Thermoacoustic Engine has Only One Moving Part

Modern internal combustion engines have around 500 parts, with many of them moving in concert with the piston. But have you seen an engine with only one moving part, out of four in total? In the thermoacoustic engine, the power piston is the only part in motion. [YTEngineer] has built a very simple prototype that works on power provided by a tealight.

His little engine, slightly larger than a cigarette lighter, is composed of a test tube that serves as the cylinder, a smaller tube, called the choke, that fits inside the test tube, the stack, which is nothing more than some steel wool, and the power piston. [YTEnginer] nicely explains how the engine works: basically a temperature difference is used to induce high-amplitude sound waves that create the piston’s back-and-forth movement. The engine can be easily converted to an electricity generator by adding a magnet to the piston and a coil surrounding it.

The thermoacoustic engine is a particular type of Stirling engine. They have been proposed as electricity generators for space travel using radioisotopes as the heat source, among other applications. You may be interested in the history of Stirling engines, or perhaps even build a simple one.

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200 Years of The Stirling Engine

In the early years of the nineteenth century, steam engines were at work in a variety of practical uses. However, they were still imperfect in many ways. One particular problem were the boilers, that had a tendency to explode, causing injuries and fatalities. Reverend Dr. Robert Stirling, a Scottish clergyman, was concerned about the death toll from exploding boilers. Based on previous work by George Cayley (known for his pioneering work on aeronautics), Stirling filed his patent for a safer engine in 1816. That makes this year the bicentenary of this engine. The Stirling engine has the highest theoretical efficiency of any thermal engine. It is also a relatively simple machine. Unlike other types of engines, there are no valves, and that makes the mechanical design much simpler.

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2-Stroke Engine too Beautiful to Behold

The sheer beauty of this build is blinding. We enjoy keeping a minimalistic household — not quite on the level of [Joe MacMillan] but getting there — yet this would be the thing we choose as decoration. It’s a hand-built 2-stroke Engine designed specifically to make the combustion process visible rather than locking it away inside of a block of metal.

If you have a nagging feeling you’ve seen this before it’s because the amazing craftsmanship is unforgettable. A couple years back we looked at the 4-stroke engine also built by [Huib Visser]. This new offering does away with the belt, leaving a build that is almost entirely glass and metal polished to a high sheen. The glass cylinder contains the combustion, pushing the graphite piston to drive the fly-wheel. A passing magnet triggers the spark plug to ignite the white-gas fuel, all of which is well-illustrated in the video after the break.

This is not for sale, which doesn’t surprise us. How hard would it be to part with something of such beauty especially knowing you created that beauty? But don’t worry, you can definitely build your own. Just make sure to set the bar lower for your first half dozen tries. We’ve even seen engine builds using hardware store parts.

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Sterling Engine Kludged Together From Whatever

Watching [Jam BD] build this working Sterling Engine from nothing is awe-inspiring. He literally did with what he had on hand. Even his build log forgoes phrases like “I ordered a…” in exchange for “I didn’t have any so…”.

The cylinder heated by a candle is a pipe stuffed with aluminum foil which was hammered flat to get the best seal possible. The CDs prominently featured on the final product act as the fly-wheel. To ensure that there is enough mass [Jam] ganged three of them together. There is also a counter-weight affixed just off-center to help keep the wheel turning. The gears shown above were actually used more like mounting plates to build a cam. Looking at the body and frame of the device makes us wonder how in the heck this thing actually came together?

We can’t get enough of these kinds of hacks, which is why we had to go back and watch the tuna can Sterling Engine one more time.

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Four-stroke engine with glass cylinder is a 2400 RPM piece of art

We know a lot about toggling bits in a register, but only a bit about how engines work. This one inspires us to throw ourselves into the field with reckless abandon. [Huib Visser] built this glass cylinder four-stroke engine and he took great care to make it beautiful. We don’t need our projects to be polished and gleaming, but we have to admit that this the opposite of what we see when popping the hood on our 12-year-old rust bucket out front.

You can’t see it in this image, but just on the other side of the fly-wheel is a smaller wheel with a cord wrapped around it that acts as the pull start. This gets the toothed timing belt going along with the cylinder. As part of the demo video we get a good look at how the rotary intake and exhaust valves work. [Huib] also took the time to demonstrate how the rare earth magnets and hall effect sensor reed switch synchronize the ignition system.

You won’t want to miss the end of the video which show it in action as It burns Coleman fuel (white gas) and is lubricated with WD-40. This is jaw dropping and it works like a charm, but still not that far removed from the concepts seen in [Lou’s] hardware store engine project.

UPDATE: Here’s write up this engine (translated) [Thanks ChalkBored]

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Sun-powered Stirling engine with automatic tracking

Check out this solar-powered Stirling engine (translated). The build is part of a high school class and they packed in some really nice features. The first is the parabolic mirror which focuses the sun’s rays on the chamber of the engine. The heat is what makes it go, and the video after the breaks shows it doing just that.

But the concept behind the mirror makes for an interesting challenge. The light energy is focused at a narrow point. When the sun moves in the sky that point will no longer be at an efficient position to power the engine. This issue is solved by a pair of stepper motors which can reposition the dish. It’s done automatically by an Arduino Uno which makes readings from four LDR (photoresistors) in that cardboard tube mounted at the top of the dish. If the light intensity is the same for all four, then the tube is pointed at the sun. If not, the motors are tweaked to get the best angle possible.

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Incredible home made miniature engines

On the heels of a small stirling engine we featured, an astute Hackaday reader sent in a few awesome builds from HMEM, the home model engine machinist forum.

First up is a fantastic looking stirling engine made entirely from scratch. The build is modeled on a Moriya Hot Air Fan, but instead of making a fan spin around, [IronHorse] put a flywheel on the engine. It also uses propane instead of an alcohol or other liquid fuel lamp for the heat source.

Next up is a pee-wee sized V8 engine by [stevehuckss396]. Unlike the model engines we’re used to, this one runs on gasoline. The engine started out as a 3 x 3 x 5 inch block of aluminum. This thread goes on an amazing 85 (!) pages and makes for great afternoon reading, but here’s a video of the engine in action.

Last is [keith5700]’s amazing 1/4 scale V8. Not only is this [keith]’s first project, he also completed this entire project on manual mills and lathes. There’s an electric starter thrown in there, and the pictures are simply incredible.

Thanks to [Norberto] for sending this one in, and if you’ve got an example of amazing machining skill, send it on it to the tip line.