Guillaume Vanhove

Time-resolved electric field measurements in nanosecond surface dielectric discharge. Comparison of different polarities. Ignition of combustible mixtures by surface discharge in a rapid compression machine.

Surface nanosecond dielectric barrier discharge has been studied in air and at pressures ranging from 1 to 5 bar, with a coaxial geometry of the electrodes for positive and negative polarities of the high-voltage pulses. Pulses of a 24–55 kV amplitude on the electrode, positive or negative polarity, 20 ns duration, 0.5 ns rise time and 10 Hz repetitive frequency were used to initiate the discharge. ICCD images of the discharge development have been taken with a 2 ns gate. In the case of discharges in nitrogen, the emissions of molecular bands of the first negative and second positive systems of molecular nitrogen have been measured, and the dependence of their ratio versus pressure and distance from the highvoltage electrode has been analyzed. A comparison of the discharge development has been made in the case of negative and positive polarities at the high-voltage electrode. Ignition delay times under the action of a high-voltage nanosecond discharge have been studied and compared with autoignition delays in a rapid compression machine (RCM). The nanosecond Surface Dielectric Barrier Discharge (SDBD) was initiated in a quasi-uniform radial geometry in the proximity of the end plate of the combustion chamber of the RCM. Experiments were performed for methane and n-butane containing mixtures diluted by Ar or N2 for temperatures and pressures at the end of compression respectively ranging from 650 to 1000 K and 6 to 16 bar. A significant decrease of the ignition delay time is observed, when compared to autoignition experiments. The possibility to ignite lean mixtures is demonstrated. Preliminary experiments in the region of negative temperature coefficient for stoichiometric n–butane:oxygen mixture diluted with argon, are performed. The threshold voltage for plasma ignition, over which the ignition delay is decreased, is studied for different mixtures.

Characterization of Aqueous and Solid Inclusion Complexes of Diuron and Isoproturon with β-Cyclodextrin

The interaction of diuron and isoproturon herbicides with β-cyclodextrin is conducive to the formation of inclusion compounds in aqueous solution as well as in the solid state. The physico-chemical study of these complexes was carried out by various analytical techniques such as ultraviolet (UV), Fourier transform infrared (FT-IR), Raman, X-ray diffraction, and 1H-NMR (nuclear magnetic resonance) spectroscopies. The existence of inclusion complexes in water solution between the β-cyclodextrin and each of the herbicides was revealed by electronic absorption and 1H-NMR spectroscopies. A 1:1 stoichiometry was determined for both complexes in aqueous medium from UV absorption spectra by using the Benesi–Hildebrand method; the relative stability constants at room temperature were calculated at 2700 ± 300 L mol−1 and 750 ± 50 L mol−1 for isoproturon and diuron, respectively. In the solid state, inclusion processes with β-cyclodextrin were characterized by means of infrared and Raman techniques and confirmed by X-ray diffraction spectra.

Energy balance in surface nanosecond dielectric barrier discharge. Plasma-assisted ignition of heavy hydrocarbons at high pressures

The paper presents experimental study of nanosecond surface dielectric barrier discharge (nSDBD) in air and application of nSDBD for initiation of the two-stage ignition of n–heptane in mixture with air. The emission spectroscopy study of rotational and vibrational structure of 2 system of N2 molecules has been performed for a classical air flow control SDBD configuration. The energy deposition into the discharge has been measured. Strongly non–equilibrium distribution of rotational population is observed in the spectra at the leading and trailing edges of the high–voltage pulse. The time resolved spatial distribution of the rotational temperature along the dielectric surface has been measured. The second part of the paper concerns the ignition of stoichiometric mixture of C7H16/O2/N2 with nanosecond SDBD in Rapid Compression Machine (RCM). Different regimes of ignition initiated by discharge are discussed, including cool flame and fast ignition.