The replacement of hydrocarbon fuels by ammonia in industrial systems is challenging due to its low burning velocity, its narrow flammability range, and a large production of nitric oxide and ...nitrogen dioxide when burned close to stoichiometric conditions. Cracking a fraction of ammonia into hydrogen and nitrogen prior to injection in the combustion chamber is considered a promising strategy to overcome these issues. This paper focuses on evaluating how different levels of ammonia cracking affect the overall burning velocity, the lean blow-off limit, the concentration of nitric oxide and nitrogen dioxide, and the flame response to acoustic perturbations. Swirl stabilized premixed flames of pure ammonia–air and ammonia–hydrogen–nitrogen–air mixtures mimicking 10%, 20%, and 28% of cracking are experimentally investigated. The results show that even though ammonia cracking is beneficial for enhancing the lean blow-off limit and the overall burning velocity, its impact on pollutant emissions and flame stability is detrimental for a percentage of cracking as low as 20%. Based on an analysis of the flame dynamics, reasons for these results are proposed.
► Laminar burning velocities of steam-diluted oxygen-enriched methane flames are measured and computed. ► Efficient technology to control the steam concentration in a reactive mixture. ► Quasi-linear ...decrease of the flame speed with increasing steam molar fraction. ► Thermal and chemical effects of steam addition investigated and discussed.
The effects of steam addition on the laminar burning velocity of premixed oxygen-enriched methane flames are investigated at atmospheric pressure. Experiments are carried out with an axisymmetric burner on which laminar conical flames are stabilized. A newly devised steam production system is used to dilute the reactants with water vapor. The oxygen-enrichment ratio in the oxidizer, defined as O
2/(O
2
+
N
2) (mol.), is varied from 0.21 (air) to 1.0 (pure oxygen). The equivalence ratio ranges from 0.5 to 1.5 and the steam molar fraction in the reactive mixture is varied from 0 to 0.50. For all compositions examined, the reactive mixture is preheated to a temperature
T
u
=
373
K. Laminar flame speeds are determined with the flame area method using a Schlieren apparatus. The deviations induced by stretch effects due to aerodynamic strain and flame curvature are assessed using Particle Imaging Velocimetry measurements and flame images, and these data are used to estimate the uncertainty of the flame speed measurements. The experiments are completed by numerical simulations conducted with the PREMIX code using different detailed kinetic mechanisms. It is shown that the laminar flame speed of CH
4/O
2/N
2/H
2O
(
v)
mixtures features a quasi-linear decrease with increasing steam molar fraction, even at high steam dilution rates. Numerical predictions are in good agreement with experimental data for all compositions explored, except for low dilution rates
X
H
2
O
<
0.10
in methane–oxygen mixtures, where the flame speed is slightly underestimated by the calculations. It is also shown that steam addition has a non-negligible chemical impact on the flame speed for methane–air flames, mainly due to water vapor high chaperon efficiency in third-body reactions. This effect is however strongly attenuated when the oxygen concentration is increased in the reactive mixture. For highly oxygen-enriched flames, steam can be considered as an inert diluent.
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 development and chemical kinetics. Electron number densities were measured in water vapor from the broadenings and shifts of the H and Hβ lines of the hydrogen Balmer series and of the atomic oxygen triplet at 777 nm. For an average reduced electric field of about 150 Td, high electron densities up to 3 × 1018 cm−3 are measured at the cathode, up to 5 × 1017 cm−3 at the anode, and up to 4 × 1016 cm−3 in the interelectrode gap. The high density near the electrodes is attributed to ionization enhancement and secondary electron emission due to the high electric field in the plasma sheath. In the middle of the inter-electrode gap, we show that the electron density mainly decays by electron attachment reactions. The dissociation fraction of water vapor is estimated to be around 2% in the middle of the gap.
Beckwith-Wiedemann syndrome (BWS) is an overgrowth syndrome associated with an increased risk of pediatric tumors. The underlying molecular abnormalities may be genetic (CDKN1C mutations or 11p15 ...paternal uniparental isodisomy, pUPD) or epigenetic (imprinting center region 1, ICR1, gain of methylation, ICR1 GOM, or ICR2 loss of methylation, ICR2 LOM).
We aimed to describe a cohort of 407 BWS patients with molecular defects of the 11p15 domain followed prospectively after molecular diagnosis.
Birth weight and length were significantly higher in patients with ICR1 GOM than in the other groups. ICR2 LOM and CDKN1C mutations were associated with a higher prevalence of exomphalos. Mean adult height (regardless of molecular subtype, n = 35) was 1.8 ± 1.2 SDS, with 18 patients having a final height above +2 SDS. The prevalence of tumors was 8.6% in the whole population; 28.6 and 17.3% of the patients with ICR1 GOM (all Wilms tumors) and 11p15 pUPD, respectively, developed a tumor during infancy. Conversely, the prevalence of tumors in patients with ICR2 LOM and CDKN1C mutations were 3.1 and 8.8%, respectively, with no Wilms tumors.
Based on these results for a large cohort, we formulated guidelines for the follow-up of these patients according to the molecular subtype of BWS.
We report a nanoscale synthesis technique using nanosecond-duration plasma discharges. Voltage pulses 12.5 kV in amplitude and 40 ns in duration were applied repetitively at 30 kHz across molybdenum ...electrodes in open ambient air, generating a nanosecond spark discharge that synthesized well-defined MoO₃ nanoscale architectures (i.e. flakes, dots, walls, porous networks) upon polyamide and copper substrates. No nitrides were formed. The energy cost was as low as 75 eV per atom incorporated into a nanostructure, suggesting a dramatic reduction compared to other techniques using atmospheric pressure plasmas. These findings show that highly efficient synthesis at atmospheric pressure without catalysts or external substrate heating can be achieved in a simple fashion using nanosecond discharges.
Results of an experimental study of the efficiency of the ignition of propane-air mixtures by a high voltage repetitively pulsed nanosecond gas discharge (10 kV, 10 ns, 30 kHz) are presented for the ...pressure range 0.35-2.0 bar. The measured minimal energy for ignition is found to decrease with the pressure. A significant reduction of the ignition delay and a decrease of the overall combustion duration were obtained by using a train of high-voltage pulses. Spectroscopic measurements in a 1-bar air just after a 10-pulse train (300 mus) of about 10 mJ in total energy show the presence of N, N + , O, and O + atomic species and a gas temperature increase up to 3000 K
In Mammals, microglial cells are considered as the resident immune cells in central nervous system (CNS). Many studies demonstrated that, after injury, these cells are activated and recruited at the ...lesion site. Leech microglia present a similar pattern of microglial activation and migration upon experimental lesion of CNS. This activation is associated with the release of a large amount of extracellular vesicles (EVs). We collected EVs released by microglia primary culture and compared two different protocols of isolation: one with differential ultracentrifugation (UC) and one using an additional Optiprep™ Density Gradient (ODG) ultracentrifugation. Nanoparticles tracking analysis (NTA) and transmission electron microscopy (TEM) were used to assess vesicles size and morphology. The protein content of isolated EVs was assessed by mass spectrometry approaches. Results showed the presence of EV-specific proteins in both procedures. The extensive proteomic analysis of each single ODG fractions confirmed the efficiency of this protocol in limiting the presence of co-isolated proteins aggregates and other membranous particles during vesicles isolation. The present study permitted for the first time the characterisation of microglial EV protein content in an annelid model. Interestingly, an important amount of proteins found in leech vesicles was previously described in EV-specific databases. Finally, purified EVs were assessed for neurotrophic activity and promote neurites outgrowth on primary cultured neurons.
This paper examines the ability of nanosecond repetitively pulsed (NRP) plasma discharges to improve stabilization and extend the blow-off limit of lean premixed methane-air swirl flames at pressures ...up to 5 bar. The effect of two discharge regimes, NRP glows and NRP sparks, was investigated. The electrical characterization of the discharges was performed and direct images at 60 Hz of the flames, with and without NRP discharges, were collected to assess the effect of the discharges on flame stabilization. Results showed that NRP discharges efficiently extended the lean blow-off and stability limits of premixed methane-air swirl flames, at pressures up to 5 bar. These results were obtained for a ratio of NRP discharge power to flame thermal power of 0.7% or less. Moreover, the peak voltage necessary to maintain constant this power ratio did not increase linearly with increased pressure, even though the reduced electric field should linearly decrease with the pressure. It was also observed that the relative effectiveness of the NRP glows and NRP sparks changed by increasing the pressure. Based on discharge physics and current knowledge of the effect of pressure on the electrical properties of flames, explanations for these results are proposed.
Nanosecond repetitively pulsed (NRP) discharges have been used for a broad range of applications, such as plasma-assisted combustion. In this paper, we use an NRP plasma discharge produced by ...electric pulses of about 10 kV during 10 ns at a frequency of 30 kHz to stabilize a lean premixed methane/air flame at atmospheric pressure. We show here that the plasma created in the recirculation zone allows the stabilization of the lean flame and a reduction of the lean extinction limit by about 10%-15%, using only a small amount of energy (the plasma power represents less than 1% of the power of the flame).
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