B. G. Cheron

Collisional-radiative model in air for earth re-entry problems

A nonlinear time-dependent two-temperature collisional-radiative model for air plasma has been developed for pressures between 1kPa and atmospheric pressure to be applied to the flow conditions of space vehicle re-entry into the Earth’s atmosphere. The model consists of 13 species: N2, O2, N, O, NO, N2+, O2+, N+, O+, NO+, O2−, O− in their ground state and major electronic excited states and of electrons. Many elementary processes are considered given the temperatures involved (up to 10 000K). Time scales to reach the final nonequilibrium or equilibrium steady states are derived. Then we apply our model to two typical re-entry situations and show that O2− and O− play an important role during the ionization phase. Finally, a comparison with existing reduced kinetic mechanisms puts forward significant discrepancies for high velocity flows when the flow is in chemical nonequilibrium and smaller discrepancies when the flow is close to chemical equilibrium. This comparison illustrates the interest of using a ti...

Decomposition of toluene in a gliding arc discharge plasma reactor

The decomposition of toluene in a gliding arc discharge (glidarc) was performed and studied. Experimental results indicate that the glidarc technology can effectively decompose toluene molecules and has bright prospects of being applied as an alternative tool to decompose volatile organic compounds. It is found that a change in the electrode material had an insignificant effect on the toluene removal efficiency. The toluene removal efficiency increases with increasing inlet gas temperature. The water vapor present in the gas mixture has a favorable effect on the toluene decomposition in the plasma. The energy efficiency is 29.46 g (kWh−1) at a relative humidity of 50% and a specific energy input of 0.26 kWh m−3, which is higher than other types of non-thermal plasmas. Too much or too little oxygen content does not favor toluene decomposition. The major gas phase products detected by FT-IR from the decomposition of toluene with air participation were CO, CO2, H2O and NO2. Some brown depositions were found on the surface of the electrodes, which were polar oxygenous and nitrogenous compounds determined by the GC-MS analysis, such as benzaldehyde, benzoic acid, quinine and nitrophenol from the reaction of toluene with radicals. A possible mechanism for toluene destruction via glidarc technology is proposed and summarized.

Plasma Vitrification of Air Pollution Control Residues From Municipal Solid-Waste Incineration

In the frame of studies devoted to hazardous waste destruction, a specially designed plasma torch with a doubleanode configuration has been developed and tested. It produces an elongated, weak-fluctuation, and reproducible plasma jet at atmospheric pressure. A calcium-rich air pollution control residue from a mechanical-grate municipal solid-waste incinerator is vitrified by this plasma arc technology. The produced slag shows a homogeneous, dense, and amorphous glassy structure, as confirmed by scanning electron microscopy and X-ray diffraction. Leaching results show that excellent immobilization of heavy metals in the silicate matrix can be achieved. Plasma vitrification also ensures high elimination efficiency (> 99.9%) of dioxins and furans. These results indicate that the slag produced has great potential for construction or geotechnical applications.

Heat flux characteristics in an atmospheric double arc argon plasma jet

In this study, the axial evolution of heat flux excited by a double arc argon plasma jet impinging on a flat plate is determined, while the nonstationary behavior of the heat flux is investigated by combined means of the fast Fourier transform, Wigner distribution, and short-time Fourier transform. Two frequency groups (<1 and 2–10 kHz) are identified in both the Fourier spectrum and the time-frequency distributions, which suggest that the nature of fluctuations in the heat flux is strongly associated with the dynamic behavior of the plasma arc and the engulfment of ambient air into different plasma jet regions.

The nature of fluctuations in a double arc argon-nitrogen plasma jet

The dynamic behavior of the double arc argon-nitrogen plasma jet is investigated by combined means of the fast Fourier transform, correlation function, and Wigner distribution. The restrike mode is identified as the fluctuation behavior in an argon-nitrogen plasma jet. The Fourier spectra exhibit two characteristic frequencies of 150Hz and 4.1kHz, which indicates that the nature of fluctuations in the double arc argon-nitrogen plasma can be ascribed to the power supply undulation and both arc roots motion on the anode channels. It is further found that the double anode torch could inhibit and reduce the restrike phenomenon.

Experimental Study of a Double Arc Nitrogen Plasma: Static and Dynamic Behavior

In the frame of studies devoted to the reentry simulations, we have devised and tested an original double arc plasma torch which provides a long-time and highly stable low-pressure supersonic nitrogen plasma jet. The arcs are investigated at both anode levels by means of spectroscopic diagnostics. They are not attached on the anode walls at single and local roots as it is generally the case at atmospheric pressure. In the first arc chamber, the plasma is totally dissociated and ionized, and the measured electron density and temperature are close to those derived from a local-thermal-equilibrium calculation. The electron density and temperature are also measured within the second arc chamber and at the torch exit where the plasma flow is abruptly released. The results allow to examine the validity of the thermodynamic equilibrium criteria in nonstandard conditions as those encountered in the arc chamber plasma. In the purpose of estimating both plasma jet specific enthalpy and torch energetic efficiency, Mach number measurements are also performed on the jet axis by using a pitot probe and they are compared to fluent numerical simulation results. The dynamic behavior of the plasma is analyzed by means of classical tools such as fast Fourier transform, correlation functions and Wigner distribution. The temporal series exhibit two main characteristic frequencies: At low frequency, the electric generators yield very stable and reproducible 150-Hz oscillations, whereas the firing of the second arc gives birth to a sharp 6.7-kHz peak which is ascribed to the generation of acoustic waves in the region of the first anode attachment. The value of this frequency that depends neither on the supplied power nor on the mass flow rate is interpreted by assuming that the arc chamber acts as a Helmholtz oscillator

Temporal description of aluminum laser-induced plasmas by means of a collisional-radiative model

A 0D numerical approach including a Collisional-Radiative model is elaborated in the purpose of describing the behavior of the nascent plasma resulting from the interaction between a laser pulse (λ = 532 nm, τ = 4 ns and F = 6.5 J cm−2) with an aluminum sample. The species considered are Al, Al+, Al2+ and Al3+ on their different excited states and free electrons. Both groups of particles are characterized by their translation temperature in thermal non-equilibrium state. Besides, each population density is assumed to be in chemical non-equilibrium and behaves freely through the seven involved elementary processes (electron impact induced excitation and ionization, elastic collisions, multi-photon ionization, inverse laser Bremsstrahlung, direct electron Bremsstrahlung and spontaneous emission). Atoms passing from sample to gas phase are described by considering classical vaporization phenomena so that the surface temperature is limited to values less than the critical point. The relative role of the elementary processes is discussed and the time-evolution of the excitation of the species is analyzed.

Vitrification of MSWI Fly Ash Using Thermal Plasma Technology

In China, municipal solid waste incinerator (MSWI) fly ash is classified as hazardous waste owing to its high concentration of leachable heavy metals and the presence of chlorinated organic compounds, such as dioxins and furans. In this study, the vitrification process based on thermal plasma technology has been employed to convert toxic incinerator fly ashes into harmless stable products. The toxicity characteristic leaching procedure (TCLP) test has been performed to evaluate the chemical resistance of the vitrified slag. The amount of heavy metals leached is much lower compared with the regulatory limit, which reveals that the contaminants are sufficiently immobilized in the silicate matrix and the produced slag satisfies the environmental standards. The microstructure, crystalline phase, as well as the density and porosity of the glass slag are also investigated. Such vitrified product with good quality has great potential to be used as a viable alternative for construction applications. These promising results indicate that thermal plasma vitrification process is very effective and reliable for stabilization, detoxification and recycling of MSWI fly ashes.

Role of molecular ions in plasmas of atmospheric and energetic interest

Molecular ions often play a very important role in plasmas. The electron energy distribution function (eedf) and density (ne) are influenced by the reactions of molecular ions with electrons. We bring these aspects into focus by studying successively the following situations: We show that the dissociative recombination of Ar+2 allows to understand the measured characteristics of an argon supersonic plasma flow where the electron density is low. Afterwards, we show the dominating role of NO+ in the chemistry of a space vehicle atmospheric re-entry air plasma. Finally, by using the Boltzmann equation in order to show the influence of molecular ions such as NO+ in air plasmas on the eedf, we comment on the common assumption of Maxwell-Boltzmann equilibrium for this distribution.