Experimental investigation of a lean, premixed gas turbine combustor using advanced laser diagnostics

Lean, premixed combustion offers great promise for meeting the increasingly stringent NO_x emissions standards for power generation and transportation. The reductions in combustion temperature provided by this combustor technology can drastically reduce NO_x generation. Additional development is required to allow widespread adoption of the technology. Specifically, a better understanding of the flame stabilization must be obtained. Additionally, to fully realize the NO_x reduction benefits of lean, premixed combustion, a better understanding of the relation between mixing, combustion temperature, and NO_x emission levels must be obtained for practical premixing technologies.; A research program was initiated to apply non-intrusive laser diagnostic techniques to measure flame structure and temperature within the combustion region of a practical, lean, premixed combustor mounted in an optically accessible test section. A combustor facility, including a LabVIEW-based data acquisition control system, was designed and built to maintain the operation of the lean-premixed combustor. Optical access was provided by a thin-walled fused silica section in the cylindrical combustion chamber surrounded by thick, fused silica plate containment windows. A translation system was developed to allow two-dimensional translation of the laser-diagnostic probe volumes through the primary reaction zone near the premixer exit.; Flame structure and stabilization were studied using planar laser-induced fluorescence of the hydroxyl radical. Four operating conditions were examined—two equivalence ratios, 0.6 and 0.7, and two combustor pressure drops, 3% and 5%. Time-resolved images were acquired at two axial locations for each test condition, revealing a combustion flow field dominated by large-scale turbulent structures. Stabilization of the flame occurred primarily in the side recirculation zone at the edge of the premixer exit. Single-shot temperature measurements were made using coherent anti-Stokes Raman scattering at the two pressure drop conditions with an equivalence ratio of 0.7. Time-resolved measurements were made at twenty spatial locations at each condition. Temperatures were below those expected based on previous cold-flow mixing investigations that revealed fuel-rich mixtures in the reaction zone of the combustor. Emissions measurements demonstrated the correlation between equivalence ratio and NO _x generation, but were generally low, indicating low levels of unmixedness.