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Propane, Pure Oxygen, and PVC

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, Pure Oxygen, and PVC

Unread postAuthor: azurex » Fri Jun 15, 2007 11:46 pm

So I made a potato gun out of just PVC and a regular propane torch that supposedly makes the right mixture all on it's own. Well, that one made around 600 feet, but I'm trying for better.

The atmosphere is only around 18% oxygen. I want to use propane, and pure oxygen. I believe the right mixture is 4% propane and the rest O2. If i make this out of PVC, will it be to withstand that kind of pressure?

I'll make it out of metal if i have to, but i'd rather not because it's heavy, probably more expensive, harder to make holes in, etc.

PVC goes up to Schedule 160? Not sure if its strong enough, and i sure as hell don't want a bnuch of PVC shards in my face

Also, i need a good way to meter the amounts of O2 and propane that go in. I saw the How To Make A Propane Meter at the top of the page. Trouble is, I'll have two bottles, one O2, the other propane. Maybe I could pot a T fitting their that could accept two bottle adapters?
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Unread postAuthor: A-98 » Fri Jun 15, 2007 11:51 pm

go all metal. and remote ignition. as for the metering, i would use a propane meter, and an oxygen meter, both made in the same, traditional way. however, im not sure about the stotiometric mixture of O2 to propane. ide say ask a mod.

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Unread postAuthor: Killjoy » Fri Jun 15, 2007 11:59 pm

Well its cheaper to buy steel pipe (sch 160 is expensive and hard to find) and safer if you want pipe which can withstand high pressure.
Don't Use PVC

Also, the 4% propane is for regular air, with 18% oxygen (as you said). So that should mean that 18% (of chamber volume) should be propane, and the rest oxygen. Someone correct me if i'm wrong though.
And you would need two meters, one for the propane that will result in 18% propane in the chamber. And one for oxygen, with a measured volume that will result in 82% of chamber with oxygen.

This is extremely dangerous though, as the O2 bottle is under extremly high pressure, and the pressure generated from the combustion is also extremly high. So you need to be extremly careful.
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Unread postAuthor: azurex » Sat Jun 16, 2007 12:08 am

Haha metal it is then. By meter do you mean the kind shown in that video on the top of the combustion page? Is there a better way to get the right mixture?
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Unread postAuthor: FeLeX » Sat Jun 16, 2007 12:33 am

Yea he means that. Meter is the only good and efficient way of measuring propane/oxygen (I might be wrong, but hell).
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Unread postAuthor: Redcoat » Sat Jun 16, 2007 12:39 am

If you want to just try it with PVC dig a small trench in the ground and bury the half of your gun with the chamber on it but leave the ignition out of the ground so you can shoot it. Hell if it blows up the dirt will make a neat combat style shell hit effect.:twisted: BUt if you want to go safer try wiring your ignition so you can stand ten metres back with the chamber still under ground.
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Unread postAuthor: ammosmoke » Sat Jun 16, 2007 1:48 am

Lol, using pvc for this is only going to produce a bomb. I wouldn't try it if I were you. Personally, I would go with just making a larger cannon.
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Unread postAuthor: SpudBlaster15 » Sat Jun 16, 2007 2:38 am

Depending upon the inside diameter, Sch 80 PVC may be able to withstand a propane/oxygen reaction, though one couldn't be certain.
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Unread postAuthor: spudthug » Sat Jun 16, 2007 9:56 am

sch 80 is usually used for hybrids and i dont think a propane/oxy mix could generate the 400 psi (estimate) that a 4x hybrid would generate would it?

if you do make it out of sch 80 make sure u dont go above 2 inch for the chamber because 3 inch may not be able to withstand the blast
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Last edited by spudthug on Sat Jun 16, 2007 11:27 am, edited 1 time in total.
4" piston valved cannon-half done..( i spilt my cement...)

Hybrid- 75% done. need to build propane holder and drill/tap sparkplug hole..
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Unread postAuthor: Jumpin Jehosaphat » Sat Jun 16, 2007 10:12 am

The words PVC, pure oxygen, and combustion dont belong in the same sentence. Metal is the only way to ensure safety.
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Unread postAuthor: sandman » Sat Jun 16, 2007 10:40 am

spudthug wrote:sch is usually used for hybrids and i dont think a propane/oxy mix could generate the 400 psi (estimate) that a 4x hybrid would generate would it?

if you do make it out of sch 80 make sure u dont go above 2 inch for the chamber because 3 inch may not be able to withstand the blast


yep, my 3" sch 80 is rated to 370 psi, and my 2" sch 80 is rated to 400 psi, so only the 2" is safe
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Unread postAuthor: Fnord » Sat Jun 16, 2007 11:14 am

I believe pure oxygen and propane mix would give about the same results as a hybrid running at 4x, judging from the gas percentages. Sch40 steel or iron would be the way to go. In that sense, a hybrid should be relatively safe using pure oxygen for normal combustion also.
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Unread postAuthor: spudthug » Sat Jun 16, 2007 11:29 am

@fnord-

r u sure just a combustion of propane/oxy (with no pressure) would create such high pressures? if this is true then there would be a very very high chance of DDT wouldnt there? because it would have a pressure spike comparable to that of a 5x hybrid mix....
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Unread postAuthor: Fnord » Sat Jun 16, 2007 11:52 am

Here's my reasoning:
Normal air is around 18-20% oxygen, with mostly nitrogen(inert) and some misc gasses here and there.

If you replace air with pure oxygen, you'll have five times more oxidizing power than normal air. replace about 18-22% with propane(rough estimation) and you'll have 4 times the normal explosive mixture in the same area.

With ultra-strong hybrids, this could be used to exceed 7.8x mix without having the propane liquifing in the chamber.

DDT is a bit of a gray area; no one has really done enough research to know what it is capable of, or the exact conditions needed for it to occur.
In short, I dont know.
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Unread postAuthor: SpudBlaster15 » Sat Jun 16, 2007 1:06 pm

*Cues GasEQ*

Oxygen/Propane, 1atm - 18.181atm (267psi)

Atmospheric air/Propane, 4atm - 38.015atm (559psi)

Oxygen/Propane, 4atm - 76.28atm (1,121psi)

Keep in mind these are adiabatic values, and the actual combustion pressures (non adiabatic) will be significantly lower.
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