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Theoretical Combustion Cannon Power Improvement

A place to ask general spud cannon related questions.
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Unread postAuthor: mobile chernobyl » Thu Nov 03, 2011 6:12 am

Goats spudz wrote:.... so uncoil a transformer or get lots of copper wire or wire and stuff up your combustion :D


Couldn't have said it better myself. :wink:
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Unread postAuthor: POLAND_SPUD » Thu Nov 03, 2011 7:24 am

I'm sure JSR would love to do some tests with the HS camera and some clear tube
Seconded :D
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Unread postAuthor: Crna Legija » Thu Nov 03, 2011 7:51 am

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Unread postAuthor: POLAND_SPUD » Thu Nov 03, 2011 9:32 am

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Unread postAuthor: Moonbogg » Thu Nov 03, 2011 2:19 pm

Maybe this is why the movie Bambi was so dramatic. I mean, with all those trees causing the flames to fold over on themselves and accelerate, that poor deer had a real hard time.
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Unread postAuthor: jimmy101 » Fri Nov 04, 2011 6:19 pm

Overall I would suspect that adding much of anything to the chamber of a typical spudgun is going to decrease performance. It will displace fuel/air mixture and also greatly increase the surface area. Surface area sucks up a heck of a lot of the energy in a combustion gun.

In a very large chamber stuff might help simply by inducing turbulence in the flame front which in turn will speed the burn rate. The bigger the chamber is the slower it burns. But in a typical spudgun sized chamber it'll just suck up heat.

In a very large chamber (like a couple hundred yards of 1' diameter sewer line) the burn rate is going to be very slow. That means the manhole covers will pop up at a fairly low pressure and percent fuel burn. Since it probably takes basically zero pressure to lift something with as much area as a manhole cover, they'll lift off after only a small percentage of the fuel has burned. Adding mesh, netting etc. may help boost the burn speed enough to get a more spectacular launch of the manhole covers.

I seriously doubt this has any application to a typical combustion spudgun/
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Unread postAuthor: Mr.Tallahassee » Fri Nov 04, 2011 7:09 pm

Here's the thing, all chamber sizes burn at the same rate but the amount that they have to burn changes. The percentage of fuel burned per second changes, not the rate. Adding the mesh also does not change the volume by that much and more volume doesn't necessarily mean more power. The burn rate and the amount of energy in the fuel are what matter most. As to thermal losses, that's negligible. MythBusters actually proved the theory by the fact that a proper mix did not low off the scaled man hole covers without the debris causing turbulence. It's well worth the shot. I intend to test this theory when I can get the materials I need.
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Unread postAuthor: MrCrowley » Fri Nov 04, 2011 7:12 pm

Mr.Tallahassee wrote:MythBusters actually proved the theory by the fact that a proper mix did not low off the scaled man hole covers without the debris causing turbulence. It's well worth the shot. I intend to test this theory when I can get the materials I need.

I thought the 'closed' proper mix did blow the covers off, the proper mix with the open end is the one that failed to remove the covers.
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Unread postAuthor: POLAND_SPUD » Fri Nov 04, 2011 7:15 pm

it'll just suck up heat
what about nonmetalic materials like asbestos? (lol yeah safety first... change that to glass fiber... )
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Unread postAuthor: jimmy101 » Fri Nov 04, 2011 8:26 pm

I can't watch the video and I am assuming they are using a fairly large piece of pipe and something similar to a manhole cover. The gun overall is the proverbial "mine sized chamber" with a low mass and basically zero friction ammo in an extremely short barrel.
Mr.Tallahassee wrote:Here's the thing, all chamber sizes burn at the same rate but the amount that they have to burn changes.

False. Chambers burn at rates that are a function of the size of the chamber. A larger chamber takes longer to burn than does a small one.
The percentage of fuel burned per second changes, not the rate.
What exactly do you think "rate" means. Burn rate is d(fuel)/d(time).
Adding the mesh also does not change the volume by that much and more volume doesn't necessarily mean more power.
But less volume rarely means more power.
The burn rate and the amount of energy in the fuel are what matter most.
Yes the burn rate is key, but adding mesh to a standard size chamber is unlikely to change the burn rate, indeed it'll probably slow it down. (Google "Davy lamp" for what metal mesh does to a flame front). A fan will do the same thing with much less loss of heat.
As to thermal losses, that's negligible.
Says who? A typical spud gun is about 10% efficient. At a CB of 0.8 the spud leaves the muzzle at about the time the pressure in the chamber drops to zero (gauge). Where do you think the other 90% of the energy goes?
MythBusters actually proved the theory by the fact that a proper mix did not blow off the scaled man hole covers without the debris causing turbulence. It's well worth the shot. I intend to test this theory when I can get the materials I need.
They proved the theory in a system that is not similar to a spudgun. The closest similar thing is Dave's "gun-o-god". Dave doesn't have debri in the gun and wouldn't even consider it. A burst disk does the job much better. At 1X, no burst disk, or debris, is needed.
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Unread postAuthor: EpicMadness » Sat Nov 26, 2011 2:16 pm

yea i know i'm new, so excuse my stupidity.

@topic:
how about throwing in crumpled chicken wire and such? metal screens?

btw i'll be making a thread in the combustion section about a design that looks like this:
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the theory i made up is that the metal rubbish would help create turbulence for the fuel to mix, and help create a stopper-like effect for increase in pressure in the main combustion chamber.

my concern is if this cannon could pull back fresh air from the exit vent after the ignition where, i've heard from people, creates a temporary vacuum(Credits for the jamjar jet theory).

PS: my fuel would be butane, i got tons of lighters here and there, if not, gasoline(would be insanely dangerous).

PSS: requesting a halt notice about the project before i post it so i wouldn't end up breaking any rules.
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