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hydrogen power

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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Unread postAuthor: benstern » Sun Dec 23, 2007 4:02 am

Don't use hydrogen unless you have a metal cannon. Period. Thats it.
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Unread postAuthor: dongfang » Sun Dec 23, 2007 4:21 pm

Hi,

Hydrogen has been discussed before. In terms of combustion energy, it is really powerful - per weight unit, that is. Per volume unit, you will need 2/3 of hydrogen, and 1/3 or oxygen: The volume of the fuel will leave much less volume for oxygen in a chamber than, say, good old propane.

In other words, you will be slightly better off with just propane and oxygen, and it is simpler too. But for just the experience of it, go ahead!

I´d also say that pure oxygen does not belong in PVC. It might rupture, and PVC has a nasty way of doing that. I would say use metal, or experiment with one of the more modern, softer plastics like PE or PP, in a SMALL scale and REMOTE triggered. Wear heave clothes and gloves and use safety goggles at least.

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Unread postAuthor: DYI » Sun Dec 23, 2007 4:40 pm

Some good thick ABS would work fine for this. It would obviously have to be custom machined if you planned on an oxy/hydrogen hybrid, but for a 1x mix (0psig), SCH 40 pressure rated ABS would likely be OK as long as it was remote triggered and didn't DDT. SCH 40 DWV ABS might work, but it could blow up due to defects.

In short, using metal would be cheaper, easier, and faster than building it safely out of plastic.
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Unread postAuthor: Flying_Salt » Sun Dec 23, 2007 4:48 pm

benstern wrote:Don't use hydrogen unless you have a metal cannon. Period. Thats it.


What he said. Hydrogen detonates, not burns.

it has been a while since I've posted here (lurk moar?)
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Unread postAuthor: DYI » Sun Dec 23, 2007 4:57 pm

What he said. Hydrogen detonates, not burns.



Wrong. Hydrogen, like any other combustible material, will only detonate if it has a long enough run-up distance. It certainly won't just detonate instantly. With a 1" chamber, it would apparently need to be 12"+ long for the mixture to reliably detonate, and that's with 3x O2/H2.

As long as the chamber is almost as wide as it is long, and is made from some reasonable diameter of pipe, the mix will not detonate.
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Unread postAuthor: Flying_Salt » Sun Dec 23, 2007 5:02 pm

Thats assuming you can mix it right. No hydrogen. At all. Its bad stuff for non-metal cannons.

You'd be safer off playing with PAM in your cannon (*cough* benstern)
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Unread postAuthor: benstern » Sun Dec 23, 2007 5:03 pm

DYI wrote:
What he said. Hydrogen detonates, not burns.



Wrong. Hydrogen, like any other combustible material, will only detonate if it has a long enough run-up distance. It certainly won't just detonate instantly. With a 1" chamber, it would apparently need to be 12"+ long for the mixture to reliably detonate, and that's with 3x O2/H2.

As long as the chamber is almost as wide as it is long, and is made from some reasonable diameter of pipe, the mix will not detonate.


Ya listen to us older members who have seen all this stuff before and heard about all the mishaps and injuries, K thanks!
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Unread postAuthor: DYI » Sun Dec 23, 2007 5:05 pm

Thats assuming you can mix it right. No hydrogen. At all. Its bad stuff for non-metal cannons.


Well, that's wrong on two points. For one, if you mix the hydrogen wrong, it will take even longer to detonate. And, in general, hydrogen does more damage to metals than plastics, although the effects are usually more pronounced with high pressure storage.
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Unread postAuthor: rp181 » Sun Dec 23, 2007 5:41 pm

well, detonation is not going to happen, my combustion chamber is a small T found at homedepot =). I belive its 1 1/2in. width, and 5.5in long, sch40. The T part is a 3/4in hole, thi is where the gas pipe will go and the ignition wires.I used plugs instead of PVC caps, this further lowers the volume. I did a couple shots, no damage so far =) I didn't glue in the back plug, so itle pop off if there is too much pressure. It didn't even budge. I let it fill with my electrolysis setup (12 carbon rods from sunbeam D batterys in a 3x4 setup, 4.5 amps goes in). I shot it, quite powerfull, but i cliked the ignitor again, and it shot again, and again. Each shot got weaker and weaker, untill it sounded like someone blowing across a battle top ( low pitched). I am wondering why this is happening, im guessing its because im letting my electrolysis run too long. Mu assumption is that the hydrogen dominates, and is pushing the oxygen out. It combustes with what it can, and more air is sucked in from the vacume, and so it can ignite again, is this right?

Thanks again for all the help.
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Unread postAuthor: benstern » Sun Dec 23, 2007 5:43 pm

Holy crap man!?!?! You are actually going to do it? Do you want to die or be seriously injured?
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Unread postAuthor: rp181 » Sun Dec 23, 2007 5:55 pm

I already did it, not one incident.
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Unread postAuthor: Novacastrian » Sun Dec 23, 2007 6:03 pm

Damage pics please.
Pics of cannon please.
Fueling station pics please.
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Unread postAuthor: rp181 » Sun Dec 23, 2007 6:18 pm

damage pics will come later, still need to find optimall run time of electrolysis, will post other pics soon.
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Unread postAuthor: DYI » Sun Dec 23, 2007 6:23 pm

If you didn't vent the chamber between shots, it was getting weaker because of water build up from the combustion.

If you really insist on doing this with unsafe materials, use DWV ABS, not PVC. It won't shrapnel when it fails. (which it almost certainly will, eventually)
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Unread postAuthor: BigGrib » Sun Dec 23, 2007 6:27 pm

Yeah you didn't have an accident this time, but that about next time you retard. I hope you like pvc embedded under you skin. The only saving grace for us is, we have told you countless times not to use plastic so if you do blow yourself up, we can't be held responsible. Oh yeah what do you want your headstone to say?
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