Characterizing lean blowout dynamics of DME/air premixed swirl flames in a gas turbine model combustor with and without confinement

Abstract

This work investigates lean blowout (LBO) dynamics of dimethyl ether (DME)/air premixed swirl flames in a gas turbine model combustor with and without confinement. CH* chemiluminescence imaging and 2 kHz high-speed OH* chemiluminescence imaging are performed to capture the swirl flame macrostructures. Particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) are used to visualize the flow fields and reaction zones, respectively. Compared to the unconfined flame, the addition of confinement results in the appearance of an outer recirculation zone (ORZ), variation in flame topology, enhanced overall heat release (HR) rate, increased turbulent kinetic energy (TKE), and extended LBO limits. Far from LBO, all flames are stabilized in the shear layer. Approaching LBO, the confinement enhances the flow vortex structures along the shear layers, which is associated with extinction at the flame base and shear layer. However, the unconfined flame is still stabilized in the shear layer due to the weaker flow vortex structures. Different extinction mechanisms during the LBO process are also discussed between the unconfined and confined flames. The unconfined flame suddenly leaves the inner shear layer (ISL) and recedes to the inner recirculation zone (IRZ) within about 100 ms before LBO. Abundant CH2O is transported into IRZ mainly by recirculation, which reduces the HR region area and give rise to LBO. For the confined flame, more and more cold reactants gather near the base plate and then are gradually brought into IRZ by ISL vortices, which makes the flame lift from the base plate and decrease the HR region area until LBO happens.