LTD Stirling Engine Development-Displacer Design

[matt brown]

[... William Beale invented the FPSE 60 years ago, but I've never seen anyone mention springs in general until it popped up here.

There has certainly been discussion of "springs" here Matt. You joined the forum when?

The elegance and simplicity of VincentG's design is brilliant IMO, and his ability to put his ideas into practice with actual prototypes in such short order is admirable.

Discussion, talk and theorizing on the subject however, is not new.

I posted this back in 2006 for example:

linkage.gif

Showing use of a "spring" to effect a "dwell".

Discussion here:

viewtopic.php?f=1&t=77&p=156

The NASA "spring" was not afaik intended for producing dwell. I think, now that I think about it more, without being attached to the crankshaft by some kind of connecting rod, the NASA flexure would not be pulled back against its own momentum to produce a dwell, as VincentG's arrangement would do (in theory).

This forum isn't a competition for "who thought of it first", I don't think. My 2006 spring/dwell idea was cumbersome at best and never implemented even as a prototype.

Tom, thanks for the link, great post !!! Detailed, yes, cumbersome, no, and awesome insight on single dwell at bottom. Did you ever notice the syncopated 'dual cycle' version akin that Novel SE that someone posted recently: (1) consider LTD with start position of displacer down and piston down (2) displacer goes up & down as an isolated event (3) then piston goes up & down as an isolated event.

[VincentG]

Yea Tom you were on to it even back then. And I'll add that if we can in fact ditch the cold side via better materials and a purely expensive driven cold end, only dwell at the hot side will be needed.

Matt, that dual cycle thing could be the ticket to multiple cylinder configurationa with just 2 working displacers 180 deg. out of phase.

One of the most interesting things about the SE to me is that with power on every stroke, the working pistons can be phased in groups 180 apart for perfect balance. No need to worry about smoothing power pulses like 4 stroke otto. But thats a topic for another thread I suppose.

[VincentG]

[quote
This forum isn't a competition for "who thought of it first", I don't think. My 2006 spring/dwell idea was cumbersome at best and never implemented even as a prototype./quote]

Agreed. I'm not claiming to be doing anything revolutionary either. At this point almost any thing you think of has been thought already. And precisely leads to my main goal, if more people were focused on SE development, we would have more ideas and more innovation. And most importantly, more iterations and prototypes, which means more progress.

[Tom Booth]

. Did you ever notice the syncopated 'dual cycle' version akin that Novel SE that someone posted recently: (1) consider LTD with start position of displacer down and piston down (2) displacer goes up & down as an isolated event (3) then piston goes up & down as an isolated event.

I'm not sure what you are referring to "syncopated 'dual cycle' " maybe if you could provide some link or reference.

I was going to post a video of my acrylic top magnetic LTD running on steam heat. The acrylic top virtually eliminates the cold side, but I covered it with the Aerogel for good measure. But, of course, can't see what's going on under the blanket.

Unfortunately I don't have a slow motion camera, but the displacer just makes a little hop to the side when the magnet gets close with the piston nearing TDC (full compression)

Watching the engine with the blanket off (on the sides) It looks like the displacer is just shifting, being pulled from side to side by the magnet first one way as the magnet approaches one cycle, then pulled back the next cycle, dragged back to the other side trailing the magnet and barely lifting from the hot bottom plate.

Maybe VincentG has some tips on taking slow motion video.

I just checked and a "You Cut" video editor on my phone does have one slow motion setting. I could try that.

Anyway if you could provide a link to that "syncopated 'dual cycle' version" it sounds interesting. I'm not sure if I've seen it but I don't think so.

[VincentG]

Tom if you have a newer Samsung phone, go to camera, then its under the "more" option just to the right of "video".

[Tom Booth]

... if we can in fact ditch the cold side via better materials and a purely expensive driven cold end, only dwell at the hot side will be needed.

My contention has been mainly that active cooling may not be necessary in order to have a running engine, and is certainly not an "efficient" use of the available heat.

The elimination of a cold "sink" could, theoretically be useful if you want an "ambient heat engine", if you are running an engine "on ice" and there is no left over "waste heat" from the ambient heat being dumped into the insulated ice box. In theory the engine could run on heat from the atmosphere indefinitely, as Tesla envisioned.

Having spent his entire life working on that, I guess it's debatable if he ever succeeded.

So far I have not been able to prove conclusively that the ambient heat engine is "impossible". The indications are quite the opposite.

Raw power output is a different story.

Even if an "ambient heat engine" is not literally "impossible" and the Carnot limit is wrong, and such an engine could keep running, I imagine getting any useable power from such a thing would be another challenge.

[Tom Booth]

Tom if you have a newer Samsung phone, go to camera, then its under the "more" option just to the right of "video".

No, an old Motorola/android. I'll check anyway, if not I'll try the app.

Oh my, look at that!!

Resize_20230329_124720_0122.jpg (107.34 KiB) Viewed 7464 times

Except on my phone the "more" is on the left. Cool!

Thanks!!!!!

[matt brown]

. Did you ever notice the syncopated 'dual cycle' version akin that Novel SE that someone posted recently: (1) consider LTD with start position of displacer down and piston down (2) displacer goes up & down as an isolated event (3) then piston goes up & down as an isolated event.

Anyway if you could provide a link to that "syncopated 'dual cycle' version" it sounds interesting. I'm not sure if I've seen it but I don't think so.

Sorry, Tom, no known video or graphic, but I think Vincent got the idea. Provided one could achieve dwell long enough, and once one sees that the displacer can/should dwell at bottom over hot plate, then a cycle idea emerges where the displacer moves 'independent' from piston. In this manner, the displacer cycle is a distinct event from the piston cycle, but when the timing of the displacer cycle equals the piston cycle (and syncopate) this changes engine potential.

Have you guys seen this twist on displacer geometry from reciprocating to rotary...the ancient Gloy (late 1800s patent).

https://www.youtube.com/watch?v=Q3KE0OBRl6E

[VincentG]

Interesting that gitPharm01 just posted plans for a rotary displacer model.

That seems to make more sense from a mechanical standpoint. But it seems to lose the two best things about the reciprocating displacer, fully shutting the heat off, and the speed of off to on time. Ok THREE things...and I now think one of the most important attributes, the tumbling effect the rising displacer has on the air.

Is the tumbling effect better, I don't really know. But I'd bet the more stagnant air pocket in the rotary chamber is slower to respond to temp change. Though after typing that I realize maybe centrifugal force is constantly mixing the air.

[matt brown]

Yep, Vincent, you sum it up well, not to mention the meager chance of any side seal without massive friction. However, this basic scheme might make a simple Otto. I thought that I'd post this as an adjunct to just how many mechanical possibilities are out there but under the radar.

[matt brown]

I found this on Koichi Hirata SE site, note the event sequence...

Koichi Hirata FPSE.png (67.13 KiB) Viewed 7431 times

[VincentG]

However, this basic scheme might make a simple Otto.

I'm picturing a two stroke otto style with a crank counterweight that acts as a displacer and port timing device as well. Crank moves gas to hot side and exposes rotary style port to power piston(s). Crank moves gas to cold side, where other rotary port allows fresh air intake.

I found this on Koichi Hirata SE site, note the event sequence...

You know I still can't wrap my head around what makes the displacer rise in a ringbom set up. Other than area on top of the displacer being slightly less due to the shaft. Is that enough to create lift under the displacer?

[matt brown]

A small area differential can make all the difference, we're just used to 1 atm as if nothing.

The Novel Hot Air Engine

https://akjournals.com/view/journals/60 ... le-p47.xml

is amusing, and buried in text is displacer volume 3x cylinder volume.

novel engine.png (121.02 KiB) Viewed 7396 times

If hot & cold were reversed than this would be just a different gamma; however, with hot & cold per diagram, I don't see how it can run.

[VincentG]

I see it working, assuming the hot air space is reduced to nearly zero with displacer full left. To me it makes more sense than normal beta, and gama, which forces hot air past cold space before expanding into piston.

[Tom Booth]

You know I still can't wrap my head around what makes the displacer rise in a ringbom set up. Other than area on top of the displacer being slightly less due to the shaft. Is that enough to create lift under the displacer?

My understanding is that, ignoring the big displacer altogether, just consider a big piston and a small piston associated with a sealed air canister.

If you push the big piston in, pressure will rise inside the canister forcing the little piston to pop out.

Now attach a very lightweight displacer to the little piston.

The displacer just goes along for the ride when the little piston is pushed out. The displacer itself is just dead weight being lifted by the "connecting rod"/little piston.

You are correct in that the area of the shaft is the only thing producing a pressure differential, why I mentioned sometimes earlier that it helps to make the displacer "shaft" a bit larger diameter depending on the weight of the displacer.

It is true, the displacer experiences equal pressure on all sides, top and bottom, which all cancels out, except for the shaft, that acts as a little pneumatic plunger to lift the displacer.

You could, I believe, actually get the same effect if the displacer were just hanging from the shaft by a string:

Resize_20230331_082126_6419.jpg (150.6 KiB) Viewed 7375 times