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How Long Do Propane Bottles Last?

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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How Long Do Propane Bottles Last?

Unread postAuthor: elitesniper » Sat Feb 23, 2008 12:21 am

Hey guys, do you know how long a 14oz propane bottle would last on a meter that is 4inches of 1/4 steel pipe and the pressure is 45psi?



Grammar Edit by MrC, you almost have 500 posts, may as well make your posts look respectable.
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Unread postAuthor: MrCrowley » Sat Feb 23, 2008 12:24 am

What pressure are you filling the chamber to?

You can only get a vague answer as the pressure of the propane changes with temperature. But most people still have their original bottles on their hybrids and combustion launchers, they last long enough.

Are you using the propane in a meter? If so give us the meter specs and the pressure you will be using the propane at.
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Unread postAuthor: elitesniper » Sat Feb 23, 2008 12:27 am

yes i am using a propane meter the propane meter is 4inches of 1/4 steel pipe and the pressure is 45psi
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Unread postAuthor: MrCrowley » Sat Feb 23, 2008 12:28 am

See my edited post, most people still have thier original bottle on their launchers.
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Unread postAuthor: elitesniper » Sat Feb 23, 2008 12:34 am

what do you mean they still have the oringinal propane bottle, does that mean it never ran out yet?
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Unread postAuthor: MrCrowley » Sat Feb 23, 2008 12:42 am

Yeah
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Unread postAuthor: elitesniper » Sat Feb 23, 2008 1:00 am

ah thanks MrC, combustions are pretty fun cause there portable and i dont needa bring my aircompressor anywhere only a propane bottle hehe :lol:
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Unread postAuthor: SpudBlaster15 » Sat Feb 23, 2008 2:07 am

The easiest way to answer that question is to do a little bit of chemistry. 14oz is ~400 grams, and the molar mass of propane is 45g/mol. One mole of gas at STP occupies 22.4 liters of volume. Your meter has a volume of ((0.364/2)<sup>2</sup>*pi*4) cubic inches (which must be converted to liters for the calc), and will be filled to (45/14.7)*V. Putting this all together we get;

# of shots = (400/45*22.4)/(0.0164*((0.364/2)<sup>2</sup>*pi*4)*(45/14.7))
# of shots = 9 528

With a meter volume that small, I doubt you will ever be required to change the bottle, unless of course you manage to fire your launcher nearly 10 000 times in its lifetime.
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Unread postAuthor: jon_89 » Sat Feb 23, 2008 2:29 am

Wow I didnt realize a bottle would last that long. I think I should make one for my combustion.
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Unread postAuthor: Lentamentalisk » Sat Feb 23, 2008 2:33 am

I'd say its probably actually a little more than that... You used STP, which is 0 deg C, which is very cold for shooting spuds... A better equation would be to use PV=nRT, but you get the point... You will never use it up
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Unread postAuthor: BigGrib » Sat Feb 23, 2008 3:50 am

I have only ever used up one bottle to completion just because it was too cold to pressure up high enough
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Unread postAuthor: jimmy101 » Sat Feb 23, 2008 6:59 pm

Like others have said, for a standard sized combustion, it is unlikely you'll ever use up a 400g (14oz) propane bottle.

I'm on my second propane bottle. But only because, apparantly, one time the bottles internal valve didn't fully seal when the external valve was removed and the propane all pissed away over a couple months.

Following up on spudblasters math;

(400g)(mol propane/44g)(22.4L/mol) = 204L propane at STP (0C, 1ATM)

Instead of figuring the meter volume just figure out what volume of 4% mix that 400g is equivalent to.

For a 4% fuel mix that is (204L)(25) = 5100L.

Figure a typical combustion chamber at 2L, then you could fire the gun 2550 times at 0C. (The correction from 0C to say 80F is pretty minimal, roughly a factor of 1.1.)

That 5100L of propane+air mixture is 1350 gallons, 311,000 in<sup>3</sup>, 180 ft<sup>3</sup>
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