Direct heating mechanism of a CO 2 –N 2 –He laser mixture in a nonself-sustained discharge

The results of the calculations of electron transport and rate coefficients in oxidized methane:O 2, propane:O 2 and H 2 :O 2 mixtures were presented for different temperatures and reduced electric fields E/N from 1 to 3×10 3 Td. The calculations were made for various oxidized fuel fractions. It was shown that fuel oxidation led to a drastic decrease in the average electron energy, electron drift velocity and attachment coefficient for E/N<60 Td. At higher reduced electric fields, the effect of fuel oxidation on the average electron energy and electron drift velocity was small, whereas the attachment coefficient increased with increasing oxidation degree. In addition, in the hydrocarbon-containing mixtures for E/N∼30 Td, the electron drift velocity varied nonmonotonously with the oxidation degree increase. The critical reduced electric field at which the average rate of electron production in the mixture was equal to the average attachment rate increased with fuel oxidation due to the increased attachment rate and decreased detachment rate. The effect of intermediate species on the electron transport and rate properties in partially oxidized mixtures was small. The calculated results were used to self-consistently simulate fuel oxidation and plasma characteristics for high-voltage nanosecond repetitive discharges in combustible mixtures. Zero-dimensional simulation in a H 2 :O 2 mixture showed that the reduced electric field at the instant when the deposited energy peaked was close to the critical values of E/N and increased with increasing oxidized fuel fraction.

Section: Simulation Modelmentioning

confidence: 99%

The effect of fuel oxidation on electron swarm properties and nanosecond discharge characteristics in combustible mixtures

Кочетов

Aleksandrov

2018

“…The calculation results in this figure are obtained for T g = 77, 300 K, adopting the discrete rotational collision operator with the cross sections of Gerjuoy and Stein or of Oksyuk and they definitely confirm the dominance of rotational collisions in the transfer of energy for E/N below a few Td. As anticipated from figure 1(a), the Oksyuk cross sections lead to much higher rotational energy losses above 0.1 Td (and consequently to a lower energy transfer in vibrational and elastic collisions), which can be relevant to properly account for gas heating due to vibrational-translation collisions [70]. Therefore, in the region of 0.2-3 Td the Gerjuoy and Stein cross sections, extended above the theoretical limit of ∼0.6 eV as done here, might fail to predict the correct transfer of electron energy to the rotational channel.…”

Section: Resultsmentioning

confidence: 64%

The role of rotational mechanisms in electron swarm parameters at low reduced electric field in N₂, O₂and H₂

Ridenti

Alves

Guerra

et al. 2015

The homogeneous Boltzmann equation for electrons in N 2 , O 2 and H 2 is solved under the classical two-term approximation, for reduced electric fields in the interval 10 − 4 −10 Td where the electron-neutral encounters are limited to elastic, rotational and vibrational collisions. Rotational excitations/de-excitations are described using the following three different approaches: the discrete inelastic/superelastic collisional operator, written for a number of rotational levels that depends on the molecular gas and the specific rotational cross sections considered; the continuous approximation for rotations; a modified version of the continuous approximation for rotations, including a Chapman-Cowling corrective term proportional to the gas temperature. The expression of the rotational collision operator for this latter approach is deduced here and the results show that it bridges the gap between the discrete and the continuous descriptions at low/intermediate reduced electric fields. The calculations are compared with the measurements for the available swarm parameters to assess the validity of the different approaches and cross sections adopted to describe the rotational mechanisms.

“…Thus, at low values of E/N the gas heating rate was controlled by an electron energy loss in elastic collisions and in the excitation of molecular rotation. In the paper [32] theoretical calculations of the swarm data were performed taking as a starting point the shape of the rotation excitation cross sections from theoretical paper [33]. Figure 2 compares the results of calculations [32] with the experimentally measured fraction of discharge power going to fast gas heating.…”

Section: Relations Between Swarm Experiments and Plasma Modelingmentioning

confidence: 99%

“…In the paper [32] theoretical calculations of the swarm data were performed taking as a starting point the shape of the rotation excitation cross sections from theoretical paper [33]. Figure 2 compares the results of calculations [32] with the experimentally measured fraction of discharge power going to fast gas heating. For comparison, the same fraction is shown calculated for the case when rotational excitation is neglected.…”

Section: Relations Between Swarm Experiments and Plasma Modelingmentioning

confidence: 99%

See 1 more Smart Citation

The value of swarm data for practical modeling of plasma devices

Napartovich¹,

Кочетов²

2011

The non-thermal plasma is a key component in gas lasers, waste gas cleaners, ozone generators, plasma igniters, flame holders, flow control in high-speed aerodynamics and other applications. The specific feature of the non-thermal plasma is its high sensitivity to variations in governing parameters (gas composition, pressure, pulse duration, E/N parameter). The reactivity of the plasma is due to the appearance of atoms and chemical radicals. For the efficient production of chemically active species high average electron energy is required, which is controlled by the balance of gain from the electric field and loss in inelastic collisions. In low-ionized plasma the electron energy distribution function is far from Maxwellian and must be found numerically for specified conditions. Numerical modeling of processes in plasma technologies requires vast databases on electron scattering cross sections to be available. The only reliable criterion for evaluations of validity of a set of cross sections for a particular species is a correct prediction of electron transport and kinetic coefficients measured in swarm experiments. This criterion is used traditionally to improve experimentally measured cross sections, as was suggested earlier by Phelps. The set of cross sections subjected to this procedure is called a self-consistent set. Nowadays, such reliable self-consistent sets are known for many species. Problems encountered in implementation of the fitting procedure and examples of its successful applications are described in the paper.