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This paper deals with the ethanol (EtOH) removal in both dry and humid air fed dielectric barrier discharges. The experimental results were compared to the predictions of a zero dimension kinetic model to elucidate the main chemical routes occurring in the plasma phase. This comparison shows that both the dissociative quenching of the nitrogen metastables and the oxidation reactions by the oxygen atom or the hydroxyl radical should be taken into account to explain the EtOH abatement in these kinds of discharges. The CHCHOH radical seems to be the main product of the nitrogen dissociative collisions, whereas radicals issued from the α- and β-H atom cleavage are the dominant ethanol oxidation by-products. These radicals account for the production of acetaldehyde, the main by-product of the ethanol/air fed discharges investigated here. Apart the complete oxidation products, i.e. carbon oxides and water, aldehydes containing up to six carbon atoms, ketones, carboxylic acids, ozone, nitrogen oxides, nitric acid and organic nitrates were found in the exhaust gas. A kinetic pathway is proposed to explain the formation of the detected by-products. Water vapour addition to the feeding gas slightly improves the EtOH removal and promotes further oxidation of the main by-products, thus enhancing the CO selectivity. This behaviour could be ascribed to the higher amount of hydroxyl radicals, which could boost the production of the direct precursors of CO. [ABSTRACT FROM AUTHOR]

The removal of 500 ppm acetaldehyde in nitrogen at 1 bar is characterized in a pulse dielectric barrier discharge generating a spatial random distribution of plasma filaments. The identification and the quantification of numerous by-products are performed. At 20 °C, CHCHO is efficiently dissociated, probably owing to quenching of N metastable states. The most abundant by-products are CO, H, and CH, in consistency with the three important exit channels for the quenching of the N(AΣ) state by CHCHO proposed by Faider et al. (). In order of importance, other products are HCN, CH, CHCN, HNCO, CO, CHCOCH, CH, CHCN, NH, CH, and a group of nitriles and of ketones. An increase of the temperature from 20 °C up to 300 °C induces a strong decrease of the removal characteristic energy, but the by-products types remain unchanged. Probably the reaction of H with CHCHO plays a role in the removal of the molecule at 300 °C. [ABSTRACT FROM AUTHOR]

Combined experimental and modeling studies of acetylene oxidation in pulsed corona discharges working in the nanosecond regime are presented. The corona cell was characterized in term of power deposition to provide input data for the model. The concentrations of ozone, CO, CO2 and residual acetylene were systematically measured for model validation purposes. The model used allows describing the detailed chemistry in the discharge and the mass transfer between the microdischarges and the discharge free regions in the corona cell. Results showed that the model allows a satisfactory prediction of the acetylene residual fraction, CO and CO2 yields and O3 concentration for a wide range of conditions. They enabled a precise identification of the product distribution and confirmed the central role of O-atom in the oxidation process. They also revealed that ketene, H2CCO, plays an important role in the oxidation mechanism and allowed drawing some conclusions on the optimization of the oxidation process. [ABSTRACT FROM AUTHOR]

Toluene removal is investigated in filamentary plasmas produced in N2 and in N2/O2 mixtures by a pulse high voltage energised DBD. Influence of the oxygen percentage (lower than 10%) and of the temperature (lower than 350°C) is examined. Toluene is removed in N2 through collisions with electrons and nitrogen excited states. The removal efficiency is a few higher in N2/O2. It increases when the temperature increases for N2 and N2/O2. Both H- and O-atoms play an important role in toluene removal because H can readily recombine with O to form OH, which is much more reactive with toluene than O. H follows from dissociation of toluene and of hydrogenated by-products by electron collisions. Detection of cyanhidric acid, acetylene, formaldehyde, and methyl nitrate strengthens that dissociation processes, to produce H and CH3, must be taken into account in kinetic analysis. Formation and treatment of deposits are also analysed. [ABSTRACT FROM AUTHOR]

Abstract. The importance of pre-ionisation for the non-chain discharge-pumped HF laser is studied through experiments on an X-ray photo-triggered laser using mixtures of Ne, SF[sup 6], and ethane. The discharge dynamic in Ne/SF[sup 6] mixtures or pure SF[sup 6], as well as the stabilisation effect induced by C[sup 2]H[sup 6] and consequences for the laser performance, are investigated for pre-ionisation electron density values, n[sup eo], ranging from 10[sup 6] cm[sup -3] up to 10[sup 9] cm[sup -3], as well as for the so-called discharge self-breakdown mode. Without ethane, the minimum n[sup eo] value which is needed to complete 100% homogeneous charge deposition in the plasma is a very sharply increasing function of the SF[sup 6] pressure. This hinders performance optimisation when the molecule used to react with F-atoms, for instance H[sup 2], has no effect on the discharge dynamic. The minimum ethane partial pressure that is needed to stabilise the discharge depends on n[sup eo], the pumping pulse duration, the deposited electric charge, and the SF[sup 6] pressure. Discharges in Ne/SF[sup 6] can be much more efficiently stabilised by addition of a small amount of ethane than by an increase of n[sup eo]. A preionisation density as low as 10[sup 6] cm[sup -3] is sufficient to achieve the maximum laser energy value, but total suppression of the pre-ionisation has a detrimental effect on the active medium homogeneity. PACS: 42.55.K; 52.80 [ABSTRACT FROM AUTHOR]

Abstract. A detailed experimental study of an X-ray photo-triggered HF laser, with an active volume of 312 cm[sup 3], has been performed in Ne/SF[sub 6]/H[sub 2] and Ne/SF[sub 6]/C[sub 2]H[sub 6] mixtures. Parameters involved have been the storage line capacitance and the circuit inductance, the capacitors charging voltage, the RH-molecule type and partial pressure, and the X-ray dose for the preionization. High laser performance has been achieved with C[sub 2]H[sub 6]: an output energy up to 3 J corresponding to a specific energy of 9.6 J/1 at an efficiency of 4.7%, which strengthens the advantage of the photo-triggering technique to energize high-power HF lasers. However the optimum performance achieved with H[sub 2], 5.75 J/l and 3.5%, are lower. It is shown, through a time-resolved study of the electrical discharge and spatial dynamics correlated to laser power and energy measurements, that discharge instabilities are responsine for the poor laser performance of the mixture with H[sub 2]. These instabilities, which lead to are development, are characteristics of the discharge in Ne/SF[sub 6]. It is demonstrated for the first time that addition of a heavy hydrocarbon, such as C[sub 2]H[sub 6], to that mixture induces the discharge stabilization so that the laser emission arises in a homogeneous active medium. This effect allows us to achieve better laser performance than with H[sub 2]. [ABSTRACT FROM AUTHOR]

Study of the output power of a XeCl phototriggered laser at high energy loading has shown a multipulse operating mode. Above a critical value giving the maximum output energy, an increase of the applied electric field induces a dramatic decrease of the power emitted in the later peaks as well as the onset of a strong increase of the densities of various excited states, while such an increase is not observed for ionic states. Continuous-Wave (cw) laser-absorption spectroscopy is proved a very sensitive diagnostic tool to study the dynamics of these processes. [ABSTRACT FROM AUTHOR]