Difference Between Internal and External Combustion Engine

Internal vs External Combustion Engine
 

Internal combustion engine and external combustion engines are types of heat engines using thermal energy produced by combustion as the main source of energy. In simple, both these machine types convert thermal energy into mechanical work in the form of rotation of a shaft, and that is subsequently used to power any machinery from automobiles to passenger aircraft.

More about Internal Combustion Engine

The internal combustion engine is a heat engine in which the combustion process of a fuel mixed with an oxidizer occurs in a combustion chamber, which is an integral part of the working fluid flow circuit.

The basic operating principle of any internal combustion engine is to combust the fuel air mixture, to create a high pressure and temperature gas volume and use the pressure to move a component attached to a shaft. The mechanisms used to obtain this functionality are varied, and the engines are specifically designed and have characteristic properties of their own.

The most common type of the IC engines is the piston engine or reciprocating engine type, where a piston connected to a crankshaft is moved using the pressure and heat generated in the combustion. They have a relatively low power to weight ratio and the working fluid flow is intermittent, hence used to power relatively small mobile units such as cars, locomotives or prime movers. Reciprocating engines are thermodynamically modelled by either Otto cycle or Diesel cycle.

The gas turbine engines are also IC engines, but use the high pressure gas to move the blades of a turbine which is connected to a shaft. The combustion of the gas turbine engines is continuous and have a very high power to weight ratio; therefore, used in large mobile units such as jet aircraft, commercial airliners and ships. The gas turbine engines operating with air as the working fluid are modelled by Brayton cycle. Fuel used in many combustion engines is petroleum fuel of different degrees.

More about External Combustion Engine

An external combustion engine is a heat engine where the working fluid is brought to high temperature and pressure by external thermal source combustion through the engine wall or heat exchanger in an external source, and the combustion process occurs outside the working fluid flow cycle.

Most types of steam engines are external combustion engines, where the water is turned into a superheated vapour by means of an external thermal source like a boiler operating from thermal energy, nuclear power, or burning fossil fuels. Depending on the mechanism and the phase change, steam engines are thermodynamically modelled by Stirling cycle (single phase – superheated vapour) and Rankine cycle (dual phase superheated – vapour and saturated liquid).

What is the difference between Internal and External Combustion Engine?

• The Combustion process of internal combustion engines is an integral part of the fluid flow cycle, and the thermal energy is directly generated within the system.

• In external combustion engines, the thermal energy is generated outside the working fluid flow cycle and then transferred to the working fluid.