Insights into the dynamics of local flame extinction events in CH4 -H2 turbulent flames
Résumé
In the present study, we have experimentally investigated the effect of H2 addition on the burning characteristics of turbulent flames in a lab-scale bluff-body burner. The burner geometry houses a large blockage ratio cylindrical bluff body (with a provision of central fuel injection) which separates the annular air passage. This work is motivated by the phenomenon where the flame exhibits intermittent oscillations and local extinction because of interaction with large-scale vortices in the shear layer. These extinction events are highly sporadic and cause alterations in the reaction zone height. The H2 addition has been studied in the past and reduction in the extinction events have been reported. However, the insights into the sporadic local flame sheet extinction and subsequent re-ignition process are not completely understood. To examine this further, we have conducted experiments with the increasing levels of a volumetric proportion of hydrogen (2) from 0%-100 % in a CH4-H2 mixture, while thermal power and co annular airflow rate are maintained constant. Time-resolved (5 kHz), simultaneous OH-PLIF, and PIV have been employed to provide a quantitative link between the hydrodynamics of surrounding co-flow and local flame extinction events. Globally, it is observed that the number of local flame extinction events along the shear layer is reduced with H2 addition, in fact, no such events are witnessed beyond 2 ≥ 0.4. Local extinction phenomenon leads to unsteadiness in the continuous flame sheet height measured from the burner exit, subsequently, autocorrelation function has been implemented to analyze the time delay associated with peak to peak variations. The obtained time delay values clearly delineate the increased tendency of flame sheet re-ignition with an increase in 2 .
Domaines
Sciences de l'ingénieur [physics]
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