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Harnessing DDT

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Harnessing DDT

Unread postAuthor: inonickname » Wed Mar 25, 2009 3:28 am

Well this project is mainly the theoretical, inspire higher thinking type. That aside, action may be taken depending on the results.

The topic is DDT. Some of you may be familiar with it, some not. The general statement is that DDT occurs when the flame front reaches a supersonic speed.

DDT

The wiki states that it can create a gigantic pressure spike that can destroy the chamber.

If one could build a strong enough chamber, surely the immense increase in pressure could give an extremely powerful shot.

Factors that increase the likelihood of DDT:
-Rapidly burning fuels (hydrogen, acetylene)
-Presence of oxidizer (oxygen)
-Longer, thinner chamber
-Higher mixes

If these factors could be combined to produce DDT on a reliable basis, could we expect much more power?

So essentially:
If one was to build a (very) small launcher what kind of reinforcement would be required to harness the DDT blast- A.K.A. how much more powerful would a (mach) flame front be than say one of 1/2 (mach). From what I've been led to see it would not have a ratio directly proportional to the speed above mach.

Any input?
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Unread postAuthor: grock » Wed Mar 25, 2009 4:04 am

when built correctly, hybrids are pretty much always more powerful. and if you can break the sound barrier on a regular basis, as opposed as to a lucky explosion (those aren't words often combined) you would definitely have more power over a subsonic launch

when i saw the title, i was thinking "DDT? dont they sell it for like pesticides or something? why didn't he go to walmart?" lol
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Unread postAuthor: inonickname » Wed Mar 25, 2009 4:13 am

Oh well.. whether or not DDT is reliable, it ought to give more power (obviously) over a subsonic launch.

Over here, anyway DDT was a pesticide that was phased out and gotten rid of due to it's toxicity and causing birth defects. We actually found a notice advising people to use DDT under our house.

Not nice stuff..
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Unread postAuthor: starman » Wed Mar 25, 2009 4:19 am

DDT hasn't come up much lately. There have been various discussions over the years about the possibility of purposely using DDT. In the final analysis, guaranteed DDT was going to require fairly large chamber dimensions and really meaty materials to pull off...and even then conditions were going to be difficult to control.

The general consensus has always fallen toward avoiding DDT and hybrid up if you need (or just want) more power with a DDT-safe chamber configuration.
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Last edited by starman on Wed Mar 25, 2009 4:26 am, edited 1 time in total.
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Unread postAuthor: starman » Wed Mar 25, 2009 4:25 am

inonickname wrote:Over here, anyway DDT was a pesticide that was phased out and gotten rid of due to it's toxicity and causing birth defects. We actually found a notice advising people to use DDT under our house.

Not nice stuff..


While this was the stated reason for its ban, the allegations have never been proven. There is even some movement to reinstating its use, particularly in malaria ridden parts of the world.

Don't believe even thing you read on wiki... :wink:
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Unread postAuthor: inonickname » Wed Mar 25, 2009 4:29 am

The health notice was a little...well..while it advised the use of DDT it also noted it was a carcinogen and that it may cause birth defects. It's sort of the "known to the state of california to cause cancer"-they reckon it'll happen, but noones volunteering to test it.

I'll accept that it's nasty enough that I wouldn't want it near me..
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Unread postAuthor: psycix » Wed Mar 25, 2009 8:52 am

Point is, that DDT does NOT release more pressure. It just burns faster.
Another point is, that effect of the "slow" deflagration is compensated by the burst disk. (or piston)
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Unread postAuthor: DonTheLegend » Wed Mar 25, 2009 12:56 pm

Didn't Larda mention something about a possible DDT shot with his 200x hybrid that was actually weaker than the other shots? Seems like intentional DDT is a lot of trouble for unpredictable results.
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Unread postAuthor: jimmy101 » Wed Mar 25, 2009 2:05 pm

Like psycix said. Why?

DDT doesn't release any more energy.

The pressure pulse may reach extremely high values but that pulse lasts for only a tiny fraction of a second. It really doesn't accomplish much if you hit 2000 PSI for 100uSec.
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