RogueRose
International Hazard
Posts: 1594
Registered: 16-6-2014
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Combustion of wicked fuels & burning fuel soaked solids
I have been trying to figure out exactly how some things burn and what prevents some flammable things to not burn while an open flame is touching or
very close.
As an example, using a piece of wick of cloth sticking out of a fuel like an oil or fat. We all know the cloth wicks the oil and it burns at the end
or the entire wick extending out of the fuel will catch fire.
My main question is why does the wick not burn at a speed anywhere near what it would without the fuel. Does the flame evaporate the fuel (possibly
cooling the wick??) which catches fire encasing the wick (but is the flame actually touching the wick)?
Another example is soaking a large pile of cloth/rags/cardboard (the fabrics would be tightly layered - no wrinkling/gaps - and the cardboard stacked
flat in layers) in something like lamp oil or maybe even kerosene/diesel. The entire stack is soaked through. Lighting the stack will most likely
result in any exposed surface eventually catching fire.
Is it possible to increase the rate of burn of either the soaked pile or the wick extending from fuel?
By substantially increasing air flow to the burning stack I would assume that it would burn better by removing any ash from the surface but are there
any other advantages or disadvantages to doing this?
To burn the soaked pile, is there benefit to heating the entire pile prior to ignition?
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Detonationology
Hazard to Others
Posts: 362
Registered: 5-5-2015
Location: Deep South
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Mood: Electrophillic
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In a candle, the wick is not consumed by the flame; only the wax. The wick is able to absorb the fuel and disperse it into fine vapor particles where
it can be make better contact with atmospheric oxygen. If you introduce energy to the fuel (without oxidation), you are adding activation energy to
the reaction. wax itself isn't considered volatile at normal temperatures; but if you heated the wax above its smoke point, the vapors given off
would certainly be much more dispersed and flammable. You have probably seen a clip of a candle re-igniting by simply blowing the flame out and
applying a flame to the smoke produced.
“There are no differences but differences of degree between different degrees of difference and no difference.” ― William James
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Sulaiman
International Hazard
Posts: 3698
Registered: 8-2-2015
Location: 3rd rock from the sun
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understanding a candle flame is fantastic; lots of chemistry and physics, really worth the effort.
(e.g. oxidizing and reducing areas of flame, flame colour ...)
for a burning wax candle the heat of the flame not only vaporizes the fuel, it decomposes the wick, especially as the wax level decreases.
even when the wick is completely carbonised it still works,
it only has to 'wick' the molten wax into the heat to be vaporized,
some oil lamp wicks are made of fiberglass for example.
EDIT: to adjust flame size adjust the rate of wax melting, 'wicking' and vaporization.
e.g. a thicker wick (or a few small ones) will give a larger flame.
loads of candle-making websites.
[Edited on 8-1-2016 by Sulaiman]
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