In recent decades particular interest in applications of nonequilibrium plasma for the problems of plasma-assisted ignition and plasma-assisted combustion has been observed. A great amount of experimental data has been accumulated during this period which provided the grounds for using low temperature plasma of nonequilibrium gas discharges for a number of applications at conditions of high speed flows and also at conditions similar to automotive engines. The paper is aimed at reviewing the data obtained and discusses their treatment. Basic possibilities of low temperature plasma to ignite gas mixtures are evaluated and historical references highlighting pioneering works in the area are presented. The first part of the review discusses plasmas applied to plasma-assisted ignition and combustion. The paper pays special attention to experimental and theoretical analysis of some plasma parameters, such as reduced electric field, electron density and energy branching for different gas discharges. Streamers, pulsed nanosecond discharges, dielectric barrier discharges, radio frequency discharges and atmospheric pressure glow discharges are considered. The second part depicts applications of discharges to reduce the ignition delay time of combustible mixtures, to ignite transonic and supersonic flows, to intensify ignition and to sustain combustion of lean mixtures. The results obtained by different authors are cited, and ways of numerical modelling are discussed. Finally, the paper draws some conclusions on the main achievements and prospects of future investigations in the field.

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Plasma assisted ignition and combustion

Adhesion of polymers

Different partial discharge (PD) detection and measurement procedures suitable for use on cables, capacitors, transformers and rotating machines are examined and compared. Both narrow and wide bandwidth PD detectors are considered; particular attention is given in regard to their suitability to different types of electrical apparatus and cable specimens under test as well as their applicability to discharge site location and their capability to detect different forms of PD. A rather substantial portion of the discussion is devoted to the use of intelligent machines as applied to PD pattern recognition in terms of either PD pulse-height/discharge epoch (phase) distributions or discharge pulse shape attributes.

Partial discharges. Their mechanism, detection and measurement

Dielectric Barrier Discharges (DBDs) are plasmas generated in configurations with an insulating (dielectric) material between the electrodes which is responsible for a self-pulsing operation. DBDs are a typical example of nonthermal atmospheric or normal pressure gas discharges. Initially used for the generation of ozone, they have opened up many other fields of application. Therefore DBDs are a relevant tool in current plasma technology as well as an object for fundamental studies. Another motivation for further research is the fact, that so-called partial discharges in insulated high voltage systems are special types of DBDs. The breakdown processes, the formation of structures, and the role of surface processes are currently under investigation. This review is intended to give an update to the already existing literature on DBDs considering the research and development within the last two decades. The main principles and different modes of discharge generation are summarized. A collection of known as well as special electrode configurations and reactor designs will be presented. This shall demonstrate the different and broad possibilities, but also the similarities and common aspects of devices for different fields of applications explored within the last years. The main part is devoted to the progress on the investigation of different aspects of breakdown and plasma formation with the focus on single filaments or microdischarges. This includes a summary of the current knowledge on the electrical characterization of filamentary DBDs. In particular, the recent new insights on the elementary volume and surface memory mechanisms in these discharges will be discussed. An outlook for the forthcoming challenges on research and development will be given. Page 1 of 47 AUTHOR SUBMITTED MANUSCRIPT PSST-101368.R1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A cc ep e M nu sc rip t Progress on DBD Sources and Filaments 2

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Dielectric barrier discharges: progress on plasma sources and on the understanding of regimes and single filaments

Atmospheric pressure plasmas are commonly used to improve the wetting and adhesion properties of polymers. In spite of their use, the mechanisms for achieving these properties are unclear. In this regard, we report on a computational investigation of the gas phase and surface kinetics during humid-air corona treatment of polypropylene (PP) and the resulting modification of its surface properties while varying energy deposition, relative humidity (RH), web speed, and gas temperature. Using results from a global plasma chemistry model validated against experiments, we found that increasing energy deposition increased the densities of alcohol, carbonyl, acid, and peroxy radicals on the PP surface. In doing so, significant amounts of gas phase O3 and NxOy are produced. Increasing the RH increased the production of peroxy and acid groups, while decreasing those of alcohol and carbonyl groups. Production of O3 decreased while that of HNO3 increased. Increasing the temperature decreased the concentrations of alcohol, carbonyl, and acid groups on PP while those of the peroxy radicals increased. For a given energy deposition, higher web speeds resulted in decreased concentrations of alcohols, peroxy radicals, carbonyl, and acid groups on PP.

/pdf/a-model-for-plasma-modification-of-polypropylene-using-4k1twd0434.pdf

A model for plasma modification of polypropylene using atmospheric pressure discharges

The pseudoglow and glow discharge behavior of a 0.5-mm metallic-dielectric electrode gap in helium under atmospheric pressure was examined as a function of ac voltage between 0.3 and 32 kHz. The number of discharge current pulses per half-cycle within the pseudoglow was found to diminish with rising frequency, as opposed to the increase observed with rising voltage. The reduction in the rise time and the quasi-monotonic decreases in amplitude of the successive discrete current pulses within the pseudoglow were attributed to the enhanced Penning ionization due to an increase in the number of energetic precursors (metastables and dimers) over the first quadrant in each half cycle. The interruption in the discharge pulse sequence, caused by a change in polarity of the ac field, greatly reduced the precursors' concentration and resulted in the first incipient pulse of the pseudoglow having the shortest rise time and width in the pulse sequence. The increase in frequency at constant voltage caused a gradual decrease in the number of discharge current pulses within the pseudoglow, until at ca. 10 kHz and beyond only a single pulse glow discharge took place. The influence of argon, nitrogen, hydrogen, and oxygen impurities was studied and interpreted in terms of Penning ionization and electron attachment.

Frequency and voltage dependence of glow and pseudoglow discharges in helium under atmospheric pressure

We compare two surface treatments of biaxially-oriented polypropylene (BOPP), which are carried out in the same dielectric barrier discharge (DBD) apparatus, namely air corona, and N2 atmospheric pressure glow discharge (APGD). Changes in the surface energy and chemistry are investigated by contact angle measurements, by X-ray photoelectron spectroscopy (XPS) and by attenuated total reflectance infrared spectroscopy (ATR-FTIR). It is shown that N2 APGD treatment leads to a higher surface energy than air corona treatment, and to the formation of mostly amine, amide, and hydroxyl functional groups at the polypropylene surface. Finally, hydrophobic recovery of the treated film is studied; for both treatment types, the increased surface energy is found to decay in a similar manner with increasing storage time after treatment.

https://link.springer.com/content/pdf/10.1023/A:1015274118642.pdf

Biaxially Oriented Polypropylene (BOPP) Surface Modification by Nitrogen Atmospheric Pressure Glow Discharge (APGD) and by Air Corona

We present experimental results of atmospheric pressure glow discharges (APGD) in a dielectric barrier discharge reactor. These are examined in different noble gases and in the N/sub 2//O/sub 2/ system (air and pure N/sub 2/), under varying experimental conditions (frequency f; gap length d; and electric field intensity E). Discharge diagnostics have been carried out using ultrahigh speed imaging, and synchronous dual-detection of light emission and current-voltage measurements, the former using a photomultiplier . The time evolutions of the discharges and of columnar patterns in regular geometric arrangements at atmospheric pressure under different experimental conditions are reported for all of the noble gases studied here. We present evidence that columnar patterns and APGD are manifestations of the same discharge physics, which is discussed with reference to recent work reported by others.

Diagnostics of dielectric barrier discharges in noble gases: atmospheric pressure glow and pseudoglow discharges and spatio-temporal patterns

We present an experimental and numerical modelling study of dielectric barrier discharges in pure, flowing helium at atmospheric pressure, in a 3.0 mm length needle-plane gap. Ultra-high speed imaging and synchronous, real-time dual detection (optical–electrical) diagnostics have been carried out. The high-voltage electrode was a hyperboloidal steel needle with a sharp point of 40 μm radius, while the grounded electrode was covered with 1.6 mm of Al2O3. The surface of the latter was either bare (case 1) or coated with ~20 nm of semiconducting graphite (case 2) or metallic aluminium (case 3), all at floating potential. Axial [z(t)] and radial [r(t)] time-evolutions (≤2 μs) of discharge propagation across the gap were found to depend very strongly upon surface charging or conduction (cases 1–3). A two-dimensional model of the needle-plane discharge, based on coupled solution of the continuity equations for electrons, ions and excited neutral particles and of Poisson's equation, was found to agree very well with the observed [r,z](t) behaviour.

https://iopscience.iop.org/article/10.1088/0022-3727/36/11/308/pdf

Dielectric barrier discharges in helium at atmospheric pressure: experiments and model in the needle-plane geometry

We present experimental results of 'atmospheric pressure glow discharges' in two different electrode configurations, plane–plane and cylinder–plane. Although many of the phenomena we report here have been observed in different noble gases, we restrict this presentation primarily to the case of helium. Discharge diagnostics have been carried out using ultra-high speed imaging, and synchronous detection of light emission and current–voltage measurements, the former using a photomultiplier. The discharge physics is discussed with reference to recent work reported by the present authors and others.

https://iopscience.iop.org/article/10.1088/0022-3727/38/4/005/pdf

I. Radu

Papers

Frequency and voltage dependence of glow and pseudoglow discharges in helium under atmospheric pressure

Biaxially Oriented Polypropylene (BOPP) Surface Modification by Nitrogen Atmospheric Pressure Glow Discharge (APGD) and by Air Corona

Diagnostics of dielectric barrier discharges in noble gases: atmospheric pressure glow and pseudoglow discharges and spatio-temporal patterns

Dielectric barrier discharges in helium at atmospheric pressure: experiments and model in the needle-plane geometry

Diagnostics and modelling of noble gas atmospheric pressure dielectric barrier discharges in homogeneous or diverging electric fields