Validation of non-equilibrium kinetics in CO2–N2plasmas

Abstract

AbstractThis work explores the effect of N2addition on CO2dissociation and on the vibrational kinetics of CO2and CO under various non-equilibrium plasma conditions. A self-consistent kinetic model, previously validated for pure CO2and CO2–O2discharges, is further extended by adding the kinetics of N2. The vibrational kinetics considered include levels up tov= 10 for CO,v= 59 for N2and up tov1= 2 andv2=v3= 5, respectively for the symmetric stretch, bending and asymmetric stretch modes of CO2, and account for electron-impact excitation and de-excitation (e–V), vibration-to-translation (V–T) and vibration-to-vibration energy exchange (V–V) processes. The kinetic scheme is validated by comparing the model predictions with recent experimental data measured in a DC glow discharge operating in pure CO2and in CO2–N2mixtures, at pressures in the range 0.6–4 Torr (80.00–533.33 Pa) and a current of 50 mA. The experimental results show a higher vibrational temperature of the different modes of CO2and CO and an increased dissociation fraction of CO2, that can reach values as high as 70%, when N2is added to the plasma. On the one hand, the simulations suggest that the former effect is the result of the CO2–N2and CO–N2V–V transfers and the reduction of quenching due to the decrease of atomic oxygen concentration; on the other hand, the dilution of CO2and dissociation products, CO and O2, reduces the importance of back reactions and contributes to the higher CO2dissociation fraction with increased N2content in the mixture, while the N2(B3Πg) electronically excited state further enhances the CO2dissociation.