CARS diagnostic and modeling of a dielectric barrier discharge

Dielectric barrier discharges (DBD) with planar- and knife-shaped electrodes are operated in N-2-O-2-NO mixtures under a pressure of 20 and 98 kPa. They are excited by means of consecutive unipolar or bipolar high-voltage pulse packages of 10 kV at a pulse repetition rate of I and 2 kHz. The rotational and vibrational excitation of N-2 molecules and the reduction of nitric oxide (NO) in the discharge have been investigated using coherent anti-Stokes Raman scattering (CARS) technique. Rotational (gas) temperatures near the room temperature and vibrational temperatures of about 800 K at atmospheric pressure and 1400 K at a pressure of 20 kPa are observed. Therefore, chemical reactions of NO with vibrationally excited N-2 are probably insignificant. One-dimensional kinetic models are developed that balance 35 chemical reactions between 10 species and deliver equations for the population density of excited vibrational levels of N-2 together with a solution of the Boltzmann equation for the electrons. A good agreement between measured vibrational temperatures of N-2, the concentration of NO, and calculated data is achieved. Modeling of the plasma discharge verifies that a DBD operated with a N-2-NO mixture reduces the NO content, the simultaneous presence of O-2, already 1%, is enough to prevent the NO reduction.