"The air tanks can be filled by any "commercial grade" air compressor at any gas station in 5 minutes, for about $2."
Several multi 1000 psi tanks can be filled from a 120 psi shop air compressor in 5 minutes!
I'm waiting for that explanation. At least you can use the exhaust for AC.
If you compress air you compress the heat contained in that air. If that air is allowed to cool when rapidly expanded, the heat content should be the same, but it would get very hot when compressed. Allowing it to cool is a serious waste of heat energy.
Maybe they transfer that heat energy to the engine from the pressure vessel.
Another problem not discussed is the fact that you are talking about air pressure at least 10 times the compression pressure of a diesel engine!
Think spontaneous combustion of any flammable lubricant.
regards
mech