The effect of radial distribution of swirl has been examined on the thermal behavior of two different premixed flames using a double concentric premixed swirl burner. The double concentric swirl burner allowed systematic variation in the radial distribution of swirl (both co- and counter-) between the inner and outer annulus of the burner. The burner had two annular jets and a central nozzle. Information on the thermal field in two flames formed by co- or counter-swirl in the outer annulus and co-swirl in the inner annulus has been examined. Specifically mean and fluctuating temperatures, integral and micro thermal time scales, and probability density distribution of temperatures have been determined at various spatial positions in the flames. The micro-thermocouple output was compensated to provide high-frequency (about 1 kHz) response of the thermocouple. Direct flame photographs were taken to provide information about the global features of flames and flame stability. The global and thermal characteristic data presented here provided a complete insight on the thermal behavior of co- and counter-swirl flames. The results show that the direction of swirl (co- or counter-) used to stabilize a flame from annular jets provides a great influence on flame symmetry. The simultaneous combination of co- and counter-swirl in the burner showed a very nonsymmetrical behavior of the flame. The global and thermal data presented here confirmed these findings. The results suggest significant effect of co- and counter-swirl distribution in flames on the NOx emission levels.
Self-excited noise generation from laminar methane/air premixed flames in thin annular jets
