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propane and oxygen

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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propane and oxygen

Unread postAuthor: super spuder » Fri Apr 06, 2007 10:27 pm

ok. i have spent like the past 2 weeks reading every thing i can about potato guns on this web site and many other web sites to. up until now all i have built is a big pneumatic cannon, and 2 mini cannons running on deodorant. but i want to make a propane metered cannon. but the distances of all the propane cannons i have seen just are not fare enough for me.so i thought i would mix oxygen in with it to give it more power. but then i read on this web site that is is a really really really bad idea to do this in a pvc or abs cannon. so i was thinking of using an old fire extinguisher as a combustion chamber.but i just wanted to know if that would be strong enough/ what is the max pressure on a fire extinguish. and i am prepared for like 5 people to answer "you are an idiot to use propane and pure oxygen" but oh well. i don't care as long as one person answers my question
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Unread postAuthor: hi » Fri Apr 06, 2007 10:33 pm

ill be the one person that answers your question. You basically need sch80, or sch160 would be even better, steel or brass. Iron would work too. When you do that, you are essentially building a hybrid, and the more oxygen you put in, the bigger the bang. You would be building up a couple hundred psi, and risk blowing your head off. I would suggest a remote ignition and that you are behind a large brick wall and in a 5 foot hole. I would also suggest that you get a little more experience with spud guns first.
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Unread postAuthor: super spuder » Fri Apr 06, 2007 10:46 pm

yea. remote igniton does sound like a good idea. but i cant get sch80 or sch160 where i live. so i think i will probly make it out of steel. ps-thanks for not calling me an idiot lol.
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Unread postAuthor: Insomniac » Fri Apr 06, 2007 10:53 pm

Yeah, remote ignition is a must. I'm not sure if propane and oxy detonates, but if it does it will make a HUGE pressure spike for a fraction of a second, and it may rupture the combustion chamber.
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Unread postAuthor: hi » Fri Apr 06, 2007 10:56 pm

If you cant get AT LEAST sch 80, then dont build it, it will just explode.
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Unread postAuthor: super spuder » Fri Apr 06, 2007 10:58 pm

That is why i am going to use really heavy steel.the thing will probly weigh allot. bot i will still be living :D now i have to figure out how to make a remote ignition system :?
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Unread postAuthor: hi » Fri Apr 06, 2007 11:08 pm

I used a stun gun on my hrbrid with a 20 foot wire, it works. it enough to let me get behind a wall or big tree or something and still be safe.
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Unread postAuthor: super spuder » Fri Apr 06, 2007 11:11 pm

i live in canada (stun guns are illegal in canada), i am only 15. so stun gun is out of the question :(
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Unread postAuthor: Scope » Sat Apr 07, 2007 12:06 am

For remote ignition you can rig a stun gun swith to a remote start up relay for a car... idno if you know how to.
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Unread postAuthor: frankrede » Sat Apr 07, 2007 12:09 am

You can get the stungun circuits though legally.
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Unread postAuthor: super spuder » Sat Apr 07, 2007 7:22 am

i don't know where to get a stun gun circuit thou. i am thinking of maybe hooking up an electric ignighter to a model rocket launcher (it has like a 50 foot cord on it)
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Unread postAuthor: sandman » Sat Apr 07, 2007 8:57 am

i wouldnt do that, model rocket launchers use pyrotechnic material and they only put out 6 volts, the best way to ignite is a spark
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Unread postAuthor: super spuder » Sat Apr 07, 2007 9:11 am

no. what i mean is. they have electric ignightors at home depot. and they run on batteries. but ensted of standing next to it and hitting the button that makes the spark on the ignightor. just use the rocket ignightor without the paper things that go on the end and just use it as more or less a switch for the electric ignightor. that would be good wouldn't it?
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Unread postAuthor: boilingleadbath » Sat Apr 07, 2007 10:42 am

I don't see why such a electrical setup wouldn't work.

That said, there are two factors to be dealt with with enriched mixtures:
1) Increased presssure... indeed, increased <a href="http://img.photobucket.com/albums/v611/car2/PandTvsOx.png">this</a> much.
(in your case, look at the blue line and the numbers on the right - that's pressure in atmospheres vs. the percent oxygen in the air part of the propane-air mixture. That is, 20% is your normal combustion. Numbers generated through gaseq.)
2) Increased rate of combustion, and decreased detonation run-up distance.

Now, I don't think I've seen any numbers on how enriched mixtures affect the run up distance of anything (much less propane), but just about everything takes long enough to transition to detonation that you shouldn't have to worry about it. (assuming your chamber is reasonably short)

Oh, and to all the people saying "I don't think it detonates"...
Just about everything can detonate, and just about nothing HAS to detonate; octane-air can detonate, C4 can burn. And C4 normally does, unless you hit it with a pretty nice cap.
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Unread postAuthor: super spuder » Sat Apr 07, 2007 12:08 pm

yea haha why wouldn't it detonate-
propane=flammable- oxygen =oxidizer- flammable+oxidizer+combustion chamber=boooooooooo, and flying spuds :D (hopefully)
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