Well,you have one problem that is a killer.First of all an air compressed car is really dangerous.Lets say someone fills up their "air" car at home(using electricity of the grid which is powered by fossil feuls in most cases),then they get into an accident but not a fender bender a serious accident like a semi or train strike.You be creating a huge explosion(like a grenade the size of your air tank),that could throw shrapnel everywhere.So theres that,not completely impossible but super difficult engineering because the general public will find a way to break it,always.So do you really want potential bombs moving at 70mph +?And then there is the whole your not rich thing,which means if you have an idea to cut out the oil company in a big way they buy you off and kill it.There is a water powered car that runs on a turbine and battery guess who owns it?.....Exxon.But if you can get a real design and solve a huge set of obstacles then kudos.