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Experiment Study of Pilot Stage Swirler Outlet Angles and Swirl Number on Flame Structures and Flow Field in a Stratified Swirl Combustor


 The stratified swirl combustor is generally used in an advanced aero-engine, in order to achieve a low emission and wide stabilization at the same time. The complex interactions between the pilot stage and main stage can determine the flame structure, flow field, further affecting the emission formation and stabilization. The present study investigates the interaction between pilot flame and flow field of a stratified swirl combustor, by varying the outlet angles and swirl numbers of the pilot stage swirler. Flame structures and flow fields are obtained while only the pilot stage working. The flame structures are represented by the OH* chemiluminescence (OH-CL) image with Abel deconvolution, non-reacting and reacting flow fields are measured by Particle Image Velocimetry (PIV). The results show that heat release from the pilot flame causes rapid expansion of the pilot gas which may significantly change flow field distribution. Two types of flame structures and flow fields are formed with different outlet angles and swirl numbers of pilot stage. The correspondence between the flame structure and flow field is obtained. For large outlet angle or high swirl number, a M-shape flame combining with a typical stratified swirl flow field and converged pilot and main flow jet are observed, including a large main recirculation zone (MRZ), a lip recirculation zone (LRZ), and a corner recirculation zone (CRZ). For small outlet angle and low swirl number, the flame structure presents a lifted inverted U-shape flame, pilot and main stage jet are separated, there are a small pilot recirculation zone (PRZ), a main recirculation zone (MRZ) and a corner recirculation zone (CRZ) in the combustor. The MRZ is broken into two parts by the accelerated of pilot flow, the LRZ is merged into the MRZ.