Designing for Torque

Discussion on Stirling or "hot air" engines (all types)
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Wellington
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Designing for Torque

Post by Wellington »

Can anyone tell me how they would go about designing an engine to have as much torque as possible. Thanks
Wellington
Ian S C
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Re: Designing for Torque

Post by Ian S C »

A motor with long stroke tends to have higher torque, and lower revs, the other way is to design for high revs, and gear it down.
Ian S C
Wellington
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Re: Designing for Torque

Post by Wellington »

Ian S C wrote:A motor with long stroke tends to have higher torque, and lower revs, the other way is to design for high revs, and gear it down.
Ian S C
Thanks Ian. Can you think of any other factors that will give higher torque?
.Wellington.
Alfista
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Re: Designing for Torque

Post by Alfista »

Ian has hit the nail on the head. Gear reduction ! The Stirling cycle alternates pressure and vacuum in more or less equal measures. It is not ideal for building big torque. I would add that pressurization and larger size also adds torque. In theory, adding cylinders adds torque but that does not always seem to work as planned. :cry:
Here is a link to a video of a build of the Kouhoupt Stirling powered tractor.
[youtube]https://m.youtube.com/watch?v=_DdkYquMOoo[/youtube]
https://m.youtube.com/watch?v=_DdkYquMOoo
If you have any problem with the link, just google it.
Kouhoupt comments on the traction and torque in the building instructions which are found in The Shop Wisdom of Rudy Kouhoupt, vol. 3


Wellington
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Re: Designing for Torque

Post by Wellington »

Alfista wrote: Ian has hit the nail on the head. Gear reduction ! The Stirling cycle alternates pressure and vacuum in more or less equal measures. It is not ideal for building big torque. I would add that pressurization and larger size also adds torque. In theory, adding cylinders adds torque but that does not always seem to work as planned......."


Thanks Alfista, Ill look into that link. Will post a pic soon as I complete my own first project. Still collecting junk as I intend to make this a lifetime hobby and hopefully find a nieche to make a little money. learning as I go.
.Wellington.
Ian S C
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Re: Designing for Torque

Post by Ian S C »

You can have high torque, and low revs, or high revs and low torque, the power out put will be the same for a motor of the same capacity. The things that will give more power(that's what you are looking for) is more heat in, and more heat out, better cooling system.
Ian S C
Wellington
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Re: Designing for Torque

Post by Wellington »

Ian S C wrote:You can have high torque, and low revs, or high revs and low torque, the power out put will be the same for a motor of the same capacity. The things that will give more power(that's what you are looking for) is more heat in, and more heat out, better cooling system.
Ian S C
So how would you go about designing the best hot end? Material selection aside how does the whole surface area thing work? If you have a naked flame and you want to get as much heat into your material as possible and then extract that heat into the inside of the tube I assume you need a high surface area inside the hot end (metal air contact) but the more surface area inside the more dead space you have that cannot be compressed. The dieter Viebeck design used high surface area on the external hot end. I have also seen engines that just use a solid chunk of metal on the hot end. Ian & alfista: Your thoughts/description on how you would design the ultimate hot end would be appreciated as I am now about to get started building my first engine. Thanks
.Wellington.
Ian S C
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Re: Designing for Torque

Post by Ian S C »

Hi ho, back again, been of line for a while. Andy Ross shows his work on increasing the heating area of hot caps in his book "Making Stirling Engines", and there is a thread on this forum(can't find it just now), of a German chap who machined slots on the interior of his hot cap with a vertical slotting machine and a rotary table.
Ian S C
Tom Booth
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Re: Designing for Torque

Post by Tom Booth »

I'm more familiar with IC engines than Stirling, but IMO timing is critical. In an IC engine if the timing is off by just a few degrees the engine could stall under any kind of load. It seems to me that Stirling engines act quite like an IC engine that is rather badly out of time. That is, lacking torque or power under load.

IC Engines have ignition. A sudden explosion. In a Stirling the "ignition" is spread out over the cycle. I think the solution might be to bring the Stirling "ignition" into tighter focus so as to mimic the concentrated explosive action of the IC engine
Ian S C
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Re: Designing for Torque

Post by Ian S C »

To a degree it is possible to adjust the timing/phase angle of the Stirling Engine, it varies a few degrees one side or other from the standard 90*. The torque increases in a pressurised engine up to a point were the engine is unable due to design, absorb any more heat, also(comparing it with an IC engine), its inablility to get rid of excess heat/ IC engine exhaust. The IC engine has the advantage of instant high pressure, an atmospheric SE has only ambient barometric pressure that (with a bit of luck)can be doubled on heating, giving about 30psi. In operation a SE has no relationship with either a steam, or IC engine, it is nearer to a gas turbine.
Ian S C
Tom Booth
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Re: Designing for Torque

Post by Tom Booth »

In a four cycle IC engine that initial spark/ignition/sudden explosion... has to carry the engine through several cycles against considerable resistance including a compression cycle and whatever load happens to be on the engine.

The timing in a Stirling could be controlled by having the displacer riding a cam instead of simply following the crank.
Tom Booth
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Re: Designing for Torque

Post by Tom Booth »

The first LTD Stirlings had a slip mechanism to increase "dwell" of the displacer so that it would linger at the hot and cold side and move more suddenly from one side to the other.

A cam could be used to produce a similar displacer motion.
Tom Booth
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Re: Designing for Torque

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