Stirling engine

11/11/2007

UNIVERSITY OF GÄVLE

STIRLING ENGINE

MAIER Christoph GIL Arnaud AGUILERA Rafael SHUANG Li YU Xue

Index Summary ........................................................................................................................ 3 Introduction .................................................................................................................... 4 History............................................................................................................................ 5 Presentation of Stirling Engines..................................................................................... 7 I.

Stirling thermodynamic cycle ............................................................................. 7

II. Engine configurations ......................................................................................... 8 1.

Alpha Stirling: ................................................................................................. 9

2.

Beta Stirling................................................................................................... 11

3.

Gamma Stirling ............................................................................................. 13

4.

Other types .................................................................................................... 14

Reasons to use a Stirling Engine .................................................................................. 15 Analyze from Economic point ..................................................................................... 18 Applications of the Stirling power ............................................................................... 20 I.

Cars ................................................................................................................... 20

II. Submarine ......................................................................................................... 21 III.

Aircrafts ......................................................................................................... 22

IV.

Heat and power System ................................................................................. 23

V. Cryocooler......................................................................................................... 24 VI.

Nuclear power ............................................................................................... 24

VII.

Solar Energy .................................................................................................. 25

Conclusion ................................................................................................................... 29 References .................................................................................................................... 31

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Summary This essay mainly makes an exposition of the Stirling Engine. Firstly, the history of Stirling Engine is showed to make a guide of first comprehension. Then the Stirling Engine’s thermodynamic cycle is explained and the configuration is analyzed, which we do to make sure a further insight into the Stirling Engine. After that, the reasons to use a Stirling Engine are discussed, especially from an economic point of view. This is to describe why the Stirling Engine is widely used in nowadays’ world.

And the last part is to show out how the Stirling Engine is applied in each field. But with a special focus on sterling engines in applications with renewable energies. This whole essay displayed a broad overall presentation to the Stirling Engine, and analyzed its intrinsic value for the future.

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Introduction "…These imperfections have been in a great measure removed by time and especially by the genius of the distinguished Bessemer. If Bessemer Iron or steel had been known thirty five or forty years ago there is a scarce doubt that the air engine would have been a great success … It remains for some skilled and ambitious mechanist in a future age to repeat it under more favorable circumstances and with complete success…"

(Written in the year 1876 by Dr. Robert Stirling [1790-1878])

Figure 1 : Sketch of Robert Stirling of his invent

The Stirling Engine was invented by Robert Stirling. This device was born as a competence to the vapor machine, since a Stirling Engine works with smaller pressures than the device created by Watt and it did not require a qualified train engineer. At the end of s.XIX with the development of the internal combustion engine and the appearance of electric engines, the machine of this study was forgotten.

Nowadays the technology that involves the invention of Robert Stirling is in completely development because of the fact that now very useful applications are available.

This document travels in the history of this curious device looking for reasons of this incredible development in this called high technology with its different applications and doing an analysis from the point of view of the economy. This project explains the principle function of the engine with a deep investigation. And we show how the Sterling Engine in combination with renewable energy sources can be part of a sustainable energy supply.

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History The Stirling Engine is one of the hot air engines. It was invented by Robert Stirling (1790-1878) and his brother James. His father was interesting in engine and he inherited it. He became a minister of the church at Scotland in 1816. At this period, he found the steam engines are dangerous for the workers. He decided to improve the design of an existing air engine. He hope it wound be safer alternative. After one year, he invented a regenerator. He called the “Economiser� and the engine improves the efficiency. This is the earliest Stirling Engine. It is put out 100 W to 4 kW. But the internal combustion engine substituted for it quickly. The Ericsson invented the solar energy in 1864 and did some improvements for after several years. Robert’s brother, James Stirling, also played an important role in the development of Stirling engines.

Figure 2 : Earliest Stirling engine

Robert Stirling gets a patent for the economizer with an air engine incorporating it in 1817. Since the Stirling engine worked at a lower pressure, and could not cause steam burns, the danger to explode is impossible. In 1818 he built the first practical exponent of his engine, used to pump water from a quarry. The inventors sought to create a safer engine instead of steam engines at that time, whose boilers often exploded as a result of high pressure of the steam and the inadequate materials.

The original patent by Reverend Stirling was called the "economizer", for its improvement of fuel-economy. The patent also mentioned the possibility of using the

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device in an engine. Several patents were later determined by two brothers for different configurations including pressurized versions of the engine. This component is now commonly known as the "regenerator" and is essential in all high-power Stirling devices.

Figure 3 : Stirling Engine’s principle of operation

Stirling engine of the second generation began in 1937.The Philips of Holland used new materials and technology to ascend a very high level. The knowledge about the heat transfer and fluid physical, which is a great significance to improving of the structure and raised the stability.

Throughout World War II and by the late 1940s, Philips’ subsidiary Johan de Witt does this work continued. And they did the Type 10, incorporated into a generator set as originally planned The set progressed through three prototypes (102A, B, and C), with the production version, rated at 200 watts electrical output from a bore and stroke of 55x27mm, being designated MP1002CA. In 1951, the price of Stirling engine is too high for the market. It made used of radios at that time. Though the MP1002CA may have been a dead end, it represents the blooming of the modern age of Stirling Engine development. In addition to which the advent of transistor radios with their much lower power requirements meant that the market for the set was fast disappearing. Though the MP1002CA may have been a dead end, it represents the start of the modern age of Stirling engine development.

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Presentation of Stirling Engines I.

Stirling thermodynamic thermodyna cycle

The Stirling engine cycle is a closed cycle and it contains, most commonly a fixed mass of gas called the "working fluid" (air, hydrogen or helium). The principle is that of thermal expansion ansion and contraction of this fluid due to a temperature differential.

So the ideal Stirling cycle consists of four thermodynamics thermodynamic distinct processes acting on the working fluid: two constant-temperature temperature processes and two constantconstant volume processes.

Each ch one of which can be separately analysed: 1-2: isothermal compression process. process Work W1-2 is done on the working fluid, while an equal amount of heat Q1-2 is rejected by the system to the cooling source. The working fluid cools and contracts at constant temperature TC. 2-3: constant onstant volume displacement process with heat addition. addition Heat Q2-3 is absorbed by the working fluid and temperature is raised from TC to TH. No work is done.

3-4: isothermal expansion process. process Work W3-4 is done by the working fluid, fluid while an equal amount of heat Q3-4 is added to the system from the heating source. The working fluid heats and expands at constant temperature TH. 4-1: constant volume displacement process with heat rejection. rejection Heat Q4-1 is rejected by the working fluid and temperature decrease from TC to TH. No work is done.

Figure 4 : A pressure/volume graph of the ideal Stirling cycle

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The process lines in the figure above reflect the properties of an ideal gas. The main processes, like for most heat engines, are cooling, compression, heating and expansion. A Stirling engine operates through the use of an external heat source and an external heat sink having a sufficiently large temperature difference between them.

Compared to the ideal cycle, the efficiency of a real engine is reduced by irreversibilities, friction, and the loss of short-circuit conducted heat, so that the overall efficiency is often only about half of the ideal (Carnot) efficiency.

The gasses used inside a Stirling engine never leave the engine. There are no exhaust valves that vent high-pressure gasses, as in a gasoline or diesel engine, and there are no explosions taking place.

Another useful characteristic of the Stirling engine is that if supplied with mechanical power, it can function as a heat pump (reversibility of the Stirling cycle).

Understanding how a Stirling engine works is not a simple matter. It is not overly intuitive. Let’s explain the device through the presentation of the different engines configuration.

II.

Engine configurations

Mechanical configurations of Stirling engines are classified into three important distinct types: Alpha, Beta and Gamma arrangements.

These engines also feature a regenerator (invented by Robert Stirling). The regenerator is constructed by a material that conducts readily heat and has a high surface area (a mesh of closely spaced thin metal plates for example).

When hot gas is transferred to the cool cylinder, it is first driven through the regenerator, where a portion of the heat is deposited. When the cool gas is transferred back, this heat is reclaimed. Thus the regenerator “pre heats” and “pre cools” the working gas, and so improve the efficiency.

But many engines have no apparent regenerator like beta and gamma engines configurations with a “loose fitting” displacer, the surfaces of the displacer and its cylinder will cyclically exchange heat with the working fluid providing some regenerative effect.

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1. Alpha Stirling: Alpha engines have two separate power pistons in separate cylinders which are connected in series by a heater, a regenerator and a cooler. One is a “hot” piston and the other one a “cold piston”.

Figure 5 : Alpha engine’s configuration

The hot piston cylinder is situated inside the high temperature heat exchanger and the cold piston cylinder is situated inside the low temperature heat exchanger.

The generator is illustrated by the chamber containing the hatch lines.

Expansion: At this point, the most of the gas in the system is at the hot piston cylinder. The gas heats and expands, pushing the hot piston down, and flowing through the pipe into the cold cylinder, pushing it down as well.

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Transfer: At this point, the gas has expanded. Most of the gas is still in the hot cylinder. As the crankshaft continues to turn the next 90°, transferring the bulk of the gas to the cold piston cylinder. As it does so, it pushes most of the fluid through the heat exchanger and into the cold piston cylinder.

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Contraction: Now the majority of the expanded gas is shifted to the cool piston cylinder. It cools and contracts, drawing both pistons up

Transfer: The fluid is cooled and now n the crankshaft shaft turns another 90째. The gas is therefore pumped back, through the heat exchanger, into the hot piston cylinder.

Once in this, it is heated and we go back to the first step.

This diagram is feature of an alpha engine.

The most important is to have the biggest grey area which represents the recuperated work during a cycle.

Figure 6 : Example of a real cycle of an alpha engine

The Alpha engine is conceptually conceptually the simplest Stirling engine configuration, however suffers from the disadvantage that both pistons need to have seals to contain the working gas.

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This type of engine has a very high power-to-volume power volume ratio but has technical problems due to the usually high temperature of the "hot" piston and its seals

2. Beta Stirling The Beta configuration is the classic Stirling engine configuration and has enjoyed popularity from its inception until today. Stirling's original engine from his patent drawing of 1816 shows a Beta arrangement.

Both Beta and Gamma engines use displacer-piston displacer piston arrangements. The Beta engine has both the displacer and the piston in an in-line in line cylinder system. The Gamma engine uses separate cylinders.

Figure 7 : Beta engine’s configuration

The purpose of the the single power piston and displacer is to “displace� the working gas at constant volume, and shuttle it between the expansion and the compression spaces through the series arrangement cooler, regenerator, and heater.

A beta Stirling has a single power piston 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 from the hot heat exchanger to the cold heat at exchanger.

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.

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Figure 8 : Beta engine with momentum flywheel

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Expansion: At this point, most of the gas in the system is at the heated end of the cylinder. The gas heats and expands driving the power piston outward.

Transfer: At this point, the gas has expanded. Most of the gas is still located in the hot end of the cylinder. Flywheel momentum carries the crankshaft the next quarter turn. As the crank goes round, the bulk of the gas is transferred around the displacer to the cool end of the cylinder, driving more fluid into the cooled end of the cylinder.

Contraction: Now the majority of the expanded gas has been shifted to the cool end. It contracts and the displacer is almost at the bottom of its cycle.

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Transfer: The contracted gas is still located near the cool end of the cylinder. Flywheel momentum carries the crank another quarter turn, moving the displacer and transferring the bulk of the gas back to the hot end of the cylinder. And at this point, the cycle repeats.

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Figure 9 : Example of a real cycle of a beta engine

3. Gamma Stirling A gamma Stirling is simply a beta Stirling in which the power piston is mounted in a separate cylinder alongside the displacer piston cylinder, but is 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 lowe compression ratio but is mechanically simpler and often used in multi-cylinder multi cylinder Stirling engines.

Gamma type engines have a displacer and power piston, similar to Beta machines, but in different cylinders. This allows a convenient complete separation between betw the heat exchangers associated with the displacer cylinder and the compression and expansion work space associated with the piston.

Figure 10 : Gamma engine’s configuration

Furthermore during the expansion process some of the expansion must take place in the compression space leading to a reduction of specific power. Gamma engines are therefore used when the advantages of having separate cylinders outweigh the specific power disadvantage.

The advantage of this design is that it is mechanically simpler because of the convenience of two cylinders cylinders in which only the piston has to be sealed. The

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disadvantage is the lower compression ratio but the gamma configuration is the favorite for modelers and hobbyists.

.

Figure 11 : Small gamma engine

Figure 12 : Example of a real cycle of a beta engine

4. Other types Changes to the configuration of mechanical Stirling engines engines continue to interest engineers and inventors who create a lot of different version of the Stirling engine.

There is also a large field of "free piston" Stirling cycles engines, including those with liquid pistons and those with diaphragms as pistons.

For example, as an alternative to the mechanical Stirling engine is the fluidyne pump, which uses the Stirling cycle via a hydraulic piston. In its most basic form it contains a working gas, a liquid and two non-return non return valves. The work produced by the fluidyne luidyne goes into pumping the liquid.

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Reasons to use a Stirling Engine There are several reasons to use a Stirling Engine:

One reason is that for this kind of engine it’s almost impossible to explode.

You don’t have to produce steam in a high pressure boiler. And inside the cylinder there are no explosions needed to run the pistons like in an Otto or Diesel engine. There are no ignitions, no carburetion because you only need one kind of gas and no valve train because there are no valves. This was a big advantage to the steam engines in the days when Stirling invented his engine because it was much less dangerous to work next to a Sterling Engine than to a common steam engine.

Inside the pistons can be used air, helium, nitrogen or hydrogen and you don’t have to refill it because it uses always the same body of gas.

Figure 13 : Schematic Stirling Engine

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To produce heat you can use whatever you want: fuel, oil, gas, nuclear power and of course renewable energies like solar, biomass or geothermal heat.

Figure 14 : Solar panel

The external combustion process can be designed as a continuous process, so the most types of emissions can be reduced.

If heat comes from a renewable energy source they produce no emissions.

They run very silent and they don’t need any air supply. That’s why they are used a lot in submarines. E.g. in the Royal Swedish Navy.

Figure 15 : Figure 16 Gotland : HMS

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They can be constructed to run very quiet and practically without any vibration.

They can run with a small temperature difference, e.g. with the heat of your hand or from a cup of hot coffee. They can be used as little engines for work which needs only low power.

Figure 16 : Low power Stirling engine

They can run for a very long time because the bearings and seals can be placed at the cool side of the engine → they need less lubricant and they don’t have to be checked very often ( longer period between the overhauls ).

They are extremely flexible. The engine can run as a CHP (combined heat and power) because the heat which is produced to run it can easily be collected. Or in summers they can be used as coolers.

Figure 17 : CHP

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Analyze from Economic point

As said above the he Stirling engine is a kind of external combustion engine, and it can use a variety of fuels. It can can be estimated that combustible gases are the best material, including gasoline, diesel, propane, sunshine and salad oil; even cow dung can be run on as fuels.

A cup of coffee cannot become a cup of gasoline, but it can be also used as a Stirling engine driver. iver. There is a famous experiment that a Stirling engine can easily run on a cup of coffee. The Stirling engine is a kind of piston engine. In the external heating sealed chamber, the expansion of gases inside the engine promotes the pistons work. After the he expanded gases cooling down in the air-conditioned air conditioned room, next process is taking on. As long as a certain value of the temperature difference exists, a Stirling Engine can be formed.

Figure 18 : Stirling Engine working on a cup of coffee

This experiment shows that only a very small power operation can carry out a Stirling engine, which contributes a lot to energy conservation. This characteristic especially shows out on economy point. The benefits obtained from the Stirling engine ne are definitely far beyond the costs.

So once solar is used to produce energy for the Stirling engine, the cost would surely be cut down for quite a lot. As long as there is sunshine, the Stirling engine will run on and on. Of course it costs much to manufacture manufacture a Stirling engine, as it requires

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a high level of the materials and manufacturing processes. The expansion-side heat exchanger’s temperature is often very high, so the materials must stand the corrosive consequences of the heat. Typically these material requirements substantially increase the cost of the engine. The materials and assembly costs for a high temperature heat exchanger typically accounts for 40% of the total engine cost.

But once the Stirling engine is made and put into a proper condition, quite a few costs would be paid for keeping it running.

Some engines cause a lot of pollution, so much is cost for pollution control and government. On contrast, Stirling engine exhausts cleanly and avoid this type of matter. Development and utilization of solar will not pollute the environment, as solar is one of the cleanest energy. While the environmental pollution is becoming more and more serious today, this characteristic is extremely valuable. It saves the cost for a lot while making sustainable development.

At the end of 18th century and the early 19th century, heat engine generally is steam engine. Its efficiency is very low, only 3% to 5%, that is, over 95% of the heat is not used. Stirling thermodynamic theory is aiming to improve the thermal efficiency. Stirling proposed that the Stirling cycle efficiency, under the ideal condition, may get the infinite enhancement. Certainly it cannot come to 100% due to the physical limitation, however the theory provide a direction for improving the thermal efficiency. In fact, now the efficiency of Stirling engine can come up to 80% or even more. So another part of cost is saved.

Nowadays, more and more countries have recognized that a society with sustainable development should be able to meet the needs of the community without endangering future generations. Therefore, use clean energy as much as possible instead of the high carbon content of fossil energy is a principle which should be followed during energy construction. Vigorously develop new and renewable sources of energy utilization technology will be an important measure to reduce pollution.

Energy problem is a worldwide one, and it is sooner or later to get into the transitionto-new-energy period. Because of its sustainability, renewably and efficiency, the Stirling engine is just the very one being consistent with the requirements of the times.

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Applications of the Stirling power I.

Cars

In the ages of 1970s and 1980s several automobile companies like “General Motors” or “Ford” were researching about Stirling Engine. This device is good for a constant power setting, but it is a challenge for the stop and go of the automobile.

A good car can change the power quickly. One possibility to obtain this important characteristic is design a power control mechanism that will turn up or down the burner. This is a slow method of changing power levels because is not enough to accelerate crossing an intersection.

The best solution in spite of these difficulties in automobiles is hybrid electric cars where Stirling Engine could give enough power to make long trips where could get burn gasoline or diesel, depending on which fuel was cheaper. The batteries could give the instant acceleration that drivers are used to. This invention makes the car silent and clean running.

On March 20, 2002 I delivered one of our KY-2000 Stirling engines to the Mechanical Engineering department at San Diego State University. While I was there I had the opportunity to see their hybrid diesel/electric car. It has a 60 hp diesel engine and a 200 hp electric motor. The extra power (above 60 hp) for the electric motor is of course supplied by the batteries when needed.“Brent Van Arsdell", March 21, 2002.

Figure 19 : Hybrid car designed by GM 1

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II.

Submarine

“Kockums”, a Swedish defense contractor, produce Stirling Engines for the navy making the quietest submarines in the world.

Figure 20 : AIP system

This high-technology is named air-independent propulsion (AIP). There are four submarines equipment with Stirling AIP. The models are HMS Näcken, which was launch in 1978 and after ten years 1988 became the first submarine equipped with AIP system, by means of a cut and lengthened by an intersection of a Stirling AIP section, which before the installation is equipped by two Stirling units, liquid oxygen (LOX) tanks and electrical equipment.

Successful demonstration of AIP system during many routine patrols of HMS Näcken made that Gotland, another type of submarine, was the first submarine designed from the beginning to operate with AIP system.

The other four submarines that operates with this technology are two Söderman class were upgraded by 2004.

If the Stirling was designed to operate at ambient pressure (and had a valve system to ensure such) then it could be enclosed in a small bubble of gas that would slowly be crushed by the pressure of the ocean and increase the internal working volume of gas to a level that could not be easily achieved at sea level. With such enormous internal pressure the power output would be huge!

“Mick Viner, June 23, 2002” Figure 21 : Stirling engine in Näcken

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III.

Aircrafts

In relation about Stirling engines in aircraft, the communities near airports could benefit from the quiet engine. Unlike other types of aircrafts this kind of aircrafts increases the performance climbs to altitude.

Figure 22 : Torque-Crankshaft Angle

Like is showed above vibration is an area that Stirling excel. The shaft torque on four cylinders varies from 100% negative to 350% positive in each revolution.

Only 5% of variation characterised the quiet engine obviously increasing the comfort of occupants as well as airframe fatigue is greatly reduced and isolator’s materials.

Less vibration is good advantage for the propeller in means of torque, nowadays the propeller is designed considering the pulse of torque As long as the prop is also the flywheel it must be heavy and robust.

Figure 23 : Altitude-Airspeed

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Usually the first failure is the ignition system, in the Stirling the ignition is necessary at the beginning to start the fire after is not needed.

Another hamper is eliminated

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without valves. In the following graph it is possible see that the performance of the Stirling engine increases with altitude because the system is sealed without reference of ambient air density. As the outside temperature declines, engine power increases.

This compounds the natural ability of the aircraft to fly faster as air density decreases.

Stirling allow the plane to cruise above the weather rather than trough it thus it is a safety aspect because there are many accidents because the weather. In addiction, the possibility of the pilot to choose the altitude could benefit the optimize use of the winds.

There are several reasons for the superior fuel economy. First, the Stirling is a much more efficient powerplant. An internal combustion engine takes in new air and fuel for each stroke, saving nothing from the previous one. But the Stirling re-uses the same heat energy on successive strokes; the fuel is only needed to make up the losses.

The second reason is that the fuel is always burned full lean, at the best air/fuel ratio, while normal aircraft engines actually use gasoline as a coolant. The Stirling also uses the exhaust from the burner to preheat the incoming combustion air. Since the Stirling exhaust is cool, it is obvious that less energy is being thrown away.

“Darryl Philip, April 1993”

IV.

Heat and power System

This device replaces traditional boilers in houses. It is an innovative system developed to provide central heating, water heating and electricity.

Usually this device is called “Micro Combined Heat and Power (CHP)” and produces much less carbon dioxide than other ways of providing heat and power. In fact, if the level of CHP was increased to the Government's target of 10,000 MW, the UK could be one third of the way to meeting its international commitments to reduce carbon dioxide emissions. “...We can combine the building of homes with building communities with combined heat and power...”

Figure 24 : AC Whisper Gen

“Rt Hon Gordon Brown MP, Prime Minister”

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The company Whisper Gen has launched to the market the market MkV AC gas fired that consists in four cylinders with double acting Stirling cycle. It is possible coach heat output from 7.5-12KW at 220-240V Benefits: • • • •

Savings through the production of own electricity.

Reduce emissions of CO2 and other emissions.

Avoiding peak-load costs when the network is overloaded.

Allows for rapid introduction of new generation capacity.

The performance is over 90% of the fuel energy resulting in a cleaner and more cost effective alternative to traditional electricity generation. Electricity generated can be fed back into the electricity grid or used in the home, reducing electricity costs even further. Invent provides an average household with a saving of about £150 per year. It also reduces carbon dioxide emissions by up to 1.5 tonnes per year, a real contribution towards tackling the effects of global warming. That’s 20% less carbon dioxide per household.

V.

Cryocooler

If It is applied mechanical energy instead of cold and heat sources by means of external engine, It is possible reach temperatures like 10 K (-263°C) in machines of high technology.

The first Stirling-cycle cryocooler was developed at Philips in the 1950s and commercialized in such places as liquid nitrogen production plants. This company is still active in the development and manufacturing Stirling cryocoolers and cryogenic cooling systems.

A wide variety of smaller size Stirling cryocoolers are commercially available for tasks such as the cooling of sensors.

Thermoacoustic refrigeration uses a Stirling cycle in a working gas which is created by high amplitude sound waves.

VI.

Nuclear power

Steam turbines of a nuclear plan can be replaced by Stirling engine thus reduce the radioactive by-products and be more efficient. Steam plants use liquid sodium as

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coolant in breeder reactors, water/sodium exchanger are required, which in some cases that temperature increase so much this coolant could reacts violently with water.

NASA has developed a Stirling Engine known as Stirling Radioisotope (SRG) Generator designed to generate electricity in for deep space proves in lasting missions. The heat source is a dry solid nuclear fuel slug and the cold source is space itself. This device converter produces about four times more electric power from the plutonium fuel than a radioisotope thermoelectric generator.

These generators have been extensively tested but have not yet been deployed on actual missions.

Thus each SRG will utilise two Stirling converter units with about 500 watts of thermal power supplied by two GPHS (General Purpose Heat Source) units and will deliver 100-120 watts of electric power. Each GPHS contains four iridium-clad Pu-238 fuel pellets, stands 5 cm tall, 10 cm square and weighs 1.44 kg. The hot end of the Stirling converter reaches 650째C. Figure 25 : Conceptual design of the SRG by Lockheed

The power output of the generator will be greater than 100 W at the beginning of life, but the wear out of plutonium decrease the heat source. However control system allows long life.

VII.

Solar Energy

Placed at the focus of a parabolic mirror a Stirling engine can convert solar energy to electricity with efficiency better than non-concentrated photovoltaic cells.

In 2005 It is created a 1 kW Stirling generator with a solar concentrator, this was a herald of the coming of a revolutionary solar, nowadays It generates electricity much more efficiently and economically than Photovoltaic (PV) systems whit technology called concentrated solar power (CPS). Nowadays the company Infina Applications has development a 3 kW Solar Stirling Product.

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Figure 26 : Solar Dynamic Brayton Schematic

Some companies are launching technology using steel, cooper, aluminium and glass in the same low cost manufacturing techniques used to make consumer products.

The equipment is well characterized with over ove 25,000 hours of on-sun sun time.

This technology is the world´s most efficiency for the conversion of solar energy to grid delivery electricity, roughly twice as efficient of the others alternative solar technologies.

By a mirror to focus the sun’s rays on the receiver end of a Stirling engine. The internal side of the receiver then heats hydrogen gas, which expands.

The pressure created by the expanding gas drives a piston, crank shaft, and drive shaft assembly much like those found in internal combustion engines but without igniting the gas. The drive shaft is connected to a small Figure 27 : Solar Dynamic Brayton

electricity generator.

Schematic

This solar application is called concentration solar power (CSP) and is significant potential grid for water pumping or electrification.

In California there here is a big contract where the electrical output represents from approximately 1.4 percent to 2.6 percent of Edison’s annual sales.

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Seller

Gen. Type

Initial Size (MW)

SES Solar One LLC

Solar Thermal (Stirling Dish)

500

Possible Expansion Size (MW)

Estimated Annual Energy Based on Initial Size (GWH)

850

1,047

Estimated Annual Energy Based on Expansion Size (GWH)

Initial Phase OnLine Date

Completion Date for Initial Size

Term of Agreement (Years)

Estimated Capacity Factor

1,780

Jan. 2009

Dec. 2012

20

23.90 percent

Tabla 1: www.stirlingenergy.com/breaking_news.htm

Next year the Stirling solar dish will be able to be in the market, therefore high capacity to produce energy with the power of sun helping to reduce emissions of CO2 gases.

It is possible nowadays dream with CHP plants working with Stirling Engines and it is expected that this technology will be commercially available within the next few years.

Electric power output - Stirling engine KW 35

70

Thermal power output - Stirling engine kW 105

210

Thermal power output - CHP plant

kW 230

460

Fuel power input (based on NCV)

kW 300

600

Electric efficiency - Stirling engine

%

25,0

25,0

Overall electric efficiency - CHP plant %

11,7

11,7

Overall efficiency - CHP plant

%

88,3

88,3

Working gas Mean pressure

Pa

Helium Helium 4,5 4,5

Temperature of hot heat exchanger

C

750

Revolution speed Engine weight

pm 1.010 kg 1.600

750 1.010 3.500

Tabla 2: www.stirling.dk/default.asp?ID=120

NASA uses an advanced system to concentrate the sunlight. Waste heat is removed through a heat exchanger and dissipated by radiator panels to space. The power and distribution system is based on the closed Brayton cycle. A recuperative heat exchanger between the turbine discharge and receiver inlet is used to improve

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cycle efficiency. Long life is made possible through the use of non-contacting gas bearings, hermetic sealing of the gas circuit, redundant electronic components, and ultraviolet/atomic oxygen protective coatings on all optical surfaces. Radiation degradation is reduced relative to solar photovoltaic arrays since semi-conducting materials are not used on the large exposed surfaces.

Figure 28 : Solar Dynamic Brayton Schematic

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Conclusion

Stirling engines qualify for “free energy� designation when they allow us to tap previously inaccessible sources of naturally occurring energy. Stirling cycle engines are very efficient for a given temperature difference between the heat source and the heat sink. Actually, steam engines (the Rankine cycle) fall into this category, too. But depending upon what kind of hardware and its maintenance you prefer, one or the other will be preferred. Steamers have fewer parts and higher power density.

Other fluids, such as a variety of refrigerants, can be used instead of water. Stirlings avoid fluid containment problems, as they can run with air as the working fluid, and will have less maintenance issues.

Stirling Engines are very flexible. There are a lot of different types of engines.

They can be very small and run with only a small temperature difference, they are very quiet, for example to use them in submarines or they can be used as a CHP plant.

Another good point is that they can be constructed in a way that they produce no emissions. That means, in combination with solar or geothermal heat, they can be used as a renewable energy source to produce electricity.

As is showed above, the Stirling engine has strong economic practicality.

Above all, the original cost is quite lower than for any other engines. Even a few calories can drive it and keep it running. The next point is that the auxiliary costs are low, because the Stirling engine costs little on environment protection. The fuels it uses can be clean, so it costs little to handle with pollution governance. What is more, the profit of the Stirling engine is far beyond the cost. And the high efficiency can bring the maximum utilization. And last but not least, the Stirling engine is consistent with the requirements of sustainable development. It is the main development way in the future, so the Stirling engine does not only meet the economic needs at present time, but also in the future.

The Stirling engine is an interesting device like it is showed in this document with various applications and high development. Its advantages are really beneficial for the environment because it is possible produce electricity with the power of sun with high efficiency (theorically like the Carnot Cycle). It is a huge advantage to the economy because is possible to burn the cheapest fuel and it is working instead of the more expensive one. And this engine is comfortable for the people because is quiet and not noisy like an internal combustion engine.

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The real renewable energy is the solar application for this device because the other ways to produce the heat source are burning something. It is possible to decrease the emissions of CO2 or other toxic gases but not eliminate completely this problem for the earth and therefore for humans. This application could be one of the different ways to solve the problem of greenhouse gas emissions and to continue and also to develop our comfort.

In all applications that was showed in this presentation the performance the devices are better, obviously increase the efficiency is good Depend of which kind of fuel is getting burn in process. The Stirling Engine is a machine of external combustion thus if it is burned fuel the emissions of CO2 is not solved. It is showed that the performance is better but in the point of view of environment the real problem continues existing.

Find a heat source to make it works, this is the case of biomass fuels in connection with a Stirling engine are concentrated on transferring the heat from the combustion of the fuel into the working gas and in the same way the solar application.

Because, as companies look increasingly to alternative power units, it is entirely possible that the Stirling engine will find its own niche in the marketplace, perhaps as part of a hybrid power plant, or through further development and optimization. No high-tech materials are needed. This competes with solar cells.

Taking one with another, Stirling engine bring a tremendous revolution to human being. We think there is also a lot of potential in this area because modern industrialization should be sustained by regenerate power system. It is not a dead end but a new start.

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References In order to accomplish the current project, the following web pages have been consulted. The authors of the project would like to thank the following for their accuracy, clarity and conciseness.

• • • • • • • • • • • • •

• • • • • • • • • • •

http://en.wikipedia.org/wiki/Stirling_engine http://www.kockums.se http://www.grc.nasa.gov/WWW/tmsb/index.html http://www.infiniacorp.com/main.htm http://www.stirlingenergy.com http://www.whispergen.com/index.cfm http://www.sunpower.com/index.php http://www.sesusa.org/index.html http://news.soliclima.com http://www.nrel.gov/csp http://www.bekkoame.ne.jp/%7Ekhirata/english/others.htm http://www.cec.uchile.cl/~roroman/ http://www.stirlingengine.com/bboard/q-and-a-fetchmsg.tcl?msg_id=00000D&topic_id=Power%2dproducing%20Stirling%20engi nes&topic=4 www.blog.steamshift.com www.techfreep.com www.sensi.org www.energytech.at www.Sterlingenergy.com www.Stirlingengine.com www.logicsys.com.tw/wrkbas.htm. www.bbc.co.uk/dna/h2g2/A9042707 www.ent.ohiou.edu/~me321/chapter4th.info/Chapter3.html www.ent.ohiou.edu/~urieli/stirling/me422.html www.stirlingengine.com/faq/one?scope=public&faq_id=1#4

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References of figures: Last visit of these websites: 10/11/2007

Figure1

www.sunpower.com

Figure2

www.creusot.net/archives/idee/stirling/img/stirling.gif

Figure3

tw.f14.yahoofs.com/myper/38.gq_GFHRT.YwEw_4YGB5QSPA-/blog/ap_20060827013919701.jpg?TT_8kNHB1B7ghYo0

Figure4

http://mac6.ma.psu.edu/stirling/ideal_stirling_cycle/index.html

Figure5

http://www.ent.ohiou.edu/~urieli/stirling/engines/engines.htm

Figure6

http://www.moteurstirling.com/alpha.htm

Figure7

http://www.ent.ohiou.edu/~urieli/stirling/engines/beta.html

Figure8

http://en.wikipedia.org/wiki/Stirling_engine

Figure9

http://www.moteurstirling.com/beta.htm

Figure10

http://www.ent.ohiou.edu/~urieli/stirling/engines/gamma.html

Figure11

http://www.moteurstirling.com/gamma.htm

Figure12 http://www.diracdelta.co.uk/science/source/s/t/stirling%20engine/source.html Figure13

http://blog.steamshift.com/2005/05/

Figure14

http://techfreep.com/category/energy/

Figure15

http://www.kockums.se/News/photostock/photo.html

Figure16

http://www.sensi.org/~svo/stirling/

Figure17

http://energytech.at/(en)/kwk/portrait_kapitel-2_6.html

Figure18

jiucifang.blog.bokee.net/bloggermodule/blog_viewblog.do?id=961285

Figure19

www.autobloggreen.com/tag/ford/

Figure20

www.kockums.se/Submarines/aipconversion.html

Figure21

www.kockums.se/Submarines/aipconversion.html

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Figure22

www.cse.iitk.ac.in/.../371/abhishe/main1.html

Figure23

www.cse.iitk.ac.in/.../371/abhishe/main1.html

Figure24

www.whispergen.com/main/acwhispergen/

Figure25

www.grc.nasa.gov/.../5000/5490schreiber.html

Figure26

www.stirlingenergy.com/solar_overview.htm

Figure27

www.stirlingenergy.com/images.asp?Type=solar

Figure28

www.grc.nasa.gov/.../doc/adv_sd_tech.html

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