Dual Acting Cylinders

[SScandizzo]

Has there been much work done on dual acting cylinders for Stirling engines? (A dual acting cylinder is commonly found on 20th century steam locomotives. It is a design in which steam flows into a chamber first on one side of the power piston and then the other side, functionally acting as a two cylinder engine).

Furthermore, does anyone know the basic performance differences of a dual acting cylinder vs. a two cylinder design of similar volume?

-Stefan

[stanhbaker]

Has there been much work done on dual acting cylinders for Stirling engines? (A dual acting cylinder is commonly found on 20th century steam locomotives. It is a design in which steam flows into a chamber first on one side of the power piston and then the other side, functionally acting as a two cylinder engine). -Stefan

IIRC this is usually referred to as a double acting piston, per your description.
A bi-rotor double acting piston is shown at: http://www.rotarystirlingengines.com/birotor.htm This is only example I recall having seen.

Hydraulic cylinders are refered to as double acting, when moving in both directions, or single acting when moving in only one.

[SScandizzo]

You got me there, Stan. The correct term is "double acting cylinder". After looking at the bi-rotor engine, I still believe a conventional layout is more practical in terms of serviceability and experimentation. Granted there would be at least 3 seals (one on each displacer cylinder and one on the power cylinder) but the output shaft would already be external.

-Stefan

[stanhbaker]

OK It's a double acting cylinder/(piston). Now how do you arrange the two displacer cylinders, 180 deg. apart? Add a throw to the crankshaft and now you require two furnaces (heat sources)!

What is the advantage of a double acting cylinder/(piston) arrangement?
Looks to be more trouble than it's worth, unless it is a pressurized engine and then the advantages may not outweigh the disadvantages.
s/Stan

[SScandizzo]

My thought was that this configuration could develop power similar to a normal paired two cylinder configuration with the advantages of having only one output crank and less friction from having only one power cylinder/piston. I've seen a double hot capped alpha using only one power piston but that requires the heat sources to be on opposite sides of the engine. A gamma configuration could allow the two burners to be very close to each other (or possibly be only one if the two displacers were "siamesed" into one tube with two separate chambers.

http://www.stirlingengine.com/file-stor ... ion_id=252

As I said before, just thinking out loud and wondering what might come of it...

-Stefan

[stanhbaker]

Re:
http://www.stirlingengine.com/file-stor ... ion_id=252
As I said before, just thinking out loud and wondering what might come of it... -Stefan

I've been trying to figure out Why Bother? It would be an interesting display or demo engine. Still not a serious power contender! It would be a fun project to use up a bit of shop time and a real conversation piece. Otherwise it is still another variation of more of the same.

Will backtrack on the link to see what comments were associated with the drawing at the site of origin.

s/Stan

[stanhbaker]

http://www.stirlingengine.com/file-stor ... ion_id=252
As I said before, just thinking out loud and wondering what might come of it... -Stefan

Comment: The pressures on the double acting piston will more than likely not be balanced throughout the cycle. This will result is less output than for two engines running in parallel and phased 180 deg apart.

Perhaps a demonstration/display model could be built to permit changing from one configuration to the other.

Don't miss the adjacent post regarding Daniel Lyonet's Stirling engines.

stanhbaker

[SScandizzo]

Stan,

I started thinking about your notes and I admit that I will have to chew on that design a bit more before I try to build it. I agree that it seems straight forward at first glance, but think you may be right that since pressure changes on both sides may not always be reciprocal there could be some loss of performance.

Right now, I'm more curious about trying out the intermittent displacer idea. As soon as I have the second version of my test bed engine completed, I will be able to modify my original in order to make comparisons of this design.

-Stefan

[SScandizzo]

(Stan) Comment: The pressures on the double acting piston will more than likely not be balanced throughout the cycle. This will result is less output than for two engines running in parallel and phased 180 deg apart.

Well, I just started reading chapters of Rizzo's Volume One that I had passed up before, and sure enough, there was the exact same configuration I proposed in a working model.

Interestingly, he had a similar observation to the one you predicted in that the engine never produced the expected RPMs. One of the aspects of Stirling engines that I have to keep reminding myself is that the return stroke of the power piston is powered by atmospheric pressure... a trick that steam engines and IC engines can't do because they aren't closed systems! One of these days I will sit down and figure out the pressure curves on both sides of a double acting piston.

-Stefan

[spinningmagnets]

SScandizzo, the force of the piston is PSI X square inches of area of the piston face. In a double acting cylinder, the cross-section of the rod takes up a small amount of area. So, when retracting it will have slightly less power than extending.

The Stanley steam car had two double acting cylinders. This meant that it had 4 power pulses per revolution, and was self-starting when stopped in any position.

The benefit of a double-acting cylinder is that it is more compact and lighter than two single-acting cylinders. (Both would have two power pulses per revolution).

A large single-acting piston needs a large flywheel, but....two single acting cylinders or one double-acting can use a smaller flywheel.

Many other differences, but IMHO nothing else stands out as a clear benefit or drawback.

[speedless]

Hi
Maybe i got it wrong! ?
To me the stirling is a double-acting engine.
A double-acting steam engine press the piston both back and forth.
On the stirling its a "press and suck" action,thereby double-acting !
The piston dosnt care if its pushed or sucked ! It moves!
No matter if its athmosferic pressure or pressurized,as this is just a reference point .
Jan

[Cartech]

Speedless,
I think you have it right. A Stirling engine is actually a one-stroke engine. Power is produce in each direction of piston travel. I too have been contemplating a “double action” Stirling for some time and have a pneumatic “push-pull” cylinder perfect for the task. I posted this topic on another tread not realizing this topic was already covered here. I have seen working double action Stirling’s since I posted and the claim is higher output. Mine will be in the LTD verity and I hope to build it eventually. I still wonder if the output is any real gain over the extra displacer action required to make it possible. I also wonder how it will be affected by lack of atmosphere pressure in the cycle? I will post my results when I make it.

[idkleine]

I am new here and I am very interested in this topic but for a different reason
I believe Jim Symanski's 2.5 Hp wood fired gamma employs this:
http://www.starspin.com/stirlings/jimd6.html
He uses 2 displacer units which alternate cycles. but are both heated by the same heat source.
They are piped in to each side of the power piston chamber so one pushes while the other pulls. The beam at the top of his engine allows the displacers to be side by side.
what I am wondering is do you need a configuration like this in order to run a pressurized gamma engine? Seems to me that a single displacer gamma engine cannot be pressurized because if one side of the power piston cylinder is open to the atmosphere, the pressure would push it up and it wouldn't come back down. I know that is a little bit off topic, but not completely. Im sure someone must build a model based on this concept but I haven't seen one yet.
I'm sure he (Jim) got this idea somewhere. But I don't know where. Anyone know?
thanx

[Cartech]

idkleine,
Thanks for the link! I think I came accross that one a while back too. I have drawn up a model with two displacers and a double action power cylinder (which I have now) but have not had time to build it. My model will be small and not much in the way of power producing. I was mainly interested if was possible or if it had been done in my original post but I now know it is. I will be able to see when I build it, if it can produce any significant power over a regular small gama engine. My current poject is a rotory displacer engine. I have a good start on it and just purchased a lathe to make better parts. I'll post more on that when it's done. (unknown time line with the holidays coming)

Your question about pressurizing a Stirling is a good one? I have thought the same of single action types. I have read of pressurized engines but have not heard anything regarding how it is done.

[idkleine]

From what Ive read most stirling engines produce significantly more power when pressurized. Some of the designs that car companies, GM I believe, have used were pressurized to 2000 psi!
The Jim Dandy #6 runs at 150 I believe.
I want to build a rotary displacer engine as well. I believe them to be less efficient because they have less air turbulence therefore less air contacts the hot and cold surfaces inside. Also of course they don't have regenerators. I am still fascinated by them just because of their awesome simplicity. I see the potential for DYIers to build a much larger engine than usual because the chamber wouldn't have to be made to such close tolerances as a conventional Stirlings.
I want to build a rotary that has 2 horizontal chambers side by side, And the displacers spinning in the same direction (probably connected by a belt or chain) but are timed 180 deg off from each other. there would be a power piston and cylinder connected between the two displacer cylinders in a perpendicular fashion. So from a top view it would be sort of shaped like a big fat H. The middle of the H being the power piston cylinder. From the side it would look something like 0-0 The power piston would be then connected with a rod to a crank on one (or both) sides of the engine and it would be double acting as well. If it was connected to cranks on both sides maybe it would not need a chain or belt to connect the displacers because the power pistion would keep them timed. Not so sure about that last part.
Hows that for a crazy idea.
Oh yes another thing Ive heard about rotary displacer engines is that they typically have much higher rpm's than most Stirlings