How I'll be spending my time in the shop for the next week or however long it takes
https://youtu.be/2JHHLZvyJAY
https://youtube.com/playlist?list=PLpx2 ... NpM8_4oZ-o
Portable generator to Ringbom converstion
Re: Portable generator to Ringbom converstion
I’m thinking about doing a Ringbom for my own project, and have looked at a lot of different “expert” advice on the displacer-drive science/magic. There’s no question it works, and of course I get the pressure/displacement premise, but available tuning advice looks like mostly a bunch of buffoonery. If you got it figured out in plain language you’d be my hero.
Bumpkin
Bumpkin
Re: Portable generator to Ringbom converstion
"Ringbom" may be a misnomer. I'm actually going to be trying the Ringbom-ish-like attached canister idea described in the V-twin compressor conversion thread:
viewtopic.php?f=1&t=5481
I suppose if that Idea doesn't work, I might fall back on an ordinary Ringbom with a cold side rather than my air spring idea.
Either way it's all experimental for me.
I'd be interested in this "tuning advice" you mention anyway. Any information regarding Ringbom engines seems herd to come by. Virtually non-existent. Not sure why, seems like so much potential there.
viewtopic.php?f=1&t=5481
I suppose if that Idea doesn't work, I might fall back on an ordinary Ringbom with a cold side rather than my air spring idea.
Either way it's all experimental for me.
I'd be interested in this "tuning advice" you mention anyway. Any information regarding Ringbom engines seems herd to come by. Virtually non-existent. Not sure why, seems like so much potential there.
Re: Portable generator to Ringbom converstion
There is, as far as I know, just one significant "tuning" that would be necessary in a Ringbom.
There were specific problems I/we used to look for in the repair shop(s) I worked in. No fuel, No spark, No compression, and timing problems.
Fuel and ignition issues are not really applicable to Stirling engines, compression is different but pretty transparent. So that leaves timing.
In a lawnmower, timing is usually fixed, so the most common reason for timing being off is the mower hit a rock and the flywheel key was sheered.
In a Ringbom the power piston pushes air into the displacer chamber until the pressure builds enough to cause the displacer to lift off the hot plate and admit heat into the engine. At that point the gas gets heated and expands and the power piston is driven out by the blowback from the displacer chamber.
There are slight delays between pushing the air into the displacer chamber, heating up the gas and it's expansion so this series of events needs to take place around TDC in such a way that the compression of gas into the displacer chamber takes place before the piston reaches TDC and the blowback that drives the piston back out needs to take place late enough that it doesn't drive the piston backwards before it passes TDC but not so late that the piston is already running ahead of the expanding gas
So, I believe this means the displacer has to have some resistance to movement so it does not actuate too soon, but not so much resistance that it actuates too late or not enough or not at all.
My plan for controlling the resistance and therefore the timing of the displacer is to have it held down by a spring with a tension adjustment. In that way, whatever compression is generated by the power piston the displacer spring resistance can be adjusted to the optimal spring pressure.
A lessening of spring pressure would advance the timing so the "blowback" takes place sooner and an increase in spring pressure would delay the "blow back".
I have no real idea what the "optimal resistance" might turn out to be so I plan on having a spring with a lot of room for adjustment.
There was a book about running two cycle engines that had a lot of stuff about pipe lengths and diameters and the like, but that, if it has any effect would be to inhibit or delay the flow of gas to or from the displacer chamber, so is largely irrelevant and all that can be compensated for one way or the other by the "resistance" to movement of the displacer, in my design, the spring tension.
There were specific problems I/we used to look for in the repair shop(s) I worked in. No fuel, No spark, No compression, and timing problems.
Fuel and ignition issues are not really applicable to Stirling engines, compression is different but pretty transparent. So that leaves timing.
In a lawnmower, timing is usually fixed, so the most common reason for timing being off is the mower hit a rock and the flywheel key was sheered.
In a Ringbom the power piston pushes air into the displacer chamber until the pressure builds enough to cause the displacer to lift off the hot plate and admit heat into the engine. At that point the gas gets heated and expands and the power piston is driven out by the blowback from the displacer chamber.
There are slight delays between pushing the air into the displacer chamber, heating up the gas and it's expansion so this series of events needs to take place around TDC in such a way that the compression of gas into the displacer chamber takes place before the piston reaches TDC and the blowback that drives the piston back out needs to take place late enough that it doesn't drive the piston backwards before it passes TDC but not so late that the piston is already running ahead of the expanding gas
So, I believe this means the displacer has to have some resistance to movement so it does not actuate too soon, but not so much resistance that it actuates too late or not enough or not at all.
My plan for controlling the resistance and therefore the timing of the displacer is to have it held down by a spring with a tension adjustment. In that way, whatever compression is generated by the power piston the displacer spring resistance can be adjusted to the optimal spring pressure.
A lessening of spring pressure would advance the timing so the "blowback" takes place sooner and an increase in spring pressure would delay the "blow back".
I have no real idea what the "optimal resistance" might turn out to be so I plan on having a spring with a lot of room for adjustment.
There was a book about running two cycle engines that had a lot of stuff about pipe lengths and diameters and the like, but that, if it has any effect would be to inhibit or delay the flow of gas to or from the displacer chamber, so is largely irrelevant and all that can be compensated for one way or the other by the "resistance" to movement of the displacer, in my design, the spring tension.
Re: Portable generator to Ringbom converstion
BTW That book also implied that there was some correspondence between lengths of pipes and "vibrations" as if the engine were a wind instrument so had to have pipes "tuned" to the appropriate length and diameter to have the right harmonic vibration... Like a pipe organ.
Just silliness IMO
Just silliness IMO
Re: Portable generator to Ringbom converstion
The tuning I’m referring to would be the force to move a certain weight and aero resistance (the displacer) at a certain speed with a certain pressure — as in how much of the pressure pulse needs to be sacrificed, (the displacement of the displacer drive) and is it a consistent value through different rpms and temperature differences? I suspect it varies and so — how to deal with that? You mention the need for resistance to moving too soon; I’ve wondered about causing a delay with magnets at each end; but again, I suspect there’s information out there that knowing would save some trouble. I’ve searched different Ringbom stuff and it always comes back a bit elementary. I’d hate to think that we’re the experts. It leads me back to thinking of a kinematic drive, but with a delay sorta like Vincent’s spring to bottom out the displacer.
Bumpkin
Bumpkin
Re: Portable generator to Ringbom converstion
I got as far as cleaning/tapping the threads to accept some stainless pipe;
https://youtu.be/_SsNgoaFS6I
I put the camera on pause to get one of the "time capsule" stainless steel canisters I had sent away for just for this project a long time ago...
They were not where I thought I had them on the shelf with some SS water bottles.
I looked all around the shop. They were nowhere to be found. Stopped the camera. Went home. Checked the basement, everywhere...
A few months ago I had begun noticing several things had gone missing. Vacuum pump, tap and die set, now the SS canisters, along with a bunch of SS pipe fittings.
The fittings I can get locally, but the canisters had to be ordered online. I had everything I needed for this project, waiting for the moment when I'd have some spare time to work on it, now I'm going to have to put it off again I guess, for about another week until I can replace the missing materials.
https://youtu.be/_SsNgoaFS6I
I put the camera on pause to get one of the "time capsule" stainless steel canisters I had sent away for just for this project a long time ago...
They were not where I thought I had them on the shelf with some SS water bottles.
I looked all around the shop. They were nowhere to be found. Stopped the camera. Went home. Checked the basement, everywhere...
A few months ago I had begun noticing several things had gone missing. Vacuum pump, tap and die set, now the SS canisters, along with a bunch of SS pipe fittings.
The fittings I can get locally, but the canisters had to be ordered online. I had everything I needed for this project, waiting for the moment when I'd have some spare time to work on it, now I'm going to have to put it off again I guess, for about another week until I can replace the missing materials.
Re: Portable generator to Ringbom converstion
I had a simplified design, but can't find the envelope I drew it on.
If I recall, though, it looked like this:
As hopefully can be seen, the transfer pipe goes straight from the hot end of the displacer to the power piston. (Other than the turn through the pipe elbow)
The pipe is also through the center of the displacer, and, so will be somewhat insulated by it.
There is still an "air spring" but the displacer will be sliding on a bushing slipped over the pipe. The diaphragm will be sealed around the bushing.
The bushing will allow some leakage for pressure equalization between displacer chamber and air spring.
After drawing this, seemingly "spontaneously" I realized, other than the air spring in place of a cold side, the design is very similar to what is found on "toy" Ringbom engines recently (recently as far as I know anyway. Not sure where or when exactly this displacer arrangement originated).
https://youtu.be/55WfzFj-Vwo
The center rod in the toy engine though is solid and the working gas goes around the displacer rather than through it
Maybe like the toy, it could have a speed control
If I recall, though, it looked like this:
- Resize_20230525_011358_8718.jpg (135.72 KiB) Viewed 7016 times
The pipe is also through the center of the displacer, and, so will be somewhat insulated by it.
There is still an "air spring" but the displacer will be sliding on a bushing slipped over the pipe. The diaphragm will be sealed around the bushing.
The bushing will allow some leakage for pressure equalization between displacer chamber and air spring.
After drawing this, seemingly "spontaneously" I realized, other than the air spring in place of a cold side, the design is very similar to what is found on "toy" Ringbom engines recently (recently as far as I know anyway. Not sure where or when exactly this displacer arrangement originated).
https://youtu.be/55WfzFj-Vwo
The center rod in the toy engine though is solid and the working gas goes around the displacer rather than through it
Maybe like the toy, it could have a speed control
- Resize_20230525_013802_2424.jpg (146.54 KiB) Viewed 7012 times
Re: Portable generator to Ringbom converstion
After trying to map out the cycle for what I plan on trying for this project: (penciling in the pipe from the air spring to the crankcase was an afterthought, though an afterthought I've thought before).
It started to look a lot like an Alpha type configuration, not only in general appearance, but the timing of offset of the "pistons" the diaphragm effectively makes the displacer into a kind of piston. Also the connection between the crankcase and air spring.
I've always thought, (well, not always..). On past occasions, I've thought that the hot piston in an Alpha type Stirling is really acting as a displacer while the cold piston is the actual power piston. This still seems true to me now, even more.
Now it occurs to me that to convert a compressor to Alpha, one of those two stage compressors with one piston bigger than the other should be used and the smaller of the two pistons should be the actual power piston and the larger treated as a displacer, that is, when considering the offset and direction of rotation
The resemblance to an Alpha is also apparent in my previous drawings on the V-twin conversion thread.
In a way, this project designing a "new" kind of Ringbom-ish Stirling is helping me to more fully understand and appreciate the Alpha configuration (I think ?)
In a way, the "delay" I'm worried about trying to achieve with this conversion, using some kind of adjustable spring tension in the "air spring" chamber area, (alternatively a sealed and pressurized air spring might work) is accomplished in the Alpha by way of the offset connection between the hot piston/displacer and the crank.
Ribgbom-diaphragm-Alpha, whatever you want to call it, having found my canisters, and another on the way, after thinking they might have been stolen, this project is back in business, and my faith in humanity somewhat restored.
- Resize_20230527_112242_2825.jpg (154.93 KiB) Viewed 7002 times
It started to look a lot like an Alpha type configuration, not only in general appearance, but the timing of offset of the "pistons" the diaphragm effectively makes the displacer into a kind of piston. Also the connection between the crankcase and air spring.
I've always thought, (well, not always..). On past occasions, I've thought that the hot piston in an Alpha type Stirling is really acting as a displacer while the cold piston is the actual power piston. This still seems true to me now, even more.
Now it occurs to me that to convert a compressor to Alpha, one of those two stage compressors with one piston bigger than the other should be used and the smaller of the two pistons should be the actual power piston and the larger treated as a displacer, that is, when considering the offset and direction of rotation
The resemblance to an Alpha is also apparent in my previous drawings on the V-twin conversion thread.
- Resize_20221206_063014_4498.jpg (133.95 KiB) Viewed 7001 times
In a way, the "delay" I'm worried about trying to achieve with this conversion, using some kind of adjustable spring tension in the "air spring" chamber area, (alternatively a sealed and pressurized air spring might work) is accomplished in the Alpha by way of the offset connection between the hot piston/displacer and the crank.
Ribgbom-diaphragm-Alpha, whatever you want to call it, having found my canisters, and another on the way, after thinking they might have been stolen, this project is back in business, and my faith in humanity somewhat restored.
Re: Portable generator to Ringbom converstion
This seems like it might have real high rpm power potential.
Re: Portable generator to Ringbom converstion
The generator is rated at 450 watts.
This is an old engine, there has been some obvious carbon fouling, but seemed like mostly wet oil in the cylinder head. Seems to still have good compression.
I've read a Ringbom conversion can only reach something like 80% of the rated power of the gas engine. I'm not sure if that includes conversion from 4 cycle to, shall we call it 2 cycle? Or 1 cycle?
It is pretty much impossible to reach the high internal temperature and pressure of an IC engines by external heating remote from the power piston.
Ringbom engines seems to like to start up by running backwards and forwards for a while before kicking in, not sure if that could cause any problems, potentially running backwards.
The valve springs may not be strong enough to prevent leakage during the "contraction" stroke.
So many potential problems, I'm pretty sure it will be a learning experience trying to solve them all.
The electrical generating system is pretty much a complete mystery to me. It's an older model so hopefully not too many hidden "safety" kill switches or the like that might prevent it from working.
As a second hand "as-is" machine I bought for $10 I have no idea if the generator is functional.
If my hybrid diaphragm-Alpha/air spring-Ringbom contraption turns over and runs, even no-load at all I'll be pretty happy. If it can trickle charge a 12 volt battery from the DC output, or even just charge a cell phone or something that would seem like an achievement.
I'm not setting my expectations too high.
I'm also not sure what to use for high temperature displacer material. Most of my experiments in that direction have been less than ideal, but I suppose just a wooden block or something would due for testing.
Re: Portable generator to Ringbom converstion
Maybe that could actually be a good thing,
Could the "leaky" valves function as "sniffer valves".?
Re: Portable generator to Ringbom converstion
Unless you lower the valve spring pressure drastically, I don't think they will leak at all.
Re: Portable generator to Ringbom converstion
It seems unlikely, but there are a few things that make me think it could be an issue.
First, in taking the engine apart, I thought the valve springs were unusually weak. If I were doing an actual repair for a customer, I would have replaced them. Valve springs in an old engine can become fatigued.
In my observations of Stirling engines generally, the return (vacuum) stroke appears to have as much or more force/momentum behind it than the power/expansion stroke, as evidenced by the plotted, real time PV diagrams.
- Resize_20220309_050739_9244.jpg (119.68 KiB) Viewed 6905 times
101.325 kPa the horizontal red line is likely too high at about 101.4
My reasoning being, in order to exceed atmospheric pressure at the end of the compression stroke the vacuum generated at the beginning of the return stroke must have been considerable.
That diagram was generated from an LTD, with a flywheel, but the PV diagram presented by Andrew Hall from his Stirling engine with the flywheel removed is similar:
- Resize_20230530_074601_1305.jpg (92.58 KiB) Viewed 6905 times
Well, with atmosphere at about 15 psi, Halls PV diagram shows the readings dropping to 0 psi which seems quite extraordinary.
We see the same effect in "free piston"/"thermoacoustic" engines with what in terms of stored momentum in the piston? A graphite piston and, I guess aluminium connecting rod. The vacuum that causes a reversal of the cycle from expansion to contraction in opposition to the momentum of the piston must be rather intense IMO.