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22mm pipe DDT?

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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22mm pipe DDT?

Unread postAuthor: Biopyro » Sun Jun 29, 2008 2:57 pm

Note: This isn't for use in a cannon!

Just wondering what sort of length of 22mm pipe would generate DDT. The fuel is a ~1.1x oxy/hydrogen mix, and will have a single ignition at one end.

I have heard that hydrogen on its own will make the transition in 30cm of 50mm pipe (from an engineering PHD), but this doesn't sound right to me.

Any ideas?
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Unread postAuthor: DYI » Sun Jun 29, 2008 3:39 pm

When we were discussing my proposed DDT gun, we decided that 20" of 1" pipe with oxy/hydrogen ignited at one end would detonate every time. For 22mm pipe, the required length would be a bit less.

If you want to reliably avoid DDT, don't use more than 3 times the diameter of the pipe for its length.

I don't know where the exact line is, but I'm fairly confident that these numbers, used properly, will achieve their desired affects. I'm assuming that, since you're using oxy/hydrogen, you want to generate DDT, probably for a noisemaker or something similar.

The D*6 number given by that PDF (?) sounds pretty close to me.
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Unread postAuthor: Biopyro » Sun Jun 29, 2008 3:47 pm

Thanks DYI, yeah it is for a noisemaker, simple but always impressive, most people don't appreciate the beauty of a silenced marble gun, but rather just enjoy a loud boom. PDF? PHD as in a doctorate, the guy was working on pharmaceutical production which involved piping in hydrogen - on a large scale production line DDT would be absolutely catastrophic.
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Unread postAuthor: DYI » Sun Jun 29, 2008 4:29 pm

PDF? PHD as in a doctorate, the guy was working on pharmaceutical production which involved piping in hydrogen - on a large scale production line DDT would be absolutely catastrophic.


Ah, okay. The way you formatted the sentence made it seem as though you meant "from an engineering PDF", not "quoted from a PhD in (insert field of engineering here)".

My cannon designs usually achieve the favourable attributes of both noisemakers and launchers on each shot, which is the effect I go for: impressive to bystanders, but still serving some more useful function than going BOOM.
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Unread postAuthor: McFear » Sun Jul 27, 2008 6:02 am

can i ask a question?

wtf is DDT. i keep hearing about it, and no amount of searching will show up what it actually stands for.

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Unread postAuthor: DYI » Sun Jul 27, 2008 9:53 am

wtf is DDT. i keep hearing about it, and no amount of searching will show up what it actually stands for.


The hundreds of combined hours of work on the SpudWiki weren't just done for sh*ts and giggles you know.

By opening a new tab, going to Spudfiles, then clicking on the SpudWiki link and typing "DDT" into the search bar, I found this in less than 30 seconds.
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Unread postAuthor: McFear » Mon Jul 28, 2008 6:37 am

ok. my bad

that was one place i didnt think to look. i didnt even realise we had a wiki here. woops. sorry mate.

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