limiting oxygen concentration - one way direction?
limiting oxygen concentration - one way direction?
(OP)
Hi,
the concept of LOC does it relate to adiabatic flame temperature?
LOC is the point in ppO2 where the gas mixture does not combust when you try to ignite it. Combustion defined as: no flames, no explosion. Slow (flame-less) oxidation is possible though below LOC.
When I have a combustible gas mixture with a vol% O2 slight above the LOC (say O2 = 12% where the LOC = 10%). When this mixture is ignited will the flames stop when the oxygen vol% has depleted to 10%? Or does the flame continue until all oxygen is depleted?
I would guess it continues because that would explain why for instance in a methane fed gas burner, the max adiabatic flame temperature is reached at stoichiometric air supply. So, apparently all methane is combusted in a burners despite the O2 falling below the LOC of methane (which is temperature dependent ofcourse) during burning.
In other words: Is the concept of LOC one-way directed?
thanks if you can shine some light here
Kappie
the concept of LOC does it relate to adiabatic flame temperature?
LOC is the point in ppO2 where the gas mixture does not combust when you try to ignite it. Combustion defined as: no flames, no explosion. Slow (flame-less) oxidation is possible though below LOC.
When I have a combustible gas mixture with a vol% O2 slight above the LOC (say O2 = 12% where the LOC = 10%). When this mixture is ignited will the flames stop when the oxygen vol% has depleted to 10%? Or does the flame continue until all oxygen is depleted?
I would guess it continues because that would explain why for instance in a methane fed gas burner, the max adiabatic flame temperature is reached at stoichiometric air supply. So, apparently all methane is combusted in a burners despite the O2 falling below the LOC of methane (which is temperature dependent ofcourse) during burning.
In other words: Is the concept of LOC one-way directed?
thanks if you can shine some light here
Kappie





RE: limiting oxygen concentration - one way direction?
I usually see the discussion centered around the fuel concentrations in air instead of the oxygen combustion limit. For example, methane LEL (lower explosive limit) is 5% in air. The methane UEL is 15% in air. Since air is nominally 20% oxygen, I would expect the actual ratio for the onset of combustion is for methane to be between 1/4 and 3/4 of the oxygen percent. That means that in your 10% oxygen scenario, methane would be flammable between 2.5% and 7.5%.
David
RE: limiting oxygen concentration - one way direction?
It is interesting that you mention the LEL and UEL here because they relate to flammability range when added with air.
the LOC ( http://e
is the concentration of O2 where, no matter what amount of fuel present, no combustion will take place
kappie
RE: limiting oxygen concentration - one way direction?
Very interesting question. I don't know, but now that you have asked, I wish I did know. I knew a guy many years ago that may know. Laurence Britton. He knows a lot about fire, static ignition, dust exlosions and such. He's got a book and several articles on it too. Google him. He'd help you out if you needed to know. It may cost you though. He's a Consultant now.
Good luck,
Latexman
RE: limiting oxygen concentration - one way direction?
The are several process where his happens. Below the stoichiometric ratio you get the desired product and at the ratio you get a bang. Anything way above this ratio you get soot.
Here is a plethora of information on gas + air from GEX-CON AS.
http://www.gexcon.com/handbook/GEXHBchap1.htm
RE: limiting oxygen concentration - one way direction?
Good luck,
Latexman
RE: limiting oxygen concentration - one way direction?
RE: limiting oxygen concentration - one way direction?
I have checked sciencedirect, and the encyclopedia but could not find it that specific. But after reading the final reply it becomes clearer. So in a batch process the flame will stop after falling below below, but in a stocho fed continuously fed and intimiately fed gas burner it does not (Because on average the O2 concentration is probably > LOC). Thanks alot
kappie