Compressing flames for focused heat

[moonfly7]

So, this is a bit of a cross over topic as it is related to a fantasy subject, but I'm in need of a scientific response so I'm putting it here.

If you had a way to completely shape fire anyway you like, would it become hotter and have a more focused heat if enough of it was compressed into a thin enough line? I'm not sure if it would, but if I could compress say, 5 cubic feet of fire into a few inches, would it become hotter and if so how much?

[warty goblin]

If you take a gas and compress it, its temperature rises. Fire, as in the red stuff that appears above burning wood, is a gas. So yes, compressed fire would be hotter. How much hotter is rather difficult to say, because fire isn't a uniform thing; propane burns hotter than wood, and there's substantial temperature variation even within wood.

Also the hottest parts of a fire - as a collection of burning material - with organic fuel often don't produce much in the way of flame - the licking red tongues bit. Wood for instance burns in two phases; the first phase produces some heat and quite a lot of glowing gas as various interesting chemicals get vaporized out of log. This is your classic merrily dancing campfire. The really hot part of the fire however is the bed of coals at the base, which consist of charcoal; i.e. highly purified carbon with most of the impurities burned out by the first phase. This produces some visible flame, but is generally far hotter than the flashier burning that happens before. This is the stuff that keeps a house warm over a cold winter's night, or, when burned in bulk with good draft control to feed it plenty of oxygen, you can use to smelt or forge iron. Including occasionally your wood stove, if you get a bit overeager with the draft.

[Keltest]

Thats sort of a weird question from a physics/chemistry standpoint because if you compress fire into that small of an area, its probably going to be unable to sustain itself and go out entirely, or at least burn itself down low real quick. For the purposes of your fantasy question, the answer is basically going to boil down to "its magic, so it would work however you want it to in your magic system. There is no real life scenario to compare it to."

A combustion reaction needs heat/energy (which the reaction itself is providing at that point), Oxygen (in the ambient air) and some other fuel (ie wood) to go off. Thats why drafts make fires hotter, and is the basic premise of a blast furnace. More O2, more combustion, more heat. But in that small of an area, youre going to be limited in how much O2 you could take in at once, and obviously something needs to actually be burning; flame doesnt just exist independently. The way the question is set up, youve kind of already broken the physics and chemistry so far that there isnt really a correct answer besides the one you like the most.