Three-dimensional temperature diagnostics based on thermally-assisted volumetric laser-induced fluorescence

This research introduces a novel application of three-dimensional (3D) combustion thermometry through the thermally-assisted volumetric laser-induced fluorescence, namely the TAVLIF technique. The TAVLIF method is designed to provide quantitative 3D temperature diagnostics using a single dye-laser system, combining the advantage of tomographic imaging with the thermally-assisted LIF approach. The technique employs the A²Σ⁺←X²Π (0, 0) band Q₁(7) transition to excite OH radicals within a controlled Bunsen burner flame. Following excitation, the fluorescence emitted from the resonant (0, 0) and non-resonant (1, 0) vibrational bands is captured sequentially by an intensified camera, facilitating the reconstruction of the 3D fluorescence field. Utilizing the axisymmetric and stable properties of the burner flame, we reconstruct the 3D distribution of fluorescence signals from both bands. The resulting 3D temperature field is determined by the ratio of fluorescence intensities between the two bands, employing a novel ternary model calibrated experimentally to relate temperature to fluorescence ratio. After accounting for acquisition errors such as reflection and scattering of excitation light, as well as reconstruction and temperature calculation errors, the relative error remains below 6%. This research demonstrates the cost-effectiveness (only one dye laser system), accuracy, and reliability of the TAVLIF technique in diagnosing 3D temperature fields within combustion processes.