Many of us have read about Stirling engines, engines which form mechanical heat pumps and derive motion from the expansion and contraction of a body of air. A very few readers may have built one, but for many they remain one of those projects we’d rather like to try but never quite have the inclination. The YouTube channel of [Geral Na Prática] should provide plenty of vicarious enjoyment then, with the construction of a range of Stirling engines from commonly available materials. We have Coke cans, PVC pipe, and nebuliser cartridges forming pistons and cylinders, with wire wool serving as a regenerative heat store. The latest video is below the break, an amazing 10-cylinder rotary device.
The Stirling engine is perhaps the quintessential example of a device whose time never came, never able to compete in power and efficiency with first steam engines and then internal combustion engines, it has over the years been subject to a variety of attempted revivals. Today it has appeared variously in solar power projects and in NASA’s hypothetical off-world power plants, and will no doubt continue to be promoted as an alternative energy conversion mechanism. We’ve featured many working model Stirling engines in our time and even done a longer investigation of them, but sadly we’ve yet to see a story involving a practical version.
Our thanks to [TheFinn] for the tip!
Stirling engines found a home in AIP (a catch-all term for subs in the traditional “diesel” class with improved underwater loiter/travel endurance) subs for a time. The Swedish Gotland-class, which famously “sunk” a US supercarrier in exercises (after which the US borrowed one for a while to develop counter tactics), uses one to generate electricity for propulsion. A Stirling engine was used due to its efficiency and extremely low noise.
I think that Stirlings’ time is past in subs, though, as battery technology has improved enough to obsolete it as a generator. It was a narrow sweet spot in time and application, but it was there.
Well… One major reason the the stirling engine was selected for air independent propulsion of the Gotland and her sisters was a unique property of stirlings and that is that the combustion chamber is not connected to the piston. If you tried to run a diesel submerged youll flood the cylinders and crank case. The combustion pressure in a diesel isnt high enough to push the exhaust against the water pressure.
But a stirling doesnt suffer from that. You can burn diesel and liquid oxygen att pressures high enough to dump the exhaust overboard, since there is no cylinder in contact, you can run the engine itself at a suitable pressure regardless of combustion pressure.
I think Stirling engines might well have a home in long term space missions.
A chunk of plutonium and a sterling engine could generate more power than a RTG. But have more moving parts, and for space missions reliability is higher priority than efficiency.
There are zero-touching-moving-parts free piston stirling engines, and they’re designed specifically for exactly this: RTG generators, using linear alternators. I think a few have even been deployed on spacecraft.
Your plutonium and a simple thermocouple provide electricity with zero moving parts. As you said, less efficient, but more reliable. JPL has used this style in some space missions.
There are actually Stirling engines used in space missions… as cryocoolers for infrared sensors. A stirling engine can be driven “backwards” to provide cooling, and you can make a completely sealed engine that is just driven by alternating current through a coil. they are more complex than Peltier elements, but provide higher temperature differentials at a higher efficiency.
Here’s a relevant link: https://www.nasa.gov/mission_pages/landsat/multimedia/TIRS_Image2_Cryocooler.html
and a document from the manufacturer: https://cryocooler.org/resources/Documents/C17/003.pdf
I wonder if a stirling engine with a sufficiently large thermal ballast could be used for thermal energy storage.
Yes, but round-trip efficiency is much below 50%. But, there are companies like Azelio, which store heat in molten aluminum and then drive a stirling engine with that.
I’ve seen an example Stirling engines put to practical use at my hardware store, in the wood stove section. Many companies sell fans that you set on top of your wood stove. They use a Stirling engine to spin the fan blades , distributing heat within the room. An example: https://www.stirlingengine.co.uk/d.asp?product=VULCANSTOVEFAN
Another example of a possible use of a Sterling Engine:
Read more: https://www.tweaktown.com/news/9051/msi_employs_stirling_engine_theory/index.html
I think, you can dinamically shut down some cylinders to save fuel.
How about a single cylinder Stirling Engine, where the piston is a powerful magnet, as part of a linear generator, buried somewhere with plenty of geothermal energy preferably with a cold air temperature ?
Stirling engines don’t have much torque. You’d be better off using the heat to generate pressurised steam for a steam engine.
A Stirling engine can have lots of torque, but the usual models and ones used for stove fans etc won’t as its not what they are for. Same way a steam engine has no torque when you talk about the early or low pressure ones but the super heated high pressure steam engine has oodles, built for the usecase. I’d agree its harder to get lots of torque out of a Stirling than steam, but it is entirely possible to do so…
And for such a low torque application as waving a magnet through a coil it really won’t matter anyway, it only needs enough to move the rather light magnetic piston through the coil. I’d be more concerned that over time the magnet would end up cooked…
Microgen’s free piston linear alternator SE claims a 45000 hour run time on any fuel. It’s derived from similar linear alternator FPSE’s developed for space programs.
I guess the question is, how repairable is it after that time? Would it be cost/carbon effective? At least, when in, operation it should run 24/7 – so maybe handy for baseload?
Nice build, lots of effort, but just a toy. Not long life with wear on the crank system. Was hoping he’d show an application of some sort. Fan maybe or ??? How much torque? Didn’t even show that it would run in both directions.
Bruh
If it cannot power a small town, what’s the point, eh? /s
It’s made from rubbish, of course it is a toy – where did the creator say it was a production ready device, or even claim that it had any particular utility?
Sometimes things can just be cool for what they are. Although I think Joe put it better than me.
The displacer is actually the rengenerator as well. Thats sort of cool.
One Weird Place You’ll Never Believe that stirlings are already in regular use, and probably the most common hardware for the application, is cryocoolers: running them in reverse and using the cold side for generating and maintaining ultralow temperatures for long periods of time at relatively high energy efficiency.
Sunpower makes a bunch.
Even just pointing one side at the sun and insulating it from the cold side would be good at certain distances. Cooling is the hard part. Perhaps a rotating craft might be a good way to go. Periodically heating and cooling each side.
To expand on what Rog77 has said,
I always thought that good application for Stirling engine would be Arctic and Antarctic. Bury hot side into the ice or ground. The cold side is open to the air. Presto, up to 50 or even 90 C temperature difference, enough to efficiently drive any Stirling engine.
This is the closest I’ve ever seen a stirling engine get to actually being useful. That fan is almost powerful enough to make a bit of wind. The builder really knows what he is doing. Bravo!!
They are used in javelin missiles to pre cool the thermal sensors ( or was that the stinger??, Or both)
A practical, industrially built stirling generator: https://www.oekofen.com/en-gb/myenergy365/
I wouldn’t mind having a good efficiency range extender in an electric car, wouldn’t harm if that could use logs as well in addition to gasoline/diesel/biomethanol/methane, batteries aren’t yet good enough to not get empty.
One good use case would be houses in cold climates where half the year one would need heating anyway, a stirling engine coupled to an always hot fireplace could give electricity when solar panels wouldn’t. That’s pretty much the idea in Ökofen’s pellet burner with Stirling, but no convenient retrofit options available.
Anyway, I love this – shows that such an engine doesn’t need anything fancy as such, but also shows some of the problems. Trying to develop a sellable product has taken several companies to bankruptcy.