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Posted: Wed Dec 12, 2007 7:31 pm
by MrCrowley
Not all of it, just skim read over it.

I found that information in my other post for you, so i'm sure you can help yourself out and spend 15minutes having a read of the important stuff, after all you are the one asking for help.

I only know a bit more then you do, yet I still read some of it, so help yourself for once and that link should contain most of your answers as they do an experiment in metal pipe.

Come on don't be lazy just help yourself out until sme more knowledgeable members help you.

Posted: Wed Dec 12, 2007 7:35 pm
by bigbob12345
Okay Ill read it

Posted: Wed Dec 12, 2007 7:37 pm
by Fnord
Hey it's only 28 pages. ;)
Not War and Peace or anything.

I read through some of it once, but the original pdf is easier to understand because it has graphs and pictures.

Basically, there's almost no chance of getting DDT in a *normal chamber with propane as fuel and normal mixes.

*Normal meaning ~12" of 2" steel, and mixes under 10x.

Posted: Wed Dec 12, 2007 7:57 pm
by SpudBlaster15
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Posted: Wed Dec 12, 2007 7:59 pm
by DYI
You would really have to be trying to achieve DDT for it to happen. Even then you would likely have a difficult time with it. Without fuels like acetylene or hydrogen, and assuming that you don't have a 3' long 2" ID chamber with 3 running fans, there is extremely little chance of DDT ocurring. It's amazing how people used to think that they were risking DDT in 3" ID chambers only 12" long at 7x.

Without DDT, you have a very small chance of even reaching 2000 psi with C3H8/air combustion. At very high mixes, the combustion actually proceeds more slowly, and energy in the form of heat is dissipated through the walls of the pipe. So you really need not worry about blowing up a steel hybrid.

Posted: Wed Dec 12, 2007 8:12 pm
by bigbob12345
I m done readin now :P

Posted: Wed Dec 12, 2007 8:14 pm
by Novacastrian
bigbob12345 wrote:I m done readin now :P
Better go through it again to make sure you didn't miss anything.
Have you taken the Hybrid quiz?

Posted: Wed Dec 12, 2007 8:21 pm
by SpudBlaster15
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Posted: Wed Dec 12, 2007 8:24 pm
by bigbob12345
I have taken the hybrid quiz and got 9/10

Posted: Wed Dec 12, 2007 8:28 pm
by MrCrowley
bigbob12345 wrote:I m done readin now :P
Thanks for reading it, shows that your not some cold hearted, lazy spoonfeedee(?) :lol:




Note: If you can have 'employee', you can have 'spoonfeedee'.

spoonfeedee (spoon-feed-ee)

n.

A person who doesn't help themselves and seeks 'spoonfeeders' to supply them with simple information.

Posted: Wed Dec 12, 2007 8:41 pm
by DYI
Eh, the flame front velocity at high mixes is not *that* much slower. Scaling as 1/PChamber0.17, the flame front velocity in a chamber with an internal pressure of 8 atmospheres is only ~30% slower than it is in a chamber with an internal pressure of 1 atmosphere. Given that this decrease is relatively insignificant, (combustion will still occur within 50ms or so no matter the internal pressure) heat loss is not an issue in a properly sized hybrid chamber. Steel is effective in terms of heat reflection, which is much more important than heat conduction during the small time periods in which combustion occurs
You may very well be right, but you seem to disagree with Jimmy. I don't know a lot of the physics behind it, I just kind of learn as I go along. But either way, he's going to need a mix of about 20x or so to rupture the pipe, so he probably doesn't have to worry.

Posted: Wed Dec 12, 2007 8:47 pm
by MrCrowley
I think FAE's (fuel air explosives) produce around a 20atm mix, and they blow up buildings and what not :twisted:

Posted: Wed Dec 12, 2007 9:03 pm
by bigbob12345
I only plan to take it up to 4x but would it be safe if I went higher

Posted: Wed Dec 12, 2007 9:08 pm
by MrCrowley
Yeah, I would think 8x would be high enough and that's perfectly safe with the metal you're using. Just remember your launcher is as strongas it's weakest component.

Posted: Wed Dec 12, 2007 9:18 pm
by bigbob12345
I think Ill revise my 4x to 6x max