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Combustion gun won't fire... nothing seems wrong though.

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Combustion gun won't fire... nothing seems wrong though.

Unread postAuthor: Pete Zaria » Tue Apr 18, 2006 2:31 pm

I have a pretty typical combustion gun, 24"x4" chamber > 1.5"x5ft barrel, propane meter and direct injection (but with no regulator), dual spark ignition, bbq ignighter. Last week my cannon would fire every time I tried it, I usually didnt even have to pull the trigger twice. This week it barly fires at all. Nothing seems different. Same amount of fuel, spark gaps are the same (although Ive tried bigger and smaller spark gaps), etc... Any ideas? My only ideas are that A) its too cold (around 55F) to get propane to ignight properly, or B) this BBQ sparker is a peice of $h17 and wont produce big enough / hot enough sparks.

Thanks a bunch.

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Pete Zaria.
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Unread postAuthor: MisterSteve124 » Tue Apr 18, 2006 2:40 pm

well just look in the back of your chamber when there isn't any fuel in it of course and look to see if its sparking. You should be able to see the sparks, but it might be hard with the light on so go somewhere dark and you should see the spark. If not then its not the ignition.
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Unread postAuthor: Pete Zaria » Tue Apr 18, 2006 2:45 pm

Of course it's sparking, or at least 8 out of 10 tries (no offense but I'm not that stupid). The spark gaps are only about a 1/16th of an inch though, because this BBQ sparker doesn't like to jump two gaps much bigger than that. Think it's an ignition problem or a fuel/air problem?

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Unread postAuthor: MisterSteve124 » Tue Apr 18, 2006 2:47 pm

it shouldn't really matter how big the spark is that much. As long as the fumes are getting to it it should light. Where is the ignition on your chamber? Is it near the back or more toward the barrel?
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Unread postAuthor: Pete Zaria » Tue Apr 18, 2006 2:51 pm

One set of electrodes (steel machine screws) about 2-3" from the back of the chamber, another set almost exactly in the middle. One srew was a bit too short, so I put an alligator clip on the end of it to tigthen up the spark gap.

My propane meter is a bit of a ghetto job. It's a simple setup, hose and hose clamps from the torch to a ball valve to a meter pipe to another ball valve, to the chamber. Last week, it'd fire with anywhere from 3 to 6 "shots" of propane, though 4 seemed to produce the best results.

The problem either has to be ignition or fuel to air mix, right? Any ideas which one?

Thanks for your help, Steve.

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Pete Zaria.
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Unread postAuthor: MisterSteve124 » Tue Apr 18, 2006 3:05 pm

Well maybe your either getting it too much on the screws or u just dont have the right fuel mix. Try using aerosol just for comparison. and no problem
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Unread postAuthor: drac » Tue Apr 18, 2006 3:23 pm

Get a chamber fan. There's some information about it at http://burntlatke.com/

They can really boost performance.
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Unread postAuthor: MisterSteve124 » Tue Apr 18, 2006 3:37 pm

but he shouldn't need for it to work if the sparks are like 3" from the back of the chamber. I agree that would help but he's just trying to get it to work.
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Unread postAuthor: Pete Zaria » Tue Apr 18, 2006 5:53 pm

I have quite a few spare computers in my garage, so I'll grab a fan from one. What size would work best? I have 60, 80, and 120mm but I don’t think a 120mm would fit. I'll mount it with a steel elbow bracket, just behind the back electrodes (between the electrodes and the end cap), is that OK? I assume it'll run fine on a 9 volt battery and a toggle switch in a little plastic enclosure glued to the chamber.

I was hesitant to use a chamber fan because, though I know the chamber is only hot for a few hundredths of a second at a time, it still seems like the fan would get gummed up/melted after awhile.

By the way, what's the disadvantage of using a propane meter without a regulator? I know it's not as precise, but it seems to work fine. Or maybe that's the problem...?

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Unread postAuthor: MisterSteve124 » Tue Apr 18, 2006 6:30 pm

The fan should be fine unless ur firing it a lot with like no breaks in between. The 120mm probably won't fit so you can use which ever one you want.
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Unread postAuthor: Pete Zaria » Wed Apr 19, 2006 12:01 pm

I don't mean to bump my threads, but...

Any info about using a propane meter system without a regulator? Is this a bad idea?

Also, what are the odds of the chamber fan creating enough of a spark to ignight the fuel? I'll try to use a brushless fan to be sure, but still...

Thanks for the info, everyone.

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Unread postAuthor: nicholai » Wed Apr 19, 2006 12:30 pm

how do you know how much propane is in your chamber without a regulator? you can assume that the propane tank is pushing anywhere from 80 psi to 110 depending on the temperature but you really should regulate the propane, chances are that you are flooding out the chamber with too much propane if your sparks work good. I used a BBQ clicker for my ignition on my propane launcher and it works fine, also i use a fan to mix up the air/propane gas so it fires more efficent and consistant. Also, you got a big chamber too so you should really invest in a fan to mix up the propane and air.

its also important that your propane tank is sending 100% propane gas, not liquid as the liquid wont burn and will flood the chamber. As long as the propane has to flow up to the meter pipe, not down, you shouldnt have to worry about this

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here are some pics of my propane launcher, the chamber is about half the size of yours but it has all the goodies except a stun gun ignition and it fires every time
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Unread postAuthor: Pete Zaria » Wed Apr 19, 2006 12:50 pm

I'm buying the project box and switch to wire my chamber fan today. Where in the chamber is the best place to mount it?

Thanks for the tip on the propane. If it's cold out, I can see a bit of liquid propane in the clear plastic tubing between the propane tank and meter pipe. I'll make sure to point the cannon upright while filling in the future.

I didn't do any real precise math to calc my chamber volume, but I got it close enough. I'm not exactly a mathematician but I'll see if I can figure it out a bit more precisely. Would you really recommend a regulator? I can't find one for any less than $25 (which isn't a big deal, but if it's not necessary, then...).

Thanks a bunch, Nicholai.

Peace,
Pete Zaria.
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Unread postAuthor: nicholai » Wed Apr 19, 2006 10:33 pm

yes, to accuratly gauge the volume of propane you are dumping into the chamber you must be sure of the pressure, the $25 regulator will solve that problem, beware though, most (if not all) pressure regulators are designed for non flammable gas, ex: air, so their method of dropping the pressure is to simply vent off the excess pressure into the air. Its really not a big deal just dont fuel it while you're smoking a butt or standing next to a campfire.

the best place to mount your chamber fan is in the rear of the chamber, with the air blowing towards the barrel. its easiest to mount and provides the most efficency
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