[en] The properties of a surface barrier discharge in atmospheric-pressure air at different polarities of applied voltage were studied experimentally. The influence of the voltage polarity on the spatial structure of the discharge and the electric field in the discharge plasma was determined by means of spectroscopic measurements. It is found that the energy deposited in the discharge does not depend on the voltage polarity and that discharges of positive polarity are more homogenous and the electric fields in them are higher.

[en] Two-dimensional hydrodynamic numerical modelling of a cathode-directed streamer discharge at a constant anode voltage of 100 kV in a 13 cm long gap filled with a nitrogen-oxygen mixture at atmospheric pressure is performed. The dynamics of main discharge parameters is analysed and quite good agreement with experimental measurements is obtained. It is shown that, when the electron loss processes in the streamer plasma are neglected, the discharge dynamics changes insignificantly: the electric field in the streamer head changes by less than 1% and the streamer propagation velocity changes by 7%, while the anode current and the electric field in the streamer channel change by a factor of about 2. The calculated anode current is found to coincide with the experimental one only when kinetic processes in the streamer channel are taken into account

[en] Plasma decay after a high-voltage nanosecond discharge has been studied experimentally and numerically behind incident and reflected shock waves in high temperature (600-2400 K) air and N₂ : O₂ : CO₂ mixtures for pressures between 0.05 and 1.2 atm. Time-resolved electron density history was measured by a microwave interferometer for initial electron densities in the range (1-3) x 10¹² cm^-3 and the effective electron-ion recombination coefficient was determined. A numerical simulation was carried out to describe the temporal evolution of the densities of charged and neutral particles under the conditions considered. It was shown that the loss of electrons in this case is determined by dissociative recombination with O₂⁺ ions, whereas the effect of complex ions is negligible. Electron attachment to O₂ to form negative ions is not important because of fast electron detachment in collisions with O atoms produced in the discharge. In the absence of O atoms the electron density could decay as if the loss of charged particles were governed by electron-ion recombination with the effective rate coefficient being much higher than the dissociative recombination coefficient.

[en] The stagnation dynamics of a cathode-directed streamer discharge in two-dimensional geometry has been studied for the first time. It has been shown that as the streamer decelerates the radius of the streamer head decreases more rapidly than its potential, which, in turn, leads to an increase in the maximum electric field as well as an increase in the charged particle densities in the streamer head. (brief communication)

[en] Ignition of hydrocarbon-containing gaseous mixtures has been studied experimentally and numerically under the action of a high-voltage nanosecond discharge at elevated temperatures. Ignition delay times were measured behind a reflected shock wave in stoichiometric C_nH_2n+2 : O₂ mixtures (10%) diluted with Ar (90%) for n = 1-5. It was shown that the application of the gas discharge leads to more than an order of magnitude decrease in ignition delay time for all hydrocarbons under consideration. The measured values of ignition delay time agree well with the results of a numerical simulation of the ignition based on the calculation of atom and radical production during the discharge and in its afterglow. The analysis of simulation results showed that a non-equilibrium plasma favours the ignition mainly due to O atoms produced in the active phase of the discharge. (fast track communication)

[en] Plasma decay after a high-voltage nanosecond discharge was studied experimentally and numerically in room temperature N₂, CO₂ and H₂O for pressures between 1 and 10 Torr. The time-resolved electron density was measured by a microwave interferometer for initial electron densities in the range 8 x 10¹¹-3 x 10¹² cm^-3 and the effective electron-ion recombination coefficient was determined. It was shown that this coefficient varies in time and depends on pressure. A numerical simulation was carried out to describe the temporal evolution of the densities of charged particles under the conditions considered. A good agreement was obtained between the calculated and the measured electron density histories. It was shown that the loss of electrons is governed by dissociative recombination with complex ions, their density being dependent on pressure. In N₂ at low pressures, a hindered electron thermalization in collisions with molecules led to a delay in the plasma decay. This effect was observed both experimentally and theoretically

[en] This paper presents a detailed explanation of the physical mechanism of the nanosecond pulsed surface dielectric barrier discharge (SDBD) effect on the flow. Actuator-induced gas velocities show near-zero values for nanosecond pulses. The measurements performed show overheating in the discharge region on fast (τ ≅ 1 μs) thermalization of the plasma input energy. The mean values of such heating of the plasma layer can reach 70 K, 200 K and even 400 K for 7 ns, 12 ns and 50 ns pulse durations, respectively. The emerging shock wave together with the secondary vortex flows disturbs the main flow. The resulting pulsed-periodic disturbance causes an efficient transversal momentum transfer into the boundary layer and further flow attachment to the airfoil surface. Thus, for periodic pulsed nanosecond dielectric barrier discharge, the main mechanism of impact is the energy transfer and heating of the near-surface gas layer. The following pulse-periodic vortex movement stimulates redistribution of the main flow momentum.

[en] Results from experiments and numerical modelling of streamer propagation are presented. The 2D hydrodynamic numerical description of the pulsed discharge based on the local ionization and photoionization models adequately describes the streamer shape and dynamics over a wide range of pressures and voltages. This work presents a method for imaging the instantaneous emission distribution in the streamer head. A method for restoring the electrodynamic radius of the streamer head was developed on the basis of the streamer head images that were obtained with subnanosecond exposure time. The electrodynamic radius has been determined as the distance between the maxima of the electric field at the position where the streamer head transforms into the streamer channel. The dependence of the electrodynamic radius on voltage and pressure has been determined. We show that a 2D numerical model using hydrodynamic approximation predicts the streamer characteristics with an accuracy of about 15% in the 0.5-1 atmosphere pressure range and up to 40% in the 0.2-0.3 atmosphere pressure range for a voltage of U from 20 kV up to 40 kV in the 30 and 40 mm discharge gap.

[en] Slow oxidation of n-butane and n-decane in lean mixtures with oxygen under the action of a nanosecond pulsed discharge has been experimentally investigated. The discharge was excited by 25 ns pulses with an amplitude of 22 kV on high-voltage electrode and repetition frequency of 40 Hz in a 20 cm long quartz tube. The initial pressure of the mixtures was varied within the range from 0.8 to 10 Torr. The energy input in the discharge has been measured. The radiation intensities of the following molecular bands have been measured in time-resolved and integral modes: CO₂⁺(B²Σ → X²Π, δv=0), CO₂⁺(A²Π → X²Π), OH(A² Σ, v' = 0 → X² Π, v-prime = 0), CO(B¹ Σ, v' = 0 → A¹ Π, v-prime 2). It has been demonstrated that, under the same experimental conditions in lean mixtures with oxygen, the times for the n-decane and n-butane oxidation are equal

[en] The decay of air plasma produced by a high-voltage nanosecond discharge at room temperature and gas pressures in the range of 1–10 Torr was studied experimentally and theoretically. The time dependence of the electron density was measured with a microwave interferometer. The initial electron density was about 10¹² cm⁻³. The discharge homogeneity was monitored using optical methods. The dynamics of the charged particle densities in the discharge afterglow was simulated by numerically solving the balance equations for electron and ions and the equation for the electron temperature. It was shown that, under these experimental conditions, plasma electrons are mainly lost due to dissociative and three-body recombination with ions. Agreement between the measured and calculated electron densities was achieved only when the rate constant of the three-body electron-ion recombination was increased by one order of magnitude and the temperature dependence of this rate constant was modified. This indicates that the mechanism for three-body recombination of molecular ions differs from that of the well-studied mechanism of atomic ion recombination.