Lean blowout characteristics of spray flame in a multi-swirl staged combustor under different fuel decreasing rates

Lean Blow Out (LBO) poses a significant safety hazard when occurring in aero-engines. Understanding the lower stability limits of gas turbine combustors and the characteristics of spray flame close to LBO are imperative for safe operation. The objective of this work is to evaluate the effects of fuel decreasing rates and pressure drops of the injector on LBO performances in a multi-swirl staged combustor equipped with an airblast injector. A set of hardware and control system was developed to realize a user-defined fuel supply law. High-speed imaging was applied to record complete LBO processes under the conditions of linear fuel reduction and stable airflow. Partical Image Velocimetry (PIV) and Planar Mie (PMie) scattering were used to acquire the flow fields and spray fields under non-reacting conditions. Experimental results have shown that LBO limits extend to leaner conditions as the pressure drop of the injector increases. With an increase of the fuel decreasing rate, the exhaust temperature before flame extinction increases, and the LBO Fuel-to-Air-Ratio (FAR) decreases. The time evolution of the integral CH* intensity conforms to a linear function during the LBO process. Proper Orthogonal Decomposition (POD) was used to analyze the dynamic characteristics of lean-burn flames. Under different fuel decreasing rates and pressure drops of the injector, flames close to LBO present similar modal spatial distributions, alternately appearing axial, radial, high-order axial, and high-order radial oscillations.