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Metered propane Problems

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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Metered propane Problems

Unread postAuthor: frankrede » Mon Nov 20, 2006 2:02 am

This weekend I built a propane setup similiar to the one shown on Burntlatke and I have a Bbq igniter ignition.6 in meter pipe
I have tryed 30 60 90 psi of propane into the meter pipe and I still cant get ignition. Is there something I did wrong?
when I take off hte endcap and press the igniter I get spark and flames shoot out. Should I upgrade my ignition or what?I can get oxygen, would adding a tiny bit to my mixture help it?
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Unread postAuthor: CS » Mon Nov 20, 2006 2:08 am

Where did you get the calculation in which to determine how big to make your metering pipe?

If you tell me both your chamber volume, and meter volume, I may be able to help you out.
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Unread postAuthor: mark.f » Mon Nov 20, 2006 8:29 am

What method are you using? Are you just hooking the tank right up to the meter, and adjusting the meter pipe volume so that it'll provide the right amount of fuel at the tank pressure, (90 PSI)? Or, are you hooking the tank up to a regulator or have a gauge so you can fill a meter pipe to a specific pressure so that it provides the right amount of fuel?

If you're using the first method, remember that it is very cold right this time of year. Your tank pressure might get very low.

Therefore, make the meter pipe larger, so that it'll work off a lower pressure, like 30 PSI. Then, use a regulator or a gauge and needle valve, (conveniently provided on torch heads), to fill it to that pressure.
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Unread postAuthor: CS » Mon Nov 20, 2006 6:08 pm

Mark, I suspect his problem is that he had no idea as to that the meter pipe had to be in any particular ratio with his chamber, or that he built his meter to similar dimensions to that of Latkes, and his chamber volume is different. Even if your meter volume is in range with your chamber volume, the chances of you getting it right by simply trying in 30PSI increments. If you simply give us the figures I could figure it out for you in a matter of minutes using programs Latke has provided.
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Unread postAuthor: frankrede » Mon Nov 20, 2006 7:17 pm

I have 6 in meter pipe.
I have a regulator.
My chamber is.......I'll check within the hour.
Could I skip changing my meter pipe and just find a specific sweet spot of psi?
I had it fire once, sent the caulking tube 3 feet(horrible shot). . I got excited
Edit 1: The temperature is 70+F give or take 5 degrees



My chamber is approx. 1750 Milliliters give or take 100 ml
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Unread postAuthor: MisterSteve124 » Tue Nov 21, 2006 2:59 pm

You have to put the measurements of ur chamber into fuel tool to figure out how much psi of propane you need, you can't just guess. Well you could but just use fuel tool and put in the size of your chamber and your meter pipe and it will tell you how much psi of propane you need.
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Unread postAuthor: frankrede » Tue Nov 21, 2006 6:22 pm

AIght, I'll get the fuel tool.
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Unread postAuthor: MisterSteve124 » Tue Nov 21, 2006 6:40 pm

you dont get it http://burntlatke.com/ft_splash.html go to that website.
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Unread postAuthor: frankrede » Tue Nov 21, 2006 7:34 pm

MisterSteve124 wrote:you dont get it http://burntlatke.com/ft_splash.html go to that website.

You can get it I got the excel version. But the online one is alot better. Hmm, its funny, its says my mixture is fine. but I still cant get ignition. Im going to try and get stun gun ignition.
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Unread postAuthor: SpudStuff » Tue Nov 21, 2006 7:36 pm

Do you have a chamber fan? It increaced reliability on mine by a great deal. And consider adding multiple spark gaps.
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Unread postAuthor: MisterSteve124 » Tue Nov 21, 2006 8:36 pm

I would think that if you have the mixture right it wouldn't really matter what is igniting it. A bbq igniter should still work. What size is your chamber and what is the diameter of your meter pipe just so I can double check it. I agree with SpudStuff you should probably get a chamber fan.
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Unread postAuthor: frankrede » Tue Nov 21, 2006 9:32 pm

SpudStuff wrote:Do you have a chamber fan? It increaced reliability on mine by a great deal. And consider adding multiple spark gaps.

I don't have a fan and I am getting Stun Gun type ignition this weekend.
I think I'll set up a spark strip.
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Unread postAuthor: SpudBlaster15 » Tue Nov 21, 2006 9:58 pm

After using a fan in each of my cannons, I honestly cannot see how any combustion spudgun could be without one.
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Unread postAuthor: mark.f » Wed Nov 22, 2006 8:22 am

Dude, you don't need expensive crap like stun guns or spark strips.

My tennis ball cannon has a single ignition point with a gas-grill sparker. I've also seen cannons with a lantern sparker near the rear that perform equally as well. So what's the deal?

Ignition matters squat. While it would add or subtract a few feet per second, in the long run, fuel and mixing of that fuel makes the most difference.

If you're using propane, simply multiply your chamber volume by .042. That'll give you 73.5 mL, (btw, this is nearly exactly the same as my first gun, 3x12" chamber, right? :wink: ).

Then, multiply that by the conversion factor from a volume of gas to the # of moles of that gas present at STP. This will give you 0.00328125 moles propane required for combustion with 0.078125 moles of atmospheric air.

Now, you haven't said specifically, but I'm guessing your meter pipe is 1/2" steel, right? I'm assuming it is. If it's not, then just change the following equations accordingly. The volume of a 1/2" SCH-40 x 6" steel pipe nipple will be right around 30.165 mL, (converted from cubic inches using Google).

Using the ideal gas law...
<table><tr><td><pre>
P * .030165 = (.00328125)(.0821)(273.15)
.030165P = 0.07358404921875
P = 2.439
</pre></td></tr></table>

So, your meter pipe pressure should be at 35.9 PSI, (2.439 atmospheres), for a stoichiometric propane mixture.

Now, onto the bigger problem at hand...

Do you have a chamber fan?

If not, don't go running off screaming "Oh crap I've gotta find an old computer!!!". Simply go to Wal-Mart and pick up an Ozark Trails personal camping fan, (the little yellow ones with the white blade), and find a scrap length of ? " SCH-40. I know in 4", you sit the fan on top of a piece of 1" SCH-40, but in 3", you need a different kind of spacer. Maybe 1/2" or 3/4". If not, just mount the fan in the center of the chamber with #6 or 1/4" all-thread. Just flip it on with the cap, (and barrel, if it's detachable), to vent, and then leave it on when you close the cap and inject propane. This will mix the fuel and give you better ignition and a heartier BANG when you shoot.

EDIT: Oops. Math Goof. :lol:
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Unread postAuthor: MisterSteve124 » Wed Nov 22, 2006 10:07 am

I agree with mark it doesn't matter what is igniting it. A bbq should be perfectly fine for igniting propane. You just have to make sure you have the right ratio and a fan will help mix it so that you get the right amount of air and propane.
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