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

Many modifications to the combustion process are being proposed and ev aluated to lower NO(x) emissions from gas turbine engines in both stat ionary and propulsion applications. A promising technique is staged co mbustion, wherein the fuel is mixed into a fuel-rich region and the fi nal air is injected downstream to an overall lean mixture. This articl e examines the effect of dome design and operational changes on the mi xing quality in the fuel-rich region. A statistical analysis is employ ed to establish the parametric sensitivity in this complex flow. A mix ing effectiveness index is defined and used to optimize the gas specie s uniformity and the extent of reaction at the exit plane of the dome. The results reveal that mixing effectiveness is intimately tied to th e fuel and air injection locations, the macroscale structure of the do me aerodynamics, and the level of turbulence. Increases in nozzle/air to fuel ratio, reference velocities, and the dome expansion angle incr eased the level of turbulence. The optimum configuration featured coun terswirling fuel and airstreams and produced a strong torroidal recirc ulation zone, an effective spray angle of 45 deg, and azimuthal veloci ties that decayed to zero inside of two duct diameters. Due to the int imate relationship between variables, the response of mixing to change s in any single variable cannot be considered independently of the oth er variables. The results underscore the system specific nature of mix ing optimization.