Mohamed Amine Boumehdi

A novel experimental scheme to study the ignition of combustible mixtures at high pressures under the action of a high-voltage nanosecond discharge has been developed. The experiments were performed in the combustion chamber of a Rapid Compression Machine (RCM) with a specially designed system of electrodes. A nanosecond surface dielectric barrier discharge (SDBD) provided two-dimensional low-temperature non-equilibrium plasma in the vicinity of the end plate of the combustion chamber. Radially symmetric plasma channels triggered multi-point ignition of gas mixtures at controlled pressure and temperature. Ignition delay times and energies deposited in the gaseous mixtures by the discharge were measured for different parameters of high voltage pulse, for positive or negative high-voltage pulses. The propagation of the subsequent flame in the combustion chamber was recorded with the help of high repetition rate imaging. Preliminary numerical analysis of the ignition under the action of a pulsed nanosecond discharge has been made; it was shown that production of atomic oxygen by the discharge, will modify the ignition chemistry by perturbation of the radical pool. Experiments and calculations were performed in methane–oxygen and n-butane–oxygen mixtures with equivalence ratios between 0.3 and 1 diluted by 70–76% of Ar or nitrogen for temperatures between 600 and 1000 K and pressures between 6 and 16 bar.

http://www.sciencedirect.com/science/article/pii/S0010218014003484

04 avr. 2015

The chemistry associated with low-temperature oxidation and ignition of tetrahydrofuran (THF) has been probed through experimental work in two distinct devices: a rapid compression machine (RCM) and a jet-stirred reactor (JSR). Ignition delays of stoichiometric THF/O2/inert mixtures have been measured for pressures ranging from 0.5 to 1.0 MPa and core gas temperatures from 640 to 900 K. Two-stage ignition is visible up to 810 K, and the evolution of the ignition delay with the temperature shows a clear deviation from Arrhenius behavior between 680 and 750 K. Sampling of the reactive mixture during the ignition delay provided evidence of the formation of C1–C4 aldehydes and alkenes, a variety of oxygenated heterocycles, including oxirane, methyloxirane, oxetane, furan, both isomers of dihydrofuran, and 1,4-dioxene, as well as cyclopropanecarboxaldehyde and formic acid-2-propenyl ester. JSR experiments have been performed under pressure close to 1 atm, at temperatures from 500 to 1000 K, and at equivalence ratios from 0.5 to 2, with detailed analysis of the low-temperature intermediate products. Major products include carbon monoxide, carbon dioxide, C1–C2 hydrocarbons, and aldehydes, 1-butene, ethylene oxide, methylvinylether, acrolein, propanal, both isomers of dihydrofuran, furan, 2-butenal, cyclopropanecarboxaldehyde, 1,4-dioxene, and unsaturated dihydrofuranols. The obtained mole fraction profiles indicate a significant low-temperature reactivity of THF beginning at temperatures around 550 K, with a marked negative temperature coefficient zone. The results from both experimental devices are put in perspective and allow for the identification of the major formation pathways of the observed species.

http://pubs.acs.org/doi/abs/10.1021/acs.energyfuels.5b01057

26 juil. 2015

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.

http://arc.aiaa.org/doi/abs/10.2514/6.2015-0668

03 janv. 2015

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) of Lille University. 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:oxygen and n-butane: oxygen 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. Decrease of the ignition delay time is observed, when compared to autoignition experiments: instead of tens and hundreds of milliseconds, a few milliseconds are registered between the discharge initiation and sharp pressure increase in the combustion chamber.
Experiments with lean CH4:O2:Ar mixtures with different stoichiometry demonstrate that the observed ignition delay is a function of stoichiometry, that is that, at initial pressures 8

http://arc.aiaa.org/doi/abs/10.2514/6.2014-0665

03 janv. 2014

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 molecularbands 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 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.

http://arc.aiaa.org/doi/abs/10.2514/6.2013-1053

03 janv. 2013