Jimmy101: some answers to benstern's questions, and some new questions

2008-06-09T16:00:38Z

some answers to benstern's questions, and some new questions

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			I've never heard of a fan showing significant signs of melting in a correctly operating gun. I can imagine the fan melting if the cleanout plug was removed and the gun was ignited since the flame front would move through the fan very slowly.

			Typical times from click to boom for generic combustion guns is about 50 milliseconds or so. The high temp probably lasts 10~20mS. The high temperature may indeed only last a couple milliseconds after the end of combustion but it is hot in the chamber long before combustion is complete.

			I would think the risk of fan-induced DDT in a hybrid is pretty minimal. Besides, DDT <> gun failure since the energy released in DDT depends on when it happens. I suspect the main reason for not seeing many hybrids with chamber fans is because of

			1) the extremely high temp and pressures making it likely the fan will be destroyed

			2) the difficulty in installing a fan in a metal chamber (the wiring would be a PITA)

			3) hybrids often have fairly small diameter chambers and hence would need very small fans

			4) a fan wouldn't help much with venting the chamber since hybrids rarely have large diameter removable plugs (never seen a hybrid that uses a cleanout plug).

			5) Proabably the most important reason, burn speed is much less important in a hybrid than in a generic combustion gun. The hybrid's burst-disk delays the ammo's movment until most of the fuel has been burned so burn speed just isn't all that important. (In a normal combustion the ammo starts to move when only ~10% of the fuel has been burned, the fan helps to get the other 90% of the fuel burned before the ammo exits the barrel.)

			6) you don't really need one since the energy available in the chamber is so much higher than in a 1x gun, the performance increase due to a fan would be much less in a hybrid than in a 1x gun.

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			Should a section be added to the fan page discussing the size of the fan? The fan shown is nearly the same diameter as the chamber. This should be great for venting the gun but may not be optimal for mixing and turbulance induction. Indeed, it might do little in the way of inducing turbulance. Many builders use CPU fans (typically 40~50mm) instead of the much larger case fans. In a closed chamber a fan nearly the diameter of the pipe may give minimal actual gas flow since there is really nowhere for the gases to go to and no real path from the high pressure side of the fan to the low pressure side. A smaller fan allows the gases to be circulated around the fan and would be expected to give much higher gas velocities.

			jimmy101

Benstern: New page: I have a few questions. 1) By "'''quick vent plug'''", do you mean Quick disconnect? 2) I am pretty sure that I have have heard of pc case fans melting in combustion spudguns. Can so...

2008-06-04T03:43:36Z

New page: I have a few questions. 1) By "'''quick vent plug'''", do you mean Quick disconnect? 2) I am pretty sure that I have have heard of pc case fans melting in combustion spudguns. Can so...

New page

I have a few questions.

1) By "'''quick vent plug'''", do you mean [[Quick disconnect]]?

2) I am pretty sure that I have have heard of pc case fans melting in combustion spudguns. Can someone verify this?

3) I believe that good amount of high heat in the combustion chamber lasts longer then "a few milliseconds" after combustion has ended.

4)Can someone confirm or deny the statement about turbulence of the flame front being undesirable in hybrids due to increased risk of DDT?

Thanks,
benstern

Talk:Chamber fan - Revision history

Jimmy101: some answers to benstern's questions, and some new questions

Benstern: New page: I have a few questions. 1) By "'''quick vent plug'''", do you mean Quick disconnect? 2) I am pretty sure that I have have heard of pc case fans melting in combustion spudguns. Can so...