How to define a flame in numerical combustion?
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I am running an opposed jet case, where a stream of fresh reactants is opposed to a stream of burnt products. I am looking at the effects of stratification on the flammability limits of methane.
In some cases, in the reaction zone, the heat release is about 10^3-10^4 lower than compared to my reference case, which is far from the lean or rich flammability limits. Since I am sitting on or close to those limits, it is important for me to define one (or multiple) parameter for which I can say that the fuel is indeed burning.
Here is my reasoning right now, but it might be incomplete or even erroneous. To check if the fuel is indeed burning, I have been looking at the distribution of key radicals. If the mass fraction of say H2, does not have peak in the reaction zone and only diffuses from one stream to another, then I can definitely say there is no flame. But a contrario, if there is a peak, can I definitely say there is a flame? And how big does this peak needs to be compared to its corresponding value in the reactant and products stream? (I am guessing at least one full order of magnitude).
If there is a standard definition of a flame in numerical combustion, please share it, preferably with an attached reference
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In some cases, in the reaction zone, the heat release is about 10^3-10^4 lower than compared to my reference case, which is far from the lean or rich flammability limits. Since I am sitting on or close to those limits, it is important for me to define one (or multiple) parameter for which I can say that the fuel is indeed burning.
Here is my reasoning right now, but it might be incomplete or even erroneous. To check if the fuel is indeed burning, I have been looking at the distribution of key radicals. If the mass fraction of say H2, does not have peak in the reaction zone and only diffuses from one stream to another, then I can definitely say there is no flame. But a contrario, if there is a peak, can I definitely say there is a flame? And how big does this peak needs to be compared to its corresponding value in the reactant and products stream? (I am guessing at least one full order of magnitude).
If there is a standard definition of a flame in numerical combustion, please share it, preferably with an attached reference
IF YOU LIKE MY ANSWER
SO MAKE IT BRAINLIEST
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Is this a pure chemical kinetics simulation or a CFD study of opposed jets? What we in my organization usually do in the CFD simulation of furnaces is to use local CO concentrations as an indicator for the flame shape within the combustion chamber. A common threshold for methane-air combustion is 2000 ppm CO (dry). If the local value of CO is higher, we consider it to be within the flame, if it's below, we consider it to be outside of the flame. This is more of a rule-of-thumb, but it works reasonably well for us.
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