I'm proud to bring you Infinite Fuel Mod. This mod adds 0 consumption versions of the ingame engines and RCS Nozzle.
Keep in mind that you need some fuel in order to start the engines/nozzle, but they won't consume any fuel. You can use them the same as their ingame counterparts.
I hope you enjoy the mod, there's more to come (with the help of @AnotherFireFox). I'll love to read all your suggestions.