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A new concept in Combustion Cannons?

Built a combustion cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: SP00K » Sat Dec 20, 2008 10:23 am

Looks pretty nice, it kinda makes me want to build one. Right now, all I gost is a pray and spray in terms of combustion cannons and I hate it.
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Unread postAuthor: JohnnyBOOM » Sat Dec 20, 2008 12:47 pm

Holy cow, 100+ psi is up there. :shock: When I did the math, I only came up with a fudge factor of .65, which would mean a theoretical perfect burn according to my test should yield 32.5/.65 --> 50 psi. There must be something incredibly wrong with my math. Perhaps the burn temperature I used was wrong. Does 1170deg F sound too cold to you all?

Looking at specs from a PVC pipe manufacturer, Max pressure for 4" sch40 is 220 psi. Don't you worry about failure a bit with 100+ psi? I guess you could use 4" sch80 @ 320psi max or sch120 @ 430, but aren't those rather expensive and hard to find locally?
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Unread postAuthor: starman » Sat Dec 20, 2008 1:09 pm

JohnnyBOOM wrote:Looking at specs from a PVC pipe manufacturer, Max pressure for 4" sch40 is 220 psi. Don't you worry about failure a bit with 100+ psi? I guess you could use 4" sch80 @ 320psi max or sch120 @ 430, but aren't those rather expensive and hard to find locally?


220 psi is the official pressure rating. Pressures before failure is much higher.
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Unread postAuthor: john bunsenburner » Sat Dec 20, 2008 1:13 pm

People always get that mixed up:

The pressure rating is not the failing pressure but the highest recomended pressure. And if the optimum pressure is 100psi why would we be worried about that in a pipe rated 220psi?

Edit: Many charts about peak pressures can be found on the internet an don our wiki, just look around a bit.
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Last edited by john bunsenburner on Sat Dec 20, 2008 1:15 pm, edited 1 time in total.
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Unread postAuthor: JohnnyBOOM » Sat Dec 20, 2008 1:13 pm

But what sort of instantaneous "shock pressures" are exerted due to rapid expansion of gasses? Couldn't those be much higher also?

Edit: I shall indeed look around, I'm enjoying this community immensely. :D
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Unread postAuthor: starman » Sat Dec 20, 2008 1:37 pm

JohnnyBOOM wrote:But what sort of instantaneous "shock pressures" are exerted due to rapid expansion of gasses? Couldn't those be much higher also?


These are actually relatively "slow" burns and not detonations. Shock pressures aren't what you might think they are.
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Unread postAuthor: JohnnyBOOM » Sat Dec 20, 2008 1:47 pm

Lol, I was just reading that on your wiki. Guess my gut feeling about use of MAAP gas or Acetylene was right. The Wiki is also making me rethink one of my designs that has a long thin combustion chamber. I've never had problems with it, but probable better safe than sorry. :D
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Unread postAuthor: Xxplosive42o » Sat Dec 20, 2008 5:31 pm

Yea, you want to avoid those long chambers as well. It makes it VERY difficult to get a good air to fuel mix. Remember that propane/mapp gas is heavier than air. It will merely settle in your chamber. Even if you had a chamber fan which is highly recommended, you could never get a well mixed chamber with that design.

And there is no shock because our cannons work by deflagation versus detonation just so you know. :lol:
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Unread postAuthor: TwitchTheAussie » Thu Jan 01, 2009 6:37 am

Great discussions. Oh and Sp00k nothing wrong with the basics mate. Look up my cannons and youll see that Ive had fun with them all :D
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Unread postAuthor: spudtyrrant » Wed Jan 07, 2009 10:41 pm

[quote="Xxplosive42o"]His cannon has a release valve that operates the same as yours and is pictured below. The picture that shows it was apparently removed but I dug it back up. The blowtorch piece you’re using pre-mixes air exactly like his; except yours is more advanced. The only thing his setup has that yours does not is the open/close valve. It really serves no purpose because he is not using a metering system. Besides that your cannons work identically. Oh wait, yours has it's ignition built into the starter.

Cheers!


his design also uses the torch for ignition tho klugeboy's design has separate ignition
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