It Can Save The World - The Simple Genius of Hot Air aka Stirling Engines
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Published 2023-09-10
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I often make videos about ICE, internal combustion engines and from time to time I get comments saying "why do you keep saying Internal combustion engine, it's not like we have external combustion engines". Well, that's exactly what we have in today's video. A working, running, power-producing external combustion engine. This one is a hot air or Stirling engines and it runs without needing carburetors or injectors or cams or valves or timing chains or spark plugs or anything. it is incredibly simple and it can be emissions negative, running on waste heat to save the world.
So air heated here at the heat source. As it’s heated it expands but because our piston in this cylinder is loose fitting the air simply passes around it and moves through the passage between our two cylinders where it meets with our tight fitting piston. Because it is tight fitting the air cannot go around it and because it has nowhere else to go it exerts its pressure on the tight fitting piston pushing it outward. This rotates the flywheel and generates power. As you can see our other cylinder has cooling fins on it. Cooling fins dramatically increase surface area allowing this cylinder to release more heat into the surrounding air which means that once air reaches this cylinder it cools down. As it cools down it becomes less dense and pressure now reduces. But we still have ample momentum in the flywheel left over so the tight fitting piston now pushes the cooled, de-pressurized air past our loose fitting piston back to the hot side of the engine where the air heats up and expands again and the cycle repeats itself.
Now onto the issue of waste heat. It's everywhere around us. Turn off your cooking hob or oven and there's enough heat in there to run a small Stirling for a few minutes and produce electricity. When you turn of your car and park it there is enough heat remaining in the exhaust manifold to run a little Stirling for 10 or even 20 minutes. Producing electricity and charging the batteries of a hybrid vehicle while the vehicle is stationary and not plugged into anything. Thermal power-plants also produce massive amounts of waste heat. Burning garbage, the list goes on. Companies such as New Zealand's WhsiperGen and UK's Inspirit Chargers have combined gas boilers with Stirling engines and even run large scale market tests of this technology.
2 Stirling engines are the means of propulsion for what is often described as the world’s quietest submarine, Sweden’s Gotland class attack submarine, which were the first submarine’s in the world to feature a Stirling Engine air-independent propulsion. This system enables the submarine to stay submerged for weeks instead of days and it makes this submarine more difficult to detect than nuclear submarines which require large noisy motors capable of pumping massive amounts of cooling water needed for the nuclear reactor. In comparison the Gotland class submarine is almost completely silent. Liquid oxygen and diesel are stored onboard and burned together to create heat for the hot side of the Stirling engines while abundant surrounding sea water is used as a heat sink for the cold side.
A special thank you to my patrons:
Daniel
Pepe
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Joe C
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Cole Philips
#d4a #stirling #cleanenergy
00:00 How it works
06:00 Benefits
08:55 How it can save the world
15:49 Undetectable Submarine
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All Comments (21)
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Single: bit.ly/4895cZz V4: bit.ly/3EuFaCy 10% Off Coupon Code: d4a More stirlings: bit.ly/3LglOVu Motivation: www.youtube.com/channel/UCt3YSIPcvJsYbwGCDLNiIKA
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The interesting part about these engines is how efficient they can operate with some engineering considerations. A propane fired engine can operate extremely efficiently. The expansion of the fuel can be used to cool the cold side of the engine, while the fuel heats the hot side. The one i built for my engineering class was a radial 6 motor, as this worked out best for piston timing. The propane heated an flame to oil heat exchanger, the oil then got pumped round the hot pistons. The fuel lines the fed the burner were rapped around the cold side pistons. The entire engine case was sealed and pressurized to 10 bar. The motor operated at 44% thermal efficiency. Putting it on par with diesel engines. Volumetric power density was its one design flaw. But, I still think it was commercially viable for a standing power generation prime mover.
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I think the big missing reason on why these engines are not used is indeed their low power to weight ratio. But even with stationary applications, Stirlings tend to also be much larger than their equivalent power ICE counterparts, which in turn drives up costs. Those engines seem to rev quite fast, but the missing bit is the output torque, which will be very low for its size because air (and other gases) are very compressible, meaning that they don't push very hard on the pistons compared to steam or the far hotter air-fuel mix in ICE.
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It's cool that it's on a sub, I'm a retired US Navy Mechanical Tech (Machinist Mate rating) and when you were describing this the first thing that popped into my mind was these would be absolutely amazing on sea vessels. I would also think small trains may find something like this useful as well.
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Incredible. Deadly simple and eliminate 97% of engine parts. Virtually maintenance free. Near ZERO pollutions & NO dangerous chemicals.
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The 4 cylinder version looks like a steampunk contraption. I'm in love
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Well, frankly speaking, steam engine and steam turbine as used by power plants are technically external combustion engines as well. The fire burns outside the motor in a separate chamber, not inside the engine. edit: Nuclear power still counts as a combustion. Also, that's the point of these kinds of engines. The type of heat source is flexible. And even more flexible on Stirling engine as it doesn't require extreme temps to work decently. For Steam turbine, you can take nuclear as mentioned magma heat, or even recycled from gas turbine exhaust. And on Stirling, it can even run on the warmth of the hand if tuned correctly. That type is called Low-Temperature Differential Stirling Engine. HOWEVER, stirling engines may not be as efficient as Steam Turbine hence why it ain't widely used today.
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It’s a pleasure to see a video that doesn’t have an edit every five seconds. Thank you.
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They were used as water pumps at wells for years.I believe one of the 1st types used for this..run very well at a fixed rmp .
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They can also run in reverse and then work as a heat pump creating a temperature difference between the reservoirs. They are used as cryocoolers, Philips developed these in the 1950's and a spin-off company still manufactures these to this day.
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It's the quiet operations that submarines use them for. I made one for machine shop class, but the displacer cylinder was made of borosilicate glass and cracked due to handling.
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I just bought this little engine. Easy assembly, excellent instructions, stongly built. I highly recommend it!
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Very nice video. Nice explanation of the tirling engine. A way to mitigate the apparent limitation of the Stirling engine in terms of power modulation would be to use it in a Stirling/Electric system. The Stirling engine would generate electricity, which would go into a storage battery and the "throttle" of the system would be the control on the electrical current being drawn off of the battery system. No problem really.
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I Need a big block version !
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Excellent production values: lighting; audio levels; content; scripting; pacing; explanatory graphics -- Well Done, Sir.
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This is a wonderfully detailed explanation of a little know type of engine. The models are well developed and add to the visual appeal of the subject at hand. Pacing, demonstrations and introductions are all well done and very informative.
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A really impressive video. I've known about Stirling engines for ages and watched and read much about them, but I've never really understood how they work - or their advantages/disadvantages - until now. So, thank you for this - its wonderful to FINALLY understand something thats bugged me for decades!
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The steam engine, invented by Thomas Newcomen in 1712, is an external combustion engine.
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A similar engine is the Manson engine, it is basically a stirling engine but instead of cooling down and reusing the air it simply exhausts the hot air and draws in cool fresh air, very simple the displacer is part of the piston, don't think it scales up quite well though since you can't compress the air in it like with a stirling to increase energy density. Another cool one is the vacuum engine, these work in the opposite way, they draw in hot air to the cylinder usually from an open flame and then cool it down, this creates a vacuum that pulls the piston forward, these engines actually saw commercial use for things like pumping water back in the steam engine days due to how simple and safe they were
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I bought a sterling engine as a show piece at home. You taught me how smart that engine is. I can now explain how smart they are. Thank you. 😎
