According to the smoldering Wikipedia article, flaming combustion occurs in the gaseous phase. I know butane undergoes flaming combustion in a Bunsen burner because it's a gas, but how can wood undergo flaming combustion at all instead of just smouldering? What gas is there to react with oxygen in the flames? Does it smoulder to create carbon monoxide then the carbon monoxide undergoes flaming combustion? Can charcoal also undergo flaming combustion? I've never seen a piece of charcoal without wood inside it undergo flaming combustion, only smoldering.

Also, when oil undergoes flaming combustion, is it its vapour that reacts with oxygen to produce a flame?

  • $\begingroup$ I can't remember my exact state of mind at the time of asking the question which I probably wouldn't be able to determine precisely anyway because the brain does everything as a complicated system of discretion. It's okay but it seems a bit silly this question. I'm kind of like "Of course, it's flaming combustion that can only occur in the gas phase." I once learned in scouts that combustion only occurs in the gas phase. Maybe I hadn't quite figured out the answer. It seems so obvious to me now. Flames must be a combustion occuring in the gas phase. I think I once though it was the blackbody. $\endgroup$
    – Timothy
    Aug 26, 2021 at 2:01
  • $\begingroup$ radiation of the air but now think it's actual the photons released in the chemical reaction and the actual amount of blackbody radiation in the visible light would be very tiny especially for something extremely transparent like air. Combustion can occur with oxygen reacting with a solid but that's smouldering, not flaming combustion. $\endgroup$
    – Timothy
    Aug 26, 2021 at 2:04

1 Answer 1


Combustion is a gaseous phase phenomenon. Oil and gasoline have a high enough vapor pressure at ambient temperatures to produce a gaseous phase of fuel above the liquid. In contrast, hold a lighter up to a piece of wood and try to get it to light. It won't—at least not for quite some time. This is because solid fuels must first undergo endothermic pyrolysis before real combustion can occur. This produces a slew of products which are what truly undergo combustion when solids are burned. Because combustion is exothermic, once a high enough temperature is reached the solid will autopyrolyze, making combustion a self-sustaining reaction.

  • 3
    $\begingroup$ This is also why a candle uses a wick - candle wax under normal conditions won't sustain a flame. $\endgroup$
    – MSalters
    Oct 5, 2016 at 11:25
  • $\begingroup$ I read that charcoal is nearly pure carbon. Is wood a sponge like structure that's only a few atoms thick? If not, how can it possibly undergo incomplete flaming combustion to become charcoal instead instead of just forming a passivating charcoal layer which blocks further endothermic pyrolysis? $\endgroup$
    – Timothy
    Nov 2, 2016 at 1:53
  • $\begingroup$ Is there also a nonporous solid that can undergo flaming combustion for the following reason? Oxygen directly attacks the surface to create an intermadiate product releasing heat in the process and then the intermediate product slowly reacts with oxygen to produce the final product releasing even more heat and it's because the reaction to form the final product isn't very fast that the reaction is preceived as flaming combustion instead of smouldering. Can carbon undergo flaming combustion in that way with carbon monoxide being the intermediate produce if it's hot enough? $\endgroup$
    – Timothy
    Dec 13, 2016 at 23:17
  • $\begingroup$ Except it's not. Titanium's ignition temperature is below its melting temperature. $\endgroup$
    – Joshua
    Dec 1, 2021 at 19:59

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