An engine is a mechanical machine that converts fuel energy into mechanical work. The engines are used for different applications all over the world. There are multiple types of engines according to the nature of the application. However, the two most famous types of engines are external combustion (EC) engines and internal combustion (IC) engines. This article deeply explains the external combustion engine working, types, applications, and parts.
What is an External Combustion Engine?
An external combustion engine (EC engine) is a type of reciprocating engine in which an external heat source is used to heat the (internal) working fluid through a heat exchanger or engine walls. As the fluid gets heat, it expands, generates power, and moves the vehicle.
In simple words, an engine in which the combustion of the working fuel occurs outside the working cylinder is called an external combustion engine.
These types of engines use gas, steam, or liquid as a working fluid. In this engine, a fuel-air mixture is filled into the external combustion chamber. As the fuel-air mixture burns, a large amount of heat generates.
A heat exchanger or engine wall is used to transfer the produced heat from the external combustion chamber to the internal working fluid. When the internal fluid heats up, it expands and acts on the engine mechanisms, resulting in movement and available work.
A steam engine is one of the most common examples of an external combustion engine. In this engine, as the steam enters the engine, it expands and rotates the piston. The piston further converts the thermal energy of steam into mechanical power that is used to run the vehicle.
In the case of a steam engine, the steam is generated outside the engine (i.e., boiler). Therefore, it is called an EC engine.
In the present time, external combustion engines are not most commonly used in transportation applications due to the inefficiency of mobile design but are still used in power plants. External combustion engines are most commonly used in hydroelectric power plants.
These engines are less efficient and more complex than IC engines. However, they produce lower emissions than IC engines.
Working of External Combustion Engine
An external combustion engine is a type of engine in which an external heat source is utilized to ignite the internal working fluid. The Stirling engine and steam engine are the most common types of EC engines. An EC engine works in the following way:
- First of all, the burning fluid (such as coal) is supplied to the external heat source (such as a boiler).
- A feed pump is used to pump water from the reservoir to the boiler.
- As the water enters the boiler, the coal starts burning and supplies heat to the water.
- As the water temperature increases, it converts into steam.
- When the water is converted into steam, it passes through a compressor which compresses the steam and increases its pressure.
- When highly compressed steam enters the engine cylinder, it expands and forces the piston to move forward and backward inside the cylinder.
- A crankshaft is connected to the piston. The piston delivers its motion to the crankshaft.
- The crankshaft transforms the reciprocatory motion of the piston into rotatory motion and rotates the flywheel.
- As the flywheel rotates, it further delivers power to the vehicle tires and helps to move the vehicle.
Types of External Combustion Engines
The external combustion engine has the following major two types:
- Steam Engine
- Stirling Engine
1) Steam Engine
The term “steam engine” represents the reciprocating engine, not steam turbines. This type of EC engine uses steam as a working medium to produce mechanical work. A steam engine converts the thermal energy of the steam into rotational energy (i.e., mechanical energy).
It is an engine in which the working media is separated from the burning product. An ideal thermodynamic cycle known as the “Rankine cycle” is used to analyze this process.
This engine uses the thermal energy of the steam to push the piston back and forth in the cylinder. This reciprocating motion of the piston is transferred to the crankshaft and connecting rod. The crankshaft converts the piston motion into rotational motion to power the steering system of the vehicle.
2) Stirling Engine
The Stirling engine is one of the most famous types of the external combustion engines. It starts quickly in cold weather. It has high flexibility.
These types of engines have quiet operation. They have the capability to use different heat sources such as nuclear, geothermal, and biological.
Parts of External Combustion Engine
The external combustion engine has the following major parts:
- Cylinder
- Piston
- Flywheel
- Connecting rod
- Crankshaft
- External heat source
- Camshaft
1) Cylinder
The working cylinder is a part of the EC engine in which the working fuel (i.e., gas) is trapped. As it gets heat from the external heat source, it heats the working fluid, burns the fluid, and generates useful work.
2) Piston
This reciprocating component of the external combustion engine reciprocates inside the working cylinder.
When the working fuel ignites in the cylinder, the generated power reciprocates the piston forward and backward. This motion of the piston further rotates the crankshaft.
Read More: Piston Working and Construction
3) Crankshaft
As the crankshaft gets reciprocating motion by the piston, it converts this motion into rotary motion and rotates the flywheel.
Read More: Crankshaft Working and Types
4) Flywheel
When the flywheel gets power from the crankshaft, it converts the received rotary motion into mechanical power and moves the vehicle wheels.
5) Camshaft
The main function of the camshaft is to control the opening and closing of the inlet and outlet valves. This part of the engine ensures a proper opening and closing of the inlet and outlet valves and ensures a proper supply of fuel.
Read More: Camshaft Working and Function
Advantages of External Combustion Engines
- These engines have the capability to use all types of fuels.
- External combustion engines generate very low noise.
- They have a low emission rate than IC engines.
- They are best suitable for high-power generation applications.
- These engines have the ability for higher thermal efficiency than IC engines, which means that they may transform a large amount of the energy in fuel into useful work.
- They have a simple design and fewer moving parts than internal combustion engines.
- They have high durability.
- They are considered safer than IC engines.
- They need less maintenance.
Disadvantages of External Combustion Engines
- They are not ideal for low-power generation applications.
- They have working fluid leakage issues.
- They are heavy than the IC engine.
- These types of engines have slower response times than IC engines. Therefore, they are not for applications where quick deceleration or acceleration is needed.
- They consume more lubrication oil than IC engines.
- External combustion engines have higher initial costs than internal combustion engines.
- They need a longer warm-up time than IC engines.
Applications of External Combustion Engines
- Aerospace: External combustion engines are used in specific aerospace applications, such as in rocket propulsion and in experimental aircraft engines.
- Marine Applications: EC engines are used to run boats and ships, mainly in systems where emissions control and fuel efficiency are vital like in marine research and conservation.
- Electricity generation: External combustion engines are most commonly used to produce electricity in power plants, mainly in applications where renewable energy sources (such as biomass, geothermal or solar) are accessible.
- Heating and Cooling Systems: They are used to supply heating and cooling for houses and offices, especially in buildings where waste heat is easily accessible.
- Transportation: They are used to run vehicles, such as buses and trains, mainly in vehicles where emissions control and fuel efficiency are important. However, they are not famous as IC engines.
- Agricultural Applications: These engines are used in agriculture to run threshing machines, irrigation pumps, and other machinery.
External Combustion Engine VS Internal Combustion Engine
The main difference between the external combustion engine and the internal combustion engine is given below:
| External Combustion Engine | Internal Combustion Engine |
|---|---|
| In an EC engine, the burning process of the working fuel occurs outside the working cylinder. | In an IC engine, the burning process of the working fuel occurs inside the cylinder. |
| They have large size. | They have small sizes. |
| The external combustion engine needs a large installation space. | The internal combustion engine requires low installation space than the EC engine. |
| These engines have high weight. | They are light. |
| They are difficult to start. | They are very easy to start. |
| This engine requires more time for the initial start. | It starts very quickly. |
| The efficiency of the external combustion engine is between 15% to 25%. | The efficiency of the IC engine is between 35% to 45%. |
| It has a high capital cost. | It has a low capital cost. |
| The EC engine has low thermal efficiency. | The IC engine has high thermal efficiency. |
| The fuel used for EC engines has a low cost. | The fuel used for IC engines has high costs. |
| It is less efficient than an IC engine. | It is the most efficient engine. |
FAQ Section
What are the types of the external combustion engine?
The EC engine has the following major types:
- Steam Engine
- Stirling Engine
What are External combustion engines used for?
External combustion engines are used for Locomotives, vehicles, and Marine applications.
Who invented the EC engine?
In 1816, Robert Stirling invented the first external combustion engine known as the Stirling engine.
What are the examples of External Combustion Engine?
The EC engines are most commonly used in hydroelectric power plants and marine. Stirling engines and steam engines are the most common examples of external combustion engines.
What are the components of External Combustion Engine?
- External heat source
- Cylinder
- Camshaft
- Crankshaft
- Piston
- Connecting rod
- Flywheel