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In this paper we investigate temperature and pressure effects on the properties of a positive pulsed streamer plasma. We use a corona plasma setup in which we vary the temperature between 303 and 773K at atmospheric pressure and the pressure between 37.9 and 100 kPa at room temperature to achieve the same neutral gas density and compare electrical and optical (ICCD imaging) measurements carried out in both experiments. From the measurements we found that the dissipated plasma energy and the average streamer propagation velocity are both higher for the temperature experiments at the same neutral gas densities as in the pressure experiments. This suggests the existence of a specific temperature effect. A possible explanation for this effect is a higher streamer conductivity at high temperatures, as was previously found in the literature. [ABSTRACT FROM AUTHOR]

Although removal of NOx by (pulsed) corona discharges has been thoroughly investigated for high concentrations of NOx in flue gas, removal of low levels in ambient air proves to be a difficult task. (Sub) ppm NOx levels exist in traffic tunnels due to accumulation of exhaust gases. The application of pulsed corona technology for purification of traffic tunnel air is studied during a series of lab and field experiments. An industrial pilot scale wire-cylinder type corona reactor has been utilized. Lab tests have been carried out using a diesel generator as NOx source. NOx conversion levels have been determined by applying two Recordum Airpointers (chemiluminescence-based detection). The detector appeared to be cross-sensitive for HNO3 and high levels of O3. NOx removal rates of 60-80% were obtained for inlet levels of 2-10 ppm. The SIE value of 10 ppm NOx removal is 7 J l-1. The corona discharges produce ppm level NOx at high energy densities. This intrinsic NOx production limits removal of inlet levels due to equilibrium between production and oxidation. [ABSTRACT FROM AUTHOR]

The oxidative degradation of two volatile organic compounds, i.e. toluene (fossil fuel based VOC) and limonene (biogenic VOC), has been studied. A hybrid pulsed power corona reactor with adjustable energy density has been utilized for degradation of ppm level target compounds in large air flows. The observed oxidation product range features an energy density-dependent spectrum of oxygen-functional hydrocarbons, which has been qualitatively discussed on the basis of literature studies. Typically, observed stable oxidation products for both target compounds are the biocompatible carboxylic acids acetic and formic acid. Measured degradation G-values are 23 nmol J-1 at 74% conversion of 70 ppm toluene and 181 nmol J-1 at 81% conversion of 10 ppm limonene [ABSTRACT FROM AUTHOR]

Pulsed corona-induced partial oxidation of methane in humid oxygen or carbon dioxide atmospheres has been investigated for future fuel synthesis applications. The obtained product spectrum is wide, i.e. saturated, unsaturated and oxygen-functional hydrocarbons. The generally observed methane conversion levels are 6–20% at a conversion efficiency of about 100–250 nmol J−1. The main products are ethane, ethylene and acetylene. Higher saturated hydrocarbons up to C6 have been detected. The observed oxygen-functional hydrocarbons are methanol, ethanol and lower concentrations of aldehydes, ketones, dimethylether and methylformate. Methanol seems to be exclusively produced with CH4/O2 mixtures at a maximum production efficiency of 0.35 nmol J−1. CH4/CO2 mixtures appear to yield higher hydrocarbons. Carboxylic acids appear to be mainly present in the aqueous reactor phase, possibly together with higher molecular weight species. [ABSTRACT FROM AUTHOR]

X-ray emission has been detected occasionally during the streamer-corona propagation in a wire-plate corona reactor open to ambient air. A 65 kV pulse with 15 ns rise time is applied to the wire anode superimposed on a 20 kV dc bias. The duration of the driving voltage pulse (110 ns) is less than 2.5 times the primary streamer transit time. Under this condition no arc discharge occurs between the wire and the cathode plates separated by 6 cm air. The onset of x-ray emission coincides with the initiation of the primary streamers near the wire anode. No x-rays were detected later, during or after the primary or secondary streamer development. X-ray energies ranged between 10 and 42 keV, as detected by a LaBr3 (Ce) scintillator-photomultiplier combination. Time resolved imaging of the streamer propagation highlights the different stages in the streamer discharge process. The energetic electrons originate near the anode, at the moment of streamer initialization. [ABSTRACT FROM AUTHOR]