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Meter and gun measurements for propane combustion.

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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Meter and gun measurements for propane combustion.

Unread postAuthor: wangpushups » Mon Oct 22, 2007 5:41 pm

I know you guys get posts like this all the time but I've looked everywhere to try and get perfect measurements for my gun and I either don't understand how to do it or I can't find out how. I've used all the calculators so please dont post them cause I suck at math and I dont know how to use them. I'm looking for a perfect C:B ratio and I beleive that is 7:1 or something. If anyone has the same measurements as I do for the meter and/or the gun please help because I need to get this done and this is the last thing I need to do.

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Unread postAuthor: DYI » Mon Oct 22, 2007 6:40 pm

[spoonfeeding] A perfect C:B ratio is about 0.8:1 on a combustion. If you had a 4" chamber that is 12" long, for a volume of ~151 ci, you would need (151/0.8=188.75/3.14159=~60/1=60) a 60" long 2" barrel.

Your propane meter can be any size that you like, so long as it is smaller than the chamber, and large enough that you don't need any more than about 100 psi in the meter. If you had a meter volume of 1.51ci, assuming that you purged it with propane to get rid of any air or exhaust gases that may be in it, then you would need (151ci x 4.2%=6.342 ci / 1.51 ci = 4.2 x 14.7psia=61.74 psia or 47.04 psig) 47 psi in your meter.
Please note that this is a rough calculation and won't provide a perfect mix, however it will be very close. [/spoonfeeding]
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Unread postAuthor: wangpushups » Tue Oct 23, 2007 4:38 am

When i measure the chamber volume, would i include the (2) 90 degree elbos
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Unread postAuthor: Novacastrian » Tue Oct 23, 2007 4:46 am

To start with no, you will find out what works best quick smart. :P
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Unread postAuthor: wangpushups » Tue Oct 23, 2007 1:37 pm

How do i measure the tee on the meter
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Unread postAuthor: DYI » Tue Oct 23, 2007 3:03 pm

Just do a liquid volume measurement. You won't get the volume right just by measuring the length of the meter, and unless you have a chrony and a lot of free time, trial and error isn't very good either.
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