Stirling cycle machines, appropriate technology and design ideas

[Kaoron]

Hello there. I'm new!

I've been lurking around the topic of stirling engines for some time, trying to see how to integrate it in a scheme of sustainable design.
I don't have yet the luxury of being able to test what I have in my mind, but I'd like to share and receive opinions anyway. My training in physics stops at high-school level plus a bit of self learned stuff gathered along the way, I'm vaguely familiar with thermodynamics but my area of engineering is computers and algorithms, so I may not have good intuitions on how energy and matter work. Here's a data dump directly from my head.

# A renewable powered stirling heat pump to power opportunistic thermal energy storage.
When I think "appropriate technology", I contemplate what I have and I use daily, what I need almost without thinking about it, and ponder if I can understand it, fabricate and repair it, and how far do I need to fetch energy and stuff to be able to sustain this tech.
Of those things, some of the primary elements relate to heat and cold : hot water, warm air, refrigerator, air conditioning, etc.

I've been very interested in the ability to provide mechanical energy to the stirling engine in order to displace calories and create heat and cold. My first idea is to drive an array of alpha engines with a renewable mechanical power source (hydro/wind turbine) and plug the hot and cold ends into well insulated thermal batteries (sand batteries, water tanks, ...).

# A thermal/solar fluidyne pump hydroponics system
I like the idea of hydroponics, and I'd love to design a system that can run without electricity. The fluidyne got me interested because I can see it being coupled with a solar thermal + thermal battery setup to create a low tech resilient pumping system.

# A shared heat-source radial engine layout
This is an attempt at theoretically improving the radial layouts I've seen here and there. These layouts tend to have a center driving shaft and multiple heat sources. I thought that the heat source cloud also be shared, making it more practical to use and insulate against energy loss.

- start with a horizontal flywheel as a reference.
- attach a static driving ring to the wheel, offset from the center (balanced with a counterweight)
- lay X stirling engines on the inside of the ring, radially centered around the central axis of the flywheel, heat collector towards the center
- place an updraft stove under the heat collectors
- the ring drives the mechanical assembly of each of the engines (free pistons, rhombic drives, whatever)
- the central heat source and collector-ends can be insulated to minimize loss of energy
Hypotheses:
- the cold source can be arranged to benefit from the stack effect (draft) from the heat source, getting cooled by the renewed air aspired into the chimney
- the air buoyancy could further assist the flywheel's rotation (if shaped like a turbine ?), therefore extracting more energy from the heat source. Or it could create more friction, idk.

---

What do you think ?

[VincentG]

Interesting ideas. The fluidyne pump seems practical. Your other idea may work, but designing one stirling engine is difficult enough, your plan sounds extremely complex. I would recommend focusing on one engine.

The utilization of flue gas flow is worth pursuing alone, perhaps with a turbine as you mention. A wood stove is already a sort of hot air engine and there is alot of energy to be recovered in the exhaust.

[Tom Booth]

A shared heat-source....

. I thought that the heat source cloud also be shared, making it more practical to use and insulate against energy loss.
...
, heat collector towards the center
- place an updraft stove under the heat collectors
...
- the central heat source and collector-ends can be insulated to minimize loss of energy
Hypotheses:
- the cold source can be arranged to benefit from the stack effect (draft) from the heat source, getting cooled by the renewed air aspired into the chimney
- the air buoyancy could further assist the flywheel's rotation (if shaped like a turbine ?), therefore extracting more energy from the heat source. Or it could create more friction, idk.

---

What do you think ?

I spent some time with this, but how or where exactly to position a crank and flywheel seems problematic, how to make mechanical connections between flywheel, piston, displacer with a stovepipe in the way?

A flywheel above the stovepipe with shaft running down the center ? Maybe a shaft passing through an elbow in the pipe?

I do like the basic concept of a shared heat source for some kind of multi cylinder engine, with multiple "collector ends" surrounding a central heat source, like a stove pipe.

A Ringbom type engine, radial or otherwise could alleviate the several mechanical connection issues.

Maybe something like this; apologies for the crude drawing, but on the left is pictured 8 "heat gatherers" or displacers circling the heat source: the updraft chimney of a rocket stove or whatever.

On the right, a multi cylinder Ringbom. (Which could be simply a modified V8 internal combustion engine)

Resize_20230404_161451_1786.jpg (133.97 KiB) Viewed 4182 times

Not to neglect the other two ideas, but they seem pretty straightforward.

Maybe you could illustrate or describe the flywheel placement.

[Kaoron]

Thank you both for your time reading my post.

I spent some time with this, but how or where exactly to position a crank and flywheel seems problematic, how to make mechanical connections between flywheel, piston, displacer with a stovepipe in the way?

...

Maybe you could illustrate or describe the flywheel placement.

I tried to search for a demo of the mechanical movement I envisioned, and the closest I found was this : http://507movements.com/mm_425.html
This, but on the internal face of the offset transmission ring.

Here's a crude model of how it could be arranged:

radial stirling.png (30.63 KiB) Viewed 4167 times

The gray and orange pieces are the flywheel and the transmission ring, a "rotor" in suspension on the top of the assembly
The green and blue are piston shaft and cylinder, a "stator" that fits around an exhaust/chimney, and can possibly be stacked

Flywheel and transmission ring are solid, when in rotation the ring pushes/pulls on pistons.
The only obvious challenge I see is the connection between ring and pistons, which has to be some sort of low-friction rail/guided bearing, but there are probably more things that need to be considered.

[gitPharm01]

A flywheel above the stovepipe with shaft running down the center ? Maybe a shaft passing through an elbow in the pipe?

I do like the basic concept of a shared heat source for some kind of multi cylinder engine, with multiple "collector ends" surrounding a central heat source, like a stove pipe.

Many similar concepts had been tested and implemented.
Here's one example from the Stirling engine course I've been translating.
This engine's target heat source is an incinerator.
https://youtu.be/k-JfSeiuU68?t=3720
In this test, only 4 cylinders are activated.
There's a close up of the hot side at 1:02:45 , 8 black cylinders will be put into the combustion chamber of a incinerator to absorb heat.

Here's another example: V6 Stirling Engine by Andriy Lykhovoy
https://youtu.be/zYlPCFkzXCY
He made a video to show its parts:
https://youtu.be/oBmeESV14fw
And here's how to assemble them:
https://youtu.be/HHl8arLp_hc

And there's one special design called "Siemens Stirling engine"

4_piston_stirling_engine.jpg (122.27 KiB) Viewed 4166 times

Here's its description:
The Siemens configuration does not use two separate pistons, but rather uses the front and back side of one piston called a double-acting piston.
With a double-acting piston, the expansion space of the front side of one piston is connected to the compression space of the back side of the adjacent piston through the in line heater, regenerator, and cooler.

The Siemens configuration involves four cylinders each with a double-acting piston 90 degrees out of phase with the next cylinder.
The Siemens configuration greatly improves the engine efficiency over the original alpha arrangement.
These engines have the power piston connected to the crankshaft by a second connecting rod, which is itself in another small cylinder to eliminate the lateral forces from the crankshaft from putting pressure on the engine cylinder walls.
This arrangement is called a "crosshead".
A seal is used between the cross-head and piston to separate the high pressure area from the low pressure zone.
This allows the crosshead surfaces to stay lubricated in the low pressure area while preventing fouling in the high pressure engine system.

[Tom Booth]

..
Here's a crude model of how it could be arranged:
radial stirling.png
...
The only obvious challenge I see is the connection between ring and pistons, which has to be some sort of low-friction rail/guided bearing, ...

I had a similar in appearance image amongst my doodlings yesterday:

Resize_20230405_110621_1764.jpg (179.64 KiB) Viewed 4148 times

Those "pistons" in my drawing, however are displacers not power pistons.

The inner circle in my drawing is simply the stove pipe. The view is looking down into the chimney. The outer ring just connects the displacer shafts together.

The displacer cylinders penetrate through and are affixed to the stove pipe/chimney.

From there I basically drew a blank, other than to dispense with the outer ring connecting the displacers and make it a Ringbom type engine.

My imagination is so far failing to understand your description.

Where is the stove pipe in relation to your png image?

Are those displacer "pistons" or power pistons?

Maybe a Siemens configuration arranged in a loop surrounding the stove pipe?

Thermoacoustic engines?

Are the "blue things" the actual pistons or the cylinders with pistons inside?

[skyofcolorado]

I think they might be referring to this kind of design, except the hot part would go in the center and incoming cool air would enter from the perimeter over the cold side of each engine.


https://www.youtube.com/watch?v=K-DUXHRjWKw

[Kaoron]

I made some animations I hope will better explain the dynamic. Here the red cylinder is the chimney.

I left the power-piston/displacer assembly out as it would be time consuming to animate, and it's not really the focus of the design.
Engines modules ould be beta, gamma, free-piston or whatnot, the main idea is to gather the engines' hot ends around the chimney, and to have mechanical transmission on the power end (the eccentric transmission ring).

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[Tom Booth]

The idea has been kicked around before. I happened across this earlier thread


viewtopic.php?f=1&t=1159

I left the power-piston/displacer assembly out as it would be time consuming to animate, and it's not really the focus of the design.
Engines modules ould be beta, gamma, free-piston or whatnot, the main idea is to gather the engines' hot ends around the chimney, and to have mechanical transmission on the power end (the eccentric transmission ring).

A Free Piston design could also potentially simplify things. Rather than a mechanical transmission, the stove pipe/central heat source circled by linear electrical generator coils. Then you just need to deal with rectifying the electric output.

[dlaliberte]

I've been thinking about a rotary Stirling engine with a design that is very similar in having a synchronized rotating central structure, but quite different in that I am trying to do away with most of the moving parts, all the cylinders, pistons, and displacers. Basically, there is only a moving ring attached to the drive shaft.

Screen Shot 2023-04-06 at 17.06.30.png (182.18 KiB) Viewed 4099 times

The idea is that the gray ring would be pushed around by an imbalance in the amount of heat that builds up inside the gray ring on one side or the other side of the hot central core (i.e the hot side). As soon as the gray ring starts moving, this turns the drive shaft which converts some of the heat to mechanical work, which cools the hot area. The gray ring also has lots of inward pointing arrows which represent Tesla valves which extract any extra pressure from the cooler area outside the gray ring and inject it into the inside warmer area. The gray ring might wobble a few times back and forth before it gets enough momentum to carry it all the way around the cycle.

I have no idea whether this might function as I imagine. I have a few ideas on how to construct it, and I'd like to prove its feasibility before investing more time in making improvements. I've also got a 3D rendering of a helical stack composed of several layers of this flat model.

[dlaliberte]

Here is an image without the debugger selection overlay.

rotary-stirling.png (206.47 KiB) Viewed 4098 times

[Kaoron]

@Tom : nice find! too bad the thread stopped quite early.

@dlaliberte : Thanks for sharing ! If I got my mechanics correctly, what's driving my version is a delta in pressure between the pistons that are out of phase from the symmetry axis of the eccentric ring, resulting in a force putting the assembly in motion. In your design, I think this wouldn't apply because the pressure would equalize on both side of this axis, I'm not sure what would cause the ring to move then (but I'm an absolute novice in fluid dynamics, I may have overlooked something).

[dlaliberte]

I'm speculating that, even though the pressure would tend to equalize, any small motion of the ring would change that stability because that motion would be caused by converting some amount of the heat to mechanical force, and the motion itself would amplify the instability if it goes too far.

[matt brown]

https://www.youtube.com/watch?v=-IPW0l8dvoo

The rotary crowd here appears to have missed the liquid ring pump. A basic engine scheme would simply be connecting two pumps together with hot liquid in one and cold liquid in the other (water is a common liquid in these pumps). Surely, someone must have tried this (Dean Kamen has a 20 yr old patent with a liquid ring pump for water purification app).

[Tom Booth]

https://www.youtube.com/watch?v=-IPW0l8dvoo

The rotary crowd here appears to have missed the liquid ring pump. A basic engine scheme would simply be connecting two pumps together with hot liquid in one and cold liquid in the other (water is a common liquid in these pumps). Surely, someone must have tried this (Dean Kamen has a 20 yr old patent with a liquid ring pump for water purification app).

The "liquid ring" that allows these pumps to function depends on the pump being driven by a motor. Centrifugal force created by the huge powerful motor spinning the pump forces the liquid outward to form the ring.

So Matt, do you seriously believe putting two of these together and filling one with hot and the other with cold water would produce some sort of motor.

Without some external motor driving the assembly pretty obviously there would be no centrifugal force to form a liquid ring, just gravity, and the liquid pooled at the bottom.

Resize_20230408_035907_7478.jpg (75.56 KiB) Viewed 4051 times