compressed air propulsion

Discussion in 'DIY Marinizing' started by bnhk88, Aug 8, 2009.

  1. portacruise
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    portacruise Senior Member

    This air car concept has been promoted for well over 10 years with nothing to show, even the pictured one was due last year! Read some of the comments below the article written by engineers to get an idea why this is so inefficient and why it is being promoted. Not even the liquid nitrogen cars which are way more efficient than compressed air are close to being COST effective. Liquid nitrogen is available in most large cities at prices considerably above petrol. Or you extract liquid nitrogen from the air with a cryogenic refrigerator using electricity at home. But again, why not just power an electric motor directly with a recharged battery which is more efficient and cheaper?

    That's just the way I see it, anyway.

    Porta



     
  2. hoytedow
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    hoytedow Wood Butcher

    Isn't regular compressed air already about 70% nitrogen?
     
  3. Submarine Tom

    Submarine Tom Previous Member

    Closer to 80 % nitrogen. Why?
     
  4. hoytedow
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    hoytedow Wood Butcher

    Submarine Tom,
    I ask because some auto service advertise nitrogen for filling tires, on the claim that the N2 molecules are larger than the O2 molecules. While I do not dispute this, I figure that if as the tire loses pressure due to O2 sized micro leaks, the remaining gas in the tire will have a higher N2 percentage, anyway, so why pay a higher premium on inflation? This LOGIC? would also be applicable to the pressure tanks for propulsion, no?
     
  5. wardd
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    wardd Senior Member

    we're running out of oil now they want to use up all the air too
     
  6. portacruise
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    portacruise Senior Member

    Nitrogen molecules (formula weight 28) are smaller than oxygen molecules (formula weight 32). I think the reason for using nitrogen in tires has more to do with the fact that nitrogen does not significantly react with rubber, whereas oxygen (20% of air) would cause some degree of oxidation with rubber over time and possible leaks. I am not convinced that the DIFFERENCE is particularly significant unless 100% oxygen were being used in tires- without documented lab proof. On the surface, this just appears a case of marketing taking command over scientific illiteracy, IMHO.

    Nitrogen is fairly inert and not reacted or converted to another compound in most applications including the filling of air in tires. Some amounts are consumed in making fertilizer and explosives and by plant life in nitrogen fixation. But there's enough around and it gets regenerated enough to have remained at 80% as long as man has been around. The bigger threat to air would appear to be pollution from human activity added to whatever already occurs from natural processes.

    Porta

     
  7. mark775

    mark775 Guest

    I think that one advantage to nitrogen in tires is because some race cars might do it for the lower expansion, therefore greater control of pure nitrogen. Although gasses all expand at, I think, 33% per 100C, the deal is, you get pure nitrogen without water vapor which would change pressure much more as it converts to steam in a race tire. You also get a green valve-stem cap which screams "my wrung-out Corolla would be more capable than your rapped-out Civic at speeds we couldn't possibly achieve."
    See also: Folgers can exhaust for stimulating visual effect...
    images.jpg

    And: ricer wing conversation pieces ("Just think how much that stupid **** spent on that!")
    Split_Wing_Ricer.jpg
     
  8. hoytedow
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    hoytedow Wood Butcher

    Thanks for the enlightening.
     
  9. Submarine Tom

    Submarine Tom Previous Member

    I was tempted to put argon in my car tires at one point.

    It's readily available at dive shops now but figured it wasn't worth it.

    I know at one time ~100% nitrogen was being used in commercial aircraft tire inflation.
     
  10. Submarine Tom

    Submarine Tom Previous Member

    Compressed CO2 would be the way to go for propulsion. Phase change and expansion characteristics are impressive.

    Perhaps that's already been covered on this thread I can't recall and don't have time to review.

    Tom
     

  11. apex1

    apex1 Guest


    Lets make it short.........
    yes, but who would be soo stupid?
     
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