Not to imply that these might actually work, but - if magnets don't affect non-metallic substances, how do MRI scanners work?
The answer of course is that a (powerful) magnet can align the electrons surrounding atoms regardless of which substance it is. How this can possibly relate to improving fuel efficiency is, however, beyond me.
But only in materials with magnetic susceptibility - presumably there aren't many 13-C atoms in the carbon atoms present in the fuel. Either way, you're not going to fit a superconducting magnet into the front of a Mondeo
