Build Stirling but torque not good

[Datenfeld]

Hi,

I'm new to this Forum! I build a bigger stirling motor but I'm not happy with the torque. Please see video here:
http://www.youtube.com/watch?v=FJljYbmd ... e=youtu.be

Actually I want produce power with this stirling engine and want a much better torque performance. I did design this engine in 3D, so I'm looking for a stirling expert who can review my 3D design and give me some advise what I design wrong or bad!! I can send you the file in .step format!!

Hope for some answers and help!!

Thanks and regards,
Michael

PS: I just upload the File!!

[bladeattila]

Dear Michael!
The engine is pretty nice! :)
I found 4 little things for you on your engine.
No heat trap ( too much heat you lose it). Not stabilised the engine (opposit moving=loss energy). Not enough cold the cold side (water cooling continously=The inlet energy should be go out there). Not separated hot/cold side (heat conduction is dropped the efficienct).
If you can solve these little problems, then your engine has a better performance in the future.
If you can use some graphite powder for piston, rod, bearings then the friction will be lower too.
I try to open your file later, but I think the heat exchangers surface are too low actually.
Best regards!
Blade

[bladeattila]

I checked your CAD drawing in Solid Works. The file format not was perfectly translated but the engine's geometry was What I need to see on it.
If your engine is perfectly same as like this CAD drawing then first, the dead volume is too big in it.
The power stroke is not enough. Too much the gap between the power piston's bottom and the cylinder's bottom.
The displacer's end is curved, but your hot end is flat. There is a big dead volume too.
I'm not pretty shure the gaps and tubes diameter in the connector part. But there is a dead volume too.

If I've right then you use regenerator gap (not solid regenerator) between the cylinder's wall and the solid displacer's wall.
I know it is a simple solution for a model engine, but you need usable power. It is not enough here.
Should to use some surface extension in the hot also the cold side's walls. Also should to use some INOX foam/wool regenerator between this two sections. The solid displacer is good for this change.
What is your displacer's material? Stainless steel or Calcium-silicate or something other?
Did you read Stirling books from Andy Ross? There is some usable things for a good performance homemade Stirling engine.

Kind regards!
Blade

[Ian S C]

I agree with Blade on most of what says, the heating and cooling should be looked at first, friction is the next thing to look at, take the shields off of the bearing races, flush out the grease, and replace with light oil. Then lighten the flywheel, leave a substantial rim, and thin the area between the rim and the hub, then in this area drill holes to form the equivalent of spokes, five or six would be good, it's the weight at the rim that is needed, the rest is weight that causes friction. Ian S C

[Datenfeld]

I checked your CAD drawing in Solid Works. The file format not was perfectly translated but the engine's geometry was What I need to see on it.
If your engine is perfectly same as like this CAD drawing then first, the dead volume is too big in it.
The power stroke is not enough. Too much the gap between the power piston's bottom and the cylinder's bottom.
The displacer's end is curved, but your hot end is flat. There is a big dead volume too.
I'm not pretty shure the gaps and tubes diameter in the connector part. But there is a dead volume too.

If I've right then you use regenerator gap (not solid regenerator) between the cylinder's wall and the solid displacer's wall.
I know it is a simple solution for a model engine, but you need usable power. It is not enough here.
Should to use some surface extension in the hot also the cold side's walls. Also should to use some INOX foam/wool regenerator between this two sections. The solid displacer is good for this change.
What is your displacer's material? Stainless steel or Calcium-silicate or something other?
Did you read Stirling books from Andy Ross? There is some usable things for a good performance homemade Stirling engine.

Kind regards!
Blade

Dear Blade,

Many thanks to your kind reply and support!!

No heat trap ( too much heat you lose it). Not stabilised the engine (opposit moving=loss energy). Not enough cold the cold side (water cooling continously=The inlet energy should be go out there). Not separated hot/cold side (heat conduction is dropped the efficienct).

It was my first test run, actually I plan a heat trap and would like to run the engine with electrolytic gas. Also the cooling side I want improve.
How you mean with "separated hot/cold side"? Should I separate the cylinder and isolate with ceramic, between the hot and cold side?

The power stroke is not enough. Too much the gap between the power piston's bottom and the cylinder's bottom.The power stroke is not enough. Too much the gap between the power piston's bottom and the cylinder's bottom.

The stroke is on both sides 30mm, then there is a gap of 3mm. Is this already too much? Kindly advise! The air-hole is 12mm.
Please see attachment "picture1".

The displacer's end is curved, but your hot end is flat. There is a big dead volume too.

Can I make the displacer without curve (more easy to manufacturing)? on both sides (hot/cold) the dead volume is 3mm. Is this also too big?? Please see attachment "picture2".

I'm not pretty shure the gaps and tubes diameter in the connector part. But there is a dead volume too.

It is at the moment 0.50mm (see picture2). Do you think it is too much? How much gap you would recommend?

If I've right then you use regenerator gap (not solid regenerator) between the cylinder's wall and the solid displacer's wall.
I know it is a simple solution for a model engine, but you need usable power. It is not enough here.
Should to use some surface extension in the hot also the cold side's walls. Also should to use some INOX foam/wool regenerator between this two sections. The solid displacer is good for this change.

I not fully understand what you mean? Would it be possible you upload a small sketch??
The Gap between cylinder's wall and the solid displacer's wall is 0.50mm.

What is your displacer's material? Stainless steel or Calcium-silicate or something other?

It is Aluminum.

Once again thank you very much for all efforts and your support!! If some people want 2D drawings then just let me know!!

Thanks and regards,
Michael

[Ian S C]

You may find the trouble is the aluminium displacer (a) it conducts heat too well from hot end to cold end, (b) you stand a good chance of it over heating, and collapsing, I had this happen twice on one of my motors, cured the problem by changing to thin walled stainless steel.
IAN S C

[Longboy]

I'm looking at your video and the layout of your Gamma engine. You've taken the right step in the flywheel being heavy and solid to store the engines input torque when draging your fingers across the flywheel. The dead space is fine. With the cylinders mounted to a common block heat can migrate over to the cold cyl quickly so you need a big heat sink or radiator over the hot cyl. The wet rags are temporary and effective but having each cyl. mounted on separate blocks connected by the air transfer tube will allow your engine to run at same no load RPM with lower heat input. An air transfer tube from each block joined with a silicon fuel tube as used in model airplanes eliminates heat transfer though any metal between blocks if the engine is mounted on a non metal base and the cold side would just be warmed by air then. A radiator over the cold cyl. can help some too as would a belt drive from the flywheel axle to a cooling fan next to radiators can stabilize block heat........... A major area to increase output of Stirling is weight reduction of the recipricating parts. Aluminum over brass and steel. Round shafting over flat beam for connecting rods. Thin wall pistons. Delrin over metal for joints. Ball bearing over bushings.......all this said what is your concern over the torque output? The nature of Stirling is low torque. If you want to drive something with your model remember that the same applys to the item driven be it a water pump or generator. Is it sized for the capacity of your Stirling? Or do you need a larger Stirling with 1 3/8 inch cylinders and 6inch flywheel!

[Ian S C]

You don't need a big motor to generate power, have a look at my album, and you will find a 2.5cc motor, it's got a 5/8" bore on the power piston, uses a motor from an old cassette tape recorder, and generates enough to run a 3 volt transistor radio, the motor is fuelled with methylated spirits, and has a water hopper around the cold end of the displacer cylinder.
Your motor would benefit from a water jacket around the cold end of the displacer cylinder, with a water tank, or radiator to cool the water, a pump is not required, thermosyphon will circulate the water quite well enough. Ian S C

[bladeattila]

Dear Michael,
The ceramic, or graphite ring is a good solution for the heat separation. But you should to seal it perfectly with some temperature resistant seal ring or grease.
The dead volume on the ends are too much.
If you can reduce it, then use only 0,5-1 mm.
The curved bottom help the displacer piston's disengagement from the bottom. But you can use other solution: cut some radial trenches on the cylinder's bottom surface (also the wall if you need). (It can help the heat exchange too)
Displacer...
The aluminium is one of the worse material what you can choose.
Ian said stainless steel, that is ok. Another solution is the Calcium-silicate (fire protection material).

If you are using solid displacer, in the case of every inch diameter from 0.25 mm air gap must fall. I read it somewhere earlier...maybe in Darlington's book...but I never used this, because my displacers was also regenerator, so there is not valid.

Kind regards!
Blade

[Datenfeld]

Dear Michael,
The ceramic, or graphite ring is a good solution for the heat separation. But you should to seal it perfectly with some temperature resistant seal ring or grease.
The dead volume on the ends are too much.
If you can reduce it, then use only 0,5-1 mm.
The curved bottom help the displacer piston's disengagement from the bottom. But you can use other solution: cut some radial trenches on the cylinder's bottom surface (also the wall if you need). (It can help the heat exchange too)
Displacer...
The aluminium is one of the worse material what you can choose.
Ian said stainless steel, that is ok. Another solution is the Calcium-silicate (fire protection material).

If you are using solid displacer, in the case of every inch diameter from 0.25 mm air gap must fall. I read it somewhere earlier...maybe in Darlington's book...but I never used this, because my displacers was also regenerator, so there is not valid.

Kind regards!
Blade

Dear Blade & Lan S C,

Thanks again for your kind advice!! I will modify the SE accordingly and let you know the result soon!

Best regards,
Michael

[Ian S C]

The displacer can be made of thin walled stainless tube, with a flat disc welded on the hot end (TIG), an aluminium plug works well in the cold end, and it can be glued in with high strength Loctite, or similar.
Ian S C