Quote Originally Posted by Hans Pearson View Post
Thanks for the comments and tips Marv. I am still at the cylinder and piston stage so pretty flexible as to the road ahead. I have seen some with radiators and water pumps, even a radiator fan, which must be pushing the limits of the engines output. Your description also highlighted a problem I had not taken into consideration. I live at an altitude of 5550 ft. so atmospheric pressure is only 12 psi. Time is my problem so the project is not advancing at a rapid rate.
Thanks again, HANS.
Both my atmospheric engines use stainless steel pistons in aluminum cylinders. It works but one has to be careful to allow for the different rates of expansion of the dissimilar metals.

The right piston material for these engines is probably graphite. I use graphite pistons in many of my Stirling engines and it works perfectly. In addition to being lightweight, an important concern in low temperature differential Stirlings, it's self-lubricating, which is really important. Oil drag in an LTD Stirling can easily overcome their miniscule power. Graphite's thermal expansion coefficient is about half that of stainless so that's another plus for this material.

The other problem with oil in a flame-eater is that it will form a carbonized residue in the cylinder from the heat of the hot gas. This means that it must be cleaned periodically. A graphite piston will solve that problem too.