Compressed Air Cars

[Tau Meson]

So, I've been looking at compressed air cars: http://www.popularmechanics.com/automotive/new_cars/4251491.html

 

They apparently have zero pollution and low running costs, and seem really really cool! Any idea as to when I can get one? On a more serious note, is the air car a credible alternative to the gasoline cars that are polluting our atmosphere?

[npts2020]

So, I've been looking at compressed air cars: http://www.popularmechanics.com/automotive/new_cars/4251491.html

 

They apparently have zero pollution and low running costs, and seem really really cool! Any idea as to when I can get one? On a more serious note, is the air car a credible alternative to the gasoline cars that are polluting our atmosphere?

 

Compressed air cars have limited range because of the storage limitations of compressed air, i.e. the materials used for the storage tanks will only take so much pressure before rupturing which means you are taking up lots of space just for storage. Secondly, you still have to compress the air. That inevitably means you get less energy from the compressed air than you use in compressing it.

[louis wu]

Pressure vessels have special regulatory requirements. In the UK the safety relief systems need to be reset every 12-14 months. The pressure vessel itself requires an internal and external examination by an expert; alternatively a hydraulic pressure test to 1.5 times the rated pressure is carried out.

This is not a convenient procedure to carry out on a vehicle.

 

The weight penalty from containment for gas at 4000psi is high but somewhat offset by weight savings on a simpler engine. The real problem is that compressed air is outperformed as an energy source by just about any other option usable in a vehicle.

 

Compressed air cars are not coming to a showroom near you because they do not make engineering sense.

[CaptainPanic]

Compressed air cars also pollute. But the pollution does not come from the car's exhaust. Instead, it comes from the chimney/exhaust of the air-compression-facility.

[Cap'n Refsmmat]

Compressed air cars are not coming to a showroom near you because they do not make engineering sense.

Also, a car whose engine sounds like a prolonged fart would have trouble catching on.

 

It is interesting that the Popular Mechanics article claims a 800- to 1000-mile range for a compressed-air engine. For a small car, either that's a whole lot of compressed air or something else clever is being done...

[Mr Skeptic]

What about using compressed air for a large truck? The bigger the better, as the volume of air grows with the cube and the area with the square of size. Essentially, it is like a battery since it would need to be recharged, presumably with grid electricity. I wouldn't want to crash one of them though.

[louis wu]

Also, a car whose engine sounds like a prolonged fart would have trouble catching on.

 

It is interesting that the Popular Mechanics article claims a 800- to 1000-mile range for a compressed-air engine. For a small car, either that's a whole lot of compressed air or something else clever is being done...

Popular mechanics are not themselves claiming anything.

They are reporting claims from a company, who say they are on the verge of putting such a car into production. Apparently such claims have been made for years with no actual cars being produced and no prototypes actually demonstrating the claimed range.

Even at 60MPa pressure ~9000psi compressed air contains far far less energy than petrol per litre.

Compressed air is just not a good enough energy source for long distance car journeys.

 

Using grid electricity to compress the air is highly inefficient, as all the heat energy imparted to the compressed gas is wasted. As the air expands upon release for use in the engine it cools drastically, some sort of heater or heat exchanger will be needed to keep the system at reasonable temperature.

Do not mortgage your house to invest in this technology as thermodynamics says it cannot work.