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Combustion pressures

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Combustion pressures

Unread postAuthor: Jolly Roger » Sun Sep 17, 2006 8:25 am

Hey just wondering if anyone knows how to find the combustion pressures of different gases or at least what I would search on google to find them. For example, how would someone calculate the peak combustion pressure for a stoichiometric mix of butane and oxygen, just an example. Im trying to figure out what materials would be best suited to handle my next project..
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Unread postAuthor: Jolly Roger » Mon Sep 18, 2006 11:14 am

i mean, come on.. dont make me double post until someone replies please... 24 people have veiwed the post and have absolutely no suggestions or answers.. i dont really believe that...
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Unread postAuthor: POS » Mon Sep 18, 2006 12:00 pm

Sorry dude, dont know that myself, but i realy want to know to. As far as I know are those pressures not that high, unless you use pressurised gasses (hybrides).
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Unread postAuthor: Jolly Roger » Tue Sep 19, 2006 12:44 am

Depends, I would be assuming accetylene and pure oxygen would create a decent pressure, but I'm not that keen to find out. I plan on using the info to construct an alloy hyrbid, not so much for shooting stuff, mainly to test the materials and how prone they are to detonation. Then I'll build I custom replicated rifle once I know the what is safe and what is not. ProMeterSuite has a simple linear graph showing the propane and air combustion pressures for hybrids up to 6x mixes although I don't know how accurate it is, plus I plan on testing different fuels and pure oxygen mixes.
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Unread postAuthor: POS » Tue Sep 19, 2006 2:06 am

copying a rifle is nice, but very difficult. Why not try to make your own rifle. Someone somewhere in time had to do that to. The Dutch designed the concept of the Armalite (yes, it were the Dutch) and the US bought the plans of it, and made it bether.

I just mean, wy always copying. You are perfect capable to create your own gun if you can copy a real one.
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Unread postAuthor: Jolly Roger » Tue Sep 19, 2006 4:04 am

Thats what I was doing, looking at rifles until I found one aspect of one that I like and used that in the design. And in the end it was just the same as the m107 anyway... But off that subject, can anyone help with my question?
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Unread postAuthor: DonTheLegend » Tue Sep 19, 2006 9:10 pm

I think i've seen approximate temperatures of different gases when burned someplace on the web, but i don't remember where. If you could find the temperatures produced, you could get rough estimates with the combined gas law (P1*V1)/T1=(P2*V2)/T2, but i doubt this would be very accurate, and i have no idea how to take into account the fact that there is an opening in the chamber, but only after so many miliseconds.
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Unread postAuthor: Jolly Roger » Wed Sep 20, 2006 6:49 am

Yeah I was thinking the same thing... Any smart engineers know the answer?
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Unread postAuthor: boilingleadbath » Wed Sep 20, 2006 5:18 pm

You'll get a bit of a pressure spike (wave related) in the chamber - which I don't know how to adjust for - and some pressure loss while the fuel is burning which probably <i>shouldn't</i> be accounted for.

...other than that, I've just been estimating them via the abdiatic (or however one spells it...) flame temp and the initial moles:final moles ratio.
That is:

P1/(T1*N1)=P2/(T2*N2)
(N=#moles)

So, for propane and O2 (making up temperatures)

C3H8 + 5O2 -> 3CO2 + 4H2O
6 moles to 7 moles

15PSIA*290K*6 = 175PSIA*2900K*7
(numbers estimated... whatever)
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