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Supersonic non-hybrid combustion gun - it's feasible!

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: drac » Sun Aug 27, 2006 7:29 pm

Although I like it alot, I agree that it isn't safe. Get some metal pipe and redo that, I would LOVE to see a metal version that could be made more powerful.

I'm surprised you're still alive too, although it looks like you put a shitload of research into this!
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Unread postAuthor: huse_spud » Sun Aug 27, 2006 7:39 pm

i'm laughing about how u guys aren't bashing this guy because he used dwv pipe simply because he's a genius and knows WAY more than you do!!! :lol:
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Unread postAuthor: Jolly Roger » Mon Aug 28, 2006 10:53 am

dongfang wrote:I wonder about one thing, though: Is a stoichisometric mixture really the best? It will definitely be the mixture that leaves the least residual oxygen and fuel in the chamber, but that is not an issue.

It will also be the mixture with the highest combustion energy, but will it make the biggest BANG? In my experiments with the gun above, I got the best performance somewhat below stoichisometric. I still wonder why.


Thats kinda strange... I would think that if it did create the highest combustion energy it would make the biggest bang. I've always known the stoichiometric oxygen to propane ratio as 4.3:1. Thats the perfect ratio for oxyfuel cutting. I know its worked out through atomic structure and so forth though I did some research and that ratio popped up alot, more than the 5:1 ratio as described in spud wiki... Strange
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Unread postAuthor: dongfang » Mon Aug 28, 2006 12:48 pm

It's actually not so hard to calculate the stoichiometic ratio -- you need to, basically, find out how many molecules of the gas react with hoe many of oxygen. Then, you multiply both with the molar mass of the gas vs. the oxygen, and you have a gram:gram ratio. Then, you just divide both by the respecitve specific masses, and you have a volume:volume ratio. In air, you will need 5 times as much as oxygen, since only one fifth of it is oxygen.

The pipe is not drain pipe, but sewer pipe (stronger). I'd love to make one of metal; all I need is some friendly soul to teach me how to obtain the materials and weld them together, before I blow my hands off :lol:

As for the best mixture, I think it has something to do with flame propagation velocity, apart from total combustion energy, and, again, I got the best results with a lean mix. If some of you guys with precision gas meters could make a test firing series and publish the results here, I think that could be really interesting. My gun is stowed away now; I moved to Switzerland shortly after Mach 1 was passed.

Søren
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Unread postAuthor: Jolly Roger » Tue Aug 29, 2006 12:58 am

Yeah thats what I was saying Soren, calculating the stoichiometric ratio through molecular structure SHOULD give you the perfect firing ratio, but I've found alot of sources that suggest the oxygen to propane ratio as 4.3:1 and not 5:1. Well thats for oxyfuel cutting anyway... I'll see if I can do some tests on it for you with combustion...
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Unread postAuthor: dongfang » Tue Aug 29, 2006 11:34 am

I just re-did the numbers - - no rocket science.

Propane:

    2 C_3H_8 + 8 O_2 - - > 4 H_2O + 6 CO_2
    ==
    2 mols of propane to 8 mols of oxygen
    ==
    88 grams of propane to 256 grams of oxygen
    ==
    48 liters of propane to 853 liters of air
Propane is 5.3 % of the mixture



Butane:

    2 C_4H_10 + 13 O_2 - - > 10 H_2O + 8 CO_2
    ==
    2 mols of butane to 13 mols of oxygen
    ==
    116 grams of butane to 416 grams of oxygen
    ==
    46 liters of butane to 1386 liters or air


Butane is 3.2 % of the mixture.



The cigarette lighter gas you get is pure butane, or a butane-propane mix of some kind, as far as I know.

Soren
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Unread postAuthor: hoastmaster » Fri Jun 22, 2007 5:12 am

to answer your
one might as well save the propane and add a little more air instead, right?

yes the optimal for single fuel to oxy is around 2:1 (2 oxy for 1 fuel)
but when you use mix gas fuel it gets more complex

it depends ont the 2 (or more!!?) fuels you use, and this is where carbon chemistry is needed

somthing with high carbon chains meens more air is needed so the fuel with the highest carbon cain cont is used less/ 2 oxy to 1 high carbon fuel and 3 oxy for 2 low carbon fuel

so it becomes 5:2:1

but its always god to add in oxy to carbon accelerants
chemicals that increas the rate of cobustion (remeber to use more oxy if "bonding" accelarents are used

Merged:

note my ratios are from me and a few mates with higher understandings of phys-chem then me sitting around playing with the numbers intill we get the best combustion rate

the ratios you guys use are for optimal combustion preasure
so id say that your ratios would be bettre for that perpouse

where mine are for mass acceleration on high mass objects(grate big nasty dirty explosions that make things go boom)

the 5:2:1 ratio we tested and found that the rate of combustion per ltr of mix gas was 2.5 times faster then the 5.1:1, and we used more gasses
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Unread postAuthor: lukemc » Fri Jun 22, 2007 7:42 am

could you take a picture of your bbq lighter because mine is very inconsistant even with 2 spark gaps.
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Unread postAuthor: joannaardway » Fri Jun 22, 2007 10:07 am

Impressive though this is, the topic has lain dormant for almost 10 months, and I don't recall having seen dongfang around recently.

Thread necromancy is isn't a good thing. It's a sin against the natural order of the forums!
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Unread postAuthor: sandman » Fri Jun 22, 2007 10:18 am

well, im glad it came up, lol this was before me time here and i really like this guys creativity and performance
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Unread postAuthor: noname » Fri Jun 22, 2007 10:22 am

Lukemc, your spark gaps are probably too big. Use 2 1/8" gaps and it should work fine.
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Unread postAuthor: Spedy » Fri Jun 22, 2007 10:28 am

Wow. That is pretty cool. I wonder if anyone else has acomplished this. Nice job on the cannon. :notworthy:
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Unread postAuthor: jimmy101 » Fri Jun 22, 2007 2:47 pm

Not to keep kicking this long dead topic, but...

Nobody noticed that dongfang got his chemistry wrong?

dongfang wrote:I just re-did the numbers - - no rocket science.

Propane:

    2 C_3H_8 + 8 O_2 - - > 4 H_2O + 6 CO_2
    ==
    2 mols of propane to 8 mols of oxygen
    ==
    88 grams of propane to 256 grams of oxygen
    ==
    48 liters of propane to 853 liters of air
Propane is 5.3 % of the mixture

Soren


Uh, that equation for propane should be;
    2 C_3H_8 + 10 O_2 - - > 8 H_2O + 6 CO_2
    ==
    2 mols of propane to 10 mols of oxygen

The propane volume is 1/5th of the oxygen volume. Since air is ~20% oxygen then the propane volume to air volume is (1/5)(0.2)=4%, not 5.3%.
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Unread postAuthor: sandman » Fri Jun 22, 2007 3:02 pm

lol, hmm, i thought that looked wierd but i thought nothing of it, good job in catching it
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Unread postAuthor: TwitchTheAussie » Fri Jun 22, 2007 5:37 pm

Mate allow me to say this in the typical aussie way: You sir are bloody crazy. But nice work :lol: Did you say you used coil guns to help shoot it through the barrier? If you did and also if you didnt I think you are the first one to use electromagnets on a cannon (correct me if Im wrong seniors). Nice work on everything mate and also next time hope to god your safe. :lol:
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