The Stirling engine is a type of heat engine. Its operation is based on the expansion and contraction of a gas. This gas flow cyclically from a cold focus where it contracts to a hot area where it expands.
The Stirling engine was invented by Robert Stirling in 1816. He is considered one of the fathers of hot air engines. The goal was to get a less dangerous engine than the steam engine.
Originally, the Stirling engine was conceived as an industrial main engine to compete with the steam engine. In practice, for more than a century it was only used for domestic applications and for low-power motors.
Development is still under investigation. The fact that you only need an external heat source gives it great versatility. This feature gives the possibility of using many energy sources for its operation such as solar energy or hydrocarbons.
How does a Stirling engine work?
The Stirling engine in a thermodynamically "closed" regenerative cycle. It works with cyclical compression and cyclical expansion of the working fluid at different temperature levels.
Like the steam engine, the Stirling engine is traditionally classified as an external combustion engine. All heat transfers with the working gas are done through the engine wall. It differs from internal combustion engines in that heat is supplied externally.
Unlike a steam engine, the Stirling engine closes a fixed amount of fluid in a permanently gaseous state such as air. On the other hand, in the steam engine, the working fluid undergoes a phase change from liquid to gas.
The pressure variation occurs in the displacer cylinder. The displacer is in the cold zone. The heat supplied at this point rotates the flywheel and the crankshaft. With this, thermal energy is converted into mechanical energy.
The efficiency of the process is highly restricted by the efficiency of the Carnot cycle. According to the Carnot cycle, the efficiency depends on the temperature difference between the hot and cold tanks.
Stirling engine characteristics
The Stirling engine is characterized by:
-
Its high efficiency compared to steam machines
-
Quiet operation
-
Ease with which almost any heat source can be used.
This compatibility with renewable and alternative energy sources has become increasingly important as the cost of conventional fuels has risen.
Stirling cycle
The ideal Stirling cycle consists of processes:
At point 1, the gas is highly pressurized and at a high temperature.
-
1-2 isothermal expansion of the working fluid with the heat supply from the heater.
-
2-3 corresponds to the elimination of isochoric heat from the hot gas to the regenerator. Process at constant volume.
-
3-4 isothermal compression of the working fluid with heat removal to the refrigerator.
-
4-1 Isochoric heating of the working fluid with the supply of heat from the regenerator. Process at constant volume. At this point is where the gas is at a lower temperature.
Stirling engine applications
Stirling engines have multiple applications in different fields such as:
-
Mechanical output and propulsion. These types of engines have been used in the automotive industry and in marine propulsion, among other examples. Compared to heat engines, good performance can be obtained.
-
Power generation using nuclear power and solar power. In this case, there are applications related to nuclear energy and solar energy. In both cases, it is a question of using these resources as a heat source to drive a steam turbine.
-
Stirling engines can work as a heat pump. Thanks to the heat exchanger of these systems and the fact that they are reversible.
