Right. that's why, when I think of ways to save the world for heat engines after TSHTF, I restrict myself to nitrogen- (separated air ), or hydrogen (separated water) as the only sane choices for working fluid. Nitrogen is sluggish but ok, and hydrogen is just great, but has bad habits re alloys and such. So, nitrogen. Then you have a big sort of ugly engine, but works well enough. I am talking about the one you put on a tractor train to haul all the neighbors into town for the week end party, using moldy hay as fuel.

Truth of it is that I still can't beat a plain old IC engine running on a wood gasifier. Anybody can do it. Does not take any superannuated dreamers like me.