We all know an engine converts one form of energy to another form, which is usually a work. The type of engines which are generally used to move vehicles are combustion engines.
Combustion engines are the engines which burn fuel to obtain energy and they convert that energy into work.
Combustion engines are of two types.
Internal combustion engine and external combustion engine.
In internal combustion fuel burns inside the engine unit.
How internal combustion engines work, it not a topic of discussion in this article. In this article we are focused on external combustion engines.
Working of external combustion engine
In an external combustion engine, the fuel is burnt outside the engine and the energy which is obtained by the combustion of fuel is then carried to the engine with the help of a heat carrying medium.
In case of many engines the heat carrying medium is water but in several other cases it can also be air.
One of the most common example of external combustion is the steam engine developed by great scientist James Watt.
In that engine steam is obtained with the help of heat obtained by burning coal. The steam then sent to an engine where its pressure energy gets converted into work. The engine that was used was used at that time was of reciprocating type.
These kinds of reciprocating external combustion engines are not in use now. They have been totally replaced by internal combustion engines. The reason of the replacement was their big size and inefficiency. Also, they require a lot of maintenance.
Reciprocating External combustion engines can be seen easily in various museums today.
Are all the external combustion engines not in use today?
The answer is no, not all the external combustion engines are obsolete. In fact, many of them are very popular today.
One of the most popular example of external combustion engine today is steam turbine. A steam turbine is an external combustion engine which expends steam and converts its energy into useful work. Since the steam is produced somewhere outside the turbine (which is an engine) it is known as external combustion engine.
In most of the power plants in the world steam turbines are used to generate electricity. The reason of their popularity is that since they are external combustion engines so they have nothing to do with the type of fuel which is used to convert water into steam. All the steam turbines need is good quality steam.
The variety of fuel which can be used to generate steam in steam turbine is very large. It can be coal, wood, grass straw, liquid or gaseous fuel.
Another important type of external combustion engine which is used today is gas turbine. Working of gas turbines is similar to steam turbine but the only difference is the heat carrying medium used here is air instead of steam.
Advantages of external combustion engines
- Almost any kind of fuel that is available can be used
- Since power is not generated due to detonation of fuel hence very less noise is generated.
- Engine emissions are also very low
- Very economical for huge power generation
Disadvantages of external combustion engines
- Not suitable for low load requirements
- Leakage of working fluid
- Lubricant consumption
- Size of engine is relatively big
- Overall working temperature is high so great care and special building materials are required
Types and Applications of external combustion engines
- Steam engines: Locomotive, Marine
- Stirling Engines: Experimental space vehicles
- Steam Turbines: Power, Large Marine
- Closed Cycle Gas Turbine: Power, Marine
You can read this article to understand applications of Internal combustion engines.