If you want to make an engine of any kind with a fuel tank and a separate combustion chamber, it's currently impossible in TPT. You need to have a way of defining a region of unignitability (I don't mean a region of normal space that is simply enclosed in the wall, but rather a region which is defined by the presence of the wall in that region, much like the gravity wall blocks Newtonian gravity wherever that wall is present, and the "electricity generating if particle present" regions defined that type of wall). Best way to do that is to make wall type element, and place it in the fuel line. It will be a wall that will pass any type of particle but fire, and any particle in that region defined by the wall's presence can not catch fire (nor receive any heat transfer from fire particle) even if it's on the edge of that region, and in contact with a fire particle which is outside that region.

@macquarry (View Post)
Sorry, but there is no wall that only blocks gas. The only type of "gas wall" that exists is the type that allows all particles EXCEPT gas. I wish though that gas blocking walls were added into TPT at some point though.