Well seems like an almost feasable idea to me, the energy going in is the power that makes the compressor run then it's all potential energy until it's run through the turbine axels or whatever. or it could be a pumped circut where the compressed air would be pumped past the contact points causing the wheels to turn, then it would be diverted back into the tank or to power a small compressor. This idea could be used well with hydrogen, the hydrogen would run a compressor while the air would run the car.