An experimental study on the effect of a turbulence generating plate in low swirl combustor

Abstract

Turbulence generator (Called turbulence generating plate or perforated plate) of a swirler in low-swirl combustion plays an important role in generating a stable lifted flame with an isotropic turbulence intensity and forming a uniform flow field. According to the previous experimental studies, the typical porosities of the generator in a low-swirl combustor have been reported between 25 % and 40 %. This study focused to confirm these results in terms of various porosities and hole patterns of a turbulence generator in a lab-scale based low swirl combustor. The pressure drop, the flame shapes, the velocity profiles and the emission performances were experimentally investigated to confirm the flame characteristics of low swirl combustion. The outer diameter(2R c) of the turbulence generator was taken to 2R c = 20 mm, and the porosity and the diameter of the circular hole pattern were varied in ranges of 15 - 35 % and 1.5 - 4.5 mm, respectively. The results show that as the porosity decreases, the occurrence of attached flame is encouraged, the lean flammable limit is extended, the flow rate through the turbulence generator decreases, the swirl intensity increases. The central velocity increases, so that the V-shaped flame changes into a flat flame. Also, the minimum velocity in the central low velocity zone increases and the flame liftoff height increases. As the axial velocity increases and the swirl intensity decreases, the effect of outer recirculation decreases, thereby, the temperature of the outer recirculation zone decreases and the exhaust gas temperature increases. Therefore, the NOx emission slightly increases because the flame temperature is increased due to the reduction of outer recirculation influence. As the hole pattern of the turbulence generator becomes a configuration with having more holes for the same porosity, the stable flame region is widened. Also, the velocity uniformity of the central low velocity zone is improved and the turbulence intensity is decreased. These results confirm that the factors of flame stabilization of low swirl combustor are velocity uniformity and turbulence intensity of the turbulence generator.