The Stirling engine is a closed-loop external heat engine that converts heat into useful mechanical work. This type of engine was originally invented to compete with the steam engine, but due to various limitations, even after many years, the Stirling engine was not widely used in the market and was only used in some professional applications.
Stirling engine gas does not come out of the engine. They heat up and cool down frequently, so they aren't released as explosive fumes like petrol engines. This regenerative engine is capable of repeatedly using the same gas to generate electricity. Therefore, the Stirling engine can be more efficient than the internal combustion engine used in modern vehicles. Since no explosions occurred, the Stirling engine is very quiet.
How does a Stirling engine operate?
The Stirling engine generates mechanical energy from thermal energy by moving two or more pistons in a cylinder. There is a certain amount of gas in the cylinder and the change in gas pressure caused by the Stirling cycle causes the Stirling engine to run.
In a twin-cylinder Stirling engine, one cylinder is heated by an external heat source and the other by an external cooling source. The twin-cylinder air chambers are connected and the pistons are mechanically connected.
The sterling cycle includes the following steps:
1. Isothermal expansion
The energy of the external heat source increases the internal temperature and thus the gas pressure in the cylinder. As the gas pressure increases, the piston moves down, and work is delivered.
2. Isochoric heat removal
The piston pushes the heated gas into the second cylinder (or regenerator), where the gas cools, reducing its pressure so it can be compressed more easily. The heat absorbed by the regenerator in this phase will be used in the last phase of the cycle.
3. Isothermal compression
The gas is compressed in a space that is kept constant at a low temperature so that the gas can be easily compressed isothermally. During the compression process, the gas releases heat into the cold trap.
4. Isochoric Heat Addition
The second piston moves up and injects the compressed gas into the heated cylinder, where it heats up again quickly. The pressure in the cylinder gradually increases, undergoes isothermal expansion, forcing the piston to move, and the Stirling cycle continues.
Advantages and disadvantages of Stirling engines
The biggest advantage of Stirling engine is that they are more efficient than steam engines (mainly due to closed loops and regenerative heat exchangers). They don't have an explosive boiler, they don't require a water source, and they don't have the complex valve switching system required by a steam engine. This is one of the reasons they are quieter than steam engines, as they don't necessarily burn fuel and can be much cleaner. Unlike steam engines, which usually burn coal and water, Stirling engines can run on a variety of fuels.
The downside is that Stirling engines do not start immediately (the most important heat exchanger takes time to warm up and accelerate the flywheel) and do not perform well in stop-start operation. They also need large heat sinks that can dissipate residual heat, making them unsuitable for certain applications.
What can a Stirling engine use?
Sterling engines work best on motors that must use the difference between hot and cold to continue generating electricity. They are ideal for solar power plants, where the sun's heat on the glass acts as a heat source and high-efficiency cogeneration plants need to produce a stable power supply. Recently, Segway pioneer Dean Kamen used the Stirling engine as the basis for a compact home generator called the Beacon 10, which is the size of a home washing machine and helps revive people's interest in Stirling engines.
