An experiment in a turbulent non-premixed flat flame was carried out in order to investigate the effect of swirl intensity on the flow and combustion characteristics. First, stream lines and velocity distribution in the flow field were obtained using PIV (Particle Image Velocimetry) method in a model burner. In contrast with the axial flow without swirl, highly swirled air induced streamlines going along the burner tile, and its backward flow was generated by recirculation in the center zone of the flow field. In the combustion, the flame shape with swirled air also became flat and stable along the burner tile with increment of the swirl number. Flame structure was examined by measuring OH and CH radicals intensity and by calculating Damkohler number (Da) and turbulence Reynolds number (Re T ). It appeared that luminescence intensity decreased at higher swirl number due to the recirculated flue gas, and the flat flames were comprised in the wrinkled laminar-flame regime. Backward flow by recirculation of the flue gas widely contacted on the flame front, and decreased the flame temperature and emissions concentration as thermal NO. The homogeneous temperature field due to the widely flat flame was obtained, and the RMS in the high temperature region was rather lower at higher swirl number. Consequently, the stable flat flame with low NO concentration was achieved. Nomenclature AlphabeticsD = diameter of the burner throat R = radial distance R/D = non-dimensional radial distance X = axial distance X/D = non-dimensional axial distance S = swirl number S L = laminar flame speed Author for correspondence, E-mail: chjeon@pusan.ac.kr. 232 J.-H. KWARK ET AL. T = instant temperature of the flame T = average temperature of the flame T = fluctuating temperature of the flame U = radial velocity component of the flame V = axial velocity component of the flame U avg = air speed through the burner throat Da = Damkohler number Re T = turbulence Reynolds number v rms = turbulent intensity of the flow Greeks δ L = laminar flame thickness = slit angle of a swirler σ r = ratio of the inner and outer diameters of a swirler ν = dynamic viscocity

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