Abstract
It was shown in a theoretical study that a unique relation exists between the emission intensity ratio of the C_2 Swan Bands (515, 470nm bands) and the flame temperature in hydrocarbon/air premixed flames. It implies that the flame temperature of hydrocarbon/air premixed flames can be estimated by measuring emissions of the C_2 Swan Bands. However, emissions of the C_2 Swan Bands are feeble especially in lean hydrocarbon/air flames. In order to detect feeble emissions of the C_2 Swan Bands in lean hydrocarbon/air flames, a spectrometer, composed of dichroic mirrors, band pass filters, photo-multiplier tubes and an I/V amplifier has been newly developed in our laboratory. Use of the newly developed spectrometer together with Cassegrain optics enables to detect feeble emissions of the C_2 Swan Bands with high spatial resolution on the order of 0.1mm. In order to explore the behavior of the near extinction flamelet in turbulent premixed flames, the relation between the emission intensity ratio of 515/470nm band of C_2 (C_2*(0,0)/C_2*(1,0)) and the flame temperature for various strain rates has been sought in both unstrained and strained flames by using a rectangular nozzle burner and a counter-flow burner, respectively. The relation between C_2*(0,0)/C_2*(1,0) and the flame temperature obtained from both unstrained and strained propane/air premixed flames. For unstrained flames, as the equivalence ratio of the mixture decreases in the lean side, C_2*(0,0)/C_2*(1,0) and the flame temperature decrease. A unique relation is experimentally found to exist between C_2*(0,0)/C_2*(1,0) 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 C_2*(0,0)/C_2*(1,0) decreases slightly. It can be concluded that if the equivalence ratio of the mixture is known, the flame temperature of strained flames can be estimated.
