Multistep dump combustor design to reduce combustion instabilities

Abstract

Based on the understanding of the critical role of large-scale structures as drivers of pressure oscillations, a multistep dump was sucessfully tested to suppress pressure oscillations in a coaxial dump combustor. The multistep concept, which prevents development of large-scale structures, was studied in nonreacting air and water flows and in an annular diffusion flame before it was applied to the dump combustor burning gaseous fuel. The nonreacting tests in water and air showed that there is an optimal geometric configuration of the multisteps to achieve the highest level of turbulence. At this geometry the shear layer that is separated from the upstream step impinges on the next downstream step edge. When this geometry was tested in a dump combustor, the fuel injection pattern was found to be critical to obtain suppression of instabilities . With fuel injection distributed into the small-scale turbulence downstream of each step and not interfering with the flow impingement, the pressure oscillation in the dump combustor was suppressed.