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20x-30x hybrid gun

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Is it possible to avoid DDT in this case?

Yes
5
83%
Maybe
1
17%
 
Total votes : 6
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Unread postAuthor: SpudMonster » Fri Aug 08, 2008 5:40 pm

benstern wrote:Correct me if I am wrong, but wouldn't the propane change to an unusable liquid state at the pre-ignition pressures we are talking about here?
benstern wrote:No, propane liquefies much lower then around 2000 psi.
Around the 250 psi range is more accurate.

benstern wrote:Yes but the air pressure + the propane pressure is what matters.


Dude, you've been corrected. Accept it.

Also

Image
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Stupid quote of the now:
joestue "The chamber is rated to 100 psi, it don't say that on the side, but the 2 inch stuff is rated to 300, so by analogy..."
"only the last two feet hear the end is black cellular core"
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Unread postAuthor: DYI » Fri Aug 08, 2008 7:37 pm

Yeah, pure propane liquefies at around 120psi at room temperature. We're talking about 4.2% propane, which means the propane portion will liquefy at around 2900 psi.

As long as you have a decent percentage of buffer gas left in the chamber, no high energy ignition, and no absurdly long runup distances, you really don't need to worry too much about DDT in propane/air mixes no matter how highly pressurised they are prior to ignition. Larda's 200x hybrid is living proof of those guidelines.
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Unread postAuthor: SpudFarm » Sun Aug 10, 2008 10:11 am

psycix wrote:Guys, this thread is not about the partial pressure on propane liquefying it, but about DDT.

An important factor of inducing DDT is the chamber size. With a thin, long chamber, DDT is more likely to happen then a spherical one.
Spark gap placement may also play a role.
Its all about the "runup distance" that the flamefront gets.


if he is worried he can just inject some inert gas like argon, Co2, nitrogen or helium..

DDT just wont happend here
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Unread postAuthor: Gunner » Sun Aug 10, 2008 3:05 pm

I am not worried about it anymore, BTW I have designed my next weapon very much and I think that I will starting to construct it someday and it will be MUCH more powerful than the old one :twisted:
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Unread postAuthor: SpudFarm » Sun Aug 10, 2008 3:07 pm

sounds good
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Unread postAuthor: Gunner » Sun Aug 10, 2008 3:14 pm

Spudfarm: I have added you on msn but there is something error? I cant write to you?
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Unread postAuthor: SpudFarm » Sun Aug 10, 2008 3:16 pm

hmm, people have the same problem on my msn..:S
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Unread postAuthor: Gunner » Wed Aug 20, 2008 9:38 am

Hmm...what do you think that can I use square chamber, does it make DDT easier?
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Unread postAuthor: Gunner » Wed Aug 27, 2008 1:22 pm

I mean this kind of chamber:
Image

Comments please! :D
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Unread postAuthor: Sticky_Tape » Wed Aug 27, 2008 1:43 pm

It makes the chamber more likely to exsplode most pressure vessels are cylindrical so there is less surface area for pressure to work on. Circles have less circumference than a square with the same diameter.
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You can tell how awesome a cannon is by the pressure used.
http://www.spudfiles.com/forums/high-pr ... 12803.html
xnt rnm ne z ahtbg
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Unread postAuthor: Gunner » Thu Aug 28, 2008 11:19 am

OK, but How about if thickness is enough much so there shouldnt be then any problems?
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Unread postAuthor: Pilgrimman » Thu Aug 28, 2008 11:40 am

I wouldn't trust it. It's weaker by far than cylindrical pipe because of the shape, and it appears welded together. The wall thickness looks very low, too.
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Unread postAuthor: SpudFarm » Thu Aug 28, 2008 3:32 pm

you can try to find something to sleeve it in, to make it thicker.

also, this insane finnish dude did charge copper pipe to 16x so that shows that things DO take more then you think.
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Unread postAuthor: Gunner » Fri Aug 29, 2008 10:56 am

Spudfarm, I am sorry but I did read wrong the pressure,it was 13bar and it means 14X but today I did really to put in it 15bars=16X and it was mistake, when I fired it, solder joint cracked :evil: well, that was this guns story, but next will be much better :wink:
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Unread postAuthor: SpudFarm » Fri Aug 29, 2008 11:55 am

picspicspicspicspicspicspicspicspicspicspicspicspicspics
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