The Effects of Strong-Weak Swirling Interaction on Emissions In a Multi- Nozzle Model Combustor

A linearly three-nozzle rectangular model combustor is designed in this study to investigate the effects of strong-weak swirling interaction on emissions. The swirl number of the nozzles on both sides is 0.72 and that of the middle nozzle are 0.72 and 1.02 respectively. High-frequency particle imaging velocimetry (HPIV) and RANS numerical calculation methods are applied to study the influence of swirling interaction on the flow field and emission characteristics. During reacting experiments and simulations, the fuel flow rate remains unchanged and the equivalence ratio varies from 0.53 to 0.83 by increasing the air flow rate. Experimental and calculation results show that with the swirl number of center swirler increasing from 0.72 to 1.02, the "strong-weak" swirling interaction between center and side swirlers strengthens the turbulence intensity of the swirling shear layers, which can effectively improve mixing between the fresh premixed gas and the burned high-temperature gas to promote combustion characteristics. CO emissions are reduced from 20 to 40 ppm in the equal-strength swirling interaction to below 4 ppm in the "strong-weak" swirling interaction. NOx emissions remain basically unchanged. The "strong-weak" swirling interaction also raises the vorticity of the main recirculation zone, this strengthens the entrainment of high-temperature burned gas into the recirculation zone to stabilize flame combustion and widen the operating conditions which make the extinction equivalence ratio change from 0.59 to 0.53. In this paper, the equal-strength swirling interaction is transformed into a "strong-weak" swirling interaction through increasing the swirling number of center nozzle, which reaches the goal of extending the blowout equivalence ratio and reducing pollutant emissions to achieve stable, high-efficiency, low-emission combustion.