Autoignition and flame lift-off behavior of a fuel jet mixing with turbulent hot air coflow

Abstract

For advanced lean premixed gas turbine combustors that have high inlet air temperatures, autoignition that occurs during the fuel/air mixing process is becoming an issue, which can cause flame-holding inside the premixing device and burn the hardware. This paper reports an experimental study on the autoignition and flame lift-off behavior of a fuel jet injected into hot air coflow that mimics the fuel/air mixing process of lean-premixed combustors. Autoignition occurred when a fuel jet (diluted with N2 or CO2) was injected concentrically into the hot turbulent air coflow. Three distinctive types of autoignition behavior were observed at increasingly higher jet velocity: (1) attached flame; (2) lifted flame followed by intermittent autoignition spots; (3) lifted flame. Lift-off height of the flame was measured at various fuel jet velocities and dilution ratios. The liftoff height increases monotonically with fuel jet velocity and dilution ratio. The CO2-diluted flame has higher lift-off height than the N2-diluted flame. The lift-off height data were fitted to various models to determine the flame stabilization mechanism. A modified large-scale mixing model can capture the effects of both turbulence mixing and autoignition kinetics on lift-off height, underscoring the importance of both turbulent mixing and autoignition kinetics in flame stabilization.