THESTIRLING ENGINE

IT’S Just an Temporary PPT which will give you an brief idea of Stirling

Engine. Final PPT is under constructionBy-Madhur Jhawar, Sachin Ghongade, Sourabh Joshi, Yash Jain.Co-suppoters: Ankit Goratela, Amar Dusa, Amol Kadam, Harsh Chaurasia

ROBERT STIRLING

Scottish scientist(25 October 1790 to 6 June 1878)

Achievements: Heat Economiser (now generally

known as the regenerator) In 1818 he built the first practical

version of his engine incorporating heat economiser in it, used to pump water from a quarry.

STIRLING CYCLE

TH TL

QH

Process 1-2: Heat is transferred isothermally at TH, the left piston moves outward and develops work.

Work

Process 2-3: Constant volume process, gas is pushed to the right chamber through the regenerator. Heat stored reversibly in the regenerator. The gas temperature drops to TL.

Process 3-4: Compressing the gas reversibly gas pressure increases, isothermal heat rejection to the heat sink at TL.

THTL

QL

Win

Stirling Cycle

Regenerator

TH TL

TH

Process 4-1: Constant volume, the gas is pushed to the left chamber through the regenerator. Gas temperature increases to TH.

Stirling Cycle

Regenerator

BASIC TYPES OF STIRLING ENGINE

ALPHABETA

GAMMA

Alpha EngineThe four basic stages :

1.1. Heating :

The gas arrives in the hot cylinder coming from the cold cylinder. it is heated.

1.2. Expansion :The two pistons descend. Total volume increases : it is the phase of relaxation.

1.3. Cooling :

The gas goes towards the cold cylinder from the hot cylinder. During this phase, it is cooled.

1.4. Compression :

The two pistons go up at the same time. Total volume decreases: it is the phase of compression.

The following animation shows the complete cycle of a alpha engine.

Beta EngineThe four basic stages :

1.1. Heating :

The gas is transferred from the cold part towards the hot part.- the operating piston is almost motionless.- the displacer goes down.

1.2. Expansion :

It is the expansion phase, the gaz is near the hot part.- the operating piston goes down.- the displacer too.

The gas is transferred from the hot part towards the cold part.- the operating piston is almost motionless.- the displacer goes up.

1.3. Cooling :

1.4. Compression :

The gas is compressed, it is near the cold part.- the operating piston goes up.- the displacer is almost motionless at the top.

The following animation shows the complete cycle of a beta engine:

Gamma Engine1. The four basic stages :

1.1. Heating :

During this phase, the engine piston moves slightly, the overall volume is minimal. In contrast, the displacer carries out a long race and the gas is heated.

The displacer moves little. In contrast, the operating piston carries out more than 70% of its race. It recovers energy.

1.2. Expansion :

1.3. Cooling :

The displacer carries out most of his race: the gas is cooled. The operating piston moves little.

The displacer remains at the top: the gas is cold. However, the piston engine performs the majority of its race: it compresses the gas by yielding mechanical energy

1.4. Compression :

The following animation shows the complete cycle of a gamma engine:

Other Engine

         

The operating piston moves according to the pressure of the engine. When the pressure increases, it is pushed in one direction. When the pressure decreases, it returns in the other direction to its initial position. This requires the presence of an average force on the "outside" face of the piston, it is generated by a gas enclosed in a chamber or by the relief of a spring. If the piston engine is a magnet, one can install a linear alternator for generating electric current.

In contrast to the previous one, the piston is mechanically driven. The displacer moves according to the pressure of a gas enclosed in a capacity and the pressure of the engine 

1. The free piston engine or Martini engine :

2. The free displacer engine or Ringbom engine: :

3. The free piston Stirling engine :

This engine combines the advantages of the previous models.The great advantage is that one can obtain an absolute sealing because there does not exist any mechanical connection with outside. Produced energy is evacuated by a completely tight linear alternator

The animation of NASA

4. The double-acting piston engine :

The principle consists in putting several alpha engines in “series”. There is only one piston by cylinder which has the function of displacer and the function of operating piston. The phase angle difference between each piston is 90°.

- The silence of operation : there is no expansion in the atmosphere like in the case of an internal combustion engine, combustion is continuous outside of the cylinders. In addition, its design is such as the engine is easy to balance and generates few vibrations.

- The high efficiency : it is function of the temperatures of the hot and cold sources. As it is possible to make it work in cogeneration (mechanical and caloric powers), the overall efficiency can be very high.- The multitude of possible “hot sources” : combustion of various gases, wood, sawdust, waste, solar or geothermic energy...

- The ecological aptitude: to respond to the environmental requirements on air pollution. It is easier to achieve a complete combustion in this type of engine.

- Reliability and easy maintenance: the technological simplicity makes it possible to have engines with a very great reliability and requiring little maintenance.

- An important lifetime because of its “rusticity”.

- The very diverse uses because of its autonomy and adaptability to the needs and the different kinds of hot sources

APPLICATIONSThe advantages :

The disadvantages :

- The price : its cost is probably the most important problem, it is not yet competitive with other means well established. A generalization of its employment should solve this problem inherent in any novelty. 

- The ignorance of this type of engine by the general public. Only a few fans know it exists. It is therefore necessary to promote it. 

- The variety of models prevents standardization and, consequently, lower prices.

- The problems of sealing are difficult to solve as soon as one wishes to have high pressures of operation. The choice of “ideal” gas would be hydrogen for its lightness and its capacity to absorb the calories, but its ability to diffuse through materials is a great disadvantage.

- Heat transfers with a gas are delicate and often require bulky apparatuses.

- The lack of flexibility : the fast and effective variations of power are difficult to obtain with a Stirling engine. This one is more qualified to run with a constant nominal output. This point is a great handicap for an utilisation in car industry.

The current and past applications of Stirling engines

1.Research and university world: Stirling engine is the subject of theoretical studies and practical works in order to better know it, to improve its output and to increase its competitiveness facing other energy sources. This works enable the modelization of this engine, i.e. to put in equations the heat transfers, the flows of the fluids, to simulate certain configurations without having to build an engine...When one studies something at school or university, this promotes its introduction in everyday life. No doubt that will happen for the Stirling engine.

2. Military uses:If weapons dissuade countries from going to war (we can dream !), then we can be delighted by introduction of Stirling engines into the military field.- an attack submarine of Swedish army is equipped with Stirling engines for its auxiliary electrical production in order to provide the vital functions in the event of unavailability of the main source. Its silence of operation is a major asset in this application. In the same context, the Australian navy has also adopted it for a 3000 tons displacement submarine.- some military ships also use this technology : corvettes or boats for mine detection or acoustic monitoring.

3. Spatial domain:

Some satellites get energy through a Stirling engine. The efficiency is particularly high considering the great differences in temperature. The hot source consists of radioactive isotopes. The use of radioactive elements is not very ecological, it presents risks at the time of the take-off of the rocket. The justification comes owing to the fact that solar panels can be dirtied or be destroyed in certain zones of space, as near Mars.

4. Solar applications:

When one takes advantage of energy from the Sun, one uses a reflective dish which concentrates the sunbeams in only one point: the focus of the dish where you install the Stirling engine.In the United States, great reflective dishes were installed in the desert with Stirling engines to generate electricity without buying fuel!

5. Domestic uses:Small installations were developed in order to function in cogeneration: electricity supply and dwelling heating. One chooses fuel (oil, wood, wood pellets…) to make electricity and to heat a house. During certain periods, it is possible to sell excess electricity if one is connected to the grid.Some pleasure boats are equipped like that.

Future Applications

1. In the military field:It is possible to envisage a generalization of the use of Stirling engine as an auxiliary source of electricity for submarines and surface vessels, like what is being done today in the Swedish and Australian navies. An appropriate choice of fuel (liquid oxygen and liquid hydrogen, for example) would reduce the risk of pollution in case of an accident.

2. For merchant-ships or pleasure-ships:Why not take advantage of advances in the military sphere? If we can not consider the use of the Stirling engine as the mean of main propulsion, we can imagine its use as an auxiliary source of electricity and heating. Its vibratory level and its faint noise are great assets for its use.3. In the industrial field:The recovery of all energies released directly to the atmosphere or into rivers can be a motivation for the industry. Indeed, many industrial processes in the areas of chemistry or generation of electricity emit huge quantities of energy in the environment. For example, a nuclear plant sends twice more energy to the river than in the electric wires!Moreover, one estimates at 10% the energy dissipated in these same electric wires. One thus sees the interest of the cogeneration (electricity + heat) and of a production decentralized nearest the consumers and dimensioned with their needs.