The Application Of The Computed Tomography Of Chemiluminescence (CTC) Technique To The Study On Structure Of Flame

One of the key technologies of scramjet is supersonic combustion. Because of the three-dimensional turbulent and unsteady properties of supersonic combustion flows, planar laser diagnostic techniques are difficult to fully describe the whole precise combustion flow field. Computed tomography?CT? can get the 3D image of structure through reconstruction on the basis of different section projections. Chemiluminescence, which can reflect the information of combustion and flame structure, is photon radiation emitted by excited-state particles produced in chemical reactions. The computed tomography of chemiluminescence?CTC? technique is developed from the mature CT technique combined with chemiluminescence measuring technology and is especially suitable for the study of 3D unsteady combustion flow fields and flame structure, witch has important research value and good prospects for development. This paper carries out a preliminary research on the CTC technique, and three groups of steady-state flames are reconstructed by using the CTC technique and analyzed by comparing with the results of numerical simulation.Firstly, this paper carries out the study of CTC reconstruction algorithm. The various factors influencing the reconstruction resaults are analyzed and studied by simulation through constructing phantom. The study found that the use of simplified calculation method of weight coefficient matrix and iteration?including the initial field? limit method can effectively improve the efficency of reconstruction. It will not only lead to rapid decrease of the reconstruction speed but also a drop in the quality when the number of projection angle is too large.The greater the number of projection rays in each angle is, the higher reconstruction quality we can get, but the speed is contrary. The selection of relaxation factor?is associated with noise. If the noise is loud, only smaller?less than 0.1? ? can lead to the iterative convergence. On the basis of the above studies, the reconstruction algorithm is extended to three dimentions. The simplified calculation method of 3D weight coefficient matrix together with the method of segmentation of the reconstruction area and calculation process can bring good reconstruction results by overcoming the disadvantage of wasting too much computing resources in 3D reconstructions.Secondly, 2D laminar premixed flame is studied through numerical simulation method. Excited-state particle and relevant reactions, which can bring chemiluminescence, are introduced into the reaction mechanism models. As a result, the OH* molar concentration and reaction heat release rate fields of H₂/Air 2D laminar premixed flame are achieved.Finally, by using the CTC technique, correlative experimentations are carried out. Excited-state particle OH*?or CH*? chemiluminescence fields of three kinds of flames are reconstructed by the CTC technique. The feasibility of the CTC technique is verifed by comparing the reconstruction image with the actual image of OH* chemiluminescence field of CH₄/Air 2D laminar premixed flame. Through the comparison of OH* chemiluminescence and OH* molar concentration and reaction heat release rate fields, it is found that all three can reflect the position of reaction zone, for they are occurred near the reaction zone of flame. OH* chemiluminescence field cannot characterize OH* molar concentration field, but can partly be characterization of reaction heat release rate field. The reaction in flame will gathered to the top when the flow rate increases. But the specific rules of the influence of equivalent ratio changes are not clear, which need further research. Through the analysis of the section reconstruction images of 3D chemiluminescence field, we can find that the reconstruction result can partly relfect the actual information of flame structure, but in the areas with large gradient, the reconstruction precision is not high enough.