Air Powered Car

[big tim]

Check this out:

http://news.en.autos.sympatico.msn.c...mentid=5044057

Tim

[Ed62]

I wonder how long it will take to squash that one.

Ed

[rbfunk]

I know that my local gas station doesn't supply air at 4000 psi at any price. And I am not sure if I want the guy down the street playing around with high pressure air. But I like the idea.
BTW I almost got run over by a Pirus. In electric mode those things are almost silent
Bob

[gerti]

Yeah, the 4000 psi from a gas station sounds very bogus to me to. And I wonder what the result of a crash test with an F150 would be...

I'd be scared to drive it here, but for inner-city traffic in Germany it would be ideal.

[LCHIEN]

Like you guys, I have yet to find a gas station with 4230 PSI at any price, let alone for free.
52 gallon tank, at 4000+ PSI? Going to be pretty big and heavy.
Thermodynamic motor? sounds like just compressed air in a piston.
I wonder how many facts in that article are wrong.

And, if you fill it up in Los Angeles and drive it to Orange County, you may be polluting as much as any gasoline powered car. (e.g. releasing all the smoggy air from LA in OC.)

P.S. OK - here';s the dope. MDI says that they ANTICIPATE that gas stations will install high pressure compressors (like the one pictured below) that can refil your car in 3 minutes. But, what a compressor!

[Slik Geek]

Check my calculations...

A 4,350 psi, 52 gallon tank of air contains a potential energy of 1.64 kW-hr. (Note that not all of that energy is usable, as the pressure drops, so does the useful power available. Nevertheless, lets assume every bit of energy is usable at 100% efficiency).

That amount of energy will deliver 1 horsepower for 2 hours, 15 horsepower for less than 9 minutes, 22 horsepower for less than 6 minutes.

Let's say it runs most efficiently at 20 mph (little drag from wind at that speed). The most efficient speed would be used to determine the maximum distance it could travel. 125 miles at 20 miles per hour would take 6-1/4 hours. At 100% efficiency and complete capacity utilization, our 1.64 kW-hr energy source would only be able to supply 0.35 horsepower during that period.

For reference purposes, the solar-powered "cars" seen in competitions have 2 to 10 horsepower motors. I'm guessing that this air-powered vehicle's claims are off by about a magnitude (factor of 10).

At best, the claims are theoretical assumptions by an inexperienced engineer who is ignoring drag, friction, inefficiencies, etc. Or, somebody is hoping to get a government grant from a well-meaning, gullible politician, and then later "discover" that "complications" prevent the vehicle from achieving its anticipated goals.

[cwsmith]

Seems to be some erroneous information or perhaps they're just assumptions on the part of the author. A 5,000 psi compressor is certainly going to cost some change. I worked for a compressor company for 30 years and I've seen some really huge compressors (oil refinery and pipeline applications) and some really small very high pressure systems; but with the latter, they don't supply much in the way of volume. To fill a 52 gallon tank would take some time and the cost would be substantial. (As would the electric bill, I'm sure.). But, a really big challenge would be supplying a 52 gallon receiver that could sustain 5,000 psi. While it's easy to see a tank of this size for 150 psi pressures, it would have to have much thicker walls, material, etc. for such very high pressure and that would increase its size and weight substantially I would think. You'd end up driving a two passenger, two or three ton Van with no cargo room!

And if the thing ever ruptured, the first thoughts of any surviving bystanders was that you must have been a terrorist!

CWS

[Uncle Cracker]

If they build a car that runs on hot air, then my ex-wife will be mobile for life...

[Anna]

Check my calculations...

A 4,350 psi, 52 gallon tank of air contains a potential energy of 1.64 kW-hr. (Note that not all of that energy is usable, as the pressure drops, so does the useful power available. Nevertheless, lets assume every bit of energy is usable at 100% efficiency).

That amount of energy will deliver 1 horsepower for 2 hours, 15 horsepower for less than 9 minutes, 22 horsepower for less than 6 minutes.

Let's say it runs most efficiently at 20 mph (little drag from wind at that speed). The most efficient speed would be used to determine the maximum distance it could travel. 125 miles at 20 miles per hour would take 6-1/4 hours. At 100% efficiency and complete capacity utilization, our 1.64 kW-hr energy source would only be able to supply 0.35 horsepower during that period.

Slik, how did you get to those numbers? My brain is too mushed right now to do the unsteady state calculations, but the equation should be

shaft work = change in enthalpy + change in kinetic energy

assuming there's no heat exchange (either adiabatic or isothermal). It's a typical classical thermo problem. Too tired to work on the differential equations and look up the enthalpy stuff. Can't assume ideal gas if it's isothermal because enthalpy change will become zero. I'd still be interested to know how you arrived at your values, though.

Anna

[LCHIEN]

I calculated based upon the formulaes in Wikipedia for energy storage.
Actually I found another page which took evaluated the constants for 24C and said
the energy per Std Cubic meter (KJ/NM^3) was
= 110 ln(PB/PA)
assuming the air is reduced from 4350 to 14.5 (300 ATM)
then I get 627 KJ/NM^3

and since 300 Atm in 52 Gal = 300*52 Std Gal (at 1 atm)
or 300 x 52 x .003785 M^3

then the stored energy is 37KJ or around 10.3 KW-Hr - the upper theoretical limit.

THis of course assumes that we can hold the temperature constant while we compress the air and then release it back which is in practice extremely difficult to do - it'll want to heat up when compressed and cool off when released both of which will rob the system of energy.

It also assumes you can extract useful work when the pressure differential gets very low, another problem.

[cabinetman]

Slik, how did you get to those numbers? My brain is too mushed right now to do the unsteady state calculations, but the equation should be

shaft work = change in enthalpy + change in kinetic energy

assuming there's no heat exchange (either adiabatic or isothermal). It's a typical classical thermo problem. Too tired to work on the differential equations and look up the enthalpy stuff. Can't assume ideal gas if it's isothermal because enthalpy change will become zero. I'd still be interested to know how you arrived at your values, though.

Anna

WHOA NELLIE!!! All I can say is "What the heck is all this?" I musta missed class the day they went over this. Anyway, I learned a long time ago, never argue with a woman.
.

[Stytooner]

I think it's quite doable for a downhill ride from Mt Everest. Wouldn't a 150 gallon air tank filled at sea level have more pressure if you took it up to the summit of Everest?. I am certain those speeds are easily attainable on the way down as well.

[Hellrazor]

Take a politician along, you will have enough hot air for many trips.

[Ed62]

Maybe I'm the only one in the world that thinks these alternative technologies are worth a look. Who's to say that new ways to make things work, can't happen? Maybe in the not too distant future, we can see cars running on air, and it will be practical. It might not be practical now, but I don't think we should give up on it just yet. No doubt, if it ever looks promising, the lobbyists will have their jobs to do. I think we should look at any possible technology, even if it appears not to have a chance. There was a time when people thought that saving an image (photography) was not possible.

Ed

[Stytooner]

I agree, Ed. I actually posted a link to an article a while back about these vehicles. In that particular article, it stated that there is also an onboard compressor that you could plug in and it would fill the tank overnight if there were no service centers available in the area. Sounds feasible to me.
I don't think this is a good comparison to new technologies, but if I had accepted that the blade guards that were available a while back were the best that this day and age could provide, there would be no Shark Guard.