Car that Runs on Air

It’s zero emission and can be refuelled in two minutes with the stuff you breathe

The idea that a car could run on air and emit only pure air out of its exhaust pipe sounds a little farfetched. But French company MDI has developed an engine that does exactly that and built a car around it, the AirPod.

The physics involved is simple. A compressed gas in a confined space is a way to store energy. When the air is allowed to expand, energy is released that can do work. In MDI’s engine, air moves pistons up and down rather than an explosion generated when small amounts of fuel are injected.

But there are a few major obstacles to making a practical compressed air car, such as the issue of driving around with a large tank of highly compressed, potentially explosive gas. Safety concerns were addressed with the invention of an air tank made from carbon fibre and thermoplastic, designed to split with a hiss rather than shatter with an explosion.

Cleverly, the engine is reversible, so it could act as a compressor to fill the air tank when driven by an external electric motor. “Or you could fill the tank in under two minutes from a special air station,” says Cyril Negre, engineer and son of MDI’s founder. “But of course, compressing the air in the first place requires energy. If this is powered by renewable energy, the CO2 cost would be zero.”

MDI’s plans for the AirPod are advanced. “The car and engine are ready to go, and we want to sell it by the middle of next year,” says Negre. Car company Tata has also signed a deal to develop the engine for its own cars in India.

4 steps for AirPower

1. About 260 litres of air is compressed into a super-strong carbon fibre and thermoplastic tank at a pressure of around 258 bars.

2. The air is then fed into a pair of interconnected cylinders that contain two pistons.

3. The air entering the first cylinder creates a force on the first piston – just like the explosion phase of a regular petrol engine. This turns the crankshaft, providing the physical drive of the engine.

4. When the first cylinder’s piston reaches full extension, the leftover air forces its way through to the second cylinder, which also helps drive the crank.