On the efficiency of using different excitation lines of (1−0) two-line OH fluorescence for planar thermometry

The paper presents the results of simulation and experimental study on the efficiency of selecting a pair of excitation lines of OH hydroxyl radical for the (1−0) transition for the A²Σ⁺−X²Π system for local temperature measurement in a hydrocarbon flame. The LASKIN software was used for the numerical simulation. The temperature field for a laminar methane-air premixed flame (with equivalence ratio equal 1.1) at the atmopsheric pressure was measured. Different combinations of literature-recommended pairs of excitation lines were considered. The results of numerical simulation agree with a theoretical dependency for the temperature range of 1200–2100 K for the coupled excitation lines Q₁(5):Q₁(14) and Q₁(5):Q₂(11). However, a moderate discrepancy is observed for the pairs R₂(2):R₂(13) and R₂(2):R₂(10). It is concluded that the coupled excitation of Q₁(5):Q₁(14) and R₂(2):R₂(13) lines provide a higher sensitivity to the temperature variation. The benefit of the latter pair is that these transitions correspond to close values of the excitation wavelengths in the vicinity of 282 nm. Therefore, this can be convenient for the arrangement of experiments.