Home General Compressed Air: The Ultimate Alternative Fuel or a Load of Hot Air?

Compressed Air: The Ultimate Alternative Fuel or a Load of Hot Air?


Climate change and the impact of automotives on the environment is quite often the elephant in the room when it comes to discussing cars; while we’re quite comfortable talking up the horsepower and traction control a particular new motor happens to have, the issue of emissions and fuel consumption is often quietly swept under the carpet or framed through the prism of cost rather than impact on the environment.

Unfortunately, the impact of cars on the environment is something we won’t be able to avoid much longer. The Earth is getting hotter as the levels of CO2 in the atmosphere increase; in fact, we may have already passed the tipping point at which we can avert potential ecological disaster. Similarly, fossil fuel is running low. We are literally running out of ways to keep our cars running.

It’s not all doom and gloom, however. In recognition of the impending environmental issues we’re all facing, car designers and manufacturers have been scrambling around for a way to make automotives more sustainable. And for a while, compressed air seemed to be the answer.

If you’re not familiar, air compression is the process of taking air and…well, compressing it into a smaller size. The energy generated by this compression can then be converted into mechanical energy, the kind of energy that potentially be harnessed to power a vehicle. A car, powered entirely by air – the answer to all of our problems, surely?

The idea of powering a car isn’t exactly a new one; for decades, Motor Development International have been hard at work trying to incorporate compressed air technology into commercial vehicles. More recently, they’ve cut out the middleman and developed their own vehicle, the AirPod.

The AirPod is a city car with a difference; rather than a steering wheel, it’s controlled by a joystick. It’s lightweight and kind of looks like a bubble car.  Most importantly, it’s powered entirely by compressed air.

Rather than filling the AirPod up at a petrol station, you instead use an air compressor to charge it up. This compressor takes around 2-3 minutes to fill the car, which can then trundle through the streets at a top speed of 28mph for around 137 miles (according to MDI). The car itself only costs around £5000.

Well, it would – if the car was actually available on the market. Unfortunately, like many of MDI’s previous ventures, the AirPod has yet to reach production. Production of the vehicle was first promised in the year 2000.

So what has stopped the AirPod from reaching the commercial market? One of the main reasons is the relative inefficiency of compressed air in relation to traditional fuel; a 200 litre tank, for example, only produces the energy of just over a litre of gasoline.

The loss of energy across the air compression process is quite drastic too; to reach the point at which at it can be used to power a vehicle, electricity is required to power an air compressor, which in turn compresses air, which is then converted into mechanical energy. At each point of this process, energy is lost, leading to an overall loss of power that is dramatic compared to other forms of powering a car.

Although compressed air is often sold on its zero-emission merits, this isn’t strictly true either. While air itself is an entirely clean resource, air compressors are notorious for their high levels of electricity consumption. Essentially, fossil fuels are still required in the process of powering the car, making the process not quite as clean and eco-friendly as it would first appear.

The nature of compressed air also presents a problem. As air expands, it loses heat. This heat, however, is essential in powering the engine of the vehicle. Therefore, heaters need to be installed into order to keep the air from cooling down too much, consuming a significant proportion of energy.

Another issue lies with icing, which occurs when the humidity in compressed air condenses and freezes. This icing can lead to vital lines being blocked, hampering the operation of the engine. In industrial compressed air systems, this is dealt with using a compressed air dryer, a device that removes moisture from air. Unfortunately, these devices are quite bulky and incorporating such a device into a vehicle would present a design challenge.

Compressed air, then, faces a lot of obstacles before it can be harnessed solely as an alternative fuel – if, indeed, it ever can be.

That doesn’t mean that it is entirely useless, however; Peugeot Citreon have recently announced a range of vehicles combining compressed air and gasoline. The new vehicles will use regenerative braking to store energy as compressed air for later use. Compressed air could yet still represent the future of motoring.

About our Guest Author:
Chris Smith is an automotive enthusiast currently working with Excel Compressors, a company specialising in the supply of air compressors for automotive purposes.

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