Turbulent CH_4/O_2/N_2 premixed flames opposing a jet of products of combustion in chemical equilibrium at 1800 K are studied experimentally by OH-PLIF. The focus is on characterizing conditions of departure from the flamelet regime in a broad range of turbulent Reynolds numbers from 200 to 700 and turbulent Karlovitz numbers from 1 to 400. Seemingly paradoxical observations include local extinction at Karlovitz numbers of order unity. These findings can be rationalized in terms of the effects of strain, heat losses, and the composition of the hot combustion product stream, all of which are present in practical systems. The extended Borghi diagram for turbulent premixed combustion is an idealization that does not account for these effects. The present combustion system allows for their systematic examination.
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