more air

MIT's Technology Review has more on MDI's Air Car.

The Air Car was supposed to hit the streets years ago, but its release always seems just around the corner. MDI announced in 2002 that the cars would be used to replace taxis in Mexico City, but nothing resulted.

Tata's involvement this time around, combined with the fact that oil recently hit $100 a barrel, could change the game. India's largest automaker announced last February that it had struck a deal with MDI to further develop and refine Negre's compressed-air engine technology, with the intention of producing and selling the emission-free cars in India. It has since been reported that Tata invested nearly $30 million in MDI as part of the agreement.

The Review say experts have doubts about the energy efficiency of the compressed air motor.

"The main problem is that air gets hot when you compress it, so much of the energy input goes into raising the temperature of the air as you try to raise the pressure," explains Doug Nelson, a professor of mechanical engineering and an expert on advanced vehicle systems at Virginia Polytechnic Institute.

But, apparently the engine is much more efficient at using energy:

To propel the vehicle, compressed air from the tanks is injected into a small chamber, where it expands and cools. This expansion drives a downstroke of the piston. But as the ambient temperature begins to reheat the air in the first chamber, that air is forced into a second neighboring chamber, where it expands again to drive an upstroke. Using ambient heat helps capture more of the energy in the compressed air, ultimately improving the efficiency and expanding the range of MDI's Air Car. And compared with four-stroke combustion engines, in which half of the strokes are wasted to pull air and fuel into the chamber, the air engine makes use of every stroke.

...Even though one of MDI's compressed-air tanks would carry the energy equivalent of just one gallon of gasoline, the use of that air in the engine is 90 percent efficient.

The first production model will feature a hybrid engine and will sell at more than double the price of the Tata Nano:

The first CAT car to be produced is called the OneCAT, a "utilitarian" car for urban and rural driving that's specifically designed for use in overcongested cities and priced in a range ($5,100 to $7,800) within reach of consumers in a developing economy, such as India.

The ultralight bodies of the vehicles would be made of glued-together fiberglass and injected foam, and the aluminum chassis would also be glued, not welded, to simplify manufacturin

Let's see where this goes...