A Green Driver's Dream - a Compressed Air Car.

India's Tata Motors plans to introduce the first mass produced car powered entirely from compressed air. The CityCat model, shown above, has a range of 125 miles, and scoots around at up to 68 mph. Filling up is a breeze - either use a special air compressor at a gas station for about $2.00, or just plug it in for 4 hours at home.

Unfortunately, there's no plans to export these to the United States - yet. Link via Digg

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Gerry raises a good point about the potential energy involved in carrying around a lot of compressed air in a high speed vehicle. The storage systems (tanks, lines, etc.) need to be VERY robust (which add mass and suck up useful range).

Others raised issues with the energy required to compress air. This is frequently neglected, but is NOT trivial for air as it is not trivial for systems which compress natural gas to 3000 - 5000 psig for natural gas vehicles. Adding the electricity cost is essential! It seems the article is saying that $2.00 will get you 125 miles range. That implies a public (not home) high pressure dispensing and thus *should* have electricity cost already included... but be wary. The numbers sound fairly attractive, but I'd need more details to do the energy analysis.

One thing people have missed is that there is a big thermodynamic problem with compressing a gas into a tank and then running off the accumulated pressure. The compressed gas gets (Boyle's Law) quite a lot hotter as it is compressed. Unless the tank is very well insulated, as it loses this heat and drops back to room temperature, you lose pressure (and range) -- a big loss of energy. These systems need to take great pains to conserve the enthalpy of the compressed air. That's a major reason why to date, there have been no practical public highway compressed air vehicles. They are more feasible for short term / short range use on scooters, fork trucks, etc. inside large factories (no emissions inside the building). In that application they are easily "charged up" and the slower travel speeds mitigates the need for serious crash protection. The fairly short time (hours, not many days) between recharges reduces the need for exotic tank insulation schemes.
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Ever see a really big truck tire or scuba bottle explode?
It's like dynamite (I know one garage worker who was killed when a truck tire exploded as he filled it).

Compressed air is DEADLY. Trucks carrying compressed air are REQUIRED by law to display hazmat warning signs.

Can't wait for the first traffic accident that sets off the tanks in this crackerbox. The ambulance-chasing lawyers will line up to sue the pants off of the company and anyone driving one for putting such a danger on the road....
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