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That title is really long... but the essence of this question is basically asking whether a complete combustion flame would be more destructive(burn things faster? and spread faster?) than a incomplete combustion flame?

Say if a dragon, any dragon, doesn't matter in this case decided to wipe a village off the map with its Flame breath.

It can produce a complete combustion flame breath (Blue and is of a higher temperature usually) or a incomplete combustion flame breath (the usual red-orangey flame and is usually of a lower temperature than the complete one) assume it won't move its head around as well, it starts it flame breath on one point and ends it there.

Thus, which one would be able to burn and spread through a presumely nice flammable target(it can be a village or forest for all I care) better?

I'm assuming that the complete combustion flame breath would be like holding a Bunsen burner sideways. It would probably be like a really really big jet engine, so it would probably produce a very long swath of blackened ground. So I guess it spread would be quite bad?

This question was inspired when a fantasy book stated that a complete combustion fireball(thus it's a blue fireball) dwarfed the damage a normal fireball (orange,red and yellowy fireball) could do.

No, the fires are not liquid based. Assume the dragon makes some flammable gas, nevermind, I have no idea how it would work anyway.

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The difference between what you're calling complete and incomplete combustion flames is the amount of oxygen that has reacted. With gaseous fuels containing carbon, if there hasn't been enough oxygen to burn all the fuel, then you get those red-orange flames of hot carbon that hasn't actually burned. If you have enough oxygen for what's called "stoichiometric" combustion, where all the fuel burns, then the result of combustion is usually only hot gas, which is what you see as a blue flame with a correctly adjusted Bunsen burner.

The counter-intuitive result of all this is that adding more fuel to a gas flame can make it cooler, rather than hotter.

The hotter flame will usually heat up things it hits more, doing more damage to them and making them more likely to catch fire. If a dragon is skilled in setting fire to things, he may well use a very lean fuel:air mixture, so that there is still oxygen in the flame and targets catch fire immediately, rather than only when the flame moves away from them.

Edit: the choice of lean or stoichiometric mixture depends on what you're trying to set fire to. For stuff that burns very easily, use a lean mixture and save fuel. For things like wet wood, or people, which you need to dry out, use stoichiometric mixture, to put as much heat as possible in, and drive off as much water as possible.

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  • $\begingroup$ So this means it's better to have that that lean fuel air mixture compared to using up all the oxygen? $\endgroup$
    – Skye
    Commented Sep 27, 2016 at 11:38
  • $\begingroup$ See revision to answer. $\endgroup$ Commented Sep 27, 2016 at 18:08
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I suggest looking up on this wiki site on combustion.

Generally, people use complete combustion flames due to efficiency over incomplete combustion flames. A complete combustion flame would completely combust the fuel and tend to be of a higher temperature than incomplete combustion flames as such.

If we take a look at space shuttle launches, enter image description here As you can see from that massive fireball, it would definitely scorch the surroundings black. However, (I can kinda understand that you seem to be talking about those stable flames compared to those flickering ones) while your dragon would definitely scorch a massive area black, the fires that would spread would be those incomplete combustion ones.

In essence, your dragon would be a giant blowtorch.

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