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What is an External Combustion Engine?

An external combustion engine is a heat engine in which the working (internal) fluid is heated by the engine wall or the heat exchanger by combustion from an external source. The fluid then expands and acts on the motor mechanism to create the available work and movement. The liquid is then cooled, compressed, and reused in a closed circuit. Unlike steam engines, which use water in the liquid and gaseous phases as the working fluid, the Stirling engine contains a constant volume of permanently gaseous fluid, such as air or helium.

Working of External Combustion Engine

In external combustion engines, the fuel is burned outside the engine and the energy from the combustion of the fuel reaches the engine with the help of a heat carrier. For many cars, the heat transfer medium is water, but in some other cases, it can also be air. One of the most common examples of external combustion is the steam engine built by the great scientist James Watt.

In this engine, the steam is burned by the heat extracted from the coal. The steam is then sent to the device, where its pressure energy is converted into work. The engine used at the time was a reciprocating engine.

This external combustion reciprocating engine is no longer used. They have been completely replaced by internal combustion engines. The reason for its replacement is its large size and low efficiency. External combustion engines are now found everywhere in various museums.

One of the most popular examples of external combustion engines today is the steam turbine. A steam turbine is an external combustion engine that consumes steam and uses its energy. Since the steam is generated somewhere outside the turbine (which is the engine), it is called an external combustion engine.

Most power plants around the world use steam turbines to generate electricity. The reason for their popularity is that they are external combustion engines, so they have nothing to do with the type of fuel used to evaporate the water. All a steam turbine needs are high-quality steam.

There are several types of fuel that can be used in steam turbines to generate steam. This can be coal, wood, straw, liquid fuel, or gas.

Another important type of external combustion engine used today is the gas turbine. The principle of operation of a gas turbine is similar to that of a steam turbine, but the only difference is that the heat transfer medium used here is air rather than steam.

Type of external combustion engine

1) Steam Engine

The steam engine is an external combustion engine. In a steam engine, fuel such as coal is burned in the combustion chamber. This heat converts the water in the boiler into steam. The pipeline carries the steam to the turbine with a series of blades attached to the shaft. The hot steam expands as it passes through the turbine, pressing on the blades, causing the shaft to rotate. The rotating shaft can power the generator, move the ship’s propeller, or perform other useful tasks.

Another configuration involves the injection of high-pressure steam into a chamber with a piston. It presses the steam on the piston connected to the crankshaft. The crankshaft has the ability to convert the reciprocating motion of the piston into a rotary motion which can cause the wheel or impeller to rotate.

2) Stirling Engine

The second type of external combustion engine is the Stirling engine. The difference between a Stirling engine and a steam engine is that its working fluid is always in the gaseous phase, while the steam engine converts liquid water into gaseous vapor.

Advantages of the external combustion engine

  1. Almost all available fuel can be used
  2. Since the fuel explosion produces no energy, the noise produced is very low.
  3. Engine pollution is also very low
  4. Large power generation is very convenient

Disadvantages of external combustion engines

  1. Not suitable for low load requirements
  2. Release of the operating fluid
  3. Consumption of lubricating oil
  4. The displacement is very large.


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