Speed of chemical propellants
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Have you heard of flame front propagation rates, and how they can differ?
Could atmospheric oxygen in the cartridge case, or lack of it, affect flame propagation rates?
And be part of the reason smokeless and black powders are NOT used as solid rocket fuels?
Intermediate reaction pathways?
The dynamic picture being more important than the static state of initial reactants and final products?
Maybe seeing a minor issue ignores a major issue?
Could atmospheric oxygen in the cartridge case, or lack of it, affect flame propagation rates?
And be part of the reason smokeless and black powders are NOT used as solid rocket fuels?
Intermediate reaction pathways?
The dynamic picture being more important than the static state of initial reactants and final products?
Maybe seeing a minor issue ignores a major issue?
Jim Watson
Member
Helium in your cartridges would be kind of like nitrogen in your tires. Advertising.
Sure they are. What do you think Mr Congreve used? The British used Cordite as a rocket propellant. In suitable (large) grain size, of course.
Sure they are. What do you think Mr Congreve used? The British used Cordite as a rocket propellant. In suitable (large) grain size, of course.
mcb
Member
You could not get enough helium in a conventional cartridge at 1 atmosphere pressure to make a measurable difference. I don't think the military would want a pressurized cartridge to get enough helium to make a measurable difference. The average molecular weight of the gas in the barrel would be significantly higher than pure helium as the propellant burned producing much heavier gases. Helium is also very difficult to contain as it tends to defuse through many solids especially at higher pressure making a 20 year shelf life typical of military ammo difficult to maintain.
And yet black powder and nitrocellulose and nitroglycerin (the two primary ingredients in smokeless powder) have all been used successfully in solid rocket motors. They are milled differently in to very different solid shapes than when used as gun powder for small arms but it is the same thing.
To produce thrust in an arena byond Earth's atmosphere, for satellites and such, where atmospheric oxygen availability is nil for practical purposes?
Well, let's see if Wikipedia can help.
"Nitrocellulose contains insufficient oxygen to completely oxidize its carbon and hydrogen. The oxygen deficit is increased by addition of graphite and organic stabilizers."
https://en.m.wikipedia.org/wiki/Smokeless_powder
But - but - but that means the powder stoichiometry isn't sufficient for complete combustion like the man said.
How do we make more gas molecules to raise the pressure?
Maybe we can react oxygen from the atmospheric air, but not helium, and not in space - so the same mass of gas isn't generated in the absence of atmospheric oxygen. And the cartridge case can hold enough if we load smart, like Quickload shows us!
And by golly, converting greater mass to gas in the same volume means pressure must increase! Then the bullet moves, but solids are still being converted, and so on until, and a short ways after, the bullet exits the muzzle. That's why muzzle flash can happen!
Not a minor point at all when & where I went to school. And Wikipedia and Google didn't exist then.
"Nitrocellulose contains insufficient oxygen to completely oxidize its carbon and hydrogen. The oxygen deficit is increased by addition of graphite and organic stabilizers."
https://en.m.wikipedia.org/wiki/Smokeless_powder
But - but - but that means the powder stoichiometry isn't sufficient for complete combustion like the man said.
How do we make more gas molecules to raise the pressure?
Maybe we can react oxygen from the atmospheric air, but not helium, and not in space - so the same mass of gas isn't generated in the absence of atmospheric oxygen. And the cartridge case can hold enough if we load smart, like Quickload shows us!
And by golly, converting greater mass to gas in the same volume means pressure must increase! Then the bullet moves, but solids are still being converted, and so on until, and a short ways after, the bullet exits the muzzle. That's why muzzle flash can happen!
Not a minor point at all when & where I went to school. And Wikipedia and Google didn't exist then.
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230RN
2A was "political" when it was first adopted.
I always thought the limit was the speed of sound in the hot propellant gases. This sort of makes intuitive sense, sans any math.
There were some German canons being built on the principle of additional chambers containing propellant along the barrel length, to keep the pressure (and the temperature) up. I believe Jules Verne used this idea in one of his novels for the moon cannon .
Terry, 230RN
REFs:
https://en.wikipedia.org/wiki/From_the_Earth_to_the_Moon
https://en.wikipedia.org/wiki/V-3_cannon
There were some German canons being built on the principle of additional chambers containing propellant along the barrel length, to keep the pressure (and the temperature) up. I believe Jules Verne used this idea in one of his novels for the moon cannon .
Terry, 230RN
REFs:
https://en.wikipedia.org/wiki/From_the_Earth_to_the_Moon
https://en.wikipedia.org/wiki/V-3_cannon
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Yes, I remember that story now that you mentioned it. A long time ago.
In chemical reactions, mass is conserved (atoms are conserved). Moles (number of molecules) and volumes are not necessarily conserved. The whole point is changing how the atoms are arranged in molecules.
Jim Watson
Member
There is not enough atmospheric oxygen in a cartridge to matter.
IMR smokeless powder is mostly nitrocellulose. The density of nitrocellulose is 1.23 gm/ml. The bulk density of IMR 4350 powder is .945 gm/ml. Therefore the powder charge in a cartridge full up to the base of the bullet is 77% (mostly) NC, 23% air, or 4.6% oxygen by volume. But the density of air is only .00128 gm/ml.
A .308 case is 3.6 ml and so holds 3.4 gm of powder, but only .0002 gm of oxygen.
Combustion product of NC smokeless propellants is carbon dioxide 28%, carbon monoxide 23%, hydrogen 8%, nitrogen 15%, and water 26%. Therefore 31% combustible gases that might react with that oxygen.
So you are making about 1 gm of fuel for .0002 gm of oxygen.
You can break it down to moles but that is not going to account for four orders of magnitude.
IMR smokeless powder is mostly nitrocellulose. The density of nitrocellulose is 1.23 gm/ml. The bulk density of IMR 4350 powder is .945 gm/ml. Therefore the powder charge in a cartridge full up to the base of the bullet is 77% (mostly) NC, 23% air, or 4.6% oxygen by volume. But the density of air is only .00128 gm/ml.
A .308 case is 3.6 ml and so holds 3.4 gm of powder, but only .0002 gm of oxygen.
Combustion product of NC smokeless propellants is carbon dioxide 28%, carbon monoxide 23%, hydrogen 8%, nitrogen 15%, and water 26%. Therefore 31% combustible gases that might react with that oxygen.
So you are making about 1 gm of fuel for .0002 gm of oxygen.
You can break it down to moles but that is not going to account for four orders of magnitude.
mcb
Member
You seem to be on a crusade so i will grant you the victory. I was wrong about nitrocellulose being balanced fuel/oxygen wise. I am a mechanical engineer not a chemist. But it's close to balanced and there is sufficient amount of self oxidizing to keep the combustion reaction happening in the absence of external oxygen sources. This has been proven many times. There are plenty of articles and video showing gun powder burning in various oxygen-less atmospheres.
This also would be another reason why double base powers produce better performance in some circumstance as the excess oxygen from the nitroglycerin no doubt gets a more complete burn of the nitrocellulose. This is also why they probably burn hotter and in many cases cause increased rates of barrel erosion.
And we are now way off topic. Shockwave propagation in the propellant gases is the prime limiting factor in what limits the maximum velocity of a gun powder propelled projectile. It is not the only thing but it is the prime factor.
Light gas guns get more velocity by using a gas with a higher speed of sound in their working gas acting on the projectile.
Rail guns by using electromagnetic forces rather than shock limited gases as there motive force. Though some rail guns still use combustion initially to inject the projectile at high speed into the rails. A rail gun's efficiency is much higher as the projectile's speed increases.
mcb
Member
Clearly you remember more of your chemistry than I do. Nicely put.
I am a Chemical Engineer not mechanical, review that in my first post this thread.
Crusade? For the facts. Can you post your source material for your post smokeless powders have stoichiometric oxygen content for complete combustion? Did you use Google as you exhorted me to do? Did you not see the graphite included in the mixture that constitutes smokeless powder further exacerbates the oxygen deficit? Read your own post I copied, it was about smokeless powder in your words, not merely nitrocellulose ingredients. Plus primers which is a different item.
Close? Quantify.
If not Google why did you choose to post something so readily shown to be devoid of fact? That is independent of any education.
Jim Watson
Member
To say that smokeless powder "burns" is a popular media simplification and leads to discussion about air and space.
Smokeless powder is predominantly one or two (or three) specific rather unstable chemical compounds. When initiated by primer flash, they decompose by deflagration into gaseous products. I guess if you want to visualize one end of a nitrocellulose molecule "oxidizing" the rest as it bursts into flame, you can think of it as burning, but it is not what I learned.
Smokeless powder is predominantly one or two (or three) specific rather unstable chemical compounds. When initiated by primer flash, they decompose by deflagration into gaseous products. I guess if you want to visualize one end of a nitrocellulose molecule "oxidizing" the rest as it bursts into flame, you can think of it as burning, but it is not what I learned.
The electrons are all there.
Here, I Googled Graphite for you. It's quite oxygen deficient and higher density, more mass per unit volume, than nitrocellulose. Lots of atoms to combust (see I used combust to be specific).
https://en.m.wikipedia.org/wiki/Graphite
https://en.m.wikipedia.org/wiki/Nitrocellulose
"Nitrocellulose contains insufficient oxygen to completely oxidize its carbon and hydrogen. The oxygen deficit is increased by addition of graphite and organic stabilizers."
The oxygen content in a cartridge is important.
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Explain the difference in pressure rise in absence of oxygen vs presence of oxygen.
"The stabilizers are added in the amount of 0.5–2% of the total amount of the formulation; higher amounts tend to degrade its ballistic properties."
mcb
Member
Where are you seeing data that shows a pressure difference between a gun at standard atmospheric conditions and in the absence of external gaseous oxygen? Share that data if you have it I would like to see it.
If you fire a pressure instrumented test barrel in a standard 1 atmosphere environment vs in a vacuum you would measure almost exactly the same pressure vs time curve altered only by the absence of 14.7 psi external atmospheric pressure and the slight reduction in friction due to viscus losses due to an absence of air in front of the bullet in the barrel. Both of those would be such small changes as to be lost in the sensor noise at the pressures typical of a firearm.
Jim Watson
Member
Are you talking about the guy with a vacuum pump and a laser?
I honestly didn't watch the video as I knew what it was posted to support, the statement there is sufficient oxygen in smokeless propellants to combust the mixture at minimum (stoichiometric) was 100% false, and still is and will be tomorrow, as there's plenty of evasion of my direct questions.
Followed by denial that was stated, along with statement about being on a crusade, no more factual than smokeless propellants containing sufficient oxygen (stoichiometric) for complete combustion.
I took the mechanical engineers post on lack of pressure to be factual as one would expect mechanical force - pressure - would be something that background would be knowledgeable about.
If you're telling us that also is untrue, fine by me on the same data caveat the evasive mechanical engineer is now requesting. What is the pressure rise ratio in the absence vs presence of oxygen. You say it doesn't matter, therefore ratio of one. Same data requirement.
Followed by denial that was stated, along with statement about being on a crusade, no more factual than smokeless propellants containing sufficient oxygen (stoichiometric) for complete combustion.
I took the mechanical engineers post on lack of pressure to be factual as one would expect mechanical force - pressure - would be something that background would be knowledgeable about.
If you're telling us that also is untrue, fine by me on the same data caveat the evasive mechanical engineer is now requesting. What is the pressure rise ratio in the absence vs presence of oxygen. You say it doesn't matter, therefore ratio of one. Same data requirement.
I continue to contend the oxygen has to go into a gaseous state to participate in combustion of propellant powders used in firearms to propel projectiles.
https://en.m.wikipedia.org/wiki/Combustion
That cannot occur in a vacuum. Furthermore using the law that total pressure = the sum of the partial pressures, and if total absolute pressure is near zero, so is gaseous oxygen. With zero gaseous oxygen, combustion of these materials cannot occur. It's clearly seen burning bits self extinguish in vacuum in the absence of gaseous oxygen.
That's what I've been, and still am, talking about in addition to the stoichiometric oxygen deficiency in smokeless powders.
The material requires external energy to initiate the combustion, this is the activation energy threshold of the overall exothermic combustion reaction.
A vacuum, by definition, is as close to devoid of gaseous materials as can be accomplished. Nil total pressure = nil oxygen partial pressure.
I also well know that such solid propellant starting out substoichiometric in oxygen simply cannot produce the same amount of solid to gas as the same solid mass with additional oxygen to convert solid matter to gas. Period. Facilitated by the additional oxygen already being in gaseous form.
Intermediate chemical reactions. Stoichiometry. Again.
https://en.m.wikipedia.org/wiki/Combustion
That cannot occur in a vacuum. Furthermore using the law that total pressure = the sum of the partial pressures, and if total absolute pressure is near zero, so is gaseous oxygen. With zero gaseous oxygen, combustion of these materials cannot occur. It's clearly seen burning bits self extinguish in vacuum in the absence of gaseous oxygen.
That's what I've been, and still am, talking about in addition to the stoichiometric oxygen deficiency in smokeless powders.
The material requires external energy to initiate the combustion, this is the activation energy threshold of the overall exothermic combustion reaction.
A vacuum, by definition, is as close to devoid of gaseous materials as can be accomplished. Nil total pressure = nil oxygen partial pressure.
I also well know that such solid propellant starting out substoichiometric in oxygen simply cannot produce the same amount of solid to gas as the same solid mass with additional oxygen to convert solid matter to gas. Period. Facilitated by the additional oxygen already being in gaseous form.
Intermediate chemical reactions. Stoichiometry. Again.
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Jim Watson
Member
I agree there is nowhere near enough oxygen in nitrocellulose to fully oxidize the carbon and hydrogen in the polymer, only about 70% enough by my back of envelope.
I don't see where a nitrated compound would have to first convert to gaseous oxygen and then that oxygen literally burn the other elements in the compound, though. I think it decomposes in one step.
Unfortunately they took down all the books on explosives and propellants from my old agency's technical library, so I can't go look stuff up. I guess they didn't want materials that The Wrong People might refer to.
I don't see where a nitrated compound would have to first convert to gaseous oxygen and then that oxygen literally burn the other elements in the compound, though. I think it decomposes in one step.
Unfortunately they took down all the books on explosives and propellants from my old agency's technical library, so I can't go look stuff up. I guess they didn't want materials that The Wrong People might refer to.
If it's all one step why doesn't it keep going when encountering vacuum?
"The problem with burning gun powder in a vacuum is not the lack of oxygen but the lack of pressure. If you do not have pressure then the gun powder will frequently stop burning due to the combustion front not being able to propagate. You see this even in standard atmosphere conditions. Go shoot a bunch of pistol ammo in short barreled handgun and you will find a bunch of partially burnt powder grain on the floor down range (380 ACP in pocket pistols due to its lower pressure is very good at this.) The powder does not completely burn before the bullet exits the short barrel and at atmospheric pressure (and the grains moving very fast through it) they can be extinguished and don't fully burn despite having sufficient oxygen."
You have the whole internet at your fingers.
"The problem with burning gun powder in a vacuum is not the lack of oxygen but the lack of pressure. If you do not have pressure then the gun powder will frequently stop burning due to the combustion front not being able to propagate. You see this even in standard atmosphere conditions. Go shoot a bunch of pistol ammo in short barreled handgun and you will find a bunch of partially burnt powder grain on the floor down range (380 ACP in pocket pistols due to its lower pressure is very good at this.) The powder does not completely burn before the bullet exits the short barrel and at atmospheric pressure (and the grains moving very fast through it) they can be extinguished and don't fully burn despite having sufficient oxygen."
You have the whole internet at your fingers.
If it all goes at once, how do we have partial combustion products? And how do the oxygen atoms pick which other atoms they combine with especially when deficient in oxygen (substoichiometric)?
I'm off to watch the Thunderbirds fly over our area.
I'm off to watch the Thunderbirds fly over our area.
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