Stirling engines have been in use since 18th century, way before internal combustion engines were introduced. These engines are simple to make with materials easily available in our homes and hence you can always find mechanical engineers looking to work on a project idea based on Stirling engine. Keeping that in mind we are going to provide all detail about working principal of Stirling engines.

What is Stirling Engine?

Stirling engine is a heat engine which operates on cyclic compression and expansion of working fluid (air or any other gas like hydrogen etc) kept at different temperature levels. There is direct conversion of heat energy into mechanical work. The engine contains a permanent gaseous working fluid inside and hence is an example of closed system (only heat transfers through the boundary of the cylinder). The cylinder also acts as heat exchanger.

Now let’s discuss the brief history of this amazing engine.

A Scottish inventor MR. Robert Stirling  in 1816 invented the first practical closed cycle air engine The then inventors were motivated with this engine to create safer and efficient steam engines of the time because of the following reasons—

-The explosion in the boilers was frequent thus causing injuries and deaths of the workers

– Its working was quiet unlike steam engine.

– Its efficiency was high and could have operated by any source of heat thereby saving fuel.

However later it was not able to compete with steam engines as they become safer and efficient. It was limited to domestic motor and in the early of 20TH   century Stirling engine was then replaced by electric motors and internal combustion engines. Stirling engines then was completely forgotten and merely used for the ventilating fans and toys etc. later in 1950 Philips was expanding its sale of radios but electricity and batteries were not available everywhere hence they came up with the idea to a portable electric generator which can be used easily hence Stirling engine solved this problem which had the ability to run on a variety of heat sources.­­­­­

Working of Stirling engines

The design of the engine is such that the working fluid is compressed in the colder portion of the engine and expanded in the hotter portion which results in the net conversion of heat into external mechanical work. The efficiency of the Stirling heat engine is increased by an internal heat exchanger.

Watch this amazing animation to get the basic idea of its working.


The Stirling engine is classified as external combustion heat engine as all the heat transfers to and from the working fluid (air) takes place through the boundary of the cylinder hence isolating the combustion process and any contaminants it may produce from the working part of the engine. Unlike the internal combustion engine where burning of the fuel takes place inside the engine. It may also fall into the category of reciprocating piston engine.

Types of Sterling Engines:

Now lets take a look at different types of Stirling Engines. For more details on working of  various types of Stirling engines click on respective links.

There are two types of Stirling engines:

  1. Alfa Type Stirling Engine:

    These engines have two pistons in independent cylinders as shown in figure.
    One cylinder (expansion cylinder) is kept at high temperature while another (compression cylinder) at low and the passage between the two cylinder contains the regenerative fluid (gas).

  2. Beta Type Stirling Engine:

    These are displacement type Stirling engines and are further divided into beta and gamma type.
    Beta type sterling engine consists of only one cylinder with hot and cold ends, a loosely fitted displacer which shunts the air (working gas) between hot and cold end and a power piston at the end of the cylinder which drives the flywheel. The flywheel is connected to the piston with help of connecting link.
    A gamma Stirling is similar to beta Stirling having the power piston mounted in separate cylinder alongside the displacer piston cylinder. It is still connected to the same flywheel.


With this we come to end of this article. To know more about different types of Stirling engines, click on respective links provided.  Check out various project ideas based on Stirling engine which you can build at home as minor project or major project.

If you have any queries about any project or you want to know more about any project related to mechanical engineering, please let us know.

I am a "Mechanical Engineer" and a part time Blogger. I love to write technical stuff specifically. I have an experience in automobile and design field. Now I want to share my Engineering knowledge with you.


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