A numerical investigation of effects of chemical kinetic mechanisms on the structure of turbulent jet diffusion H2/air flame with Lagrangian PDF method

Abstract

Many physical phenomena characteristic of reactive flows are controlled by the detail of the chemical kinetics of combustion. These include, for example, the ignition and extinction of a flame and the formation of polluting species. These phenomena require the use of detailed kinetic schemes including hundreds of species and thousands of reactions.The main objective of this work is to highlight the influence of chemical kinetics on the structure of turbulent jet diffusion H2/air flame. Five improved hydrogen kinetic mechanisms have been tested in order to validate, compare and evaluate their effect on the scalar and dynamic fields of such flames. The effect of number particles used in Lagrangian PDF method on the temperature evoltution is also studied. A hybrid method, PDF Lagrangian coupled to the RSM turbulence model, is used in this work, for the numerical simulation. The micro-mixing term of the TPDF is modeled by the EMST model. This model, which describes well the physical process of mixing, has shown its capabilities to give good numerical results. The impact of these mechanisms on the numerical results of scalar and dynamic fields was discussed and compared with the experimental data. The scalar field is well influenced by the choice of the chemical kinetic mechanism. This is not the case of the dynamic field. A good agreement with experience is observed for detailed kinetic mechanisms. However, it has been noticed that simple and reduced mechanisms give also satisfactory results, particularly the reduced kinetic mechanism R12 wich includes 12 reaction and can be considered as a compromise among the five kinetic mechanisms. These mechanisms allows for a significant reduction in CPU time and storage memory. It was also observed that, for the two chemical kinetic mechanisms R12 and R27, the number of particles only affects the radial evolution.