The safety of tanks being driven around at 80 miles an hour while filled to a pressure of 300 atmospheres – which is a whopping 4,410 PSI (pounds per square inch), must come into question. The tanks AFAIK hold about 90 cubic metres of air at 300 bars. A regular metal tank exploding at this pressure would be quite dangerous.
So are these tanks a danger?? It would seem that the answer is NO. Why is that so? That, they say, is because these tanks have been tested to explosion level and all that happens, apart from a VERY VERY LOUD BANG, is the tanks split length ways but do not shatter.
The reason for this is because the tanks are made from what amounts to a wound fabric of carbon fibre. What would happen in an accident is; “An elongated crack would appear in the tank, without exploding, and the air would simply escape, producing a loud but harmless noise”. In fact they have been officially approved to carry an explosive gas such as methane (so they say).
The tanks can be filled by using a small on board compressor plugged into any electrical socket or by using a special high-power compressed air filling station. The on-board compressor would take a good deal of time to fill the tanks, whereas the specially designed filling station would do the job in minutes or a bit more in the case of the bigger US car with an extended range.
A refill in a filling station is estimated to cost about $2 - $3 US. When out of range of a compressed air source, or at night in the driveway, the owner can plug it into any household power socket, reducing the filling cost to the amount of electricity used.
An air engine would essentially be somewhat similar to a steam engine in its basic concept. But instead of steam pushing the pistons, you would have compressed air.
With steam engines you carried your gas in highly compressed liquid form – i.e. water. The water was turned into gas by a fire and the resultant steam pushed the pistons. The fuel to make the gas was the bulkier and heavier part of the load.
The air car in its simplest form will use only air and nothing else to run the car. This simple car will have a limited range. The bigger car planned will be more like the steam engine analogy in that it will use a heater to expand the air and give greater efficiency and a greater range.
The bigger car called the CityCat has a heater to heat the air before it is delivered to the piston. This expands the air and increases the pressure and the range of the car. The burner can burn many types of liquid fuel. They say that the car will do the equivalent of 120 mpg on long journeys. For shorter town journeys where it will run on air only it will be cheaper to run and be zero carbon.