Hmmm. Quite interesting bit about the Enchanters. Especially the air shields. Though how air could shield you from anything is beyond me. It is like making a shield out of party balloons. Yeah, couldn’t really make any sense of it.
Also, still for me, it is the boom (euphemism for explosion) that make things work. The boom happens because when substances burn they create gases. Volume of gases created from explosive substances are often many times larger than the volume of the substances itself, sometimes in the factor of hundreds. So when these substances burn (almost in an instant) they turn to gas and expands to hundred times their volume. This expansion creates the boom. This expansion (explosion, boom) gives the power for your bombs, guns, and car engine. As I say, in another sense, air pressure to explosion: propellers to jet engines. They just not the same.
By the way, you can create a combustion (car) engine with just one piston but it is close to useless. It vibrates a lot, as in, bone shattering vibrations. All car engine is designed with multiple pistons not only for power but also for smoother operation. The pistons are timed and placed so that they cancel their shaking causing motions. The timing of pistons to act like your bicycle pedal analogy is just an added bonus from having multiple pistons, but is not really necessary for a working engine.
Hmm. Weird rocks, you mean lodestone? Wow, they are more advanced than I thought they were. But then, you know you can make these devices (or one of similar function) without the stone right?