What is an External Combustion Engine?

External Combustion Engine

An external combustion engine (ECE) is a heat engine in which the engine wall or heat exchanger heats the working (internal) fluid by combustion from an external source. The fluid then expands and acts on the locomotor mechanism to create useful work and movement. The liquid is then cooled, compressed, and reused in a closed circuit. 

The EC engine has a piston, connecting rod, crankshaft, camshaft, and crankcase. These components play an important role in the working of the external combustion engine. The camshaft controls the opening and closing of the inlet and outlet valves. The function of the crankshaft is to move the piston while connecting rod transfers the motion of the connecting rod to the piston.

 Unlike steam engines, which use water in the liquid and gaseous stages as the working fluid, the Stirling engine contains a constant amount of permanent gaseous liquid such as air or helium. Like all heating machines, it includes the general cycle of cold gas compression, gas heating, hot gas expansion, and finally gas cooling before repeating the cycle.

Working of the External Combustion Engine

In an external combustion engine, the fuel is burned outside the engine and the energy from the combustion of the fuel is supplied to the engine by means of a heat transfer device. For many machines, it is a means of transferring the heat of the water, but in many other cases, it can also be air.

One of the most common examples of ECE is the steam engine, developed by the great scientist James Watt.

In this machine, the steam is extracted from the heat extracted from the combustion of coal. The steam is then sent to the device, where the energy of the pressure is converted into work. The device used at the time was a replacement engine.

This type of compatible ECE is no longer used. They have been completely replaced by internal combustion engines. The reason is the change in size and its low efficiency. In addition, they need a lot of care.


One of the most popular examples of outdoor combustion engines today is the steam turbine. A steam turbine is an external combustion engine that consumes steam and converts its energy into useful work. 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 the needs of a high-quality steam turbine.

There are several types of fuels that can be used in steam turbines to generate steam. This can be coal, wood, straw, liquefied petroleum gas, 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.

Types and applications of external combustion engines

  1. Steam engine
  2. Closed gas turbine 
  3. Steam turbine
  4. Stirling Engine

1) Steam engine

The steam engine is an external combustion engine. In a steam engine, coal-like fuel burns in the combustion chamber. This heat causes the water in the boiler to heat up. The pipeline transmits steam to the turbine, which has a series of blades per shaft. The hot steam expands as it passes through the turbine, compressing the blades and spinning the shaft. The rotating shaft can run a generator, move the ship’s propeller, or perform other useful activities.

Another configuration involves the injection of high-pressure steam into a chamber with a piston. Press the steam of 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 difference between a Stirling engine and a steam engine is that its working fluid is always filled with gas, while the steam engine converts liquid water into gaseous vapor. In addition, the Stirling engine continuously circulates its working fluid, while the steam engine emits a dense steam engine after passing.

Advantages of external combustion engines

  1. Almost all available fuel can use
  2. Since the fuel explosion does not gain power, it produces very little noise.
  3. Engine emissions are also very low
  4. Very convenient for large power generation

Disadvantages of external combustion engines

  1. Not suitable for low load conditions
  2. Make work fluid
  3. Consumption of lubricant
  4. The displacement is very large
  5. The overall working temperature is high, which requires special care and special building materials.

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