I. A. Kossyi

A freely localized microwave discharge for removal of chlorofluorocarbon contamination from the atmosphere

Intense microwave beams are proposed to be used for cleaning atmospheric chlorofluorocarbon contamination which is destroying the ozone layer of the Earth. It is shown that it may be possible to excite microwave discharges freely localized in the troposphere. The relation between the quantity of the destroyed chlorofluorocarbons and discharge parameters is established, the energy required for destruction is evaluated and possible unfavourable consequences of the accompanying effects (such as nitrogen oxides production) are analysed. The mechanism of dissociative electron attachment which is manifested in a cold decaying plasma of a pulsed microwave discharge is considered to be a principle mechanism causing dissociation of chlorofluorocarbons (CF2Cl2, CFCl3, etc.). The results are presented of a model laboratory experiment in which, under conditions close to those of free space, a study is made of the efficiency of chlorofluorocarbon dissociation under the action of the discharge produced in air by intense microwave radiation. The experimental results do not contradict the conclusions of the analysis of elementary processes causing the destruction of the chlorofluorocarbon component.

UV treatment of microorganisms on artificially-contaminated surfaces using excimer and microwave UV lamps.

An XeBr excilamp having a peak emission at 283 nm, and microwave UV lamps with peak emissions at 253.7 nm that also generate ozone, have been tested for ability to eradicate high populations of microbial vegetative cells and spores (of bacteria and fungi) artificially added to filter surfaces. The study examined the energy required to completely eradicate large populations on filter surfaces. It was found that both the excilamp and microwave UV lamps were effective at killing large populations on surfaces with killing efficiency dependant on the type of organism, and, whether present in its vegetative or spore forms. The main killing factor is UV radiation following short treatment times. It is considered that for longer irradiation periods that are required to facilitate complete destruction of surface microorganisms, ozone and other oxidising species produced by microwave UV lamps would act to enhance microbial destruction.

Ignition of a combustible gas mixture by a laser spark excited in the reactor volume

Ignition of a stoichiometric CH4: O2 mixture by a laser spark excited in the reactor volume is studied experimentally. It is found that the spark initiates a feebly radiating incomplete-combustion wave, which is much faster than the combustion wave, but is substantially slower than the detonation wave. With a time delay of 500–700 μs, a bright optical flash occupying the entire chamber volume is observed, which indicates fast (involving branching chain reactions) ignition of the gas mixture. A conclusion is drawn regarding the common nature of the process of ignition of a combustible gas mixture by a laser spark excited in the reactor volume and the previously investigated initiation of combustion by laser sparks excited at solid targets, high-power microwave discharges, and high-current gliding discharges.

A nonequilibrium plasma accompanying the ignition of methane-oxygen mixtures

Measurements of electron density and electron‐neutral collision frequency in combustion-produced plasmas in methane‐oxygen stoichiometric mixtures are presented. The electron density in the developed flame was found to be at a level of ne ≈ (2‐6) × 10 12 cm −3 , which exceeds the values obtained or predicted in the previous experimental and theoretical works. The collision frequency between electron and neutral components is νen ≈ 10 12 s −1 , thus exceeding that in the preflame mixture by more than an order of magnitude. Based on the calculations performed within the framework of a multicomponent kinetic scheme the most important processes of chemi-ionization in methane‐oxygen flames are determined. It is shown that the maximum electron density in the developed flame is close to ∼3 × 10 12 cm −3 , which is in reasonable agreement with the measured values. (Some figures may appear in colour only in the online journal)

Application of MW Plasma Generator for Ignition of Kerosene/Air Mixture

The goal of this paper is to determine the range of dependable ignition and combustion stabilization of lean mixtures and to extend the working range with the aim to improve efficiency and environmentally acceptable characteristics of jet engines. Microwave (MW) plasma generators were employed to initiate combustion in kerosene/air streams. Experiments were carried out in a model frontal device (MFD) of turbojet combustor under different ignition and stabilization conditions. The MW plasma igniter was mounted behind an MFD of the turbojet combustor. The MFD was flowed around by air stream parameters: Mach number <i>M</i>_air = 0.1-0.35, temperature <i>T</i>_air = 280&nbsp;K - 565&nbsp;K, and the kerosene/air mixture equivalence ratios were phi = 0.3-1.5 . Results were compared with the ignition data by a standard aviation spark plug. It was shown that, in the case of the use of the MW igniter, the stable ignition range is expended to lean fuel/air mixtures or larger air flow velocities.

Ignition of a combustible gas mixture by a high-current electric discharge in a closed volume

Results are presented from experimental studies and numerical calculations of the ignition of a stoichiometric CH4: O2 gas mixture by a high-current gliding discharge. It is shown that this type of discharge generates an axially propagating thermal wave (precursor) that penetrates into the gas medium and leads to fast gas heating. This process is followed by an almost simultaneous ignition of the gas mixture over the entire reactor volume.

Ring-shaped electric discharge as an igniter of gas mixtures

Results are presented from experimental studies of ignition of a stoichiometric methane–oxygen mixture in a closed chamber by a ring electric discharge. It is shown that the process of fast (explosive) ignition of the reactor volume starts on the axis of the ring, near its centre, i.e. at a distance from the annular region of power deposition. Experimental evidence suggests that the ignition of a combustible gas mixture near the axis is triggered by strong gas-dynamic perturbations converging to the axis, radially propagating from the ring discharger.

Pulsed microwave discharge in a capillary filled with atmospheric-pressure gas

A pulsed microwave coaxial capillary plasma source generating a thin plasma filament along the capillary axis in an atmospheric-pressure argon flow is described. The dynamics of filament formation is studied, and the parameters of the gas and plasma in the contraction region are determined. A physical model of discharge formation and propagation is proposed. The model is based on the assumption that, under the conditions in which the electric fields is substantially below the threshold value, the discharge operates in a specific form known as a self-sustained-non-self-sustained (SNS) microwave discharge.

Conversion of methane in a coaxial microwave torch

A microwave coaxial plasmatron (microwave torch) is used as a plasmachemical converter of methane into hydrogen and hydrocarbons. The measured energy cost of methane decomposition is close to its minimum theoretical value. Such a low energy cost is unsurpassed for reactors operating at atmospheric pressure. A model of the plasmachemical converter is constructed. The results of calculations in the frame-work of this model agree well with experimental data.

Multispark Discharge in Water as a Method of Environmental Sustainability Problems Solution

Multispark discharge excited in water is described, and its useful physical and chemical properties are discussed in the light of some environmental issues. Discharge of such a type generates hot and dense plasmoids producing intense biologically active UV radiation and chemically active radicals, atoms, and molecules. Simultaneously, discharge creates strong hydrodynamic perturbations and cavitation bubbles. Particular attention is given to factors influencing on water purity with special reference to discharge application for effective sterilization of water and its cleaning of harmful chemicals. The gas discharges of this type show considerable promise as a means for solving some actual plasma-chemical problems. The above-mentioned discharge properties have been demonstrated in a series of laboratory experiments, which proved the efficiency of disinfection of potable and waste water, water cleaning of pesticide (herbicide) contaminations, and conversion (recovery) of natural methane.