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saftey of acetlene or oxygen in Sch80

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: bigbob12345 » Sat Dec 01, 2007 9:27 pm

I actually have alot of experience I have built 4 combustions and 3 nuematics Its just I started my account here This morning.
And Ill try putting just a litle oxygen in with propane
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Unread postAuthor: DYI » Sat Dec 01, 2007 9:42 pm

If you're planning on using oxy-propane, you might want to think about using an ABS gun rather than a PVC one. Handles the shock a bit better. But unless the whole thing is sealed up and you are using hybrid O2/propane mixes ( what I did :roll: ), then you should be relatively safe.
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Unread postAuthor: bigbob12345 » Sat Dec 01, 2007 10:01 pm

My gun is ABS And for added safety Ill use remote ignition
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Unread postAuthor: From_Hamsterdam » Sat Dec 01, 2007 10:51 pm

1. It can spontaneously detonate, even in the absence of oxygen or air. It is so prone to autodetonation that a cylinder of compressed acetylene has to have several things added to it to keep the tank from detonating all by itself (usually a mixture of acetone and crushed brick IIRC).

acetylene will explode when pressured to 103bar. if you have a gun that can handle 103 bar more power is the least of your worries.
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Unread postAuthor: benstern » Sat Dec 01, 2007 11:05 pm

Lost of misinformation in this thread from new members.

We do not condone the use of acetylene on spudfiles because it is extremely hard to make a cannon that can contain it safely. IE: perfect welds and very thick steel pipe.

Adding oxygen to a combustion cannon won't necessarily increase power. If you are at a stoichiometric mix, adding extra oxygen will only decrease power.

Again.. Oxygen is not flammable or explosive it is simply an oxidizer for a fuel.
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Unread postAuthor: bigbob12345 » Sat Dec 01, 2007 11:12 pm

So theres absolutly no point of oxygen
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Unread postAuthor: octane89 » Sat Dec 01, 2007 11:31 pm

It is pointless for it.
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Unread postAuthor: bigbob12345 » Sun Dec 02, 2007 12:04 am

Is there any other way I can get my combustion performing better
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Unread postAuthor: benstern » Sun Dec 02, 2007 12:59 am

If you don't already have them: propane meter and fan
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Unread postAuthor: pyrogeek » Sun Dec 02, 2007 1:15 am

jimmy101 wrote:There is really no advantage to using acetylene in a spud gun. The energy content of acetylene is really not significantly different than propane or butane, roughly 15% more energy in acetylene. See the spudwiki page on fuels or the acetylene page.

Acetylene has several problems that make it unique among spudgun fuels.

1. It can spontaneously detonate, even in the absence of oxygen or air. It is so prone to autodetonation that a cylinder of compressed acetylene has to have several things added to it to keep the tank from detonating all by itself (usually a mixture of acetone and crushed brick IIRC).

2. It is more likely to reach DDT (deflagration to detonation transition) than most other fuels. If the fuel reaches DDT it is possible to get very high pressure spikes that put the gun at risk of exploding.


Acetylene is stored in tanks at around 90 PSI, like propane. It becomes unstable at about 15PSI. In the tanks, there is acetone and asbestos, both long and short fiber to keep it from sloshing around.
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Unread postAuthor: Killjoy » Sun Dec 02, 2007 3:41 am

^^Didn't they switched to something other then abestos in modern tanks?
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Unread postAuthor: jimmy101 » Sun Dec 02, 2007 11:55 am

From_Hamsterdam wrote:
1. It can spontaneously detonate, even in the absence of oxygen or air. It is so prone to autodetonation that a cylinder of compressed acetylene has to have several things added to it to keep the tank from detonating all by itself (usually a mixture of acetone and crushed brick IIRC).

acetylene will explode when pressured to 103bar. if you have a gun that can handle 103 bar more power is the least of your worries.

Hmmm, you appear to have been grossly mis-informed on this matter.
Compression

Due to the carbon-to-carbon triple bond, acetylene gas is fundamentally unstable, and will decompose in an exothermic reaction if compressed to any great extent. Acetylene can explode with extreme violence if the pressure of the gas exceeds about 100 kPa (≈14.5 psi) as a gas or when in liquid or solid form, so it is shipped and stored dissolved in acetone or dimethylformamide (DMF), contained in a metal cylinder with porous filling (Agamassan), which renders it safe to transport and use.
(From the wiki on acetylene, emphasis added.)

So, it can auto-explode at ~1 bar, not 103 bar!
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Unread postAuthor: jimmy101 » Sun Dec 02, 2007 12:03 pm

benstern wrote:Lost of misinformation in this thread from new members.

I'll say! Even some bad (or poorly worded) info from people that should know better.

benstern wrote:We do not condone the use of acetylene on spudfiles because it is extremely hard to make a cannon that can contain it safely. IE: perfect welds and very thick steel pipe.

And it really doesn't boost the performance all that much. So, it is too risky for the fairly minor increase in performance you might get. There are other, somewhat safer ways to boost a guns performance.

benstern wrote:Adding oxygen to a combustion cannon won't necessarily increase power. If you are at a stoichiometric mix, adding extra oxygen will only decrease power.

Yep, if you are dumb enough to go to all the trouble of being able to add oxygen and then used the gun at a 1x mixture, then adding oxygen won't help. Usually, people are a little smatter than that. The whole point of using pure oxygen is that you can use more fuel as well and still be at a stoichiometric mixture. This will significantly increase the performance of the gun. But, you can easily exceed the safe pressure range of PVC with pure oxygen. Hence, most people that use pure oxygen build metal guns.

benstern wrote:Again.. Oxygen is not flammable or explosive it is simply an oxidizer for a fuel.

Yep. But combustion requires both fuel and oxidizer. To increase power you have to increase both.
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Unread postAuthor: bigbob12345 » Sun Dec 02, 2007 12:25 pm

So I will be able to put alot more in the chamber and still have it ignite if I put oxygen in with it which would boost performance but is it safe to do this
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Unread postAuthor: benstern » Sun Dec 02, 2007 12:28 pm

But then is it considered a hybrid?
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