Increasing Gas Pressure Research Articles

Experimental assessment of ozone production by multichannel plasma discharges for automotive applications

Ozone addition has come under study as a means of controlling ignition timing in low temperature combustion using highly dilute homogeneous mixture. In this context, this work aims to improve ozone production from air and simulated exhaust gas recirculation (EGR) in a homogeneous charge compression ignition engine using a cold plasma reactor based on multichannel dielectric barrier discharges. Ozone concentration was investigated as a function of energy deposition, gas characteristics, and distance from the source to measurement points. At a given specific input energy, experimental outcomes indicate a relatively high influence of the feeding EGR composition (O2–N2–CO2–CH4–H2O) and flow rate on the ozone production. However, no changes within experimental accuracy in ozone concentration were seen when changing the distance plasma-measurement points, allowing us to find the optimum position of the plasma reactor with respect to the engine inlet. In air, ozone concentration increased from 120 ppm to 1600 ppm, as the flow rate decreased from 200 to 2 slm. At a given voltage set point, the increase in gas pressure causes the decrease in energy deposition and thus the ozone concentration. In EGR mixtures, the lowest ozone concentration tends to stabilize around 50 ppm, which is acceptable for LTC applications.

Investigation of the power transfer efficiency in a radio-frequency driven negative hydrogen ion source

The radio frequency power transfer efficiency is experimentally and numerically investigated in an inductively coupled negative hydrogen ion source. The discharge is operated in a low pressure range of 0.1–3 Pa at a driving frequency of 2 MHz and an applied power of up to 6 kW. In the experiment, the power transfer efficiency value is determined by measuring the applied power and current through the antenna coil both with and without discharge operation. Fundamental properties, such as electron density and effective electron temperature, are obtained by means of a Langmuir probe. The effect of the antenna coil turns, N, is also studied in a range of 5–9 turns. It is found that more coil turns can significantly enhance the power transfer efficiency due to the remarkably increasing quality factor of the system. Moreover, the experimental results show that the power transfer efficiency first increases and then reaches the maximum with increasing applied power, while it first increases quickly and then rises at a slower rate with increasing gas pressure. In order to give a comprehensive knowledge of the power absorption mechanism, a self-consistent hybrid model is developed. It is found that the numerical results are in reasonable agreement with that measured in the experiment. The numerical results and the analytic solutions in the limit cases of low and high pressures can well explain the various trends of the power transfer efficiency obtained in the experiment. These trends mainly depend on the quality factor Q, the electron density, and the effective electron collision frequency.

Ion formation in an argon and argon-oxygen gas mixture of a magnetron sputtering discharge

Formation of singly and doubly charged Arq+ and Tiq+ (q = 1,2) and of molecular Ar, ArTi+, and Ti ions in a direct current magnetron sputtering discharge with a Ti cathode and argon as working gas was investigated with the help of energy-resolved mass spectrometry. Measured ion energy distributions consist of low-energy and high-energy components resembling different formation processes. Intensities of Ar and ArTi+ dimer ions strongly increase with increasing gas pressure. Addition of oxygen gas leads to the formation of positively charged O+, , and TiO+ and of negatively charged O− and ions.

Plasma density measurement and downstream etching of silicon and silicon oxide in Ar/NF3 mixture remote plasma source

In this study, plasma density measurements were performed near the plume region of the remote plasma source (RPS) in Ar/ gas mixtures using a microwave cutoff probe. The measured plasma density is in the range of 1010–1011 cm−3 in the discharge conditions with RPS powers of 2–4 kW and gas pressures of 0.87–4 Torr. The plasma density decreased with increasing gas pressures and RPS powers under various Ar/ mixing ratios. This decrease in the plasma density measured at the fixed measurement position (plume region) can be understood by the reduction of the electron energy relaxation length with increases in the gas pressures and mixing ratio of We also performed downstream etching of silicon and silicon oxide films in this system. The etch rate of the silicon films significantly increases while the silicon oxide is slightly etched with the gas pressures and powers. It was also found that the etch rate strongly depends on the wafer position on the processing chamber electrode, and that the etch selectivity reached 96–131 in the discharge conditions of RF powers (3730–4180 W) and gas pressures (3.6–4 Torr).

Frequency dependence of plasma characteristics at different pressures in cylindrical inductively coupled plasma source

The effects of driving frequency on plasma parameters and electron heating efficiency are studied in cylindrical inductively coupled plasma (ICP) source. Measurements are made in an Ar discharge for driving frequency at 13.56/2 MHz, and pressures of 0.4–1.2 Pa. In 13.56 MHz discharge, higher electron density (ne) and higher electron temperature (Te) are observed in comparison with 2 MHz discharge at 0.6–1.2 Pa. However, slightly higher ne and Te are observed in 2 MHz discharge at 0.4 Pa. This observation is explained by enhanced electron heating efficiency due to the resonance between the oscillation of 2 MHz electromagnetic field and electron-neutral collision process at 0.4 Pa. It is also found that the variation of Te distribution is different in 13.56 and 2 MHz discharge. For ICP at 13.56 MHz, Te shows an edge-high profile at 0.4–1.2 Pa. For 2 MHz discharge, Te remains an edge-high distribution at 0.4–0.8 Pa. However, the distribution pattern involves into a center-high profile at 0.9–1.2 Pa. The spatial profiles of ne remain a center-high shape in both 13.56 and 2 MHz discharges, which indicates the nonlocal kinetics at low pressures. Better uniformity could be achieved by using 2 MHz discharge. The effects of gas pressure on plasma parameters are also examined. An increase in gas pressure necessitates the rise of ne in both 13.56 and 2 MHz discharges. Meanwhile, Te drops when gas pressure increases and shows a flatter distribution at higher pressure.

The Influence of Sorption Pressure on Gas Diffusion in Coal Particles: An Experimental Study

Gas pressure changes during the process of coal mine gas drainage and CBM recovery. It is of great importance to understand the influence of sorption pressure on gas diffusion; however, the topic remains controversial in past studies. In this study, four samples with different coal ranks were collected and diffusion experiments were conducted under different pressures through the adsorption and desorption processes. Three widely used models, i.e., the unipore diffusion (UD) model, the bidisperse diffusion (BD) model and the dispersive diffusion (DD) model, were adopted to compare the applicability and to calculate the diffusion coefficients. Results show that for all coal ranks, the BD model and DD model can match the experimental results better than the UD model. Concerning the fast diffusion coefficient Dae of the BD model, three samples display a decreasing trend with increasing gas pressure while the other sample shows a V-type trend. The slow diffusion coefficient Die of BD model increases with gas pressure for all samples, while the ratio β is an intrinsic character of coal and remains constant. For the DD model, the characteristic rate parameter kΦ does not change sharply and the stretching parameter α increases with gas pressure. Both Dae and Die are in proportion to kΦ, which reflect the diffusion rate of gas in the coal. The impacts of pore characteristic on gas diffusion were also analyzed. Although pore size distributions and specific surface areas are different in the four coal samples, correlations are not apparent between pore characteristic and diffusion coefficients.

DC discharge with high secondary electron emission oxide cathode: Effects of gas pressure and oxide cathode structure

In present study, DC discharge with high secondary electron emission (SEE) oxide cathodes (NiO/Ni and MgO/NiO/Ni cathode) is characterized with a significant increase in discharge current compared to the one with normal Ni cathode at different gas pressures from 400 to 700 torr. The increase multiple value of the discharge current decreases as the gas pressure increases, which can be related to a relative weakened ion-induced SEE process at high gas pressure. The NiO intermediate layer plays an important role in a sandwich MgO/NiO/Ni cathode for DC discharge, which may be due to the fact that its high resistance favors field-enhanced SEE process. Regardless of the gas pressure, the structural characteristics (thickness and roughness) of oxide layer have an effect on the enhancement of the discharge current, which can be attributed to field-enhanced SEE process. Additionally, the increase in the number of needle electrodes is conducive to the increase of discharge current with oxide cathode, which is related to an increase in the discharge area on the cathode surface according to the discharge images.

Crystallization kinetics study of In-doped and (In-Cr) co-doped TiO2 nanopowders using in-situ high-temperature synchrotron radiation diffraction

The influence of TiO2 nanopowder doping with 4 wt% indium and 2 wt% each of indium and chromium on phase transformation was studied. Samples were heated from ambient temperature to 950 °C in sealed quartz capillaries, and in-situ synchrotron radiation diffraction measurements were obtained. Capillary sealing yielded an increase in capillary gas pressure to 0.42 MPa at 950 °C in proportion to absolute temperature by Gay-Lussac’s Law. The initial synthesized samples were amorphous, and crystalline anatase appeared at 200 °C. Crystalline rutile appeared at 850 °C for the nanomaterials that were doped with In and In and Cr. A change in sealed-capillary oxygen partial pressure yielded a decrease and an increase in crystallization temperature, respectively, for the amorphous-to-anatase and anatase-to-rutile transformations. Crystalline titania (anatase and rutile) formed from the amorphous titania by 800 °C and 900 °C, for materials doped with In and In-Cr, respectively. The anatase concentration that was dominant in the In-doped materials up to 950 °C and the higher rutile concentration for the In-Cr doped materials from 900 to 950 °C results from the defect structure that was induced by doping. Cr-ions in the Ti sub-lattice retarded the transformation of anatase to rutile when compared with the retarding effect of mixed In/Cr ions. The transformation results because of the relatively smaller radius of Cr-ions when compared with the In-ions. The differences in phase-transformation kinetics for In, In-Cr and for undoped nanopowders in the literature agree with the calculated transformation activation energies.

Microstructural and mechanical properties of high-performance Inconel 718 alloy by cold spraying

As a precipitation-hardening nickel-based superalloy, Inconel 718 has decent corrosion resistance, high strength at ambient temperature, excellent creep and fatigue strengths at high temperature. In this work, high performance Inconel 718 alloy was fabricated by cold spray process. The microstructure evolution, hardness, adhesive strength and tensile strength were investigated systematically on the cold-sprayed Inconel 718 in as-sprayed and heat-treated conditions. The N2-processed Inconel 718 samples demonstrate a decreasing porosity with the increasing gas pressure, whereas the fully dense coating was obtained by using He gas. Consistent with the particle velocity measurement, higher adhesive and tensile strength were obtained at higher pressure of N2 propelling gas. Through the heat treatment at 990 °C for 4 h, the adhesive strength of N2 and He-processed Inconel 718 reached as high as 435.4 and 899.4 MPa, which is comparable with the tensile strength of bulk material. The microstructure and EBSD examination indicate the disappearance of particle boundaries after the diffusion during heat treatment. Besides, the He-processed Inconel 718 samples show a significantly improved ductility and ultimate strength comparable and even higher than those of bulk material. The results show that the high-performance Inconel 718 alloys can be fabricated by CS process for the application of damage repair and additive manufacturing.

Test and analysis of mechanics and permeation properties of raw coal

AbstractIn this paper, we investigated the mechanics and permeation properties of the raw coal sample during loading and unloading process, and come to some conclusions: the permeability of the sample increases nonlinearly during the unloading confining pressure process. The larger the gas pressure is, the greater the increase range of the permeability will be. The larger the confining pressure unloading amplitude is, the greater the increase range of the permeability will be. In the loading process, the permeability and the axial strain of the specimen change in a “V” shape. As the gas pressure increases, the peak strength of the specimen gradually decreases, and fitted the gas pressure and the peak strength are accordance with the linear relationship. As the confining pressure increase, the peak strength of the sample gradually increases, and fitted the confining pressure and the peak strength are accordance with the exponential function. The internal friction angle of the coal sample was 43.22°, and the cohesion was 3.77 MPa. The relationship between the fitted gas pressure and internal friction angle, gas pressure and cohesion is in line with linear functions. Maintain an axial stress constant, unloaded confining pressure to a constant state of target value, the permeability of specimen shows a constant pressure boosting flow zone, the relationship between permeability and deviatoric stress is accordance with the ExpDec1 function during the process of unloading confining pressure and prepeak loading axial stress.

Experimental Study on the Wet Electrostatic Precipitator for Purifying Converter Gas

Converter gas must be purified by the wet electrostatic precipitator for the combined cycle power plant because of its high dust concentration. However, most of the electrostatic precipitator is placed after the gas tank in order to operate safely. This will result in larger amounts of dust entering into the gas tank or the atmosphere. It causes the gas tank’s seal damaged and air pollution. Based on the above reasons, the authors put forward a new process which places the wet electrostatic precipitator before the gas tank for purifying the converter gas, and analyzed the feasibility of this process. The research on corona discharge of converter gas in electrostatic precipitator, V-I characteristics affected by the water pressure and collection efficiency of the dust particles was carried out at an experimental system. The results show that corona discharge performance of converter gas was good and the V-I characteristic curve gradually moves down when the gas pressure increases. Spraying water can promote the collection efficiency of the dust particles. When the water pressure is 0.3MPa, the collection efficiency is 97.4%. The optimal water pressure in wet electrostatic is 0.3~0.5 MPa. From the results and analysis, it is feasible to purify converter gas by using the wet ESP which is placed before the gas tank.

A high sensitivity gas pressure sensor based on femtosecond laser micro/nano processing

A compact and novel Mach-Zehnder interferometer used for gas pressure sensing is proposed and demonstrated experimentally. The sensor is constructed by fusion splicing a short piece of dual side-hole fiber (DSHF) in between two sections of multimode fibers (MMF). Interference occurs as the optical path length difference (OPLD) between light beams along air holes and silica of the DSHF. With the opening drilled on one air hole by femtosecond laser micro/nano processing, the filled gas directly affects light beam along this air hole, which results in the interference spectrum shift. Experimental results show that the sensor exhibits a high sensitivity of −8.58 nm/MPa with the increasing gas pressure. The sensor has potential application in gas pressure sensing for its advantages of high sensitivity, low temperature crosstalk and easy fabrication.

Laser-Assisted Synthesis of Cu-Al-Ni Shape Memory Alloys: Effect of Inert Gas Pressure and Ni Content.

The paper explores the applicability of laser-assisted synthesis for producing high density Cu-Al-Ni alloys with shape memory characteristics, that could be further developed towards a method of additive manufacturing of large size Cu-based shape memory alloys (SMA). The manufacturing approach consists in laser melting of elemental powder mixture in a controlled atmosphere of varying relative pressure of protective argon gas, producing alloys of 14.2 wt.% Al and Ni content varying between 2 and 4 wt.%. All the fabricated alloys are found to have attained martensitic microstructures capable of SMA specific phase transformations in the temperature range from 85 to 192 °C. Both gas pressure and content of Ni are found to affect the specific transformation temperatures, transformation enthalpies, and mechanical properties. In particular, increasing gas pressure suppresses the austenite to martensite transformation reducing microhardness. In conclusion, the selective laser melting (SLM) employed in this work is shown capable of producing high density Cu-Al-Ni SMA (porosity ≈ 2%).

Air-Core-Liquid-Ring (ACLR) Atomization: Influences of Gas Pressure and Atomizer Scale Up on Atomization Efficiency

Air-core-liquid-ring (ACLR) atomizers present a specific type of internal mixing pneumatic atomizers, which can be used for efficient atomization of high viscous liquids. Generally, atomization efficiency is considered as a correlation between energy input and resulting droplet size. In pneumatic atomization, air-to-liquid ratio by mass (ALR) is commonly used as reference parameter of energy input. However, the pressure energy of the atomization gas is not considered in the calculation of ALR. In internal mixing ACLR atomizers, it can be assumed that this energy contributes to liquid disintegration by expansion of the gas core after exiting the atomizer. This leads to the hypothesis that droplet sizes decrease with increasing gas pressure at constant ALR. Therefore, the use of volumetric energy density (EV) as a reference parameter of energy input was investigated at different gas pressures between 0.4 and 0.8 MPa. Furthermore, scale up-related influences on the atomization efficiency of ACLR atomization were investigated by use of an atomizer with enlarged exit orifice diameter. We can conclude that EV can be applied as a reference parameter of ACLR atomization processes with different gas pressures. However, within the range investigated no clear influence of gas pressure on atomization efficiency was found. Up-scaling of ACLR atomizers allows production of similar droplet sizes, but atomization efficiency decreases with increasing exit orifice diameter.

Aging characteristic of effective distance on injecting N2 to displace CH4 in anisotropic coal seam

ABSTRACTGas injection is an effective way to enhance methane drainage in a low permeability coal seam, and the reasonable distance between injection holes and drainage holes depends on effective influence distance of injection gas in a coal seam. For anisotropic permeability of coal seam, the variation of the gas-flow rate from a test hole in the anisotropic coal seam is measured as nitrogen is injected into the injection hole near the test hole. The effective distance regularity is revealed by nitrogen injection in an anisotropic coal seam, and the model of nitrogen injection is established to numerically analyze the aging characteristic of effective influence distance in the anisotropic coal seam. The results show that the permeability in coal seam reduced exponentially with the increase in gas pressure, and it is larger in the direction of parallel to bedding than that in the direction of perpendicular to bedding. The effective distance with nitrogen injection increased exponentially in the direction of parallel/perpendicular to bedding, and the effective distance in the direction of parallel to bedding is bigger than that in the direction of perpendicular to bedding. The optimum distances between injection hole and test hole, with 0.5 MPa of injection gas pressure and 8.36 h of injection gas time, are 2.05 m in parallel to bedding direction, and 1.53 m in perpendicular to bedding direction. This study will have important theoretical and practical significance for a reasonable layout of injection-drainage holes during injecting gas to enhance methane drainage.

Growth control of corundum-derivative MnSnO3 thin films by pulsed-laser deposition

The periodic arrangement of equimolar two cations in the corundum structure produces the ilmenite-type and LiNbO3-type orderings. The phase (polymorphism) control is one of the important topics in solid-state chemistry. Using a pulsed-laser deposition technique, we examined the formation of MnSnO3 films as a function of oxygen gas pressure. Under the optimal low oxygen gas pressure, c-axis oriented single-crystalline films of the ilmenite-type MnSnO3 were synthesized on Al2O3 (0001). We found that, with an increase of oxygen gas pressure, x-ray diffraction peaks characteristic of the ilmenite-type ordering disappeared and the c-axis length approached that of the LiNbO3-type MnSnO3 while the crystal structure retained basic features of corundum derivatives. The optical bandgap measurement revealed the decrease of bandgap in the LiNbO3-type (or disordered corundum-type) MnSnO3. The thin-film approach can add a new degree of freedom in the control of structural and physical properties in corundum-derivative oxides.

Continuous bubble reactor using carbon dioxide and its mixtures for ballast water treatment

The treatment of ballast water is indispensable for preventing ecological and economic damage from the spread of invasive species. In this study, a continuous gas bubble reactor (CBR) system was developed for the efficient disinfection of microorganisms in ballast water. Ballast water treatment (BWT) in the CBR was experimentally performed to disinfect Artemia salina in seawater by using 1) pure CO2 and 2) mixtures with CO2, N2, and/or SO2 as a simulated flue gas (CO2/N2: 20%/80% and CO2/N2/SO2: 19.2%/77.0%/3.8%). The BWT efficiency was improved with an increase in gas flowrate, residence time, gas pressure, and CO2 concentration in the gas. The toxicity of SO2 in the CO2 mixture significantly improved the mortality of microorganisms. Since good dispersion of bubbles and effective contact between bubbles and liquid were important factors in the BWT, a 100% mortality rate of microorganisms could be achieved by controlling the operating conditions in the vertical-type CBR with a counter-current flow between the gas bubbles and seawater. The CO2 gas distribution, CO2 solubility, and gas bubble size distribution in the CBR were determined using computational fluid dynamics (CFD) and experimentally confirmed using a high-speed camera. Since excess gas can be recovered from a gas-liquid separator before a ballast tank, the CBR system can be operated without using any toxic or explosive gases in an eco-friendly and energy saving manner.

Methane spikes, background seasonality and non-detections on Mars: A geological perspective

The story of methane (CH4) on Mars continues to grow. A long series of CH4 detections (spikes, plumes, seasonal variations) and non-detections in the martian atmosphere suggest that CH4 is occasionally released from subsurface rocks, but also that an unknown process of rapid CH4 removal in the atmosphere must exist. The observations can be interpreted integrating concepts of subsurface geological gas source variability (CH4 seepage flux patterns), atmospheric chemistry (CH4 removal processes), and atmospheric circulation (CH4 transport and dilution). While the last two are widely studied, potential gas seepage patterns on Mars have never been discussed. In this work, we use the factors controlling gas seepage flux patterns observed on Earth to address key questions about the significance of the martian detections and non-detections. As on Earth, CH4 seepage on Mars must occur mainly through advection (non-diffusion) mechanisms, driven by pressure gradients and permeability, typically related to faults and fracture networks, which control release patterns, in terms of intensity, duration and variability. CH4 release may occur, therefore, whenever gas pressure and/or rock permeability increase (e.g., via destabilization of storage bodies such as clathrates or zeolites; breaching of seals such as permafrost; planetary stresses, impacts, or gas pressure build-up along faults). Rapid atmospheric pressure changes, due to storms and winds, may also play a role. All these forcings can lead to local, episodic, irregular or seasonal gas releases, which may explain the observations acquired so far if relatively rapid (month or day time-scales) mechanisms of CH4 removal exist in the lower atmosphere or near-surface. The release patterns cannot reveal whether CH4 is biologic or abiotic. If CH4 sensors operate discontinuously and only in one site or over limited regions, then, non-detections will be the rule and detections will be relatively rare. The chances of CH4 detection may increase if the observations are focused and repeated on specific, potential areas of gas release determined by geological analysis.

Evidence for radiation pressure compression in the X-ray narrow-line region of Seyfert galaxies

The observed spatial and kinematic overlap between soft X-ray emission and the Narrow Line Region (NLR) in obscured Active Galactic Nuclei (AGN) yields compelling evidence that relatively low-density gas co-exists with higher density gas on scales as large as 100s of pc. This is commonly interpreted as evidence for a constant gas pressure multiphase medium, likely produced by thermal instability. Alternatively, Radiation Pressure Compression (RPC) also leads to a density distribution, since a gas pressure (and hence density) gradient must arise within each cloud to counteract the incident ionising radiation pressure. RPC leads to a well-defined ionization distribution, and a Differential Emission Measure (DEM) distribution with a universal slope of $\sim-0.9$, weakly dependent on the gas properties and the illuminating radiation field. In contrast, a multiphase medium does not predict the form of the DEM. The observed DEMs of obscured AGN with XMM-Newton RGS spectra (the CHRESOS sample) are in striking agreement with the predicted RPC DEM, providing a clear signature that RPC is the dominant mechanism for the observed range of densities in the X-ray NLR. In contrast with the constant gas pressure multiphase medium, RPC further predicts an increasing gas pressure with decreasing ionization, which can be tested with future X-ray missions using density diagnostics.

Diagnostics of low-pressure capacitively coupled RF discharge argon plasma

Low-pressure capacitively coupled RF discharge Ar plasma has been studied using Langmuir probe. The electron temperature, electron density and Debay length were calculated under different pressures and electrode gap. In this work the RF Langmuir probe is designed using 4MHz filter as compensation circuit and I-V probe characteristic have been investigated. The pressure varied from 0.07 mbar to 0.1 mbar while electrode gap varied from 2-5 cm. The plasma was generated using power supply at 4MHz frequency with power 300 W. The flowmeter is used to control Argon gas flow in the range of 600 standard cubic centimeters per minute (sccm). The electron temperature drops slowly with pressure and it's gradually decreased when expanding the electrode gap. As the gas pressure increases, the plasma density rises slightly at low gas pressure while it drops little at higher gas pressure. The electron density decreases rapidly with expand distances between electrodes.