scaling it up

[antidartan]

I have successfully built a tin can engine. Verry cool. I was thingking of scaling it up to coffee can size. Are there things I should concider if I want power or speed, other than of course heat source?

Thanks

[alpha stirling]

Well, first of all the ratio between the displacer swept volume to the power cylinder swept volume will determine the required temperature differential. the larger the displacer, the lower the difference needs to be to operate. (a rule of thumb)
Then the stroke to diameter ratio of the power cylinder tels us if the engine is built for speed or torgue. Having long stroke makes the engine have more torgue but less speed and vice versa. (another rule of thumb)
There are a lot of variables and thus there's no way to be 100% sure unless you can do a complete analysis (with the thermodynamical system calculations, friction calculations and the like). This is something not for tin can engines as they're only demonstration pieces.

[antidartan]

The coffee can that I want to make my displacer cylinder out of is a 3 lbd. coffee can. The diameter is 6 inches and the height is 7 inches. I have read that my displacer piston should be 1/3 the height of the displacer cylinder, but how do I figure the clearance for the diameter of the piston? Also is the location of the pipe going to the power piston critical.(obviously it has to be on the cold side) Lastly , with a displacer of the size I will have with this can, is there a safe bet for power piston size? I realize this thing will not run anything but I would like it to have a bit more power than the tin can engine.
Double lastly can I put a wad of steal wool any place between the displacer and the power piston for the regenerater? Quadrupal lastly would a regenerater on the tin can engine improve performance?

Thanks
Antidartan

[alpha stirling]

well, the position of the pipe to the power cylinder ain't very critical since we are only interested to connect these two cylinders pneumatically. It is better to have it on the cold side though, to keep the air going into the power cylinder cool. A regenerator in this manifold might or might not improve efficiency, but in our scales, I suggest you don't use it since it is bound to create more flow friction than crank up the efficiency...

Umm... well actually you should have the swept volume 1/3 times the total volume of the cylinder. Thus, the volume of the displacer piston should be around 2/3 of the total volume of the displacer cylinder: if the OD of the piston is close to ID of the cylinder, then the height of the displacer should be approximately 2/3 of the height of the cylinder. The designs vary great deal, but this is a rule of thumb. It all kinda depends on how large areas are actually heated or cooled and how large lenghts of the cylinder wall have to be insulated from the working fluid during the cycle.

I hope this helps