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Author: Subject: Fuel-Air Explosives
hiperion42
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[*] posted on 24-7-2012 at 23:49


Maby there was a few percent of the fuel that initially did detonate
but one can clearly see the flamefront not propagating through the whole
cloud at supersonic speed.
Fast deflagrations are capable of producing substantial overpressures though
and i would not have liked being close to that cloud when it was initiated.




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[*] posted on 25-7-2012 at 00:00


It is not a matter of detonating or not detonating, it is a matter of the % of the fuel that detonates. Fuel continuing to burn long after the first 10 ms is not proof that no detonation was reached. It is extremely hard to get 100% of the fuel mixed at the correct ratio for detonation, particularly when using a fuel that remains largely in liquid form after dispersal (because of relatively high bp vs ethylene oxide, and the apparently low air temperature during the test.) Even modern military FAE systems are not fully reliable at lower air temperatures. More trial and error testing of the fuel mix, delay length and bursting charge size could undoubtedly improve the fraction of fuel reaching detonation. Adding lower boiling fuels is likely the easiest way to ensure better performance. Even a small (10-25%?) fraction of something like propane, butane, or better dimethyl ether would undoubtedly help by increasing the vapor concentration and by forming a finer fuel mist via the sudden boiling of each particle.





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[*] posted on 25-7-2012 at 05:39


At initiation one could indeed see a fraction of the fuel possibly detonating.
But it did not connect to the majority of the fuel which clearly deflagrated.
But your are right with some tweaking...
The fuel vapour phase plays a substantial role in getting the cloud to detonate
especially for relatively insensitive fuels as well as using a oversized initiator.
I would not categorize heptane sensitized with a nitrate as unsensitive but the
concept would still apply.
Apparently straight low vapour pressure nitrated fuels would not require extensive evaporation to be detonable.
I read the buster was 9g for a fuel mass of 1400g.
That would mean a F/B of more than 150.
Maby lowering to a ratio of 80-90 would be better.
Again great testing!

[Edited on 25-7-2012 by hiperion42]

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[*] posted on 25-7-2012 at 06:00


This "cut line" you see (I saw it after magnification of the picture) in the half of the picture is caused by the non-infinite speed of the camera (those who shot explosions know what i am talking about) and has nothing to do with detonation or not of the fuel.

You actually see 2 frames here, the down one is the "recent (after ignition)", the upper part of the picture with unburned fuel, the "former (before ignition)". This is just the event when the digital camera changed frames.


[Edited on 25-7-2012 by simply RED]




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[*] posted on 25-7-2012 at 15:17


Good point about the camera. Unfortunately it seems the frame rate was too slow to be able to determine anything with great certainty. Looking at the effects of the blast wave on the surroundings may be a better indicator. I think that would indicate at least a partial detonation, as it is doubtful that the ETN <50g initiator could have done that on its own.

I believe it says it is sensitized with a nitrite not a nitrate. Nitrites have been shown to be inferior sensitizers, although still better than nothing, and far easier to synthesize.




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[*] posted on 25-7-2012 at 23:36


Excuse me yes the test used nitrite.
I confused it with the military who used the
nitrate to be able to make larger heptane
aerosol particles detonable.
Finding a place to test is another matter but
maby this would be less of a concern with the
available wide plains in America.
Man i drool when i see photo's of them.
:D

[Edited on 26-7-2012 by hiperion42]




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[*] posted on 26-7-2012 at 09:27


Quote: Originally posted by simply RED  
This "cut line" you see (I saw it after magnification of the picture) in the half of the picture is caused by the non-infinite speed of the camera (those who shot explosions know what i am talking about) and has nothing to do with detonation or not of the fuel.

You actually see 2 frames here, the down one is the "recent (after ignition)", the upper part of the picture with unburned fuel, the "former (before ignition)". This is just the event when the digital camera changed frames.


Well RED you got me thinking alright...

You say the cut area is there because the camera
switched frames. The casio records the 600 frames/s
as progressive native input so it recorded that picture for
that frame at that precise moment leaving in the middle
how the flame propagation visually looked at that time.

So subtly i think there is a difference.

You say the horizontal line is there because the camera
switched frames. I think the flame propagation at that
precise time for that frame looked like it did with the horizontal
shaped appearance and the camera captured this.
Or am i messing things up? :)




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[*] posted on 26-7-2012 at 20:26


Quote: Originally posted by simply RED  
This "cut line" you see (I saw it after magnification of the picture) in the half of the picture is caused by the non-infinite speed of the camera (those who shot explosions know what i am talking about) and has nothing to do with detonation or not of the fuel.

You actually see 2 frames here, the down one is the "recent (after ignition)", the upper part of the picture with unburned fuel, the "former (before ignition)". This is just the event when the digital camera changed frames.


[Edited on 25-7-2012 by simply RED]


Yes. RED is correct. I have a Casio Exlim EX-FS100 which is the smaller version of the camera that captured that frame. I have experienced 'Cut Lines' before, especially when filming explosions. This cut line is not as defined as others, but you can see the 2 frames overlapping.
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[*] posted on 26-7-2012 at 21:03


I am not an expert on cameras but this 'Cut Line' or "2 frames overlapping" was a common effect with digital cameras when filming explosions. This is extremely obvious at night when filming fuel rich explosions and you see half the screen white-yellow and half the screen black.



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[*] posted on 12-8-2012 at 20:10


As far as I know Propyl Nitrate or Iso-Propyl Nitrate is one of the materials used as a thermobarric fuel as one of the above has the ability to detonate while being a vapor.
Primary charge detonates and vaporizes the PN or the IPN (cant remember which one or both) and then a secondary timed (critical) detonator .... detonates the vapor ...... generating a massive pressure wave lasting mili seconds instead of micro seconds.
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[*] posted on 13-10-2012 at 10:12


Related threads

http://www.sciencemadness.org/talk/viewthread.php?tid=7769

http://www.sciencemadness.org/talk/viewthread.php?tid=21691

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[*] posted on 14-10-2012 at 11:15


They used to use mixtures of nitromethane and propylene oxide for fuel in small pulsejets to break speed records but don't allow propyl anymore because of it's health hazards. A typical Bailey or Dynajet pulsejet fires 220 to 240 cycles per second.
http://www.youtube.com/watch?v=z67nZrdf7gc
http://www.youtube.com/watch?v=68MRkGxhvRE&noredirect=1

"Some fuels used, such as ethylene oxide and propylene oxide, act like mustards. A device using such fuels can be dangerous if the fuel fails to completely ignite; the device is at risk of producing the effects of a chemical weapon."
http://www.huliq.com/34060/thermobaric-bomb-features-of-worl...
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[*] posted on 16-10-2012 at 10:05


@ Morgan

The article you cite defines if somewhat clumsily the distinction between
thermobaric and fuel air devices.

A Fuel Air Explosive F A E consists of fuel and a dispersing mechanism ,
and uses oxygen in the air. The first explosive charge ( or some other
dispersal mechanism ) bursts open the container and disperses the fuel in a cloud
that mixes with air. Once the fuel is appropriately mixed , the second
charge detonates , propagating an explosion ( blast wave ) through the cloud.


"Thermobaric weapons do not disperse the fuel before igniting it , but are single stage
bombs having one explosive charge that both ignites and disperses the fuel.
"
The explosive is highly oxygen deficient producing reactive products which
then additionally burn with air. These are solely intended for use in confined
spaces such as bunkers.

" Some fuels used, such as ethylene oxide and propylene oxide, act like mustards "
Probably more like CX Phosgene oxime. Propylene is the anhydride of it's glycol ,
when hydrolyzed it generates considerable heat much as caustic soda
when hydrated.

In 1978 Tarragona Spain
A tanker truck overturned ejecting Propylene aerosol onto a crowded
picnic ground , then ignited , incinerating everything within sight.
( I can tell you they still talk about this one there )
http://www.wordola.com/wusage/alfaques/all.html
http://en.wikipedia.org/wiki/Los_Alfaques_Disaster
This is a Spanish language Documentary of it.
http://www.youtube.com/watch?v=K37kNwt1nyk
http://www.youtube.com/watch?v=xh4N37azEMM

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[*] posted on 7-5-2018 at 07:47
Ferrocene as liquid FAE catalyst?


Quote: Originally posted by -=HeX=-  
I tested a bunch of single step FAE's as per the patent - Kudos to Carbonfiend who found the optimal ratio to be 6% Ferrocene, 47% Diesel, 47% Ether. No second charge, and they went to full detonation


Quote: Originally posted by -=HeX=-  
IN our experiments, also done by Carbonfiend, we found, in long grass, the thing blasts away 15cm radius with a mere 15ml, set off with 0.75g AgN3. However, I got a radius of 19cm using 0.70g RDX, 200mg DPNA primary.

Philou Zrealone reckons it may be ineffivient, but hey, it works especially in 1 litre amount set off by 100g RDX. That made a HUGE BANG but it was in the open. I felt a pressure wave, and I was about 600m away.

I personally think at least SOME makes the DDT. Soon I will build a plywood 'house' (i.e. box) and see can I blast that to shreds


Apologies for dredging up an old thread- Somehow I missed this at the time this thread was active.

Have any here either links to or files saved regarding the original work on developing this mixture?




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[*] posted on 7-5-2018 at 13:51


This is of great interest to me also. Good find Bert. Hopefully someone can help us
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[*] posted on 7-5-2018 at 14:55


God helps those who help themselves... I'll have another helping of pie now, please.

:P



Attachment: Single_Event_catalyzed_FAE.pdf (427kB)
This file has been downloaded 245 times

I suspect this is the source of the idea, they mention diesel and ferrocene, the ether used by Carbonfiend and Hex isn't mentioned- But far less benign things certainly are.

After reading up on ferrocene, I begin to understand why the patent describes blowing a separate ferrocene filled compartment outward into a previously separated liquid fuel-

Jolly hints from the high-powered rocketry community about the need to pre-dissolve ferrocene into the liquid components of the fuel, and not just for even dispersion, finished propellant with increased sensitivity to accidental ignition and a statement about the slight volatility of ferrocene leading to other fuel grains and motors merely stored nearby ALSO having their burn rates increased by cross contamination from the volatilized ferrocene slowly escaping from a motor made with this.



20180507_174614.png - 306kB




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[*] posted on 7-5-2018 at 22:32


ShowImage.png - 111kB

Are all you guys from NASA ? Anyway I think its possible coffee creamer dispersed by a consumer fireworks mortar shell minus the lift charge would work. I think the stars from the shell would be accelerated faster then the dust cloud by the burst and ignite it uniformly.

"Here, one hard hat full (11 lbs. or 5 kg.) of coal dust is placed in a trough approximately 2/3 of the height of the enclosure, which measures 10 ft. wide x 12 ft. deep x 15 ft. high. A small charge was then introduced to disturb and suspend the dust followed by an ignition source (bottle rocket)." https://www.youtube.com/watch?v=RZLRbVw3RnM
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[*] posted on 8-5-2018 at 06:56


I'm not from NASA, although thanks to Terry McCreary, I have credentials as a rocket scientist. (I also have credentials as a pope, courtesy of the church of the subgenni. Credentials are easy to come by).

There is a difference between a deflagration and a detonation. Shot plenty of Cremora buckets, it has always been a deflagration. Same with bucket shots of oven dried flour or sawdust lifted with black powder, garbage bags of gasoline lifted from a sheet of cardboard on the ground with a coil of det cord underneath and gasoline or colorant+methanol lifted with black powder soft bombs from a steel mortar.

I HAVE seen an Aluminum dust cloud make D to D, THAT was quite different and scary. Don't try the Cremora bucket effect with flash grade Aluminum powder.

In 2014, there was a dust explosion in a Chinese factory finishing Aluminum wheel rims for GM where the management didn't install proper air handling or do enough house cleaning, plus, jammed too many workers and machines into the production area. When Aluminum dust ignited, the destruction was spectacular. 146 killed, 75 of them nearly instantly by blast/overpressure

Inside a mine gallery or mill, it doesn't matter as much. The energy released as heat and a long duration pressure pulse from a large volume dust cloud deflagration indoors can kill people and is likely to destroy some of the structure, no matter if the reaction moved through the cloud faster than speed of sound.

Out in the open, things are different- If the thermal effects from a fuel cloud deflagrating don't kill you, the overpressure is not likely to. In a similar volume of the same fuel initiated by an HE charge or otherwise achieving an open air detonation, the over pressure can do structural dammage and injure unprotected people farther away than the thermal effects. If the linked test gallery shot had been initiated with a small but properly timed HE, those concrete walls might gave been severely dammaged. As it was, they just got scorched.

In a mill dust explosion, it is usually the SECOND explosion that does the major dammage. First, a shock or small explosion occurs in some part of the structure which shakes accumulated dust off the interior walls and ceiling, rafters, etc. A dust cloud may be created throughout the dust contaminated parts of the building/neighboring structures all at once, if it ignites, buildings often go away.



[Edited on 5-8-2018 by Bert]




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[*] posted on 8-5-2018 at 10:02


Simple 0.2 kg HE bursting charge with a 2 kg of isopropyl alcohol/Al gives a ~ 3 kg TNT eq.

http://yadda.icm.edu.pl/baztech/element/bwmeta1.element.bazt...


[Edited on 8-5-2018 by Rocinante]
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[*] posted on 8-5-2018 at 10:22


Link is broken-



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[*] posted on 8-5-2018 at 12:54


A pyrophoric substance (from Greek πυροφόρος, pyrophoros, "fire-bearing") ignites spontaneously in air at or below 55 °C (130 °F)...

Searched 'ignites on contact with air' and learned a new word today. And I have KNO3 and sugar so I too am a rocket scientist.

But I would think a cloud of a pyrophoric substance like aluminum dust mentioned by Bert would like doing their spontaneous igniting on the leading edge of blast wave getting nice and tight with the O2 in the air.
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[*] posted on 29-1-2019 at 15:28
cornstarch detonation? how is this possible?


So recently, I was researching some stuff about dust explosions as well as detonation in fuel-air mixtures. I wanted to know if a pre-mixed cloud of dust in air could support a true shock wave I came across the following link:
https://deepblue.lib.umich.edu/handle/2027.42/38590

In many dust explosion accidents, most of the dust starts out deposited as a layer on a solid surface, and surrounded by clean air. Then, a small volume of air mixed with dust or fuel deflagrates, and in a partially confined space this causes movement in the surrounding air, mixing it with the dust. This creates a cloud of dusty air which also deflagrates, and which displaces more air, causing more violent mixing. In a pipe (or mineshaft) with sufficient dust on the walls, this process will create a wave of moving air and increased pressure which will travel through cold, clean, oxygenated air ahead of the fireball at roughly the speed of sound.

In this video, you can clearly see a surge of fast moving air and coal dust which is transmitted ahead of the actual fireball:

https://youtu.be/kacen528Kl0

https://youtu.be/VApk-oaeb-4?t=184

Anyhow, according to my understanding of explosions, this pressure wave travelling through unignited material ahead of the actual reaction zone is only possible with deflagrations. As far as I know, detonation involves the pressure pulse igniting material as soon as it reaches it, which would be impossible if the dust had not yet been mixed.

And yet, in that paper, it is said that a dust explosion went from a deflagration with a pressure pulse "precursor" in front of it to a full-fledged, supersonic (about 1 km/sec VOD) detonation! Before ignition, the dust was said to have been laid down as a layer on the bottom of the tube, not suspended in the air.

My only theories are

a) the detonation occurred in a cloud of dust and cold air which had been pre-mixed by previous deflagration closer to the ignition source. This would be similar to Bert's experience with the aluminum powder being dispersed in the air by a deflagration, mixing with the air, and then detonating with a loud bang.

b) the detonation front emitted so much thermal radiation that it caused the organic dust to pyrolyse into gas ahead of it.

c) the speed of sound along the wall of a steel tube is well over 1 km/sec. Perhaps the detonation caused violent movement or vibration of the entire tube, leading to mixing of dust and air prior to arrival of the shock front.

d) I am totally wrong about the way a detonation works. As in, perhaps a combustion reaction ocurring several feet behind the shock front could be enough to sustain a 1 km/sec shock velocity and a pressure of over 10 atmospheres?

e) The measurements taken by Li et. al. are grossly inaccurate, and no supersonic detonation took place.
Sorry for the long post, but I'd like to hear what others think.

[Edited on 29-1-2019 by C6(NO2)5CH2CH(CH3)N(NO2)2]




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[*] posted on 30-1-2019 at 12:02


Your understanding of detonation is correct. The pressure wave that disperses dust from the walls is not limited to the speed of sound however, but can move at any speed as long as its pressure is high enough.

I skimmed through the paper and their measurements and results looks solid. I think the key here is that it is a transitional state. Their pipe ends just after the reaction zone has caught up with the shock front. Therefore, we can't really use normal steady-state detonation theory here. In fact I think the detonation becomes too unstable to propagate much further as a true detonation, because of the mixing problem you discussed.
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[*] posted on 26-4-2020 at 22:25


For a mainly visual effect, you can try making “nap bombs”. As you’ll see in the link, it sounds kewl bombzy but it’s not really a “bomb”, it’s what they used to use to simulate explosions in Hollywood! Basically just a fireball of burning old fashion moth balls, but technically a fuel-air explosive because the oxygen is supplied by ambient atmosphere.

EDIT: Forgot the link http://www.angelfire.com/on/pyrotechnicalities/naphthalene.h...

[Edited on 27-4-2020 by Katie]
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[*] posted on 27-4-2020 at 20:52


http://pyrobin.com/files/Thermobar2.pdf
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