Bluff body stabilised non-premixed flames are usually used as pilot flames in lean-premixed combustors. Experiments are conducted to investigate the characteristics of the flame. Typical flame modes are investigated in both stable and unstable conditions. The flow structures, the reaction zone, and the dynamics of unstable flames are measured with PIV, ICCD and a high speed camera, respectively, based on which the inherent mechanisms that influence the configuration and stabilisation of the flame are analysed. Stable flames are apparently influenced by the mixing characteristics in the recirculation zone. Flame detachment, a typical phenomenon of stable flames in a turbulent air flow, can be explained by the distribution of fuel concentration in the recirculation zone. The Reynolds number of air has different effects on different parts of the flame, which results in three unstable flame modes at different Reynolds numbers of air. These results could be helpful for the design of stable burners in practice.

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