Flame Structure and Combustion Capability of Non Premixed Rifled Nozzles

Abstract

The target of this study is to promote combustion capability using a novel rifled nozzle which was set at the outlet of a conventional (unrifled) combustor. The rifled nozzle was utilized to adjust the flow swirling intensity behind the traditional combustor by changing the number of rifles. The rifle mechanism enhances the turbulence intensity and increases the mixing efficiency between the centralfuel jet and the annular swirled airjet by modifying the momentum transmission. Specifically, direct photography, Schlieren photography, thermocouples, and a gas analyzer were utilized to document the flame behavior, peak temperature, temperature distribution, combustion capability, and gasconcentration distribution. The experimental results confirm that increasing the number of rifles and the annular swirling airjet velocity (ua) improves the combustion capability. Five characteristic flame modes—jetflame, flickeringflame, recirculatedflame, ringflame and liftedflame—were obtained using various annular airjet and central fueljet velocities. The total combustion capability (Qtot) increases with the number of rifles and with increasing ua. The Qtot of a 12rifled nozzle (swirling number (S) = 0.5119) is about 33% higher than that of an unrifled nozzle. In addition, the high swirling intensity induces the low nitric oxide (NO) concentration, and the maximum concentration of NO behind the 12rifled nozzle (S = 0.5119) is 49% lower than that behind the unrifled nozzle.