Oxy-Acetylene.

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 TurboSuper » Sat Oct 21, 2006 2:58 pm

Yes, we have something called hybrids which involve adding compressed air to a propane mix to enrich the mixture.
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Postby blackspire » Sat Oct 21, 2006 3:28 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by TurboSuper
[br]Yes, we have something called hybrids which involve adding compressed air to a propane mix to enrich the mixture.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">DOH! :oops:
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Postby sgort87 » Sat Oct 21, 2006 6:38 pm

He's not asking about hybrids. He's asking about oxy-enriched mixtures at STP.

Yes, oxygen has been used with propane to enhance the combustion.
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Postby blackspire » Sat Oct 21, 2006 6:40 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by sgort87
[br]He's not asking about hybrids. He's asking about oxy-enriched mixtures at STP.

Yes, oxygen has been used with propane to enhance the combustion.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Do you have any idea how much it would enhance the combustion of propane? Basicly I want something that is going to give me quite a bit more power than ether.
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Postby SpudBlaster15 » Sat Oct 21, 2006 8:27 pm

Propane burns at stoichiometry with atmospheric air at about 4.2%. Atmospheric air is approximately 20% oxygen. By switching to pure oxygen, you have 5 times the available oxidizer, and can thus multiply your fuel value by the same figure, giving you 21%. This means that 5 times the energy is available to propel the projectile. If you add a longer barrel to harness this energy, you will gain a huge amount of distance.

Oxy/acetylene is a bad idea, due to the ease at which it DDTs at stoichiometry. Deflagration speed is approximately 300m/s, but a transition to detonation rises the speed to 3000m/s, causing a massive pressure spike, which can blow even steel cannons apart.
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Postby sgort87 » Sun Oct 22, 2006 12:52 am

So 100% oxygen and 21% propane? That's 121%! I didn't know you could do that.

By the way, air is closer to 21% oxygen. And I think the numbers you are looking for are about 84% oxygen and 16% propane.

If you are absolutely sure your launcher will hold up to this the best way to do it is to flood the chamber with oxygen and then inject a calculated amount of propane to give you the 16% propane.

Edit: Why am I telling you this? No offense to you at all, but if you don't know this already then you probably shouldn't build a high power launcher like this. Building something you don't understand is one of the worst things you can do. Be careful dude.
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Postby Navigator7 » Sun Oct 22, 2006 9:55 am

Matt,
If shooting a potato is the goal....an oxy/act mix, done properly will vaporize it....so then what?
That's fun once or twice but it does get boring shooting potato slurry.

I'm not keen on a member here making headlines killing himself or others, drawing unneeded and negative attention to the hobby that otherwise is an elegant display of math, science and physics.

Asking the question:
<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote"> My only real worry, is that on here I saw a thread where a guy had made a metal potato gun, and when he put the oxy-acetylene into the gun, he screwed the endcap on and someone pointed out that may be a bad idea due to any static electricity that may be created. If anyone can point out a major design flaw, let me know. I already have all the metal, so I can't just "not make it". I would like to be as safe as reasonably possible with this gun, as I know that oxy-acetylene can be dangerous. Any input is greatly appreciated.~Matt<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Produces the answer.....You don't have the experience to build the cannon!
Experienced combustion guys here are saying don't build the cannon.
I'd guess most experienced combustion guys would not attempt what you are saying.

Your turn! ;-)
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Postby jimmy » Sun Oct 22, 2006 11:55 am

"<i>4 inch, by 2 foot long chamber, with a 2 inch by 4 foot long barrel</i>"

It really won't matter what you use for fuel the gun'll perform like crap. Your chamber to barrel ratio is about 2:1 ... the barrel should be twice as long for this size chamber.

Acetylene is a bad idea and completely unnecessary. Like Nav said, you'll vaporize a spud. If you shoot something stronger than a spud then you're liable to vaporize yourself.

Look closely at the barrel of a real rifle. The barrel wall is a heck of a lot thicker than 1/8" and it is made of steel specifically selected for high pressure, high temperature and high impulse use.

Stick with metered and mixed propane to start with. Once you have that figured out then perhaps progress to O<sub>2</sub> + propane.
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Postby SkweezMyCheez » Sun Oct 22, 2006 12:03 pm

oxy + MAPP, i wouldn't dare try anything more powerful... acetylene is scary shit.


H-C#8801;C-H

see those three lines stacked on top of each other? SCARY THREE LINES! dont touch those three lines, dont even think about it.


[edit] hmm, dammit, "#8801" is supposed to be the symbol for "identical to" which i used to represent a triple bond... oh well

<img src="http://upload.wikimedia.org/wikipedia/commons/thumb/9/97/Acetylene-2D.png/150px-Acetylene-2D.png">
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Postby blackspire » Sun Oct 22, 2006 12:03 pm

"It really won't matter what you use for fuel the gun'll perform like crap. Your chamber to barrel ratio is about 2:1 ... the barrel should be twice as long for this size chamber." That's just the dimensions I used for my first ABS potato gun, and it works awesome...? So how do I do a propane metering system so that I don't blow myself up?
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