Login    Register
User Information
Username:
Password:
We are a free and open
community, all are welcome.
Click here to Register
Sponsored
Who is online

In total there are 76 users online :: 7 registered, 0 hidden and 69 guests


Most users ever online was 155 on Mon Aug 15, 2016 1:40 am

Registered users: Bing [Bot], farcticox1, Google [Bot], Gussmoore, Majestic-12 [Bot], MSNbot Media, Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

DDT

A place to ask general spud cannon related questions.
Sponsored 
  • Author
    Message

DDT

Unread postAuthor: microman171 » Sun May 04, 2008 9:01 pm

I was reading through the hybrids and the word/acornym 'DDT' came up. What is DDT? I hope this is the right forum for this kind of thing.

I gather that it is a bad thing (metal shards sticking out of my flesh yay!!).

Thanks

Microman171
  • 0


microman171
Sergeant Major
Sergeant Major
 
Posts: 189
Joined: Wed Apr 30, 2008 11:49 pm
Reputation: 0

Unread postAuthor: DYI » Sun May 04, 2008 9:04 pm

Deflagration to Detonation Transition. The flame front experiences a sudden acceleration from turbulent flame front velocities to detonation velocities (over 3km/s in some cases). The mechanisms behind this are numerous, and not fully understood, although dieseling may be the problem in some cases.
  • 0

Spudfiles' resident expert on all things that sail through the air at improbable speeds, trailing an incandescent wake of ionized air, dissociated polymers and metal oxides.
User avatar
DYI
Lieutenant General
Lieutenant General
 
Posts: 2861
Joined: Sat Jul 07, 2007 8:18 pm
Location: The People's Republic of Canuckistan
Country: Turks and Caicos Islands (tc)
Reputation: 9

Unread postAuthor: JDP12 » Sun May 04, 2008 9:23 pm

DDT=bad.. hahahaha... avoid long chambers at all costs.
  • 0

"Some say his pet elephant is pink, and that he has no understanding of "PG rated forum". All we know is, he's called JSR. "
User avatar
JDP12
Major General
Major General
 
Posts: 1943
Joined: Fri Mar 30, 2007 8:34 pm
Reputation: 0

Unread postAuthor: microman171 » Sun May 04, 2008 9:51 pm

So it is a sudden increase in the speed of the flames? I dont get it... :oops:
  • 0


microman171
Sergeant Major
Sergeant Major
 
Posts: 189
Joined: Wed Apr 30, 2008 11:49 pm
Reputation: 0

Unread postAuthor: D_Hall » Sun May 04, 2008 10:36 pm

microman171 wrote:So it is a sudden increase in the speed of the flames? I dont get it... :oops:

What's not to get? The flame front accelerates to detonation velocities. That's what DDT is. That's ALL that it is. What part of that is escaping you?
  • 0

Simulation geek (GGDT / HGDT) and designer of Vera.
User avatar
D_Hall
Donating Member
Donating Member
 
Posts: 1759
Joined: Thu Feb 07, 2008 7:37 pm
Location: SoCal
Reputation: 6

Unread postAuthor: biggsauce » Sun May 04, 2008 10:44 pm

Regardless of the reasons for it happening, as D-Hall said, its pretty simple. "Something" causes the speed of the flame front to surpass the speed of sound in the gases in the chamber.

Try google and this http://www.galcit.caltech.edu/EDL/publications/reprints/jannaf99_paper.pdf
  • 0

User avatar
biggsauce
Captain
Captain
 
Posts: 338
Joined: Thu Jun 07, 2007 9:42 pm
Reputation: 0

Unread postAuthor: joestue » Sun May 04, 2008 11:04 pm

Not completely off topic, but is the shock wave as a side affect of DDT the 'bad' thing, or is it the pressure generated?

As an example if you fill a 20 oz soda bottle with H2 O2 (styrometric) at STP and detonate the mix, the bottle will not explode, a 2 liter will though.
-basically >6inch dia. pvc can't contain the pressure either, I wouldn't recommend it, but am willing to test it.

It seems to me most of you are pushing this limit frequently with 4x or higher propane mixes in 4 inch PVC.
  • 0


joestue
Private First Class
Private First Class
 
Posts: 38
Joined: Thu Jan 03, 2008 12:49 am
Reputation: 0

Sponsored

Sponsor
 


Unread postAuthor: biggsauce » Sun May 04, 2008 11:11 pm

joestue wrote:Not completely off topic, but is the shock wave as a side affect of DDT the 'bad' thing, or is it the pressure generated?

As an example if you fill a 20 oz soda bottle with H2 O2 (styrometric) at STP and detonate the mix, the bottle will not explode, a 2 liter will though.
-basically >6inch dia. pvc can't contain the pressure either, I wouldn't recommend it, but am willing to test it.

It seems to me most of you are pushing this limit frequently with 4x or higher propane mixes in 4 inch PVC.


Who is running a 4x in PVC? I didn't think anyone did that anymore...

As for the danger, it is the sudden pressure spike. The shock wave is what facilitates DDT. When the shock wave forms, IT causes the gasses to react instead of "burning" causing the reaction as in deflagration.

And how do you detonate the h2 o2 mix? Have you tried this?
  • 0

User avatar
biggsauce
Captain
Captain
 
Posts: 338
Joined: Thu Jun 07, 2007 9:42 pm
Reputation: 0

Unread postAuthor: MrCrowley » Sun May 04, 2008 11:21 pm

joestue wrote:It seems to me most of you are pushing this limit frequently with 4x or higher propane mixes in 4 inch PVC.

No one 'frequently' builds PVC hybrids anymore, haven't seen one for months.

Edit: Beaten, didn't refresh the page.
  • 0

Last edited by MrCrowley on Sun May 04, 2008 11:28 pm, edited 1 time in total.
User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10207
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Unread postAuthor: joestue » Sun May 04, 2008 11:25 pm

I have done a number of experiments with hydrogen and oxygen, the largest was 200 gallons. *electric ignition via a light bulb filament.

However my question was, is it a shock wave (which could cause instantaneous pressures in excess of the average pressure) or is it the average pressure causing the "bad thing"

From my point of view it is neither a bad thing or a good thing.

I don't have any real examples of someone running 4X propane, but i just assumed that was standard. Has anyone measured combustion pressures?
  • 0


joestue
Private First Class
Private First Class
 
Posts: 38
Joined: Thu Jan 03, 2008 12:49 am
Reputation: 0

Unread postAuthor: MrCrowley » Sun May 04, 2008 11:32 pm

People still run 4x propane, even more. But not in PVC chambers.
  • 0

User avatar
MrCrowley
Moderator
Moderator
 
Posts: 10207
Joined: Fri Jun 23, 2006 10:42 pm
Location: Auckland, New Zealand
Country: New Zealand (nz)
Reputation: 4

Unread postAuthor: Pilgrimman » Mon May 05, 2008 12:26 am

To my knowledge, the flame front exceeds the speed of sound, thus classifying it as a detonation. The shock wave (this is a detonation, remember) produces a huge pressure spike at its point of origin, and this very quick shock load can compromise even very strong chambers. It's the same reason that acetylene is unsafe. The energy density is lower than propane, but it is more prone to detonation as opposed to deflagration (burning). In the case of hybrids, the detonation is classified as DDT, as it won't happen unless some conditions are met. As DYI said, not every aspect of DDT is understood, but that's the best (flawed) explanation I can give :D .
  • 0

Yeah, we wouldn't want to anger the bees, now would we??

I HATE YOU BEES! I HATE YOU BEES! I HATE YOU BEES!

LMAO Classic!!!! I love Family Guy!
User avatar
Pilgrimman
Lieutenant Colonel
Lieutenant Colonel
 
Posts: 481
Joined: Thu Jun 28, 2007 1:10 pm
Location: Grants Pass, OR
Reputation: 0

Unread postAuthor: microman171 » Mon May 05, 2008 1:17 am

Ohhhh I get it now :D Thanks. So the flames themselve reach detonation speeds and forces? Sorry I havnt relly made and combustion spud guns let alone hybrids.
  • 0


microman171
Sergeant Major
Sergeant Major
 
Posts: 189
Joined: Wed Apr 30, 2008 11:49 pm
Reputation: 0

Unread postAuthor: biggsauce » Mon May 05, 2008 9:49 am

  • 0

User avatar
biggsauce
Captain
Captain
 
Posts: 338
Joined: Thu Jun 07, 2007 9:42 pm
Reputation: 0

Unread postAuthor: microman171 » Tue May 06, 2008 12:21 am

got it now! thanks guys!
  • 0


microman171
Sergeant Major
Sergeant Major
 
Posts: 189
Joined: Wed Apr 30, 2008 11:49 pm
Reputation: 0

Return to General Spud Cannon Related

Who is online

Registered users: Bing [Bot], farcticox1, Google [Bot], Gussmoore, Majestic-12 [Bot], MSNbot Media, Yahoo [Bot]

Reputation System ©'