Look, this is the last I'm posting in one of these threads because they become worse and worse as they go on. This probably belongs in the unicorn corral for math failures being interpreted as over unity garbage.
A 2L diesel going down the highway at 60 mph is turning 2000 rpms. This imaginary diesel is drawing 2L into itself every other revolution. 16.7 times/sec. So 33.3L/sec. For simplicity I'm going to say 2:1 air to your atmospheric pressure tank. So about 10L/sec from your 250L tank is 25 seconds. Or 0.4ish miles traveled.
Or generating it from an onboard battery? So you're going to take a 1kw battery, use it at 50% efficiency to make this gas, then burn that gas 30% efficiency in an engine. Thereby getting 167wh of motive force from it and adding a 9ft^2 tank "somewhere" in the car.
You could literally get more than twice this improvement in FE by throwing an extra (small) deep cycle battery in your car and disabling the alternator for a while.
None of this even approaches making basic, logical sense enough for it to even be a valid thought experiment.