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First Time Propane User: How much fuel to use?

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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First Time Propane User: How much fuel to use?

Unread postAuthor: Squerl101 » Tue Jun 25, 2013 3:04 pm

Hey guys, I have been spudding with AquaNet for about a year now. The glue-like residue was starting to get old, so I decided to convert to propane because I heard that it burns cleaner and better. I have built a cheap but functional propane meter, now all I need is someone to help me figure out how much PSI I need to inject into the combustion chamber.

This is my setup.
Image

This is the propane meter (I know, it's not that good but it gets the job done.)
Image

Here are the measurements.

The combustion chamber is 3 inch PVC. It is 14 inches long.
The barrel is 1.5 inch PVC. It is 35 inches long.

So, for you calculator people out there, how much PSI of propane do I need to use?

Thank you!
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Unread postAuthor: dart guy » Tue Jun 25, 2013 10:27 pm

it can be an exact science but its not nessasary start out small with like idk maby about 3 psi and just increase from there and see what works well for you but dont start to high
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Unread postAuthor: jackssmirkingrevenge » Wed Jun 26, 2013 3:42 am

dart guy wrote:it can be an exact science but its not nessasary


no no no!

It SHOULD be an exact science.

http://www.spudfiles.com/forums/viewtop ... tml#366310

http://www.spudfiles.com/forums/viewtop ... tml#318219
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Unread postAuthor: jimmy101 » Wed Jun 26, 2013 3:41 pm

What jack said.

And, try it first with just a syringe. Much easier and more accurate than the setup you have now.

The setup you have now has a some serious problems. The main one is the big hunk of clear tubing. That tube contains air, or an undefined mixture of air and propane. The stoichiometric quantity of propane for a chamber that size is somewhere in the vicinity of 50 to 100 cc at 1 ATM. The volume of that hunk of tubing looks to be much more than the needed volume of propane. When you plug that big hunk of tubing into the quick connect on the chamber then open the down stream valve of the meter you'll mostly push whatever was in the tubing into the chamber, not pure propane.

Loosing that big hunk of large ID tubing will help. Directly attaching the quick connect to the meter pipe would help even more.

My SWAG would be that the meter should be rebuilt such that the pieces of steel pipe are replaced by the shortest threaded pipe nipples you can find. The volume of just the T fitting, the gauge, 2 short nipples and the volume in the two valve fittings is probably several tens of cc (at least). So the pressure in the meter would be only a couple atmospheres to get the correct amount of propane for you chamber.
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Unread postAuthor: Squerl101 » Wed Jun 26, 2013 10:09 pm

jimmy101 wrote:What jack said.

And, try it first with just a syringe. Much easier and more accurate than the setup you have now.

The setup you have now has a some serious problems. The main one is the big hunk of clear tubing. That tube contains air, or an undefined mixture of air and propane. The stoichiometric quantity of propane for a chamber that size is somewhere in the vicinity of 50 to 100 cc at 1 ATM. The volume of that hunk of tubing looks to be much more than the needed volume of propane. When you plug that big hunk of tubing into the quick connect on the chamber then open the down stream valve of the meter you'll mostly push whatever was in the tubing into the chamber, not pure propane.

Loosing that big hunk of large ID tubing will help. Directly attaching the quick connect to the meter pipe would help even more.

My SWAG would be that the meter should be rebuilt such that the pieces of steel pipe are replaced by the shortest threaded pipe nipples you can find. The volume of just the T fitting, the gauge, 2 short nipples and the volume in the two valve fittings is probably several tens of cc (at least). So the pressure in the meter would be only a couple atmospheres to get the correct amount of propane for you chamber.


Thank you for the reply.

I will remove the tube tomorrow. It makes sense that we don't know what's in there. It used to be connected directly to the meter, but it was hard to put on. I'll grab some fittings from work to make it easier.
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Unread postAuthor: jackssmirkingrevenge » Thu Jun 27, 2013 1:20 am

Jimmy has a point about syringe metering. There really is nothing to it, very simply and accurate:

[youtube]http://www.youtube.com/watch?v=0nM603eOQU4[/youtube]
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