Lean blow-off of premixed swirl-stabilised flames with vapourised kerosene

Abstract

Lean blow-off (LBO) conditions, duration of the extinction transient, and flame structure were investigated for swirl-stabilised, fully-premixed flames operated with methane and vapourised kerosene. High-speed (5 kHz) OH* chemiluminescence, OH-, and Fuel-PLIF imaging were used. Low-speed (10Hz) CH2O-PLIF imaging was also implemented to visualize the structure of CH2O. OH* chemiluminescence imaging of the LBO transient suggested that the primary reaction regions were confined within the central recirculation zone (CRZ). Sharp temporal increases in OH* signal were observed in the CRZ for both fuels, possibly due to flame re-ignition events during LBO transients. Both fuels showed a decrease in flame length and an increase in fragmentation in downstream regions. In the OH-PLIF images, pockets void of OH entered the CRZ from downstream. The CH2O- and Fuel-PLIF images suggest that these pockets contain either partially burned or fresh reactants. Furthermore, the CH2O- and Fuel-PLIF images indicated that CH2O and Fuel exist in the outer recirculation zone (ORZ) during the early stages of the LBO transient. The blow-off duration was calculated by integrating the OH* signal and for kerosene was found to be 1.5 times longer than for methane. In addition, the equivalence ratio at which kerosene blew-off was consistently lower than that of methane for a range of bulk flow velocities. These results indicate that fuel chemistry effects are important for the LBO condition and duration.