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.
If you are using Windows search the LocalLow folder, there you will find a folder called Jundroo. Move the SimpleRockets 2 file inside the .zip to Jundroo and it will install all the parts automatically.