Dual Acting Cylinders

Discussion on Stirling or "hot air" engines (all types)
rmej2000
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Joined: Wed Nov 17, 2010 9:59 pm

Re: Dual Acting Cylinders

Post by rmej2000 » Fri Dec 03, 2010 11:38 pm

idkleine wrote: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
I'm building a stirling engine in same configuration as Jim Symanski's 2.5 HP engine. I pick this one because it is easier to build one out of a scrap yard stuff and it only needs three smaller piston rod gasket diameter to keep high pressure gas from leaking into atmosphere. The piston's ring sealing is not as much of a concern, since because a little bit of leak will allow both displacer cylinders to equalize in pressure during the normal operation.

rmej2000
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Re: Dual Acting Cylinders

Post by rmej2000 » Sun Sep 01, 2013 8:36 am

Yes, it would be based on Jim Symanski's 2.5HP wood-fired gramma stirling engine. The whole thing will be pressurized with 150 PSI or so, with only the atmosphere pressure pulling the piston rod out, will depend on how big the rod diameter it is. The atmosphere pressure will have little impact in this case because the rod diameter is much smaller than piston diameter. Rod seal ring is more of concern than of the piston seal ring due to huge pressure differential between atmosphere and the engine pressure. I would add a small pump to re-pressurize the engine to compensate for rod seal leak. A very small air pump will do the job with a pressure regulator. I'm not concerned about engine performance, just what I can build with given tool and materials on hand.

Ian S C
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Re: Dual Acting Cylinders

Post by Ian S C » Mon Sep 02, 2013 4:09 am

I don't know if you realise the both sides of the piston are pressurised, the main seals that are required are for the crankshaft where it exits the crankcase. Ian S C

rmej2000
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Re: Dual Acting Cylinders

Post by rmej2000 » Mon Sep 02, 2013 10:11 pm

Yes, both sides of the piston are to be pressurized. I ran some tests on the power piston with total pressure differential up to 25 PSI, when the "crankcase" was at 150 PSI initially. I measured output stoke of about 485 pounds of force (steady). The engine is not complete at this point, just testing each part are being made or modified. The only hard part is to keep the rod from rubbing against the main seal, causing it to wear out faster.

Bumpkin
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Re: Dual Acting Cylinders

Post by Bumpkin » Tue Sep 03, 2013 8:37 am

That's a neat side-benefit of the double-acting design - allowing a pressurized engine without a closed crankcase. About rod-seal wear from side load: If you're using a standard cylinder, (5 inch?) perhaps you could find a rod that's over-long and just run the extra through a bushing to handle the side thrust. It wouldn't be as purpose-built as the flat slides used in steamers, but it'd be simple, and you don't have to deal with as much pressure as they did. Bumpkin

rmej2000
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Re: Dual Acting Cylinders

Post by rmej2000 » Thu Sep 12, 2013 12:23 pm

Exactly, that's what I could do without closed crankcase design. It is 5 inch cylinder by 12 inch stoke, you figured out the diameter size right on. I only use 6" of the 12" stoke movement and rest of the extra space for larger port openings and rod support. I will fill in extra space inside the cylinder with solid block of material, so not to have so much dead space. I'm considering side thrust bearing just like what you discribed above. I'm looking at brass flex coupling for the "floating" main rod seal to allow for more toterance and reduced wear. The other idea would be to use a special space filler oil and oil scrapper rings to seal against the compressed air. My worry is that people might use wrong kind of oil for this machine and could possibly blow it up. It may be better not to use oil at all where it might creep into the engine.

Ian S C
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Re: Dual Acting Cylinders

Post by Ian S C » Fri Sep 13, 2013 3:21 am

If you decide to use ring type seals, I would suggest making them from PTFE or similar. If you need oil, and are worried about combustion, synthetic (100%) oil as used in gas turbine engines is the stuff, if you have an aircraft maintenance place near by, at an airport, you might be able to get some there, just a few Mililitres, the few drops from an 'empty' can. Ian S C

mlebois
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Re: Dual Acting Cylinders

Post by mlebois » Thu Jul 03, 2014 6:16 am

This is a great device! I found some more information on this website: http://www.directindustry.com/industria ... 87093.html

Ian S C
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Re: Dual Acting Cylinders

Post by Ian S C » Fri Jul 04, 2014 2:46 am

mlebois, You might find a pneumatic cylinder there of some use, you'd probably need lighter seals, and piston rings. Also needed, deep pockets, they won't be cheap. Ian S C

rtg593
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Re: Dual Acting Cylinders

Post by rtg593 » Wed Sep 03, 2014 8:06 pm

I had an idea which brought me to this board on this forum, but doesn't quite match what I see here...

What about an alpha variant, parallel chambers, a pair of gears for flywheels. Each chamber is, oh, 50% longer, with a regenerator filled tube connecting both ends of both chambers. One chamber is dual cold, the other dual hot, with the pistons kinda doubling as displacers, but not really...

This way, I think, when either piston is moving, it has positive pressure on one side and negative on the other every movement... Would this still be less efficient as the other designs tested were said to be above?

Getting ready to build my first Stirling, I'm a designer at heart, so I'm exploring every design variant I can think up:)

Edit: wait, only one piston has power, right? So just the one would have power from both sides on each movement... Am I thinking about this right? Lol

Bumpkin
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Re: Dual Acting Cylinders

Post by Bumpkin » Thu Sep 04, 2014 9:24 am

The hot cylinder rod seal might be a problem, but I guess you could shroud it, sorta the same effect as an Alpha-type insulating piston crown. You've brought to mind this though: There is a type of double acting four cylinder Alpha where each cylinder bottom connects to the next cylinder's top at 90 degree phase. I can't remember the name of the design right now to look it up, but the neat thing is the seals are in the cool end. It could use common cylinder sets and be pressurized. The one I'm thinking of used a swash-plate drive, but with a little ingenuity there's no reason it couldn't use a normal crankshaft. Anyway, as to double-action efficiency, I think negative comments upthread came before the topic was well understood. My two cents.

Bumpkin

vamoose
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Re: Dual Acting Cylinders

Post by vamoose » Fri Sep 05, 2014 3:16 am

Hey Guys,

I think the configuration is referred to as a Siemins or also a Rinia type.
By having four double acting cylinders you can configure a 90deg relationship, also if you use a 3 cylinder configuration it operates at a 120deg relationship which is potentially a better ratio for an alpha engine (from what I’ve read).

Philips, Nasa, General Motors, Kockums, and others have used the Siemens / Rinia format to create some very high output engines (up to hundreds of horsepower).
Much time and money has been spent on research by these groups trying to determine the best type of engine and I think their general consensus and experience is that this type produces the best power combined with the highest efficiencies.

vamoose

Ian S C
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Re: Dual Acting Cylinders

Post by Ian S C » Fri Sep 05, 2014 4:26 am

The Whispergen is also a Swash plate type motor, making it quite compact.
Ian S C

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