stirling engine

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STIRLING ENGINE ABSTRACT The quest of human beings to develop engines with high power, high torque, less vibration and most essentially with no pollution is on since the discovery and development of engine. Stirling engine is just one step forward towards the creation of a noise free and pollution less engine. The Stirling engine is the engine, which uses a fixed amount of gas sealed inside a cylinder. The expansion and contraction of the gas, using heat from external source, creates the useful work. The main advantage of this engine is its capability to use any type of fuel and the emission of no exhaust gases. Due to this pollution free and use of any type of fuel characteristics the Stirling engine has greater potential over any other type of engine existing today. Hence this engine is highly preferred in automobile sector finding its application in submarines to hybrid cars. Due to the above specified advantages the Stirling engine is giving a cutting edge to all other engine existing today and is viewed as an answer to the existing energy crisis Dept. of Mechanical Engineering REC Hulkoti

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a complete seminar report on stirling engine

Transcript of stirling engine

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STIRLING ENGINE

ABSTRACT

The quest of human beings to develop engines with high power, high torque,

less vibration and most essentially with no pollution is on since the discovery and

development of engine. Stirling engine is just one step forward towards the creation of a

noise free and pollution less engine.

The Stirling engine is the engine, which uses a fixed amount of gas sealed inside

a cylinder. The expansion and contraction of the gas, using heat from external source,

creates the useful work. The main advantage of this engine is its capability to use any

type of fuel and the emission of no exhaust gases.

Due to this pollution free and use of any type of fuel characteristics the Stirling

engine has greater potential over any other type of engine existing today. Hence this

engine is highly preferred in automobile sector finding its application in submarines to

hybrid cars.

Due to the above specified advantages the Stirling engine is giving a cutting edge

to all other engine existing today and is viewed as an answer to the existing energy crisis

Dept. of Mechanical Engineering REC Hulkoti

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STIRLING ENGINE

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.

A Stirling engine is a heat engine operating by cyclic compression and

expansion of air or other gas, the working fluid, at different temperature levels such

that there is a net conversion of heat energy to mechanical work.

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STIRLING ENGINE

Or more specifically, a closed-cycle regenerative heat engine with a

permanently gaseous working fluid, where closed-cycle is defined as a thermodynamic

system in which the working fluid is permanently contained within the system,

and regenerative describes the use of a specific type of internal heat exchanger and

thermal store, known as the regenerator. It is the inclusion of a regenerator that

differentiates the Stirling engine from other closed cycle hot air engines.

Originally conceived in 1816 as an industrial prime mover to rival the steam

engine, its practical use was largely confined to low-power domestic applications for over

a century.

The Stirling engine is noted for its high efficiency compared to steam

engine, quiet operation, and the ease with which it can use almost any heat source. This

compatibility with alternative and renewable energy sources has become increasingly

significant as the price of conventional fuels rises, and also in light of concerns such

as peak oil and climate change.

This engine is currently exciting interest as the core component of  micro

combined heat and power (CHP) units, in which it is more efficient and safer than a

comparable steam engine.

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STIRLING ENGINE

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

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

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.

Dept. of Mechanical Engineering REC Hulkoti

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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.

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PRESENTATION OF STIRLING ENGINES

I. Stirling thermodynamic 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 and contraction of this fluid due to a temperature differential.

So the ideal Stirling cycle consists of four thermodynamics distinct processes

acting on the working fluid: two constant-temperature processes and two constant volume

processes.

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

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1. Isothermal expansion: The expansion space is heated externally, and the gas

undergoes near-isothermal expansion.

2. Constant-volume (known as isovolumetric or isochoric) heat removal: The gas

is passed through the regenerator, thus cooling the gas, and transferring heat to the

regenerator for use in the next cycle.

3. Isothermal compression: The compression space is intercooled, so the gas

undergoes near isothermal compression

4. Constant-volume heat addition: The compressed air flows back through the

regenerator and picks up heat on the way to the heated expansion space.

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.

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.

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.

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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.

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”.

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.

Figure 5 : Alpha engine’s configuration

This type of engine has a high power-to-volume ratio but has technical problems

due to the usually high temperature of the hot piston and the durability of its seals.

In practice, this piston usually carries a large insulating head to move the seals

away from the hot zone at the expense of some additional dead space.

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Action of an alpha type Stirling engine:

The following diagrams do not show internal heat exchangers in the compression

and expansion spaces, which are needed to produce power. A regenerator would be

placed in the pipe connecting the two cylinders. The crankshaft has also been omitted.

1. Most of the working gas is in contact with the hot cylinder walls, it has been heated and expansion has pushed the hot piston to the bottom of its travel in the cylinder. The expansion continues in the cold cylinder, which is 90° behind the hot piston in its cycle, extracting more work from the hot gas.

2. The gas is now at its maximum volume. The hot cylinder piston begins to move most of the gas into the cold cylinder, where it cools and the pressure drops.

3. Almost all the gas is now in the cold cylinder and cooling continues. The cold piston, powered by flywheel momentum (or other piston pairs on the same shaft) compresses the remaining part of the gas.

4. The gas reaches its minimum volume, and it will now expand in the hot cylinder where it will be heated once more, driving the hot piston in its power stroke.

Figure 6: Action of an alpha type Stirling engine

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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 arrangements. The Beta

engine has both the displacer and the piston in an in- line cylinder system. The Gamma

engine uses separate cylinders.

The purpose of 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.

Figure 7 : Beta engine’s configuration

A beta Stirling has a single power piston arranged within the same cylinder on

the same shaft as a displacer piston. The displacer piston is a loose fit and does not extract

any power from the expanding gas but only serves to shuttle the working gas between the

hot and cold heat exchangers.

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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.

Action of a beta type Stirling engine:

Again, the following diagrams do not show internal heat exchangers or a

regenerator, which would be placed in the gas path around the displacer

1. Power piston (dark grey) has compressed the gas, the displacer piston (light grey) has moved so that most of the gas is adjacent to the hot heat exchanger.

2. The heated gas increases in pressure and pushes the power piston to the farthest limit of thepower stroke.

3. The displacer piston now moves, shunting the gas to the cold end of the cylinder.

4. The cooled gas is now compressed by the flywheel momentum. This takes less energy, since its pressure drops when it is cooled.

Figure 8: Action of an beta type Stirling 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

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same flywheel. The gas in the two cylinders can flow freely between them and remains a

single body.

This configuration produces a lower compression ratio but is mechanically

simpler and often used in multi-cylinder Stirling engines.

The advantage of this design is that it is mechanically simpler because of the

convenience of two cylinders in which only the piston has to be sealed. The disadvantage

is the lower compression ratio.

Figure 9 : Gamma engine’s configuration

4 . Other types:

Changes to the configuration of mechanical Stirling 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 valves. The work produced by the

fluidyne goes into pumping the liquid.

Dept. of Mechanical Engineering REC Hulkoti

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STIRLING ENGINE

ANALYSIS

Comparison with internal combustion engines:

In contrast to internal combustion engines, Stirling engines have the potential to

use renewable heat sources more easily, to be quieter, and to be more reliable with lower

maintenance. They are preferred for applications that value these unique advantages,

particularly if the cost per unit energy generated is more important than the capital cost

per unit power. On this basis, Stirling engines are cost competitive up to about 100 kW.

Compared to an internal combustion engine of the same power rating, Stirling

engines currently have a higher capital cost and are usually larger and heavier. However,

they are more efficient than most internal combustion engines. Their lower maintenance

requirements make the overall energy cost comparable. The thermal efficiency is also

comparable (for small engines), ranging from 15% to 30%. For applications such

as micro-CHP, a 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 energy, and biomass such as agricultural waste and other waste such as

domestic refuse. Stirlings are also used as a marine engine in Swedish Gotland-

class submarines. However, Stirling engines are generally not price-competitive as an

automobile engine, due to high cost per unit power, low power density and high material

costs.

Comparison from economic point:

As said above the Stirling engine is a kind of external combustion engine, and it

can use a variety of fuels. It 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. 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 expanded gases cooling down in the air-conditioned room, next process is

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taking on. As long as a certain value of the temperature difference exists, a Stirling

Engine can be formed.

Figure 10. 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

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 a Stirling engine, as it requires a

high level of the materials and manufacturing processes.

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. Energy problem is a worldwide one, and it is sooner or

later to get into the transition-to-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.

Dept. of Mechanical Engineering REC Hulkoti

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REASONS TO USE STIRLING ENGINES

There are several reasons to use a Stirling Engine:

Stirling engines can run directly on any available heat source, not just one produced

by combustion, so they can run on heat from solar, geothermal, biological, nuclear

sources or waste heat from industrial processes.

A continuous combustion process can be used to supply heat, so those emissions

associated with the intermittent combustion processes of a reciprocating internal

combustion engine can be reduced.

Some types of Stirling engines have the bearings and seals on the cool side of the

engine, where they require less lubricant and last longer than equivalents on other

reciprocating engine types.

The engine mechanisms are in some ways simpler than other reciprocating engine

types. No valves are needed, and the burner system can be relatively simple. Crude

Stirling engines can be made using common household materials.

A Stirling engine uses a single-phase working fluid which maintains an internal

pressure close to the design pressure, and thus for a properly designed system the risk

of explosion is low. In comparison, a steam engine uses a two-phase gas/liquid

working fluid, so a faulty overpressure relief valve can cause an explosion.

In some cases, low operating pressure allows the use of lightweight cylinders.

They can be built to run quietly and without an air supply, for air-independent

propulsion use in submarines.

They start easily (albeit slowly, after warmup) and run more efficiently in cold

weather, in contrast to the internal combustion which starts quickly in warm weather,

but not in cold weather.

A Stirling engine used for pumping water can be configured so that the water cools

the compression space. This is most effective when pumping cold water.

They are extremely flexible. They can be used as CHP (combined heat and power) in

the winter and as coolers in summer.

Waste heat is easily harvested (compared to waste heat from an internal combustion

engine) making Stirling engines useful for dual-output heat and power systems.

Dept. of Mechanical Engineering REC Hulkoti

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DISADVANTAGES

Stirling engine designs require heat exchangers for heat input and for heat output, and

these must contain the pressure of the working fluid, where the pressure is

proportional to the engine power output. In addition, the expansion-side heat

exchanger is often at very high temperature, so the materials must resist the corrosive

effects of the heat source, and have low creep. 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.

All thermodynamic cycles require large temperature differentials for efficient

operation. In an external combustion engine, the heater temperature always equals or

exceeds the expansion temperature. This means that the metallurgical requirements

for the heater material are very demanding.

A Stirling engine cannot start instantly; it literally needs to "warm up". This is true of

all external combustion engines, but the warm up time may be longer for Stirlings

than for others of this type such as steam engines. Stirling engines are best used as

constant speed engines.

Most technically advanced Stirling engines, like those developed for United States

government labs, use helium as the working gas, because it functions close to the

efficiency and power density of hydrogen with fewer of the material containment

issues. Helium is inert, and hence not flammable. Helium is relatively expensive, and

must be supplied as bottled gas.

Some engines use air or nitrogen as the working fluid. These gases have much lower

power density (which increases engine costs), but they are more convenient to use

and they minimize the problems of gas containment and supply (which decreases

costs). The use of compressed air in contact with flammable materials or substances

such as lubricating oil introduces an explosion hazard, because compressed air

contains a high partial pressure of oxygen.

Dept. of Mechanical Engineering REC Hulkoti

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APPLICATIONS OF THE STIRLING POWER

1. 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.

2. Aircraft engines

Stirling engines may hold theoretical promise as aircraft engines, if high power

density and low cost can be achieved. They are quieter, less polluting, gain efficiency

with altitude due to lower ambient temperatures, are more reliable due to fewer parts and

the absence of an ignition system, produce much less vibration (airframes could last

longer) and use safer, less explosive fuels. However, the Stirling engine often has low

power density compared to the commonly used Otto engine and Brayton cycle gas

turbine. This issue has been a point of contention in automobiles, and this performance

characteristic is even more critical in aircraft engines.

3. 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.

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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.

4. 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.

On August 11, 2005, Southern California Edison announced an agreement with

Stirling Energy Systems to purchase electricity created using over 30,000 Solar Powered

Stirling Engines over a twenty-year period sufficient to generate 850 MW of electricity.

5. Marine engines

The Stirling engine could be well suited for underwater power systems where

electrical work or mechanical power is required on an intermittent or continuous

level. General Motors has done a considerable amount of work on advanced Stirling cycle

engines which include thermal storage for underwater applications. United Stirling,

in Malmo, Sweden, is developing an experimental four–cylinder engine using hydrogen

peroxide as an oxidant in underwater power systems. The SAGA (Submarine Assistance

Great Autonomy) submarine became operational in the 1990s and is driven by two

Stirling engines supplied with diesel fuel and liquid oxygen.

6. 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.

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.

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7. 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

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.

Figure 11 . Conceptual design of the SRG by Lockheed

8. Acoustic Stirling Heat Engine

Los Alamos National Laboratory has developed an "Acoustic Stirling Heat Engine"

with no moving parts. It converts heat into intense acoustic power which (quoted

from given source) "can be used directly in acoustic refrigerators or pulse-tube

refrigerators to provide heat-driven refrigeration with no moving parts, or ... to

generate electricity via a linear alternator or other electro-acoustic power transducer".

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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.

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.

In all applications that was showed in this presentation the performance the

devices are better, obviously increase the efficiency is good.

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.

Dept. of Mechanical Engineering REC Hulkoti

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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

· www.Sterlingenergy.com

· www.Stirlingengine.com

Dept. of Mechanical Engineering REC Hulkoti