Spatially constrained two-line laser absorption spectroscopy for thermochemical profiling of McKenna flames

Quantifying temperature and species concentration in non-uniform McKenna flat flames via laser absorption spectroscopy (LAS) is critical for understanding reaction kinetics and validating kinetic models, numerical simulations and diagnostic techniques in fundamental combustion research. Traditional discrete tomography approaches suffer from limited performance with sparse sampling, while existing profile fitting strategies rely on extensive multispectral and prior field information to address the multi-solution issue. This work introduces spatial spectra from multiple radial positions into profile fitting, achieving high-precision inversion using only two absorption lines. Experiments were conducted at various heights above premixed CH 4 /air McKenna flames ( Φ = 0.8, 1.0) using the H 2 O absorption lines at 6807.83 cm −1 and 7444.36 cm −1 , yielding quantitative, high-resolution, two-dimensional temperature and H 2 O mole fraction distributions. Validation against thermocouple measurements identifies Δ R = 6 mm as a critical sampling resolution threshold for balancing accuracy, stability, and simplicity for the standard McKenna burner investigated in this study. Uncertainty analysis reveals that the inversion performance is highly dependent on both the number of optical paths and their spatial arrangements. This study provides a more robust optical measurement scheme for the quantitative diagnostics of axisymmetric reactive flows.