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 ne similar to 1014 cm-3 and the plasma ionization degree were determined by measuring the Stark broadening of the hydrogen H beta line (lambda H beta = 486.1 nm). The estimates of the electric field (E similar to 100 V cm -1 divided by 600 V cm-1) in the discharge positive column were found using time-synchronized high-speed video recordings and oscillograms. The gas rotational temperature Tg = 7000-9500 K and the vibrational temperature Tv = 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.

A microwave discharge in high-velocity (150–250 m/s) air flows induced on a half-wave vibrator is studied. A cw magnetron microwave generator with a frequency of 2.45 GHz and an output power of up to 5 kW was used for initiation of the microwave discharge. The high-speed video imaging was used for studying the discharge structure, determining the diameter and length of the plasma channel as a function of flow velocity and pressure. Electron concentration and temperature, along with characteristic gas temperature, were determined based on the optical spectra. The possibility of using this microwave discharge for ignition of hydrocarbon–air mixtures in combustion chambers of ramjet engines is proved experimentally.

Three-dimensional distributions of velocity, temperature and pressure in the supersonic air flow at M = 2, as well as the current density in the discharge initiated in it, are obtained. A direct current gas discharge of 10 A is considered in the hydrodynamic approximation within the channel model. The evolution of a transverse–longitudinal discharge is considered in the time range t up to 20 µs. It is shown that the discharge moves almost at the velocity of the main supersonic air flow disturbing it rather weakly. Based on the characteristic values of the current density and gas temperature of 8000–10 000 K obtained in the calculations, the electron density in the discharge channel is estimated as ne ~ 1016 cm–3. The field strength of E ~ 125 V/cm is estimated and the reduced field strength in the discharge channel E/N is about 30 Td. In the configuration of an aerodynamic model with shortened electrodes, the transition to the discharge phase fixed at their ends is shown.

Steady supersonic air flow in a diverging aerodynamic channel of rectangular cross-section is numerically simulated. The channel represents a laboratory model of an air-breathing straight-flow engine. The aerodynamic model is validated using the experimental data for the case in which the zone of volumetric heat release is absent. After the model has been validated a supersonic flow with a built-in zone of volumetric heat release was numerically simulated. Three-dimensional distributions of the velocity, temperature, and pressure in a steady supersonic air flow are obtained. It is shown that in the case, in which the volumetric density of the heat power of the source is equivalent to the mean total power of the discharge W = 10 kW, the discharge heats the gas up to the temperature T = 1700 to 4200 K, which leads to flow acceleration without its thermal choking. When the thermal power density of the source is equivalent to the mean common discharge power W = 20 kW, the gas is heated more strongly, up to 6700 K, but then local thermal choking of the flow occurs.

The paper presents the results of experimental studies of an unsteady pulsating transverse–longitudinal discharge created in high-speed air and propane–air mixture flows. It is shown that, under the conditions of such a discharge, near the electrodes, the gas is strongly heated, to temperatures of 6000–9000 K, and the gas temperature increases with increasing discharge current and airflow velocity. Test experiments were carried out, the results of which show that, under the conditions of an electrode transverse–longitudinal discharge, quasi-steady non-self-sustained combustion of a supersonic flow of a propane–air mixture is realized.

A nonstationary, transverse-longitudinal electrode discharge was obtained and was generated in a wide variation range of external conditions: the air-flow velocity was varied from 150 to 550 m/s, the minimal interelectrode gap was varied from 0.2 to 0.8 mm, and the maximal pulsating discharge current was varied from 5.5 to 16 A. It is shown that an increase in the discharge current leads to an increase in the maximally attainable plasma channel length and a decrease in the longitudinal electric field and plasma loop pulsation frequency. An increase in the interelectrode gap leads to an increase in voltage across the discharge, the plasma-channel length, and the longitudinal electric field intensity in plasma, whereas the pulsation frequency of voltage across the discharge gap, discharge current, and plasma loop decreases. An increase in flow velocity leads to an increase in electric-field intensity in the plasma and discharge pulsation frequency, whereas the voltage drop across the discharge does not depend on the flow velocity, and the full plasma loop length decreases. It is shown that the addition of propane into the air flow entails an essential change in the dependence of the plasma-loop pulsation frequency on the flow velocity, discharge current, and propane equivalence ratio in the fuel mixture.

The paper presents the results of experimental studies of the parameters of unsteady pulsating transverse–longitudinal discharge plasma created in high-speed airflows. It is experimentally shown that, under the conditions of the discharge under study, the electron density in the channel plasma of a pulsating discharge increases from ~1016 to 4 × 1016 cm–3 with an increase in the discharge current from 4 to 16 A and increases with an increase in the flow velocity at a constant value of the discharge current. It is also shown that the electron temperature in the pulsating discharge plasma is about 1 eV and the channel plasma is a strongly ionized medium, the degree of ionization of which increases from 1 to 30% upon transition from subsonic to supersonic air flows.

The parameters of the plasma of a unsteady, pulsed, transverse-longitudinal discharge generated in subsonic and supersonic air flows are determined. It is shown that the longitudinal electric field strength, as well as the electron density and temperature in the anode part of the plasma loop, exceed the corresponding values in the cathode part of the loop. The effect of the gas flow rate and the discharge current on the electron temperature in the plasma of the pulsed discharge in air and the propane-air mixture is studied.

Under the conditions of a nonstationary pulsating longitudinal-transverse discharge produced in a supersonic cold (T = 175 K) air flow, the combustion of a propane–air mixture has been stabilized. It has been shown that the completeness of propane combustion after stabilization under the conditions of low-temperature plasma amounts to about 95%. The combustion occurs at a flame temperature of 1800–2000 K. A propulsion thrust of about 55 N has been obtained the course of an experiment with plasma-assisted combustion of propane in an expanding channel with a length of 50 cm and a ratio of the inlet and outlet cross sections of S2/S1 = 12.7 at mass flow rates of 105 and 4.9 g/s for air and propane, respectively. This shows good agreement with the value of 60 N calculated under the conditions of complete propane burning.

The plasma parameters of an unsteady pulsating transverse-longitudinal discharge created in subsonic and supersonic air flows are determined. It was shown that in the anode part of the plasma loop, the longitudinal electric field, as well as the electron density and temperature exceed the corresponding values in the cathode part of the loop. The effect of gas flow rate and discharge current on the temperature of electrons in plasma of a pulsating discharge in air and propane-air mixture is also shown.

The ionization degree of the plasma in a nonstationary pulsating discharge created by a stationary power source in subsonic and supersonic airflows has been determined. lt was experimentally found that the electron density in the plasma near electrodes varies from 1015 to 3.7 × 1016 cm–3 and the gas temperature increases from 400 to 1250 K when the flow velocity varies from 150 to 520 m/s at a constant discharge current of 15.5 A. It is shown that the gas ionization degree in the pulsating discharge plasma is on the order of l0–4 at low subsonic airflow velocities, while with the increase in the flow rate it increases sharply and reaches the value of 10–2 at the velocity of 500 m/s.

Results are presented from experimental studies of a pulsating discharge produced by a dc power source in subsonic and supersonic cold ( T = 150–300 K) air flows at static air pressures in the flow of 40–760 Torr. Two modes of pulsating discharge were implemented experimentally: without and with (from one to five) intermediate breakdowns. The discharge pulsation frequency, the maximum attainable voltage across the discharge gap, the length of the plasma channel, and the electric field in the discharge plasma were studied as functions of the air flow velocity and discharge current.

A dc discharge in a cold ( T = 200 K) supersonic air flow at a static pressure of 200–400 Torr was studied experimentally. The excited unsteady pulsating discharge has the form of a thin plasma channel with a diameter of ≤1 mm, stretched downstream the flow. Depending on the discharge current, the pulsation frequency varies from 800 to 1600 Hz and the electron temperature varies from 8000 to 15000 K.