Atmospheric pressure plasma diagnostics by OES, CRDS and TALIF

Abstract

Nanosecond repetitively pulsed (NRP) discharges were used to generate atmospheric pressure plasmas in air or nitrogen preheated at 1000 K. In order to understand the physico-chemical mechanisms that control the number densities of active species, in situ optical diagnostic techniques were developed. The ground state of atomic oxygen was measured by two-photon absorption laser induced fluorescence (TALIF), the density of N2(A) was measured by cavity ring down spectroscopy (CRDS) and the densities of N2(B) and N2(C) were measured by optical emission spectroscopy (OES). Temporally and spatially resolved density measurements were performed in the main operating regimes of the NRP discharge, namely the diffuse and filamentary regimes. The diagnostic techniques and associated challenges are presented and the effects of these discharges on the chemistry are discussed.

Dynamic and hydrodynamic response of premixed methane-air flame to nanosecond pulsed discharges

“…Then, excited N 2 molecules are quenched by oxygen molecules, producing atomic oxygen radicals and heat release in the afterglow. In previously studies, the two-step process mechanism was verified by the experimental observation of the ultrafast production of O atom [15] and the measured high rotational temperature of N 2 with the assumption that the rotational and translational modes of N 2 are equilibrated at all times [16]. More plenty of transient information about the process and direct evidences to further confirm the ultrafast heating are needed in order to prove or supply the mechanism and to understand the nonequilibrium process of NPD.…”

Comprendre la CRDS pulsée

“…Il est important de noter que la longueur d'absorbance n'est pas nécessairement égale à la distance entre les miroirs d. La méthode ne nécessite pas de connaître les coefficients de réflexion des miroirs. Lors des études en flamme ou dans les plasmas, le milieu réactif est placé au centre de la cavité optique [3,4], comme le montre la figure 2.…”

Plasma-Assisted Ignition and Combustion

“…That is why some authors prefer to use controlled inhomogeneous excitation instead. For example, in papers [Bak et al, 2011;Stancu et al, 2010;Grisch et al, 2009;Wu et al, , 2011 the point-to-point electrodes geometry was used. This geometry generates non-uniform streamer-like discharge but because of its high reproducibility allows to reconstruct the spatial distribution of excitation and kinetics in plasma.…”

“…OH and CH PLIF experiments were performed to confirm the large OH and CH streamer-induced production over the discharge volume. Papers [Bak et al, 2011;Stancu et al, 2010] discuss an important question on the channels of molecular oxygen dissociation in pulsed discharges. In [Bak et al, 2011] time-resolved emission measurements for N 2 (C-B) and N 2 (B-A) transitions were carried out in nanosecond pulsed discharges in air and pure nitrogen.…”

“…The dissociative quenching was found to be responsible for 82 % of O production whereas the electron-impact dissociation was ~5%. Papers [Pai et al, 2009, Stancu et al, 2010 reports the results of investigations of nanosecond repetitively pulsed discharge in atmospheric pressure discharge in air or nitrogen preheated at 1000 K. The ground state of atomic oxygen was measured by two-photon absorption laser induced fluorescence, the density of N 2 (A) was measured by cavity ring down spectroscopy and the densities of N 2 (B) and N 2 (C) were measured by optical emission spectroscopy. Measurements of O, N 2 (B) and N 2 (C) densities have confirmed that the formation of atomic oxygen occurs through the fast two-step mechanism through excitation and quenching of nitrogen triplet states [Stancu et al, 2009].…”