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I'm not getting Combustions

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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I'm not getting Combustions

Unread postAuthor: The_Crackerjack_Man » Sat Feb 03, 2007 10:43 pm

Please dont yell at me but none of my searchs found this. I just want to know how the whole combustion cannon ends up fireing? I thank anyone who take there time to awnser.
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Unread postAuthor: Mr.Russ » Sat Feb 03, 2007 10:47 pm

Well basically, there is a chamber and a barrel.

You jam a potato down the barrel, then unscrew the end on the chamber and spray in a few seconds of hairspray or another flammable material. You then screw the lid back on, aim the gun and press the trigger. The trigger is normally a lantern sparker, or a sparker from a bbq lighter/stove. pressing the button sends a spark between 2 screws in the chamber, igniting the flammable material. It makes pressure, once the pressure is high enough it shoots the potato out of the barrel.

Sorry for not using paragraphs.
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Unread postAuthor: Hawkeye » Sat Feb 03, 2007 10:47 pm

You know when you hear about a gas line being left open in a house and someone walks in a lights up a smoke? Like that.
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Unread postAuthor: shud_b_rite » Sat Feb 03, 2007 10:48 pm

Well what do you think happens when you take flammable hair spray and a hot spark?
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Unread postAuthor: ballad of NJ » Sat Feb 03, 2007 10:48 pm

use axe or tag not hairspray thats all i can say
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Unread postAuthor: The_Crackerjack_Man » Sat Feb 03, 2007 10:49 pm

Okay, thanks. I wanted to make one and my dad asked why I needed a fan. And then I didnt know the awnser.
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Unread postAuthor: Mr.Russ » Sat Feb 03, 2007 10:52 pm

i dont even think you need fans for basic cannons? or am i wrong
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Unread postAuthor: sjog » Sat Feb 03, 2007 11:04 pm

A fan helps. The chamber needs air between shots. If it's windy hold back of gun into wind, that helps. The first add on for me was the fan,
more consistant, less miss fires.

Computer fans are cheap new, and much easier to get at the"dump".
I got 5 in one hour at the"dump" with a screw driver and a hammer.
Fly back circut wire too! TV's are fun, smash the top and yank wire.
It's right on top. DON"T smash picture tube!!!!!!!!
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Last edited by sjog on Sat Feb 03, 2007 11:12 pm, edited 1 time in total.

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Unread postAuthor: Insomniac » Sat Feb 03, 2007 11:08 pm

You don't need a fan, but if you can get one it's a good idea to use it.

The reason why is that in a normal combustion gun, the flammable air/fuel mix inside won't be mixed very well. It will be made of pockets of gas, some with lots of fuel and not much air, and some with lots of air and not much fuel. If one of these pockets of gas that has too much/too little fuel, it won't ignite. That means that if your spark gap happens to be inside one of these un-ignitable pockets when you hit the trigger, the gun won't fire.

If you have a fan in the chamber, it blends up all these little gas pockets and makes the fuel/air ratio the same all over the chamber, so when you hit the trigger the spark will be able to ignite it.

Also, if you leave the fan running when you fire it it makes turbulence in the chamber, which makes the fuel burn faster, making your gun more powerful.

I hope I'm making sence.
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I wonder how much deeper the ocean would be without sponges.
Right now I'm having amnesia and deja vu at the same time. I think I've forgotten this before.

Add me on msn!!! insomniac-55@hotmail.com
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Unread postAuthor: The_Crackerjack_Man » Sat Feb 03, 2007 11:12 pm

Yes that made a lot of sence and now I get the basic of who these guns work.
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Unread postAuthor: Mr.Russ » Sat Feb 03, 2007 11:27 pm

Have fun building your gn, I hope its succesful.
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Unread postAuthor: SpudBlaster15 » Sat Feb 03, 2007 11:43 pm

Proper mixing of the air and fuel within the chamber doesnt just aid in ignition, it also greatly increases the burn rate of the air/fuel mix. Latke found that the muzzle energy of a launcher increases by roughly 40% when a fan is used.

I suggest using a camping fan as opposed to a PC fan. A camping fan will spin around twice as fast, while using 1/4 of the voltage.
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Unread postAuthor: willarddaniels » Sun Feb 04, 2007 12:04 am

What do you mean, a "camping fan"?
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Unread postAuthor: SpudBlaster15 » Sun Feb 04, 2007 12:10 am

Image
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Unread postAuthor: MrCrowley » Sun Feb 04, 2007 12:11 am

A fan people use for camping, e.g in tents at night it may get hot and stuffy in a sleeping bag.....why not use a fan and cool yourself down 8)

Hence the camping fan :P
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