My contribution to the ECE

[VincentG]

Its also worth noting that the basic LTD design is the only one(I'm aware of) that is in use for wood stove fans today. That says alot about ease of manufacturing and practicality.

[Tom Booth]

Tom, I wish this forum allowed editing, to be clear I'm looking for suggestions for types of electric generator motors to power with the stirling.

Yes, I'm skeptical such a little LTD could turn a gear at that ratio, let alone any kind of generator in addition, without a great deal more heat than what it would generally be capable of utilizing with plastic/foam rubber parts.

I've often thought the best chance of getting such an engine to generate any output would be to build an axial flux type low RPM permanent magnet generator into the flywheel to eliminate losses due to gearing.

Something like this:

Resize_20230301_144221_1536.jpg (68.68 KiB) Viewed 3329 times

I'm not experienced at motor/generator winding enough to have tried it as yet though.

[VincentG]

I've often thought the best chance of getting such an engine to generate any output would be to build an axial flux type low RPM permanent magnet generator into the flywheel to eliminate losses due to gearing.

That may be the answer. I found this 5 watt permanent magnet generator I might try. https://www.aliexpress.us/item/22518327 ... _shipto=US

I did manage to mount the gear on the engine.

LTD with drive gear mounted.jpg (226.24 KiB) Viewed 3322 times

Next up is designing and printing the cam shaft for the displacer. I did realize that gravity should be sufficient enough at these low engine speeds to lower the displacer instead of having a separate closing camshaft.

I found this promising video that shows the potential of just altering the displacer phasing and speed of travel. This is a brilliant solution to the problem. Just a bit lacking in exact timing control.

https://youtube.com/shorts/WwBepzAfr-s?feature=share

[Tom Booth]

I found this promising video that shows the potential of just altering the displacer phasing and speed of travel. This is a brilliant solution to the problem. Just a bit lacking in exact timing control.

https://youtube.com/shorts/WwBepzAfr-s?feature=share

Personally I would not consider an LTD with a magnetic lift for the displacer a "Ringbom". A Ringbom engine uses the compression from the power piston to lift the displacer, not a magnet.

Aside from that, both these magnetic type, and actual Ringbom type engines have timing that is more "ideal" as far as "dwell". The displacer rests on the bottom until either the magnet comes around or the pressure builds up enough to lift the displacer.

I have a couple of very inexpensive magnetic type. They run very steadily in speed, though the displacer movement appears rather erratic. If it gets going very fast the magnet will fly right past without lifting the displacer at all, skipping a cycle. If the engine starts to slow down, the magnet will have more time as it passes by to lift the displacer, introducing more heat so the engine will pick up speed again, so, running on hot water, these magnetic engines do not gradually slow down as the water cools, they just run at a steady speed, then abruptly stop altogether.

Either type does accomplish an improved timing with a dwell period, without the additional drag and/or friction from a cam type mechanism.

[VincentG]

Agreed Tom, not a Ringbom at all. Keep in mind that although the magnet system is near frictionless, the piston must overcome the full force of the magnetic pull at bottom dead center to allow the displacer to fall away, so it is not a free lunch. Also note that dwell is only accomplished at the hot plate and in fact total time spent near the cold plate is even less than a conventional crank driven displacer.

I have designed the cam and should be printing a V1.00 tonight. The promise of greatly improved performance is encouraging to say the least.

[Tom Booth]

Agreed Tom, not a Ringbom at all. Keep in mind that although the magnet system is near frictionless, the piston must overcome the full force of the magnetic pull at bottom dead center to allow the displacer to fall away, so it is not a free lunch. Also note that dwell is only accomplished at the hot plate and in fact total time spent near the cold plate is even less than a conventional crank driven displacer.

I have designed the cam and should be printing a V1.00 tonight. The promise of greatly improved performance is encouraging to say the least.

There is an advantage though, as far as the magnetic lift. The "lifting" occurs while the flywheel/connecting rod is sweeping horizontally (mostly). Mechanically that is advantageous as opposed to lifting the displacer vertically. Also the magnetic pull to the extent the flywheel does move vertically, pulls the flywheel down in the direction it is already traveling. The displacer is then basically dropped quickly, rather than lifted as the magnet moves away. Seems like less/easier work than carrying the displacer for a full rotation.

Personally I don't believe there is any advantage to having any "dwell" at the cold plate, so I think less time spent there might also be an advantage.

[Bumpkin]

Sorry, Tom, looks like I dropped in right behind you and might have hidden your post. Some random thoughts: Vincent, you mentioned “no free lunch” with the magnetic actuation, I reckon that would apply to most all of the start-and-stop methods except maybe your desmo cam where just like a crank, the power used to accelerate the displacer would be returned on deceleration. I’ve seen, (or at least read of,) the simple slotted rods Tom mentioned working though. I imagine that would be a somewhat slam-bam affair; but so is a Ringbom, and some of them seem pretty successful. Another no-free-lunch thing about displacer dwell that I never see mentioned is that for a given rpm, the displacer has to stroke faster with commensurate higher aero drag. Again; there are successful examples, but everything is a trade-off. So you reminded me and I had to go look —The book “Air Engines” by Finkelstein and Organ mentions a cam drive displacer engine made in Germany about 1860. It mentions a 120 degree travel, 60 dwell, 120 travel, 60 dwell. In that case, maybe the average displacer aero loss wouldn’t be any greater than from a crank.

Bumpkin

[VincentG]

Bumpkin, thanks for that great resource. I found the full text version of the book online and just read through the section on cam drive on my lunch break. The duration of my cam is quite different to theirs so I'm eager to test the results. I imagine all interest in hot air engines faded away as steam took over, so not much further development was made.

On the subject of free lunch, I believe it to be inconsequential anyway. The valve train loss of an ICE is significant as well but necessary for any real power production. I think the same will hold true with the Stirling.

[VincentG]

Just printed out the first cam. Waiting on some parts in the mail to modify the displacer connecting rod to a ball bearing roller follower. This video shows the timing compared to standard configuration. For this first cam the displacer is 30 degree behind on the cold stroke compared to the hot. I did this as I imagine the cold, slower air may need more time. This can of course be completely changed if needed. The cam here is set up to have full displacer lift approximately 30 degrees before TDC of the compression stroke and subsequently 60 degrees before BDC of the expansion stroke. I have also added slightly more stoke to the displacer. The full movement of the displacer is accomplished in only 30 degrees and the rest of the time is "dwell" period where hopefully the respective side of the displacer will gain or lose heat. Eventually I'll add some copper to either side of the displacer as per my original posts. Can anyone help me to directly display youtube videos instead of just a link?

https://youtube.com/shorts/wPOkNvzOJzk?feature=share

[Tom Booth]

...Can anyone help me to directly display youtube videos instead of just a link?

https://youtube.com/shorts/wPOkNvzOJzk?feature=share

Apparently "shorts" cannot be embedded. With a regular YouTube video it is automatic. Just post the link.

[VincentG]

Sucess!

At least it seems that way. I have sort of cobbled together the cam and ball bearing follower to rush into results. Friction IS an issue at low temperatures and could most likely be improved a variety of ways. Thats besides the point for this small test platform. At higher temperatures, the power difference seems significant. I have written a more detailed explanation in the video but in short the power characteristics are completely different compared to stock. Where before the hot stroke was soft and the brunt of the power seemed to be from the end of the cold stroke, now the hot stroke hits HARD and the cold stroke hits earlier and harder but not the same at the hot. I have used slow motion and an applied load to try and demonstrate this for now. So if you look carefully at the mark on the flywheel you can track its acceleration through the cycle. In person, I can feel and see this when holding the shaft back with my fingers. Still looking into a way to analyze this digitally.

At this point I think the pressure changes are enough that a snifting valve may be of benefit. It seems to gas itself out faster than in stock configuration.

This is stock. (unfortunately youtube will not let you post a short "regular video" anymore so I cannot embed this one.

https://photos.app.goo.gl/564ThJ2hseLRrSLv7

And this is with the cam drive.
https://youtu.be/HCerbJr4BuY

[VincentG]

I have done some further modifications to the displacer in hopes of a more balanced cold stroke. The cold stroke seems to start a bit sooner now and the ice lasts longer. Not surprising considering the stock displacer could not rest on the cold plate like is does on the hot plate with the cam drive. (note with the stock crank, the displacer did not rest on either, causing excessive temperature mixing) I think I will order a .030" diamond drill bit to make a small atmospheric intake port in the working cylinder that is only exposed on BDC. This should allow some air in to equalize the engine. I expect a significant power improvement from this.

I have added a piece of foam on top of the displacer shaped to allow it to rest on the cold plate while still allowing gas to flow to the cylinder. At the same time it is raising the compression ratio. Combined with the latest cam timing, the little LTD happily drives my pinion gear(even with my finger dragging it) while the stock engine would quickly stall out on a free spinning gear.

displacer modification.jpg (392.14 KiB) Viewed 3248 times

Driving the gear...
https://photos.app.goo.gl/Ue5mL9cokU5atZ3H9

Steadily chugging along and sounding like a much bigger engine. By coincidence, the spur gear perfectly mixes the ice water in the containment ring.
https://photos.app.goo.gl/FStnM1PrmWcEKXVk8

The cam drive seems to have worked out so well I don't know if I can hold back from jumping right into a 55 gallon drum sized version. I had plans to create at least 1 or 2 smaller test beds before that. There are further tweaks that need to be made that are not practical on this little engine. It's also time to step up to an open flame heat source and suitable materials.

[Tom Booth]

You are doing some fantastic work! Nearly unbelievable.

I keep looking for where you have hidden the little electric motor and batteries.

To have one of those little engines running with cam and gearing is quite a feat of engineering!

[VincentG]

Thank you Tom, for the encouraging words. Maybe I should post a 360 video of it running in my hand to prove there are no wires I have run into a wall it seems with the current design. After some more tweaking the cold plate is now completely inadequate for cooling the gas. While the engine does run cooler under load, the engine seemed to get stuck and stop working. While attempting to figure this out, I successfully drilled an equalization hole that is only exposed at BDC of the working piston stroke.

What I found while running the engine like this was that there is still hot expanding gas at BDC. The new vent hole now sounds like a little exhaust port every cycle, letting out the hot gas. So what appears to be happening is that the glass piston is overheating and sticking in the cylinder. I see three ways to fix this. One, liquid cooling of the cylinder/piston. Two, shorten the duration of displacer lifting off the hot plate. Three, increase the stroke of the power piston.

The first two might work but then we will be going backwards. So now I'll have to try and increase the stoke of the working piston. Luckily the cylinder is much longer than needed so I should be able to get a lot more out of it. This will add displacement and increase the compression ratio. On top of that, hopefully the hot air will just start to expansively cool before BDC, greatly improving the cold power stroke. This is why the cold stroke has so far needed so much more advance....I think.

Long story short, it seems there is much more power still stuck in this little engine. And we haven't even begun to use high temperature components. I have a feeling this thing will be able to charge a phone by the time we can put a real candle under it.

[VincentG]

It appears I was mistaken and the cylinder was not overheating. I was having the same issue that plagued the Ericcson caloric engine before it was fitted to the ship. Water vapor had entered the engine and was wreaking havoc. The engine is running over simmering water in these videos and I accidentally splashed some water into the port. In any event, the main issue still is unused heat. This video shows the engine running with the open cylinder port at BDC. If you listen closely you can hear the rush of air leave on each stroke. I supposed in this configuration it is operation more like an open cycle caloric engine.

The engine actually has more power like this, as it allows the still expanding gas to vent before the piston is forced to compress it again. And yet in this configuration, there is NO cold stroke power at all. I have watched the port with a flame next to it and after spending the hot gas, it draws in fresh air for a split second as the displacer exposes the cold plate and the internal air begins to cool. In this way it seems to sort of ram itself with a fresh charge of air, and the subsequent hot stroke is stronger than the combined strokes of closed operation.

I will try to make a new long stroke crank shaft for further testing. I wonder though, if this open cycle can be optimized for even more power than the Stirling cycle. I was imagining, perhaps, a sort of two stroke expansion pipe attached to the exhaust port that could force even more air back into the system each cycle. Or maybe there would be two pipes with check valves. One for exhaust and the other would be water cooled and only allow fresh cold air back in. I tend to think an optimized Stirling cycle would have more potential power.

You can see in this video, that the engine actually speeds up when it is placed under load, and the hot air is forced to do work and therefore cool more efficiently.
https://photos.app.goo.gl/GVhhcrwwuMnMsHHH6