An external combustion engine, for instance, would heat water to produce steam, which would then be used to drive a turbine. Internal combustion engines vary from external heat engines in that the heat source is isolated from the working fluid. External heat engines are often steam engines.
This is not the same as internal combustion, such as that which occurs in an automobile engine, when fuel ignites within a piston, performs its function, and is subsequently released. External heat engines are all external combustion engines. Certain types of EHEs are not external combustion engines, such as solar thermal, nuclear, and geothermal power plants.
Well, in this reading, I’ll be exploring what an external combustion engine is, its application, its diagram, example, advantages and disadvantages & how it works.
Let’s Get Started!
Contents
What is an External Combustion Engine?
An external combustion engine is a heat engine where a (internal) working fluid is heated by combustion of an external source, through the engine wall or a heat exchanger.
The fluid is then cooled, compressed, and reused in a closed cycle. Unlike the steam engine’s use of water in both its liquid and gaseous phases as the working fluid, the Stirling engine encloses a fixed quantity of permanently gaseous fluid such as air or helium. The fluid then, by expanding and acting on the mechanism of the engine produces motion and usable work.
Application of an External Combustion Engine
Below are the applications of external combustion engines and their examples:
- Steam engines: Locomotive, Marine
- Stirling Engines: Experimental space vehicles
- Steam Turbines: Power, Large Marine
- Closed Cycle Gas Turbine: Power, Marine
Examples of External Combustion Engine
- Engine Stirling
- Coal-fired power plant
- Steam locomotive (although there are very few operational examples left)
- Solar thermal power plant
- Natural gas power plant
Diagram
How External Combustion Engine Works
An external combustion engine works by using an external heat source (like burning coal) to heat a working fluid (like water). As the temperature of the fluid increases, the fluid expands, and this expansion is harnessed and used to do work (like moving a vehicle). The intake function involves drawing a mixture of air and fuel into the combustion chamber. The compression function compresses the mixture.
The power function involves igniting the mixture and harnessing the power of that reaction. The exhaust function expels the burned gases from the engine. Both types operate in a cyclic process in which every cycle involves intake of fuel and air, compression, ignition, combustion, expansion of the gas against the piston, and exhaust of combustion products.
It may be the first working external combustion engine in history. In 1672, Dutch missionary Ferdinand Verbiest created a steam-powered toy car for the Chinese emperor, which may be the first steam-powered vehicle in history. In 1698, Thomas Savery of England patented the first commercial steam engine. In the spark-ignition engine, an electrical spark ignites the combustible mixture.
Advantages of External Combustion Engine
Below are the benefits of external combustion engine
- Almost any kind of fuel that is available can be used
- Since power is not generated due to the detonation of fuel hence very little noise is generated.
- Engine emissions are also very low
- low levels of exhaust pollution
- Quiet operation
- High starting torque
Disadvantages of External Combustion Engine
Below are the disadvantages of external combustion engines:
- The size of an engine is relatively big
- Slow start-up
- Bulkiness due to an external boiler
- lower efficiency at partial loads
- Leakage of working fluid
- Lubricant consumption