The Pecular Behavior of Fire

[ApeNotKillApe]

Which you won't get from me. I never had a deeper understanding of anything in my entire life, and I don't plan to start now.

[Fireball]

Ever wonder why the plume coming out of the back end of a rocket gets so big the higher the rocket goes?

Less air pressure up there, so the exhaust fans out more.

Then the first few seconds after take off are the most dangerous because of backup. I'm sure NASA has come up with a way to minimize that danger.

The rocket plume is ducted away from the launch pad through a flame trench, at ignition and early ascent.

As far as the "triangular" shape of the flames is concerned, there is convection sweeping in from the sides, plus there is cooler denser air to the sides, as was mentioned by ApeNotKillApe.

[Amarok]

The details are naturally more complex, but that's my understanding as a layman.
Crackling is the result of a build-up of pressure in pockets of moisture in the burning material (notably wood) as it vaporizes into steam, expands and bursts out.

Devil in the details.  Guess that would take a deeper understanding of exactly what fire is. e=mc2 kind of stuff.

It's all physics and chemistry my friend and it's glorious

[downbeatplumb]

Fire gives off light but does not act like light.

If you light a torch and hold it aloft the fire will shoot upward. But if you hold the torch horizontally, the fire will still shoot upward. Whereas if you hold source of light, such as a flash light, horizontally the light will continue horizontally.

No matter how far fire spreads it maintains its triangular shape, sometimes producing several triangles with one angel pointing upwards, unless it encounters a downward facing surface such as a ceiling. Then the fire spreads along the surface and that surface becomes it's base. It resumes its triangular shape when it eats through the surface to the air above.

Is there a scientific theory of fire that accounts for this behavior?

Fire is a light source not light itself.

[chimp3]

Fire is plasma

[Gawdzilla Sama]

The flashlight is designed to send a focused beam in the direction the "torch" is pointed. That's what the concave reflector is for. Not rocket science.

[Thumpalumpacus]

Yep, as noted above, the shape of the flame is mostly a matter of convection. Fun fact: In zero-G, fire is a ball.

[Fireball]

Yep, as noted above, the shape of the flame is mostly a matter of convection. Fun fact: In zero-G, fire is a ball.

Fireball, hell yeah!

[Gawdzilla Sama]

Yep, as noted above, the shape of the flame is mostly a matter of convection. Fun fact: In zero-G, fire is a ball.

And quickly snuffs itself as the oxygen adjacent is consumed, IIRC.

[Anomalocaris]

Fire is plasma

Not any fire you can easily light.

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Fire gives off light but does not act like light.

If you light a torch and hold it aloft the fire will shoot upward. But if you hold the torch horizontally, the fire will still shoot upward. Whereas if you hold source of light, such as a flash light, horizontally the light will continue horizontally.

No matter how far fire spreads it maintains its triangular shape, sometimes producing several triangles with one angel pointing upwards, unless it encounters a downward facing surface such as a ceiling. Then the fire spreads along the surface and that surface becomes it's base. It resumes its triangular shape when it eats through the surface to the air above.

Is there a scientific theory of fire that accounts for this behavior?

Fire is the process of rapid exothermic oxidation chemical reaction.  What you are describing is flame, which is hot incandescent gas emitted by fire.  Light is not an intrinsic product of the reaction.  Rather light comes from incandescent radiation associated with any hot object, including the flame. Flame gives off light for the same reason the filament in a traditional incandescent light bulb gives off light when an electric current heats the filament.

Hot gas is less dense than cold atmosphere.   Flame typically starts out only 1/3 or 1/4 as dense as atmosphere.  So flame is highly buoyant and floats up rapidly.   However, as the flame rises, it both cool by radiating away some of its heat, and by mixing with cool surrounding air.  When cooled sufficiently, it stops giving off visible light.  The edges cools the quickest, as it entrained cool air as it rises right from the beginning, and therefore rises the least before stopping to give off light.   The center part of the flame is the part most protected from cool surrounding air, as a result it remains hot and incandescent the longest, and floats up the most, before it too eventually stops giving off light. This differential cooling rate between center and edge of flame is what gives it its triangular shape.