Re: Car powered by compressed air ... is that for real?

From: Ken Clements (
Date: Wed Oct 25 2000 - 17:41:09 MDT

I have thought about this idea many times over the years, and will be interested
to see how they got around the basic problems. Yes, it is possible to store
that much energy in a tank, and yes you can design a gas expansion engine to run
a car (however, there is no way the $0.30 US for 200 km can be true). The
problems come from the basic thermodynamics of the Carnot cycle. When you
compress the air, it gets very hot, and as that heat is lost into the
environment, you loose energy storage efficiency. When you expand the air in
the cylinders, it cools down below ambient absorbing heat from the environment.
If you try to run one of these where it is very cold outside, the engine temp
drops so low you get terrible efficiency, and it might freeze up on you

If you are going to operate this in a hot climate, and you do not care about the
storage loss, it is probably as good as that which can be done with electric
batteries today. An idea I had long ago was to use the space shuttle ceramic
tile insulation material to make compressed air tanks that remained at high
temperature. This way the air that goes to the engine is still hot, has not
lost so much of that energy, and then comes out of the engine warm. You can
operate it in snow and still have a heater. A major drawback is the idea of
carrying around hot tanks stressed at 300 to 500 atm.

Back before the first human powered aircraft flight, I had a related idea. This
was a human powered aircraft in which compressed air was used to overcome the
power requirements for takeoff. The basic idea was to have the human sit on the
ground for a few hours before the flight peddling a compressor that was charging
the tank. At takeoff time, those hours of human 0.2 hp goes into the expansion
engine to produce a couple of minutes approaching 100 hp (the Wright brothers
got off the ground in 1903 with 12 hp). This would be a cool bird to fly in
hops across the country for fun, but it is in the list of projects I know I am
not going to get around to.

Back at cars, all of the above is cute, but fuel cell designs will win soon and
then evolve as we get to nanotech.


Max M wrote:

> A French company called "ZERO POLLUTION MOTORS Inc." apparently has
> developed a motor that runs on compressed air. A little data:
> range: 200km (120 miles) for only 30 US cents.
> using 300 liters of compressed air (300 bar)
> 10 hours in an urban environment at an average speed of 80km/h.
> refill: 4 hours in a 220 V plug at home, 3 min at servicestation compressor.
> price: $10,000
> weight: 700 kg
> Max Speed: 130km/h (aprox. 85 miles/h)
> This technology sounds a little to good to be true, but I don't know enough
> physics to be able to se through it easily.
> Is it possible to compress enough air and keep it in tanks small enough to
> fit into a car?
> Here is a link from the BBC:
> And the companys own website:
> If something like this was for real it would have a huge socio economical
> influence on the world.
> Max M. W. Rasmussen (NOT Max More)
> Denmark. New Media Director
> private: work:
> -----------------------------------------------------
> Specialization is for insects. - Robert A. Heinlein

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