Calcium CArbide

Post questions and info about combustion (flammable vapor) powered launchers here. This includes discussion about fuels, ratios, ignition systems and anything else relevant to launchers powered by igniting things like hairspray or propane.

Postby markfh11q » Fri Dec 08, 2006 11:08 pm

I've got a can of calcium carbide in the utility closet.

The reason you are underestimating acetylene gas is because all you've seen so far are laminar and turbulent diffusion flames at constant pressure. Cute, really...

At constant volume with a premixed flame, you have one hell of a different beast on your hands. I think that with the proper construction materials, a safe C<sub>2</sub>H<sub>2</sub>:air cannon can be made. You better know what the F*** you're doing, though. One thing I will say is that with carbide, it's really easy to get a stoichiometric ratio fuel:air. You don't need any kind of fancy meter, just a scale, and then all you need to know is the chamber volume and the volume of water you added to the cannon.
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Postby BewareOfDog » Sat Dec 09, 2006 12:22 am

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote"><b>Originally posted by jimmy</b>
Exactly what advantages does calcium carbide have over right gaurd, propane, butane ... anyway?

[disadvantage blah-blah]****[/disadvantage blah-blah]

So exactly why would you use carbide other than to see if it works?
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Because the measured peak explosion pressure of acetylene is 10.6 bar, which is a significant increase over ther peak explosion pressure of propane!

To everyone: I'm sure that natanddianne gets the point!- Although I personally frown on the thought of injecting acetylene gas into a closed vessel and have even made a STICKY about the dangers of acetylene, it doesn't mean that I haven't tried it myself! ;)

Calcium Carbide is... "neat" to play with, but it <b>is</b> kinda messy. Propane is readily available, relatively safe to use, and gives a lot of bangs for the buck.

Regardless of conflicting opinions, we always seem to jump up someone's ass with both feet when they try to argue a point. - But <b>what</b> point is anyone REALLY trying to make, other than "I'm right, you're wrong" ???

Let it die.
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Postby natanddiane » Sat Dec 09, 2006 12:09 pm

you all are indeed comitting an unsafe act using PVC for any purpose other than plumbing. Spud guns will all blow up, sooner or later. Dancing with the devil? We ALL are in here! Ok, wrong? i will admit mistakes indeed. The topic can be considered dead. AFTER you folks look at how carbide was indeed used as a stable fuel in the past. MIners used it in their head mounted lights for the cry eye! CArbide is not nitroglycerine! Is indeed generates acetylene, but not the pure gas you would find in a welder's tank.
SOme call me a fool for wearing my helmet on my motorcycle. I am just as dead with a skid lid at 60mph as i am without. Ok, I am a fool. Even wear a ballistics coat as well. There is no safe act. People die in their sleep. Does that mean we do not sleep anymore? Every 11 seconds someone dies in a traffic accident in the US. Every 18 sec, someone is killed by a drunk driver. Do we all stop driving? No. What I am sayiong, is spudguns by their nature ARE unsafe! We all assume a modicum of risk toying with them. For another analogy, why are there Ferraris when Chevys will get us there? The danger? The speed? the POWER? Hmmm.

To anyone I offended, I vehemently apologise. I deeply regret any ill feelings I may have inflicted. However, give the Devil his due. If your'e gonna play, play hard
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Postby TurboSuper » Sat Dec 09, 2006 1:08 pm

Spudguns by nature, are only as unsafe as you make them.

Any spudgun horror story i've read involves improper construction techniques, or the use of (oxy)acetylene (and a few other dangerous fuels).

you didn't offend anyone, and if you did they would be rather foolish to take a fuel reccomendation as a personal insult, the idea is just that experimental and theoretical evidence point to the use of acetylene or a similar fuel as unsafe and unpractical for a PVC-based combustion.

Like it or lump it.
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Postby clide » Sat Dec 09, 2006 1:41 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by natanddiane
give the Devil his due. If your'e gonna play, play hard
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

So if you're going to do something unsafe you might as well do it in a way that makes it more unsafe? Or because we are constantly doing unsafe things it can't hurt to add one more? Do I really need to point out how flawed that logic is?

As far as carbide as a stable fuel. We've told you before that using it as a source for constant flame in an open, constant pressure environment is completely different than closed vessel combustion. And carbide does generate the acetylene you find in a welders tank, it just doesn't generate the pure oxygen that usually accompanies it and makes it very dangerous.
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Postby benstern » Sat Dec 09, 2006 1:47 pm

"For another analogy, why are there Ferrari when Chevys will get us there?"

Chicks would rather go to bed with someone who owns a Ferrari than one who owns a chevy. It is more of a status symbol than a car.



"Spud guns will all blow up, sooner or later."

That is the biggest piece of bullshit ever. They won't blow unless you used sloppy construction and usage techniques.
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Postby Mr.Plow » Sun Dec 10, 2006 1:39 am

There is nothing inherently dangerous in making spudguns, just as there is nothing inherently dangerous in making blackpowder rifles. The danger is a factor contributed by those who incorrectly construct or operate potato guns. You can use modern powder in an old blackpowder rifle for a while before it blows up and maims/kills you... but that doesn't mean that your rifle under safe operation (with blackpowder/pyrodex) would've blown up eventually. The operator causes the danger. I've tried my hardest to think up appropriate analogies to this, but if you can't get that then I give up. I mean, if you honestly think that because something has a degree of danger associated with it, then you can forget all safety procedure, you might as well not wear a seatbelt or bring a backup parachute when skydiving.
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Postby natanddiane » Sun Dec 10, 2006 12:02 pm

we are currently working up a steel, trailered cannon, carbide fired, remote controlled ignition. I do indeed realise the dangers of persuing this, and do indeed respect your opinions as those of experience. Our v 2.0 is going to be clear pvc, propane fired. v3.0 will be the remote steel cannon, towed behind suitable vehicle, and fired from a respectable distance. Using of course, taters as fuel.. love the smell of french fries in the morning.. smells like victory (s)
Thank you all for your indulgence. We'll check back often, and advise on the status of our projects. Noone gets hurt, nobody dies. many bushels of taters , shot to the skies
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Postby boilingleadbath » Sun Dec 10, 2006 12:23 pm

Oh, come on DR. You've said that you fill your pneumatics to rather high pressures, so I'm very surprised that you are intimidated by the "10.6 bar" max pressure generated by oxyacetelene.

...I mean, after all, that's only 156 psi.

Increased acoustic energy, decreased DDT runup distance, and more spontaneous ignition? Sure. OMG-chamber-rupturing-pressure? Not with pressure rated (and under 8", IIRC) pipe.
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Postby BewareOfDog » Sun Dec 10, 2006 1:52 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by boilingleadbath
[br]Oh, come on DR. You've said that you fill your pneumatics to rather high pressures, so I'm very surprised that you are intimidated by the "10.6 bar" max pressure generated by oxyacetelene.

...I mean, after all, that's only 156 psi.

Increased acoustic energy, decreased DDT runup distance, and more spontaneous ignition? Sure. OMG-chamber-rupturing-pressure? Not with pressure rated (and under 8", IIRC) pipe.
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Oh, come on boilingleadbath and re-read my post. You fail to realize that I was actually advocating the use of acetylene because of the increase in power ! - Duh!

And as far as chamber-rupturing pressure is concerned:

We all are very well aware that acetylene gas will self-ignite if compressed to 15psi or higher, right? We are all aware that acetylene gas will ignite, even though the percentage by volume of the fuel may be close to 100%, right? And we're all aware that acetylene can violently decompose, right?...

Well, let's just say that someone were to (accidently) put in twice the stochiometric mix of acetylene in the PVC cannon (around 14-15 percent by volume). Once ignited, the pressure wave compresses the (still unburned) acetylene and air to 10.6 bar ...

So now we have a 10<sup>+</sup>X mix in our PVC-based cannon, right?

Let's see: 156psi plus itself ... ten times, equals 1,1560
14.7 plus itself... 9 times, equals 132.3
1,560 + 132.3, equals...


Hmmm,
I mean, after all, that's only <b>1692.3 psi !!!</b>

Decreased ignition energy, increased burning velocity and a peak rate of pressure rise @ 1,415 bar-meters per second? Sure. OMG-chamber rupturing pressure?

Yeah, even when using 1/8" SCH80 !
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