ORIGINAL: earlwb
Maybe if the piston has the room for it you could cut a ring groove in it. Or why not make a aluminum piston and put in a piston ring.
I got to thinking about cutting a ring groove in a few pistons for some DEEZIL engines I have and either making or get made some piston rings to fit and see if the engines would run OK or not. As it is the pistons are a bit too loose in the cylinders. The Deezil engines have really tall or long pistons, one could likely put on two rings on them if they really wanted to.
You know, the Russians are getting really good with ceramics. They have been making ceramic coated cylinders for engines for a while now, but I was surprised to see they are making ceramic wrist pins for the engines now too. The Cyclon engine folks are the ones doing it too with their engines. I wonder how well a ceramic piston would hold up.
Wood piston. That might be interesting. Maybe use some of that really hard wood that comes out of Africa or someplace, and soak it in superglue for a while to maybe toughen it up even more. or maybe pressure inject it with high temperature epoxy resin.
Oddly enough, I've worked with several exotic wood species from all over the world. South America, and Africa have some of the hardest woods. Many Australian woods are very dense and extremely hard. Most exotic wood has 2 things going for it; very hard, and very oily. My favorite is Ipé (Brazilian Walnut). It is to my knowledge the hardest known hardwood at 3360 on the Jahnka hardness scale. This specie would probably be the one I would try
if I were to try something like that.
No amount of impregnation will permeate the oily dense woods like Ipé, Cumaru, or Jarrah. As a test, my old boss took a chunk of Ipé (kiln dried tongue & grooved flooring) and put it in a bucket of water for an hour. After that hour, it had the same moisture content as it did before the dunk. (5% moisture) Once sanded, if not sealed in short order the oils in the wood come to the surface. I dont think you would need to "seal" this stuff, its basically self-lubricating.
I would think a piece of endgrain Ipé with a ring would probably work rather well for awhile. Dont know about a tapered bore though.
(I've been a hardwood flooring install/finish guy for 12 years)