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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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Ignition with Rocket engine igniters?

Unread postAuthor: unhipjuffowupp » Tue Sep 30, 2008 1:15 am

So i decided to skip the whole grill ignitor idea and just use rocket engine ignitors to ignite the fumes... Is this possible?

I hooked everything up, sprayed in my hairspray, and for some reason the fumes didnt ignite. So i thought maybe they were creating enough of a spark or something... So then i wrapped matches around the end of the ignitor. I tried it again and nothing happened. All the matches lit, but it didnt ignite the fumes.

Whats wrong here? Can anyone explain this to me?

Do potato cannons NEED to be ignited only by a spark?
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Unread postAuthor: ALIHISGREAT » Tue Sep 30, 2008 1:40 am

how do rocket ignitors actually work? i had a rocket a few years ago, but only used it a few times so i'm not knowledgable on the subject.

however it sounds odd that even the match could not ignite the mix... so maybe you are using way too much fuel, or way too little fuel sothe mix can't ignite (i'm guessing way too little as the match lit)
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Unread postAuthor: jook13 » Tue Sep 30, 2008 1:45 am

I would guess that the problem is fuel amount... I have used rocket ignotors to start up black powder things, but we cant talk of that on this site. the point is, I think the rocket ignitors should work....
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Unread postAuthor: unhipjuffowupp » Tue Sep 30, 2008 2:49 am

The rocket engine igniters are just little two wiers attatched to the positive and negative of a battery, then they have nichrome wire in between with a small amount of powder on the tip of it, so it gets red hot and ignites the powder.

i was using hair spray.. that didnt work so i tried axe, that didnt work either. When i spray it in, it seems like alot of it just pours back out The problem im having is im very restricted to my chamber size. I have a 2 inch barrel, with a 2 inch chamber. Thats all i can work with for what im trying to build. The chamber is about 3 inches longer than the barrel. But when i go to spray the propelant in, it all sprays back out becuase of the small size. Maybe i should just use the oldschool method with lighter fluid. Do you think that would work?

I was also thinking of ditching the rocket engine igniters and using a piece of nichrome wire and then just cutting a slit in the match head and placing it on the wire.

Im not really looking for serious power here, Just enough to shoot about 300 feet.
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Unread postAuthor: Hotwired » Tue Sep 30, 2008 6:38 am

You might be surprised at how little you need to put in, if you're getting a cloud of spray coming out of the breech you're going over the top.

For a demonstration of how little you really need, get a transparent empty drinks bottle and some way of igniting the contents without having your hand above the bottle mouth (burnt hair and or skin...).

Spray the hairspray in for the shortest possible time you can hold the button down for. Then hit the igniter. It will ignite the spray. Mess about with the length of time you can spray into the bottle before it stops working. Need to blow out the bottle between tests or just swing it about a bit to refresh the air inside.


It's fairly amusing just doing that for a bit, you can any kind of effect from a light blue flame front slowly(ish) travelling down the bottle to a roaring blue or yellow flame filling the bottle and gushing out of the top :P
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Unread postAuthor: TurboSuper » Tue Sep 30, 2008 7:05 am

I'll assume you could use a rocket ignitor, but why the hell would you want to? They're one-time use and will end up getting pretty expensive pretty quickly. They won't accomplish anything any other type of ignition source would, either.

It doesn't matter if you hold up a dragon who just drank hotsauce to the thing, it won't fire if the fuel mix ain't right.
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Unread postAuthor: unhipjuffowupp » Tue Sep 30, 2008 7:22 am

Ok ill mess around with how much fuel im using... Do you thing red hot wire will ignite fumes? or does it not get hot enough?
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Unread postAuthor: mark.f » Tue Sep 30, 2008 9:13 am

It's hot enough, but like TurboSuper said, the get pretty expensive really fast... especially if you are still messing around with the fuel mixture.
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Unread postAuthor: Gippeto » Tue Sep 30, 2008 12:01 pm

Would replacing the igniter with a piece of slightly heavier nichrome wire still work? Kind of like a home made glow plug.

I'm sure I've seen that somewhere here.

A quick search for "glow plug" does turn up results. :)
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Unread postAuthor: unhipjuffowupp » Tue Sep 30, 2008 9:18 pm

Im trying to avoid using nichrome wire becuase theres no were around here to buy it. Id have to order it.

I heard you can use a violin string though... o.O
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Unread postAuthor: Gippeto » Tue Sep 30, 2008 10:40 pm

Have a small airport or performance shop nearby? Stainless steel safety wire works too.
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Unread postAuthor: unhipjuffowupp » Tue Sep 30, 2008 11:15 pm

well... i needed this thing done by the end of the week... so i said screw all the other designs and decided to use the grill ignitor. It works fine. Ill post up the finished product later.

But theres one problem... I want to be able to shoot waterballoons out of it. I made little sabots for it and everything, but it isnt getting enough range. I get about 60-70 feet out of it. Im using aqua net, and Rave 4x hairspray.

Why am i not getting enough power? I want to be able to shoot at least 300 feet.

Could it be the dimmensions im using? I have a 18" chamber and a 10" barrel. Both the chamber, and the barrel are 2" PVC. Should the chamber be longer? should the barrel be longer? Is there anything to calculate lengths of chambers?

I hope it doesnt need a 3" chamber, becuase it has to fit inside a 3" pipe.
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Unread postAuthor: rp181 » Wed Oct 01, 2008 6:53 pm

piano wire works too
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Unread postAuthor: grumpy » Wed Oct 01, 2008 8:21 pm

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.
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Unread postAuthor: VH_man » Wed Oct 01, 2008 8:27 pm

What ever happened to Allligator CLips and Steel Wool?
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