This car runs on the ultimate emissions-free fuel: air.

In 2007, Mumbai, India-based Tata Motors signed a licensing deal with Motor Development International, a French design firm. The idea was to build a car that could run on compressed air. Now Tata says it has tested two cars with the engines. The next step is setting up the manufacturing plants to actually build them.

Compressed air engines aren’t a new idea. The first models were proposed more than a century ago, and they were used in the mining industry for decades before electric motors became commonplace. Even now, compressed air powers all kinds of tools, notably the pneumatic impact wrenches in auto body shops.

A compressed air car engine works in a way similar to the internal combustion version: Fuel forces pistons to turn a crankshaft and power the car. The difference is that in a compressed air engine, the pistons are moved by air and not gasoline. Researchers in Sweden have experimented with single-cylinder engines of this type. 

The only problem is power. Air compression alone only gets a car moving to about 30 to 35 miles per hour. So to supplement that, the car could take in more air as it moves faster, using an onboard air compressor. The air compressor could be electric or, more likely, gasoline-powered. But even that would reduce emissions a lot, since the gasoline engine wouldn’t be running at lower speeds.

Tata seems to be the only manufacturer that has committed to actually building an air-powered car. Honda unveiled an air-powered concept car in 2010, and a company called Zero Pollution Motors had promised to deliver one to the United States — but that was two years ago. (The company’s website domain is no longer in use.) If Tata is successful, it will go