Modern Uses of Stirling Engines

Their Practical Applications Today

A combined heat and power plant engine, manufactured by Wudag in Germany. The Stirling engines are green and the fireboxes are blue.

You’re probably saying something like this to yourself: “If Stirling engines are so cool, what are they being used for today?”

Today’s uses of Stirling engines range from toys and wood stove fans to combined heat and power plants for businesses, to powering the most silent and deadliest submarines in the seas.

So What Uses are Included in This Article?

This page ONLY includes Stirling engines that are readily available products. It doesn’t include research project or historic Stirling engines.

I’ve also written about why some specific uses of Stirling engines like engines for your car and efficient solar Stirling engines are not likely to catch on either.

Click or tap on the links below to jump to that section:

  1. Toys
  2. Teaching Tools
  3. Wood Stove Fans
  4. Combined Heat and Power
  5. Cool 3D Printing Example
  6. Submarine Power
  7. Air Conditioning and Refrigeration
  8. Cryocoolers
  9. Welfare for Scientists and Engineers
  10. Investment Scams
  11. Stirling Engines for Cars – Never
  12. Solar Power Generators – Efficient and Overpriced
  13. Deep Space Nuclear Power Stirling Engines

Toys

Stirling engine toys can be enchanting and this has been true since since Robert Stirling invented them.

There are still antique Stirling engines toys that were built shortly after Robert Stirling invented the engine.

Oldest Existing Antique Stirling Engine

An Antique Stirling engine model toy

Typically, they run on an alcohol flame and there are thousands of variations of possible engine designs.

My personal favorites from a visual point of view are the ones that just have a lot of moving parts.

Low-Temperature Difference Toys

I’m also a big fan of low-temperature difference Stirling engines that can run on the heat of a cup of hot water or the heat of your hand.

Eco Power Stirling Engine

Eco Power Stirling Engine

Prices start around $30 and go up to however much you want to pay.

Teaching Tools

Stirling Engines Help Engage Students in a Safe Way

MM-7 Stirling Engine

MM-7 Stirling Engine

Stirling engines have a special place in university and school classrooms.

This is especially true for the low-temperature difference Stirling engines that can be run without filling up your classroom with carbon monoxide fumes.

There’s something about seeing an engine run on the heat of a cup of hot water or the heat of your hand that is inspiring. These engines pull science and engineering students into a deeper interest in and understand of, all types of engines.

Physics and engineering labs especially can benefit from an instrumented Stirling laboratory engine that can be run without a fume hood and without the risk of carbon monoxide leaks.

Wood Stove Fans

One of the big problems with using a wood stove to heat a house is that it will usually be too hot near the stove while other parts of the room will be too cold.

Obviously, you need a way to move the air around the house and, in some cases you will be using the wood stove in an area where electricity is not available or you just don’t want to use it for some reason.

That’s where Stirling engine wood stove fans shine. We have a detailed page on antique and modern Stirling fans that you might enjoy.

Move Air Without Electricity

You can buy wood stove fans in order to move the air gently around the room without electricity.

Simply set the fan on top of the wood stove, wait for it to get hot, turn the fan blades over, and you’ll have a fan that moves the air gently and silently around the room.

Don’t expect this to move the air like a strong electric fan would. But if you have a wood stove and are reading this, you might enjoy using a Stirling engine fan to make the temperature in your room more even.

Combined Heat and Power

A Combined Heat and Power Engine in the home, manufactured by Ökofen.

One of the problems with all types of engine is that they aren’t efficient enough. Any time an engine has hot gasses going out the exhaust pipe, that hot exhaust stream is energy that you paid for, but didn’t get to use.

But what if you could set up an engine so you were doing two things that were valuable to you at the same time? For instance, generating electricity while and also making hot water to heat your house.

There are several companies with products on the market today that make electricity and also generate hot water for use in heating homes and buildings or domestic or commercial hot water needs.

You may enjoy reading about our recommended Combined Heat and Power engines.

Cool 3D Printing Example

When 3D printers first became available, I immediately realized they could be used to build a Stirling engine. A lot of other people did, too.

The only question was how much of the engine could you actually print? Obviously, the most interesting and the most difficult thing to do would be to print the entire engine with no non-printed parts required.

Partially Printed Engines

The first few printed Stirling engines I saw were only partially printed.

They used ball bearings for the flywheel and a few metal parts along with an Airpot brand very slick graphite piston running in a glass cylinder.

There were a lot of expensive purchases components in the fist 3D printed Stirling engines.

I knew that it would be much more interesting if someone could figure out a way to print the entire engine.

Coolest 3D Print Example Ever

A fully, 3D printed Stirling Engine developed by Don Clucas.

Well, Don Clucas of Christ Church, New Zealand, figured out how to print an entire Stirling engine without using any expensive purchases components.

Don had previously designed the Whispergen combined heat and power Stirling engine and he finally figured out how to build a low-temperature difference Stirling engine and print everything.

Print an Engine for Every Student

Now if your school has a 3D printer and you want to have a classroom experiment with Stirling engines, you can simply print one for every student in the class.

That’s much more interesting than only having a few engines for the students to look at.

Don’s Solution to the Printable Piston Problem

The difficult part with printing an entire 3D Stirling engine is the piston. Current printers don’t let you print a small diameter piston accurately enough for it to work.

Don’s solution was to print a much bigger piston so the entire top of the engine became a piston. Each change of temperature inside the engine would then pulse the top of the engine up and down.

Submarine Power

Submarine Power – Air Independent Propulsion

The US Navy hired Swedish-designed submarines, made by SAAB (formerly Kockums) to engage in war games with. Their silent submarines which utilize Stirling engines, proved “deadly” in simulation.

Stirling engines excel in any applications where people place a very high value on silence.

Since Stirling engines can be built to be essentially silent, they’re a natural match for powering submarines.

The Swedish submarine builder Kockums (now owned by SAAB) has added a Stirling engine to their Gotland and Södermanland classes of submarines.

Diesel + Batteries + Stirling

These submarines use what is called air-independent propulsion to enable them to stay submerged in full operational capacity for up to several weeks.

They are essentially diesel electric submarines that simply can extend their operational time (by up to two weeks) with the Stirling engine topping off the batteries.

Stirling engines also power the Japanese submarine Soryu class submarine and are rumored to power some new Chinese submarines¹.

Air Conditioning

What’s not immediately obvious when you look at a Stirling engine is that every Stirling engine can be turned into a heat pump by attaching an electric motor to the output shaft and running the motor.

This doesn’t work very well with low-temperature difference Stirling engines and here’s why: engines that were designed to run on such small temperature differences also only produce small temperature differences when they are operated by a motor.

Try Motoring a Flame-Heated Engine

But, if you attach an electric motor to the output shaft of any Stirling engine designed to run on higher temperature differences, and run the electric motor, one side will get hot and the other side will get cold.

You can do this even with very simple models and it’s safe, so try it.

Stirling Engines Can Be Used as Air Conditioners

Any Stirling engine can be operated in reverse as a cooler. Obviously, purpose-built coolers will perform better than engines operating as coolers.

If you want to build one to air condition a house, you’ll be competing against well-established vapor cycle cooling technology that has been reduced in price over many generations of manufacturing.

It’s likely a Stirling engine air conditioner would be much more expensive. While Stirling engines refrigerators have been made, don’t expect to be able to buy one at a store near you any time soon.

Cryocoolers

A Cryocooler made by Janis, used in static exchange gas.

If you want to achieve very cold temperatures for cooling electronics to achieve superconductivity or for research purposes, Stirling engines that have been specifically designed to be coolers are an excellent choice.

Coolers like this were originally developed at Phillips Electronics in the 1950s and continue to be sold and used today.

If you need one for your industrial applications, they’re available.

Two-stage Stirling coolers can produce temperatures down to about to 20 degrees Kelvin, which is cold enough to liquefy hydrogen and neon.

Welfare for Scientists and Engineers

On this subject, it sounds like I’m not being serious, but really I am.

A certain amount of the government’s research budget is spent every year on new technology development projects.

In the many years that I have been interested in Stirling engines, I’ve seen many people apply for, and receive, government research grants in order to develop Stirling engines.

Why is This a Problem?

The problem with this government-funded research is that it rarely results in new products for people to buy. Products are often engineered to a high level of efficiency, complexity, and cost, that makes them impossible to produce and sell commercially.

Take the company Sunpower of Athens, Ohio for example.

They’ve developed lots of cool products over the years, but try to find any of them on the market today. You really can’t.

The Customer is the Next Government Research Grant

Sunpower has spent so many years creating interesting products that never reached the market, that my only assumption can be that they really didn’t intend to bring products to the market.

Instead, they created these products in order to get the next round of government research.

There isn’t anything necessarily wrong with that, just remember that government grants often do not result in new products.

Investment Scams

Lots of Stirling engine companies have come and gone over the years. Both the technology and the markets are difficult, so I suppose some of that should be expected.

But there is a special type of company that has come and gone that seems to never have had any intention of doing anything other than raising money from investors and paying high salaries to the directors.

They always have beautiful websites and beautiful offices.  Often they even have a prototype that they bought from a developer.

But there seems to have been no real attempt to bring Stirling engines to market with some of these scammers/companies.

How They Make it Look Real

The prototype will usually be purchased from an engineer who spent a huge amount of time developing it.

He sells it to the scammers on the story that they are going to bring his product to market with their superior marketing expertise.

They take pictures of it, build a beautiful website, publish glossy brochures, raise a lot of money from investors, and fade in the history.

The Scam and Vanish Cycle Seems to Repeat Itself

This has happened so many times that I just get depressed every time I see a new one.

So, scammers, please find a different technology center your scams around.

There obviously is a need for new investor money to do the right type of Stirling engine development, but companies with a history of having good marketing staff and no engineering staff are probably not the ones to bring new Stirling engine products to market.

Now, I’m going to talk about government research projects or other projects which, while they are real and have produced prototypes, seem unlikely to ever bring any products to market.

Why Stirling Engines in Cars are Unlikely

Stirling engines make sense for a lot of applications, but powering automobiles is not one of them.

Why?

  1. They’re slow to start
  2. It’s difficult to change power levels quickly
  3. They don’t accelerate quickly
  4. They’re heavier and more expensive

Stirling Engines Like to Run at a Constant Speed

 Stirling engines are not right for anyone who wants to go from “0 to 60” quickly.
 They’re better at a constant speed, so if you need to accelerate quickly when the light turns green, Stirling engines are not the engine for you.

All of these things, plus the fact that they’re more expensive than a typical internal engine, make them a bad mix for cars.

Hybrid Vehicles

Now that we’re seeing more hybrid vehicles, more people are considering what impact a Stirling engine could have.

Stirling engines do make sense as a prime mover or power source in an electric hybrid vehicle, but, once again, they tend to be heavy.

Solar Power Generators

What About Stirling Engines for Solar Power?

It seems fairly obvious that Stirling engines can be used to run on concentrated solar power.

The problem with this approach is that the engineering programs to develop these engines have usually had high efficiency as the goal. This means that expensive high-temperature alloys will be used and by the time the engine gets running as expected, it’s too expensive to compete with solar cells.

Concentrating sunshine produces high-temperature engines that have to use expensive high-temperature metals and, while a lot of research has been done in this area, no commercial products are available in the market today.

Deep Space Nuclear Powered Stirling Engines

Stirling engines can run on any form of heat. As far as the engine is concerned, heat from a nuclear isotope is as good as any other form of heat.

This has been well researched in what is called Stirling radioisotope generators for use in space exploration.

Important When Satellites Aren’t Close to the Sun

It’s easy to think that solar cells can be used everywhere in space, but they can’t.

As a satellite flies further away from the orbit of the Earth around the Sun, the solar density is simply not enough to power the electronics in the satellite and you need another method for producing power.

Stirling engines have been developed for this application, using a radioactive isotope as the heat source connected to a Stirling engine.

More Power From the Same Plutonium

Stirling engines configured like this, can produce about three times as much electricity as they would get by using a thermoelectric device².

The engines can be developed to run four years without any maintenance but, since these are government research projects, don’t expect them to be available any time soon.

Sunpower of Athens Ohio, builds these for NASA³.

Please Comment Below

Thank you for reading this page.

Please leave your questions, comments, or suggestions below.

Be sure to check out our other pages on Do-It-Yourself Stirling engines.


¹Farley, R. (2018). “Air-Independent Propulsion Submarines: Stealthy, Cheap and the Future?” The National Interest. Washington, D.C. Center for National Interest. Retrieved from http://nationalinterest.org/blog/the-buzz/air-independent-propulsion-submarines-stealth-cheap-the-24245

²Schreiber, J., & Wong, W. (2007). Advanced Stirling Radioisotope Generator for NASA Space Science and Exploration Missions. Cleveland, OH: National Aeronautics and Space Administration. Retrieved from: https://web.archive.org/web/20120929064709/http://www.grc.nasa.gov/WWW/TECB/RPS_ASRG_%20Handout.pdf

³National Aeronautics and Space Administration. (April 2018). NASA Glenn Research Center. Retrieved from https://tec.grc.nasa.gov/rps/stirling-research-lab/advanced-stirling-convertor/

Editor: Make all photo credits be a superscript number link which takes the reader to footnotes and from the footnotes link to the external site. I don’t want any photo credit links in the body of the text.

Try to find an antique stirling engine model with a known date of mfg and use that date and photo if it is a good photo.

picture of partially printed Stirling engine with a graphite piston in a glass cylinder.

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