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have an idea on a combustion cannon AFTERBURNER ?

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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have an idea on a combustion cannon AFTERBURNER ?

Unread postAuthor: chrissilvermancs » Sun Mar 29, 2009 3:27 am

i was thinking if you had a regular combustion. for our purposes lets say its 3" chamber by 3' and reduced to a 2" pipe that was 1.5' then went to the barrel. with all the regular stuff on the 3" area: spark strips, fans, propane injection and meter, ball valve on back and even cam locks on the barrel.

but in the 2" area there would be two sprayers that sprayed rubbing alcohol from a compressed tank on top activated by a 2 stage switch on the trigger

(like a digital camera you half push the button down it focuses then all the way it takes. and this case it starts spraying half way down then sparks the propane.)

so once the propane is lit the flame heads towards the barrel but once it goes to the 2" section there's a second combustion potentially giving you more power

please comment on whether this could work or not
here is a 2 min drawing of my idea
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combustion with after burrner.JPG
everything i mentioned above is in the picture
combustion with after burrner.JPG (25.7 KiB) Viewed 1131 times
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Unread postAuthor: inonickname » Sun Mar 29, 2009 4:29 am

By spraying rubbing alcohol at any kind of speed you will get an inaccurate mix, thus reducing the power of your shot. It could only increase the amount of power if the propane mix was lean, even then a standard propane mix would probably give more power as the rubbing alcohol would be very hard to meter. Not worth it really.
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Unread postAuthor: chrissilvermancs » Sun Mar 29, 2009 5:04 am

now that i look back i meant to put the cam locks between the 3" to 2" so u put your burst disk between the cam locks and it would be the right mixture but after it ignites it will re ignite when passing through the 2" in theory

i will try to be more clear and look over my work next time but ya the cam locks are suppose to be between the 3" and 2" pieces
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combustion with after burrner redo.JPG
redo fix the cam lock problem and forgot to show burst disk's added interchangeable barrels too
combustion with after burrner redo.JPG (33.4 KiB) Viewed 1117 times
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Unread postAuthor: inonickname » Sun Mar 29, 2009 6:05 am

It will take a stroke of luck for that to work..rarely, due to the gasses momentum it may actually vacuum in fresh air and hot gasses after the shot, then ignite the mixture and burn your barrel..kind of like a pulsejet. You could try it, but flooding would be a serious enemy.
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Unread postAuthor: Ragnarok » Sun Mar 29, 2009 6:47 am

No. Afterburners can only work because there's still air left to burn any fuel in - which is why they can't be used on a conventional pulsejet (which is the closest jet engine relation to a combustion spudgun).
A properly metered propane cannon should have no excess air (else the fuel mix was lean), so an afterburner cannot help.

Sorry.
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Unread postAuthor: CpTn_lAw » Sun Mar 29, 2009 7:40 am

What if you were to find a flammable liquid that contains its own oxidizer? Or pressurizing the rubbing alcohol with gazeous oxygen...?
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Unread postAuthor: Biopyro » Sun Mar 29, 2009 8:51 am

Why not just have a normal propane mix inside this chamber? I don't really see what you gain by using rubbing alcohol as opposed to just having this part as an extension of the chamber.

If you did have atomised alcohol in this separated second chamber, it could be excellent for night shots because it wouldn't burn in the barrel. The burning propane would heat it up to combustion temperature, but it wouldn't burn until it hit the oxygen outside (hopefully), giving a nice fireball effect.
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Unread postAuthor: CpTn_lAw » Sun Mar 29, 2009 10:15 am

What do you do of the air already present in the atomising compartment f the barrel?
I think it's to much trouble than it's worth...
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Unread postAuthor: Biopyro » Sun Mar 29, 2009 10:18 am

I agree, but, although there will be some air in the atomising compartment, there won't be enough.
I don't think it's that worthwhile and there are probably better ways to do it, but I'm just looking for some good in the idea.
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Unread postAuthor: CpTn_lAw » Sun Mar 29, 2009 10:22 am

Plus, adding another fuel will take some of the combustion energy, just to propel and perhaps ignite. The result might be a "fwomp" due to a rapid decrease in chamber potential energy, plus a flammable liquid spray in the shooting direction.
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Unread postAuthor: Ragnarok » Sun Mar 29, 2009 10:25 am

CpTn_lAw wrote:What if you were to find a flammable liquid that contains its own oxidizer?

Which would be against forum Rule 3.

Or pressurizing the rubbing alcohol with gazeous oxygen...?

A complete excess of effort for less gain - why not just use the oxygen to allow you to burn more fuel in the chamber?
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Unread postAuthor: jimmy101 » Sun Mar 29, 2009 11:24 am

Ragnarok wrote:A complete excess of effort for less gain - why not just use the oxygen to allow you to burn more fuel in the chamber?

Or just increase the volume of the chamber by 10%. That would probably boost the gun's performance more than the very complex afterburner setup.
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Unread postAuthor: starman » Sun Mar 29, 2009 1:19 pm

I pondered this very afterburner setup (close to your second picture) about a year ago now. Basically a double burst disk setup with standard 1x mixtures in both chambers.

When it comes down to it, you have a 1x gun with a total chamber size of chamber 1 + chamber 2. As Jimmy mentioned, you could get roughly the same effect by just increasing the original chamber.

What hasn't been studied (that I know of) is could there be any dynamic, impulse type advantage to having the first chamber act as sort of a very high powered, directed thrust ignition of the second chamber, with possibly staggered burst disk values.

Another interested change would be to have the second chamber say a 5x hybrid and the first chamber act as a 1x "high thrust" ignition source.

Nice thinking Chris. I believe the idea could be developed some. However, I believe any advantages would come from an exotic setup.
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Unread postAuthor: D_Hall » Sun Mar 29, 2009 1:21 pm

CpTn_lAw wrote:What if you were to find a flammable liquid that contains its own oxidizer?

Then you're most likely playing with hydrazine. Would it work? Yes.

But let me put it this way... From time to time "play" with hydrazine at work. We wear "moon suits" when we do so and it *still* scares the crap out of me.
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Unread postAuthor: starman » Sun Mar 29, 2009 1:34 pm

starman wrote:Another interested change would be to have the second chamber say a 5x hybrid and the first chamber act as a 1x "high thrust" ignition source.


Now that I think about it, the pressure differential required to break a 5x burst disk (60 psi) could not be attained by a 1x ignition...you would need about 120 psi minimum on the ignition side to break it. Looks like you would be limited to 3x in the second chamber and minimum burst disk values entering it.

Another interesting experiment would be to have the 5x hybrid first followed by a 1x afterburner chamber.
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