Stirlingengineforum.com

I am attempting to create an engine that will generate some significant amount of power (ideally at least 1KW). It seems that one of the main issues to work out is how to create the power piston.

I have seen some solutions here, but they seem to have some inherent problems. Are there any accepted solutions for a real power piston that include lubrication considerations?

Thanks for any suggestions.

Stirling engines cannot be lubricated by oil. This is due to potential explosion danger and also the fact that oil will clog the regenerator and heat exchanger.
The pistons of a really powerful engine are usually made of aluminum alloy for light weight, while having sliding piston rings made of self-lubricating material like Teflon or graphite. While teflon is somewhat more durable and free-moving due to it's low friction ratio, graphite can withstand very much heat while it's thermal expansion is very small (so it won't really jam the engine when it heats up. Graphite is, however, pretty brittle, and getting it in large diameter chunks or bars can be difficult. It is extremely self-lubricating due to it's atomic structure, but pretty messy to work and play with. It will also, over time, form a fine carbon dust inside your engine...

These alternatives are about all I know. Some people have used teflon piston rings with graphite grease on them, but I don't know how it came out. I, personally started with polyacetal since it is cheap and easy to machine, and offers low friction ratio (0,2). I just recently started making tests with a Teflon based piston (teflon has a friction coefficient of 0,04)so it might work better than polyacetal. It isn't hard to machine also, but it is slippery and very expensive. A 2/3 foot piece of 1" bar cost me arm and leg (not really but a one-weeks worth of school meals anyway :P ). the price per foot was around 25$ larger bars or pipes may turn out to be very expensive...