Stirlingengineforum.com

Hi everyone!

i am making an alpha Stirling engine for a school project.

I am using stainless steel flasks as cylinders and they have an inside diameter of 8cm but my pistons are about 6.2cm in diameter.
I have thought about using some steel wool to fill in the space between the piston and the cylinder wall but haven't taken into consideration that it would leak air.

What should I do instead? I currently have limited access to machinery.

Hi User1, If you are building an ALPHA motor, it"s worth down loading Andy Ross's book "Making Stirling Engines", it's a free download, if you print it out it's 68 pages.
No, steel wool won't work, you must have 2 well fitting pistons in proper cylinders, one the hot cylinder has an extension, the hot cap, and the hot piston has a bit on top, similar construction to a displacer in an ordinary Stirling Engine, it's called a Heylandt Crown, I don't have any info on the dimensions of the crown, so when I built my ALPHA I made it quite tall, I think it was more than 2 diametres high, and it has about 1 mm clearance from the inside of the hot cap.

Your simplest design would probably be a V ,L shaped motor, you only need 1 pin on the crankshaft.

If you can put up a sketch or drawing of your ideas, I might be able to help(or maybe hinder) you on your build.

Here's my attempt at an unpressurized Ross Yoke ALPHA motor.

Ian S C

The same motor before I changed it to air cooling, with the little power hacksaw that sometimes replaces the generator. It will actually cut a 13 mm steel bar in a bit over 20 minutes, not too bad for about 5Watts of power.
Ian S C

Here's a what I plan on it to look like and what parts I currently have (Now without the cans as they won't be useful as pistons unless I find a way to make them fit)

Here's a rough(very)sketch of an ALPHA hot end, note where the air transfer port is.

The piston in any Stirling Engine should fit very well, if you place the piston in the open (at each end) cylinder it should slide through under it's own weight, and if you block one end the piston should stop sliding down. The best material to make pistons is cast iron, the cylinder may be cast iron or steel.

The hot cap on most of my motors is made of stainless steel, and I run the motors on LPG, and the hot cap is red hot.
Ian S C

Then I should make it like this?

Yes, but you need to add the Heylandt Crown on top of the hot piston. Give it 1 mm to 1.5 mm clearance on the diameter, and 2 mm on the end, the crown should be as light as possible, mild steel is OK, but thin stainless steel is better. Make the bore of the cylinder and hot cap the same. If you use fan cooling, one fan should do, and if you select the right one, and fit a generator/small electric motor that will generate the voltage of the fan all will be self contained. The motor should run quite well with just natural airflow.
I do have one motor with an electric fan, it is a water cooled motor with a radiator.

Ian S C

Like this?

Yes

User1, spot on. Remember to down load Andy Ross's book.
Ian S C

Before I do anything. I would like to know if there were any advantages or disadvantages of using a V Layout or an Inline layout.
I've considered both but the fact that the Hot cylinder would be further away from the cold cylinder in the V layout made me choose it.
is there were any discernable difference between the output of an alpha engine with a V layout and one using an inline layout.

Also, which one would be more efficient?

The V motor is more simple to build as you only need one pin on the crankshaft without extra links. I have only built one ALPHA motor, the one in the photos with the Ross Yoke, one advantage this type has is the elimination of side thrust on the pistons, this gets rid of a source of friction.
Ian S C

Hey again,

I need to find something that I could use as a piston, the diameter of the cylinder is about 7.4cm. (not sure about the diameter as I am not home right now and I can't recall the last time I measured it).

The cylinders must be round, parallel, and well honed, then the pistons made to fit the clearance will be between .01 mm and .03 mm, the best way of testing this fit is to insert the piston in the cylinder dry, and it should just slide through under it's own weight and if you place the palm of your hand over the end of the cylinder the piston should stop, if it keeps sliding the piston is too small and you need to start again with a new one. This is precision engineering, and if you want it to work you need a lathe, and know how to use it.

Your stainless flasks are no good as cylinders, they are not round or parallel in engineering terms. You should be building something much smaller, 30 mm to 40 mm bore is a good size for a starter engine, that size or smaller will give a good running engine at a reasonable cost. My motors range from 10 mm to 55 mm bore. I have a lathe, and a vertical milling machine, also welding equipment. this is the smallest one with a bore of 10 mm and a stroke of 12.5 mm. Made entirely from scrap found in the workshop.
Ian S C

Well, the problem is that those flasks are the only things that I own that "can" be used as cylinders, I also have very limited time to finish the project and have no machine to work on any metal at home.