It was shown in a theoretical study that a unique relation exists between the emission intensity ratio ofthe C2 Swan Bands (515, 470nm bands) and the flame temperature in hydrocarbonlair premixed fiames. It implies that the flame temperature of hydrocarbonfair premixed flames can be estimated by measuring emissions of the C2 Swan Bands.However, emissions ofthe C2 Swan Bands are feeble especially in lean hydrocarbonlair fiames. In order to detect feeble emissions of the C2 Swan Bands in lean hydrocarbonfair flames, a spectrometer, composed of dichroic mirrors, band pass filters, photo-multiplier tubes and an IfV amplifier has been newly developed in our laboratory. Use ofthe newly developed spectrometer together with Cassegrain optics enables to detect feeble emissions of the C2 Swan Bands with high spatial resolution on the order of O.lmm. In order to explore the behavior of the near extinction flamelet in turbulent premixed flames, the relation between the emission intensity ratio of 515f470nm band of C2 (C2'(O,O)fC2"(1,O)) and the flame temperature for various strain rates has been sought in beth unstrained and strained flames by using a rectangular nozzle bumer and a counter-flow burner, respectively. The relation between C2'(O,O)fC2*(1,O) and the flame temperature obtained from both unstrained and strained propanefair premixed flames. For unstrained fiames, as the equivalence ratio of the mixture decreases in the lean side, C2'(O,O)/C2*(1,O) and the flame temperature decrease. A unique relation is experimentally found to exist between C2*(O,O)fC2'(l,O) and the flame temperature, For strained flames, as the strain rate increases with the equivalence ratio of the mixture is constant, the flame temperature decreases, and C2*(O.O)fC2*(1,O) decreases slightly. It can be concluded that ifthe equivalence ratio of the mixture is known, the flarne temperature of strained fiames can be estimated.
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