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Stirling engine
Post: #1

The Stirling engine, is a heat engine of the external combustion piston engine type whose heat-exchange process allows for near-ideal efficiency in conversion of heat into mechanical movement by following the Carnot cycle as closely as is practically possible with given materials.


Its invention is credited to the Scottish clergyman Rev. Robert Stirling in 1816 who made significant improvements to earlier designs and took out the first patent. He was later assisted in its development by his engineer brother James Stirling.



The inventors sought to create a safer alternative to the steam engines of the time, whose boilers often exploded due to the high pressure of the steam and the inadequate materials. Stirling engines will convert any temperature difference directly into movement.



The Stirling engine works by the repeated heating and cooling of a usually sealed amount of working gas, usually air or other gases such as hydrogen or helium. This is accomplished by moving the gas between hot and cold heat exchangers, the hot heat exchanger being a chamber in thermal contact with an external heat source, e.g. a fuel burner, and the cold heat exchanger being a chamber in thermal contact with an external heat sink, e.g. air fins.



The gas follows the behaviour described by the gas laws which describe how a gas' pressure, temperature and volume are related. When the gas is heated, because it is in a sealed chamber, the pressure rises and this then acts on the power piston to produce a power stroke.

When the gas is cooled the pressure drops and this means that less work needs to be done by the piston to recompress the gas on the return stroke, giving a net gain in power available on the shaft. The working gas flows cyclically between the hot and cold heat exchangers.

The working gas is sealed within the piston cylinders, so there is no exhaust gas (other than that incidental to heat production if combustion is used as the heat source). No valves are required, unlike other types of piston engines.

To summarize, the Stirling engine uses the potential energy difference between its hot end and cold end to establish a cycle of a fixed amount of gas expanding and contracting within the engine, thus converting a temperature difference across the machine into mechanical power.

The greater the temperature difference between the heat source and cold source, the easier it is for the Stirling engine to operate and the less efficient the design has to be for the engine to run.

But small demonstration engines have been built which will run on a temperature difference of around 15 degrees C, e.g. between the palm of a hand and the surrounding air, or between room temperature and melting water ice.
Post: #2
Prepared by:
Avijit Singh Rathore
Nikhil Athale

[attachment=10971]
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.
• Robert Stirling was the Scottish inventor of the first practical example of a closed cycle air engine in 1816 i.e. Stirling Engine.
Key Components:
• Heat source
• Recuperator
• Heater
• Regenerator
• Cooler
• Heat sink
• Displacer
Principle:
• Isothermal Expansion. The expansion-space and associated heat exchanger are maintained at a constant high temperature, and the gas undergoes near-isothermal expansion absorbing heat from the hot source.
• Constant-Volume (known as isovolumetric or isochoric) heat-removal. The gas is passed through the regenerator, where it cools transferring heat to the regenerator for use in the next cycle.
• Isothermal Compression. The compression space and associated heat exchanger are maintained at a constant low temperature so the gas undergoes near-isothermal compression rejecting heat to the cold sink
• Constant-Volume (known as isovolumetric or isochoric) heat-addition. The gas passes back through the regenerator where it recovers much of the heat transferred in 2, heating up on its way to the expansion space.
Steps Of Operation:
 Cooling
 Compression
 Heating
 Expansion
Applications:
• Solar power generation
• Marine engines
• Nuclear power
• MicroCHP
• Chip cooling
Advantages:
• Stirling engines can run directly on any available heat source, not just one.
• It can provide emission less power generation.
• No valves are needed ,as there is no mass transfer.
• The risk of explosion is low as Stirling engine uses a single-phase working fluid .
• They start easily and run more efficiently in cold weather, in contrast to the IC engine which starts quickly in warm weather, but not in cold weather.
Disadvantages:
• Size and cost issues
• Power and torque issues
• Gas choice issues
Post: #3
[attachment=15301]
Stirling engines can be hard to understand. Here are the key points. Every
Stirling engine has a sealed cylinder with one part hot and the other cold. The working gas inside the engine (which is often air, helium, or hydrogen) is moved
by a mechanism from the hot side to the cold side. When the gas is on the hot side
it expands and pushes up on a piston. When it moves back to the cold side it
contracts. Properly designed Stirling engines have two power pulses per
revolution, which can make them very smooth running. Two of the more common
types are two piston Stirling engines and displacer-type Stirling engines. The two
piston type Stirling engine has two power pistons. The displacer type Stirling
engine has one power piston and a displacer piston.
Displacer Type:
The displacer type Stirling engine is shown here. The space below the displacer
piston is continuously heated by a heat source. The space above the displacer
piston is continuously cooled. The disp
 

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