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Anyone looking at the Volt, electric delivery trucks, and other stored energy vehicles should keep an eye on MDI (privately owned) and their air storage technique. This could be formidable competition in the field. Performance of this PHAV is close to the better known PHEV designs, but since there are no batteries, the retail price looks like about half that of the more ballyhooed machines. The quickest way to get current news is to search on ("zero pollution motors" AND (minicat or citicat)). I've gone through the basic physics, which is good as far as I can tell. They are using a new business model, a variation on franchising. I picked up one share a few years ago as a speculative investment.

Most people thinking of air power think in terms of isentropic compression, which wastes energy by heating the air, and isentropic expansion, which wastes energy by cooling the air. They are using a triple compression/expansion design (with reheat and recool) approximation to isothermal. A pure isothermal would waste no stored energy but seems to be impossible. The best I've read of is 95% of isothermal and is not practical for transportation. MDi seems to approach 80%.

Basically, they have lower first cost, and lower storage efficiency. They've solved the safety issues also. Production is expected around '10.
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I'm personally looking at the Tesla roadster.
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From a chemist's point of view, one volume of gasoline produces 2036 volumes of gases at STP. I'm estimating a pressure of 31,000 psi to contain that much energy in compressed air. Then you have about a 5 fold increase in temperature.

So I suspect a compressed air vehicle is going to be short range unless there are major improvements in efficiency compared to an internal combustion engine.
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I'll believe it when I see it. These compressed air mini-cars have been '2 years away' since 1999. It doesn't seem practical to me to get the energy density required from compressed air. A private company with no 3rd party verification can say pretty much whatever they want ...
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I'll believe it when I see it. These compressed air mini-cars have been '2 years away' since 1999. It doesn't seem practical to me to get the energy density required from compressed air. A private company with no 3rd party verification can say pretty much whatever they want ..

Their business model is untried, and may not work. However, the basic physics is right, and there is no information that would eliminate the machinery working. Don't invest unless you have speculative interest and free cash - but if interested in this field, keep an eye on them. I spent several years checking everything about them that I could before taking the chance.
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