alpha bore to strke ratio

[richp85elco]

Hello all, I am new here and looking for some advise. I have long wanted to build my own stirling engine. I would like some advise on bore to strke ratio. It will be an alpha config. with 1.5 in dia. bore I would like to be able to rev it to 2000-2500rpms or higher. I read the stirling engine manual and seen it suggest a 1:1 to 2:1 ratio but was not sure for what config that referred to. Would it be possible to have a longer stroke than dia. for an alpha or would it be inefficient? Or should I stick to 1:1 to 2:1
Thank you. Sorry for my English i am using a translator

[Ian S C]

If you are making an ALPHA motor, the ratio should be 1:1, to get the revs you want, I'd look at about 1" to 1.25" stroke, it's quite possible to have a longer stroke, say 2", but if you want revs, you reduce the stroke, and 2000-2500rpm is quite high. The 1:1 ratio is not the bore to stroke ratio, but the ratio of the volume of one cylinder to the other.
Ian S C

[Aviator168]

RPM of these low power engine depends on the amount of friction from the side load, axial and pumping lost. Less friction, higher rpm, and among those 3, pumping lost is the biggest.

[Ian S C]

To reduce friction from side load you either use something like the Ross Yoke, or long con rods. It should be posible to use a BETA type motor, in which case a Rhombic type motor would eliminate the side thrust.
Ian S C

[Aviator168]

The side load is another thing that work against stirling engines since you don't want oil to lubricate the cylinder wall. The mechanism indicated by Ian can also benefit IC engines; but we have seen any of them been put into practice. Too many parts, too heavy?

[richp85elco]

Thanks for the responses, for an alpha I understand both piston volumes should be the same, I was just wondering how the distance the piston would have to travel would effect the overall performance. I think based on suggestions i will try to keep it about the same or a little less than the diameter. I think that would also help reduce the overall size. As far as side load i plan to keep the connecting rod/ piston motion pretty linear to combat those losses. I am also planning on reducing as much pressure loss as possible out the back of the piston where it meets the connecting rod, but am still thinking about how to do so without creating extra friction from tightening up the tolerance of the piston.

As far as the expansion cylinder goes i am thinking 316 ss and for the piston i am not so sure, possibly grafite. I am planning to run on a propane burner ,so i am unsure if they will stand up to the heat. Is there any preference for the cylnder and pistn material? Thanks again

[Aviator168]

Without change volume, increase of stroke leads to reduce in bore. That means less torque and I don't think there is a change in power output.

[Ian S C]

With a reduced stroke, more revs can be obtained with the same piston speed.
Ian S C