Online tomography algorithm based on laser absorption spectroscopy br

Conventional calibration-free wavelength modulation spectroscopy generally requires complex absorptionspectrum simulations in combination with spectral databases and laser modulation parameters, placing highdemands on the accuracy of a priori spectral parameters and hardware parameters. Meanwhile, inappropriateinitial values can increase the computation time and even lead to local optimal solutions. In order to improvethe computational efficiency, a rapid calibration-free wavelength modulation spectroscopy to obtain theintegrated absorbance is presented in this work. First, this method is computationally efficient, requiring onlyalgebraic calculations by using the 2nd, 4th, and 6th harmonic center peak height parameters to obtain theintegrated absorbance, eliminating the need for computationally intensive harmonic fitting calculations.Secondly, this method has low dependence on the spectral database, requiring only line intensity and low-stateenergy level spectral parameters. Finally, this method is highly adaptable and does not require scanning thecomplete absorption spectral line shape, which solves the problem of incomplete harmonic signals caused by theconventional method at high temperature and high pressure due to the broadening of the absorption spectralline. This method has previously been used only for line-of-sight measurements at low-frequency experimentalsignals in stable environments, and for calculating the integrated absorbance at average temperature,concentration and pressure states. In this work, the method is applied to non-uniform complex combustion fieldtomography and combined with the proposed tomographic system to achieve online reconstructing temperatureand concentration distributions. The accuracy and computational efficiency of the method in obtaining theintegrated absorbance are verified by numerical simulations and experiments on the butane burner flame. Theresults show that the presented method is consistent with the reconstructed distribution compared with theconventional wavelength modulation method, with a maximum relative deviation of only 0.94% from themeasurement and 3.5% from the thermocouple measurement, verifying the accuracy of the method. Thecomputational efficiencies of the two methods for obtaining the integrated absorbance are analyzed. The averagecalculation time per path is 0.15 s for the present method and 21.10 s for the conventional method. Thecalculation efficiency of the present method is at least two orders of magnitude higher than that of theconventional method, which provides a fast and reliable research method and technical means to realize theindustrial-grade online reconstruction of temperature and concentration distribution of combustion fields