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Motivated by the question Titan vs Mars for colonization, I wonder what exactly happens if human exhalation products are released into Titanian atmosphere and, say, a spark igniter happens to be active in the vicinity.

Does it have to be raining methane in order for a combustion to take place? Or is the average ambient concentration of methane sufficient to this end? What temperatures would be reached by the reaction, i.e. could it actually be called a fire?

Also, how would this change if larger amounts of pure oxygen were involved?

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Wikipedia says of the composition of the lower atmosphere:

Because methane condenses out of Titan's atmosphere at high altitudes, its abundance increases as one descends below the tropopause at an altitude of 32 km, leveling off at a value of 4.9% [the rest is mostly nitrogen] between 8 km and the surface.

and in a separate article

The average surface temperature is about 98.29 K (−179 °C, or −290 °F).

so any combustion would need to cope with a lot of very cold nitrogen absorbing all the heat.

We can find some specifics: still trawling wikipedia we find this page which has a large table which gives the lower flammability limit of methane in air as 5%. Air is roughly 80:20 nitrogen:oxygen, so if we added 20% oxygen to some Titan atmosphere which originally had 5% methane in it, we would get (cold) air with 4% methane in it, which will not quite burn even at Earth temperatures. So releasing oxygen into Titan's atmosphere is unlikely to make a flammable mixture at local temperatures.

What might work is playing a jet of warm ( by local standards) oxygen onto a puddle of liquid methane, or a surface wet with liquid methane. That might push the methane concentration locally up past 5% and eventually reach a flammable mixture. It seems like methane on Titan (with some oxygen added to the air locally) would behave about like kerosene on Earth -- it won't really burn unless you do something to heat and/or vaporise it.

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