You have probably already heard, probably through the media, the - too - famous air car and his equally famous air motor.
Since 1996, numerous reports and articles devoted to it regularly to revive the ultimately false good idea of the air motor.
Indeed, the overall performance of the primary energy of the compressed air can not be that bad (all industrial air will tell you) that this be compared to a thermal car but also in relation to electric cars that they even still have many problems and disadvantages. But the air car "competes" directly with the electric car (small "clean" urban movements).
The use of compressed air should, we believe, be limited to the recovery of braking energy with a completely independent embedded system with an electric or thermal main propulsion. That is, we should not be able to recharge in air: the autonomy of the tank is limited to a few accelerations or decelerations (be, at most, a few hundred kJ) ...
The recess would give different if the air is compressed was by renewable energy sources, but renewables are already missing while wasting green energy by compressing air is this really wise?
The Ecole des Mines de Paris conducted in 2003, 2 studies on propulsion by air, you can download here. Interestingly, or rather appalling to hear from MDI company that developed this air motor, they do not know these 2 reports.
To better understand the phenomenon of the "air car", here is a Video investigative Supplemental Survey released just a few days.