Beta Stirling engine

[oilman]

Hi
i am trying to work out dimensions for my beta stirling engine.
I have an aluminium cylinder of 40mm dia. I am thinking to fix a 1 1/2 inch SS tube to make displacer cylinder.
I want to know the length of displacer tube.
I worked out some configurations on MS Excel sheet attached with this post.
For configuration A the total length is coming out to be Power piston length + Power piston stroke + Displacer length + displacer stroke + end clearance.
For configuration B the total length is coming out to be Power piston length + Power piston stroke + clearance between power piston and displacer + Displacer length + 1/2 displacer stroke + end clearacne
Which of the two configuration is better? In configuration B I get more compression than in A.
Also what type of linkage should I use? Rhombic drive seems to be beyond my machining capabilities.
Thanks
Oilman

[Ian S C]

Oilman, if you are going to make the displacer from the 40 mm aluminium tube, don't(I know, I tried[twice]). If you want to get any power out of the motor, you need more heat than the aluminium will stand.
The displace should be three time it's diameter long, and from what I see of your diagrams (B) is the one, you want say a mm or so clearance between the displacer and the piston, and the same at the other end.
You will be ok with a normal crankshaft and con rods. To get the correct ratio 1.5 : 1, you just have to make the displacer crank a bit longer, and remember that the cranks are at 90*. An example is my second motor the power stroke is 3/4", and the displacer stroke is 1 3/16". With a GAMMA motor you can keep tme both the same, and reduce the bore of the power cylinder. Ian S C

[oilman]

Hi Ian
I am thinking about making displacer out of SS tube.
My power cylinder is of aluminium. I will braze a SS tube on it to make displacer cylinder.
Power piston is of teflon rod. I have used teflon on one of my gamma engine. It works OK. only you have to make it slightly more undersize. It will expand while working and have a good seal.
Oilman

[oilman]

hi
Will an eccentric for displacer work instead of crank?

[Ian S C]

Oilman, the first motor I made was a GAMMA motor in a V form the displacer was driven by a Scotch Yoke, this meant that a joint was not required in the displacer rod, and the motor could be made shorter, it seemed to work ok, not that I had anything to compare it with, an eccentric would work, but a crank might be better as it needs a longer throw than the power crank.
Ideally an aluminium cylinder would be hard anodized, or chromed, but with the right grade it should be ok.
If you make the Teflon piston with a cup like bit at the crown end, that should help with the sealing.
I prefer cast iron pistons and cylinders, stainless steel and Teflon, or brass and Teflon work well.
Ian S C