The car that runs on thin air

The 'air car' plugs into a wall outlet, allowing an on-board compressor to pressurize the car's air tank to 4,500 pounds per square inch.

It takes about four hours to get the tank to full pressure and the cold air is then released gradually to power the car's pistons. Only fresh air comes out of the almost frozen exhaust pipe at low speeds.However engineering experts are skeptical of the technology, saying it is clouded by the caveat that compressing air is notoriously energy intensive.

'Air compressors are one of the least efficient machines to convert electricity to work,' said Harold Kung, professor of chemical and biological engineering at Northwestern University.

'Why not use the electricity directly, as in electric cars? From an energy utilization point of view, the compressed (air) car does not make sense.
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