Thermal flame thickness measurements in laminar premixed H2/air Bunsen flames using composition corrected Rayleigh thermometry

Rayleigh scattering thermometry with composition correction was applied to laminar premixed hydrogen/air Bunsen flames at atmospheric pressure for ϕ = 0.6 –1.4. Local temperature profiles were used to extract thermal flame thickness while accounting for composition-dependent Rayleigh cross sections, flame angle, and finite spatial response. The Rayleigh signal was referenced to air, normalized in the fresh gases, and corrected iteratively using species mole fractions from one-dimensional Cantera flames. The comparison used profiles over y = 5 –9 mm above a 7 mm burner. The local measured thickness decreases from 0.397 mm at ϕ = 0.6 to 0.318 mm at ϕ = 1.4 , while the maximum normal temperature gradients remain 6.5%–16.3% below the filtered 1D reference. A measured thickness below the 1D value therefore does not indicate a steeper front but reflects the combined evolution of the normal gradient and local product-side temperature.