i was looking at http://www.theaircar.com and they are using compressed air in order to power a vehicle. it is a fairly simply concept but i am curious every one talks about using diesel generators and such in order to make a hybrid but why not use the same concept as the air car but using the air power to charge the system, batteries etc. yes would require more computer parts to regulate when it would kick in etc. but if could simplify a little why would it not work. if can recharge the new lithium batteries that quick charge when say at 50% power till able to recharge then if able to produce enough power both run car and recharge battery. or just recharge battery at faster pace then it is draining.
ok i realized that the setting for lithium phosphate would have to be recharged at around 80% but that would increase the life of the batteries to about 4-5 years. is this beyond anyone else. it shouldn’t be maybe time ot start looking at the specs for the air car and see what i can find in order to make a generator out of it.
i understand this may not be what you are looking to answer but i am trying to find something better then what is available right now. nothing will be perfect but doesn’t mean i can’t try and any input makes it more reasonable to be done.
Interesting idea. I have no clue how well the whole air powered motors are. I’ve seen a couple things on Discovery channel. I guess the biggest thing with gas/diesel generators is they are already engineered and can be purchased. Something like this is probably an item you’d have to make yourself and most people aren’t up for that 
Brian
This sounds like a fun problem.
I know pneumatic systems are really heavy, so weight would be one of my concerns. I went into the FIRST robotics competition, and we had a set weight limit (for our robot). and we decided to opt out of the pneumatic propulsion because the equipment was so heavy. However if you are just storing a few tanks (or a big one) for a quick on-the-go charge it might be worth it.
One thing to remember though, weight decreases a electric car’s rage, and top speed. This is something I’ll look into more when I have some more free time.
Good Luck