Experimental investigation of the ignition dynamics in an annular premixed combustor with oblique-injecting swirling burners

In this work, a new concept of annular combustor with 16 oblique-injecting swirling burners is innovatively proposed to induce a gyratory flow motion for better circumferential mixing and ignition performance. The cold flow fields were obtained by the PIV method, which clearly verified the existence of the gyratory flow motion. The light-round sequences were recorded by a high-speed camera and compared with that of the straight-injecting combustor in two ignition modes, thus the SFFL (Spark First, Fuel Later) and the FFSL (Fuel First, Spark Later) modes. The light-round time, flame propagating positions, flow acceleration coefficient and circumferential flame spreading speed were obtained and discussed. The effects of the thermal expansion, velocity convection and the gyratory flow motion to the light-round process were systematically studied. The results show that the two combustors feature different light-round sequences, indicating that the flow characteristics play an important role in determining the ignition process. In the SFFL mode, the flame only propagates in one direction, which is consistent with the direction of the gyratory flow motion. While in the FFSL mode, the light-up of the oblique-injecting combustor is faster than that of the traditional combustor, when the bulk velocity Ub is above 5.0 m/s. The light-round sequences in the oblique-injecting combustor are obviously asymmetrical, while those in the straight-injecting one are nearly symmetrical. The difference of the circumferential flame spreading speed between two branches of the flame fronts is mainly depended on Ub and little correlated with the equivalence ratio, when Ub>4.0 m/s.