Premixed flame flashback in wall boundary layers studied by long-distance micro-PIV

Premixed flame propagation against the main flow direction in wall boundary layers, a situation known as wall flashback, has been studied by long-distance particle image velocimetry with spatial micron resolution (mu-PIV) and simultaneous flame luminescence recordings. Numerical simulations of laminar wall flashback assist the interpretation of the experimental results. Inside a turbulent boundary layer, the flame propagates in discrete flame cusps pointing in upstream direction and showing a well-defined pattern of formation and break-up. In a laminar boundary layer, the leading flame region is smooth and exhibits low curvature. The instantaneous velocity fields reveal a backflow region upstream of the flame during flashback, which is constrained to the leading flame zone. The backflow is caused by an interaction between the pressure increase upstream of the flame and the boundary layer. The flashback limit is controlled by thermal quenching of the flame tip in the backflow region.