  A combined experimental and numerical investigation of partially premixed
laminar methane-air flames undergoing side-wall quenching (SWQ) is performed. A
well-established SWQ burner is adapted to allow the seeding of the main flow
with additional gaseous products issued from a (secondary) wall inlet close to
the flame's quenching point. First, the characteristics of the partially
premixed flame that quenches at the wall are assessed using planar
laser-induced fluorescence measurements of the OH radical, and a corresponding
numerical simulation with fully-resolved transport and chemistry is conducted.
A boundary layer of enriched mixture is formed at the wall, leading to a
reaction zone parallel to the wall for high injection rates from the wall
inlet. Subsequently, in a numerical study, the wall inflow is mixed with
dimethylmethylphosphonat (DMMP), a phosphor-based flame retardant. The DMMP
addition allows the assessment of the combined effects of heat loss and flame
retardants on the flame structure during flame-wall interaction. With an
increasing amount of DMMP in the injected mixture, the flame stabilizes further
away from the wall and shows a decrease in the local heat-release rate.
Thereby, the maximum wall heat flux is significantly reduced. That results in a
lower thermal load on the quenching wall. The flame structure analysis shows an
accumulation of the intermediate species HOPO at the wall similar to the CO
accumulation during the quenching of premixed flames without flame retardant
addition. The study shows how the structure of a partially premixed flame is
influenced by a wall that releases either additional fuel or a mixture of fuel
and flame retardant. The insights gained from the canonical configuration can
lead to a better understanding of the combined effects of flame retardants and
heat losses in near-wall flames.
