You have probably heard, probably by media, of the - too - famous air-powered car and its equally famous air-powered engine.
Since 1996, many reports and articles are devoted regularly to revive the, ultimately, false good idea of the air motor.
Indeed, the overall efficiency on the primary energy of compressed air can only be bad (all the air industry will tell you) that this is compared to a thermal car but also compared to electric cars which, themselves, still pose many problems and disadvantages. However, the air-car "concurence" directly the electric car (small "clean" urban movements).
The use of compressed air should, in our opinion, be limited to the recovery of braking energy with a completely independent on-board system with main electric or thermal propulsion. That is to say that we should not be able to recharge in air: the autonomy of the tanks is limited to a few decelerations or accelerations (are, at most, a few hundred kJ) ...
The situation would obviously be different if the air was compressed by renewable sources of energy, but renewable energies are already lacking so wasting green energy by compressing air is really wise?
The Ecole des Mines de Paris has realized, in 2003, 2 studies on the propulsion by compressed air, you can download here. It is interesting, or rather appalling, to hear from MDI, the company that developed this air engine, that they do not know these 2 reports.
To better understand the phenomenon of the "air car", here is a Investigative Supplement Investigative Video broadcast a few days ago.