I am trying to simulate laminar premixed flame, according to previous suggestion found here I used coupled solver, poor initial mesh, firs cold simulation ( without problem, i set courant number = 100 and reached very low residual level ). When I turn on the reactions ( one single fuel-oxigen premixed reaction ) flame is not stable ( I set courant = 0.05 to at least have a beginning of convergence behaviour, but after 200 it flame spread across all field, and then divergengence occurs ). Since now I have not been able to simulate any FINITE RATE COMBUSTION flame. Any suggestion?

I don't think Fluent works for finite-rate combustion problems at all after lot of bad experience. Sometimes you may get lucky, but overall it is not worth the effort. Don't waste your time.