Could a car run on compressed air?

[The Batt?sai]

Could a car run on compressed air?

Yes, it could. You could compress the air at your house using an air compressor, fill a compressed-air tank in the car, and the car could run off of it. You could use an engine very similar to a steam engine (using pressurized air instead of pressurized steam) to convert the compressed air to rotational energy.

The main problem you would have is the size of the "gas tank" you would need to get any kind of reasonable range. You would need a LOT of compressed air to take a car very far.

An alternative would be to use a liquefied gas like liquid nitrogen. You can think of liquid nitrogen as air that has been compressed so much it has liquefied. Liquid nitrogen is much denser than compressed air, so you could store enough in a car to give it reasonable range. You could then fill up at the liquid-nitrogen station.

A compressed air car would generate no pollution while you are driving. However, the power plant that produces the electricity that compresses the air (or liquifies the nitrogen, for that matter) is probably generating pollution from the coal or oil it is burning. Power plants are relatively clean and very efficient compared to car engines, so this is not a bad trade-off. Still, it's important to compare apples to apples.

Another thing that would be interesting to figure out is the efficiency of a liquid-nitrogen engine. If you burn gasoline in a car engine, only about 20 percent of it powers the wheels. The rest creates wasted heat. It would be interesting to see how efficient a power plant is, plus how efficient a nitrogen liquefier is, plus how efficient a liquid-nitrogen engine is -- that would tell you whether you were creating a technology that is better or worse than the gasoline engine in terms of efficiency.

 

[ch33zw1z]

hydrogen! similar problems though, but at least the biproduct is h2o.

 

[dartworth]

 

[ballmode]

taco bell can

 

[compnovice]

Your poll stinks

 

[JDrake]

I farted chalupas (compress that )

 

[TitanDiddly]

This has been minced and diced by the engineering community, including a variable camshaft engine that will let you run internal combustion and compression with the same engine block. The short of the matter is that it's far too inefficient.

 

[xSauronx]

seems like i recall reading an article last year about some group who invented a life-size shark (great white, maybe?) submarine. one diver can fit in, and instead of a propeller, it uses a closed compressed-air system to wave the tail for motion so there wouldnt be any bubbles

or am i crazy?

 

[LordMorpheus]

you get much more energy per volumn by running compressed hydrogen through a fuel cell, and much more still be storing the hydrogen in some other form (a lithium slurry, for example, or perhaps a nanotube storage tank (nanotubes can absord some ridiculous amount of hydrogen - i've seen figures of up to 60% their own weight, though the real number is probably closer to 30-40%)).

 

[Iron Woode]

there is a company in Europe experimenting with compressed air cars. I saw videos of the cars and the most notable thing was the noise (very loud), but its cool nonetheless.

 

[Cattlegod]

sure, but you will only make it around the block... if you are lucky

 

[CycloWizard]

I've built a car based on this principle. Instead of using compressed air/liquid nitrogen, I created a pressure buildup using a chemical reaction that gives a gaseous product from two liquid/solid reactants (for example, acetic acid and sodium bicarbonate). While the concept is appealing, the energy density is very low relative to gasoline, which is why gasoline is used currently instead of other potential fuels.

 

[MovingTarget]

Yes, it is possible, but probably more efficient in a hybrid setup. Text

 

[HamburgerBoy]

This reminds me of the movie where the guy opens the glove compartment of his car where a small oven is located inside. He carried around a pack of compressed air containers and threw them into the oven every once and a while to fuel his car.

 

[TitanDiddly]

Originally posted by: CycloWizard
I've built a car based on this principle. Instead of using compressed air/liquid nitrogen, I created a pressure buildup using a chemical reaction that gives a gaseous product from two liquid/solid reactants (for example, acetic acid and sodium bicarbonate). While the concept is appealing, the energy density is very low relative to gasoline, which is why gasoline is used currently instead of other potential fuels.

You're telling me that you ran a car on vinegar and baking soda?

 

[CycloWizard]

Originally posted by: TitanDiddly
You're telling me that you ran a car on vinegar and baking soda?

Didn't say how big the car was or how much vinegar/baking soda I used, but yes. It was for a national competition for super-dorks.

 

[GalvanizedYankee]

No, kinda silly idea. Compessed hydrogen for fuel, yes.

The huge diesel engines used in ships are started with compressed air. Half the cylinders have the vales open while the others spin it up to starting speed with compressed air. The fuel is turned on as the valves are closed. Starts with mucho smoke. Once running the other cylinders are fired.

Ships have large quantities of compressed air stored for clearing ballasts or flooded compartments once repair is done.

I know...OT in OT


...Galvanized

 

[TitanDiddly]

Originally posted by: CycloWizard

Originally posted by: TitanDiddly
You're telling me that you ran a car on vinegar and baking soda?

Didn't say how big the car was or how much vinegar/baking soda I used, but yes. It was for a national competition for super-dorks.

So this was a matchbox car, then.

 

[FoBoT]

keep thinking brainiacs

 

[Evadman]

That would take an insane amount of air. Remember, an internal combustion engine is basicly an air pump, so it will work in theroy. Lest bust out some math to see just how impractical it is. I don't usually do match in OT unless it is to own someone, but in this case Iw ill make an exception.

Lets assume we want to make the equivelent of 100 HP at 6000 RPM in a 200 cubic inch displacement engine. That is a pretty small engine for aUS car but the math will be slightly easier to assume with the round numbers. Lets also assume 100% efficency (zero friction loses). the average automotive engine is <30% efficient, but what the hey. It's easier for math

First, we need to figure out the pressure that must exist in the cyl to produce 100 HP at 6000 RPM. Horsepower is just a measure of torque over time. The way to figure this out is Horsepower = (Torque * RPM)/5252. But since we have a HP rating, we need to go backwards and more in depth. History lesson time!

Way back when we were trying to figure out how to compare work done by an engine (be it a horse or a gas motor) we had to have a baseline. Some guy named 'Watts' 9hence the term watt) decided thoughe experementation that a hourse could do 33,000 ft/lbs of work per minute. That means a horse generating 1 hp can raise 330 pounds 100 feet in one minute, 33 pounds 1,000 feet in one minute, or 1,000 pounds 33 feet in one minute. It doesn't matter what combination of feet and pounds; as long as the product equals 33,000 foot-pounds in one minute you have 1 hp. So lets break that down into what it means for a gasoline engine.

so we need to lift 33000 lbs in one minute for 1 HP. So that means that 33000 lbs must be supported by the 6000 revolutions that occour in that 1 minute time. We are going to further assume that the 4 strokes can be reduced to 2 (power on the down stroke, and not wory abouit expelling gasses. remember we are 100% effective for this. So, in that 6000 RPM, there are 6000 power strokes. That means that each stroke must do 5.5 lb/ft of work within that stroke time. 33000 ft/lbs divided by 6000rpm = 5.5 ft/lbs per horsepower, and we need 100 horsepower, so we need 550 ft/lbs per power stroke.

So how do you compute how much air that takes? You need to take the average pressure over the stroke of the piston from top dead center to bottom dead center and include the swept volume (cubic inch displacement). Now, we picked 200 Cubic inches earlier, but it doesn.t matter since we are assuming 100% efficiency. A higher pressure would take less volume at that pressure to do the work. likewise a lower pressure would take more volume at that pressure. But anyway, lets do the math.

200 cubic inch displacement means that for every revolution of the engine, 200 cubic inches are displaced. So the 6000 RPM we were at would require 6000 * 200 Cubic inches of air. That means we need 1,200,000 Cubic inches over 1 minute. But what pressure is this required to be at? We know we need 550 ft/lbs of work, and we have 200 cubic inches to do it in. convert the 200 cubic inches into feet and we get (200/(12*12)) = 1.39 cubic feet. And we need lbs, so we bust out the physics and start canceling units. So we get 550/1.39 pounds or 395.69 lbs per square foot mean pressure. Then turn that back into Inches, and we end up with 395.69/(12*12) = 2.74 PSI

What you say?! 2.74 PSI mean? that's easy. But you forget that we need 1.2 million cubic inches. that's 833 Cubic feet per minute at 2.74 PSI. But wait, there's more. As we said, that 2.74 needs to be the mean pressure. Since we are assuming 100% efficecy, that means that the pressure should be zero at the end of the stroke. So the mean of 2.74 PSI means that when 'injected' we need that pressure to be 5.48 PSI.

Ok, now we know how much air we need (833 CFM) and the pressure (5.48 PSI). Now, how do you store that? 5.48 PSI is a waste. That needs to be much much higher. Lets say we store it at an accident unfriendly 2000 PSI. (if you get in an accident, the tank will explode and kill everyone for 100's of miles . Ok, not really. but that is really high) So, how much room do we need? Simple math. Double the pressure, double the capacity. So we only need 415 CFM at 11 PSI. Now, lets say we have a tank that is the same size as 20 gallons of gas. one gallon is 231 cubic inches. 20 gallons is 4620 cubic inches, or 32.01 Cubic feet. (4620 / (12*12)) So at 2000 PSI we could store the equivelent of 2000/5.48 = 364 times more than we could at 5.48. That means that a 32 cubic foot tank has the equivelent of 364 * 32 = 11648 cubic feet of air. Or, using our 833 CFM needed above, that means that we have 11648/633 = 13.9 minutes of drive time, assuming we can use every last bit of stored power at 100% efficeincy.

Remember the 30% efficeint above? that means that in real life we would have about 13.9 * 0.3 = 4.1 minutes of drive time. I don't think I can make it that far in 4 minutes.

Originally posted by: FoBoT
keep thinking brainiacs

I thunk above.

 

[TWills2]

wow, no one has said ****** yet??? zzz

EDIT: meh ok sauron did nvm

 

[Evadman]

Originally posted by: GalvanizedYankee
Ships have large quantities of compressed air stored for clearing ballasts or flooded compartments once repair is done.
...Galvanized

They have it on board or they have big compressors?

 

[Iron Woode]

http://auto.howstuffworks.com/air-car.htm

fascinating.