Can the specification of a patent application be accompanied by non-patented elements?

Yes, the attached drawings in the instruction manual are to show your invention and creation scheme more clearly, as long as it helps. But in the text of the instruction, you must clearly describe where your invention is and how to realize it. If the engine is necessary to realize your invention, you must write it out unless you write it clearly. If you have to, but it has nothing to do with your invention, you don't have to write it.