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HELP can't understand propane meter

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: auxiliary » Wed Nov 19, 2008 8:35 pm

If there is an overload of propane in the combustion chamber then it won't even ignite. The ratio of propane to atmospheric air must remain around 1:20 (4.2% propane). Because of this, you don't have to worry about 14psi being safe or not.

If you live in a cold place, then I would recommend having a larger propane meter because you can just regulate the propane pressure down to maintain the optimum amount of propane and this would solve the problem of a propane tank not generating enough pressure because of cold weather. If you live in a warm place then don't bother with this and just use the volume you calculated. Here is a good website that will answer more questions of yours: http://www.burntlatke.com/lp.html
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Unread postAuthor: spudkilla224 » Wed Nov 19, 2008 8:37 pm

Ok thank you, now i understand.

Thank You For all of the pointers everybody
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Unread postAuthor: starman » Wed Nov 19, 2008 8:42 pm

spudkilla224 wrote:Thank You, is 40-60 PSI ok to use though? i havn't done propane meters before so if i have like 40 PSI of propane, how many PSI should i expect to see in my combustion chamber when firing? less than a 100 PSI?

Sure it is...it just depends on how big your meter is. The bigger the meter volume the less psi of propane you will need. The smaller the meter the more psi you will need. Keeping the psi somewhat low is a good thing. Have you done a meter calculation for your cannon yet?

As stated before, your shooting psi's will be below 100. If your chamber is sealed, the pressure will rise only slightly in it when you load the propane..... .6psi I believe...I'm too lazy to look it up now.
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Unread postAuthor: jmeyer1022 » Wed Nov 26, 2008 3:21 pm

I will be running my Regulator at 35 psi for a 4.6% fuel mixture. If your looking for exact specs I'm sure someone wouldn't mind helping with a chamber design. My mom freaks out but I explain to her everything on the gun to its safety features.

In my opinion aerosol is more dangerous cause most people use cleanouts and after a while they get stuff in the threads from the explosions and your spraying the hairspray in and then quickly getting the cleanout on and after a while it that cleanout doesn't go on as good as it use too. I've blow a cap off before and trust me its scary.
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Unread postAuthor: Insomniac » Thu Nov 27, 2008 5:19 am

Wait a minute, you seem to be a bit confused when it comes to what mixes actually mean.

You CANNOT physically get anything higher than a 1x mix in a regular combustion. A 2x mix means the entire contents of the chamber (both air and fuel) is pre-pressurized to two times normal atmospheric pressure. The only way to do this is to use some kind of pressure-activated valve (such as a burst disk) to contain the high pressure fuel/air mix before ignition. (have a look at the 'Hybrid' guns on this forum for more info into the specifics)

If you try and put too much fuel in a regular combustion, you will simply end up with a very rich 1x mix that probably won't even ignite. You will only get a powerful, clean combustion with a certian ratio of air-to-fuel. Since you can only fit a certain amount of this gas mixture into a bit of pipe due to how much room it takes up, the pressure generated is limited at somwhere around 90-120 psi. Regardless of how much, or how little fuel you put in you cannot go above this limit. It just won't happen.

This is why hybrid guns need a burst disk. This allows more fuel/air to be squeezed into the chamber before firing.
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