Axial Swirler Design Influences on NOx Emissions for Premixed Combustion in Gas Turbine Combustors With all the Combustor Air Flow Passing Through the Swirler

Abstract

This work investigates a single axial swirler combustor using flat bladed axial swirlers at atmospheric pressure, 600K preheat, with premixed propane and air. The aim was to investigate the axial swirler design influences on flame stability and NOx emissions, for fully premixed combustion in a single swirler cylindrical combustor configuration. A reference Mach number of 0.05 at 600K was used, which represents all the combustion air passing through the swirler. This maximum swirler airflow is required for the highest turbine entry temperatures with low NOx emissions. The axial swirler design had only a small influence on the weak extinction, but it had a greater influence on NOx. The swirlers with a large central hub had greater NOx emissions, as this created a larger central recirculation zone and greater residence time of the hottest part of the flame. It was preferable to stabilise the flame with an outer expansion shear layer as this minimised the size of the inner recirculation zone and this minimised the NOx. The influence of the swirl angle, 30, 45 or 60° for the same flow capacity was that the swirler had to be a larger diameter as the vane angle was increased, to keep the blockage and pressure loss the same. This removed the possibility of having either an inner or outer flow expansion for the 60° swirler, but the flow expansions were maximised for the 30° swirler. The effect of the swirl vane angle on NOx was mainly due to the associated changes in the flow expansion. 45° swirlers with no central hub and a large outer expansion were the best design for the lowest NOx emissions and could achieve 15ppm NOx at 15% oxygen at 2000K.