Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
 Pages:  1  2    4  
Author: Subject: Fuel-Air Explosives
grndpndr
International Hazard
*****




Posts: 508
Registered: 9-7-2006
Member Is Offline

Mood: No Mood

[*] posted on 10-5-2009 at 17:43


Maybe I misunderstand but the surround charge of a thermobaric warhead contains its own oxidizer/fuel so outside atmosphere isnt nesscessary in fact the attraction of thermobaric warheads is they work in low/no 02 enviroments.
So I do not understand how a gasoline fuel cloud surround of a thermobaric warhead would starve it(thermobaric warhead) of oxygen?

[Edited on 11-5-2009 by grndpndr]

[Edited on 11-5-2009 by grndpndr]
View user's profile View All Posts By User
NameWithheld
Harmless
*




Posts: 6
Registered: 10-4-2009
Member Is Offline

Mood: Sensitive. (0.3 Nm)

[*] posted on 10-5-2009 at 19:57


Quote: Originally posted by grndpndr  
Maybe I misunderstand but the surround charge of a thermobaric warhead contains its own oxidizer/fuel so outside atmosphere isnt nesscessary in fact the attraction of thermobaric warheads is they work in low/no 02 enviroments.


Thermobarics, more or less by definition, utilize atmospheric oxygen.

"Thermobaric weapons distinguish themselves from conventional explosive weapons by using atmospheric oxygen, instead of carrying an oxidizer in their explosives."

"Volumetric weapons include thermobaric and fuel-air explosives (FAE). Both thermobaric and FAE operate on similar technical principles. In the case of FAE, when a shell or projectile containing a fuel in the form of gas, liquid or dustexplodes, the fuel or dust like material is introduced into the air to form acloud. This cloud is then detonated to create a shock wave of extended duration that produces overpressure and expands in all directions. In a thermobaric weapon, the fuel consists of a monopropellant and energetic particles. The monopropellant detonates in a manner simular to TNT while the particles burn rapidly in the surrounding air later in time, resulting an intense fireball and high blast overpressure."

Etc.




Whats the worst that could happen...

I'm amused that my rank is "harmless" of all things :P
View user's profile Visit user's homepage View All Posts By User
497
International Hazard
*****




Posts: 778
Registered: 6-10-2007
Member Is Offline

Mood: HSbF6

[*] posted on 10-5-2009 at 22:41


Quote:
Would it be possible to use such a setup to ignite a FAE? If you can extend the burning time of your alumnium long enough for the cloud to mix with the air properly, it might be possible to use such a charge to spread the fuel, as well as igniting it at the same time.


Probably not. It's a great way to make a fireball though. Very similar to the sort of thing they use at the Boomershoot. There will not be enough time for the fuel to mix in the proper proportions with air before igniting. Even if it did mix in perfect proportions, the chances of achieving a detonation from a weak ignition source like burning Al would be slim.

Quote:
the surround charge of a thermobaric warhead contains its own oxidizer/fuel so outside atmosphere isnt nesscessary


There is never enough oxidizer added to fully burn the metallic fuel. It is simply added to increase the ease/reliability of ignition of the metallic fuel. Probably 75-90% of the oxygen needed comes from the air.

The reason metalized thermobarics are popular for enclosed oxygen poor spaces is not because they carry their own oxygen, it's because they use a metallic fuel that can effectively pull oxygen from almost anything that contains it (such as CO, CO2, H2O, SiO2, etc). On the other hand, hydrocarbon fuels used in FAEs cannot do that, so they must be used in the open with sufficient air.
View user's profile View All Posts By User
grndpndr
International Hazard
*****




Posts: 508
Registered: 9-7-2006
Member Is Offline

Mood: No Mood

[*] posted on 10-5-2009 at 23:41


Are you saying to me name withheld that thermobarics do not contain an oxidizer?

If so I think your more confused than I.
patent 6955732 and many other related patents describe oxidizers such as AP,AN,
etc etc. In amounts up to 36% in combination with various reactive metals.AL,MG,Boron Titanium. Often with binders that contribute to the detonation like nitrocellulose

497,your maintaining FAEs do not contain reactive metals in your last paragraph?

With all due respect Im not exactly sure whos the most confused here?

Namewithheld flatly states no oxidizers are used in thermobarics all patents to the contrary and your convoluted explanation doesnt hold water either regards the reactive metal claim,Im well aware FAEs must be used in the open or 02 rich enviroments, weather permitting,another reason for thermobarics but FAES use reactive metals as well as thermobarics.You yourself when we discussed dust explosions explained that AL dust was the only dust IIRC that would make a detonateable FAE.All due respect gents but theres holes here a man could walk through. Why not just dispense altogether with oxidizers /explosive in thermobaric surrounds and rely on residual / chemically scavenged 02 in all cases assuming reactive metals are so efficient in scavenging oxygen from any source?Mood?Dubious!
However it is late perhaps Ill dream of solid rocket fuel components that detonate w/o 02 and SFAE.


[Edited on 11-5-2009 by grndpndr]

[Edited on 11-5-2009 by grndpndr]

[Edited on 11-5-2009 by grndpndr]
View user's profile View All Posts By User
Leander
Harmless
*




Posts: 28
Registered: 23-2-2008
Member Is Offline

Mood: No Mood

[*] posted on 11-5-2009 at 01:04


The amount of oxidizer available in such burst surround setups is by far not enough to reach oxygen balance.

When talking about aluminized explosives, there´s simply no such thing as oxygen balance! As 497 already mentions, reactive metals can rip off oxygen from most combustion products produced by the detonation. Magnesium and alloys can even react with nitrogen. In theory, if the total amount of oxygen present in the charge compared to the amount of aluminum powder is 2 : 3, you can get full combustion. This is only limited by the fact that above 30% inerts charges become more difficult to detonate. Also, to make the metals react you need a sufficient temperature and pressure, than practically cannot be reached this way.

In real life you can really see a significant difference in composition of thermobaric charges. In for example torpedo´s, where charges detonate under water away from any atmospheric oxygen, they can contain up to 60% AP. The only reason this is not done in above ground situations, is because apparently the metals can react with atmospheric oxygen quite effectively.
View user's profile View All Posts By User
grndpndr
International Hazard
*****




Posts: 508
Registered: 9-7-2006
Member Is Offline

Mood: No Mood

[*] posted on 11-5-2009 at 02:13


Clearly Im behind the times.Ive never heard of a thermobaric torpedo. I am also still skeptical of AL having the ability to scavenge as it were 02 from any oxygen containing materials.
Admittedly Im a rank amateur here having read few papers or patents concerning the properties of AL in SFAE/thermobaric devices and never seeing the properties attributed to AL mentioned in any I cant argue a point Im unsure of.So,I appreciate your kind responses,thanks.:D
The AL reaction,basically'stealing' oxygen, o is this akin to what happens in a thermite reaction to the iron oxide?
[Edited on 11-5-2009 by grndpndr

[Edited on 11-5-2009 by grndpndr][Edited on 11-5-2009 by grndpndr]

[Edited on 11-5-2009 by grndpndr]
View user's profile View All Posts By User
497
International Hazard
*****




Posts: 778
Registered: 6-10-2007
Member Is Offline

Mood: HSbF6

[*] posted on 11-5-2009 at 15:40


Quote:
497,your maintaining FAEs do not contain reactive metals in your last paragraph?


True, an FAE could contain a metallic fuel.. But AFAIK there has never been one used in practice that contained much more than some kind of hydrocarbon mixture. I didn't say FAE's can't contain metal powders, just that they rarely if ever do in practice.

NameWithheald never said they couldn't contain oxidizers, just that they never contain a very significant amount of the oxygen needs of the metallic fuel.

Yes its kinda like a thermite reaction. Basically Al is a very strong reducing agent, strong enough to reduce most any common oxygen containing compounds, and even release a good amount of energy too (not quite as much as it would if reacting with O2, but its not a bit difference usually).
View user's profile View All Posts By User
markgollum
Harmless
*




Posts: 46
Registered: 21-2-2004
Member Is Offline

Mood: No Mood

[*] posted on 11-5-2009 at 16:09


If you are wondering if one metal or other fuel can "strip" the oxygen from another, an Ellingham diagram is very useful. Basically it plots the thermodynamic equilibrium vapour pressure of oxygen above the fuel/metal as a function of temperature. The substance with the lowest oxygen partial pressure at the temperature of interest is the "winner" in the fight for oxygen. You can use the data to quantitatively determine equilibrium constant assuming that the activities of the solids are 1 (not always the case, there things you can do to affect the activities, reducing them or even increasing them beyond one, but this is (to me) a complex topic).
An important note, Ellingham diagrams give thermodynamic solutions and do not consider kinetics, so it is possible that if the reaction conditions are not maintained for a sufficient time, then the equilibrium constant may be far from realized. However, metal powders typically have rapid kinetics which become exponentially more rapid as both temperature increases or particle size decreases. Also, I beleive that in thermobaric/enhanced blast devices, appreciable metallic fuel is likely in the gas phase, making for exceedingly fast kinetics.

A simple google search for "Ellingham diagram" brings up some excellent diagrams along with a tutorial.
View user's profile View All Posts By User
grndpndr
International Hazard
*****




Posts: 508
Registered: 9-7-2006
Member Is Offline

Mood: No Mood

[*] posted on 11-5-2009 at 21:29


Thank for all the informative replies.Its very much appreciated
particularly the collective patience shown.:)

[Edited on 12-5-2009 by grndpndr]

[Edited on 12-5-2009 by grndpndr]
View user's profile View All Posts By User
497
International Hazard
*****




Posts: 778
Registered: 6-10-2007
Member Is Offline

Mood: HSbF6

[*] posted on 12-5-2009 at 23:56


Here is a very useful document. I've been looking for it for a while now, finally got it. Thought I'd share it..

"Of the more than 25 different homogeneous additives tested, the strongest ignition promoters, by far, were found to be the alkyl nitrates and nitrites..."

"The ignition delay at 1000*K, of Shelldyne-H or H-HCPD was reduced from 180 and 110 milliseconds to 3.5 and 5.3 milliseconds respectively, upon the addition of 25 volume percent n-propyl nitrate."

"Other additives such as H2O, N2O, CO, H2 or peroxides, esters, polyethers and alcohols had little or no effect on
promoting the autoignition of various hydrocarbons..."

EDIT: The damn file is slightly too big to attach. I'll post a link as soon as I can.

[Edited on 13-5-2009 by 497]


Here's the file I mentioned above. It's worth a read.

http://savefile.com/files/2104562

[Edited on 17-3-2011 by quicksilver]
View user's profile View All Posts By User
Bikemaster
Hazard to Others
***




Posts: 120
Registered: 8-10-2008
Member Is Offline

Mood: No Mood

[*] posted on 27-1-2010 at 12:16


Do it append any probleme to you, because your youtube account have been shout down???
View user's profile View All Posts By User
-=HeX=-
Hazard to Others
***




Posts: 109
Registered: 18-4-2008
Location: Ireland
Member Is Offline

Mood: Precipitating

[*] posted on 23-2-2010 at 11:21


497: Check your U2U's.

I reckon AL powder MAY make an alright FAE. 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




If you give a man a match he will be warm for a moment. Set him alight and he will be warm for the rest of his life.
View user's profile View All Posts By User This user has MSN Messenger
simply RED
Hazard to Others
***




Posts: 165
Registered: 18-8-2005
Location: Stelianovsk
Member Is Offline

Mood: booM

[*] posted on 1-3-2010 at 01:08


Hex, this is extremely interesting. May you provide more information on the actual experiments with this one-event FAE.

How powerful is it, does it really detonat and not just burn?




No gun - No fun!
View user's profile Visit user's homepage View All Posts By User
-=HeX=-
Hazard to Others
***




Posts: 109
Registered: 18-4-2008
Location: Ireland
Member Is Offline

Mood: Precipitating

[*] posted on 12-3-2010 at 14:37


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




If you give a man a match he will be warm for a moment. Set him alight and he will be warm for the rest of his life.
View user's profile View All Posts By User This user has MSN Messenger
Lord Emrone
Harmless
*




Posts: 30
Registered: 5-2-2010
Member Is Offline

Mood: No Mood

[*] posted on 17-3-2011 at 07:46


I have the idea to make a fireball with gasoline. 1 liter of it on top of a 200 gr ANFO charge by example. I could use BP or FP but I'm used to detonations, so I'll use that.

I was thinking to use several grams of red phosphorus tightly packed in tape and place that on top of the gaz bottle. The shock will cause the RP to burn and burst out of the tape and light the gaz cloud.

Anyone other ideas or suggestions ?
View user's profile View All Posts By User
Jimbo Jones
Hazard to Others
***




Posts: 102
Registered: 15-10-2009
Member Is Offline

Mood: No Mood

[*] posted on 17-3-2011 at 09:58


Yeah. Shredded to pieces, dusted with fine aluminum powder Teflon tape. You will also need heavily aluminized booster, but that’s ok. The main problem will be the choice of good fuel. A charcoals and liquid oxygen are supposed to be nice and spectacular mixture.
View user's profile View All Posts By User
quicksilver
International Hazard
*****




Posts: 1820
Registered: 7-9-2005
Location: Inches from the keyboard....
Member Is Offline

Mood: ~-=SWINGS=-~

[*] posted on 18-3-2011 at 07:46


Exceptional book that deals with ancient examples of fuel/air concepts from beginning of recorded history: "GREEK FIRE, Chemical Warfare In The Ancient World" {A. Mayor, 2003}ISBN-158567-348. One of the better historical accounts of chemical-bio usage in antiquity. Was one of the best [bibliographic-notation & researched] books of it's genre' I have read in a damn long time.
Points to ancient period of air-fuel usage testing from natural occurring (naphtha & lower hydrocarbons) dispersal mechanisms.




View user's profile View All Posts By User
Rosco Bodine
International Hazard
*****




Posts: 6334
Registered: 29-9-2004
Member Is Offline

Mood: analytical

[*] posted on 18-3-2011 at 08:24


Quote: Originally posted by Lord Emrone  
I have the idea to make a fireball with gasoline. 1 liter of it on top of a 200 gr ANFO charge by example. I could use BP or FP but I'm used to detonations, so I'll use that.

I was thinking to use several grams of red phosphorus tightly packed in tape and place that on top of the gaz bottle. The shock will cause the RP to burn and burst out of the tape and light the gaz cloud.

Anyone other ideas or suggestions ?


Titanium coarse powder granules or magnesium turnings in a baggie on top of the charge and underneath the gasoline should ignite and remain burning long enough to make a good igniter for the dispersed vapor cloud of gasoline which otherwise will probably not be ignited by the charge alone.
Coarse graulated magnalium might work also.

[Edited on 18-3-2011 by Rosco Bodine]
View user's profile View All Posts By User
Lord Emrone
Harmless
*




Posts: 30
Registered: 5-2-2010
Member Is Offline

Mood: No Mood

[*] posted on 19-3-2011 at 09:39


@Jimbo Jones : pieces of Teflon tape dusted with fine aluminum powder ? Is that tape an oxidizer ?

@Rosco : I only have fine Al and magnesium powder. I'll try with RP.
View user's profile View All Posts By User
Jimbo Jones
Hazard to Others
***




Posts: 102
Registered: 15-10-2009
Member Is Offline

Mood: No Mood

[*] posted on 20-3-2011 at 02:31


Quote: Originally posted by Lord Emrone  
@Jimbo Jones : pieces of Teflon tape dusted with fine aluminum powder ? Is that tape an oxidizer ?


It’s just more exotic form of thermite.
View user's profile View All Posts By User
White Yeti
International Hazard
*****




Posts: 816
Registered: 20-7-2011
Location: Asperger's spectrum
Member Is Offline

Mood: delocalized

[*] posted on 2-8-2011 at 06:56


This is probably a stupid question, but how do you ignite the cloud of explosive vapour when the first charge blows up the container and everything in its proximity? This means that the second igniter has to be far away from the conventional charge, somewhere inside the cloud. Could you use something similar to an electric arc (not a spark gap) to ignite the cloud? Since the mix will not ignite when it is fuel rich, the arc would only ignite the mix when the right fuel air ratio is established. Also, wouldn't the heat of the initial explosion be enough to also ignite the fuel air mix?
View user's profile View All Posts By User
hiperion42
Hazard to Self
**




Posts: 75
Registered: 24-8-2009
Location: european mainland
Member Is Offline

Mood: overwhelmed

[*] posted on 1-7-2012 at 10:41


Quote: Originally posted by White Yeti  
This is probably a stupid question, but how do you ignite the cloud of explosive vapour when the first charge blows up the container and everything in its proximity?


The energy of the dispersal charge is almost completely absorbed and converted
into the outward movement of the fuel. It is therefore possible to
have the initiating charge located very close to the fuel.


46848644.jpg - 66kB


[Edited on 1-7-2012 by hiperion42]




.....ejuu....................................................................Ffg..............................g.............
View user's profile View All Posts By User
matheusfredrich13
Harmless
*




Posts: 3
Registered: 23-7-2012
Member Is Offline

Mood: No Mood

[*] posted on 23-7-2012 at 21:01


A Fuel Air Explosion is achieved by using a blast to disperse the 'Fuel' into the air and then igniting the fuel cloud allowing all the 'fuel' to burn within a few milliseconds.

Fuel Air Explosive's rely on the oxygen in the surrounding air, rather then self oxidizing. The fuel is dispersed into the air to forming a cloud of very small droplets, and exposing a large amount of the 'Fuels' surface area. When the fuel cloud is ignited the 'Fuel' is able to burn almost instantly due to the fact that its in very small droplets. The smaller the droplets are the faster the fuel cloud will burn, this is the same as with Flash Powders or Black Powder.

Common fuels like gasoline, kerosine and diesel will not be able to achieve the Fuel Air Effect. To achieve the Fuel Air Effect you will need to use faster burning fuels such as Isopropyl Nitrite, Diethyl Ether or Heptane. Their are many other fuels that are suitable for use in a FAE but i don't want to mention them all. :P

Here is a great video of a True Fuel Air Explosion uploaded by AnonymousUploads (who sadly had to shut down his account due to a explosives related injury) :(
Here is the link: http://www.youtube.com/watch?v=7dW1qkBg8sM

I hope you find this useful and if you have any questions please ask :D
View user's profile View All Posts By User
hiperion42
Hazard to Self
**




Posts: 75
Registered: 24-8-2009
Location: european mainland
Member Is Offline

Mood: overwhelmed

[*] posted on 24-7-2012 at 06:41


Quote: Originally posted by matheusfredrich13  


Here is a great video of a True Fuel Air Explosion uploaded by AnonymousUploads (who sadly had to shut down his account due to a explosives related injury) :(
Here is the link: http://www.youtube.com/watch?v=7dW1qkBg8sM

I hope you find this useful and if you have any questions please ask :D


Maby you should go study a little bit extra before giving more advise.

While namewithheld's test was admirable it was not a full detonation.
The camera was running at 600fps and is played back at 30p which
means every second watching the movie is seeing 50ms elapse.
A fuel air cloud detonates in less than 10ms.
The cloud in the movie deflagrates for more than 200ms.
I recall he used a bag of cast etn of unknown quantity to initate the cloud.
Maby it was to little i don't know.

Again i respect the testing he did alot.

http://www.youtube.com/watch?v=j9xCgNdZPKk

[Edited on 24-7-2012 by hiperion42]




.....ejuu....................................................................Ffg..............................g.............
View user's profile View All Posts By User
matheusfredrich13
Harmless
*




Posts: 3
Registered: 23-7-2012
Member Is Offline

Mood: No Mood

[*] posted on 24-7-2012 at 19:10


Yes, the FAE in the video i linked to did burn slower than the Fuel Air Cloud in the video you linked to. This could be because the fuels used in the videos were different. Or because the dispersion charges were different sizes. Either way the Fuel Air Cloud in the video i linked to still burnt at a abnormally fast rate, and you can clearly see the increase in blast pressure. The fuel might not have detonated as fast as in the video by Discovery Channel but it still did detonate.

[Edited on 25-7-2012 by matheusfredrich13]
View user's profile View All Posts By User
 Pages:  1  2    4  

  Go To Top