Quantitative measurements of one-dimensional OH absolute concentration profiles in a methane/air flat flame by bi-directional laser-induced fluorescence

The one-dimensional (1D) spatial distributions of OH absolute concentration in methane/air laminar premixed flat flame under different equivalence ratios at atmospheric pressure are investigated by using bi-directional laser-induced fluorescence (LIF) detection scheme combined with the direct absorption spectroscopy. The effective peak absorption cross section and the average temperature at a height of 2 mm above the burner are obtained by exciting absorption on the Q₁(8) rotational line in the A²Σ⁺ (′ = 0) ← X²Π (″ = 0) at 309.240 nm. The measured values are 1.86×10^-15 cm² and 1719 K, respectively. Spatial filtering and frequency filtering methods of reducing noise are used to deal with the experimental data, and the smoothing effects are also compared using the two methods. The spatial distribution regularities of OH concentration are obtained with the equivalence ratios ranging from 0.8 to 1.3. The spatial resolution of the measured result is 84 μm. Finally, a comparison is made between the experimental result of this paper and other relevant study results.