How Do Stirling Engines Work? Are there Different Types?

Since the Industrial revolution, several engines have been producing power for intake. Very first, there were steam engines that ended up powered using coal. These times, there are cleaner and more effective engines this sort of as piston engines, rotary engines, and boxer engines. But, 1 motor sort has stood the examination of time: the Stirling motor.

A Stirling motor is a warmth motor that operates by cyclic compression and expansion of air or other gasses (the doing work fluid) at different temperatures. This engine is the best selection for renewable strength applications. It makes use of much considerably less gasoline than traditional engines. It is also tranquil and creates no emissions at all!

The engine depends on the regenerative principle that permits it to change close to 50% heat into valuable function. So, it is more successful than any other heat motor. Besides, in contrast to other shut-cycle warmth engines, it can begin and operate with out any exterior electrical power supply or prime mover.

To know how Stirling engines function, we’ve developed this helpful guidebook. Preserve studying to find out a lot more about Stirling engines’ procedure and other vital factors of this engine.

How Does a Stirling Engine Work?

Stirling engines are warmth engines that use regenerative cooling. They make mechanical energy and convert warmth into mechanical energy. So, they produce web positive mechanical operate from minor temperature variances. Let’s very first look at the primary areas of a Stirling motor to aid you realize greater how it operates.

Stirling Engine
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Primary Components of a Stirling Engine

  • Heat Source: The heat source is the driving force behind the Stirling engine’s movement. It’ll heat the air inside the Stirling engine. Then, it’s transferred to the cylinder. But since it’s a closed system, there’s no way for it to escape. So, ensure that your heat source has enough power to keep your engine running at a constant temperature. Stirling engines don’t burn fuel compared to internal combustion engines. They only need a temperature difference between the heat source (where the energy emanates) and the heat sink (where it ends).
  • Flywheel: The flywheel is a heavy wheel mounted to a spinning shaft. It conserves angular momentum and reciprocating engines. The flywheel is located on the outer part of the crankshaft, similar to an Internal Combustion Engine. The power piston and the displacer are connected to a flywheel. It stores the power output of the Stirling engine for further transmission.
  • Gas: It can be any gas, provided it has a low boiling point to be used in a Stirling engine. It can be hydrogen, helium, or ordinary air. The gas is inside a cylinder, and this cylinder is connected to a piston. As the piston moves back and forth, it pushes the gas into another chamber, where it expands. This way, it pushes the next piston. The gas used should remain in the gaseous state whether it’s heated or cooled. The primary purpose of the gas is to transport heat energy from the heat source to the engine’s heat sink. The heat energy powers the piston that operates the machine.
  • Heat Exchanger: It’s also known as the regenerator. You can find the heat exchanger between the heat sink and the heat source. Usually, the heat exchanger is made of copper or aluminum because they have high thermal conductivity. The heat exchanger holds heat from the hot gas that goes past it. When the hot gas moves back, it gathers this heat again. The heat can be wasted and lost in the outside air if the Stirling engine doesn’t have a heat exchanger. The regenerator enhances your engine’s power and efficiency. Several Stirling engines have many regenerators.

Now you know the primary components of a Stirling motor. Here’s how a Stirling motor works.

How A Stirling Engine Works

The exterior heat resource begins when the operator switches on the engine starter. The operator regulates the pressure by means of the provided system. Warmth transfer begins from the heat supply to the cylinder’s hot stop when the operator activates the exterior heat supply.

This heat transfer process qualified prospects to a temperature enhance in the fuel molecules ensnared in the very hot stop of the cylinder. As the fuel molecules’ temperature raises, there’s an interference between them. The gas molecules increase within the cylinder.

It, in switch, will increase the stress on the surface of the piston. This way, the piston is pushed, creating useful function. A plunger (displacer piston) is joined to a crankshaft. The crankshaft’s motion can make the plunger go amongst the very hot and chilly ends of the cylinder.

It also leads to an trade of gasses from the cold end to the sizzling end of the cylinder and vice versa. The gasoline at the sizzling end drives the displacer piston. Then, it transfers the fuel into the cylinder’s chilly conclude.

When the scorching fuel is introduced into the cold finish, the cooling gadget extracts heat from the hot gasoline and cools it.

After the gasoline has cooled, the piston compresses it into the cylinder’s chilly end. A cooling system receives rid of extra heat from the gas. After the compression procedure is complete, the displacer piston returns the compressed gas to the cylinder’s scorching end. Then, the cycle repeats itself.

Position to Observe: The Stirling motor does not have an exhaust stroke like other engines. So, it’s eco-welcoming and more successful than an internal combustion engine.

What Are the Different Types of Stirling Engines?

Listed here are the two main varieties of Stirling engines.

  • Displacer Type Stirling Engine: A displacer Stirling engine is more like a heat pump than an internal combustion engine. It runs using a displacer and a piston. It also uses the temperature difference between two reservoirs (one hot and one cold) to create energy. Usually, the hot reservoir is heated by burning fuel. The cold reservoir can be air or water. The most basic design uses a sealed cylinder with connecting ports on opposite sides. One side connects to a cold reservoir, while the other side connects to a hot reservoir. There’s also a sealed chamber in the middle. It contains an expanding gas. As long as there’s enough heat differential between these two sides, there will be a motion that drives this engine forward. The displacer type engine is used in Beta and Gamma Stirling engines.
  • Two-Piston Type Stirling Engine: The two-piston type Stirling engine is one of the most basic types of Stirling engines. This Stirling engine uses two pistons to compress and decompress air to heat or cool it down. These pistons move in a circular motion. They alternate between heating and cooling with each stroke. A crosshead connected to both pistons moves them back and forth. The movement of these pistons switches the position of the displacer piston between the Stirling engine’s hot end and cold end. It causes a pressure difference between these two ends. The pressure makes them move back and forth. These types of Stirling engines are used in applications where a high power output is needed. They can be used for things like powering heat pumps or even homes.

Where Is a Stirling Engine Used?

Stirling engines have numerous programs. They operate properly in equipment that generate energy repeatedly. They can also be used as a energy source for spacecraft, boats, and even trains. In addition to, NASA has created a Stirling motor utilized to power their spacecraft.

These engines have a lot of positive aspects more than other engines. They do not use fossil fuels or radioactive materials to produce power. Aside from, they create significantly less air pollution than gasoline-run engines. Also, they’re much lighter than standard inside combustion engines.

In addition to area exploration, Stirling engines are also frequently employed in agricultural equipment. These equipment need to be effective ample to operate huge blades or relocating components. These equipment really don't want a whole lot of torque or velocity like an vehicle demands.

Stirling engines can also be utilized as refrigerator engines, prime movers, and warmth pumps. Apart from, they are utilised at drinking water pump stations, for photo voltaic energy technology, and in submarines.

The Stirling motor operates efficiently at low speeds, generating it excellent for these apps. The products could be stationary most of the time but even now demands electricity when functioning with large loads.

Advantages of a Stirling Engine
  • More efficient compared to steam engines
  • Operates quietly
  • Need minimal maintenance
  • Highly flexible
  • It can operate on any heat source available. It includes geothermal, biological, and nuclear sources.
  • Ideal for powering appliances in areas with limited fuel supply
  • Can operate at low temperatures
  • Low emissions, making it eco-friendly
  • Simple design and doesn’t have movable parts, making it highly dependable
  • Compact size
  • Consumes low mechanical power
  • Fewer resonations compared to internal combustion engines
  • Can run at high speeds with small temperature changes
Disadvantages of a Stirling Engine
  • It takes a lot of time to start
  • Must have large radiators to drive out waste heat
  • Heavy due to an extra heat source
  • Need an extra external source of heat to heat the operating fluid (gas)
  • It doesn’t operate effectively in hot weather
  • Expensive compared to other engine types
  • It doesn’t operate effectively at high altitudes
  • Starting it is challenging during cold weather
  • It can only run on direct mechanical power
Stirling Engine
Image Credit: Erhard Ernst, Shutterstock

How to Increase the Stirling Engine’s Efficiency

Stirling engines are recognized for their substantial efficiency and silent operation. But, you can make it more successful. Below are several ways to do it.

  • Increase the Power in the First Stage: The first stage is the compression stage, which converts the heat into mechanical energy. The hot gas generates pressure to push the piston to work in the first stage of the Stirling cycle. The power output of the Stirling engine is higher if the gas pressure in this stage is high. One way of increasing the pressure is to increase the temperature of the gas.
  • Reduce Power Consumption in the Third Stage: The piston uses part of the energy produced to compress the gas in the third stage of the cycle. This way, the pressure reduces in the third stage. The pressure reduction minimizes power consumption. Engine power also increases as a result of this. Another effective method of reducing pressure is cooling the gas.
  • Make the Temperature Difference Large: Your Stirling engine will also be more efficient if there’s a large temperature difference between the cold and hot cylinders. You’ll create a large temperature difference by increasing the gas pressure in the first stage and minimizing it in the third stage.

History of the Stirling Engine

The first Stirling motor was utilised in 1818. It was a pumping equipment employed to pump h2o in a mine. Earlier, there were trials to manufacture an air motor, but the Stirling engine was the 1st to be used. Robert Stirling and his brother James had been the initial people to invent it. The identify Stirling was not presented to the motor quickly right after its invention right up until afterwards on when a Dutch engineer, Rolf Meijer, gave it the identify Stirling. It delineated all shut regenerative gasoline engines.

The Stirling motor was a safer alternative than the steam motor. The steam engine was risky due to large-pressure boiler explosions. Even though this was not the major goal of the Stirling engine, it was utilized as a trusted and risk-free source of minimal to medium energy.

It was used to pump h2o and a cooling enthusiast. In the 1970s, the Stirling motor started becoming employed in refrigerators. Several companies utilised them for central heating techniques. The best achievement of Stirling engines was the potential to make green power.


1. Who invented the Stirling engine?

Stirling Engine
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The Stirling engine was invented by Robert Stirling in 1816. He was born in 1790 and later died on June six, 1878. Robert Stirling was a Scottish clergyman. He used his expertise of steam engines to design and style an air-cooled warmth engine. It didn’t have the down sides of traditional steam engines. From 1818 to 1922, his company made these engines. The engines pumped h2o to farms and developed electric power.

2. Why are Stirling engines not used these days?

Stirling engines count on hot air growth and compression for their procedure. So, they need time to achieve running temperature before generating any valuable power output. It is not an problem for massive stationary purposes like drinking water heating or steam generation, but it helps make them unsuitable for cell purposes, such as automobiles. The Stirling motor doesn’t alter its output power fast compared to internal combustion engines.

3. What is special about a Stirling engine?

The Stirling engine utilizes an external warmth supply to heat and awesome the identical mounted amount of gas, relatively than employing a different fuel provide for every single cycle. It lowers the amount of vitality necessary for operation.

The gasoline pressure is controlled by removing or adding warmth. Removing heat decreases the fuel pressure. On the other hand, including heat will increase the gas strain.

4. Which gas does a Stirling engine use?

Stirling engines are similar to steam engines in that they use a functioning fluid (liquid or gasoline) heated by exterior means. But they vary in making use of the expansion and contraction of that fluid as opposed to steam strain. Stirling engines use hydrogen or helium to operate. These gasses are used due to the fact of their improved thermal houses.

5. Why are Stirling engines expensive compared to internal combustion engines?

Stirling engines are much more effective than inside combustion engines, but they are also a lot more pricey. The major reason is that Stirling engines need a lot more difficult elements than other engines.

One particular component of the Stirling motor that helps make it expensive is the warmth exchanger. Warmth exchangers require particular supplies that need to get a high-temperature difference. This temperature variation tends to make the motor obtain higher efficiency.


Stirling engines are fascinating machines. They’re tranquil and vitality effective. They function by utilizing the warmth differential among the two sides of a piston. That is it!

Now that you have gotten an overview of the concept powering Stirling engines, it’s probably time to feel of approaches to harness the power of this technological innovation.

Even if you have never ever encountered a Stirling engine before, we are certain you can feel of a single or two apps in which you want to electricity anything with this motor.


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