The Volute Spring Displacer for the Stirling Engine

[@AttilaBlade]

This is a really interesting idea. I will read more about it because I have a similar idea, but with no spiral springs in. Congratulation! BLADE

[@David_Mash]

Blade, lookup flexure spring, this is apparently not new and already used in cryo stirlings

[@AttilaBlade]

@@David_Mash I know that, I used that. But here the displacer is the spring.

[@BASIL_LEAV]

I know this is silly but as an artist I am trying to make a robot design and this video was rather helpful, thank you for posting!

[@teslababbage]

What a fascinating new approach to the design of the displacer. I look forward to seeing it's further development.

[@ShanePomeroy]

I think this is a truly novel design and shows real lateral thinking. Very well presented

[@tiredironrepair]

When you mentioned the displacer spring having a resonance where the piston didn't and how that increased efficiency I pictured in my mind a displacer piston with springs mounted between the connecting rod and wristpin that might allow a second resonance to help transition the piston between cycles.

[@millamulisha]

Beautiful design and idea! So quiet. 🤩 If the cross sections of the spring from the side profile were aerodynamic (streamlined shape) and fit into similarly shaped grooves, the energy transfer per cycle would be less dissipative.

[@kreynolds1123]

Making a minor point. The air doesnt have to move around a displacer. Depending on the displacer design, It could in fact also move through the displacer.

[@ET_AYY_LMAO]

Yeah, but this is definetely non conventional, like first of all isn't this engine technically a linear stirling engine where the flywheel is replaced with an internal oscillating spring? Could actually be efficient but idk... How does the spring even begin to oscillate?

[@David_Mash]

​@ET_AYY_LMAO I think the spring would have to have near sealing quality when in its neutral state. The hot air would expand to initiate movement of the hot spring as if it were a piston. And the cold side would do the same with contraction. Actually, it seems as if a single spring could act as piston and displacer to simplify the unit. This might get its own comment haha

[@kreynolds1123]

@@ET_AYY_LMAO depends on conditions, like If there's sufficent temperature difference, then a minor vibration might just get it started. At some point, it could be that keeping it from starting to vibrate would be like trying to balance a pencil on its tip where the slightest nudge is all that's needed to get it started.

[@bobcannon9157]

The displacer is driven by an electromagnet at the resonant frequency of the displacer system, this means that a minimum amount of external (electrical) energy input is required to maintain the oscillation.

[@kreynolds1123]

@@bobcannon9157 as to electromagnets use in the displacer possibly as I didn't see the construction. But it would appear that they would not be needed. Thus is a normal stirling cycle engine where the displacer's momentum rather a crank causes it to lag the power piston with the weight and tension of the displacer spring having its own resonance that inturn drives the resonance of the power piston. I question the regeneration capacity of the displacer, as in how much energy can be stored in the springs. Although, between the top and bottom springs, one could add steel wool. Iron can absorbe a great deal of heat energy per per degree of Celsius rise per cubic cm of material. In the form of steel wool, that mass has a high ammount of surface area to quickly absorbe that heat while letting the air pass through it. Thus the displacer may double in function as an efficent stirling regenerator.

[@Lechoslowianin]

It seems to me that there is little working air. This limits its heat capacity. I wouldn't expect much power, but the efficiency may be high

[@bertjesklotepino]

i have found that you can also use the air bellow from a truck as a displacer. Works pretty well.

[@RJ-xv1nh]

A normal displacer also stores energy in the flywheel so convinced by his logic there. Also where would the regen go ?

[@justalabratmr.6858]

Wow very interesting. Instead of the springs pushing the displacer, the springs are the displacer.😀

[@bertjesklotepino]

Ok. So you have the chamber you have to construct. You have the springs you have to construct. And all the rest of it. Why would i use that if i can use an air bellow from a truck? It can function as a displacer.

[@mungewell]

In your animation the back of the piston is open to the atmosphere. You could use a double ended piston, and use two :engines' (running out of phase). This would also mean it would be easy to increase the pressure of the working gas. For solar (your application I believe) they could be side-by-side. Or the arrangement could be 'folded' to be either side of a rocket stove....

[@ikbwanabe]

Interesting to hear how little energy was required to keep the displacer at resonant frequency.

[@millamulisha]

It’s so quiet. 🤩

[@kreynolds1123]

I question the regeneration capacity of the displacer, as in how much energy can be stored in the springs. Although, between the top and bottom springs, one could add steel wool. Iron has a density of 7.874 g/cm³ and can absorbe a great deal of heat energy per per degree of Celsius rise per cubic cm of material. The specific heat of iron is 0.451 J/g °C. That is higher than most materials one would use for a stirling regenerator. Iron in the form of steel wool has a high surface area to quickly absorbe that heat while letting the air pass through it. Thus the displacer may double in function as an efficent stirling regenerator.

[@andrewhall2702]

Keith - I agree with your query. There is space between the two displacer springs. Room for regenerator. We have yet to do any power measurements. But this is a subject area I too am interested in.

[@kreynolds1123]

@@andrewhall2702 You might want to think in terms of a material's volumetric heat capacity (J/cm³·K) Why? To compare material's ability to store energy in a given volume of material and a given volume of dead space. For instance, take a 1cm cube of iron. It's 1cm³ volumetric heat capacity is approximately 3.62 J/(cm³·K) and contrast that with nylon 66 has an aproximat volumetrric heat capacity of 1.4 J/(cm³·K) Both 1 cm³ cubes of material can be shredded to the same surface area and 1 cm³ dead space to each may be added for air to pass through. But wher as iron wool may absorbe 3.62 joules per degree temperature rise, the nylon wool could only absorbe 1.4 joules per degree temperature rise. Down side of iron is its potential for oxidation, so it might be desirable to use a working fluid that is innert to iron. Or use another material.

[@David_Mash]

If the spring had a near sealing quality when in its neutral state. The hot air would expand to initiate movement of the spring as if it were a piston. And the cold side would do the same with contraction. It seems as if a single spring could act as piston and displacer to simplify the unit. The center of the spring should support a rod extended below with a permanent magnet oscillating within a coil on the cold side as a linear generator.

[@johnslivka3181]

What's the cost to build what you have there

[@nathanmullikin9641]

I've been studying wood burning stoves lately and i just happened to come across your video. It seems like you invented a brilliant way to maximize heat transfer in the high frequency/low flow conditions of a sterling engine. The springyness/resonance of the displacer seems like a bonus! How difficult is it to machine a piece like that?

[@mungewell]

I assume the spring could be laser cut. It would be interesting to place two of these either side of a rocket stove and have a double ended piston connected between them.

[@DavoRavo]

Seems as though if you had to partition this concept, you'd simply end up with the basic cylinder concept as we know. What's the benefit to the spiral? And if it's the flexing; why not just use air pockets for oscillation?

[@ieatYTP59]

I see a lot of sirtling engines with that kind of spring inside!

[@canonicaltom]

Yeah, it's normal for Stirling engines to use flexure bearings, but their only function is to keep things aligned.

[@bertjesklotepino]

use air bellows from a truck. Works perfectly as a displacer.

[@Mattthewanderer]

That is so obvious that it makes me wonder why it wasn't done long ago!

[@ET_AYY_LMAO]

Im a little confused, how does it begin to oscillate and how does it continue to oscillate? Is it just pressure differencial that makes it "tick" or is there an initial external force required to start or sustain the oscillation? Interresting idea for sure, glad that you shared it, is the engine a linear piston engine? So there is not even a flywheel?! Edit: Okay you drive it electro mechanically I assume, like a speaker?

[@andrewhall2702]

The oscillation is maintained by a voice coil. It requires very little energy.

[@billybrant6818]

Very cool

[@AdamBechtol]

Thx.

[@David_Mash]

You would have to match the frequency of the piston with the frequency of the displacer

[@bobcannon9157]

Yes much like a Martini engine, but advances in microcontrollers sensor technology make this far more straight forward than it was in the 1960s when Martini was developing the concept.

[@tibsim]

Putting in a displacer with a cold side spring seems better because the engine can be thicker and the spring isn't subject to heat stress.

[@tibsim]

It is not entirely clear what drives the coil spring displacer. Or it works similarly as a membrane phase-shifting themoacoustic engine? If it's that thin the engine, then in theory the heat will pass through at a higher temperature without work, but of course the test of the pudding is eating... But I like this very much! I congratulations! I think, you could try to change the power piston for a longer and thinner tube and use turbine generator on it. Check the Metronome Heat Engine!

[@andrewhall2702]

Hi - the displacer oscillation is sustained by a voice coil. The power needed is very low.

[@tibsim]

@@andrewhall2702 I understand. Thanks your answer!

[@tibsim]

@@andrewhall2702 I don't think the spiral spring displacer is a good idea, but a electronically driving displacer - spring system, in a thermoacoustic engine with turbine generator seems good.

[@justalabratmr.6858]

Just wanted to send some good luck to you all. Can't wait to see it pressured to 1000 psi using hydrogen or helium!

[@PALM311]

I have to disagree that it’s the first radical development in 200 years. I have been building engines with rotary displacers for years. And this was not my idea, the rotary displacer has been around for a long time.

[@andrewhall2702]

Yes - the rotary displacer - I agree. But they spin - this one flexes - moves up and down to shift gas into out of finned regions.

[@K1VV1939]

run it between 8 and 9 Hertz and test the numbers - you'll get back to me ...

[@David_Mash]

I am sorry but this is a flexure spring and is far from new. Only took 5 minutes of Google searching.

[@andrewhall2702]

David Thanks for your comment vs flexural springs. Yes, 5 minutes with Google has a wealth of info. I think the big difference is that there has been a lot of work about using flexural springs to drive the displacer. The video shows another step forward - the flexural spring becomes the displacer. The traditional displacer is no longer. The design of the hot cap is changed radically to become a dome of spiral grooves Likewise the cold cap Andrew