Parametric Study to Optimize Air/Fuel Mixing for Lean, Premix Combustion Systems

New designs of gas turbine combustors for power generation applications have to meet ever-tightening emission standards (mainly NOx, CO and UHC) while operating at high combustor pressures. This requires a detailed understanding of the physical processes involved. The air-fuel mixture preparation is a critical step in most advanced gas turbine combustion strategies to achieve lower emissions. It has long been established that the level of unmixedness between the fuel and air is strongly tied with NOx levels. The present paper applies the statistical technique of Design Of Experiments (DOE) to a generic mixer set-up that includes an axial swirler, with fuel injected at discrete locations and transverse to the flow. The objective is to identify influential design and operating parameters that will provide rapid and enhanced mixing. The parameters tested include Swirl strength as measured by the Swirl number, Swirl type (Constant angle vs. Free vortex), number and momentum of fuel injection sites and gas temperature. Planar Laser Induced Fluorescence of acetone (PLIF) was used to quantify mixing at various planar locations in the mixing section. Commercial CFD software is used to model the flow field and predict the spatial mixing at selected conditions. Comparisons are made with experimental measurements with the aim to validate the CFD code and also on comparing the model results with the measurements.