Reconstruction Technique Of Real Three-Dimensional Emission Computerized Tomography For Combustion Visualization

The visualizations of the combustion fields are the basis for the researches of modern military equipment and the designs of industrial instrument.Emission computerized tomography(ECT),combining optical measuring methods with computerized tomography,does not require external light sources and relies on multidirectional projections carrying the measured field information to reconstruct the combustion fields.It can achieve non-contact,non-destructive and transient whole-field three-dimensional(3D)visualizations of the measured field.And it is the rapidly developing method of the combustion field visualizations in recent years.To solve the problem of neglecting the connection between various parts of the measured field during the imaging process,this paper starts from the perspective of improving the ECT model,and the main works are summarized as follows:1.The establishment of the real 3D ECT model.In view of the limitations of the traditional ECT model,this paper establishes the real 3D ECT model based on the Radon transform in 3D space.The reconstruction of 3D ECT is transformed into the obtainment of projections,the calculation of the weight matrix,and the implementation of the reconstruction.2.The research on real 3D ECT.Aiming at the obtainment of projections in real 3D ECT,this paper combines the parallel projection model and considers the imaging effect of camera lens to establish a 3D space camera imaging model that is more suitable for real 3D ECT.For the calculation of the weight matrix,the algorithm based on linear interpolation theory and the algorithm based on high-density sub-grids are studied.The projection results from different angles of numerical simulation are consistent with the actual projection.To solve the implementation of the reconstruction,the multiplicative algebraic reconstruction technique(MART)is studied.By simulating the reconstruction results of the axisymmetric field and the non-axisymmetric field,it is proved that the weight matrix calculation algorithm based on the linear interpolation principle can effectively improve the reconstruction quality,but the reconstruction using this algorithm takes longer.By establishing sub-grids with different densities for the simulated field,it is proved that the high-density sub-grids of a conventional grid can effectively improve the calculation accuracy of the 3D weight matrix,and this algorithm improves the efficiency of reconstruction.The reliability of the real 3D ECT model is verified by calculating the re-projection of the combustion field.3.The research on camera spatial arrangements for ECT.To investigate the impact of the number and arrangements of cameras on reconstruction accuracy,the arrangement condition of cameras is analyzed theoretically.Through numerical simulation,it is found that the 2D coplanar arrangement shows higher accuracy than the 3D non-coplanar arrangement when the number of cameras is fixed.And if there are environmental restrictions that the 2D coplanar arrangement cannot be satisfied,3D non-coplanar arrangement can be adopted while the cameras should be widely distributed in the hemispherical space.4.The establishment of the multidirectional ECT system.ECT systems are established in3 D space to obtain multi-directional projections.Based on the real 3D ECT model and the camera calibration method considering the focusing effect of the camera,the visualizations of the combustion fields are achieved.The visualization results under different camera arrangements are consistent with the numerical simulation results of the camera spatial arrangement.