Small scale experimentation using particle image velocimetry investigated the effect of the diffusive injection of methane, air, and\ncarbon dioxide on the coherent structures in a swirling flame. The interaction between the high momentum flow region (HMFR)\nand central recirculation zone (CRZ) of the flame is a potential cause of combustion induced vortex breakdown (CIVB) and occurs\nwhen the HMFR squeezes the CRZ, resulting in upstream propagation. The diffusive introduction of methane or carbon dioxide\nthrough a central injector increased the size and velocity of the CRZ relative to the HMFR whilst maintaining flame stability,\nreducing the likelihood of CIVB occurring.The diffusive injection of air had an opposing effect, reducing the size and velocity of\nthe CRZ prior to eradicating it completely. This would also prevent combustion induced vortex breakdown CIVB occurring as a\nCRZ is fundamental to the process; however, without recirculation it would create an inherently unstable flame
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