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hydrogen help

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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hydrogen help

Unread postAuthor: steel spuds » Sun May 11, 2008 4:50 am

hi all my spud guns are steel (mild steel) and i was considering making a h2 generator and running them off h2 to get a bit of extra power but i heard of hydrogen weaking some steels and being a bit dogey any help?
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Unread postAuthor: psycix » Sun May 11, 2008 6:45 am

AFAIK hydrogen doesnt react with steel.
It does burn off with quite a shockwave, so make sure your gun is strong enough.
Im happy that you are not using PVC. :)
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Unread postAuthor: brogdenlaxmiddie » Sun May 11, 2008 7:49 am

The easiest way to produce Hydrogen is by using sodium hydroxide with aluminum... but make sure you run the gases through water to collect the water out of the gas. Thats the easiest way i know of...
Psycix, are we talking about replacing say propane with hydrogen? cuz thats rather dangerous..... Make sure your steel is pretty damn strong!
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Unread postAuthor: D_Hall » Sun May 11, 2008 10:37 am

psycix wrote:AFAIK hydrogen doesnt react with steel.

Then you've learned something new today.

http://en.wikipedia.org/wiki/Hydrogen_embrittlement



Note: It's probably not a problem for the limited exposure something like a spud gun would have, but it is a very real phenomena.
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Unread postAuthor: dongfang » Sun May 11, 2008 4:42 pm

Hi,

The last time that I (and others) calculated on it, replacing propane by hydrogen did not improve performance.

Hydrogen does have a huge combustion heat per weight unit, but also a lot of volume per weight unit. If you do the figures, you will find that you can't stuff more combustion heat into the same combustion cannon chamber by using hydrogen instead of propane...

... but of course you might find it fun to try! It would be extra cool if you would evaluate the relative performance of the fuels in practice. Just to confirm.

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Unread postAuthor: steel spuds » Sun May 11, 2008 11:58 pm

Thanks for the advice ,dongfang i am not actually running them off propane as i am not really sure were to get a bottle without paying a fortune (i live in nz) so i was looking for a a gas with good preformance but realitively easy to get ( i can make a h2 generator from things i have at home) but yea thanks.
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Unread postAuthor: Lentamentalisk » Mon May 12, 2008 12:49 am

The benefit of hydrogen, is that it burns at near 8 times the rate of propane if I remember correctly, and because it doesnt produce CO2 and you rid the chamber of air (so no N2 is left after combustion) your product gases have a much higher speed of sound, as all that is left is H2O, which is just a little more than 1/2 the mass of N2.

To sum up all of that physics/chemistry gibberish, H2O/O2 mixes are good for really light projectiles aiming at supersonic velocities.

Also, reading the article on hydrogen imbrittlement, your cannons should be fine as long as you store them without hydrogen in them. Just let them air out after you are done using them for the day, and the hydrogen atoms can seep back out of the steel. I suggest that you don't heat your cannon while there is hydrogen in there (why you would I don't know) because that increases the rate at which it diffuses in, and allows it to create methane molecules, buy combining with the carbon in the steel.
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Unread postAuthor: steel spuds » Mon May 12, 2008 1:23 am

thanks Lentamentalisk so you are saying that after the h2+02 combustion has occoured all that will be left in the chamber is water and you wont have to worry about venting that sounds good.
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Unread postAuthor: dongfang » Mon May 12, 2008 1:54 am

Hi,

I am surprised that propane can cost so much down there ... how about a cigarette lighter refill aerosol thing?

And yes OK, for high-speed high-performance guns, hydrogen might have its advantages. I don´t understand still what hydrogen has to do with getting rid of air ;) You can use pure oxygen with any fuel (in a sufficiently strong gun - it goes quite BOOOM)

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