Igor V. Kochetov

Plasma-Assisted Combustion of Gaseous Fuel in Supersonic Duct

The field of plasma-induced ignition and plasma-assisted combustion in high-speed flow is under consideration. Nonequilibrium, unsteady, and nonuniform modes are analyzed as the most promising in reducing a required extra power. Numerical simulations of uniform, nonequilibrium, continuous, and pulse discharge effect on the premixed hydrogen and ethylene-air mixtures in supersonic flow demonstrate an advantage of such a technique over heating. At the same time, the energetic price occurs rather large to be scheme practical. A reduction of the required power deposition and mixing intensification in nonpremixed flow could be achieved by nonuniform electrical discharges. Experimental results on multielectrode discharge maintenance behind wallstep and in the cavity of supersonic flow are presented. The model test on hydrogen and ethylene ignition is demonstrated at direct fuel injection

Plasma-Induced Ethylene Ignition and Flameholding in Confined Supersonic Air Flow at Low Temperatures

The results of laboratory-scale experiments on plasma-induced hydrogen and ethylene ignition and flameholding by means of near-surface electrical discharge are presented. The ignition and flameholding were demonstrated for direct fuel injection into the supersonic air. A two-zone model of plasma-induced ignition is proposed to explain the experimental data. Numerical simulations were performed to confirm the two-zone model of plasma-assisted ignition.

Modeling of Plasma Assisted Combustion in Premixed Supersonic Gas Flow

A model for plasma assisted combustion of ethylene-air mixtures at conditions typical for scramjet combustion chamber is developed combining classical mechanisms of thermal combustion with non-thermal plasma chemistry. Numerical simulations showed that sufficiently strong reduction of ignition induction time at a reasonable energy cost can be realized with help of filamentary discharges. Starting from the discharge region, the gas mixture is heated due to exothermic reactions involving atomic oxygen and secondary chemical radicals. Temperature increment to the end of this stage for ethylene-air mixture is relatively small. An important effect of this stage is not heating but production of transient species. Then, a period with slow growth of temperature follows, which terminates by fast combustion. Processes causing the first fast growth of gas temperature are analyzed, and intermediate species controlling acceleration of ignition are determined numerically for plasma assisted combustion of stoichiometric mixture of ethylene with air. The value of the calculated induction time defined as a moment of the fast combustion is rather sensitive to the particular combustion mechanism adopted. This manifests a necessity to refine combustion mechanisms for conditions typical for scramjet combustion chamber with plasma initiation ‐ one atmosphere pressure, static gas temperature around 700 K and appearance of atomic oxygen † .

Plasma-Assisted Chemistry in High-Speed Flow

Fundamental problems related to the high-speed combustion are analyzed. The result of plasma-chemical modeling is presented as a motivation of experimental activity. Numerical simulations of the effect of uniform non-equilibrium discharge on the premixed hydrogen and ethylene-air mixture in supersonic flow demonstrate an advantage of such a technique over a heating. Experimental results on multi-electrode non-uniform discharge maintenance behind wallstep and in cavity of supersonic flow are presented. The model test on hydrogen and ethylene ignition is demonstrated at direct fuel injection to low-temperature high-speed airflow.

Low-temperature ignition of methane-air mixtures under the action of nonequilibrium plasma

A plasma-chemical kinetic mechanism of the low-temperature (600 < T < 1000 K) oxidation/combustion of methane under conditions of nonequilibrium plasma over a wide pressure range (P = 0.1−100 atm) is developed and verified. The mechanism is comprised of three types of elementary processes: chemical reaction of neutral atoms and molecules, primary plasma-chemical processes involving electrons, and secondary plasma-chemical processes involving atomic and molecular ions and excited species. Application of the developed mechanism to describing the plasma-assisted oxidation of methane shows that this mechanism can describe the experimental results qualitatively and quantitatively.

Generation of atmospheric pressure non-thermal plasma by diffusive and constricted discharges in air and nitrogen at the rest and flow

Main subject of this paper is low current atmospheric pressure gas discharges powering with DC power supplies. These discharges are widely used for generation of non-thermal or non-equilibrium plasma in air and nitrogen which are much cheaper compared to rare gases like He or Ar. Molecular nitrogen as plasma forming gas has a unique capability to accumulate huge energy in vibration, electron (metastables) and dissociated (atomic) states. Besides, all active species have a long life-time, and they can be therefore transported for a long distance away from the place of their generation. Different current modes (diffusive and constricted) of these discharges are discussed. Experimental and numerical results on generation of chemically active species in the diffusive and constricted mode are presented.

Unstable Pulse Discharge in Mixing Layer of Gaseous Reactants

The paper describes results of experimental and computational efforts on the filamentary transversal pulse discharge dynamics in ambient conditions, different gases (mixtures), and high-speed airflow. The effect of fast turbulent expansion of the post-discharge channel is studied experimentally in order to enhance mixing processes of fuel and oxidizer and reduce the time of ignition. The idea of extra benefit possessed with nonequilibrium, unsteady, and non-homogeneous discharge is verified numerically.

The methods of singlet oxygen detection for DOIL program

The problem of development of a singlet delta oxygen O2(1Δg) (SDO) generators alternative to chemical one needs application of the accurate methods of measuring the SDO concentration. A chemical SDO generator providing efficient operation of a chemical oxygen-iodine laser (COIL) is proposed to be used as a reference source for absolute calibration of the system measuring the SDO concentration. The principle of the COIL operation results in the threshold and output COIL parameters make it possible to evaluate the SDO yield with a satisfactory accuracy. A convenient sparger chemical SDO generator was applied as a reference source for absolute calibration of detectors of dimole (λ=634nm) and b→X (λ=762 nm) radiations. The values of b-state concentration formed in a longitudinal electric discharge were evaluated. The intracavity laser spectroscopy (ICLS) was absolutely calibrated for measuring the SDO concentration. ICLS method has a very high sensitivity and makes it possible to monitor the absorption corresponding to the O2(1Δg)→O2(1Σg+) (λ = 1.91 μm) transition. The cross-sections of lines of the Q - branch of the vibrational 0-0 band of the a1Δg → b1Σg+ transition of molecular oxygen were measured. The method developed was applied to measure the concentration of singlet oxygen produced in the microwave discharge. He - Ne laser (λ = 633 nm) was used for absolute calibration of a system monitoring the dimole radiation. The rate constant of the process responsible for dimole emission was measured. The value obtained kd=7.34•10-23 cm3/s is in agreement with literature.

RF discharge in CO2 laser mixtures at moderate pressures

The voltage-power characteristics and spatial structure of an RF discharge in the mixtures of CO2 and N2 molecular gases with He at total pressures of tens of torr are studied. One-dimensional numerical simulations of an RF discharge are carried out within two approaches: (i) the distribution function and the related kinetic coefficients are assumed to be functions of the local reduced field, and (ii) the kinetic coefficients are functions of the electron mean energy, which is calculated with allowance for both electron heat conduction and diffusion. The latter approach is shown to better describe the existing experimental dependence of the discharge voltage and the phase shift between the discharge current and voltage on the driving power.

Theoretical and experimental investigation of a waveguide CO2 laser with radio-frequency excitation

A comprehensive experimental and theoretical study of the optimization of a continuous-wave radiofrequency (rf) excited CO2 waveguide laser is presented. The numerical simulation includes the modelling of the gas-discharge plasma parameters like the plasma impedance and energy deposition, the laser kinetics and finally the influence of the resonator feedback on the lasing process. Along with this theoretical study, an extensive experimental research program enabled us to optimize the laser performance of the CO2 waveguide laser. As a result, a total output power of 42 W and a specific output power of 1.1 W/cm were obtained.