Gamma type cylinder and displacer

[Ian S C]

The displacer should be three times it's diameter long.
Ian S C

[czakun]

Ian, we stil dont understand to each other
I mean that proportions 3:1 (displacer length to its diamater )and 1,5:1 (displacer cylinder volume to power piston cylinder volume) dont define displacer cylinder volume (which means displacer stroke indirectly). Take a look at this picture:

I was asking is there any recommended ratio of dsiplacer length to displacer stroke?

[Ian S C]

No, just make the volume 1.5 x the displacement of the power piston.
Ian S C

[czakun]

Thanks ;)

[Ian S C]

Area of diametre x stroke - volume, but you know all that, someone else may not.
Ian S C

[czakun]

Hi after little break,
collecting of materials has go forward since last time (sorry for propably incorrect verb form):
- displacer is gonna be made of fused quartz test-tube (beacuse of its light weight, low conductance, and temperature durability)
- material for hot cylinder and pistons cylinder is stainless steel
And there is a problem with pistons material: which bronze would be better B101 or BA1032?
Pistons cylinder is already made; its diameter is 30mm comparing to 25mm displacer diameter (26mm displacers cylinder). Is that difference too big, isnt it?

[Bumpkin]

Looks like it's been worked out, but if we would say SWEPT volume for the ratio of displacer to power, it might save some confusion.

Bumpkin

[Ian S C]

Yes Bumkin is correct.
About the bronze, I can't help much there, some bronzes are harder than others, and I would go for the harder of the two. You should aim for as polished as possible for the bore of the power cylinder.
It's usually best to have the displacer cylinder the same or larger than the power cylinder, but the swept volume can be adjusted at the crankshaft.
Ian S C

[czakun]

You right ;)
English isnt my native language, thats why I may have some lacks of terminology. Sorry for that.
Isnt cylinder too big? Am I right that the smaller piston is better (lighter and smaller circumference - less leaks and friction)? Amount of air pushing the piston is same coz it depends on displacer and its cylinder. I see there only adventages.
What about displacers swept volume? There must be some relationship between it and displacer size. With biggest stroke we get more air to push the piston (but not too big - displacer will not displace enough of air). Smaller stroke - less air to push and we could achieve same result with smaller, lighter displacer.

[Ian S C]

When I design my motors, I like to make the power piston stroke the same or shorter than the diameter of the piston, and calculate the swept volume, then I select the tube to make the displacer, and if I can make it a little larger in diameter, and with luck it is near enough that if the same stroke is used the ratio between the two is 1:1.5, if not the stroke is adjusted to suit.
Ian S C