Stirlingengineforum.com

I have recently build a coffee cup LTD engine.

It is happy to chugg round at 50 -60 rpm for a hour but i would like to get it to go faster, any ideas about what effects speed would be helpful.

I could fiddle with the two piston sizes and their clearances but would welcome some pointers in the right direction as to what might be the best thing to try first

The top and bottom and the flywheel are all 1/8 aluminium discs, DVD disc size.

Displacer piston 3 9/16

Displacer bore 3 7/8

Power piston .522

Power cylinder .530

Stroke total on both cylinders half an inch

I know the power piston is "sloppy" and i am having a nylon piston made with .002/ 003 clearance on the bore, at the moment it needs oiling in the power piston to make it run because of the excessive clearance.

Any thoughts?

David

If speed is desired over power then a short stroke on the power cylinder is generally used. Your engine is close to what is called a "square" engine, meaning the stroke and bore are the same. I see many Stirling's with long power strokes and I believe this helps over come the friction by increasing torque. for a LTD engine with a low temp differential the stroke seems to be shorter but the precision of construction needs to be higher. Also, a lighter flywheel will increase speed but if it's too light it will stall or run erratically. From what I have seen of typical "coffee cup engines" they all run on the low RPM side. Single tea candle engines seem to get 200-500 RPM. More heat = more speed in most cases. Keeping the weight down on the displacer will help considerably too.