Christophe O Laux

CentraleSupélec | ECP · Department of Energetics

We present quantitative schlieren measurements and numerical analyses of the thermal and hydrodynamic effects of a nanosecond repetitively pulsed (NRP) discharge in atmospheric pressure air at 300 and 1000 K. The plasma is created by voltage pulses at an amplitude of 10 kV and a duration of 10 ns, applied at a frequency of 1–10 kHz between two pin...

A detailed experimental investigation of the mechanism of ultrafast heating and oxygen dissociation produced by nanosecond repetitively pulsed discharges in atmospheric pressure air preheated at 1000 K is presented. The ultrafast mechanism creates excited electronic states of nitrogen, which then dissociate molecular oxygen through quenching reacti...

We report on an experimental study of a Nanosecond Repetitively Pulsed (NRP) discharge in atmospheric pressure water vapor at 450 K. The discharge is created by voltage pulses of amplitude 0 - 15 kV, duration 10 ns, applied at a frequency of 10 kHz between two pin electrodes. The electrical energy of each pulse ranges from 1 to 10 mJ. Gas chromatog...

Direct current (DC) electric arcs are of particular interest because they can produce large volumes of thermal plasmas with controlled energy deposition. When such discharges are applied in a gas flow, convection displaces the top of the arc downstream while the arc roots remain attached to the electrodes, thus increasing the length of the arc over...

A key challenge in the use of hydrogen in practical combustors is to stabilize the flame at equivalence ratios closeand even below the LBO limit. Plasma-Assisted Combustion (PAC) has been shown to improve the ignition,stabilization, and blowout margins of combustion systems for a great variety of fuels. In this work, NanosecondRepetitively Pulsed (...

This paper presents an experimental study of lean flames stabilization with nanosecond repetitively pulsed discharges. The two-stage, swirled-stabilized, multipoint injector BIMER operates at atmospheric pressure with methane-air mixtures in the present study. It is representative in its design of a realistic lean premixed prevaporized injector of...

We investigate the conversion of CO2 into CO and O2 with nanosecond repetitively pulsed discharges (NRP) in a high-pressure batch reactor. Stable discharges are obtained at up to 12 bar. By-products are measured with gas chromatography. The energy efficiency is determined for a range of processing times, pulse energy, and fill pressures. It is only...

This paper presents an experimental study of lean flames stabilization with nanosecond repetitively pulsed discharges. The two-stage, swirled-stabilized, multipoint injector BIMER operates at atmospheric pressure with methane-air mixtures in the present study. It is representative in its design of a realistic lean premixed prevaporized injector of...

Optical Emission Spectroscopy (OES) has been frequently used to measure the rotational temperature of a plasma. The technique is relatively simple to implement and non-intrusive. However, in the visible and ultraviolet spectral regions, it relies on emission from excited vibronic states whose rotational and vibrational temperatures might not be equ...

Measurements of high-temperature air emission spectra between 150 and 250 nm (VUV/UV) are presented. These measurements are calibrated in absolute intensity. The high-temperature air was produced using an atmospheric pressure plasma torch facility. The centerline temperature of the plasma jet is approximately 6700 K. A VUV emission spectroscopy sys...

This experimental and numerical study is focused on the formation of fully ionized plasmas in ambient air by nanosecond pulsed discharges, namely the thermal spark. The first contribution of this article is the experimental charaterization of the electron number density during the pulse. The increase of the electron number density from 10 ¹⁶ to 10...

The efficiency of the conversion of CO$_2$ into CO with nanosecond repetitively pulsed discharges (NRP) is investigated in a high pressure batch reactor. Stable discharges are obtained at up to 12~bar. By-products of CO$_2$ splitting are measured with gas chromatography. The energy efficiency is determined for a range of processing times, pulse ene...

Plasma technologies are considered a promising solution to answer challenges in combustion including the ignition and stabilization of lean flames, the control of thermoacoustic instabilities, the reduction of pollutant emissions, or the development of CO2-free combustion chambers with hydrogen or ammonia. In this article, we present an overview...

Multi-temperature models are often used as a simplified way to describe nonequilibrium gases. These models assume Boltzmann distributions within each energy mode, which is useful for reducing the number of parameters in computations. This assumption requires that the energy modes are properly separated (which is valid, for instance, for vibration a...

The prediction of a flame response to plasma assistance requires extensive knowledge of discharge-induced plasma kinetics. Detailed studies of nanosecond discharges are common in N 2 /O 2 and fresh combustible mixtures but are still lacking in burnt gases. To fill this gap, we define a combustion reference test case and investigate the effects of N...

This work presents a femtosecond two-photon absorption laser-induced fluorescence (fs-TALIF) diagnostic for measuring ground-state atomic nitrogen in nanosecond repetitively pulsed (NRP) discharges. Absolute atom density is obtained from the TALIF signal via a novel calibration technique based on one-photon direct absorption measurements performed...

View Video Presentation: https://doi.org/10.2514/6.2022-0831.vid Plasma-assisted combustion (PAC) is a promising technology that could lead to a breakthrough in propulsion systems. Many plasmas can be used for such applications. Among them, DC electric arcs are interesting because they can produce large volumes of thermal plasmas with controlled en...

View Video Presentation: https://doi.org/10.2514/6.2022-1637.vid An electronic-specific collisional-radiative (CR) model of molecular nitrogen (N2) is presented and applied to the study of a recombining air plasma. This plasma is produced at local thermodynamic equilibrium at 8000 K and 1 atm by a 50-kW Inductively Coupled Plasma torch and passes t...

View Video Presentation: https://doi.org/10.2514/6.2022-2397.vid We report measurements of high temperature air emission, calibrated in absolute intensity between 140 - 250 nm. The high temperature air was produced using an atmospheric pressure plasma torch facility. The centerline temperature of the plasma jet is approximately 6700 K. A VUV emissi...

View Video Presentation: https://doi.org/10.2514/6.2022-2255.vid This article presents a joint experimental and numerical analysis of a lean turbulent premixed methane-air flame stabilized by nanosecond repetitively pulsed discharges. In the experiments, the transient effects of the discharge on combustion are quantified by optical diagnostics to c...

Infrared emission measurements from a high temperature CO2/Ar plasma are presented. An inductively coupled plasma torch was used to produce a CO2/Ar plasma jet at atmospheric pressure. The plasma jet is initially close to Local Thermodynamic Equilibrium conditions at a temperature of 6650 K. This plasma is then passed at high velocity through a wat...

View Video Presentation: https://doi.org/10.2514/6.2022-2368.vid A Nanosecond Repetitively Pulsed discharge in atmospheric pressure CO2 is characterized using Optical Emission Spectroscopy (OES) measurements. The electron density, electron temperature, and gas temperature are measured. The measurements are conducted in the forced pulsing regime. Be...

Rotational temperature measurements of N 2 (B ³ Π g ), N 2 (C ³ Π u ) and N 2 + ( B 2 Σ u + ) obtained by optical emission spectroscopy (OES) are compared with previous gas temperature measurements obtained with Raman spectroscopy in a nonequilibrium recombining nitrogen plasma at atmospheric pressure. The plasma is produced in a state of thermal a...

We present optical emission spectroscopy measurements from the vacuum ultraviolet to the near-infrared in a recombining nitrogen plasma flow. An inductively coupled plasma torch is used to create an equilibrium plasma at atmospheric pressure. This plasma is then forced to recombine by flowing through a water-cooled tube. For certain conditions, the...

Plasma, the fourth and most pervasive state of matter in the visible universe, is a fascinating medium that is connected to the beginning of our universe itself. Man-made plasmas are at the core of many technological advances that include the fabrication of semiconductor devices, which enabled the modern computer and communication revolutions. The...

p>Plasma, the fourth and most pervasive state of matter in the visible universe, is a fascinating medium that is connected to the beginning of our universe itself. Man-made plasmas are at the core of many technological advances that include the fabrication of semiconductor devices, which enabled the modern computer and communication revolutions. Th...

Quantifying the thermal response of a heat shield is a key step in the design of a spacecraft to ensure its survivability during atmospheric entry. Recession and swelling of the thermal protection material have a drastic effect on both the heat transfer within the vehicle and aerothermodynamic transients. Postflight analysis of reentry can be achie...

Plasma, the fourth and most pervasive state of matter in the visible universe, is a fascinating medium that is connected to the beginning of our universe itself. Man-made plasmas are at the core of many technological advances that include the fabrication of semiconductor devices, which enabled the modern computer and communication revolutions. The...

Reentry radiation is one of the key phenomena to take into account while designing an Entry Descent and Landing (EDL) phase for sample return and some gas/ice giants’ missions. In the case of an ablative thermal protective system (TPS), the physicochemical processes involved produce a large amount of dust and phenolic gases that can obstruct the op...

The efficiency of plasmas sources for the decontamination of heat-sensitive devices has been proven for more than 20 years, but commercial plasma-based sterilizers still have a narrow range of applications. This can be partially explained by difficulties to determine reliable bio-indicators and standardized microbiological test procedures required...

The mechanism of air ionization by a single nanosecond discharge under atmospheric conditions is studied using numerical simulations. The plasma kinetics are solved with ZDPlasKin and the electron energy distribution function is calculated with BOLSIG+. The model includes the excited electronic states of O and N atoms, which are shown to play the m...

Non-equilibrium plasmas are known to improve ignition and extend flammability limits. In this study, NRP discharges of 2 mJ are applied at 20 kHz in the recirculation zone of a premixed methane-air bluff-body burner with a lean equivalence ratio of 0.8. The operating point is close to the lean blow out limit and NRP discharges efficiently enhance t...

High resolution infrared emission measurements are performed on a high temperature CO2/Ar plasma. A 50 kW ICP torch was used to produce an atmospheric pressure CO2/Ar plasma jet close to Local Thermodynamic Equilibrium conditions at 6920 K. The emission measurements on this plasma jet were made between 0.9 and 5.6 μm. Our goal is to study the emiss...

An electronic-specific collisional-radiative (CR) model of Nitric Oxide (NO) is presented and applied to the study of a recombining air plasma. This plasma is produced at local thermodynamic equilibrium at 8000 K and 1 atm by a 50-kW Inductively Coupled Plasma torch and passes at high-velocity through a water-cooled tube that forces rapid cooling a...

The formation of thermal sparks generated by nanosecond pulses is studied experimentally and numerically. The increase of the electron number density, up to 10^19 cm^-3, is measured with sub-nanosecond resolution using Stark broadening of N+, Stark broadening of Hα, continuum emission of the electron, and the intensity of N+ lines. Our experimental...

The formation and decay of the thermal spark generated by a single nanosecond high-voltage pulse between pin electrodes are characterized in this study. The influence of air pressure in the range 50–1000 mbar is investigated at 300 K. By performing short-gate imaging and optical emission spectroscopy (OES), we find that the thermal sparks exhibit a...

Plasma-Assisted Combustion (PAC) has shown potential in improving the ignition, extinction, and dynamic performance of combustion systems. In this work, nanosecond repetitively pulsed (NRP) spark discharges are applied to extend the lean blow out (LBO) limit of the SICCA-Spray burner. This laboratory-scale atmospheric test rig is equipped with a sw...

We present absolute intensity measurements of CO 4th positive emission from a CO2/Ar plasma jet produced using an atmospheric pressure plasma torch facility. The centerline temperature of the plasma jet is approximately 6300 K. A VUV emission spectroscopy system was adapted to the plasma torch facility to measure spectrally resolved emission down t...

This article reports on experiments in a nonequilibrium plasma produced by nanosecond repetitively pulsed (NRP) spark discharges in water vapor at 450 K and atmospheric pressure. The objective is to determine the electron number density in the post-discharge, with spatial and temporal resolution, to gain a better understanding of the discharge deve...

In this paper, the mechanism of air ionization by a single nanosecond discharge under atmospheric conditions is studied by numerical simulations. The plasma kinetics is solved with ZDPlasKin and the electron energy distribution function is calculated with BOLSIG+. The originality of the model is to consider not only the excited electronic states of...

An atmospheric pressure CO2/Ar plasma is produced using an ICP torch. This plasma is passed at high velocity through a water-cooled test-section that forces rapid cooling and recombination. At the water-cooled test-section inlet, the plasma is close to Local Thermodynamic Equilibrium at about 6750 K. The subsequent thermochemical evolution of the p...

Plasma-Assisted Combustion (PAC) has shown potential in improving the ignition, extinction, and dynamic performance of combustion systems. In this work, Nanosecond Repetitively Pulsed (NRP) spark discharges are applied to extend the lean blow out limit of the SICCA-Spray burner. This laboratory-scale atmospheric test rig is equipped with a swirl sp...

We present optical emission spectroscopy measurements in recombining nitrogen plasma flows at atmospheric pressure. An inductively coupled plasma torch is used to create an equilibrium plasma, which is then forced to recombine by flowing through a water-cooled tube. For certain conditions, the plasma is forced out of chemical equilibrium. The emiss...

Three different hydrodynamic regimes induced in the NRP discharges are identified: Diffusive, Toroidal symmetric and toroidal asymmetric. Each regime is explained based on the mechanism of baroclinic torque.

The mechanisms controlling the hydrodynamic effects induced by nanosecond pulsed discharges applied between two pin electrodes in air at atmospheric conditions are investigated experimentally and numerically. A cylindrical plasma kernel is formed between the electrodes during the discharge. After the discharge, schlieren images show that the cylind...

Thermal Protection System (TPS) design of Martian missions has suffered from high mar- gins due to the lack of flight-proven data and unknown processes of ablation and radiation. We propose to fly an entry experiment mission with a compact and low cost platform based on the CubeSat standard (12 U, 34x22x22 cm3 and a mass inferior to 20 kg). This mi...

EM2C lab in collaboration with ArianeGroup has developed a combined radiation/recession payload (INES) able to perform measurements in the harsh environment of reentry. Equipped with an emission spectrometer or a photodiode, it permits to determine radiative flux and other spectral phenomena of interest. With the same configuration, the payload is...

Development of a quench-free fs-TALIF diagnostic technique for measurements of N(4S).

Measurements of long-lived emission in NRP discharges is observed to originate from the first positive system of N2. Correlations with TALIF measuremnts indicate that N2(B) state is created by three-bdy recombination involving the N(4S) atoms

Nonequilibrium infrared emission spectra representative of a Mars atmospheric entry mission are modeled using RADIS, a spectral code for CO and CO2 based on the HITEMP-2010 and CDSD-4000 databases. The modeled experimental data for the free-flow and the forebody radiation were obtained in the JAXA expansion tube facility. In the expanding flow, goo...

This work presents an experimental investigation of the hydrodynamic effects induced by nanosecond and conventional spark discharges. The energy deposited in sparks in the short breakdown time (~1 mJ mm⁻¹) induces hydrodynamic effects that redistribute the energy over a large volume (~1 cm³) surrounding the initial plasma channel. This process infl...