Has anyone heard of the air car? It runs on pressurized air which seems a better idea than using energy or water to create hydrogen.
Yes, and it seems to have a mixed crowd of doubters and supporters. Certainly, a fair amount of energy goes in to pressurizing the tanks which power the car, but if the energy used to operate the compressor comes from a clean source, then maybe we’re getting somewhere. Of course, there is the argument that if you’re going to power a compressor with -for example- a hydrogen fuel cell, and then use that compressor to fill a tank, and use the contents of that tank to power a car, why not just power the car with the hydrogen fuel cell in the first place?
Don’t really know much about them, but this is courtesy of Wikipedia (which we all know is always 100% accurate):
- Advantages -
The principal advantages of an air powered vehicle are:
- Compressed air engine reduces the cost of vehicle production by about 20%, because there is no need to build a cooling system, fuel tank, spark plugs or silencers.
- Most compressed air engines do not need a transmission, just a flow control.
- Very low self-discharge rate (most batteries will deplete their charge without external load at a rate determined by the chemistry, design, and size, while compressed gas storage will have an extremely low leakage rate)
- Long storage lifetime device (electric vehicle batteries have a limited useful number of cycles, and sometimes a limited calendar lifetime, irrespective of use). This means that batteries in operation are much more expensive than compressed air storage, and are more pollutant because a lot more pollutant material needs to be used (typical car batteries are made from sulfuric acids and lead).
- Lower initial cost than battery electric vehicles when mass produced. One estimate is ?3,000,
- Compressed air not subject to fuel tax at present (one taxing method would apply also to electric cars by taxing the electricity used for compression or charging).
- Expansion of the compressed air reduces its temperature and heat from the passenger compartment may be cooled using a heat exchanger, providing both relief from hot weather by air conditioning and increased efficiency.
- Zero pollutant emissions from the vehicle itself.
- Compressed air is not a fire hazard, only a rapid depressurization hazard (this can be mitigated by using carbon fiber tanks).
- Air turbine technology, closely related to steam turbine technology, is a practice over 50 years old. It is simple to achieve with low tech materials. This would mean that developing countries, and rapidly growing countries like China and India, could easily implement a less polluting means of personal transportation than an internal combustion engine automobile.
- Disadvantages -
Having solved most of the high pressure storage and handling problems, the main remaining disadvantages are related to the thermodynamics.
- At the supply station, compressing the air heats it, and if then directly transferred in a heated state to the vehicle storage tanks will then cool and reduce the pressure. If cooled before transfer, the energy in this heat will be lost unless sophisticated low grade heat utilization is employed (see cogeneration).
- Within the vehicle, expansion and consequent pressure reduction in the throttle or engine chills the air, reducing its effective pressure. This is called Adiabatic expansion. Addition of ambient heat will increase this pressure and this addition leads to a more complex propulsion system, and the necessity for an onboard fuel tank and heater system. While an attempt was made in the N?gre system to warm the air in a long portion of the stroke at top dead center, it appears that this scheme has been abandoned due to inherent imbalances causing unacceptable levels of vibration.
- Passenger compartment heating is more difficult since the propulsion system does not provide a source of waste heat. Some form of heat pump, or more likely, an electric heater would be required.
- Limited range due to available tank technology. The air engine suffers from similar problems to hydrogen vehicles in this regard.
- Using energy to compress air is less efficient than charging a battery with that same energy.
- Less efficient than electric motors.
- While the air engine reduces greenhouse gas emissions from the vehicle, the energy used to compress the air may not come from clean sources.
- Long refill times when compared to conventional automobiles, circa 4 Hours using a home or low-end system, though only a few minutes at a commercial refilling station, which is really an advantage because conventional cars can not be refueled at home.
- Overall efficiency is approximately one third of a comparable electric car 
Top Gear did a feature on this a while ago and another review is posted on youtube : http://www.youtube.com/watch?v=QmqpGZv0YT4
I think it’s pretty neat, and yes it does work.
Well it does not really use pressurized air as a fuel any more than a battery powered car uses electricity or a hydrogen car uses hydrogen. Hydrogen, electricity and compressed air are all just ways of storing energy. Each has its advantages and disadvantages. Each also requires some source of energy (coal oil water/wind power etc).
Compressed air only stores the energy. It has advantages, but so far does not have a viable economic use.
Pneumatic locomotives were used in coal mines and other places where a fire would be hazardous in the past.
I don’t see why it wouldn’t work today, for short trip neighborhood vehicles. Perhaps this technology could be compounded with an internal combustion engine to recover some of the energy needed to compress the natural gas burned in CNG powered cars.
Thank you Scudder . . . GREAT link! Rocketman