Will it burn?

[Sorabh]

Hello, 

I was playing with Gameslinx's planet mod. In that planet pack, there's a planet called Niebos. It has Kerbin like atmospheric pressure. However, the composition is 55% Nitrogen, 22% oxygen and 22% carbondioxide.

My question is: Will combustion take place in an atmosphere with 22% carbon dioxide? If yes, what's the minimum percentage of oxygen required?

I know the answer lies somewhere in Stochiometry, but I am not very sure about it..

[StrandedonEarth]

Carbon dioxide is heavier and will sink to the ground, smothering any ground fires. If you can get the fuel above that layer, I don’t see why it wouldn’t burn

[sevenperforce]

58 minutes ago, StrandedonEarth said:

Carbon dioxide is heavier and will sink to the ground, smothering any ground fires. If you can get the fuel above that layer, I don’t see why it wouldn’t burn

Not my area of expertise, but the level of differentiation in a gas is a function of the turbidity of the ground layer. If there is enough weather kicking the air around, the gases will stay mixed.

In a homogenous mixture of nitrogen, oxygen, and carbon dioxide, the only thing you need is a sufficient partial pressure of oxygen. Carbon dioxide only inhibits combustion by physically excluding oxygen; its presence does not retard or interfere with the reaction. 

[StrandedonEarth]

2 minutes ago, sevenperforce said:

Not my area of expertise, but the level of differentiation in a gas is a function of the turbidity of the ground layer. If there is enough weather kicking the air around, the gases will stay mixed.

In a homogenous mixture of nitrogen, oxygen, and carbon dioxide, the only thing you need is a sufficient partial pressure of oxygen. Carbon dioxide only inhibits combustion by physically excluding oxygen; its presence does not retard or interfere with the reaction. 

Yeah, I was on mobile earlier so I was being brief. Thanks for filling in the details

[Starman4308]

The CO2 might cause a little bit of slowdown thanks to Le Chatelier's principle, but combustion is such a favorable process that it'll happen anyways if the gases are well mixed.

[DerekL1963]

1 hour ago, Sorabh said:

My question is: Will combustion take place in an atmosphere with 22% carbon dioxide? If yes, what's the minimum percentage of oxygen required?

It's not the percentage that matters, it's the partial pressure.  The presence (or absence) of any other gas is irrelevant.

At Terrestrial sea level pressure, such a mixture is slightly oxygen rich compared to ours - and would support combustion.   Somebody with better math and chemistry would have to figure out at Kerbin pressure.

[Green Baron]

3 hours ago, Sorabh said:

My question is: Will combustion take place in an atmosphere with 22% carbon dioxide? If yes, what's the minimum percentage of oxygen required?

The availability of free oxygen has been pointed out. Besides that, you'll need of course fuel for combustion.

Your second question is actually very complicated to answer because it depends on the whole biosphere of the respective planet. I only have earth as an example: earth's atmosphere has an oxygen window that varied between very roughly 15 and 30% in the past billion years. In the carboniferous, when oxygen levels were much higher, a single lightning could trigger fires that burnt until fuel was depleted (carboniferous coal !). In earths biosphere you'll need something around 5% of open air oxygen partial pressure for combustion to take place. If it is enough for a bbq, idk ... ;-)

Edited January 6, 2018 by Green Baron

[Sorabh]

Oh, that's a lot of responses, thank you!.

If combustion is possible in such an atmosphere, then internal combustion engines would also work. won't they?

[Green Baron]

In earth's atmosphere normal suction engines top out at around 4000m, charged ones maybe 8000, turbines 12-15000m. Very roughly ~+- window cross :-)

Your atmosphere has a similar pressure but slightly more O(omph) ...

Edited January 6, 2018 by Green Baron

[Zeiss Ikon]

Yep.  As @Green Baron noted, as long as you have enough pressure in the combustion chambers, if fuel will burn at zero velocity and at ambient pressure, it'll burn in an engine.

[kerbiloid]

According to this, a candle fire goes out at 10% of CO₂.
(We can presume that pressure, etc are the same like on Kerbin/Earth)

But don't despair. If light a magnesium band, it can burn even in pure CO₂.
2 Mg + CO2 → 2 MgO + C

Edited January 6, 2018 by kerbiloid

[Sorabh]

Sodium, Magnesium, they burn with anything

 

[Zeiss Ikon]

9 hours ago, kerbiloid said:

According to this, a candle fire goes out at 10% of CO₂.
(We can presume that pressure, etc are the same like on Kerbin/Earth)

Assuming that's not just wonky translation from Russian, my presumption would be that they're still talking about still air in a basement, in which the CO₂ can settle out.  Then the candle starts a convection loop that draws the concentrated CO₂ from near the floor, and snuffs itself out.  If the CO₂ is uniformly mixed with air, it won't put out  a candle at 10% concentration; in fact, it has to be close to 50% to reduce the ppO₂ enough for the candle to suffocate.

This same convection loop effect can lead to a flash fire from heavier than air combustible vapors -- acetone vapor is known to do this, as is butane.  The vapor settles to the floor and spreads, then convection from a flame (candle, furnace or water heater pilot light, etc.) draws it to an ignition source, whereupon it flashes back along the vapor/air interface, causing rapid convection mixing and a near-explosive buildup of combustion.

[kerbiloid]

5 hours ago, Zeiss Ikon said:

Assuming that's not just wonky translation from Russian, my presumption would be that they're still talking about still air in a basement, in which the CO₂ can settle out.  Then the candle starts a convection loop that draws the concentrated CO₂ from near the floor, and snuffs itself out.  If the CO₂ is uniformly mixed with air, it won't put out  a candle at 10% concentration; in fact, it has to be close to 50% to reduce the ppO₂ enough for the candle to suffocate.

It's hard for me to estimate quality of this arcticle transgoogling, but it looks enough accurate for me.

According to this article CO₂ concentration:

• 300-400 ppm Atmospheric air. Ideal for human health
• 400-600 ppm Normal air quality.
• 600-800 ppm There are individual complaints about air quality
• 800-1000 ppm More frequent complaints about air quality.
• Above 1000 ppm General discomfort, weakness, headache, trouble concentrating. The number of errors in work is increasing. Negative changes in DNA begin.
• Above 2000 ppm May cause serious damage to human health. The number of errors in the work greatly increases. 70% of employees can not concentrate on work.

 

• 10% Candle fire goes out
• 30% Human dies in 1..2 hours
• 40..50% Human rapidly suffocates, falls and dies

I have googled the original source of this article:
(sorry, in Russian https://books.google.ru/books?id=X4n_AgAAQBAJ&pg=PT92&lpg=PT92&dq=концентрация+углекислого+свеча+гаснет&source=bl&ots=vbmtASqZ4J&sig=JUgWNCD2YpJELeD-T2N3QDI5RUE&hl=ru&sa=X&ved=0ahUKEwjskYzNlcXYAhWCGCwKHXkCCWEQ6AEILTAB#v=onepage&q=концентрация углекислого свеча гаснет&f=false)

This is from "Medical jurisprudence" by Alisiyevich V.I., 1968.

So, unless I get some alternative source, I would believe this.

 

5 hours ago, Zeiss Ikon said:

Then the candle starts a convection loop that draws the concentrated CO₂ from near the floor, and snuffs itself out. 

I'm not sure if this is right.
A fire draws the cold and relatively low-CO2/CO air from beneath, makes it hot and high-CO2/CO and throws it up (because it's much hotter, though CO2 is 1.5 times heavier than air).

If the furnace/oven is equipped with a smoke pipe, the high-COx hot air runs into the smoke pipe out of the room.

Spoiler

If there is no smoke pipe, the high-COx hot air rises up to the ceiling, cools and goes down along the walls, reaching the air beneath the fire and enriching it with COx, but at this time the hot air above the fire gets even more high-COx.

Partially the hot high-COx air from below the ceiling gets lost
through a hole in the roof (like in yurta)

Spoiler

or through the door or small windows below the ceiling (like in kurnaya izba)

Spoiler

(The pipeless schemes are of course a good way to die much more dangerous and are only for a true downshifter's way, don't do this at home).

Upd.
All known to me fire safety instructions recommend to get down and crawl to the exit, exactly because high-COx hot air collects in the room from ceiling to floor.

Edited January 7, 2018 by kerbiloid

[Green Baron]

This is probably a misunderstanding: yes, one shall crawl from a fire because in the open the fresh air is drawn from below, heated, and CO/CO2 rich air leaves the fire in a heated plume above. Which can cause firestorms in extreme cases. But ducking down in a ditch can save your life in such a case. It did safe the life of my neighbour when he was caught in a forest fire once.

In a CO2-flooded room (*)(this might be the sealed engine room of a ship or a server room where CO2 can be used to extinguish) the gas will collect near the floor. Crawling on the floor will kill you after a few breaths and i think that is written in the safety instructions of a CO2 extinguisher. The use of CO2 in the open will have little effect anyway as it does not cool the burning material and the gas is blown away quickly, despite the colourful images showing happy people spraying it at the flames ;-)

That CO2 is deadly to oxygen breathers (please check this, in medical journals or so) results from the fact than it is used by the body as a marker to breath more if it collects in the lung. Remember that we exhale CO2 (3% of the exhaled air if i am not mistaken), if we can't get rid of it the nervous system signals: "breathe more !". This can cause hyperventilation, etc. and, if the level of CO2 rises too high in the lungs (a few percent are enough) it will have severe effects. I do not know the details, i must admit.

Also, we as oxygen breathers need a minimum concentration of O in order for the lungs to work. Lungs are quite effective in comparison to the poor insect's tracheas, but nevertheless, less than 17% oxygen will make you gasp(**), less than 15% and it starts to get dangerous, which adds to the bad effects on health, because CO2 displaces the O in the breathable air. Clear, N is just for the pressure, apart from that its useless ... :-). So 4% CO2 would mean oxygen levels are too low for the body for an effective oxygen supply. But again, check this if you find the time.

 

(*) i mean flooded from a CO2 extinguisher, not from the fire itself. In a normal house fire you are of course right with staying low !

(**) funnily the lower frame of oxygen in earth's atmosphere lies near that value, probably besides other effects because oxygen-users fade away and wait for better times ... :-) But that is only a thought.

 

Have a nice day and stay away from a lack of oxygen :-)

Edited January 7, 2018 by Green Baron

[kerbiloid]

That's true, also we should mention limnic eruptions as a sample of the cold CO2-rich air poisoning.

To say the truth, I don't see a reason why the convection should be used here, as we are talking about a whole planet atmosphere and a tiny fire.
We could presume that the CO2 concentration is constant.

Edited January 7, 2018 by kerbiloid

[tomf]

I think there are two linked variables in play here, the partial pressure of oxygen and the partial pressure of carbon dioxide. For a candle or human metabolism roughly 2 carbon dioxide is produced for every O₂ used.

For a candle the carbon dioxide itself wont have any effect on the rate of combustion. However in a sealed chamber, or with insufficient air movement and mixing increasing CO₂ is going to correspond to decreasing O₂ so the candle will go out when there is 0.1 bar CO₂ because at that piont there is only .11 bar O₂ left.

For a human or other animal CO₂ is deadly in itself and in a sealed room will kill you long before the lack of Oxygen will. My brief googling suggests that the primary mechanism is by lowering the pH of your blood, at around 0.03 bar. That will occur long before O₂ drops below the .16 bar level considered safe (in scuba diving at least)