I am running a CFD simulation (computational fluid dynamics) 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 (different equivalent ratio on each jet) on the flammability limits of methane. 

In some cases, in the reaction zone, the heat release is about $10^3$ to $10^4$ 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 $\ce{H2}$, 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?

If there are some key parameters I can look at, please share. Note that since this is a numerical simulation, I virtually have access to all of the thermodynamic or chemical properties (chemical composition, reaction rates of each reaction etc...) at every point of the flow.


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