Effect of Quarl on N2- and CO2-Diluted Methane Oxy-Flames Stabilized by an Axial-Plus-Tangential Swirler

Abstract : Stabilization of nearly stoichiometric CO2- and N-2-diluted premixed methane/oxygen swirling flames is investigated in an atmospheric test rig equipped with an axial-plus-tangential swirler exhausting in a cylindrical injection tube eventually ended by a diverging quarl. The investigated flames are stabilized aerodynamically away from the solid elements of the combustor without the help of any central bluff body in the injector. The flowrates through the axial and tangential slits of the swirler can be adjusted separately. Effects of swirl and quarl angle on the flowfield and flame shape are analyzed. Laser tomography on small oil particles reveals that fuel, oxidizer and diluents injected in separated channels are well mixed at the injector outlet. Velocimetry measurements and flame images show that the axial plus-tangential swirler allows aflexible control of the flame leading edge position with respect to the injector outlet. For a fixed injector geometry with a given quarl angle and swirl number, it is found that N-2- and CO2-diluted flames feature the same topology if the injected combustible mixtures feature the same adiabatic flame temperature, while they may feature different bulk injection velocities and laminar burning velocities. The operability range of well stabilized CO2-diluted flames is however reduced.