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Could you create thrust with water vapor?

  1. Apr 3, 2017 #1
    Whilst I was thinking of hydrogen combustion jet engines. I thought of a little idea... What if you could create thrust with water vapor the same way you could with the exhaust gas of a jet engine. (NOTE: I have no experience in engineering and I only have a mild interest in it).
    If this is possible please let me know.
     
  2. jcsd
  3. Apr 3, 2017 #2
    Rockets that burn hydrogen produce thrust with water vapor.
    I don't believe that there are any engineering issues it making a jet engine burn hydrogen.

    The key is providing energy to the system. When you burn jet fuel, you get carbon dioxide, water vapor, and a lot of energy to drive the jet engine and produce thrust.
     
  4. Apr 3, 2017 #3
  5. Apr 3, 2017 #4
    Thank you, I just didn't know if the mass of the vapor would actually propel something at speeds that it could lift a aircraft.
     
  6. Apr 3, 2017 #5
    Back in the 60's/70's the military experimented with a rocket backpack that used hydrogen peroxide as fuel, passing it over a catalyst to produce steam. The steam exited through a nozzle, producing enough thrust to lift a man vertically. I actually saw one in use, where a guy flew in a quick circle inside a football stadium, and it was incredibly loud.
     
  7. Apr 3, 2017 #6

    berkeman

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  8. Apr 3, 2017 #7

    Nidum

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    Hydrogen peroxide / catalyst rocket engines use essentially steam for generating thrust . Some of these engines have been very powerful indeed . Other smaller ones have been used for steering thrusters and in jet packs .The same principle has also been used to drive turbines for short duration high power applications .
     
  9. Apr 3, 2017 #8
    I also was curious after reading this post and i should do research before conversing about such a topic however, i do not think that water vapor would create the power to run the rotors the same that the fuel does. while water vapor can do many tasks that gas exhaust can, i'm not sure that it would create quite enough thrust to push such a large craft through the air. while aerodynamics also play a part, the engine needs to run and water does not hold the properties necessary to generate nearly the power that gas could. this is very interesting though and if i learn any new findings i'll be sure to find your profile again so we can converse.
     
  10. Apr 4, 2017 #9

    CWatters

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    First done by Heron/Hero in the first century AD...

    first-steam-engine.jpg
     
  11. Apr 4, 2017 #10

    CWatters

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    One issue is that water has a high latent heat capacity (2258kJ/kg) so it takes a lot of energy to turn it into steam. Depending on what you were trying to do it might be better to use liquid nitrogen which has a specific heat capacity 1/10th of that of water (199kJ/kg) but isn't so readily available :-)
     
  12. Apr 4, 2017 #11

    CWatters

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    Fuel releases chemical energy when it is reacted with oxygen in the air (eg it's burnt).

    Water is burnt Hydrogen (H20) so the chemical energy has already been released when the water was made. You can't burn water again so to turn it from water into water vapour (aka Steam) another source of energy would have to be found. You would have to use another fuel to make the steam.

    The main problem is weight. An aircraft would have to carry the weight of the water as well as the fuel when really only the fuel is needed.
     
  13. Apr 5, 2017 #12
    I never thought about the fact of having to actually produce the vapor but this does make a great deal of sense. Until later years, water would not be capable of said task which I'm sure I could have summed up better than how I did.
     
  14. Apr 5, 2017 #13
  15. Apr 6, 2017 #14

    CWatters

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    Its possible but difficult to make a rocket powered by liquid hydrogen and oxygen....

    https://www.nasa.gov/topics/technology/hydrogen/hydrogen_fuel_of_choice.html
     
  16. May 29, 2017 #15
    This is amazing to me as just sitting here thinking the same possibilities. But couldn't one use sea water using the salt as a catalyst only for a short period, and then remain operational using relitive humidity? Salt or sodium reacts fiercely To h20 such as sodium metal, but what other element in reverse could control the reaction? I suppose this would reduce the amount of water or fuel you would have to carry at any given time and where ever the is water you could refuel ! Cheers Rick
     
  17. May 29, 2017 #16

    CWatters

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    With most forms of transport what matters is the specific energy. That is how much energy does each kg of fuel produce. So how much energy do you get if you react 1kg of sodium with water?....

    Google found..
    http://efce.info/efce_media/-p-1476.pdf?rewrite_engine=id
    1 mol is about 23 grams so 46 grams (23g water, 23g sodium) produce 141 kJ.
    That gives an energy density of about 3MJ/Kg.
     
  18. May 29, 2017 #17

    RonL

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    Here are a couple of examples that I crossed this morning while looking for some other answers :smile:

    https://en.wikipedia.org/wiki/Steam_explosion

    https://en.wikipedia.org/wiki/Boiling_liquid_expanding_vapor_explosion

    Have water ? Just add heat :smile:

    ps. Just an added thought, in general people think in large scale operations, but for size considerations of steam burst doing work, look at the bubble jet printer operations. :wink: :cool:
     
    Last edited: May 29, 2017
  19. May 29, 2017 #18
    While quite violent, both of the 2 examples above, It couldn't be ruled out that this sort of thing could not be controlled to a degree if not controlled in full.

    http://efce.info/efce_media/-p-1476.pdf?rewrite_engine=id And I found that this was written well, and really showed potential moving fwd
     
  20. May 31, 2017 #19
    There are also many other things to be considered. It is common in Gas Turbines to use water injection to improve efficiency. Primarily this is in stationary power plants. It is usually used to improve emissions. On the other side If we break down a Gas Turbine engine to the components of (1) Gas generator which produces high velocity gasses and (2) Power turbine which extracts energy from the moving hot gasses. In every case the power plant can observe in increase in extracted energy when water injection is used. This is due to the higher mass flow rate of the exhaust gas.. More Kinetic energy must show up somewhere.
    Stationary plants this is not unusual as it provides many benefits. In a mobile system such as a plane the additional power required to carry the water does not outweigh the cost of carrying it and so it is cost prohibitive.
     
  21. May 31, 2017 #20
    This is relative to our current technology and using a gas turbine engine fueled by petroleum products. Additionally, at 20-30-40 thousand ft above sea level, there is enough moisture in the air current aircraft I believe already do rely upon water vapour or could collect it in transit. There is nothing Economical in every sense of the word about a gas turbine engine.
     
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