http://www.cnn.com/2008/TECH/08/08/air.car/index.html full story
You've heard of hybrids, electric cars and vehicles that can run on vegetable oil. But of all the contenders in the quest to produce the ultimate fuel-efficient car, this could be the first one to let you say, "fill it up with air." Whether the engine uses just air or both air and fuel would depend on how fast the car is going. It would run purely on compressed air at speeds less than 35 mph, Vencat said. Since the car could only go a short distance when using just air, fuel is needed to get the full range, he explained. "Above 35 mph, there is an external combustion system, which is basically a heater that uses a little bit of gasoline or biofuel or ethanol or vegetable oil that will heat the air," Vencat said. "Heating the air increases its volume, and by increasing its volume, it increases [the car's] range. That's why with one gallon of gasoline or its equivalent we are able to make over 100 mpg."
