*4.5. Burner Facility*

Flat methane/air premixed flames are stabilized on a water-cooled McKenna burner at atmospheric pressure. It is equipped with a central sintered bronze matrix of 60 mm diameter for delivering the fuel/air mixture and an outer 6 mm-wide ring-shaped matrix for providing a coannular flow of dry nitrogen. All gases are metered by calibrated mass flow controllers (Bronkhorst, Kamen, Germany), while the cooling water flow for the burner matrix is circulated at 16 ◦C by a thermostat (Huber, Minichiller 600 OLÉ, Offenburg, Germany). For vertical translation with respect to the spatially fixed optical path for the absorption measurements, the burner is mounted on a lab jack. The height above burner is measured with a caliper, whose two arms are fixed to the lab jack and the breadboard, respectively, with a zero value when the traversing analysis beam is just halfway clipped by the burner surface. Premixing of fuel and oxidizer well upstream of the burner inlet improved the flatness of the flame, as is visible from flame chemiluminescence.
