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Combustion issues

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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Combustion issues

Unread postAuthor: Pax » Mon May 17, 2010 8:22 pm

Alrighty, Im leading the problem to be my igniter or my fuel I got a grill igniter, And its spark isn't big at all(How big should it be?), When i fire it ( It fires rarely) It makes a puffy fart noise and sends what I'm shooting maybe 10 feet, Doesn't sound like a normal combustion, And doesnt act like a normal combustion, Is it my igniter or fuel? Im using a grill igniter with what looks like a tiny spark and im using hairspray, Which i dont think is the problem (I don't know how to use propane and i couldn't find how)

12" long chamber of 1 1/2" pipe and i have a 8 inch long barrel of 3/4" pipe, Roughly speaking
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Unread postAuthor: Hubb » Mon May 17, 2010 8:36 pm

It's probably the fuel. How long do you spray the chamber? If it's not long enough, then the mix will be too lean. But if it's too long, the mix will be too rich. Either way, it's not going to fire right. As far as the spark is concerned, if it's sparking, it's doing its job.

You spoke of propane. Why are you having trouble figuring out how to use it? A simple search of this forum and the wiki will yield more than enough results to understand it.
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Unread postAuthor: clemsonguy1125 » Mon May 17, 2010 8:59 pm

If your really worried about the ignitor try a lantern sparker but like what hubb said all you need is a tiny spark
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That is all.
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Unread postAuthor: mark.f » Tue May 18, 2010 5:12 am

Your fuel is everything.
Simply use a syringe to meter your propane. Multiply your chamber volume by 4.2% and fill your syringe to this volume with propane. Then inject through a cracked cleanout cap.

If you can't do that for some reason, take the spray cap off of an aerosol can and attach it to the fill stem of a can of lighter butane. Experiment with different spray times until you find something that works best.

I doubt the igniter is giving you troubles. If it sparks and you get ignition, it is doing its job. Any larger spark than you are already getting (at least only one of them in the same position) won't help performance by any noticeable measurement.
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Unread postAuthor: Technician1002 » Tue May 18, 2010 5:22 am

In a spray and pray, the fuel mix can be checked after the wimpy shot. Remove the cap and try to light the remaining gas. If it burns when exposed to air, it was way too rich. If the match stays lit as you insert it way into the chamber, the chamber has too much oxygen remaining indicating a lean burn. After a powerful shot, the match won't light remaining fumes and it will go out as it is placed in the oxygen free chamber.
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Unread postAuthor: chinnerz » Tue May 18, 2010 7:21 am

Thats a good trick to know :D
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Unread postAuthor: jimmy101 » Wed May 19, 2010 6:20 pm

Ignition problems are 99% of the time related to improper fueling. You have to get propane to be between 3% and ~8% of the chamber volume to ignite. Outside that range nothing will happen even if you used a blow torch as an ignition source. Optimally, you want the fuel to be about 4% of the chamber volume.

After getting the correct fuel ratio the next thing you need is to get the fuel mixed with the air. If you use a syringe and inject exactly the right amount of fuel very slowly and near the breach (or spud) and then immediately try to fire the gun won't fire. The fuel has to be at the correct ratio and has to be well mixed. Gases mix fairly slowly. That's why advanced combustion guns have a chamber fan. The fan insures the fuel is perfectly mixed after a fan-run of just a couple seconds. Depending only on diffusive mixing it can takes tens of seconds up to a couple minutes (particular at cooler temperatures) for the fuel to mix.

Usually any visible spark is enough to ignite a proper ratio and well mixed chamber. If you can see a spark it'll work.

Adding to tech's suggestion, to check for mixing problems, let the gun sit for a minute or two after fueling. Perhaps slowly invert the gun end-to-end a couple times. If the gun fires, or if the oooomph goes up significantly with the long wait, then mixing is your problem.

One last thing, if you are using an aerosol (squirt-n-screw or spray-n-pray fueling) and you see any condensation inside the chamber you are grossly over fueling the gun. A typical size combustion gun only needs a drop or two of a liquid fuel, any more than that and the gun is over fueled.
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Unread postAuthor: MikeNice » Fri May 21, 2010 2:08 am

Hairspray?!!! HAIRSPRAY?!!! BLEEECCCCCHHHHHH!! Sticky nasty evil good for nothing other than making hair sticky and nasty. Dude, I live on spray and pray spud guns (as far as my spudding is concerned). I didn't do the math out on your cannon, c:b ratio and all that, but all my guns are S&P with a BBQ ignitor and 2 sparks. Go with a dual spark set up and quit using hair spray. Raid your moms closet for some Static Guard or get some Tag body spray (mmm smells nice when you open your chamber).
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Your face is going to freeze like that. http://iplaaz.freehostia.com/
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Unread postAuthor: jimmy101 » Sat May 22, 2010 2:31 pm

MikeNice wrote:Hairspray?!!! HAIRSPRAY?!!! BLEEECCCCCHHHHHH!! Sticky nasty evil good for nothing other than making hair sticky and nasty. Dude, I live on spray and pray spud guns (as far as my spudding is concerned). I didn't do the math out on your cannon, c:b ratio and all that, but all my guns are S&P with a BBQ ignitor and 2 sparks. Go with a dual spark set up and quit using hair spray. Raid your moms closet for some Static Guard or get some Tag body spray (mmm smells nice when you open your chamber).

Yech. If you want a fuel use something that was designed as a fuel and not as hairspray, or deodorant or ... some other goofy purpose. A disposable butane lighter costs a buck. An aerosol can of engine starter cost about $3.

(edit: engrish)
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Unread postAuthor: MikeNice » Sat May 22, 2010 8:20 pm

True blue jimmy. . . Real fuels will almost always work better than something else designed for something else . . . But You have to admit . . . Tag DOES make your chamber smell good!
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