Large eddy simulation/Flamelet progress variable approach is employed in current research to investigate how flame behaviour is influenced by bluff-body and coflow composition. We used Sydney bluff-body burner as the target burner. Computation grid in cylinder coordinates is approximately 2.7 million in total number, extended to the downstream location 80 times of jet diameter. Three coflow compositions with different oxygen ratio at the same inlet velocity are considered. Comparing to jet flames with hot and diluted coflow, instantaneous and statistical results showed that an introduction of bluff-body preheats the fuel and shortens the flame length. At lower oxygen ratio condition, a weaker reaction zone emerged, marked by lower temperature and OH concentration; the flame appeared lifted gradually, leading to a potential MILD combustion. Besides, bluff-body effect behaves differently in these flames: at lower oxygen ratio condition, a large-scale distribution of CH_2O appeared as a marker of partial premixing and preignition reaction in recirculation area; on the contrary, in higher oxygen ratio case, the recirculation area brings out more reactive fuel at lower speed and higher temperature, hence ignitable in the vicinity of bluff-body.
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