Search Results (68)

Some of the popular and successful atmospheric pressure fuel/air plasma-assisted combustion methods use repetitive ns pulsed discharges and dielectric-barrier discharges. The transient phase in such discharges is dominated by transport under strong space charge from ionization fronts, which is best characterized by the streamer model. The role of the nonthermal plasma in such discharges is to produce radicals, which accelerates the chemical conversion reaction leading to temperature rise and ignition. Therefore, the characterization of the streamer and its energy partitioning is essential to develop a predictive model. We examine the important characteristics of streamers that influence combustion and develop some macroscopic parameters. Our results show that the radicals’ production efficiency at an applied field is nearly independent of time and the radical density generated depends only on the electrical energy density coupled to the plasma. We compare the results of the streamer model to the zero-dimensional uniform field Townsend-like discharge, and our results show a significant difference. The results concerning the influence of energy density and repetition rate on the ignition of a hydrogen/air fuel mixture are presented. Full article

In current and future fusion devices, detecting hydrogen isotopes, particularly tritium and deuterium, implanted or redeposited on the surface of Plasma-Facing Components (PFCs) will be increasingly important to ensure safe machine operations. The Laser-Induced Breakdown Spectroscopy (LIBS) technique has proven capable of performing this task directly in situ, without handling or removing PFCs, thus limiting analysis times and increasing the machine’s duty cycle. To increase sensitivity and the ability to discriminate between isotopes, LIBS analysis can be performed under different background gases at atmospheric pressure, such as air, He, and Ar. In this work, we present the results obtained on tungsten coatings enriched with deuterium and/or hydrogen as a deuterium–tritium nuclear fuel simulant, measured with the LIBS technique in air, He, and Ar at atmospheric pressure, and discuss the pros and cons of their use. The results obtained demonstrate that both He and Ar can improve the LIBS signal resolution of the hydrogen isotopes compared to air. However, using Ar has the additional advantage that the same procedure can also be used to detect He implanted in PFCs as a product of fusion reactions without any interference. Finally, the LIBS signal in an Ar atmosphere increases in terms of the signal-to-noise ratio (SNR), enabling the use of less energetic laser pulses to improve performance in depth profiling analyses. Full article

Hexagonal ZnO nanowires were grown using the PLD/VLS technique on a SAW sensor active area for hydrogen sensing. The influence of different carbon and nitrogen surface contaminant concentrations on sensor output was investigated for three active area cases: a few weeks’ exposure to free ambient air contamination, 3 h at 600 °C thermal desorption of carbon, and (room temperature) plasma-activated nitrogen and carbon contamination. Correlations between sensing performance and contamination element concentration were established. To understand the adsorption versus absorption mechanisms, similar studies were further performed on circular ZnO nanowires morphology, which have a different surface-area-to-volume ratio. Comparative results show that, while a 20% carbon surface contamination variation generates a variation of 3–5% in nanostructure hydrogen sorption, nitrogen surface contamination influence depends on nanostructure morphology. Thus, in our comparative studies, for the case of a nanowire hexagonal cross-section a 12% nitrogen surface contamination variation generates a 5–7% increase in hydrogen adsorption and also an increase of 6–8% in hydrogen absorption. Consequently, the catalytic effect of nitrogen could enlarge the linear response of nanowire-based (SAW) sensors over a wider hydrogen concentration range. Full article

The development of bipolar plate materials with enhanced corrosion resistance and surface conductivity is critical for the commercial application of proton exchange membrane fuel cells (PEMFCs). The corrosion behavior and surface conductivity of electrochemically nitrided 446 stainless steel with and without the pretreatment of Cr-enrichment were investigated in the simulated PEMFC anode and cathode environments (i.e., 0.5 mol L⁻¹ H₂SO₄ + 2 ppm HF solution bubbled with hydrogen or air at 80 °C) using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma–mass spectrometry (ICP-MS), and electrochemical measurement techniques. Extending the nitriding time from 5 to 30 min enhances the surface conductivity but reduces the corrosion resistance. After the pretreatment and 30 min of nitridation, a thin film formed on the specimen surface, which mainly consists of Cr-nitrides and -oxides with atomic fractions of 0.42 and 0.37, respectively. The Cr-enriched and nitrided specimen shows spontaneous passivation in both the simulated cathode and anode environments and higher corrosion potentials, lower passive current densities, and larger polarization resistances in comparison with the directly nitrided specimens. Its stable current densities are about 0.26 and −0.39 μA cm⁻² after 5 h of polarization tests at 0.6 V_SCE in the cathode environment and at −0.1 V_SCE in the anode environment, respectively. Its contact resistance is about 5.0 mΩ cm² under 1.4 MPa, which is close to that of the specimen directly nitrided for 120 min and slightly decreases after the potentiostatic polarization tests. These results indicate that Cr-rich pretreatment improves not only the corrosion resistance and surface conductivity of nitrided specimens but also the efficiency of electrochemical nitridation. Full article

Modern industrial systems and biomass-fired furnaces require surface treatments that can withstand aggressive chemical, thermal, and corrosive environments. This study investigates the corrosion and thermal resistance of plasma-sprayed Al₂O₃-TiO₂ coatings produced using a DC air–hydrogen plasma spray process. Coatings of compositions of Al₂O₃, Al₂O₃-3 wt.% TiO₂, Al₂O₃-13 wt.% TiO₂, and Al₂O₃-40 wt.% TiO₂ were deposited on steel substrates with a Ni/Cr bond layer by plasma spraying. The coatings were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) to evaluate their morphology, elemental composition, and crystalline phases. Electrochemical tests were performed in a naturally aerated 0.5 mol/L NaCl solution and cyclic thermal–chemical exposure tests (500 °C using 35% KCl) to assess their corrosion kinetics and thermal stability. The results indicate that pure Al₂O₃ and low TiO₂ (3 wt.%) coatings exhibit fine barrier properties, while coatings with a higher TiO₂ content develop additional phases (e.g., Ti₃O₅, Al₂TiO₅) that improve thermal resistance but reduce chemical durability. Full article

Hydrogen and some of its derivatives (such as e-methanol, e-methane, and e-ammonia) are promising energy carriers that have the potential to replace conventional fuels, thereby eliminating their harmful environmental impacts. An innovative use of hydrogen as a zero-emission fuel is forming weakly ionized plasma by seeding the combustion products of hydrogen with a small amount of an alkali metal vapor (cesium or potassium). This formed plasma can be used as a working fluid in supersonic open-cycle magnetohydrodynamic (OCMHD) power generators. In these OCMHD generators, direct-current (DC) electricity is generated straightforwardly without rotary turbogenerators. In the current study, we quantitatively and qualitatively explore the levels of electric conductivity and the resultant volumetric electric output power density in a typical OCMHD supersonic channel, where thermal equilibrium plasma is accelerated at a Mach number of two (Mach 2) while being subject to a strong applied magnetic field (applied magnetic-field flux density) of five teslas (5 T), and a temperature of 2300 K (2026.85 °C). We varied the total pressure of the pre-ionization seeded gas mixture between 1/16 atm and 16 atm. We also varied the seed level between 0.0625% and 16% (pre-ionization mole fraction). We also varied the seed type between cesium and potassium. We also varied the oxidizer type between air (oxygen–nitrogen mixture, 21–79% by mole) and pure oxygen. Our results suggest that the ideal power density can reach exceptional levels beyond 1000 MW/m³ (or 1 kW/cm³) provided that the total absolute pressure can be reduced to about 0.1 atm only and cesium is used for seeding rather than potassium. Under atmospheric air–hydrogen combustion (1 atm total absolute pressure) and 1% mole fraction of seed alkali metal vapor, the theoretical volumetric power density is 410.828 MW/m³ in the case of cesium and 104.486 MW/m³ in the case of potassium. The power density can be enhanced using any of the following techniques: (1) reducing the total pressure, (2) using cesium instead of potassium for seeding, and (3) using air instead of oxygen as an oxidizer (if the temperature is unchanged). A seed level between 1% and 4% (pre-ionization mole fraction) is recommended. Much lower or much higher seed levels may harm the OCMHD performance. The seed level that maximizes the electric power is not necessarily the same seed level that maximizes the electric conductivity, and this is due to additional thermochemical changes caused by the additive seed. For example, in the case of potassium seeding and air combustion, the electric conductivity is maximized with about 6% seed mole fraction, while the output power is maximized at a lower potassium level of about 5%. We also present a comprehensive set of computed thermochemical properties of the seeded combustion gases, such as the molecular weight and the speed of sound. Full article

Aspergillus spp. and their produced aflatoxins are responsible for contaminating 25–30% of the global food supply, including many grains, and nuts which when consumed are detrimental to human and animal health. Despite regulatory frameworks, Aspergillus spp. and aflatoxin contamination is still a global challenge, especially in cereal-based matrices and their derived by-products. The methods for reducing Aspergillus spp. and aflatoxin contamination involve various approaches, including physical, chemical, and biological control strategies. Recently, a novel technology, atmospheric cold plasma (ACP), has emerged which can reduce mold populations and also degrade these toxins. ACP is a non-thermal technology that operates at room temperature and atmospheric pressure. It can reduce mold and toxins from grains and seeds without affecting food quality or leaving any chemical residue. ACP is the conversion of a gas, such as air, into a reactive gas. Specifically, an electrical charge is applied to the “working” gas (air) leading to the breakdown of diatomic oxygen, diatomic nitrogen, and water vapor into a mixture of radicals (e.g., atomic oxygen, atomic nitrogen, atomic hydrogen, hydroxyls), metastable species, and ions (e.g., nitrate, nitrite, peroxynitrate). In a cold plasma process, approximately 5% or less of the working gas is ionized. However, cold plasma treatment can generate over 1000 ppm of reactive gas species (RGS). The final result is a range of bactericidal and fungicidal molecules such as ozone, peroxides, nitrates, and many others. This review provides an overview of the mechanisms and chemistry of ACP and its application in inactivating Aspergillus spp. and degrading aflatoxins, serving as a novel treatment to enhance the safety and quality of grains and nuts. The final section of the review discusses the commercialization status of ACP treatment. Full article

In this study, we investigated the effect of plasma-activated liquids (PAL) on the cotton plant (Gossypium hirsutum L.) growth under laboratory and field conditions. We used two types of PAL: deionized water activated with plasma generated using a microwave plasmatron in atmospheric-pressure air flow (PAW) and a 1.5% KNO₃ solution activated using plasma generated in an electrochemical cell (PAKNO₃). These treatments differ in terms of their content of long-lived biologically active compounds. PAW contains a higher concentration of hydrogen peroxide (150 μM compared to 1.1 μM), while PAKNO₃ is more saturated with NO₂⁻ and NO₃⁻ (1510 μM compared to 300 µM). We found that PAW improved cotton plant growth under field conditions and in a laboratory drought stress. Additionally, PAW increased field emergence and germination of heat-treated cotton seeds in the laboratory. It was revealed that PAW prevents the drought-induced disruption of the partitioning of absorbed light energy in the photosynthetic apparatus. Meanwhile, PAKNO₃ has a positive effect on seed germination. The positive effect of PALs on cotton seeds and plants is thought to be due to the generation of long-lived biologically active oxygen and nitrogen species during plasma treatment of the liquid. Full article

Numerical investigations were conducted to analyze the coupling effects of pulsed H₂ jets and nanosecond-pulsed actuation (NS-SDBD) in a supersonic crossflow. The FVM was employed to solve the multi-component 2D URANS equations with the SST k-omega turbulence model, while H₂-air combustion was described using a seven species–seven reactions chain reaction model, and the plasma thermal effect was represented by a phenomenological model. The backward-facing step flows with an inlet Mach number of 2.5 and a pulsed jet frequency of 10 kHz under different actuation conditions were simulated. The combustion enhancement mechanism under an actuation frequency of 20 kHz was analyzed. Research indicates that compression waves induced by NS-SDBD enhance H₂-air mixing and facilitate temperature transport as the flow progresses. This progress is significantly associated with the flow structures generated by pulsed jets. Under this condition, the fuel utilization rate in the flow field increased by 61.2%, the total pressure recovery coefficient increased by 5.34%, and the outlet total temperature slightly increased even with a 50% reduction in fuel flow rate. Comparative analysis of different actuation cases demonstrates that evenly distributed actuation within the jet cycle yields better effects. The innovation of this study lies in proposing and exploring a potential method to address inadequate combustion under high-speed inflow conditions, which couples NS-SDBD with pulsed hydrogen jets. Full article

Laser-Induced Breakdown Spectroscopy (LIBS) is one candidate for analyzing the fuel retention in ITER plasma-facing components during maintenance breaks when the reactor is filled with near atmospheric pressure nitrogen or dry air. It has been shown that using argon flow during LIBS measurements increases the LIBS signal at atmospheric pressure conditions and helps to distinguish the hydrogen isotopes. However, atmospheric pressure might be suboptimal for such LIBS measurements. The present study investigated the effect of argon or nitrogen gas at different pressures on the hydrogen H_α line emission intensity during the LIBS measurements. Laser pulses with an 8 ns width were used to ablate a small amount of a molybdenum (Mo) target with hydrogen impurity. The development of the formed plasma plume was investigated by time- and space-resolved emission spectra and photographs. Photographs showed that the plasma plume development was similar for both gases, while the total intensity of the plume was higher in argon. Space-resolved emission spectra also had stronger H_α line intensities in argon. Shorter delay times necessitated the use of lower pressures to have sufficiently narrow lines for the distinguishing of the hydrogen isotopes. At the same line widths, the line intensities were higher at lower gas pressures and in argon. H_α and Mo I line emissions were spatially separated, which suggests that the geometry of collection optics should be considered when using LIBS. Full article

This research paper analyzes the use of plasma technology to process biomass in the form of dried, mixed animal manure (dung containing 30% moisture). The irrational use of manure as well as huge quantities of it can negatively impact the environment. In comparison to biomass fermentation, the plasma processing of manure can greatly enhance the production of fuel gas, primarily synthesis gas (CO + H₂). The organic part of dung, including the moisture, is represented by carbon, hydrogen, and oxygen with a total concentration of 95.21%, while the mineral part is only 4.79%. A numerical analysis of dung plasma gasification and pyrolysis was conducted using the thermodynamic code TERRA. For 300–3000 K and 0.1 MPa pressure, the dung gasification and pyrolysis were calculated with 100% dung + 25% air and 100% dung + 25% nitrogen, respectively. Calculations were performed to determine the specific energy consumption of the process, the composition of the products of gasification, and the extent of the carbon gasification. At 1500 K, the dung gasification and pyrolysis consumed 1.28 and 1.33 kWh/kg of specific energy, respectively. A direct-current plasma torch with a power rating of 70 kW and a plasma reactor with a dung processing capacity of 50 kg/h were used for the dung processing experiments. The plasma reactor consumed 1.5 and 1.4 kWh/kg when pyrolyzing and gasifying the dung. A maximum temperature of 1887 K was reached in the reactor. The plasma pyrolysis of dung and the plasma–air gasification of dung produced gases with specific heats of combustion of 10,500 and 10,340 kJ/kg, respectively. Calculations and experiments on dung plasma processing showed satisfactory agreement. In this research, exergy analysis was used to quantify the efficiency of the plasma gasification of biomass. One of the research tasks was to develop a methodology and establish standards for the further standardization of monitoring the toxic emissions of dioxins, furans, and Benzo[a]pyrene. Full article

A series of M(x)CoCeMgAlO mixed oxides with different transition metals (M = Cu, Fe, Mn, and Ni) with an M content x = 3 at. %, and another series of Fe(x)CoCeMgAlO mixed oxides with Fe contents x ranging from 1 to 9 at. % with respect to cations, while keeping constant in both cases 40 at. % Co, 10 at. % Ce and Mg/Al atomic ratio of 3 were prepared via thermal decomposition at 750 °C in air of their corresponding layered double hydroxide (LDH) precursors obtained by coprecipitation. They were tested in a fixed bed reactor for complete methane oxidation with a gas feed of 1 vol.% methane in air to evaluate their catalytic performance. The physico-structural properties of the mixed oxide samples were investigated with several techniques, such as powder X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), elemental mappings, inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction under hydrogen (H₂-TPR) and nitrogen adsorption–desorption at −196 °C. XRD analysis revealed in all the samples the presence of Co₃O₄ crystallites together with periclase-like and CeO₂ phases, with no separate M-based oxide phase. All the cations were distributed homogeneously, as suggested by EDX measurements and elemental mappings of the samples. The metal contents, determined by EDX and ICP-OES, were in accordance with the theoretical values set for the catalysts’ preparation. The redox properties studied by H₂-TPR, along with the surface composition determined by XPS, provided information to elucidate the catalytic combustion properties of the studied mixed oxide materials. The methane combustion tests showed that all the M-promoted CoCeMgAlO mixed oxides were more active than the M-free counterpart, the highest promoting effect being observed for Fe as the doping transition metal. The Fe(x)CoCeMgAlO mixed oxide sample, with x = 3 at. % Fe displayed the highest catalytic activity for methane combustion with a temperature corresponding to 50% methane conversion, T₅₀, of 489 °C, which is ca. 40 °C lower than that of the unpromoted catalyst. This was attributed to its superior redox properties and lowest activation energy among the studied catalysts, likely due to a Fe–Co–Ce synergistic interaction. In addition, long-term tests of Fe(3)CoCeMgAlO mixed oxide were performed, showing good stability over 60 h on-stream. On the other hand, the addition of water vapors in the feed led to textural and structural changes in the Fe(3)CoCeMgAlO system, affecting its catalytic performance in methane complete oxidation. At the same time, the catalyst showed relatively good recovery of its catalytic activity as soon as the water vapors were removed from the feed. Full article

The decomposition efficiency of C₂HCl₃ and CHCl₃ in a barrier discharge is very different, even though these compounds differ little in chemical composition. In both compounds, there are three chlorine atoms and one hydrogen atom. The difference between them is the presence of one carbon atom in CHCl₃ and two carbon atoms connected by a double bond in C₂HCl₃ and the higher polarizability of C₂HCl₃. The polarizability of C₂HCl₃ is 10.21 ų and that of CHCl₃ is 8.39 ų. As a result of these differences, the C₂HCl₃ conversion was two to three times higher than the CHCl₃ conversion. The main product of CHCl₃ decomposition containing chlorine was ClO₂, while Cl₂, COCl₂, HCl, CCl₄, and Cl⁻ were formed in smaller amounts. The main products of C₂HCl₃ decomposition, which contain chlorine, were COCl₂, HCl, and Cl⁻. CCl₄ was not formed. Cl₂ and ClO₂ were formed in smaller amounts. Pathways of C₂HCl₃ and CHCl₃ decomposition are shown in this paper. The process was carried out at low power (0.2–0.8 W) in air. The gas flow was 10 L/h, and the concentration of the decomposed compound was 0.4%. The volume of the gas space of the reactor (plasma zone) was 27 cm³. Full article

This work explores microcombustion technologies enhanced by plasma-assisted combustion, focusing on a novel simulation model for a Y-shaped device with a non-premixed hydrogen-air mixture. The simulation integrates the ZDPlasKin toolbox to determine plasma-produced species concentrations to Particle-In-Cell with Monte Carlo Collision analysis for momentum and power density effects. The study details an FE-DBD plasma actuator operating under a sinusoidal voltage from 150 to 325 V peak-to-peak and a 162.5 V DC bias. At potentials below 250 V, no hydrogen dissociation occurs. The equivalence ratio fitting curve for radical species is incorporated into the plasma domain, ensuring local composition accuracy. Among the main radical species produced, H reaches a maximum mass fraction of 8% and OH reaches 1%. For an equivalence ratio of 0.5, the maximum temperature reached 2238 K due to kinetic and joule heating contributions. With plasma actuation with radicals in play, the temperature increased to 2832 K, and with complete plasma actuation, it further rose to 2918.45 K. Without plasma actuation, the temperature remained at 300 K, reflecting ambient conditions and no combustion phenomena. At lower equivalence ratios, temperatures in the plasma area consistently remained around 2900 K. With reduced thermal power, the flame region decreased, and at Φ = 0.1, the hot region was confined primarily to the plasma area, indicating a potential blow-off limit. The model aligns with experimental data and introduces relevant functionalities for modeling plasma interactions within microcombustors, providing a foundation for future validation and numerical models in plasma-assisted microcombustion applications. Full article

This work presents the synthesis of tungsten nanoparticles (W NPs) using a cluster source based on magnetron sputtering combined with gas aggregation (MSGA), operated with up to 81% H₂ in the hydrogen/argon mixture used as a working gas. The results show that, with up to 41% H₂ in discharge, the synthesis rate increases by more than 60 times, rapidly decreasing for over 50% H₂ in discharge. The W dust is still produced for H₂-dominated discharges (81%), and its deposition rate is small but not negligible (0.02 mg/h). The obtained W NPs are isolated, with the diameter decreasing from 50 nm to 15 nm when the amount of H₂ in discharge is smaller than 41%. Over this value, the particles tend to agglomerate, forming structures similar to film-like deposits. Also, the diameter of the dust spots deposited on substrates depends on the H₂ content of the discharge. This allows the efficient coating of substrates up to 26 mm wide by translating them in front of the MSGA cluster source exit aperture. Additionally, for 41% H₂ in discharge, the influence of synthetic air leaks (0%–8.2%) in discharge was investigated. The deposition rate decreases rapidly (ceasing for around 6% air in discharge), and the obtained nanoparticles tend to agglomerate on the substrate (at 3.3% air content, the dust deposit has the aspect of a near-continuous film). Chemical composition investigations show a pronounced tendency for oxidation, nitridation, and oxynitride formation in the presence of air leaks. Full article