Low-current gliding DC discharge in high-speed flows

A low-current gliding discharge (current range 1–5 A) in high-speed air flows of 100–250 m s⁻¹ was experimentally studied. A high-voltage direct current source with a maximum voltage of 4.5 kV was used to create the discharge. The average electron concentration n_e ∼ 10¹⁴ cm⁻³ and the plasma ionization degree were determined by measuring the Stark broadening of the hydrogen H_β line (λ_Hβ = 486.1 nm). The estimates of the electric field (E ∼ 100 V cm ⁻¹ ÷ 600 V cm⁻¹) in the discharge positive column were found using time-synchronized high-speed video recordings and oscillograms. The gas rotational temperature T_g = 7000–9500 K and the vibrational temperature T_v = 7000–11 000 K were estimated using optical emission spectroscopy. Time-resolved spectroscopy is used to investigate the effective plasma channel spatial regions from which the N, NH, N₂⁺, O and OH molecules radiate. The difference of the obtained radii indicates the presence of a radial temperature gradient and inhomogeneous plasma composition in the discharge cross section. The possibility of using of gliding discharge to ignite hydrocarbon-air mixtures in the ramjet engines combustors has been experimentally demonstrated.