An investigation into flashback and blow-off for premixed flames stabilized without a recirculation vortex

We have recently shown that premixed CH4/air flames anchored behind flame holders can stabilize in two flame stabilization regimes characterised by the presence or absence of a recirculation vortex [1]. Focus of the present work is on the underlying mechanisms governing flames anchored without the presence of a vortex for methane-air flames. We revisit the definition of the flame anchoring location and define a new anchoring location which results from flame stretch considerations rather than heat loss considerations. This location can be unambiguously defined for flame holders of different sizes. It is argued that such an anchoring location is more relevant for flames stabilized behind flame holders with sharp corners and do take into account the multi-dimensional nature of heat transfer with the flame holder as well. A quantitative assessment of heat transfer, stretch and preferential diffusion effects is then carried out at the anchoring location for elucidating their impact on the flame speed as a function of the flame holder size. New insights into flame blow-off, flashback and emergence of a recirculation vortex are obtained as a result of this investigation