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Full auto combustion

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: jackssmirkingrevenge » Tue Nov 27, 2007 11:33 pm

if it's all metal, just dip the whole darn thing in cooking oil ;) - 'course it'll stink and be a [female doggy] to service, perhaps a water jacket would be a better idea. I doubt you'd actually need to circulate the water though, maybe put a series of aluminium discs on the barrel as cooling fins, like the Besa Mk.1:

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Unread postAuthor: Killjoy » Tue Nov 27, 2007 11:36 pm

What metal are you using? If its copper you could wrapp the copper tubing around it and solder it on to increase heat conduction. You could also solder fins on.

You could grab some of those 1/4" irrigation sprinklers hook them to a pump with a bucket of water and just spray water on the combustion chamber.
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Unread postAuthor: Hubb » Tue Nov 27, 2007 11:54 pm

Isn't some gun barrels fluted to dissipate heat?
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 27, 2007 11:59 pm

hubb017 wrote:Isn't some gun barrels fluted to dissipate heat?


That only works with bolt action rifles - full auto jobbies like the early model thompson use fins as they provide a much greater surface area for heat dissipation, just like the fins on motorbike engine cylinders.
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Unread postAuthor: mark.f » Wed Nov 28, 2007 6:18 am

Wrap copper tubing around the chamber to pump water in. Next, cover tubing coils in a heat conductive filler, (some sort of castable compound is what I'm thinking), and wrap in aluminum foil. Have the coils running to a small radiator, (out of an old car or some such), and have an electric fan running over it, (they make electronic fans for trucks trying to get max HP by not having the mechanical draw of a standard fan). Fill the system with methanol, and pump it through the coils with a small rotary vane pump.

This is the best idea I can think of to cool such an odd-shaped chamber.
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Unread postAuthor: Hawkeye » Wed Nov 28, 2007 9:32 am

Try to get some Ceramic tubing for the combustion chamber. You might as well just have a material that can take it rather than trying to cool one that can't.
There is a good supplier of Ceramic products in Sheffield.
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Unread postAuthor: paaiyan » Wed Nov 28, 2007 11:15 am

I agree with the copper tubing liquid cooled system. You can ever figure out what parts get hot and put more tubing there. Solder it to the metal with a highly thermally conductive solder. Or maybe even CPU thermal paste? I'm not sure if that would work though. Anyway, I think that's your best bet. You can use something with a very low freezing point as the liquid. Put a coil of the tubing in say, a bucket of water with dry ice in it? You could use copper tubing for the gun and coil in the water, and use regular clear tubing to connect them, so flexibility and movement aren't an issue.

EDIT: Methanol appears to have a lower freezing point than dry ice, so it could be used as a coolant
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Unread postAuthor: Ragnarok » Wed Nov 28, 2007 12:17 pm

All well and good, but not many people have access to dry ice.

I've looked over the design, and I reckon there are some changes I can make to improve things I think it can get more ROF if I change the bolt over with a multiple barrel rotary loader. Would need one hell of a motor though.

There might also be a way to change the chamber shape so it's a little more practical if I did that.
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Unread postAuthor: psycix » Wed Nov 28, 2007 5:24 pm

In fact you got 2 options:
-watercooling
-aircooling

For aircooling you will need fins or rings on the chamber to act as heatsink
You could mount a fan onto this heatsink to blow cold air through the fins.
I think that will make it very effective.

For watercooling you could OR do a spiral around OR make a direct contact between the water and the pipe (by sleeving with a small amount difference)


I believe the sleeved watercooling is overkill and will make it difficult/heavy.
I think the spiral watercooling may be effective.
But I certainly reccomend air cooling, with fans and fins.
This cools more then you think, and it will cool well enough. (UNLESS its a very very warm climate you live in, because air cooling wont cool very good when its hot weather.)
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Unread postAuthor: paaiyan » Thu Nov 29, 2007 12:58 pm

Ragnarok wrote:All well and good, but not many people have access to dry ice.


For serious? I know a couple grocery stores near me that sell it. And my mom knows a pie company that ships pies through the mail, they package them with like 2 pounds of dry ice.
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Unread postAuthor: Ragnarok » Thu Nov 29, 2007 3:05 pm

paaiyan wrote:I know a couple grocery stores near me that sell it. And my mom knows a pie company that ships pies through the mail, they package them with like 2 pounds of dry ice.

Yes, for serious. Dry ice does not come except from special order, and storing it is not something I want to think about.
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Unread postAuthor: octane89 » Thu Nov 29, 2007 4:40 pm

Well I think it really depends on your ROF.
But a idea I have is a little off the wall too. If you "inject" co2 it could keep it cool. When it expands fast it gets cold, but your cannon may sweat because of it. I haven't really thought of how you could use it, maybe adapt a 12g cartridge to a line that runs where it's needed.
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Unread postAuthor: iknowmy3tables » Thu Nov 29, 2007 5:43 pm

or at least for the prototype wrap it in wet towels, maybe paint the insides of the chamber with heat resistant paint.

you might get a cooling affect from the propane, maybe a propane coil made from compression tubing I'm sure its less dangerous than it might sound, and keep the propane bottle upside down
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Unread postAuthor: octane89 » Thu Nov 29, 2007 6:40 pm

Heat resistent paint sounds like a solid idea-there is also "high performance enamel" by rustoleum that works just as well.
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Unread postAuthor: sandman » Thu Nov 29, 2007 9:17 pm

@octane
i think your idea would make th gun heat up not cool down. the cartage pressure would drop so it would get colder, but wherever you "inject" will get hotter as the temp would go up
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