Experimental study and RANS calculation on velocity and temperature of a kerosene-fueled swirl laboratory combustor with and without centerbody air injection

Experimental study and RANS calculation were performed for a kerosene-fueled swirl laboratory combustor with and without the air injection through the cross-drilled circular openings in the centerbody of the swirler. The particular interest of the work is to explore the potential advantages of the centerbody air injection in enhancing the non-premixed combustion performance of the swirl combustor. Specifically, the velocity and temperature fields were measured under non-reacting and reacting flow conditions, respectively, to investigate the influence of the centerbody air injection on the central recirculation zone, which plays a crucial role in combustion stabilization. Numerical calculation based on RANS was conducted and compared with the experimental measurements to further quantify experimental observations. In addition, the combustion efficiency was evaluated based on the after burning flue-gas analysis. The experimental and numerical results show that an enlarged recirculation zone with higher temperature can be formed in the swirl combustor with the centerbody air injection, which therefore may hold potentials in enhancing flame stabilization and combustion efficiency. In addition, the centerbody air injection pushes the recirculation zone to the farther downstream of the fuel injector and hence can reduce the exposure of the fuel injector to the high-temperature combustion zone. Since the centerbody air injection was found to only slightly modify the effective swirl number, the modified velocity and temperature characteristics are mainly due to the changes of the shape and location of the central recirculation zone and the local stoichiometry in the vicinity of fuel injection. A parametric study for various inlet air velocities and excess air factors further substantiates the effectiveness of the centerbody air injection on improving the combustion performance although the extent of the improvement relies on other factors that therefore merits future studies for optimization design.