A collisional-radiative model for atmospheric-pressure low-temperature air discharges

Plasma-assisted combustion technology has been a hot spot in aero-engines and scramjet-engines. The electron density is a key discharge parameter related to the active-particle density. The latter has been considered playing an important role in the above applications by the kinetic effect. In this work, an atmospheric pressure air plasma collisional-radiative model considering the excited states of atomic nitrogen and oxygen is built based on previous widely kinetic investigations of molecules and radicals, as well as their excited states. The excited states, especially the atomic nitrogen and oxygen states were less investigated in previous works. The emission intensity distributions from the model have a good agreement with those measured in the glide arc plasma with two discharge modes, as well as the microwave plasma. Based on the kinetics of molecular and atomic emitting states, the line-ratio method is presented to determine the electron density. The N₂(337 nm)/O(844 nm) and N₂(337 nm)/NO(γ) line ratios are used for the glide arc plasma and microwave plasma torch, respectively. Besides, the kinetics of the excited states involved with two line-ratios are also investigated in the two types of discharges. Combined with the atmospheric pressure actinometry method, the kinetic effect of the plasma-assisted combustion can be revealed quantitatively in the future.