Study On Three-dimensional Temperature Field Tomography Of Combustion Flame Based On Spectral Imaging

The solid rocket engine is the strategic demand for air-space war in the future.It is the difficulty in the development technology of solid rocket engine to avoid the damage and ablation of engine components caused by flame temperature oscillation in unstable combustion.The traditional inversion method of flame temperature field has the defects of slow calculation speed and incomplete results.In order to study the essence of unstable combustion and the influencing factors of combustion temperature oscillation characteristics further,this paper proposed a single line-of-sight based on prism splitting method as an effective means for three-dimensional temperature field tomography measurement of combustion flame,the systematic theoretical and experimental studies are carried out.The advantages of non-contact measurement have potential application value in the field of unstable combustion diagnosis.The main work of this paper is the theoretical derivation and experimental verification of radiation temperature measurement technology based on Planck’s radiation law,the introduction and experimental verification of the basic principles of optical tomography,the design and construction of the spectral imaging tomography experimental system,and the three-dimensional temperature field tomography test of candle flame.This paper studies the following three aspects:First of all,the basic principle and method of spectral radiation temperature measurement technology are introduced which is based on Planck blackbody radiation law,The blackbody radiation calibration of the spectrometer is carried out,the corresponding relationship is fitted between the gray value of the spectrometer and the radiation intensity value of the wavelength which is used for temperature inversion.Then the emissivity and dynamic temperature of the candle flame are tested.The test results were verified by the contact thermocouple temperature measurement method.The maximum absolute error was 47.9 K,and the maximum relative error was 3.97 %.The test results proved the accuracy of the radiation temperature measurement technology.Then,this paper introduced the mathematical model of optical imaging,the basic types and determination methods of point spread function,the basic theory and concept of optical tomography technology.The tomographic imaging technology was experimentally verified using transparent text images,and the point spread function of the plane was calibrated where the text was located.The original light intensity distribution of each section was reconstructed using the deconvolution algorithm of image tomography,which proved the feasibility of the image tomography algorithm.In the last,the experimental system of spectral imaging tomography is designed and built.The composition and function of each part of the experimental system are introduced.The optical alignment calibration is carried out.After the position of the flame fault is determined by the image clarity evaluation function,the point diffusion function is calibrated by the edge method.The fitting relationship between the gray value and the radiation intensity of R and G components of the four cameras in the system is determined by the blackbody furnace radiation calibration.On this basis,the emissivity of the four sections of the flame is measured,and the original light intensity and temperature are reconstructed.The reconstructed image conforms to the shape of the candle flame section,the inversion temperature value and the thermocouple measurement value are in good consistency,The maximum absolute error was 60.0 K,and the maximum relative error was 5.48%.The experimental results prove the feasibility of the three-dimensional temperature field tomography measurement method of combustion flame based on spectral imaging.