Fine Flame Structure and Combustion Mechanism of Lean Turbulent Premixed Flames.

We observed the interaction between turbulence and combustion near the lean flammability limit of a premixed flame supported by a hot burnt-gas jet, and elucidated the detailed structure of flames varying with the Damkohler number. A typical wrinkled laminar flame appeared when the equivalence fuel-to-air ratio of the mixture was 0.6, whereas, for an equivalence ratio below the lean flammability limit (e.g., Φm=0.4), a structure which resembled a distributed reaction zone was observed. The latter showed features similar to those of the ordinary distributed reaction zone flame, which was observed in a strongly turbulent shear layer, in many aspects of the observed statistics of fluctuating properties, such as temperature, ion current, and radical chemiluminescence.