On the importance of 2D modeling for quantitative species measurements in burner-stabilized ammonia flames

Ammonia flames stabilized on porous burners are commonly modeled using steady, one-dimensional (1D), isobaric formulations that assume radial uniformity. While this approach is effective for kinetic studies, its validity under low-pressure conditions remains uncertain due to enhanced transport effects. In this work, three low-pressure NH 3 /O 2 /N 2 premixed flames ( Φ = 0.87–1.33, p = 10 kPa) were investigated using quantitative laser diagnostics and detailed-chemistry simulations. New absorption-calibrated Laser-Induced Fluorescence measurements of NH, including both axial and radial profiles, are reported together with complementary OH radial profiles, extending previously available datasets for NO and OH. Two-dimensional (2D, axisymmetric) simulations including detailed transport, radiation, and the full burner enclosure were performed and compared with conventional 1D models. While 1D simulations reproduce the general flame structure, they fail to capture the pronounced post-flame decrease of NO (up to 40% over 30 mm) observed in lean and stoichiometric conditions. The 2D simulations reproduce the measured NH and OH distributions and show that the NO decrease originates primarily from transport-induced dilution with burned gases entrained from the surrounding chamber, rather than from additional gas-phase chemical pathways. This effect extends over the axial region typically used for kinetic analysis, indicating that deviations from one-dimensional behavior cannot be neglected under these conditions. These results provide both new experimental datasets and a validated framework to quantify multidimensional transport effects, enabling a more reliable interpretation of low-pressure ammonia flames for the validation and development of detailed kinetic mechanisms. Novelty and significance statement: The paper presents the first quantitative in-situ measurements (using absorption-calibrated LIF) of NH mole fraction in low-pressure burner-stabilized ammonia flames (BSF). The radial species profiles show important inhomogeneities that call into question the validity of 1D simulations that neglect multidimensional transport effects and entrainment of the surrounding gas. In NH 3 flames characterized by low inlet gas velocity, the 2D simulation results agree well with the previously reported experimental NO and OH profiles, as well as with the present NH measurements. This study demonstrates for the first time that 2D effects, such as transport-induced entrainment of the burned gases in the chamber, strongly influence post-flame NO levels under low-pressure conditions. Recognizing these effects is essential for correctly interpreting experiments, assessing kinetic mechanisms, and improving predictive modeling of ammonia combustion. The results also provide guidance for future experimental and numerical investigations of low-speed, nitrogen-diluted reactive systems in confined environment.