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

Abstract

Strong-weak swirling interaction has been proved to be effective on combustion instability suppression. A linearly three-nozzle rectangular model combustor is designed to investigate the effects of strong-weak swirling interaction on emissions. Swirl number of swirlers on both sides are 0.72 and that of the middle swirlers are 0.72 and 1.02, respectively. Fuel flow rate remains constant and the equivalence ratio varies from 0.53 to 0.83 by decreasing the air flow rate. High-speed particle imaging velocimetry (HPIV) and RANS methods are applied to study the flow characteristics to reveal the reasons for reduction of pollutants. Results indicate that the "strong-weak" swirling interaction between central and outer swirlers strengthens the turbulence intensity of the swirling flow shear layers, which effectively improve mixing process between fresh premixed gas and burned high-temperature gas to promote combustion characteristics. CO emission varies from 20 to 40 ppm under different equivalence ratios in equal-strength swirl combustor. However, CO emission reduces to below 4 ppm with "strong-weak" swirling interaction. With the increase of swirl number of central swirler, NOx emission remains basically unchanged under the same equivalence ratio. The "strong-weak" swirling interaction also raises the vorticity of main recirculation zone, which strengthens the roll of high-temperature burned gas into the recirculation zone to stabilize flame combustion and widen the operating conditions. In this paper, the equal-strength swirling interaction is converted into a "strong-weak" swirling interaction by increasing the swirling number of central swirler, which helps achieve stable, high-efficiency, low-emission combustion.