MIXING IN THE DOME REGION OF A STAGED GAS-TURBINE COMBUSTOR

Many modifications to the combustion process are being proposed and evaluated to lower NO(x) emissions from gas turbine engines in both stationary and propulsion applications. A promising technique is staged combustion, wherein the fuel is mixed into a fuel-rich region and the final air is injected downstream to an overall lean mixture. This article examines the effect of dome design and operational changes on the mixing quality in the fuel-rich region. A statistical analysis is employed to establish the parametric sensitivity in this complex flow. A mixing effectiveness index is defined and used to optimize the gas species uniformity and the extent of reaction at the exit plane of the dome. The results reveal that mixing effectiveness is intimately tied to the fuel and air injection locations, the macroscale structure of the dome aerodynamics, and the level of turbulence. Increases in nozzle/air to fuel ratio, reference velocities, and the dome expansion angle increased the level of turbulence. The optimum configuration featured counterswirling fuel and airstreams and produced a strong torroidal recirculation zone, an effective spray angle of 45 deg, and azimuthal velocities that decayed to zero inside of two duct diameters. Due to the intimate relationship between variables, the response of mixing to changes in any single variable cannot be considered independently of the other variables. The results underscore the system specific nature of mixing optimization.