Characteristics of methane-air turbulent partially premixed flames have been determined through flame imaging. flow velocity, and temperature. NCx/CO emission indices from these flamas were also measured. Varying amounts of fuel were added to a main premixed stream to control the overall stoichiometry. At equivalence ratios from 1.4 to 2.9, the turbulent partially premixed flames exhibit a double-flame structure with a premixed dame near the burner exit and a secondary diffusion flame at a downstream location. This. structure-persists even with the Name tip opening as the fuel is added coaxially to increase the overall equivalence ratio;. The premixed flame near the burner exit tends to keep the temperature at a high level in the region between the two Names. With the flame tip opening, the temperature in this region decreases. The above Name structure has an important effect on the pollutant emission characteristics from these flames. The NOx emission index (EINOx) continues to increase gradually for overall equivalence ratio starting from 1.5 up to 10. The CO emission index (EICO), on the other hand, remains nearly constant with respect to the variations in the equivalence ratio, and shows a substantial difference depending on the mixing characteristics of the fuel with the main premixed stream. (C) 2000 by The Combustion Institute.