[marki]

That looks very interesting Chris, I wonder when it will become commercially available? Friction is the biggest killer with these engines and machining tolerences are really tight (I have a very accurate lathe). The alcohol engine is not so critical so I was able to use a phosphorous bronze liner in a brass cylinder with an ali piston which works well as it self lubricates and oil can also be used. The cold engine is a little more exotic. When I first built it I used a graphite pistion in a glass cylinder but the graphite did not last long before the seal was lost. I ended up using and acetyl piston in ali cylinder that had been highly polised and treated with a spray on teflon coat (easily renewed) that has lasted for more than a year with little sign of wear. The other critical part is the push rod that moves the displacer. This is made of graphite rod and slides through an acetyl bearing with a good seal and stuff all friction (it will run on an ice block). The hole through the acetyl bearing is 1 size smaller then the graphite rod yet it still slides easily. It's great to watch my students try and workout what is happening, keeps them occupied for hours and really is good science.

Mark