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hydrogen and oxygen as fuel

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 and oxygen as fuel

Unread postAuthor: c11man » Wed Jun 10, 2009 11:01 am

i have the ability to create oxygen and hydrogen and was wondering how good of a fuel it is.

this would be for a large mini (oxymoron?)

i have no way of seperating them so im stuck with what ever mixture electrosis gives me
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Unread postAuthor: john bunsenburner » Wed Jun 10, 2009 11:03 am

Well hydrogen and oxygen do give of alot of energy when they react. Hydrogen also reacts with oxygen in a huge range of concentrations. They burn at hgih temperatures. And with an excess of H2 you can get effects similar to using helium as a propellant in a pneumatic(higher velocities). I can only recomend it!
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Unread postAuthor: c11man » Wed Jun 10, 2009 11:08 am

i was wondering about its uses in a combustion

does 2 parts hydrogen and one part oxygen burn efficently? or does it need more oxygen?

ok i did some reasherch and it does create a prefect mixture.

now my question is how would i purge the chamber without wasteing any hydrogen because it does take quite a bit of time to generate it
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Unread postAuthor: jimmy101 » Wed Jun 10, 2009 11:24 am

john bunsenburner wrote:And with an excess of H2 you can get effects similar to using helium as a propellant in a pneumatic (higher velocities).

Why would you want that affect? Helium is used in pneumatics because the speed of sound is faster in helium than it is in air. The SOS limits how fast you can get the gas moving through the barrel which in turn limits the speed of the projectile.

With a combustion gun the speed of sound is basically irrelevant. The SOS is dependent on the temperature of the gases. In a combustion gun the couple thousand degree temperature of the gases increases the SOS substantially. The SOS is probably at least 2000 FPS and may be more than 3000 FPS in a combustion gun.

c11man: does 2 parts hydrogen and one part oxygen burn efficently? or does it need more oxygen?

Yes it burns efficiently and no you don't need more oxygen. Indeed excess oxygen will lower the energy a bit.
2H<sub>2</sub> + O<sub>2</sub> --> 2H<sub>2</sub>O

If you create the hydrogen and oxygen by electrolysis then the ratio will be correct. (Ignoring the different solubilities of H2 and O2 in water.)

Hydrogen + oxygen have a couple important differences compared to propane + air. H2 + O2 burns significantly faster and is more likely to detonate than is propane + air.
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Unread postAuthor: c11man » Wed Jun 10, 2009 11:30 am

i think john meant to use in in a pneumatic where it would be very efficent

so it is very powerful rigt? i am thinking about making this a 2x hybrid now

if i vented the chamber after each shot installed a new burstdisk then filled to the right pressure with the hydrogen oxy mixture it should work pretty good right?
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Unread postAuthor: john bunsenburner » Wed Jun 10, 2009 11:57 am

Well I assume that the change wouldn't be as dramtic so ignore that part of my post :D. I would assume purgind the chambre with what ever is cheeper and then filling the apprpiate amount of the other gas in. Would give you a hybrid though...
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Unread postAuthor: c11man » Wed Jun 10, 2009 12:01 pm

thanks for the imput. so a 2x hybrid purged with air will work well?

what kind of pressure could i expect if i had a 3/4 by 4inch steel chamber?
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Unread postAuthor: Biopyro » Wed Jun 10, 2009 1:02 pm

You would be much better off making an advanced combustion, with fuel metering. Then, you fill it like a normal advanced, and then place a balloon filled with H2/O2 inside. This will displace any air to keep any H2 being wasted. Any air which is left, will be a perfect flammable mix, and if you get bored of using H2 then you can just use the propane.

Bear in mind that a hybrid hydrogen mixture will be very powerful, and that you will lose some of the gas while using it to displace the air (unless you use a balloon). There is no point making it like a conventional hybrid because unlike propane, it already has all the O2 it needs.
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Last edited by Biopyro on Wed Jun 10, 2009 1:07 pm, edited 1 time in total.
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Unread postAuthor: psycix » Wed Jun 10, 2009 1:03 pm

How are you going to get the H2+O2 mix into your chamber at a 2x mix? SAFELY?

Pump too fast and it heats up -> boom
Pump with wrong pump, static electricity -> boom
Point is, that you are not pumping a fuel or oxygen, you are pumping a perfect mixture of the two, and that can be catastrophic.
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Unread postAuthor: c11man » Wed Jun 10, 2009 1:11 pm

no pumps involved

the pressure would be from the elecrolsis process. i know for a fact that it can reah enough pressure for the hybrid
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Unread postAuthor: Biopyro » Wed Jun 10, 2009 1:15 pm

I think you'll be hard pushed to generate 1 bar pressure from an average home electrolysis setup. Yours might be more advanced, I suppose.

Fact is, that treating this like a normal hybrid is not the way you should be going about it.
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Unread postAuthor: c11man » Wed Jun 10, 2009 1:24 pm

i have complety scraped the original design

i will post back when i have a safer desighn work discussing
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Mixed gas combustion.

Unread postAuthor: Technician1002 » Wed Jun 10, 2009 1:35 pm

[youtube]http://www.youtube.com/watch?v=TRZRhohHYn8[/youtube]

Video showing the bubbles igniting

Flashback arrestor FAIL
[youtube]http://www.youtube.com/watch?v=niC6n61dwLE[/youtube]
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Unread postAuthor: c11man » Wed Jun 10, 2009 2:33 pm

now that is why the idea was scraped

it would be very hard to keep it safe so i wont do it anymore. maybe when i have more money to spend on it and acces to better materials
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Unread postAuthor: rp181 » Wed Jun 10, 2009 3:45 pm

been there...
I made a cheap cell (later I did it with PVC, bubbler, and several different types of arrestors) with some metal plates, and a kraft Mayo jar. Lit the end, and the lid exploded off (fragmented too, flew at least 20 feet). That wasn't that bad, except my electrolyte was sodium hydroxide :roll: Got around eye (closed my eye fast enough....), and got a chemical burn.

Its fine for a small standard combustion, but designing larger, hybrid ones is just a waste.
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