Chemistry reduction of complex CO₂ chemical kinetics: Application to a gliding arc plasma

A gliding arc (GA) plasma has great potential for CO₂ conversion into value-added chemicals, because of its high energy efficiency. To improve the application, a 2D/3D fluid model is needed to investigate the CO₂ conversion mechanisms in the actual discharge geometry. Therefore, the complex CO₂ chemical kinetics description must be reduced due to the huge computational cost associated with 2D/3D models. This paper presents a chemistry reduction method for CO₂ plasmas, based on the so-called directed relation graph method. Depending on the defined threshold values, some marginal species are identified. By means of a sensitivity analysis, we can further reduce the chemistry set by removing one by one the marginal species. Based on the so-called flux-sensitivity coupling, we obtain a reduced CO₂ kinetics model, consisting of 36 or 15 species (depending on whether the 21 asymmetric mode vibrational states of CO₂ are explicitly included or lumped into one group), which is applied to a GA discharge. The results are compared with those predicted with the full chemistry set, and very good agreement is reached. Moreover, the range of validity of the reduced CO₂ chemistry set is checked, telling us that this reduced set is suitable for low power GA discharges. Finally, the time and spatial evolution of the CO₂ plasma characteristics are presented, based on a 2D model with the reduced kinetics.