Numerical Characterization of a Premixed Hydrogen Flame Under Conditions Close to Flashback

Abstract

This work presents a numerical study of a technically premixed swirling combustor with central air injection at conditions close to flashback using large-eddy simulation with flamelet modelling. The study shows the assumption of perfect premixing is valid during the stable operation of the burner up to flashback conditions. The experimental results are well predicted under inert and reacting conditions by using a perfectly premixed mixture. It is found that the non reacting flow field develops a self-excited oscillation in the form of a precessing vortex core. This oscillation is attenuated by the fuel injection due to the respective increase in axial momentum and it is ultimately suppressed in the reacting flow field. Both experiments and simulations confirm the same trends. The analysis of the flames have shown certain dynamics as the flashback point is approached. The flashback resistance of the burner is minimized due to an increase in the velocity deficit of the incoming mixture. The recirculation region is shifted upstream, the central recirculation is altered and the flame position is displaced towards the reactants. OH-PLIF measurements are compared with the OH predictions by the LES and certain level of disagreement is observed. This modelling approach is found to be valid to predict the hydrodynamic behaviour of the flames in terms of velocity fields and flow oscillations, but it can not predict the OH formation found in the post combustion zone across the reacting layer. Keywords premixed burner • swirl-stabilized flames • flashback safety • precessing vortex core • flamelet Address(es) of author(s) should be given This is a post-peer-review, pre-copyedit version of an article published in Flow, turbulence and combustion.

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