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HOT AIR?

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unclesyd

Materials
Aug 21, 2002
9,819
How about compressed air as a fuel. Maybe pollution free but not free.


Saw it on Discovery Channel (US).
 
What happens when you let a lot of air out of a high pressure cylinder?

Also, how much energy does it take to compress that air in teh first place?

Air engines have a long history, these guys seem to be intent on avoiding 120 years of experience.





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
 
UNCLESYD: I went to the website and I am still confused. As yet there is insufficient information. Greglocock is right, how much energy to charge the air tanks, what is volume/pressure/etc. The fact is that all liquid and gaseous fueled engines are "air engines". It is the air that does the work, the fuel is only there to provide the energy to heat the air. As an engineer I am interested in the "air engine" but would like to see more data and information. Look at the size of the car. Reducing the size of the engine is one way of reducing emissions and getting good mileage. Go past all the hoopla there is fuel in there somewhere, be it gasoline/diesel/or soybean, its there.

Regards
Dave
 
Arggg... That is gobbldee gook... Torque is better so force is less on the crank?
 
Like everyone else say's, compressed air ain't cheap. The first lesson learned about plant utilities when I went to work and this was when NG was $0.04/Therm.

I didn't record the episode but from my recollection they never mentioned economy only the pollution free aspects of the vehicle in a city.

The piston and crank arrangement look very familiar to a 2 cylinder steam engine that I saw in one of my fathers books.
 
The critial point, in my opinion, is that they have to throttle the air as it comes out of the tank (One way or another). As they do so, the temperature will drop and the thing will freeze up.


For compressed air torpedoes they got around this by heating the expander, by burning fuel, so they turned it into a rather complex (but very high power to weight ratio) external combustion engine.

These guys will face the same problem


Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
 
Note that the max power on the graph shown by the air car folks at is only about 24 horsepower, not much. No wonder their car is so small --

There have been air powered cars built before. I saw an article twenty years ago on a compressed air powered automobile.
 
24 hp is plenty - the original Mini had only about 35, and could cruise at 80 mph, not really a requirement for a commuter car.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
 

I wouldn't want to be traveling at 80 MPH in such a small vehicle.

Besides, higher horsepower is used for acceleration, not cruising. The HP required at cruise conditions is small ( typically 8 - 25 HP, depending on vehicle size, aerodynamics, rolling resistance, etc).

I suspect that such a small vehicle would not fair well in a crash with a delivery truck, SUV, etc.

I notice that very small cars produced today have much more more than 24 HP. The air car would have to compete, in some sense, against better powered small commuter cars.

 
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