getting the right amount of butan

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 lionex » Tue Nov 28, 2006 10:26 am

hy, well i did build myself a spudgun, worked pretty fine with normal gases like hairspray or some strange motor cleaner(extremably flamable, no notice on the bottle what is in there). but i always face problem filling it, a) because with all normal hairspray and so on, i dont know the butan/propan concentration in the bottle, and when using normal butan, i dont manage to get the right concentration...
ok i saw the propan regulator stuff on the pages an the wiki, but thei all concider a Pressure regulator, but those are very expensive and i dont have a big propan bottle(only those small for burners and so on).

i'm looking now for some useable ideas how to always get the right amount of butan into my chamber. i know all the calculation stuff so the only problem is mesuring the gas and getting it in the chamber.
the combustion chamber of my spudgun has a volume about 2000mL, so butan amount should be about 120mL(taken @ 6%). i'm using a normal butan-buner to get the gas from...
http://pollin.de/shop/images/article/big/G860822.JPG

any suggestions?
thx for reply
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Postby BewareOfDog » Tue Nov 28, 2006 12:24 pm

At 21.1 degrees Celsius (~70 degrees Fahrenheit), butane has a vapor pressure of only 2.1 atmospeheres (~31psi).

Because of this, I think that it would make for a very poor choice as a metered fuel. But let's just say (for shits and giggles) that you STILL want to use butane for a fuel...

If you can get 20psi of butane into a 3/4" NPT x 8" length pipe nipple, then you would have a 4.625% fuel mixture to inject into the chamber.

The real trick, is modifying that <b>idealgas</b> butane burner to a pressure regulator! ;)
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Postby lionex » Tue Nov 28, 2006 3:08 pm

well thx for the answer, i just returned from a local building-stuff shop, and i saw there a bottle with 70%propane and 30% @ 8bar/atm(sry i'm from europe, still got my probs with psi an inches), and only found a pressure reductor to 2.5bar or 1/2bar, will 2.5 be enough to get all the stuff into the chamber? (confuse?) ok, let me explain my thinking: i build that normal butane/propane regulator like on all the pages, add the pressure regluator of 2.5, open first valve, pressure in the pipe will rise to 2.5, closing valve 1 and opening valve 2, gas is releasing into the chamber... everthing is fine, BUT, what about the rest gas in the pipe? little calculation for example:
100ml pipe, 2.5bar pressure of propan, 250ml gas@1bar, if releasing the gas: 150ml will move to the chamber, 100ml will stay in the pipe!(correct me if my logic is wrong)


edit: i just noticed that when releasing the gas into the chamber, the pressure inside the chamber will rise, so even less gas then i wrote before will enter the chamber... tricky stuff :D
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Postby SpudStuff » Tue Nov 28, 2006 7:39 pm

Yeah, I noticed that too with my GEN II fuel tank. The pressure can jump ~5 PSI which results in an odd mix.
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Postby BewareOfDog » Tue Nov 28, 2006 9:20 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote"><b>Originally posted by lionex</b>
ok, let me explain my thinking: i build that normal butane/propane regulator like on all the pages, add the pressure regluator of 2.5, open first valve, pressure in the pipe will rise to 2.5, closing valve 1 and opening valve 2, gas is releasing into the chamber... everthing is fine, BUT, what about the rest gas in the pipe? little calculation for example:
100ml pipe, 2.5bar pressure of propan, 250ml gas@1bar, if releasing the gas: 150ml will move to the chamber, 100ml will stay in the pipe!(correct me if my logic is wrong)<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

lionex, your calculations are WAY off:

at 2.5 bar (approx 36psi) and with a meter pipe of 100ml volume, your fuel mixture would be at a whopping <b>12.25%</b> !! :D

If you were to keep the pressure at 2.5 bar:
Make yourself a meter-pipe out of a 3/4" NPT x 4" length pipe nipple.
This length will give you a 4.161 % fuel mixture.

The fuel volume in the chamber (after injection) will be 83.2 ml, which is only 4.16% of the volume of the <b>2000</b> ml chamber...

<center><img src="http://img.villagephotos.com/p/2003-9/398596/lionex1.JPG"></center>




<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote"><b>Originally posted by lionex</b>
edit: i just noticed that when releasing the gas into the chamber, the pressure inside the chamber will rise, so even less gas then i wrote before will enter the chamber... tricky stuff :D <hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

...Trust me, there will be little to NO gas left in the meter-pipe, as the pressure in the chamber will rise to less than <b>0.068bar</b> ( 1 psi)
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Postby lionex » Wed Nov 29, 2006 9:16 am

k, seems logic, will try it :) results following later :D
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Postby lionex » Wed Nov 29, 2006 12:07 pm

ok... i just returned from the hardware shop to get all the stuff where i faced a new problem, the fittings from the gas reducer or bottle do not fit to any sort of ballvalves i found O_O some guy told me that gas-fittings are different from normal sanitary fittings and they dont sell intermediate pieces O_O
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Postby TurboSuper » Wed Nov 29, 2006 2:47 pm

That's where a rubber hose, a couple of pipe clamps, and a hacksaw come in handy.

...the rest should be kinda obvious.
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Postby jimmy » Wed Nov 29, 2006 3:01 pm

The easiest way to meter butane is to just <a href="http://home.earthlink.net/~jimsluka/Fuel%20Meter%20From%20A%20Disposable%20Butane%20Lighter.html">use a syringe</a>. Avoids having to buy a regulator, valves etc. As DR pointed out, the pressure in a butane cylinder is pretty low. So low that rubber hose is adequate, no need for any metal at all in the meter.
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Postby lionex » Wed Nov 29, 2006 4:01 pm

the idea with the syringe also came up my mind, but where to buy a 100ml syringe? O_O

but i think i will build a gas meterer, looks more professional (muhahah) :D
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