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Quite interesting engines these http://birkpetersens.blogspot.com/2014/04/non-compression-engine.htmlhttps://www.eldensengines.com/Lenoir/Lenoir.HTML
Maybe I'm dense...but I read both of these articles, they both talk about introducing fuel , igniting the fuel with a spark and that pushes the cylinder. ...isn't that combustion & would that be some kind of compression to push said cylinder ?