Compressed Air Car

March 12, 2007 6:42 AM

What could be the most viable environmentally friendly car? I some how focused in compressed air powered cars.

Let's get some ideas going here.
I was looking at

http://auto.xprize.org

and started to do some research.

What could be the most viable environmentally friendly car? I some how focused in compressed air powered cars.

http://www.digitaljournal.com/article/116641/Car_Runs_on_Compressed_Air

http://www.theaircar.com

This seems to be ... from what I've read so far... the best method. It uses current technology and there is no bad byproduct. In a big picture I assume compressing air in mass can be done via wind, water, nuclear power...

There are fair amount of ethanol, hydrogen, etc powered car info.... but strangely there aren't too many compressed air car information... Is it a technology that just doesn't work? Is it not better than other technology?

Check out the digital journal video posted above.

Please tell me anything regarding the Air powered cars, X Prize, and why other technolgy is better.

I will be on THIS all day.

posted by curiousleo to Technology (19 answers total)

Well, can't go wrong reading the wikis:
http://en.wikipedia.org/wiki/Air_car
http://en.wikipedia.org/wiki/Air_engine#Advantages

Looks like heat and distance are the biggest limiting factors to the technology.
posted by cowbellemoo at 7:00 AM on March 12, 2007

Response by poster: cowbellemoo... I have read this before... The distance factor seems to be similar to other battery powered cars... but I also read that MDI cars can go reasonable commuting distances if not more... The heat though... I am having hard time understand this... Are they saying there is too much heat or too little...? hmm... I will keep on reading... (Fast simple great finds.. thanks)

I am curious if any of those air powered car companies' claims are anywhere close to realistic.....
These guys are claiming reasonable distance with extreamly low cost comparably.......

Non of other alternative cars seems to do this both....
posted by curiousleo at 7:22 AM on March 12, 2007

So what is the best way to compress air?

With a gasoline powered air compressor......
posted by JJ86 at 7:34 AM on March 12, 2007

Response by poster: JJ86... If air can be compressed in volume at a controlled place... wouldn't it save much more energy than having to use gasoline in each cars?....
posted by curiousleo at 7:42 AM on March 12, 2007

I'd be interested to hear about the efficiencies of compressed air vs. batteries for energy storage. Perhaps compressed air could be used in hybrid vehicles. At the very least an air tank has got to be lighter, less expensive, and less problematic to dispose of than a lithium battery. However, I'm not sure whether regenerative braking would be directly possible with an air tank (you'd need an electric compressor, I think).
posted by kindall at 7:47 AM on March 12, 2007

a) That car has been coming onto the market later this year for about ten years now.

b) Since you'll compress the air with coal-generated electricity, the environmental benefits are marginal.

c) Filling the tank is not an easy problem. It will have a tendency to either become extremely hot or extremely cold, depending on how it is filled. (Compressing air produces a lot of heat.)

d) Running the car is not an easy problem. It will have a tendency to freeze up. (Letting air expand from a compressed state sucks in a lot of heat, or produces a lot of cold, depending on how you look at it.) If your engine is always at -10C, moisture from the air is going to freeze onto it and you'll have a giant ice block instead of an engine.

e) Gasoline has something like 100 times the energy density of compressed air, so you'd need to carry 100 times as much compressed air to get similar cruising range in your car... Plus you've got to carry the tank itself. A car gas tank is made of thin steel and you can lift it with one hand. A 4500 psi air tank is HEAVY. The weight of the tank reduces the range of your vehicle.

f) People are killed routinely by exploding truck tires (around 90 psi); do you really want to sit on a giant (see point e) 4500 psi air tank? Really?
posted by jellicle at 7:51 AM on March 12, 2007 [1 favorite]

g) inefficiencies introduced by a non-isothermal compression and a non-isothermal expansion of the compressed air, meaning you have to burn more coal (or whatever) than you would otherwise.
posted by sergeant sandwich at 7:54 AM on March 12, 2007

Response by poster: jellicle & sergeant sandwich...
So the compress air tech from those companies are unproven in real world? I assume compressing air part is actually a easier one since what ever the machine that is compressing can be powered by environment friendly stationary power souces which can not easily be implimented to individual vehicles....

The other problems are hmmm.. problems....
The possibility of explosion does scare me... but would that be the similar problem for Hydrogen or even ACID Battery powered car?......

I guess I am hoping the dream of air-powered car can be done.... if not... what do you subjectively think is real possibility?
posted by curiousleo at 8:05 AM on March 12, 2007

curiosleo asked: If air can be compressed in volume at a controlled place... wouldn't it save much more energy than having to use gasoline in each cars?....

Centralizing air compression may not result in any savings. You would still need distribution to filling stations. Also to keep the pressure constant during transferrence of the compressed air, you will need to maintain that pressure with on-demand compressor pumps.
posted by JJ86 at 8:28 AM on March 12, 2007

well, an isothermal processes are very slow and totally impractical for things like recharging and driving around. the reality is probably an adiabatic process which basically involves a non-recoverable loss due to heating (or cooling) the air during the compression/expansion.

so while i wouldn't say that the numbers are "unproven" they reflect a 100% efficiency which is not realistic unless you're spending 2 days filling and discharging your air tank.

a real possibility is a highly porous, solid-state hydrogen storage material (not a compressed gas tank.), and a fuel cell that doesn't cost a bajiggledyzillion dollars. the chemistry is not there yet, though.
posted by sergeant sandwich at 8:33 AM on March 12, 2007

If you can get that much energy from compressed air, why have I never heard of any of the designs that use compressed hydrogen getting energy both from the storage pressure and the combustion?
posted by sfenders at 8:43 AM on March 12, 2007

If you can get that much energy from compressed air, why have I never heard of any of the designs that use compressed hydrogen getting energy both from the storage pressure and the combustion?

I'm pretty sure that we have.
posted by delmoi at 9:02 AM on March 12, 2007

Since you'll compress the air with coal-generated electricity, the environmental benefits are marginal.

There are definite benefits to favoring point over nonpoint pollution sources. Pollution controls that may be uneconomic to place on every car may be installed on a central power plant pretty easily.
posted by electroboy at 9:06 AM on March 12, 2007

The real benefit of battery/air/hamster wheel cars is not that they use less energy, (it's hard to beat the potential energy in a gallon of gasoline). It's that isolating the energy requirements to a few facilities allows for change in those facilities to affect a huge number of cars on the road. Find a more efficient or cleaner power source and retrofit your air compressor (or electric plant) and you've made a _huge_ change in one step.
posted by monkeymadness at 10:08 AM on March 12, 2007

Thanks, electroboy. You've made me redundant.
posted by monkeymadness at 10:14 AM on March 12, 2007

Then perhaps you could point to an example, delmoi? Far as I can tell, virtually all the hydrogen fuel cell and ICE designs use a normal pressure regulator. None of them that I can find on the web try to derive mechanical energy from the gas storage pressure. Waste heat from the engine can be used to warm up the gas, but I think there's typically still a surplus of heat. So maybe there's a place for an "energy recovery rotary pressure regulator" (quasiturbine) or something like it.
posted by sfenders at 1:30 PM on March 12, 2007

As I understand it, the reason it's not generally worth recovering mechanical potential energy from compressed hydrogen is that the amount of energy so available is completely dwarfed by the chemical potential energy available from the same hydrogen; you get a better overall energy return from designing out the recovery turbine's mass.

Also, from a safety point of view you want as few openings in your high pressure hydrogen tank as possible. Far better to put a simple regulator inside the tank where all the high pressure is at, and make the only opening in the tank a simple outlet for regulated (low-pressure) fuel gas.

Current high-pressure hydrogen fuel tanks run around 10000 PSI, by the way.
posted by flabdablet at 3:54 PM on March 12, 2007

the amount of energy so available is completely dwarfed by the chemical potential energy available from the same hydrogen

Well, that's what I would have guessed before considering the Air Car. At 10000psi, estimating wildly using various numbers taken from unreliable sources, I think you might potentially see a 5-15% increase in fuel efficiency. Nothing too astounding, but maybe enough to be worth thinking about. Or, it would be if we were really going to run cars on hydrogen. Safety and reliability concerns at that pressure would make it somewhat difficult, yeah.
posted by sfenders at 5:56 PM on March 12, 2007

I've just noticed that the original question was "what would be the most viable environmentally friendly car?"

The folks at Tesla Motors seem to think the answer to that is battery electric, and they appear to be putting their money where their mouth is. Their first product is a high-priced, high-performance sports car, designed to attract attention and make them enough money to extend the product range downmarket.
posted by flabdablet at 6:21 PM on March 13, 2007