What would it be like if your local garage ran out of fuel? And it will happen..the only question – is  – when?

But the air if free and pollution-free – so can cars run on fresh air?

The answers is that – yes – they can. But…

Air alone cannot be used as fuel, It has to be compressed in order to store energy – and that needs an alternative source of energy which will be polluting – tho far less of it then in conventional vehicles.

Various companies are seeking to develop compressed air cars that are efficient and safe,  cheap to run, non-polluting and acceptable to the market. But, limited range and low engine temperatures are challenges to the engineers and designers.  Yet, in fact, since 1920 there have been compressed air cars –  of sorts.


A compressed air car

A compressed air car is one that uses compressed air to power it. But hybrid forms are more likely – using gasoline, diesel, ethanol electric, and they tend to have regenerative braking.

Regenerative braking – is a clever idea.

Normally the brakes expend power by the heat of friction, but with regenerative braking this heat loss is converted back into power to run the car – clever – eh!

What a compressed air car needs

The car needs a tank to store the compressed air and a system to release the air to power the engine. You would also need a way to fill the tank – and this could be done at home – taking about 4 hours – or it could be done at a garage with the necessary equipment for about 4 minutes – take your pick!

It needs a temperature control mechanism both to prevent overheating as the air is compressed and overcooling as the air is released.

How a compressed air car works – in brief!

One way in which a compressed-air car works is that the air is stored in a tank. When you push the accelerator it releases a valve on the tank which lets air escape into a pipe. It then passes to the engine and pushes against the pistons which makes the crankshaft turn.

Advantages of using compressed air

  • Almost pollution free – if a hybrid car then the other elements may be polluting – but in far smaller quantities than when used alone.
  • Could, in theory, refuel at home say overnight
  • The can stand for long periods with a full tank and still be serviceable when required (unlike battery cars where the battery leaks)
  • When the air expands on use it cools and this cooling could be converted to temperature control within the car.
  • Recovery from the  braking energy by compressing and storing air is possible
  • Hybrid air cars are very efficient
  • Very safe in case of accident of tank rupture – air won’t poison you unless you deliberately inhale large quantities by choice.
  • Cheap to build the body of the-vehicles as a lightweight body to the car will increase efficiency.
  • And probably cheap to run.

Disadvantages of using compressed air

  • The size of the tank – it needs to be large! Compressing nitrogen until it is liquid might be one solution round as liquid nitrogen is denser than the gas and takes up far less room than the gaseous form – and yo would refill ara liquid nitrogen station!

Motor development international (MDI) a French company are pioneering the way, their cars are likely to have tanks to hold about 3,200 cubic feet of compressed air. As the air is released it will push against the pistons and power up to about 35miles per hour. After that a motor will kick in, not only to provide more power to the engine but also to compress more air as you drive.

  • There must be a power plant of some description and that needs to mechanically compress the air into the tank. The car’s engine then converts the compressed air into mechanical energy to turn the wheels and light the lights.
  • When air expands it cools down – and this can be sufficient to ice up the engine in cooler climates. So heating may be needed. Conversely, as the air is compressed it heats up – so you need a cooling system as well! A heat exchanger needs to be a part of the system.
  • Travelling distance  – The only published report of ann air-only car travelled just under 4 ½ miles. But a hybrid car could possibly go for 200 miles or more as advances in development happen. The hybrid part would be polluting.
  • The light-weight aluminium construction of the car is less of a lethal consideration than he structure of the body of the car in protecting you against collisions the larger cars are safer, not so much because they are heavier, but because their shape has extra room for cushioning than smaller cars.

What might come on the market

Peugeot and Citroen intend to build a hybrid car that uses gasoline for speeds over km/hour, or when the air in the tank has all been used up.

Enginair from Australis has a new rotary engine which might play a part.

Tata is hoping to start production of a compressed air car next year, perhaps for the Indian market.


Alternative sources of fuel for our cars must come – and the air is free and plentiful. There is a lot of interest in designing systems that allow car owners to travel distances and that are safe and economical – and the future of compressed air cars is full of potential.

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