I think I’m being stupid or overthinking this, but if for example, you’re burning in a controlled manner, a bottle of propane in a burner producing a slow burning flame, and then you ignite the entire bottle causing it to explode, are these both examples of combustion? Is an explosion just really really rapid combustion? If so, where is the line drawn between these terms and how is the chemistry different? Or have I misunderstood these terms?
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If you look at Wikipedia an explosion is
>An explosion is a rapid expansion in volume associated with an extreme outward release of energy, usually with the generation of high temperatures and the release of high-pressure gases.
An explosion does not require combustion or even any chemical reaction, a pressurized gas tank can explode from a failure of the container.
A nuclear bomb is not combustion but thy are explosion. The vast majority of the energy is from nuclear fusion and fission, there is a small amount if chemical explosives that trigger the fission reaction.
You can get an explosion by just having an object thing another object at and high enough speed. The impact heat up the material and some get vaporized to a gas. So a meteorite’s impact results in an explosion and it can be without any combustion at all like if one hit the moon.
Propane tanks explode when the internal pressure it is getting so high that tanks can no longer handle it. It can happen if the gas escapes it burns and heats up the bottle. It cant happen in the bottle because there is no oxygen there so it cant burn. If you heat up a bottle with water the same thing can happen. it became gas the pressure increased and the container burst.
After a propane container burst you have combustion of the propane. Because there is so much of it and it creates lots of hot gas that has a higher volume. You get a pressure wave the increase in gas volume. The combustion will not be faster than in a propane flame, it will be slower because it takes more time for the propane to come into contact with oxygen in the atmosphere. So the pressure vace depends on the amount of fuel that can burn not that tall if it buren after then in a propane flame
A propane flame is limited but the amount of propane that is released per unit of time, not how fast it burns when it is in contact with oxygen
If you have both the fuel and oxidizer in a container it can burn in it. All of it can quickly combust. A solid or liquid creates a lot of gas, if it starts as a gas it is the temperature and therefore pressures that increase. This is how firearms, fireworks, etc work. You can have a lot less material that burns to create high pressure in a container than if the material is out in the open air. This is a low explosive that deflagrates, the reaction propagates slower than the speed of sound. Having the material contained can cause all of it to ignite faster so a rapid combustion.
There is a high explosive to the detonate. That meant the reaction table was faster than the speed of sound. This is what TNT, C4, and other high explosives do. Because the reaction is faster than the speed of sound air can just move away, there is no need to have a container to create a pressure wave they will do that in the open. High explosive is more molecules that break apart not multiple molecules combine. The produced from the brain apart can then react.
TNT detoanion is primary 2 C7H5N3O6 → 3 N2 + 5 H2 + 12 CO + 2 C
There are some H2 + CO → H12O + C and 2 CO → CO2 + C. too but it do not real most of the energy.
There is high explosive like C4 that also can burn without detonation. It will happen at a low rate. C4 has been used a a provides fire starter in for example the Vietnam War. You need to hit it with a shockwave like a blasting cape with a simple-to-trigger high explosive.
So low is a lot like regular combustion but the material is contained so the reaction is faster and the pressure can build up. If you do not contain it it might just burn and not create a pressure wave.
A high explosive is a molecule that breaks part and it propagate faster than the speed of sound and you get a pressure wave without a container.
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