It uses the expansion of compressed air to drive the pistons in a modified piston engine. The only exhaust gas is cold air (-15º Celsius), which is also used for air conditioning in a car. The source for air is a pressurized carbon-fiber tank holding air at 3,000 p.s.i (20 MPa). Air is delivered to the engine via a pretty much conventional injection system.
This engine is used to power an urban car with room for five passengers and a range of about 100 to 200 miles, depending on traffic conditions. The main advantages are: no roadside emissions, low cost technology, engine uses food oil for lubrication (just about 1 liter, changes only every 30,000 miles) and integrated air conditioning. Range could be quickly tripled, since there are already carbon fiber tanks which have passed safety standards holding gas at 10,000 p.s.i. (70 MPa).
The tanks may be refilled in about three minutes at a service station, or in a few hours at home plugging the car into the electric grid via an on-board compressor. The cost of refilling is about $3.
However, the air engine and refueling system, considered as a system, are not pollution free, as the electric power generation will have its own environmental costs.