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proper technique of chamber fans

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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proper technique of chamber fans

Unread postAuthor: Obctg » Sat Jan 06, 2007 7:48 pm

is there a certain technique dealing with chamber fans that yeilds the most power? For instance, do you leave the fan running while injecting fuel and firing?
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Unread postAuthor: MrCrowley » Sat Jan 06, 2007 7:51 pm

most leave it while injecting the fuel to help mix it around, A few people may leave them on but I wouldnt.
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Unread postAuthor: squeaks » Sat Jan 06, 2007 8:10 pm

exactly as mrcrowley said it, it doesn't matter, just use it to mix the fuel around and to vent. You can leave it running but it really doesn't matter.

Make sure you post in the right section obctg. This belongs in the combustion discussion, not showcase-a place where people show combustion cannons.
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Unread postAuthor: Obctg » Sat Jan 06, 2007 9:57 pm

oh crap, its been so long since ive posted a new thread. sorry ill dbbl check next time
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Unread postAuthor: SpudBlaster15 » Sat Jan 06, 2007 10:38 pm

Leaving the fan on while firing makes a large difference by inducing turbulence in the chamber's atmosphere, thus making flame propogation more rapid.
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Unread postAuthor: joannaardway » Mon Jan 08, 2007 12:23 pm

I'd leave it on. There's enough evidence that it makes a noticable difference.

If you're behaving and using rechargable batteries to run it, then there shouldn't be any problems.
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Unread postAuthor: PVCMAN » Thu Jan 25, 2007 11:06 pm

Ok, tis might be in the wrong place but I couldn't figure out were to ask my question, so here it is, "don't electric motors create tiny sparks that could ignite the fuel?"
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Unread postAuthor: frankrede » Thu Jan 25, 2007 11:23 pm

Use brushless fans.
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Unread postAuthor: Pete Zaria » Thu Jan 25, 2007 11:26 pm

@ PVCMAN,
Most modern computer fans are "brushless" and don't create sparks.

I've thought about trying to find a fan that does have brushes, which could be used for both fuel mixing AND ignition. It would be handy.

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Unread postAuthor: SpudBlaster15 » Fri Jan 26, 2007 12:48 am

Many people are using mini camping fans which feature brushed motors. No accidental ignitions have been reported, due to the fact that the sparks produced by a DC electric motor are simply inadequate to begin the combustion process. Some have attempted to deliberatly ignite a fuel mixture using an electric motor, and failed.
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Unread postAuthor: Hotwired » Fri Jan 26, 2007 6:31 am

You need to make a motor yourself if you want to guarantee serious sparking.

Then because of the sparking you're getting you'll need to repair it every now and again becuase the sparking corrodes the contacts like hell.

Not really the most reliable way to ignite the mix even so.
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Unread postAuthor: mark.f » Fri Jan 26, 2007 6:52 am

Alright here's the scoop (:D )...

My friend is currently working on his launcher. Since a 6x15" chamber is rather large, he thought a normal fan couldn't do it.

He's now currently using the motor he ripped out of something-or-the-other with a 12v rechargeable battery. When you remove the leads from the battery, (which are, now, just alligator clips), you get some serious sparking. Well enough to ignite the mixture...

The important thing is to make sure you have a good connection. He's going to be using some hoop connectors with threaded studs to mount the wires to the fan, to prevent disconnecting while the launcher is fueled. Also, the fan will not be switched on or off while the thing is fueling.

You can use a brushed motor, and you can even use a high-voltage power source... you just also need to use common sense as well...
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