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Thursday, 8 July 2010


This is a zero-emission car that runs on compressed air. The air engine is made by a French company called MDI, and the car's claimed top speed and range are about 100 kph and 250 km respectively. An obvious advantage of this over an electric car with batteries is that it's very easy to re-charge - you just plug in a compressed air line for a few seconds, and then off you go.

I am old enough to remember steam railway locomotives from when I was a child. Around the age of eight I saw a very curious one like this:

Smug and thermodynamically-aware, even at eight, I realised that - if it had no funnel - it couldn't have a firebox. And - if it had no firebox - it had no source of power. Yet it was happily shunting wagons up and down the tracks with lots of hissing and steam.

My father explained that the locomotive was carefully insulated, and that all they did was to fill it with very hot water under very high pressure from a stationary boiler beside the track in the morning. Then it would shunt all day as its store of water boiled off to steam.

This has potential for cars too. With modern materials like aerogels we should be able to make an almost perfectly-insulated pressure tank.

The compressed air for the compressed-air car comes from an electric compressor. Here all that would be needed would be an electric kettle element embedded in the car's insulated tank. You would fill the tank with water in the evening when you got home, plug the car in, and switch it on. The water would be heated to a few hundred degrees under high pressure overnight, and the car would be ready to go in the morning.

And the simplicity of re-charging that the air car achieves would be retained by the stored-steam car too. At the filling station you'd just refill the car from the filling-station's boiler.

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