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Hybrid Fan

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Hybrid Fan

Unread postAuthor: Hubb » Sat Mar 22, 2008 9:31 pm

While asking questions about my hybrid, I touched on the topic of a fan. It was immediately noted that a fan would be destroyed in a hybrid. It was also noted that one is not really necessary due to the air injection.

I know a chamber fan drastically increases the performance of a combustion and thought it may do the same with a hybrid, although I'm not sure.

Here is a couple of thoughts of mine to integrate a fan onto a hybrid and keep it from being destroyed through detonation.

Both designs incorporate ball valves to protect the fan from the detonation. Open the valve(s), operate the fan, close the valve(s), fire the launcher.

Thoughts?
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hybrid fan2.jpg
This is a better design, in my opinion, than the first design. It allows the fan not only to mix fuel, but also allows it to exhaust the fumes.
hybrid fan2.jpg (7.81 KiB) Viewed 1207 times
hybrid fan1.jpg
In this design, the fan is set up similar to a metering system. Once the fuel is injected, the ball valves are open and the fan turned on, allowing the fuel to mix.
hybrid fan1.jpg (7.03 KiB) Viewed 1207 times
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Unread postAuthor: Fnord » Sun Mar 23, 2008 12:21 pm

A hybrid will not necessarily destroy a fan.

I have fired mine at least 20 times and the fan is still fine.
You'll want to mount it parallel to the chamber rather than having it across the middle; I think the pressure differential will end up dislodging/breaking it if you "block" two halves of chamber with one.
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Unread postAuthor: jimmy101 » Sun Mar 23, 2008 2:31 pm

The first design looks like what I suggested to D_Hall for his "big-ass" gun. Basically a re-circ loop.

The second... I don't think it is going to mix very well. Probably better than nothing but not nearly as effective as the first design.

Of course, a fan used in this way only gets two of the three beenies of a fan in a combustion chamber, namely, mixing and venting.

Now, how do you get all three beeinies; mixing, venting and turbulance during combustion? Of course, with a burst disk, turbulance during combustion might not be all that important.
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Unread postAuthor: jimmy101 » Sun Mar 23, 2008 2:34 pm

_Fnord wrote:A hybrid will not necessarily destroy a fan.

I have fired mine at least 20 times and the fan is still fine.
You'll want to mount it parallel to the chamber rather than having it across the middle; I think the pressure differential will end up dislodging/breaking it if you "block" two halves of chamber with one.

Interesting thought. Does that mean that a fan that is significantly smaller than the chamber would have a better chance of surviving? Say a 1.5"D fan in a 3"D chamber, with the fan shifted off center towards the chamber wall.

EDIT: Engrish
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Re: Hybrid Fan

Unread postAuthor: SpudFarm » Sun Mar 23, 2008 2:36 pm

hubb017 wrote:Both designs incorporate ball valves to protect the fan from the detonation.


big plans ? :D
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Unread postAuthor: Hubb » Sun Mar 23, 2008 3:07 pm

Jimmy: In the first design, it is just to mix the air and fuel. The second is a more conventional type, common in a lot of combustion launchers. This one may be used to generate turbulence, but I would think in a hybrid, it would be more prone to causing DDT.

Fnord: I'm not really sure I follow that. The chamber is not going to be blocked off. The first design just allows the fan to be out of reach of the chamber when it is fired to help protect it.

Spudfarm: :D
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Unread postAuthor: DYI » Sun Mar 23, 2008 7:01 pm

Both designs incorporate ball valves to protect the fan from the detonation


Ask yourself not how to protect the fan from detonation. That is impossible. Instead, only realise the truth: ...every commercially made fitting on the chamber will be blown to sh*t by detonation :D
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Unread postAuthor: Hubb » Sun Mar 23, 2008 7:08 pm

As long as I'm not standing next to it, right?

I guess you guys pointed out a typo. Maybe I meant to say destruction. I probably did. You know, I do my best thinking after a drink or twelve.

The main reason I posted this was this: My hybrid fires since I upgraded to a stun gun ignition, however, it does so after about 5 or six seconds of holding the trigger. Then it goes off and scares the hell out of me.

I figured, with a hybrid fan, it would fire when I hit the trigger and not moments after.
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Unread postAuthor: DYI » Sun Mar 23, 2008 7:24 pm

Metering may be the problem. Can you describe your fuel meter and air injection systems?
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Unread postAuthor: Hubb » Sun Mar 23, 2008 7:46 pm

I can't remember remember the volumes of each, but the meter is made of 1/4" pipe with fittings and gauge and the chamber is made of 2" pipe, 12 inches long. The volumes were checked with water and the meter needs 51psi of propane to make the correct mix. The air is injected through the meter to push the propane through the meter.
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Unread postAuthor: sniperjosh » Tue Mar 25, 2008 5:14 am

I cant see a chamber fan incurring much if any performance gains in a hybrid, the injected air does a good job of mixing...unless there is a fan which can mix at the time of ignition, that would be interesting :D. Is your hybrid having problems firing at all mixtures, i know in mine, due to the location of the air and propane injection for 1x mixes it takes a while for the propane to even out and reach the rear-located spark plug, but as soon as i go for a 2x, 3x or higher, ignition is always instant.
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Unread postAuthor: Hubb » Wed Mar 26, 2008 4:29 pm

I have yet to have it misfire, other than the burst disk not rupturing once (my error).

I shot it yesterday, after I finished its mount (pics soon). It works okay but I figured that I wouldn't even be able to hear the clicking of the stun gun. It clicks for about a second or two then fires.
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Unread postAuthor: sniperjosh » Thu Mar 27, 2008 5:51 am

Hmm, a second or two still seems wrong to me, the instant my finger pushes the trigger, there is a boom :wink:. What mixtures does this happen at?
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