Non equilibrium vibrational and electron energy distribution functions in CO_2/CO cold plasmas

摘要

Introduction In a series of recent papers [1-4], we have discussed the chemical kinetics of CO reacting mixtures under discharge and post-discharge conditions similar to those occurring in microwave, DBD and nanosecond repetitively pulsed (NRP) discharges. The latter kind of discharges are assuming large importance in plasma assisted combustion, either for reducing the ignition times or for eliminating oscillation instabilities in the combustion process. In the theoretical description of such discharges, the chemical kinetics is usually decoupled from the electron ones, a hypothesis which can be open to questions especially in the post discharge regime. This aspect can become important in NRP discharges and afterglow description, depending on both the duration of the pulse and the corresponding repetition frequency. The latter is of particular importance to establish a sort of memory on the next pulse of what occurring in the previous one. Our studies have underlined the importance of the electronic excited states of CO in affecting the electron energy distribution functions (eedf) of free electrons through superelastic electronic collisions (SEC) expecially in the post discharge, leading the corresponding eedf in the next pulse much pumped than in the previous one. A similar behavior is to be expected by the vibrational distribution function (vdf) as well. In the present contribution, we focus on the description of NRP discharges of CO plasmas by means of a selfconsistent model based on the coupled solution of the electron Boltzmann equation for the eedf and the master equations for the vibrational levels of CO as well as the electronic excited states of CO, O and C atoms. In particular, in the calculation of the electronic excited states, different models have been considered and compared. We take into account optically thin and thick plasma conditions without the inclusion of any quenching model for the electronic excited states and the same thin and thick condit