O. Eichwald

Coupling of chemical kinetics, gas dynamics, and charged particle kinetics models for the analysis of NO reduction from flue gases

A chemical kinetics model is developed to analyze the time evolution of the different main species involved in a flue gas initially stressed by a pulsed corona discharge at the atmospheric pressure and including N2, O2, H2O, and CO2 with a few ppm of NO. The present chemical kinetics model is coupled to a gas dynamics model used to analyze the radial expansion of the gas in the ionized channel created during the discharge phase. It is also meant to analyze the gas heating due to the Joule effect. This chemical kinetics model is also coupled to charged particle kinetics models based on a Boltzmann equation model to calculate the electron-molecule reaction coefficients in the flue gas and on a Monte Carlo code to estimate the energy and momentum transfer terms relative to ion-molecule collisions which are the input data for the gas dynamics model. It is shown, in particular, that the evolution of the radicals and the oxides is substantially affected by the gas temperature rise (from the initial value of 300...

Improved Monte Carlo method for ion transport in ion-molecule asymmetric systems at high electric fields

An improved Monte Carlo method is developed for the simulation of the ion transport in classical drift tube in the case of ion-molecule asymmetric systems such as O−/O2 or N+/N2. The aim of this new method is to overcome the problem of incident ions which vanish at relative high electric field due to asymmetric charge transfer or electron detachment. These ion removal processes are compensated by a fictitious ion creation which improves the accuracy of the ion distribution function and swarm coefficient calculations. The classical ion-molecule collision processes occurring in weakly ionized gases at room temperature (elastic collisions including energy exchange and thermal motion of background gases and also inelastic collisions) are taken into account. This new method is then validated and the transport and reaction coefficients have been given for a large range of E/N (a part of them for the first time in the literature) in O−/O2 and N+/N2 systems.

Ion swarm data for electrical discharge modeling in air and flue gas mixtures

The first step of this work is the determination of the elastic and inelastic ion-molecule collision cross sections for the main ions (N2+, O2+, CO2+, H2O+ and O−) usually present either in the air or flue gas discharges. The obtained cross section sets, given for ion kinetic energies not exceeding 100 eV, correspond to the interactions of each ion with its parent molecule (symmetric case) or nonparent molecule (asymmetric case). Then by using these different cross section sets, it is possible to obtain the ion swarm data for the different gas mixtures involving N2, CO2, H2O and O2 molecules whatever their relative proportions. These ion swarm data are obtained from an optimized Monte Carlo method well adapted for the ion transport in gas mixtures. This also allows us to clearly show that the classical linear approximations usually applied for the ion swarm data in mixtures such as Blanc’s law are far to be valid. Then, the ion swarm data are given in three cases of gas mixtures: a dry air (80% N2, 20% O2...

Chemical kinetics with electrical and gas dynamics modelization for NOx removal in an air corona discharge

A non-stationary reactive gas dynamics model in a mono-dimensional geometry, including radial mass diffusion, gas temperature variation and chemical kinetics, is developed in this paper. The aim is to analyse the spatio-temporal evolution of the main neutral species involved in a corona discharge used for NO pollution control in polluted air at atmospheric pressure and ambient temperature. The present reactive gas dynamics model takes into account 16 neutral chemical species (including certain metastable species) reacting following 110 selected chemical reactions. The initial concentration of each neutral species is obtained from a 1.5D electrical discharge model. The gas temperature variations are due to direct Joule heating during the discharge phase, and also result from the delayed heating due to the relaxation of the vibrational energy into a random thermal energy during the post-discharge phase. The simulation conditions are those of an existing experimental setup (anode voltage of 10 kV in the case of a point to plane geometry with an interelectrode distance of 10 mm). The obtained results show that the diffusion phenomena and the gas temperature rise affect quite well the gas reactivity and the neutral species evolution. This allows us to better understand the different reaction processes and transport phenomena affecting the NO concentration magnitude inside the discharge channel.

Electrical and spectroscopic analysis of mono- and multi-tip pulsed corona discharges in air at atmospheric pressure

This work is devoted to the analysis of experimental results obtained in dry air at atmospheric pressure in a positive point-to-plane corona discharge under a pulsed applied voltage in the cases of anodic mono- and multi-tips. In the mono-tip case, the peak corona current is analysed as a function of several experimental parameters such as magnitude, frequency and duration of pulsed voltage and gap distance. The variation of the corona discharge current is correlated with the ozone production. Then in the multi-tip case, the electrical behaviour is analysed as a function of the distance between two contiguous tips and the tip number in order to highlight the region of creation active species for the lowest dissipated power. Intensified charge-coupled device pictures and electric field calculations as a function of inter-tip distance are performed to analyse the mutual effect between two contiguous tips. The optical emission spectra are measured in the UV–visible–NIR wavelength range between 200 nm and 800 nm, in order to identify the main excited species formed in an air corona discharge such as the usual first and second positive systems with first negative systems of molecular nitrogen. The identification of atomic species (O triplet and N) and the quenching of NOγ emission bands are also emphasized.

Basic data for atmospheric pressure non-thermal plasma investigations in environmental and biomedical applications

The aim of this paper is to discuss some aspects of the optimization of the active species generated by corona or DBD discharges at atmospheric pressure which are very useful in the field of plasma environmental and biomedical applications. For such an optimization, this paper targets, in particular, the use of discharge modeling tools and the problem of accuracy of the required basic data. First of all, an overview on the different experimental diagnostics used for the characterization of these non-thermal plasmas is given followed by a short description of the different models (streamer dynamics, gas dynamics and chemical kinetics coupled with models of basic data calculation) required for complementing such experimental investigations. Then, emphasis is placed on the basic data of charged particles (electrons and ions) needed for streamer dynamics modeling and particularly on the necessity to use accurate and validated basic data in order to have a quantitative (not only qualitative) description of the phenomena and processes occurring in such discharges. An overview is given on the calculations and the fitting methods of collision cross sections and swarm coefficients of the data of charged particles and their validation using, in particular, pulsed Townsend measurements for experimental comparisons. Swarm coefficients are calculated from a multi-term solution of the Boltzmann equation or from Monte Carlo simulation. Some illustrative results are given in the case of the simulations of a dc positive point-to-plane corona discharge in air at atmospheric pressure. The effect of consideration of some basic data, particularly those of polyatomic ions, is shown on the discharge development and the radical production. (Some figures in this article are in colour only in the electronic version)

Drift and reactions of positive tetratomic ions in dry, atmospheric air: Their effects on the dynamics of primary and secondary streamers

The ion swarm data, namely, the reduced mobility, diffusion, and reaction rates of the positive tetratomic ions O4+ and N2O2+ in N2 and O2 have been determined from a Monte Carlo simulation using calculated and fitted elastic and inelastic cross sections. The elastic momentum transfer cross sections have been determined from a semiclassical Jeffreys-Wentzell-Kramers-Brilouin (JWKB) approximation based on a rigid core potential model well adapted for polyatomic ions. The inelastic cross sections have been approximated from considerations based on the N4+/O2 and N4+/N2 systems. The validated cross section sets in pure N2 and O2 have been used to determine the O4+ and N2O2+ swarm data in dry air over a large E/N range up to 1000 Td. However, due to the lack of experimental ion transport coefficients necessary for a more rigorous cross section validation, the present data, validated only at low E/N, should be regarded as a first approximation, susceptible to improvements as soon as measurements of ion transpo...

Basic data of polyatomic ion-molecule systems for flue gas discharge modelling

In the presence of an external electric field, ion transport coefficients (ion mobility and diffusion coefficients) are closely related to the ion-neutral interaction potential. A new generalized potential model, coupled to an optimized Monte Carlo technique, has been developed for the determination of the transport coefficients of polyatomic ions in weakly ionized gases. This corresponds to the polyatomic ion-molecule systems which can affect the electrical behaviour of the flue gas discharges used for the non-thermal plasma reactor for pollution control. The ion-molecule interaction has been described by a rigid core potential model which is adapted for both polar and non-polar systems and also symmetric and asymmetric systems. Momentum transfer cross sections are then determined using a semi-classical approach. The corresponding sets of cross sections including the dominant processes in our intermediate ion energy range (elastic and mainly charge transfer in certain cases) are used in the Monte Carlo code to calculate the ion transport coefficients over a wide range of reduced electric field E/N. These ion transport data fit quite well the drift tube measurements available in the literature for the CO2+/CO2 system, and also for certain weakly polar cases. The case of the H2O+/H2O system is then considered thus giving in this highly polar system the ion swarm data for the first time in the literature. Finally, we have considered with quite good reliability some asymmetric systems such as CO2+/N2 and N2+/CO2 whose ion data are also needed for flue gas discharge modelling.

Modeling and three-dimensional simulation of the neutral dynamics in an air discharge confined in a microcavity. I. Formation and free expansion of the pressure waves

A three-dimensional numerical analysis of the neutral dynamics is performed in the case of a short-gap (0.5 mm) spark discharge in air confined in microcavities at atmospheric pressure (760 Torr) and ambient temperature (293 K). This work is undertaken in the framework of silicon microsystems bearing a micropump actuated by pressure waves which result from a discharge. The short-gap discharge characteristics are taken from experimental results namely 470 ns for the duration and 13.5 W for the maximum injected power. The neutral gas evolution is described by the classical transport equations and solved by a powerful numerical monotonic upstream-centered scheme for conversion laws. The gas–solid interaction occurring in thermal and hydrodynamic boundary layers is taken into account assuming that the microcavity temperature remains invariant (293 K). This article (part I) is devoted to the first evolution phase of the neutral dynamics whose the duration corresponds to the discharge time. Our results clearly ...

Modeling neutral dynamics in pulsed helium short‐gap spark discharges

A numerical analysis of the neutral dynamics is performed in the case of helium short‐gap spark discharges to show the energy memory effect of recurring discharges. The millimetric (4 mm) and submillimetric (0.3 mm) discharges are studied at atmospheric pressure and ambient temperature (293 K). This corresponds to a neutral density of 2.5×1025 m−3. The maximum injected power is either 50 or 3 W with a duration of 1 μs, the relaxation time between the two successive injections is 5 μs. The evolution of the neutral gas is described with the classical transport equations written in a two‐dimensional cylindrical geometry with plane electrodes and solved with powerful numerical schemes. The effect of the discharge on the neutral gas is represented by energy and momentum transfers. The neutral gas is no longer considered as an infinite sink dissipating the energy of the electrons and ions acquired from the field. It is shown that the energy and momentum transfer effects initiate and control the variations of te...