India’s largest automaker is set to start producing the world’s first commercial air-powered vehicle. The Air Car, developed by ex-Formula One engineer Guy Nègre for Luxembourg-based MDI, uses compressed air, as opposed to the gas-and-oxygen explosions of internal-combustion models, to push its engine’s pistons. Some 6000 zero-emissions Air Cars are scheduled to hit Indian streets in August of 2008.

With a top speed of 68mph and a 125 mile range, this car might be a little shabby for a full-fledged family car, but they are decent enough for urban transit, especially considering the cost: 340 liters of air compressed at 4350 psi can be refilled in a few minutes, at only $2.

I have always wondered about the validity of an “air-car” though. While it certainly sounds very green – powered by air, does no harmful emissions at all – physics tells me that the work required to compress the air would have to involve some sort of energy input somewhere, whether it be at the car’s compressor, or the delivery pump. What do these pumps run on? Oil? Electricity? Is the compressed-air engine more efficient than the combustion engine?