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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: Pilgrimman » Fri Jan 25, 2008 4:58 pm

The fan mixes the gas so that it can ignite more readily. If the gas is not mixed well, one portion of the chamber is too rich to ignite, thereby making the other not rich enough. It does serve in venting too, though.
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Unread postAuthor: DYI » Fri Jan 25, 2008 5:00 pm

Pilgrim - what you state is only a secondary benefit. The primary purpose of the fan is to create a turbulent flame front.
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Unread postAuthor: jimmy101 » Sat Jan 26, 2008 11:09 am

DYI wrote:Pilgrim - what you state is only a secondary benefit. The primary purpose of the fan is to create a turbulent flame front.

I disagree. A turbulent flame front certainly is a good thing, but well mixed fuel+oxidizer is at least as important as the turbulent front.

Of course, it is kind of hard to use a fan to get a turbulent front without the fan also causing the fuel to be well mixed so it is hard to tease out exactly how much each affect is worth.

From my closed chamber studies it looks like about half the affect of a fan is due to mixing and half to the turbulent front.

One of the big benefits of well mixed fuel+oxidizer is that the gun will fire much more consistently, especially on a cold day.
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Unread postAuthor: jackh » Sat Jan 26, 2008 5:28 pm

so if im not gonna get a fan, when i spray the fuel in the chamber, would it be best to wait a little bit after screwing on the cap for the fuel to settle in the chamber and not have too rich/not rich enough areas?
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Unread postAuthor: jimmy101 » Sat Jan 26, 2008 5:56 pm

jackh wrote:so if im not gonna get a fan, when i spray the fuel in the chamber, would it be best to wait a little bit after screwing on the cap for the fuel to settle in the chamber and not have too rich/not rich enough areas?

Well, using "spray-n-pray" fueling it really doesn't much matter what you do. :? The performance is so bad that any combustion is considered a success.

You probably should screw the cap onto the chamber immediately. Inverting the gun a few times will help mix the fuel, but not nearly as well as a fan will do it. Waiting a minute or two after fueling will also help a bit.

On cold days the gun's performance will probably suck (blow?).
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