Hi,
as you can see from the title, this thread is about an effect from the animation movie "How to train your dragon". A few of you surely already know
that movie, the others should watch it - it's awesome^^. The question I want to ask now is whether the fire of a particular dragon there - the "Night
Fury" - might actually work in reality (without looking at the biological side of the matter) and if yes, in which way. I've already asked this
question in several other boards - an English fan board for this movie, a German board about explosives and pyrotechnics, and another German board
about chemical experiments (versuchschemie.de). The first two boards could not help me, the users in the third one flamed in my thread until it was
closed.
I hope I will find both competence and acceptance for my project in this board.
My goal is firstly to find out the working mechanism of that fire (not the way the movie designers animated it, but the way how they intended it to
work if it was real - all the other ways how the dragons breathe fire in this movie are simple and well-known concepts, only this one isn't), secondly
to adapt it to reality (this include conducting experiments) and finally to fully recreate it - all that without deviating from the official
information about the movie! I've already worked a lot on this project, including some experiments. Here is the link to the thread in the movie's fan
board where you can find my thoughts about it until now: http://howtotrainyourdragon.proboards.com/index.cgi?action=d...
I will write a new summary of both the analysis of the movie and the experiments I did soon. For now, feel free to post your own ideas.
[Edited on 13-8-2011 by HellstormOP]
[Edited on 13-8-2011 by HellstormOP]HellstormOP - 13-8-2011 at 14:07
OK, let's start with the details from the movie and the official website:
- The official website describes it as an "unconventional fire, a semi-solid mass, alight with an acetylene-oxygen flame, explodes its target on
impact".
- As you can see in the movie, the fire of this dragon has a decent range, without forming a fireball until impact. Therefore, it absolutely makes
sense that the fire consists of a semi-solid - liquids, gases and powdered substances would quickly disperse and burn off in a fireball before
reaching the target. On the other hand, a dragon like the Night Fury would be unable to fire a solid projectile (i. e. a grenade), as at least a
barrel would be needed for it (not to mention the internal "magazine" and "loading mechanism"...) At one point in the movie, one can see a Night Fury
"regurgitate" something before firing a small blast. This confirms the official semi-solid-mass theory and proves the movie designers actually thought
about a possible principle for the fire, instead of playing around with "ball lightning" or "energy ball" effects and throwing some science in.
- "Alight with an acetylene-oxygen flame" could have two meanings: either that acetylene is only used to set the mass alight - or that actually the
mass burns with a such flame during the flight to the target. I believe in latter, as firstly acetylene is a powerful explosive under the right
conditions, secondly that would explain why the fire doesn't go out at that high velocities, and thirdly the way like it explodes (a blue-white burst
and then a big, yellow, sooty fireball with blue-violet rings splashing away from it) fits to acetylene dissolved in something, I think.
- The explosion seems to be pretty powerful, so powerful that one blast (I guess they fire about 0,5 - 1 liter of flaming mass per blast) can crush a
catapult tower made of stone. Also, the Vikings in the movie always get in cover when they notice that dragon, so I think they fear the shockwave. But
I also think, that since the Night Fury is a kind of a dive bomber, the kinetic energy of the semi-solid contributes to its destructive potential.
- As a conclusion, I think Night Furies fire a mass which consists of acetone (burns with a blue flame with a small yellow tip and can hold a lot of
acetylene) , which holds dissolved acetylene under increased pressure. The acetone is thickened with some kind of a shear-thinning or thixotropic
thickener (would explain the semi-solid properties) and maybe also contains very fine potassium nitrate crystals (they provide additional oxygen,
which makes the fire more likely to stay burning during flight, also the explosive power gets boosted, the potassium contributes to the violet flame
color, and to the thixotropic properties). As you can see in the movie, they can also use a steady acetylene flame. I guess, in reality there would be
a kind of "second stomach", which holds the mass and acetylene gas under pressure. This would explain the "regurgitation", as well as the ability to
breathe a steady flame.
Some other details will follow soon, when I've watched the movie and gone through the screenshots another time.
Anyone has other ideas?HellstormOP - 14-8-2011 at 11:01
Does nobody have got ideas yet?
[Edited on 14-8-2011 by HellstormOP]hissingnoise - 14-8-2011 at 11:54
I'm sure there are several dragon-trainers mulling over 'whatever you're on about' as we squeak . . .
HellstormOP - 14-8-2011 at 12:38
What?Norrys - 14-8-2011 at 13:08
Quote:
On the other hand, a dragon like the Night Fury would be unable to fire a solid projectile (i. e. a grenade), as at least a barrel would be needed for
it (not to mention the internal "magazine" and "loading mechanism"...)
I think there is no reason to assume, that a hard body could be spewn worse than a fluid projectile (for example you can spew your spittle not
farther, than a cherry stone or something like that). Also a magazine-like mechanism and organic shells are nothing unusual, think about eggs. So
maybe the fireball could turn out to be in fact a solid shell coated in some blue burning goo.
Quote:
This confirms the official semi-solid-mass theory and proves the movie designers actually thought about a possible principle for the fire, instead of
playing around with "ball lightning" or "energy ball" effects and throwing some science in.
No, it confirms nothing, maybe those who made the visual effects didn't even write the explanation. Maybe the author even intended the dragon to be a
magical creature. Even if they thought about a mechanism to explain the semi solid acetylene-thing i doubt they used their ressources to do some
physical and chemical simulations or even practical experiments, which prove their theories. HellstormOP - 14-8-2011 at 13:12
Hmm, I noticed that the whole concept of a semi-solid, explosive mass based on acetylene is quite a bit strange. Just imagine: You have a mass, most
likely consisting of acetone, thickened to a semi-solid consistence. This mass holds acetylene, most likely under (slight) overpressure (therefore, I
don't think that there are more than 5% acetylene in it). Then, a ball of the mass is fired by compressed air and ignited at the muzzle. It does
neither lose its shape nor the (blue burning) fire goes out, although flying with a velocity of up to 125 mph (200 kmh). As soon as it strikes a solid
surface, it explodes in a very powerful blast, and rings of blue-violet mist splash away from the impact spot. The explosion appears blue-white in the
first few milliseconds, but then a large, smoky, red-orange glowing fireball is formed.
Now the question is: Is that possible at all? When yes, which mechanisms and reactions are responsible for it?HellstormOP - 15-8-2011 at 04:26
OK, I've calculated, that when a Night Fury fires a blast of 0,5 liters of flaming mass, and it maintains 29 psi overpressure in its organ (seems
biologically impossible, but almost all the dragons in the movie have biologically impossible attacks, including magnesium powder or eating rocks and
melting them to lava and firing them within a few minutes) , there would be 25 g of acetylene gas in this blast. This is almost equivalent to 1 mol.
Assuming it almost won't burn off during the flight, and it would all decompose at once as soon as it impacts, then we would have 227,4 kJ of thermal
energy released, as well as about 2 g of hydrogen gas - which would have a HUGE volume at this temperature! For a comparison: The same weight of RDX
(32 grams of an RDX-based plastic explosive are contained in a 40 mm grenade, so it's not a big difference) releases only around 140 kJ of thermal
energy at the explosion. So, maybe an explosive decomposition of acetylene packs enough punch to have such devastating power? But if yes, what the
heck causes the acetylene to not decompose at all when the fireball flies towards the target, and decompose all at once when it impacts?froot - 15-8-2011 at 05:02
Here's a brain fart..
Determine the solubility of acetylene in various solvents. Alcohols, ketones and low melting waxes.
Pick one that can dissolve an appreciable amount of C2H2 under low enough pressure, has a low vapour pressure, higher boiling point and neutral pH.
Not even sure how close you can get to the ideal.
Mix in an oxygen source - 50% v/v H2O2 solution? *ducks*
Hopefully this won't affect C2H2 solutbility too badly.
You may need to add something to help catalyse O2 production.
Just don't store it. Bot0nist - 15-8-2011 at 05:12
Don't go winning any Darwin awards, ok...HellstormOP - 15-8-2011 at 05:24
@frood: I rather thought about using extremely finely ground KNO3 (adding about 25%) as an oxygen source. Mixing H2O2 solution with acetone would
extremely decrease the solubility of acetylene in it. I will also add a thickening/thixotropy agent (currently silica, but I search for alternatives),
so that the KNO3 remains dispersed. For the first experiments, I thought to use a blowpipe with an attached ignitor (paper piece soaked in kerosene,
fixed on a long thick wire) to simulate a semi-solid blast being fired (with very low acetyleen contained), for latter experiments building a special
cannon (I will draw a plan of the cannon, scan and upload it here) for acetylene under overpressure.
@Bot0nist: I'm gonna wear a flame resistant Nomex version of the US Army ACU (already bought, was only 18€, which is about 25 bucks), don't worry!
Nomex will withstand 3500°F or 1900°C (temperature of acetylene burning in air) for 3 seconds without burns to the skin under it.froot - 15-8-2011 at 07:09
The problem with using KNO3 is that the flashpoint of C2H2 is much too low and won't create the thermal impulse required instantly release the O2 from
the KNO3 regardless of how finely divided it is, and, the KNO3 now has the benign emulsifying agent to hide behind further slowing the progression of
the combustion. This is why a miscible O2 source would bring you closer to the ideal creating a homogenous mixture.
You want the mass to burn during flight while instantly consume itself apon impact - and maybe stuff around it.
Nitrocellulose dissolved in acetone with a ratio to achieve optimum viscosity comes to mind. Not blue but it might have a decent result. Maybe
nitromethane? I wonder if NC is at all soluble in NM, short of doing a search. HellstormOP - 15-8-2011 at 08:29
Hmm, on a weight basis the energy of decomposing C2H2 (likely to occur in the whole mass at impact when combined with the fact that it already burns,
I think) is higher than of exploding RDX - maybe THAT could bring the KNO3 to release O2?
I've already tried to use ping pong balls as a thickener, but unfortunately I've got some which aren't made of NC...
I will get some of them from another brand, maybe its gonna boost the combustion a bit.
As soon as I can get my hands on H2SO4 conc., I will also make my own NC, which may work best.
Unfortunately, I don't know which liquid or soluble oxygen source could be mixed with the acetone without decreasing the solubility of acetylene. I
guess I don't need to do much experiments which alcohol, ketone, etc... dissolves acetylene best - the industry seems to use acetone for a good
reason. And maybe, when the KNO3 is really damn finely powdered, the locally created energy by the decomposition of C2H2 is gonna make the KNO3 to
release its oxygen. Also it would add to thixotropy. gregxy - 15-8-2011 at 10:16
You should probably forget about the C2H2. All you need is
something that burns and trying to keep a gas inside of a blob of anything is difficult. The blue/white glow looks "electric" and is more similar to
the energy weapons in other movies or "ball lightning".
There are lots of things that could form a burning blob, try checking out napalm literature. A blob that burns blue/white is difficult since it
implies a much higher temperature. To get that requires that a hydrocarbon be well mixed with oxygen. Or the use of something that burns hotter than
hydrocarbons like metals.
A blob that burns and detonates upon striking would be too unstable unless it contained some separate impact sensitive triggering device.HellstormOP - 15-8-2011 at 10:29
Well, I actually neither want to deviate from the movie nor from the official information about it - and acetylene is mentioned in the official
information. I know that the ball is looking like ball lightning, but the theory of the "semi-solid mass" is logical and especially the yellow, sooty
fireball after the explosion looks like a typical product from acetylene burning/decomposition. I don't believe that the designers just played around
with energy effects, because the fire is very well made. You can even see small burning drops at some of the screenshots, as well as the fireball
leaving trails of blue-violet burning gas. Also the blue part of the mist is visible only at night and under poor lighting - that's exactly how blue
alcohol/acetone flames behave! The much smaller, violet part is also seen at sunny days, but at night it is dominated by the blue-white part. For me
that looks like if quite little acetylene (and maybe also a bit potassium nitrate) were mixed in quite a lot of acetone.
As a conclusion, I think that the movie designers have an at least partially profound concept for that type of dragon fire.
[Edited on 15-8-2011 by HellstormOP]
[Edited on 15-8-2011 by HellstormOP]Wizzard - 15-8-2011 at 12:36
How about paintballs filled with /x/ and is violently flammable when in contact with air/nitrogen/oxygen/water?HellstormOP - 15-8-2011 at 12:56
Well, the problem is, that I want the stuff to work without a case and with burning during flight. The idea with the paintball is more like a grenade,
which of course would be possible with far simpler methods.HellstormOP - 18-8-2011 at 02:00
OK, here are some new results from the experiments I made:
Firstly, I prepared some sort of NC lacquer by dissolving 3 ping pong balls in 100 ml of acetone. Then, as soon as it was ready, I mixed 8.2 grams of
this lacquer with 2.4 grams of finely ground potassium nitrate (actually, I desired a 3:1 mix by weight, but since acetone evaporates very quickly,
this small excess of acetone is OK). The mix showed no thixotropic properties, I guess because the KNO3 was quite clumpy, probably from air moisture.
I poured some of the mixture on an ashtray and set it on fire. The mix burnt off with an orange flame without visible blue or violet parts (you hardly
see blue or violet flames at a bright sunny day anyway), but the orange part of the flame was substantially smaller than I expected from a NC/acetone
mix. It also burnt off much faster and with a less orange flame than a similar mixture jellied with silica. I made a video of it and I'm gonna
probably upload it today or tomorrow. Also, I'm gonna repeat the experiment with the remaining substance this evening, probably some blue or violet
flames will be visible then as the acetone will "wash" out the water from the now still clumpy KNO3, so I can mix it up very well.HellstormOP - 18-8-2011 at 12:50
UPDATE:
Now I burnt the rest of the mixture at night. It was very thick now, since the glass jar where I stored it in is not air tight. As I mixed that stuff,
it was liquid, but now it turned into some sort of a sticky goo paste. I didn't even get it off the spoon.
Apparently there wasn't much acetone left in it, since it was relatively hard to ignite and burnt off with a yellow flame. Despite the added nitrate,
it didn't burn off very quickly. I guess this is because I used ping pong balls as the NC source. The NC they are made from is not fully nitrated and
contains camphor. The mixture made fizzling noises while burning off. That noises were a bit similar to the noises I sometimes heard in the movie.
What I'm going to do next:
- Using dry and even finer ground potassium nitrate. I already dried and ground it with a 300W coffee grinder, and I'm gonna use it in the next
experiments.
- Dissolving acetylene in the flaming mass. I've finally got the calcium carbide today, so I'm gonna crush it a bit (it was delivered as big rocks)
and then use a makeshift gas generator (I will place the ready flaming mass in a beaker into a bigger glass jar, and then pour water into that
surrounding jar. Then, I will wrap a few grams of my calcium carbide into some paper (to delay the reaction), throw that into the water, quickly close
the jar and run away, and then wait until the reaction has stopped) to "charge" my mass with acetylene.
- Using a makeshift "blow gun" to simulate fire breathing. Since in the experiments I made the mass was simply burning on the ground, it did neither
simulate that ball in movement nor an impact on a hard surface. As soon as I can get my hands on a sufficiently long metal tube, I will fix an
ignition mechanism (a thick wire with a paper towel soaked in kerosene, fixed at one end of the tube) on it, then load it with some mass (from the
"muzzle", not from the "breech" where I'm gonna blow into the tube), and then finally "fire" it. This will practically be the first experiment which
says anything about the explosivity of a such mass at all. Or at least about the ability to keep burning in flight.
[Edited on 18-8-2011 by HellstormOP]HellstormOP - 18-8-2011 at 14:11
UPDATE²:
I've took a look at the movie again. What I've noticed, is that the yellow fireball which occurs at the explosion, releases hardly any soot.
Decomposing acetylene would yield a lot of soot, so probably the acetylene here is rather burning than decomposing. What I could think of, is that an
initial decomposition (triggered by the impact, due to the acetylene "bubbling out" from the mass, which means it's no longer stabilized) triggers an
oxidation (and the deflagration of the NC) in the whole mass. This could make the acetone evaporate in an explosion-like way, and also the KNO3
release its oxygen. Thermobaric bomb the dragonish way^^
EDIT:
Sorry for the misinformation, there is quite a bit of soot or smoke formed at the explosion. But not nearby the quantity which will form out of fully
decomposing acetylene! Also, the sound for the explosion in the movie is not a sharp bang, but rather like a combined sound of an impact and of,
maybe, deflagrating hydrocarbon vapors? The fire also apparently has VERY serious thermal effects, even if it explodes without residue. Hmm, and when
its really like 0,5 liters /1 pound of flaming mass each blast, the kinetic effect (dive-bombing dragon at maybe 160 mph + blast launched at min. 15 -
20 mph) also should play a big role.
[Edited on 18-8-2011 by HellstormOP]HellstormOP - 22-8-2011 at 01:06
UPDATE:
Alright, I did some investigations if at least the flame color could be explained with chemistry in reality. It does.
That's the steady acetylene flame you see in the movie. I guess it's combined with air, not oxygen, but since the air seems to be well mixed with the
C2H2 (contrary to acetylene flames in air where the oxygen only comes to the surface of the flame) that could work. Here is a typical acetylene-oxygen
flame from a welding torch:
[img]http://image.carcraft.com/f/25255432+w750+st0/ccrp_0901_07_z+versatile_mig_welding+mig_weld.jpg[/img]
Note that when pure oxygen is used, the flame is only blue at the tip of the torch. I guess that when air was used and premixed with the C2H2, it
would look like in that movie.
What I also would like to point out: That blue mist when a blast explodes at night looks perfectly like burning vapors of either short hydrocarbons
(propane, butane etc.) or ethanol, acetone etc. It is visible at night very well, also visible at poor lighting conditions, but invisible at day. The
only thing you see at day, is a ring of glowing violet mist. No clue how this could be realized.
OK, now since it's clear the movie designers did not simply use energy blast effects or something like this, but really used some kind of a profound
concept of fire-breathing, that concept should be transferable to reality, or at least the major part of it should be. Now, please post your ideas how
that might work!
[Edited on 22-8-2011 by HellstormOP]Norrys - 22-8-2011 at 07:31
Man, your' freaking obsessed!
Quote:
I guess that when air was used and premixed with the C2H2, it would look like in that movie.
I guess this depends on the ratio of fuel and oxygen and on camera settings. Note, that infrared light is bright purple or pink for many cam-chips.
Quote:
OK, now since it's clear the movie designers did not simply use energy blast effects or something like this, but really used some kind of a profound
concept of fire-breathing, that concept should be transferable to reality, or at least the major part of it should be. Now, please post your ideas how
that might work!
Its not clear, why this schould be clear now. You may even post that 20 times and its still nothing clear except of the fact, that this an animation
an no freaking scientific simulation and it was made by grafic experts and not by combustion chemists.
The strange ring effect and many other things arent even close to reality and there had never been any need to construct a real working concept, that
is even simple enough to be reconstructed by some random guys without any expensive equipment.HellstormOP - 23-8-2011 at 13:01
Well, I guess I'm just fascinated. And impatient, since I've practically got all the gear and materials I need (acetone, KNO3, silica, ping pong
balls, nitrocellulose, carbide, ...) but many experiments already failed. But what also is clear to me, is that of course a such effect wouldn't be
perfectly reconstructable in reality. Especially because the movie itself contains some inconsistencies about it. Exaggeration is a part of movie
business and always will be. But: A lot of signs in the movie indicate that the designers really thought about a pseudo-scientific concept for the
fire of this dragon. The few chunks of "background data" provided on the official homepage match the effects in the movie. Or have you ever seen a
semi-solid (hell, there are even small drops dispersing from the main fireball), blue burning energy ball which creates a yellow-orange, smoky cloud
on explosion?
Of course, nobody simulated a such fire in reality (yet...). But: The movie designers developed some kind of a concept how this MIGHT work, and they
took at least a little bit of care of real fire/explosion processes (e. g: the blue ring could be a burning short-chain hydrocarbon, splashed away by
the impact/explosion). Now, I want to prove that concept and find a possible way how this would at least partially work in reality. Bot0nist - 23-8-2011 at 19:40
Don't let us get you down HellstormOP. Keep experimenting and learn as much as you can on the way. Just play it safe.gregxy - 23-8-2011 at 21:33
Perhaps the movie artists watched earlier movies showing burning projectiles
being fired from catapults. (Usually balls of cloth soaked in oil or flaming jugs of oil).
And modeled the "look" after that. I know that I have seen sequences like that in movies.
They then adjusted the graphics to get a unique and interesting visual effect,
most likely by increasing the blue to make it look more electric.
The stuff about C2H2 was just made up afterwards to keep the fans interested.
If you give up on the blue-white color it should not be hard to do what you want.
Or fill a glass sphere with gasoline, cover it with blue-star pyro powder ignite
and fire from a catapult.
You can probably get some of the effects but not all of them.HellstormOP - 23-8-2011 at 23:04
I know that I can't get all the effects, especially not the explosive power. But there are 3 challenges:
- Solve this with a semi-solid mass without the usage of an encasement, because otherwise this would just be like an ordinary grenade (idea:
thickeners like silica may form a "crust" while the ball burns during flight, that way you have a self-encasement)
- Make it explode, not necessarily very powerful (idea: when a ball thickened with a thixotropic thickener, with dissolved acetylene under
overpressure, strikes a solid surface, it splashes around and divides into small drops. That way, the acetylene can decompose/burn in the entire mass)
- Make it burn blue during flight (idea: acetone generally burns blue when it moves fast. A small mistake during a previous experiment proved that.
Now I know, that small drops made of acetone, thickened with silica and containing 25% finely ground KNO3 will burn blue when they fall to the ground.
Now I have to add acetylene, but this will take a few days so that I can find an appropriate place to run a gas generator. It may explode, so I have
to seek a well-hidden place)
All the other properties (strong explosive power etc...) are not important, at least not now. I know realizing all that is gonna be hard, but I'm sure
I will manage that.
[Edited on 24-8-2011 by HellstormOP]quicksilver - 24-8-2011 at 15:02
The chemistry/physics involved in self containment explosions of low explosives can be extremely complex. Speed of deflagration vs air pressure in
generally considered to be the starting point and thus the need for a rate of burn that boarders on detonation becomes pivotal.
Flammable gases (as liquid) at sub-freezing often become examples as well. Gellfication of solvents actually has some research behind it. One example
in gaseous format is adulterated hydrogen, where a smaller unit is more "workable" than larger (Berger, Gentry 1953?).
Commercial adaptation was managed in the USA by Yaley & Co. through a product known as "Gel-Wax". If the firm still exists it's in Calif. and the
methods are most likely patent secret but the patent element may have run it's course by now. I do remember that this firm has found a method of
gelling paraffin and a variety of petroleum distillates. Polar solvents may require more work. However, it may have been done commercially already as
a bushing cleaner.HellstormOP - 24-8-2011 at 15:26
Well, jellying of that stuff shouldn't be a big deal. I will simply use silica again, and I think I'm gonna be fine with it. Also, the explosion isn't
like that normal explosions from low explosives. Acetylene has completely other properties than, for example, nitrocellulose. And actually, I meant
with self-encasement that a "crust" of silica may be the key to keep the fireball from exploding prematurely.
Fortunately, I found an article from the Encyclopedia Britannica about acetylene at Wikisource. Now, I know a few very important facts about it, which
you practically cannot find anywhere else on the Internet. First fact: Acetylene will not decompose as soon as you compress it above 15 psi. As
acetylene was discovered for lighting applications, it was even stored in liquid form. There is only one problem: Above 15 psi a triggered
decomposition of the acetylene will propagate through the entire container, and may even become a detonation. Second fact: Acetylene is not very shock
sensitive. The only danger are the formed sparks when a flask with acetylene (even in liquid form!) is dropped and ruptures. That sparks may ignite
the acetylene and/or trigger the decomposition.
I suppose that it might work this way: When the fireball is ignited and fired, the semi-solid properties of the flaming mass prevent it from
dispersing too much. Also some kind of crust forms, so that the ball doesn't burst mid-flight. If silica is used as a thickener, the three-dimensional
network of silica crystals prevents a quick decomposition in the ball, just like the porous mass in acetylene flasks. When the ball strikes a solid
surface, it breaks up and splashes around. Now, a decomposition can occur in the entire ball, so that it explodes. Burning acetone is splashed around
in the form of blue rings.
OK, the KNO3 isn't mentioned there, but the function of it is obvious: Provide sufficient oxygen for an even greater blast and a whitish acetylene
flame durnig flight.phlogiston - 24-8-2011 at 15:57
I totally understand your passion for reproducing an interesting pyrotechnic effect, but I think you should first fully appreciate that the movie or
the description is not based on fact and as such does not 'prove' or 'confirm' anything. The designers most likely thought up that description without
performing any experiment at all and I fear that if you continue to rely on it to this extent you will never reach the goal of reproducing the effect.
It may sound plausible but it is (convincing) fiction written by non-experts.
With that said, I suggest you look at what is called in pyrotechnic circles a 'comet'. Briefly, it is a chunk of pyrotechnic material, held together
by a binder. A common use is to attach them to shells so that they produce an interesting tail effect while ascending. You could prepare one that has
an outer layer that burns away producing the bright white/blue light and a dripping effect. There are numerous composiitons that will give this color.
For it to be that bright, it should be metal-powder based, most likely magnesium powder, given the color. For the dripping effect, I suggest you look
at so-called 'glitter' compositions. They tend to produce droplets of material that drip of the comet and produce delayed flashes or glowing sparks.
Chunks of glitter composition may be incorporated into the white/blue color composition, or you could glue two comets together, each with different
effect.
The fireball upon impact part of the effect will be quite difficult to produce. A layered comet, such that it breaks up when it hits a solid surface
and produces the fireball could be an option. For fireballs, the most common technique is to disperse a flammable powder using a black powder charge.
naphtalene and powdered milk are commonly used. How to make sure that the comet ignites the fireball effect upon impact, however, without resorting to
impact sensitive mixtures?? (which would be -extremely- unwise).
If you -really- want to go for this, be prepared for a lot of failed experiments. HellstormOP - 25-8-2011 at 02:34
Well, there are a few problems regarding the reproduction of that effect. When you look at the screenshots of that movie, you see that the effect MUST
include some kind of a liquid or semi-solid, when it should work in reality. Here are a few examples:
Have fun reproducing that with a comet or a ghostmine...
Of course, acetylene may be the wrong way to go for that white-blue flame, and some kind of metal powder should be actually used.. But recently I've
found out that acetylene will burn with a brilliant white flame when mixed with enough AIR (not pure oxygen!), also it seems to be the best way for
that "mushroom cloud". I think I'm gonna perform a few more experiments (I still didn't perform even one single experiment using a blowgun, also no
experiments where C2H2 and KNO3 were combined!) and then decide to either keep going with the acetylene method, or employing something like a
pyrotechnical composition... 497 - 25-8-2011 at 13:15
I'd say your best bet would likely be using flammable gelatinous binder with a high fraction of fine magnesium/aluminum/titanium powder in it. The
"explosion" effect could be achieved by the force of the impact..HellstormOP - 19-12-2011 at 05:22
UPDATE:
After putting the project on hold for a long time, I decided to continue it again. I didn't conduct any experiments with a moving mass yet. However,
now is the best time to do it anyway, as we have winter in Germany, and you can dissolve more acetylene in acetone when it's cold. And more acetylene
means more b00m xD
I've watched some making-of videos for the movie, and concluded that the designers didn't care about making it realistic at all. They even said there
that sometimes they were happy that they could make things unrealistic - and showed the scene of a catapult tower being blasted by a Night Fury!
However, I still want to try it out, as it would have some interesting potential in real applications (e. g. "assault flamethrowers" that shoot
high-speed balls of a burning semi-solid mass with acetylene dissolved/with other energetic materials mixed in it, that explodes on impact and creates
something like a thermobaric blast, or at least a fireball like from a gasoline bomb, and are relatively easy to build - due to no need for a
complicated grenade auto-loading system, instead you just need a few pipes and hoses and flasks and valves - , and you can vary the size of their
blast) and also actually that concept makes sense due to some interesting properties of acetylene, especially its high energy content!
By the way, I agree that the actual explosion mechanism is based on a fuel-air explosion, and the acetylene just keeps the stuff burning during the
high-speed flight, and serves as a spreading charge on impact, because its solubility suddenly decreases when the liquid spreads out and starts
burning, and also I know that impacts can make gases that are dissolved in liquids bubble out. Also the acetylene decomposes and yields a nice amount
of hydrogen, which is hardly soluble in acetone.
This is also the main reason why I don't want to stick to metal powders as the high-energy component in the mixture, because they can't provide that
additional explosive effect directly on impact (not after all the fuel is spread out and burning), which you can see in the movie , and which also
comes in handy in real scenarios (shockwave effect). The second reason is because I still want to find out if that will work in reality, even if it
was never intended to do so by the movie creators. It's just a too good sounding and unusual concept. The third reason is that I still have about 0.9
kg of calcium carbide left, and no metal powder at all.
I also understood that the potassium nitrate will under no circumstances serve as a thixotropic agent, because I would need it in colloidal fineness.
I only could achieve that by using a high-energy planetary ball mill. I already work on one but it will take lots of time, as I depend on a very
unreliable friend because he has a workshop where I can make the parts. However, it would increase the explosive effect due to the additional oxygen
provided, and would also yield that purplish flame color which is visible at day.
Under no circumstances will I use any kind of encasement for the mass, as it would turn it into an ordinary grenade, and I really want it to be some
kind of jelly/mass which can achieve all that without an encasement, making it possible to dose blasts and to build incredibly simple and effective
flamethrowers. Achieving the effect of an explosive/pyrotechnic charge in an encasement (grenade/ghostmine/comet) without actually using one is the
real challenge here.
By the way, I would like to know how I can make potassium nitrate particles float in thickened acetone/which kind of thickener I need to make them
float. (There should be about 25% KNO3 by weight in the acetone) The first experiments with silica (like Aerosil, about 3-5%) and potassium nitrate
(very thoroughly ground with a powerfull 300 watts coffee grinder) failed, the KNO3 sunk to the bottom even after thorough stirring of the thickened
acetone with the KNO3 in it.
I would also appreciate it very much if somebody told me a few ways to thicken acetone to a semi-solid/thixotropic/shear-thinning mass. It would be
ideal, if the mass stayed quite viscous while not under stress, and turned into a nearby water-like liquid when explosed to shear. As you know in the
thread, I already tried silica and nitrocellulose. Silica seems quite promising, but not ideal. Nitrocellulose is too hard for me to obtain in the
required quantity and quality. Ping-pong balls are unsuitable.
I also need some information about the solubility of acetylene in various flammable organic solvents. I googled it, but found only non-free material
which I would have to pay for.
[Edited on 19-12-2011 by HellstormOP]
[Edited on 19-12-2011 by HellstormOP]quicksilver - 19-12-2011 at 14:32
IF you can get back issues of the Journal of Explos & Pyrotechnics, there is a great many features of (relativity) safe flame spread effects.
Gases have a real drawback with wind and what is known as the "lake effect", while dual ignition of Al powder is much more controllable for film and
placement.
Another issue is the speed of effect filming in relationship to the effect. What has been deemed a safer alternative is a small ignition charge
encompassed by an float of Al within wet conditions to control flame spread. A great amount of effects material IS available if you hunt for technique
and safety in filming. Often film is used rather than digital for a sequence as the use of film in a more manipulative form of photography.
Gases are subject to a great many unpredictable forces such as wind, timing sequence and temp. Whatever you do: read a great amount of special effects
techniques, prior to experimentation. A little goes a long way. remember you don't want to move air (noise) you want contain effect for the scene
recorded. Rubber containment is subject to freezing, pooling and poor longevity. Kerosene is much more predictable and vapor containment is much more
predictable
Fire hazard demand location and fire extinguisher needs to be well through through. Vapor spread had always been a challenge and the results are much
too fast for hand-held recording devices. Always experiment with tiny examples and progress; studying the recording issues that accomplish you end
result. Search "special effects" quite a bit before you attempt to re-invent the wheel. This is where "flame" inducement rather than imitation
(explosion) is much more value and timing is generally an electric affair. Self and surrounding issues should take president that volume as you can
always scale up by use of special effect recording.
Let safety be your guide more than anything else.HellstormOP - 19-12-2011 at 14:48
Thanks for your safety tips, but I don't fully grasp what they have to do with my experiment, besides that it's a flame/explosion effect. It won't be
like normal pyrotechnic charges.
Regarding the safety, I will wear a flame-resistant surplus US Army ACU, which is made of "Defender M". This fabric is made of 65% cotton with flame
retardants directly incorporated into the fiber (can't be washed out), 25% kevlar and 10% nylon (no clue why they used that...). This textile is
specifically tuned to withstand short exposures to flame, like fuel-air explosions or electric arcs. It won't rip even when exposed to exploding
plasma (from electricity).
Small amounts and a careful choice of the location are mandatory for me anyway, as some things aren't fully legal in Germany and hence I need to stay
undetected by unwanted observers. This will reduce the hazard to other, unprotected people (standing or walking by) to a minimum. Since it's winter
now, the weather here is very wet and cold. No hazard to ignite natural flammable materials is given.
I can't afford making large amounts anyway, and I also would need too large devices to accelerate them to appropriate speed. The limit will be around
100 ml of flaming mass.HellstormOP - 23-12-2011 at 04:58
Another question: Can acetylene decompose when it is dissolved in acetone by 10 to 15 percent by weight and exposed to flame and impact at the same
time? If yes, can the local overheating caused by this make potassium nitrate crystals (that are dispersed in acetone and are about 10 microns small)
release their oxygen?
If no, is there an oxidizer that
- is obtainable and affordable by the average non-professional?
- can be mixed with, dissolved, dispersed or emulsified in acetone without separating after that?
- will release its oxygen fairly easily, but will neither react spontaneously with acetone nor with acetylene?
- won't decrease the solubility af acetylene in the acetone?HellstormOP - 5-1-2012 at 06:42
Nobody has ideas about that?Neil - 5-1-2012 at 06:58
Your last question is a little bit bonkers with the level of complexity that would be needed to answer it.HellstormOP - 5-1-2012 at 07:29
Well, in this case leave out the thing with the decomposing acetylene. I guess that will require several experiments anyway.
But what's actually about the oxidizer? I thought the users in this board had a lot of knowledge about various oxidizing agents and were willing to
share it by answering such questions...Neil - 5-1-2012 at 08:10
Hoho don't try the kicked puppy approach. They are but they also know you could have found that out for your self just as they did, by doing a bit of
reading.
KNO3 is used, dissolved in methanol, to make pink/purple flames. The decomposition point for KNO3 is well above the boiling points of acetone or
methanol so the likelihood of getting it to dump its oxygen while sitting in a pool of cold fuel is low.
You can bind KNO3 powder in molten sugar - something that could not be done if it did not have a high melting point and a relatively high level of
stability. HellstormOP - 5-1-2012 at 08:28
That's why I supposed that maybe the local overheating of decomposing acetylene may cause temperatures such great that small crystals might release
their oxygen, and get the acetylene boiling and that way the mass exploding as well.Neil - 5-1-2012 at 09:12
Boiling = cooling. HellstormOP - 5-1-2012 at 12:09
Well, then the released (atomic?) hydrogen from the decomposition of acetylene might reduce the nitrate directly or combust with any released oxygen
from local overheating? And then release enough heat to vaporize the acetylene to a point where the sheer pressure of forming vapor would blow the
mass apart?
The other option, of course, would be the pure heating effect of decomposing acetylene, which might vaporize acetone, and the released hydrogen. Both
will increase the pressure, and that's the point. Boiling might be cooling, but it builds up pressure which could further trigger acetylene
decomposition, or turn the mass into something like a "gasoline bomb" with additional oxidizer.
Regarding oxidizers, something that releases its oxygen very easily, but not spontaneously, might be useful, as it would make combustion within the
fireball possible and greatly increase pressure and temperature. The explosions in the movie look "semi-energetic" to me, something between a fuel-air
explosion or gasoline bomb and an ordinary explosive. Maybe a kind of semi-solid, very fuel-rich TBX?fledarmus - 5-1-2012 at 14:04
Wouldn't it be easier just to get the movie company to send you a sputum sample from the dragon? Then you could analyze it and determine exactly what
it was composed of.Neil - 5-1-2012 at 17:25
They look like CGI to me. unless you are trying to compress and contain the
mixture and then super heat it, the cooling effects of the gas leaving the acetone and the acetone will prevent the nitrate from getting hot enough to
decompose.
Containing such a mixture is asking for some kind of detonation or at least explosive event.
I'm going to go out on a limb and say making a pressurized oxidizer/fuel slushy is harder then you'd expect. I've never lite such a mixture on fire
but I have tested butane slushy fuels and for the most part the evaporating gas cooled the fuel to the point where it would burn more tamely then
gasoline. mixing very fine Zr dust with a very volatile fuel might work but then you are approaching the level of insanity that applies to white
phosphorus solutions.
HellstormOP - 6-1-2012 at 02:15
Of course they are CGI, but if you would see the same picture happening in reality (and I want to reproduce it in reality), it would look like, I
don't know, low-order TBX?
The fact, that escaping gas actually COOLS the mixture, is actually EXCELLENT - as long as the fireball flies. It would actually stabilize the
fireball and prevent the acetylene inside from decomposing. (But don't forget that escaping acetylene would have far less of a cooling effect than
vaporizing butane.)
But as soon as it strikes on a surface, other effects should take place, I think. For example, when you gently hit an open soda bottle, gas starts to
bubble out. Now imagine the same with acetylene, 10% by weight, dissolved in a semi-solid mass where it can't escape that easily, striking a surface
with 250 km/h...
As soon as the acetylene leaves the acetone and forms these bubbles (probably under VERY high pressure), the acetone can't prevent it from decomposing
anymore. Therefore, the bubbles could decompose, producing hydrogen gas under pressure. This could produce even more heat (adiabatic compression).vaslop - 6-1-2012 at 05:29
Im not suggesting that anyone tries this, but all the properties could be replicated by using a gell of methanol stabalised methyl nitrate, with
nitrocellulose.
This would burn blue and yellow, be inexstinguishable at any wind speed, and (with the help of an impact sensitive detonator) explode on contact.HellstormOP - 6-1-2012 at 06:51
Hmm, I already thought about using some kind of energetic material which I mix into the acetone. Alcohol nitrates could be worth a try, however I have
concerns that they may trigger an explosion when the ball catches fire, or they also may decrease the solubility of acetylene in acetone. Another
option would be, of course, TATP. It would make the mass burn *VERY* vigorously and additionally shock sensitive.
However, what I need most now are ideas about suitable thickeners and oxidizers. I already described the criteria above. A combination of silica and
very finely ground potassium nitrate might be the right way to go, and I already did a few experiments with it (however, I conducted no experiment
where silica, acetylene, acetone and KNO3 were combined) and noticed that KNO3 doesn't release its oxygen when it's mixed into thickened acetone (with
silica), and set on fire.HellstormOP - 16-1-2012 at 11:39
UPDATE:
After a few weeks of very slow preparation and a complete redesign of the launcher device today, I'm finally able to proudly announce that the first
real test will come very soon. I will use a mixture of 37.5 g acetone, 12.5 g finely ground KNO3 and 2.5 g silica. It's already prepared and standing
in a not completely airtight container in the freezer compartment of a fridge for more than a week, so I may need to add some acetone to restore the
original proportions.
I will charge this mixture with acetylene using calcium carbide. For that purpose, I will use a makeshift gas generator comprising a small plastic
beaker with the mass, standing in a larger glass jar with an airtight seal (the thread of the jar will be tightly wrapped with a sealing strap), where
the water is and where the calcium carbide chunks will be thrown into. The plastic beaker will be prevented from floating on the water by a steel rod
that forces it to keep some distance to the lid. I will use a total of 10 g calcium carbide pieces, in 4 batches of about 2.5 grams each. That way I
can ensure a safer charging procedure (not such a high pressure rise as with one batch) and also a more thorough saturation of the acetone-based mass
(I will thoroughly stir the mass between the reactions of the batches).
Since acetone dissolves far more acetylene when in cold state (58g/l at 0°C vs. 28g/l at 20°C), I will keep the semi-solid mass in the freezer
compartment before charging it. I also will use a mix of water, ice and salt for the reaction of the carbide, as this will decrease the temperature
and also make the process safer and more efficient (the reaction will be slowed down by the cold and the loss at the begin, where the chunks are
thrown into the jar and the lid is still open, is minimized and since brine can hardly dissolve acetylene (5g/1000l), there will be more of it left
for the mass.). Depending on the temperature outdoors, where I will perform the experiment, I may also use styrofoam around the gas generator as an
insulation.
The launcher itself will be a pretty simple pneumatic cannon, comprising a 400 mm 3/4" steel tube which serves as the barrel, a ball valve, probably
outfitted with a self-made spring mechanism to open it faster, and a plastic bottle which will hold the compressed air for the shot. A steel rod
attached to the muzzle, with a paper towel wrapped around it, which is soaked in kerosene, will (hopefully...) ignite the mass when it's launched.HellstormOP - 21-1-2012 at 06:22
UPDATE:
I got all the necessary parts and the experiment will be performed either today or tomorrow. I will shoot a portion of the mass that will weigh 5
grams. There will be a pressure of 0.5 bar (g) in the plastic bottle, the calculated muzzle energy willl be 12 joules (friction losses not taken into
account) and the muzzle velocity will be around 90 m/s. The plastic bottle will be connected to the ball
valve using a 1/2" hose and an a 1/2" (hose) to 3/4" (ball valve) adapter. There will be no spring mechanism for fast opening.
I decided to modify the acetylene generator/charger. Now it will comprise a bigger glass jar, filled with brine, which will serve as the gas
generator, and will be connected with a PVC hose (6 mm inner diameter /1.5 mm wall thickness) to a 100 ml glass jar with a very long lid thread and a
very tight lid. All threads, both on the acetylene generator and the launcher device, will be carefully sealed with lots of Teflon sealing strap. I'm
also thinking about using a salt/ice freezing mixture in order to cool down the acetone even further, so that it can hold even more acetylene.HellstormOP - 23-1-2012 at 04:30
UPDATE:
Unfortunately, I failed to comduct the experiment yesterday due to lack of time. But I think I will be able to do it this week, as I bought everything
I need.
Any ideas/suggestions about the experiment are still very welcome.HellstormOP - 5-2-2012 at 15:46
UPDATE:
2 weeks have passed, and the experiment yet has to be done. I know, I can be REALLY really lazy...
However, I've almost finished making the gear needed for the experiment, and also all the equipment is now gathered at one spot, while previously it
was scattered over 2 flats (the flat of my mum and me and the flat of my dad). Here's a picture of the almost-finished gear:
Note that the bicycle valve which should be integrated into the bottle for pressurization is still missing, and I also need a 3/4" to 1/2" adapter.
However, these problems will be fixed soon, and then hopefully I can do the experiment. Actually, it'S very good that I didn't perform it yet, as we
have a massive cold snap in Germany, which makes my experiment safer, easier and more effective. Last week we had around 5 °C average temperature at
day, while now we have like -10°C.
BTW: Could anybody provide a solubility table of acetylene in acetone at temperatures lower than 0°C?
[Edited on 6-2-2012 by HellstormOP]Bot0nist - 5-2-2012 at 20:02
please re-size your pictures smaller. It messes up the screen scrolling.HellstormOP - 6-2-2012 at 11:19
Done.freedompyro - 8-2-2012 at 02:22
You know... This thread kind of reminds me of that firestarting gun with a range upto 600 feet they use for controlled fires. It fires flaming
paintballs full of some sort of liquid coated with another liquid I think. Should be easy to find it's video on youtube... I saw it the other day. I
so want one...
