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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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Full auto combustion

Unread postAuthor: Ragnarok » Tue Nov 27, 2007 7:35 pm

As I mentioned in another thread, I'm working on plans for an auto combustion - and I'll have an nice little animation soon for you to look at soon.

I'll want the concept looked over when I'm done, but right now, my main concern relates to overheating from the ROF. At the likely speeds, the combustion will give off more energy than an electric fan heater.
The operation cycle is designed to cool as much as it can, but it can only do so much.

Water cooling was my first thought.
Just sleeving the chamber with a slight gap and and running water that would be easy if it were a shape that would make that possible - through necessity, it isn't.

The best I can think of is copper tubing coiled around the outside of the chamber with water running through it, but that's going to have poor heat conductivity, and cause other problems - I don't think it's a viable option.

Any ideas - any kind of cooling, but I've thought of the obvious heat sink.

I'm going to put a thermal cutout to override the electronic trigger anyway, like you tend to get on shooter games with some weapons that stop working if they overheat, but that should be a last resort.
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Unread postAuthor: Hubb » Tue Nov 27, 2007 7:39 pm

Are you concerned with the launcher performing poorly / failing or getting burned? If it is the latter, you may can build a shroud for it, similar to those used on machine guns to air-cool the barrels.
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Unread postAuthor: sandman » Tue Nov 27, 2007 7:54 pm

sleve the barrel in the air tank that you might use to purge the chamber, so as the gun fires the tank will lose pressure and get cooler and maybe cool the barrel.

Just a thought.
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Unread postAuthor: Hawkeye » Tue Nov 27, 2007 8:04 pm

Duct tape a cold pack to it for each shooting session ;)
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Unread postAuthor: Ragnarok » Tue Nov 27, 2007 8:11 pm

hubb017 wrote:Are you concerned with the launcher performing poorly / failing or getting burned?

Both. If it gets too hot, the structure will be compromised, and I risk injury.

@Sandman: Nice idea, but I'm not sure it's going to help much. The barrel isn't going to take that large a portion of the heat.
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Unread postAuthor: Zen/// » Tue Nov 27, 2007 8:48 pm

Copper FTW!

The great thing about copper is that you can submerge it in liquid nitrogen and it will still retain it's excellent failure characteristics - Steel will go brittle though, so if you accidentally drop your steel cannon in LN2 then you might want to let it warm up a bit before using it.

Hmm, ductility.

Maybe use liquid nitrogen?

Filling a sleeved chamber (over the barrel) would cause a problem, LN evaporating into regular nitrogen and pressurizing it. (boom?)
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Unread postAuthor: Ragnarok » Tue Nov 27, 2007 9:32 pm

Sensible suggestions only please. I don't have any spare liquid nitrogen about.
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Unread postAuthor: Mateo » Tue Nov 27, 2007 9:42 pm

well you could integrate a small fan from a hairdryer. or if you werent woried about weight you could maybe make a sleeve around the combustion camber and fill it with water. but if you do that you should make the sleeve so you can empty out the water.
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Unread postAuthor: thespeedycicada » Tue Nov 27, 2007 9:49 pm

Cooling fins and a high velocity fan shold work well.
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Unread postAuthor: Hawkeye » Tue Nov 27, 2007 9:51 pm

A water sleeve around the chamber does sound most sensible. It could be done with some of the large complex copper fittings available here.
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Unread postAuthor: sandman » Tue Nov 27, 2007 10:02 pm

Ragnarok wrote:@Sandman: Nice idea, but I'm not sure it's going to help much. The barrel isn't going to take that large a portion of the heat.
it does not necessarly have to be the barrel, if resourceful enough you could do it with any part.
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Unread postAuthor: Ragnarok » Tue Nov 27, 2007 10:23 pm

No sleeve around the chamber is possible, the shape doesn't allow it at all - I said that in the first post.

Fins are going to be hard to make and not much improvement... I need some outside the box thinking here really, most of this stuff occurred to me before.
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Unread postAuthor: Fnord » Tue Nov 27, 2007 10:25 pm

Edit: ok, outside-of-box idea #1: Water injection.
OOB idea #2: Heat pipe your propane tank to your chamber walls. Let the cooling/heating effects cancel eachother out (to an extent).

You can employ things like cooling fans, heat pipes, radiators and water jackets, but these are all likely to be temporary solutions.
Eventually, you're just going to have to suck it up and go metal.
Really, you just need a metal chamber/bolt/barrel, and the rest of the components can be crappy plastic as long as you put some heat spreaders between them and the CC.

Plus, nothing beats a gun that glows at night

This would be easier if we had some pictures, btw. Just a 5 minute mspaint drawing would be fine for this discussion.
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Unread postAuthor: bluerussetboy » Tue Nov 27, 2007 11:03 pm

how about a peltier cooler and a water bladder. if i recall AGV had an air conditioned motorcycle helmet that used a similar system.
some one also did a usb-powered peltier cooler for their guiness.

they do cool CPUs fairly well.
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Unread postAuthor: Ragnarok » Tue Nov 27, 2007 11:11 pm

@_Fnord: It will be metal, but it still needs to be kept cool.

Well if you need pics, here's a half complete diagram:
Image

It's missing most of the special valves and stuff, but that;s the approximate shape of the chamber - I said it would be hard to sleeve.
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