Modern Uses of Stirling Engines
Their Practical Applications Today
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:
- Teaching Tools
- Wood Stove Fans
- Combined Heat and Power
- Cool 3D Printing Example
- Submarine Power
- Air Conditioning and Refrigeration
- Welfare for Scientists and Engineers
- Investment Scams
- Stirling Engines for Cars – Never
- Solar Power Generators – Efficient and Overpriced
- Deep Space Nuclear Power Stirling Engines
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
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.
Stirling Engines Help Engage Students in a Safe Way
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
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[photo 1]
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 purchased 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.
I also spent a lot of time developing my own 3D printed Stirling engines. It wasn’t easy.
Coolest 3D Print Example Ever
Fortunately, Don Clucas of Christ Church, New Zealand, figured out how to print an entire Stirling engine without using any purchased components at all.
Don had previously designed the Whispergen combined heat and power Stirling engine, so he was an experienced Stirling engine designer and figuring out how to print an entire Stirling engine without having to buy an additional components was almost miraculous.
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 piston that works like a bellows. In the image above, the piston is white. His website is called Projects to Print and there is a link to it here from our Stirling engine links page.
Submarine Power – Air Independent Propulsion
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 SAAB (formerly Kockums) 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 submarines².
It’s not immediately obvious when you look at a Stirling engine but every Stirling engine can be turned into a heat pump by attaching an electric motor to the output shaft and running the electric motor.
Of course low-temperature difference Stirling engines, that were designed to run on small temperature differences will only produce small temperature differences when they are operated by a motor.
So don’t try doing this with a low temperature difference Stirling engine.
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, so try it.
Stirling Engines Can Be Used as Air Conditioners
Obviously, purpose-built coolers will perform better than engines that have been converted to be 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.
So since most people make their purchasing decisions for new refrigerators and air conditioners based largely on initial purchase price and since a new Stirling engine air conditioner would probably be initially more expensive, this is not an application that you are likely to see in wide use any time soon.
But where Stirling cycle technology really shines is where other technologies can’t easily compete, for example in cryocoolers.
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 are available.
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. This is a matter of public policy.
In the many years that I have been interested in Stirling engines, I’ve seen 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 interesting 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 money.
There isn’t anything necessarily wrong with that, just remember that government grants rarely result in new products.
If you are interested in why research projects, often don’t result in new products, read my page on why Stirling engines are not more popular.
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.
Why Stirling Engines in Cars are Unlikely
Stirling engines make sense for a lot of applications, but powering automobiles is not one of them.
- They’re slow to start
- It’s difficult to change power levels quickly
- They don’t accelerate quickly
- They’re heavier and more expensive
Stirling Engines Like to Run at a Constant Speed
All of these things, plus the fact that they’re more expensive than a typical internal combustion engine, make them a bad mix for cars.
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 power source in some 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 is running as expected, it’s too expensive to compete with solar cells.
Concentrating sunshine produces high-temperature engines that must 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 kind 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 device⁴.
The engines can be developed to run four years without any maintenance.
Sunpower of Athens Ohio, builds these for NASA⁵.
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Be sure to check out our other pages on Do-It-Yourself Stirling engines.
¹Photo Credit: Ökofen
²Farley, 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
³Photo Credit: Janis
⁴Schreiber, 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
[photo 1] picture of partially printed Stirling engine with a graphite piston in a glass cylinder.