Reconstruction Of Two-Dimensional Of Temperature And Gas Concentration In Combustion Field Based On Hyperspectral Tomography

In recent decades,Tunable Diode Laser Absorption Spectroscopy(TDLAS)has become one of the indispensable optical measuring techniques in the diagnosis of combustion flow field due to its advantages such as fast response time,strong anti-interference ability and simultaneous measurement of multi-parameters.TDLAS can measure the line of sight along the absorption path,this technology can only realize the calculation of path average value.Therefore,it needs to be combined with other imaging techniques before it can be extended to the two-dimensional distribution reconstruction of combustion flow field.The linear reconstruction method directly combining traditional tomography and TDLAS technology requires high projection data in practical measurement applications,and the reconstruction error is large in the case of limited optical path arrangement.Therefore,this paper studies the method of hyperspectral reconstruction of combustion flow field under the projection of fewer beams.The Simulated Annealing algorithm(SA)used in the reconstruction process is also improved to solve the problem of the low computational efficiency of the hyperspectral reconstruction,and the two-dimensional reconstruction of the field distribution of the flame field in the laboratory flat flame furnace and the rear expansion section of the engine combustion chamber is realized.H2O,the main product of hydrocarbon fuel,is selected as the target gas molecule,and the optimal combination of spectral lines is selected.Hyperspectral Tomography(HT)technology based on direct absorption spectrum and wavelength modulation spectrum are studied for the inversion of combustion field.The accuracy of reconstructed images with three combustion distribution models and four beam layouts under different noise levels are quantitatively analyzed.In the selection of optimal line combinations,12 absorption lines suitable for simple flow field are selected in advance,and the optimal selection of all 5 line combinations and 8 line combinations are further selected according to the basic two-region method.Which verifies the importance of incorporating spectral information and selecting the optimal line combinations to improve the reconstruction accuracy.The simulated annealing algorithm used in the reconstruction process is improved on the model perturbation mode and annealing strategy,which ensures that the algorithm is able to jump out of the local optimal solution to find the global optimal solution,and at the same time,the running efficiency of the algorithm is improved nearly 40 times compared with the traditional simulated annealing algorithm.The effects of different distribution models,different beam layouts and noise levels on the two methods are analyzed.The reconstruction accuracy of the two methods decreases slightly with the complexity of the combustion model and increases with the augment of the number of light beams.The reconstruction accuracy of the fan-shaped beam is higher and has better anti-noise performance than the parallel beam.Compared with DAS-HT,WMS-HT has better reconstruction adaptability and noise immunity.The spectral parameters of H2O absorption line are calibrated by using 2f/1f signal with background deducted.Combined with the laboratory's high temperature furnace spectrum parameters calibration device,taking the absorption lines of 6807.83 cm-1 and 6808.04 cm-1 as examples,adopting the full-line fitting method,utilizing the WMS heat absorption model and combining with the optimized L-M fitting method.When comparing with the measured 2f/1f signal,peak spectral absorbance is successfully simulated under the high temperature environment to invert H2O spectral parameters.The deviation of line strength was 3.91%and 5.40%respectively compared with HITRAN database.The uncertainties are 1.05%and 1.96%,which are far less than the linear intensity uncertainties of 10%-20%in the database,verifying the feasibility and reliability of inversion spectral parameters by high-temperature absorption model.Using the TDLAS-HT system integrated in the laboratory,the two-dimensional field distribution of the flat furnace flame field and the rear expansion section of the engine combustion chamber are reconstructed.In the measurement of flame flat flame furnace in the laboratory,the flame field distribution of flat furnace is reconstructed by placing steel ruler to form different combustion distributions and the reconstruction results restore the original distribution well.Besides,the rear expansion section of the engine bench combustion chamber is measured,and the experiments of different operating conditions and different vehicle numbers are reconstructed.The results are consistent with the physical actual combustion process,which verifies the feasibility and applicability of the hyperspectral reconstruction method.Hyperspectral reconstruction method combining TDLAS technology and HT technology is developed through the selection of optimal spectral lines,field distribution reconstruction,algorithm research,verification of reconstruction method,accurate calibration of spectral parameters and experimental measurement verification.In the method of hyperspectral reconstruction based on wavelength modulation spectrum,the broadening is also taken into account to improve the noise tolerance and achieve high precision reconstruction of complex combustion flow field.The reconstruction time is greatly shortened through the improvement of the reconstruction algorithm,which can better deal with the rapidly changing turbulence field.It provides an important theoretical basis and experimental basis for the measurement of industrial combustion process and harsh combustion environment in aerospace propulsion system.