3D Temperature Imaging of Dynamic Flames by Three-Wavelength Lateral Shearing Interferometry

3D temperature imaging of dynamic flames was realized by three -wavelength lateral shearing interferograms. Lasers of different wavelengths are combined into a single three-wavelength laser. The phase difference is initially extracted by identifying the centerline of the fringes before determining the optical path difference. Templates were proposed to improve the efficiency of fringe centerline phase extraction. An iterative correction method is introduced to improve the accuracy of the optical path difference. After inversion of the optical path, the refractive index was reconstructed by inverse Abel transform. The temperature distribution is calculated by the Gladstone-Dale model combined with the ideal gas equation. Numerical simulations were performed to evaluate the performance. The optical path difference and the refractive index errors were 0.0256 and 0.0473, respectively. The temperature images had reconstructed errors of 0.0941. In the experiments, the Bunsen burner with acoustic excitation at 100 Hz produced dynamic flame, and the temperature variation was captured by the measurement system at a frame rate of 20k fps. Continuous fluctuations in the flame temperature distribution were clearly captured, and the profile of average temperature values agrees with the radiation intensity profile obtained from the photodetector. The spectral intensity profile of the mean temperature had a distinct peak at 100 Hz and its multiples, consistent with acoustic excitation.