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Ignition with Rocket engine igniters?

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: Gippeto » Wed Oct 01, 2008 9:11 pm

grumpy wrote:
Gippeto wrote:Would replacing the igniter with a piece of slightly heavier nichrome wire still work? :)


rocket ignitors are made from a bent piece of nichrome wire with a chemical on the bend. the cigarette lighter in cars is made from a heavier nichrome wire.


I have a roll of 26ga nichrome wire, (36 feet to be exact) left over from a hot wire project. That's what I had in mind when I proposed the "slightly heavier nichrome wire".

Just wondering if it would have uses in this hobby too. :)
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Unread postAuthor: Lentamentalisk » Wed Oct 01, 2008 10:01 pm

If you aren't getting it far enough, then increase the lengths of your chamber and barrel. Ideally you would have a 3" chamber, for a faster burn rate, but that is not too crucial. Just make both the chamber and barrel at least 2' long each, and that is realllllly minimal. Shooting potatoes out of my spray and prey, i got at max 400', and that was with a 1.5"x4' barrel and a 3"x18" chamber, which is much larger.
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Unread postAuthor: unhipjuffowupp » Wed Oct 01, 2008 10:13 pm

the problem is.. it cant be that long. It has to fit inside an empty tube i have which is 30 inches long. And it has to be 2" pipe. Is there any way to get this to work? And still get a 300' range?
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Unread postAuthor: Lentamentalisk » Wed Oct 01, 2008 10:48 pm

Without getting into much more complicated stuff, the answer is no. One thing you can to do increase your performance is add a burst disk between the chamber and barrel. This is basically just a threaded union with many layers of tape across the opening. This allows the pressure to build up more before the tape bursts, and the gases start pushing the balloon. The only risk with that is you risk applying too much force to the balloon at once, and popping it in the barrel, though I doubt you will do that at such low pressures.
If you don't know what a burst disk is, look around in the combustion showcase section for examples.
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Unread postAuthor: fogus » Tue Nov 04, 2008 2:34 pm

VH_man, have you had success with steel wool? If so, or if anyone else has, I would be interested in knowing what thickness they were using.

I would like to try to to ignite a mix using around 9V and a piece of steel wool. Any success stories?
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Unread postAuthor: Floyd » Tue Nov 04, 2008 4:39 pm

Steel wool should work fine. If using a 9 volt battery make sure to keep the amount small. As for the type, pretty much any thickness will work, if you want it to glow without burning out you will probably want the thickest kind possible.

I was just experimenting with a camera flash circuit and steel wool. It is pretty sweet.
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 04, 2008 4:47 pm

Gippeto wrote:Just wondering if it would have uses in this hobby too. :)


Electrically fired burst disk ;)
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Unread postAuthor: The Engineer » Tue Nov 04, 2008 6:09 pm

You could change your barrel to a smaller size, like 1 inch. You would be surprised at what can still fit in there. If you don't want to go that small, then try 1.25 or 1.5 inch.
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Unread postAuthor: jimmy101 » Wed Nov 05, 2008 4:38 pm

Estes rocket igniters, steel wool + 9V battery, fine nichrome wire with a 12V battery, 14G copper wire with an automotive type battery ... All of those will ignite propane in air. If it doesn't, the chances are about 99% that the problem is not the igniter but the fuel mixture. Most likely, the fuel mixture is too rich (too much fuel).
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