PPS : Very sorry to write again, but yes, I have looked very closely and you are right it is not conformal on some nodes.

However, why would that cause the quenching in the vertical region up the nozzle ?

I would imagine that it creates some kind of discontinuity between the two non conformal meshes but here it simply does not burn vertically... Would you be able to tell me more about this ? Finally, this non-conformity is caused, I think, by the fact that I meshed without refinements on ICEM and then I refined via "refinement boxes" directly on Fluent because ICEM was not very practical for refinements...

How could I have done this better ? The refinement part I mean ? Are there other software that would have worked better to refine or is there a better way to refine an already existing mesh in Fluent with the certainty that it will remain conformal ?