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Chamber fan question.

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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Chamber fan question.

Unread postAuthor: Jumpin Jehosaphat » Mon Jun 25, 2007 3:15 pm

I'm planning on making a metered propane combustion, and I want to use a chamber fan.

The pictures of cannons with fans confuse me. Aren't the fans exposed to the combustion when it is ignited? How do you prevent damage to a chamber fan?
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Unread postAuthor: psycix » Mon Jun 25, 2007 3:37 pm

I dont know the answer but i think chamber fans dont get damaged by the combustion, they just get warm. (correct me if im wrong)

I would like to add aswell:
What if the fan SPARKS inside!? Ehhh BOOM?
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Unread postAuthor: Flying_Salt » Mon Jun 25, 2007 3:40 pm

The fans are supposed to be in the chamber. They are exposed to the combustion, but don't get damaged, unless it's a crappy cheap fan that gets clogged with hairspray or something. But you'll be using propane so it'll be fine.
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Unread postAuthor: lukemc » Mon Jun 25, 2007 3:47 pm

psycix wrote:I dont know the answer but i think chamber fans dont get damaged by the combustion, they just get warm. (correct me if im wrong)

I would like to add aswell:
What if the fan SPARKS inside!? Ehhh BOOM?



that is why you use computer fans they are brushless and dont produce sparks

but yea they stay intact because is only a split second of combustion
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Unread postAuthor: jrrdw » Mon Jun 25, 2007 8:09 pm

Mount it in the end cap/clean out plug. Thats what i plan on doing.
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Unread postAuthor: Scotty » Mon Jun 25, 2007 9:47 pm

You could do as i have done and mount it in the middle of the chamber using silicone. Then just drill out a hole for the wires and silicone that up.
Silicone rocks!!

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Unread postAuthor: SpudBlaster15 » Mon Jun 25, 2007 10:16 pm

Most people fail to realize that combustion completes within ~50ms, which is nowhere near enough time to damage a fan.
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Unread postAuthor: psycix » Tue Jun 26, 2007 4:25 am

Another question:
Doesnt the fan block some explosion or airflow from the explosion?
It may divide your chamber into 2.

I once saw a few frame by frame pics wich showed he had 2 seperate combustions in his gun (though very very short after each other i kno) First one in the front, then one behind the fan.
It worries me....
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Unread postAuthor: TwitchTheAussie » Tue Jun 26, 2007 7:06 am

Put the fan in the back. I had no problems destroying my cannon by mixing butane with it :lol:
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Unread postAuthor: mark.f » Tue Jun 26, 2007 8:45 am

psycix wrote:Another question:
Doesnt the fan block some explosion or airflow from the explosion?
It may divide your chamber into 2.

I once saw a few frame by frame pics wich showed he had 2 seperate combustions in his gun (though very very short after each other i kno) First one in the front, then one behind the fan.
It worries me....


The fan may block the actual flame front slightly, but the pressure rise will still be pretty much the same. The raise in reaction rate due to the consistent mixture and turbulence would easily make up for any obstructions to the flame front.
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Unread postAuthor: psycix » Tue Jun 26, 2007 9:12 am

If i put the fan completly in the back, does it have any use then?
I can imagine that a fan in mid-chamber mixes more effectively..

Im thinking about fitting a very small fan (60x60mm) in my future gun so it blocks less and still can be mid-chamber, good idea or should I take the hugest fan that fits in?
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Unread postAuthor: Jumpin Jehosaphat » Tue Jun 26, 2007 11:45 am

Thanks for all the tips guys, It seemed like fans are exposed to flames in most cannons that use them, but I just wanted to be sure.

@ psycix: It seems like a big fan will mix faster, but a small fan will obstruct flow the least. There is a trade off, you could always go with a mid sized fan.
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Unread postAuthor: SnowFlox » Sat Jun 30, 2007 4:09 pm

how much does a fan increases the combustion ?
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Unread postAuthor: jimmy101 » Sun Jul 01, 2007 4:05 pm

SnowFlox wrote:how much does a fan increases the combustion ?

I don't think anybody knows the precise answer to that. Besides, a fan really does three things in a combustion gun.

1. It mixes the gases. This all by itself may well double the velocity that the gun shoots at. If nothing else, it will reduce the shot-to-shot variablity from perhaps 50% to ~10%.

2. If the fan is running during firing it should boost the burn rate and increase the muzzle velocity. Exactly how much is hard to say. An increase in muzzle velocity of perhaps 20% would seem reasonable.

3. The fan helps to air out the chamber between shots. That means you are much less likely to have CO2 and water vapor carrying over from shot to shot. Any CO2 or water vapor in the chamber displaces a like amount of oxygen.
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Unread postAuthor: iPaintball » Sun Jul 01, 2007 4:23 pm

Just mount the fan behind your spark gap to minimize obstruction of the flame front.
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