Research On Three-dimensional Flame Reconstruction Method Based On Chemiluminescence

The flame propagation in gasoline engines,significantly dependent on the in-cylinder turbulence and the heterogeneity of the charge,is featured by complex spatial structure,which further influences the development of the flame itself and its interaction with the unburned mixture.Therefore,it is necessary to study the three-dimensional(3D)flame structure and reveal its coupling mechanisms with heat transfer,mass transfer and chemical reaction kinetics.One of the obstacles that limit the research is the mismatching between the 2D measurements obtained by traditional combustion diagnostics and the 3D characteristics of complex turbulent flame.As a solution,the technique of flame reconstruction based on chemiluminescence(FRBC)was applied,in which 3D distribution of radiation intensity was reconstructed by using flame image data from different directions.A simplified flame imaging model was established on the basis of five assumptions which simplifies the photoelectrical process in ICCD cameras,the imaging geometrical model and the radiation field in combustion region.It mathematically describes the radiation intensity distribution and pixel intensities in flame images.With the model,the reconstruction problem was converted into the solution of an ill-posed problem where the radiation intensity distribution is to be solved.The coefficients in the illposed problem were calculated based on the characteristics of convex polygons and Quasi-Monte Carlo method.The algebraic reconstruction technique(ART)was selected to solve the ill-posed problem.Based on the simplified flame imaging model,a platform for phantom study was built in MATLAB.A series of flame phantoms was constructed by referring to the flame features in hybrid combustion model in gasoline engines,and the phantoms were then utilized in the platform to study the effects of the number of camera angles and the image resolution on reconstruction accuracy.The error distributions in reconstruction phantoms were discussed and the strategy to terminate the iteration computation was optimizedA multi-angle image capturing system for Meker burner flame was built,and based on the simplified flame imaging model,a platform for Meker burner flame reconstruction was established in MATLAB.By using the image data acquired from different directions,the 3D distribution of CH* was successfully reconstructed.The results revealed the 3D structure of the flame fronts,demonstrating the validation of the methodology and the potential for combustion diagnostics.