exchanger be cold heat in thermal contact with an external heat sink, such as air fins. A change in gas temperature will cause a corresponding change in pressure gas, while the movement of the piston causes the gas to be alternately expanded and compressed.
The gas follows the behavior described by the gas laws which describe how the gas pressure, temperature and volume are related. When the gas is heated, because it is in a sealed chamber, the pressure increases and this then acts on the power piston to produce a power stroke. When the gas cools, pressure drops and this means less work has to be done by the piston to compress the gas in the career of return, which gives a net power output.
When one side of the piston is open to the atmosphere, el funcionamiento es ligeramente diferente. As the workload of gas sealing contact with the hot side, it expands, doing work both in the piston and the atmosphere. When working contacts the cold side of gas, its pressure drops below atmospheric pressure and atmospheric pressure on the piston and do work on the gas.
In summary, the Stirling engine uses the temperature difference between its hot end and cold end to establish a cycle of a fixed mass of gas, heating and expanded, and cooled and compressed, thus converting thermal energy into mechanical energy. The greater the temperature difference between hot sources and cold, the greater the thermal efficiency. The theoretical maximum efficiency is equivalent to the Carnot cycle, however, the real engine efficiency is lower than this value due to friction and other losses.
Video showing the compressor and displacer of a small Stirling engine in action
Very low power engines are have built will run on a temperature difference of only 0.5 K.
Pressurization
In most high-powered Stirling engines, both minimum pressure and medium pressure liquid work are above atmospheric pressure. This initial pressurization motor can be performed by a bomb, or fill out the engine of a compressed gas tank, or simply sealing the engine when the average temperature is lower than the average temperature of the intervention. All these methods increase the mass of working fluid in the thermodynamic cycle. All heat exchangers must be of sufficient size to supply the heat transfer rates required. If the heat exchangers are well designed and can supply the flow of heat needed to heat transfer by convection, then the engine a first approximation to produce power in proportion to the average pressure, as predicted by the number of the West, and the number of Beale. In practice, the maximum pressure are also limited to the safe pressure of the pressure vessel. Like most aspects of Stirling engine design, optimization is multifactorial and often have conflicting requirements.
Lubricants and friction
A modern Stirling engine and generator set with 55 kW of electric power, combined heat and power applications
At high temperatures and pressures, oxygen in air pressure housings, or work of gas engine hot air can combined with engine oil and exploit. At least one person had died in an explosion.
Lubricants can also clog heat exchangers, especially the regenerator. For these reasons, designers prefer non-lubricated, low friction coefficient materials (eg, Rulon or graphite), with lower than forces normal moving parts, particularly for sliding joints. Some designs to avoid completely the sliding surfaces by using a diaphragm for sealing pistons. These are some of the factors that allow Stirling engines to have lower maintenance requirements and life as internal combustion engines.
Analysis
The comparison with internal combustion engines
Unlike internal combustion engines, Stirling engines have the potential to use renewable heat more easily, to be quieter and more reliable with less maintenance. They are preferred for applications that the value of these unique advantages, especially if the cost per unit of energy generated ($ / kWh) is more important than the capital cost per unit of energy ($ / kW). On this basis, his Stirling engine cost competitive to about 100 kW.
Compared to an internal combustion engine of the same power, Stirling engines currently have a higher capital cost and are generally larger and heavier. However, they are more efficient than most internal combustion engines. Its low maintenance requirements make The total cost of comparable energy. The thermal efficiency is also comparable (for small engines), ranging from 15% to 30%. For applications such as micro-CHP Stirling engine is often preferable to an internal combustion engine. Other applications include water pumping, astronautics, and electrical generation from plentiful energy sources that are incompatible with the internal combustion engine, such as solar and biomass such as agricultural residues and other waste and domestic refuse. Stirling has also been used as a marine engine in the Swedish submarine Gotland class. However, Stirling engines are generally not price competition as an engine of a car, due to high costs per power unit, low power density and high material costs.
Basic analysis is based on analysis of the closed form Schmidt.
Advantage
Stirling engines can run directly on any heat source available, not just one produced by combustion, so it can run on heat from solar, geothermal, biological, nuclear or waste heat sources from industrial processes.
A combustion process DC can be used to supply heat, so most types of emissions can be reduced.
Most Stirling engines have the bearing and stamped on the cold side of the motor, and require less lubricant and last longer than others types of piston engines.
Motor mechanisms are somehow more simpler than other types of piston engines. No valves are needed and the burner system can be relatively simple.
A Stirling engine uses a single phase working fluid maintaining an internal pressure close to the pressure, and thus for a properly designed system the risk of explosion is low. In comparison, a steam engine used a two-phase gas / liquid working fluid, so a faulty relief valve can cause an explosion.
In some cases, the operating pressure low allows the use of lightweight cylinders.
Can be scheduled to run quietly and without an air supply for the use of air independent propulsion submarines.
They start easily (albeit slowly, after warming) and run more efficiently in cold weather, in contrast to the combustion internal promptly initiated in warm weather, but not in cold weather.
Uses a Stirling engine to pump water can be configured so that the water cools compression chamber. This is most effective when pumping cold water.
They are extremely flexible. They can be used as cogeneration (production combined heat and power) in the winter and cooler in summer.
The waste heat is easily harvested (compared to waste heat from a combustion engine internal) making Stirling engines useful for dual output heat and power systems.
Disadvantages
Size and cost issues
Stirling engine designs require heat exchangers for heat input and heat output, and these must contain the fluid pressure of work, where the pressure is proportional to the power engine. In addition, the heat exchanger expansion side often at very high temperature, so that the materials must withstand the corrosive effects of the heat source, and have low creep (deformation). Typically these material requirements substantially increase the cost of the engine. The materials and assembly costs exchanger high temperature heat normally represents 40% of the total cost of the engine.
All thermodynamic cycles require large temperature differentials for operation efficient. In an external combustion engine, the heater temperature always equals or exceeds the expansion temperature. This means that the metallurgical requirements heating the material are very demanding. This is similar to a gas turbine, but unlike an Otto or Diesel engine, where the temperature can exceed the extent of expansion metallurgy materials limit the engine, because the heat input is not carried out through the engine, so engine materials operate more near the average temperature of the working gas.
Residual heat dissipation is particularly complicated because the coolant temperature is kept as low as possible to maximize thermal efficiency. This increases the size of the radiators, which can make it difficult to packaging. Together with cost of materials, it has been one of the factors limit the adoption of Stirling engines as automotive prime movers. For other uses, such as propulsion, and stationary microgeneration systems using combined heat and power (CHP) of high power density is not necessary.
Power and torque problems
Stirling engines, especially those that run in small temperature differentials are quite large for the amount of energy produced (ie, have low specific power). This is mainly due to the convection heat transfer coefficient of gas that limits the flow of heat that can be achieved in a typical cold heat exchanger of about 500 W / (m2 K) and in a hot heat exchanger to about 5005000 W / (m2 K). Compared to internal combustion engines, this makes it more difficult for the designer the engine for heat transfer in and out of working gas. Increasing the temperature differential and / or pressure allows Stirling engines to produce more energy, assuming that the heat exchangers are designed for the rise in temperature, and can give the convection heat flow is necessary.
A Stirling engine can start right away, but literally has to "warm." This is true for all external combustion engines, but the heating time can Stirling be longer than others of this type, such as steam engines. Stirling engines are best used as constant speed motors.
An output power Stirling tends to be constant and to adjust sometimes require careful design and additional mechanisms. Generally, changes in production are achieved by varying the displacement engine (often through the use of a swashplate crankshaft arrangement) or changing the amount of working fluid, or altering the piston / displacer phase angle, or in some cases simply by altering the engine load. This property is less than a drawback in hybrid electric propulsion or "base load" generation utility where constant power output is actually desirable.
Gas choice issues
The gas used should have a low heat capacity, for what a particular amount of heat transfer leads to a large increase in pressure. Given this issue, helium gas is the best because of its ability to fire very slow. Air is a viable working fluid, but the oxygen in an air motor at high pressure can cause fatal accidents caused by explosions of lubricating oil. Following of an accident such as Philips pioneered the use of other gases to prevent the risk of explosions.
hydrogen low viscosity and high thermal conductivity make it the most powerful working gas, mainly because the engine can run faster than other gases. However, due to absorption of hydrogen, and given the high diffusion Death rate associated with this low molecular weight gas, especially at high temperatures, H2 will leak through solid metal stove. The diffusion in steel carbon is too high to be practical, but may be acceptable for metals such as aluminum, or stainless steel. Some ceramics also greatly reduce diffusion. Hermetic seals for pressure vessels are required to maintain the pressure inside the engine without the replacement of lost gas. For HTD engines, systems may be necessary to add auxiliary to maintain high working pressure fluid. These systems can be a gas storage bottle or a gas generator. Hydrogen may be generated by electrolysis of water, the action of steam on red hot fuel from coal, gasification of hydrocarbon fuel, or by the reaction of acid in the metal. Hydrogen can also cause the embrittlement of metals. Hydrogen is a flammable gas, which is a security problem although the amount used is very small, and is probably safer than other commonly used gases.
More technically advanced Stirling engines, as those developed for the U.S. government laboratories, using helium as working gas, because it functions close to the efficiency and power density of hydrogen less than the material issues of contention. Helium is inert, which eliminates all the risk of fire, both real and imagined. Helium is relatively expensive and must be delivered in the form of bottled gas. One test showed that the hydrogen of 5% (absolute) more efficient than helium (24% relatively) in the GPU-3 Stirling engine. The Allan Organ investigator demonstrated that a well designed engine air is theoretically an engine as efficient as hydrogen or helium, but helium and hydrogen engines are several times more powerful per unit volume.
Some engines use air or nitrogen as the working fluid. These gases have a much lower energy density (which increases costs of the engine), but are easier to use and they minimize the problems of gas supply and containment (which reduces costs). The use of compressed air in contact with flammable materials or substances such as lubricating oil, introduces a risk of explosion, because compressed air contains a high partial pressure of oxygen. However, oxygen can be removed from air through an oxidation or nitrogen bottle can be used, which is almost inert and very safe.
Other possible lighter than air gases are: methane and ammonia.
Applications
It has been suggested that this section be split into a new article Stirling engine applications. (Discuss)
A desktop alpha Stirling engine. The working fluid in this engine is air. The heat is hot the glass cylinder right, and the cold heat exchanger is the cylinder with fins on top. This engine uses a small alcohol burner (bottom right) as a heat source
Heating and cooling
If supplied with mechanical energy, a Stirling engine can run backwards as a heat pump for heating or cooling. The experiments were performed using wind power driving a Stirling cycle heat pump for domestic heating and air conditioning. In the decade 1930, the Corporation Philips of the Netherlands successfully used Stirling cycle cryogenic applications.
Combined heat and power
Hostels fuel thermal electric network used to generate electricity, however, large amounts of waste heat that is often not used. In other situations, high-grade fuel is burned at high temperatures for low temperature application. According to the second law of thermodynamics, a heat engine can generate energy from this temperature difference. In a cogeneration system, the high temperature heat heater main entrance Stirling engine, then part of the energy is converted into mechanical energy in the engine, and the rest passes through the refrigerator, where it exits at a low temperature. The "waste" in heat actually comes from the main refrigerator motor, and possibly other sources such as exhaust gases from the burner, if there is one.
In a combined heat and power (CHP) system, mechanical or electrical energy is generated in the usual way, however, waste heat emitted by the motor is used to supply a secondary heating application. This can be almost anything that uses low-temperature heat. It is often a pre-existing energy use, such as commercial space heating, water heating, residential or industrial process.
The energy produced by the engine can be used to execute an activity industrial or agricultural process, which in turn creates biomass waste refuse that can be used as motor fuel for free, thereby reducing disposal costs waste. The overall process can be efficient and profitable.
Disenco, a UK company are going through the final stages of developing their HomePowerPlant. Unlike other devices combined m-that came to market in the HPP generates 3 kW and 15 kW electric heat, which makes this device suitable for both market and national SMEs.
WhisperGen, a New Zealand company with offices in Christchurch, has developed a micro AC "Combined Heat and Power" motor Stirling cycle. These units are microCHP central heating boilers, gas heating to sell unused power back to the grid. WhisperGen announced in 2004 they were producing 80,000 units for the residential market in the United Kingdom. A trial of 20 units in Germany was initiated in 2006.
Solar power generation
Placed at the focus of a parabolic mirror a Stirling engine can convert solar energy into electricity with an efficiency better than photovoltaic cells, not concentrated and comparable to photo voltaic concentrated products. On August 11, 2005, Southern California Edison announced an agreement with Stirling Energy Systems to buy the electricity created more than 30,000 solar engines Stirling twentieth year over a period of time sufficient to generate 850 MW of electricity. These systems, in a 8000 acre (19 km2) solar park will use mirrors to concentrate sunlight and the engines in turn drive generators. The construction is expected to begin on the farm in 2010, although there are disputes over the project due to concerns about environmental impact on animals that live on the site.
Stirling cryogenic refrigeration systems
Any Stirling engine will also work in reverse as a heat pump, when a movement is applied to the shaft, there is a temperature difference between the reservoirs. Components an essential mechanical Stirling cryocooler are identical to a Stirling engine. In both the engine and heat pump, heat flows from the expansion space of the camera compression, however, work input is necessary for the flow of heat against a thermal gradient, especially when the compression is more space hot expansion space. The outside of the heat exchanger expansion of space can be placed in an insulated compartment like a thermos. Heat is in effect pumped out of this compartment, through the working gas cryocooler and space compression. The compression space is above the room temperature and the heat flow into the environment.
One of their modern uses is in cryogenics, and to a lesser extent, the cooling. A refrigeration temperatures typical Stirling coolers are generally not economically competitive with less expensive general Rankine cooling systems, even though they usually are 20% more energy efficient. However, below the 40-30 C, Rankine cooling is not effective because there is appropriate cooling and boiling points level so low. Stirling cryogenic refrigeration systems are able to "lift" the heat to 200 ° C (73 K), which is enough to liquefy air (oxygen, nitrogen and argon). They can go as low as 4060 K, depending on the particular design. Cryogenic cooling systems for this purpose are more or less competitive cryocooler technology with others. The coefficient of performance at cryogenic temperatures typically 0.040.05 (equivalent to an efficiency of 45%). Empirically, the devices show a linear trend, where typically the COP = 0.0015 0.065 Tc, where Tc is the cryogenic temperature. At these temperatures, solid materials have values low specific heat, so the regenerator should be made of unexpected materials, like cotton. [Citation needed]
The first Stirling-cycle cryocooler was developed by Philips in the 1950s and commercialized in such places as liquid air production plants. The Philips Cryogenics business evolved until it was separated in 1990 to form the Stirling Cryogenics BV, Netherlands. The company remains active in the development and manufacture of cryogenic refrigeration systems and systems Stirling cryogenic cooling.
A wide variety of smaller Stirling cryogenic refrigeration systems are commercially available for tasks such as cooling of electronic sensors and microprocessors sometimes. For this application, Stirling cryogenic refrigeration systems are the most important technology in performance available, due to its ability to lift heat efficiently at very low temperatures. They are silent, vibration, and can be reduced to small sizes, and have high reliability and low maintenance. Since 2009, cryogenic cooling systems are regarded as the devices only commercially successful Stirling. [Citation needed]
Heat pump
A Stirling heat pump is very similar to a Stirling cryocooler, the main difference is that normally operates at room temperature and main application to date is the heat pump from outside a building inside, which cheaper than heating.
As with any other device Stirling, heat flows from the expansion space of the compression chamber, however, in contrast to the Stirling engine, the expansion space is at a lower temperature than the compression chamber, so instead of producing work, mechanical work input is required by the system (to meet second law of thermodynamics). When the mechanical work of the heat pump is provided by a second Stirling engine, then the whole system heatpump is called a "heat-driven."
The expansion of the heat pump is thermally coupled to the heat source, which is often the external environment. The compression side of the Stirling device is placed in the environment to be heated, for example a building, and the heat is "pumped" into it. Normally there will be insulation between the two parties as there will be a temperature rise inside the insulated space.
Heat pumps are by far the most energy efficient types of heating systems. Stirling heat pumps also often have a higher coefficient of performance than conventional heat pumps. To date, these systems have seen limited commercial use however, use is expected to increase along the market demand for energy conservation and is likely to be accelerated by technological improvements.
Marine Engines
The Swedish Kockums shipyard has built successful Stirling powered submarines in August since the late 1980s. They allow compressed oxygen while submerged combustion fuel that provides heat for the Stirling engine. It is currently used in the Gotland class submarines and Sdermanland. They are the first submarine the world with a Stirling engine powered air independent (AIP) system, which extends under the water resistance from a few days to two weeks. This capacity has been available only to nuclear submarines.
A similar system also powers the Japanese Sry class submarine.
Energy nuclear
There is great potential for nuclear-powered Stirling engines in electric power generation plants. Replacing the steam turbines nuclear power plants with Stirling engines might simplify the plant, yield greater efficiency, and reduce radioactive byproducts. A number of breeder reactor designs uses liquid sodium as a coolant. If the heat is to be used in a steam plant, water / sodium heat exchanger is required, which raises some concern as sodium reacts violently with water. A Stirling engine eliminates the need for water in any part of the cycle.
Laboratories of the U.S. government have developed a design modern Stirling engine is known as the Stirling Radioisotope Generator for use in space exploration. It is designed to generate electricity for the probe deep space missions lasting decades. The engine uses a single displacer to reduce moving parts and uses high energy acoustics to transfer energy. The heat source is a bullet dry solid nuclear fuel and the heat sink is the space itself.
Automotive engines
It is often said that the Stirling engine has a very low power to weight ratio, a cost too high and too long to start for automotive applications. They are also complex and heat exchangers expensive. A Stirling cooler to reject heat twice Otto engine or Diesel engine radiator. The heater should be stainless steel, exotic alloys or ceramic withstand high temperatures needed for heating high power density, and to contain hydrogen gas often used in Stirling to maximize the power of the car. The main difficulties arising from the use of the Stirling engine in an automotive application is the startup time, the throttle response, time off, and weight do not all have easy solutions. However, a modified version of the Stirling engine has recently been introduced that uses concepts from a patented motor internal combustion with a combustion chamber side wall (U.S. Patent 7,387,093) that promises to overcome the poor power density and specific energy issues, and the problem of slow response acceleration inherent in all Stirling engines. However, it might be possible to use these cogeneration systems that use residual heat of a conventional piston engine exhaust gas turbine and the use of this well for auxiliary power (eg alternator) or even a turbo-compound system that adds power and torque to the crankshaft.
At least two cars exclusively with Stirling engines were developed by NASA, as well as previous projects Ford Motor Company and American Motors Corporation. The vehicles were designed by NASA and contractors appointed MOD I and MOD II. The Ministry of Defense II replaced the normal the spark ignition engine in a 1985 Chevrolet Celebrity four-door Notchback. In 1986 MOD II Design Report (Appendix A) the results show that highway mileage gas increased from 40 to 58 miles per gallon and the urban mileage 26-33 mpg with no change in gross weight vehicles. start time in the vehicle NASA reached the maximum of 30 seconds, [citation needed], while Ford vehicle research used an internal electric heater to start the vehicle, allowing it to start in just seconds.
Electric vehicles
Many people believe that Stirling engines as part of a system hybrid electric traction can ignore all perceived design problems and disadvantages of a non-hybrid car Stirling.
In November 2007, a prototype hybrid car using solid biofuel and a Stirling engine project was announced by the prayers in Sweden.
The Manchester Union Leader reports that Dean Kamen has developed a series plug-in hybrid car with a Ford Think. DEKA, Kamen company's sawmill technology in Manchester, has recently shown a car electric DEKA's Rebellion, which can go about 60 miles (97 km) on a single charge of its lithium battery.
Aircraft engines
Stirling engines theory may hold promise as aircraft engines, if the high power density and low cost can be achieved. They are quieter, cleaner, efficient gain with altitude due to lower temperature, are more reliable due to fewer parts and the absence of an ignition system, produce much vibration less (airframes last longer) and safer, less explosive fuels may be used. However, the Stirling engine often has a low energy density compared with common usage Otto engine and gas turbine Brayton cycle. This issue has been a point of contention in cars, and this feature is still performance more critical in aircraft engines.
Low temperature difference engines
A low temperature difference Stirling engine shown here is running in the heat of a warm hand
A low temperature difference (Low Delta T, or LTD) Stirling engine will run on any low temperature differential, for example the difference between the palm of one hand and the ambient temperature or ambient temperature and an ice cube. A record of only 0.5 K was achieved in 1990. View also shows a cartoon of this kind. Usually are designed with a gamma setting, for simplicity, and without a regenerator, although some cuts in the normal movement made of foam, for partial regeneration. They are typically without pressure, running at close to 1 atmosphere pressure. The energy produced is less than 1 W, and are for demonstration purposes. They are sold as toys and educational models.
Larger (typically 1 m square) engines were built low temperature for pumping water in direct sunlight with minimal or no enlargement.
Other recent applications
Acoustic Stirling Heat Engine
Los Alamos National Laboratory has developed an "Acoustic Stirling Heat Engine" no moving parts. It converts heat into intense acoustic power which (quoted from a given source) "is can be used directly in acoustic refrigerators or pulse tube refrigerators to provide heat-driven refrigeration with no moving parts, or … to generate electricity through a linear alternator or other electro-acoustic transducer.
MicroCHP
WhisperGen, a company based in New Zealand has developed engines Stirling can be powered with natural gas or diesel. Recently an agreement has been signed with Corporacin Mondragon Cooperative, a Spanish company to produce microCHP WhisperGen and be available for the internal market in Europe. Some time ago, E. ON UK announced a similar initiative for the United Kingdom. Stirling engines are provided to the customer with hot water, space heating and a surplus of electricity that could go to swell the mains.
But preliminary results an energy Saving Trust performance review units microCHP WhisperGen suggested that their benefits were marginal at best in most homes. However, another author shows that micro-Stirling engine is the most cost-effective microgeneration technologies diverse in terms of CO2 reduction.
Chip cooling
MSI (Taiwan) recently developed a miniature Stirling engine cooling system for personal computer chips uses waste heat from the chip to drive a fan.
Alternatives
alternative energy devices include thermal Thermogenerator collection. Thermogenerators allow conversion of less efficient (5-10%), but may be useful in situations where the final product must be electricity and a small conversion device is a critical factor.
Photo Gallery
Canned examples of former Rider hot air engines – an alpha configuration Stirling
See also
Thermo generator
Beale number
Western Number
Schmidt number
Fluidyne Engine
Stirling Radioisotope Generator
Cost on electricity generated by different sources
Distributed generation
References
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