Search Results (30)

Supercritical combustion is a promising technique for improving the efficiency and reducing the emissions of next-generation gas turbines. However, accurately modeling combustion under these conditions remains a challenge, particularly due to the complexity of chemical kinetics. This study aims to evaluate the applicability of a reduced global reaction mechanism compared to the detailed Foundational Fuel Chemistry Model 1.0 (FFCM-1) when performing hydrogen combustion with supercritical carbon dioxide and argon as diluents. Computational fluid dynamics simulations were conducted in two geometries: a simplified tube for isolating chemical effects and a combustor with cooling channels for practical evaluation. The analysis focuses on the evaluation of velocity, temperature, and the water vapor mass fraction distributions inside the combustion chamber. The results indicate good agreement between the global and detailed mechanisms, with average relative errors below 2% for supercritical argon and 4% for supercritical carbon dioxide. Both models captured key combustion behaviors, including buoyancy-driven flame asymmetry caused by the high density of supercritical fluids. The findings suggest that global chemistry models can serve as efficient tools for simulating supercritical combustion processes, making them valuable for the design and optimization of future supercritical gas turbine systems. Full article

This experimental study examines the particle-level combustion behavior of high-volatile bituminous coal and walnut shell particles in oxyfuel environments, with a particular focus on the gas-phase ignition characteristics and the structural development of volatile flames. Particles with similar size and shape distributions (a median diameter of about 126 µm and an aspect ratio of around 1.5) are combusted in hot flows generated using lean, flat flames, where the oxygen mole fraction is systematically varied in both CO₂/O₂ and N₂/O₂ atmospheres while maintaining comparable gas temperatures and particle heating rates. The investigation employs a high-speed multi-camera diagnostic system combining laser-induced fluorescence of OH, diffuse backlight-illumination, and Mie scattering to simultaneously measure the particle size, shape, and velocity; the ignition delay time; and the volatile flame dynamics during early-stage volatile combustion. Advanced detection algorithms enable the extraction of these multiple parameters from spatiotemporally synchronized measurements. The results reveal that the ignition delay time decreases with an increasing oxygen mole fraction up to 30 vol%, beyond which point further oxygen enrichment no longer accelerates the ignition, as the process becomes limited by the volatile release rate. In contrast, the reactivity of volatile flames shows continuous enhancement with an increasing oxygen mole fraction, indicating non-premixed flame behavior governed by the diffusion of oxygen toward the particles. The analysis of the flame stand-off distance demonstrates that volatile flames burn closer to the particles at higher oxygen mole fractions, consistent with the expected scaling of O₂ diffusion with its partial pressure. Notably, walnut shell and coal particles exhibit remarkably similar ignition delay times, volatile flame sizes, and OH-LIF intensities. The substitution of N₂ with CO₂ produces minimal differences, suggesting that for 126 µm particles under high-heating-rate conditions, the relatively small variations in the heat capacity and O₂ diffusivity between these diluents have negligible effects on the homogeneous combustion phenomena observed. Full article

The production of very-low-sulfur residual fuel oil is a great challenge for modern petroleum refining because of the instability issues caused by blending incompatible relatively high-sulfur residual oils and ultra-low-sulfur light distillates. Another obstacle in the production of very-low-sulfur residual fuel oil using hydroprocessing technology is the contradiction of hydrodesulfurization with hydrodemetallization, as well as the hydrodeasphaltization functions of the catalytic system used. Therefore, the production of very-low-sulfur residual fuel oil by employing hydroprocessing could be achieved by finding an appropriate residual oil to be hydroprocessed and optimal operating conditions and by controlling catalyst system condition management. In the current study, data on the characteristics of 120 samples of heavy fuel oils produced regularly over a period of 10 years from a high-complexity refinery utilizing H–oil vacuum residue hydrocrackers in its processing scheme, the crude oils refined during their production, the recipes of the heavy fuel oils, and the level of H–oil vacuum residue conversion have been analyzed by using intercriteria and regression analyses. Artificial neural network models were developed to predict the characteristics of hydrocracked vacuum residues, the main component for the production of heavy fuel oil. It was found that stable very-low-sulfur residual fuel oil can be manufactured from crude oils whose sulfur content is no higher than 0.9 wt.% by using ebullated bed hydrocracking technology. The diluents used to reduce residue viscosity were highly aromatic FCC gas oils, and the hydrodemetallization rate was higher than 93%. Full article

Porous materials are used in many important applications, such as separation technologies, catalysis, and chromatography. They may be obtained from various monomers via diverse polymerization techniques and a wide range of synthesis parameters. The study is devoted to the synthesis and characterization of crosslinked porous polymeric spheres containing pyrrolidone subunits. To achieve this goal, two methods were applied: direct synthesis from N-vinyl-2-pyrrolidone (NVP) with ethylene glycol dimethacrylate (EGDMA) and via a modification reaction of porous poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) with pyrrolidone (P). The polymerization was carried out with the use of different molar ratios of the monomers. In order to obtain highly porous materials, pore-forming diluents (toluene, dodecane, and dodecan-1-ol) were used. The synthesized copolymers were characterized using size distribution analysis, ATR-FTIR spectroscopy, scanning electron microscopy, thermogravimetry, and inverse gas chromatography. Determined by the nitrogen adsorption/desorption method, the specific surface area was in the range of 55–468 m²/g. The good thermal properties of the poly(VP-co-EGDMA) copolymers allowed them to be applied as the stationary phase in gas chromatography. Full article

Non-thermal plasma (NTP) conversion applications have become an emerging technology of increasing global interest due to their particular ability to perform at atmospheric pressure and ambient temperature. This study focuses on a specific case of a dielectric barrier discharge NTP reactor for carbon dioxide conversion with the usage of argon as diluent gas. The plasma computations in COMSOL^® Multiphysics are compared to experimental results and coupled with previous thermodynamic characterization of argon species and fluid dynamic calculations. The model is defined as a time-dependent study with a 2D-Geometry of pure argon, with both fluid flow and plasma phenomena. Firstly, the model showcases an accurate understanding of the plasma physics involved, in the form of electron density, excited argon, argon ions, and mean electron energy. It also allows a direct comparison of the velocity, vorticity, pressure, and dynamic viscosity results with fluid flow computations. Secondly, the impact of several variables is studied, notably the inlet volumetric rate, dielectric barrier thickness and material, and reactor length. Limitations in the plasma characterization can occur by not including packed material or all relevant species in experimental CO₂ conversion and their respective reactions, which should be aimed at in future contributions. Full article

Ultraviolet (UV) curing is an efficient and environmentally friendly curing method. In this paper, UV-cured polyurethane acrylates (PUAs) were investigated as potential military coatings to serve as barriers against chemical warfare agents (CWAs). Seven UV-cured PUA coatings were formulated utilizing hydroxyethyl methacrylate-capped hexamethylene diisocyanate trimer (HEMA-Htri) and trimethylolpropane triacrylate-capped polycarbonate prepolymer (PETA-PCDL) as the PUA monomers. Isobornyl acrylate (IBOA) and triethyleneglycol divinyl ether (DVE-3) were employed as reactive diluents. Gas chromatography was utilized to investigate the constitutive relationships between the structures of the PUA coatings and their protective properties against simulant agents for CWAs, including dimethyl methylphosphonate (DMMP), a nerve agent simulant, and 2-chloroethyl ethyl sulfide (CEES), a mustard simulant. The glass transition temperature (T_g) and crosslinking density (υ_e) of PUAs were found to be crucial factors affecting their ability to serve as barriers against CWAs. The incorporation of IBOA units led to enhanced T_g and barrier performance of the PUAs, resulting in a DMMP retention of less than 0.5% and nearly 0 retention of CEES. However, an excessive introduction of polycarbonate chains decreased the υ_e and barrier performance of the PUAs. These findings may offer valuable insights for enhancing the protection of UV-cured PU coatings against CWAs. Full article

The thermodynamic modeling of waste oil (WO) gasification by a high-temperature gasification agent (GA) composed of an ultra-superheated H₂O/CO₂ mixture is carried out. The GA is assumed to be obtained by the gaseous detonation of fuel–oxidizer–diluent mixture in a pulsed detonation gun (PDG). N-hexadecane is used as a WO surrogate. Methane or the produced syngas (generally a mixture of H₂, CO, CH₄, CO₂, etc.) is used as fuel for the PDG. Oxygen, air, or oxygen-enriched air are used as oxidizers for the PDG. Low-temperature steam is used as a diluent gas. The gasification process is assumed to proceed in a flow-through gasifier at atmospheric pressure. It is shown that the use of the detonation products of the stoichiometric methane–oxygen and methane–air mixtures theoretically leads to the complete conversion of WO into a syngas consisting exclusively of H₂ and CO, or into energy gas with high contents of CH₄ and C₂-C₃ hydrocarbons and an LHV of 36.7 (fuel–oxygen mixture) and 13.6 MJ/kg (fuel–air mixture). The use of the detonation products of the stoichiometric mixture of the produced syngas with oxygen or with oxygen-enriched air also allows theoretically achieving the complete conversion of WO into syngas consisting exclusively of H₂ and CO. About 33% of the produced syngas mixed with oxygen can be theoretically used for PDG self-feeding, thus making the gasification technology very attractive and cost-effective. To self-feed the PDG with the mixture of the produced syngas with air, it is necessary to increase the backpressure in the gasifier and/or enrich the air with oxygen. The addition of low-temperature steam to the fuel–oxygen mixture in the PDG allows controlling the H₂/CO ratio in the produced syngas from 1.3 to 3.4. Full article

In this paper, we investigated the behaviors of bubbles entrained in a film coating during spray coating. Air bubbles that remain in a film coating after diluent evaporation cause coating defects called bubbling defects, including fish-eye and crater defects. In this study, the visualization of a film coating revealed that smaller bubbles in the film shrank slowly and disappeared, while larger bubbles remained. These remaining bubbles grew during the heating process for the drying of the film coating. The shrinking phenomenon was explained using bubble dynamics based on the Young–Laplace equation of a bubble’s inner pressure and Henry’s law for bubble gas dissolution into the film coating. This shrinking model is often used in studies on microbubble dynamics. The results suggested the importance of avoiding the entrainment of large bubbles during the spraying process and enhancing the release of air bubbles from the film coating’s surface through the appropriate usage of defoaming agents. Full article

The MAX phases exhibit outstanding combination of strength and ductility which are unique features of both metals and ceramics. The preparation of pure MAX phases has been challenging due to the thermodynamic auspiciousness of intermetallic formation in the ternary systems. This review demonstrates the power of the self-propagating, high-temperature synthesis method, delivers the main findings of the combustion synthesis optimization of the MAX phases, and reveals the influence of the combustion wave on the microstructure features thereof. The possibility of using elements and binary compounds as precursors, oxidizers, and diluents to control the exothermicity was comparatively analyzed from the point of view of the final composition and microstructure in the following systems: Ti-Al-C, Ti-V-Al-C, Cr-V-Al-C, Ti-Cr-Al-C, Ti-Nb-Al-C, Ti-Al-Si-C, Ti-Al-Sn-C, Ti-Al-N, Ti-Al-C-N, Ti-Al-B, Ti-Si-B, Ti-Si-C, Nb-Al-C, Cr-Al-C, Cr-Mn-Al-C, V-Al-C, Cr-V-Al-C, Ta-Al-C, Zr-S-C, Cr-Ga-C, Zr-Al-C, and Mo-Al-C, respectively. The influence of sample preparation (including the processes of preheating, mechanical activation, and microwave heating, sample geometry, porosity, and cold pressing) accompanied with the heating and cooling rates and the ambient gas pressure on the combustion parameters was deduced. The combustion preparation of the MAX phases was then summarized in chronological order. Further improvements of the synthesis conditions, along with recommendations for the products quality and microstructure control were given. The comparison of the mechanical properties of the MAX phases prepared by different approaches was illustrated wherever relevant. Full article

Procedures for determination of the residual solvent and volatile impurity content in pharmaceutical products usually rely on dissolution in a solvent, followed by headspace-gas chromatography (HS-GC) analysis. Whereas chromatographic systems can utilize a wide variety of solvents, direct-injection mass spectrometry (DIMS) techniques have fewer solvent options, because elimination of the chromatographic column means that the instrument is more susceptible to saturation. Since water has the lowest impact, it has almost always been the default solvent for DIMS. In this study, selected ion flow tube mass spectrometry (SIFT-MS)—a DIMS technique—was applied to the systematic evaluation of the proportion of solvent that can be utilized (with aqueous diluent) without causing instrument saturation and while maintaining satisfactory analytical performance. The solvents evaluated were N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), 1,3-dimethyl-2-imidazolidinone (DMI), dimethyl sulfoxide (DMSO), methanol, and triacetin. All solvents are compatible with headspace-SIFT-MS analysis at 5% (min) in water, while DMI, DMAC, and DMSO can be used at higher concentrations (50, 100, and 25%, respectively), though suffering substantial diminution of the limit of quantitation for non-polar analytes at higher proportions of non-aqueous solvent. Analytical performance was also evaluated using linearity, repeatability, and recovery measurements. This work demonstrates that organic solvents diluted in water can be utilized with headspace-SIFT-MS and provide an approach for evaluation of additional diluent solvents. Full article

In this work, the mutual solubilities of sets of organic diluents (CHCl₃, C₆H₆, C₂H₄Cl₂, CCl₄, C₆H₁₂, and n-hexane) with the organic compound ethylene glycol are investigated via gas chromatography (GC). The experimental data measured for these binary organic systems are used to adjust the future nonaqueous systems for the solvent extraction of various metals with ligands. The obtained results showed that the solubility of ethylene glycol decreased in the order CHCl₃ > C₆H₆ > C₂H₄Cl₂ > CCl₄(0%) ≈ C₆H₁₂ ≈ n-hexane. On the other hand, the solubility of the tested traditional organic diluents in ethylene glycol decreased in the following order: C₆H₆ > CHCl₃ > C₂H₄Cl₂ > n-hexane > C₆H₁₂ > CCl₄. ¹H NMR was also used as an analytic method in order to compare the obtained results for the samples showing significant solubility only, including an additional study with 1,2- or 1,3-propanediol. The enhanced solubility of the C₆H₆ compound in ethylene glycol was identified here as critical due to the GC technique, which will be without future consequences in chemical technology. Therefore, it was found that the best molecular diluent for the recovery of metals among the tested ones is C₆H₁₂, with a green protocol as the new paradigm, replacing the aqueous phase with another nonaqueous phase, i.e., a second organic diluent. Full article

This study numerically investigates the effects of diluent gas proportion, the overdrive factor, and throat width on the wave structure and thrust performance of a ram accelerator operating in super-detonative mode. For premixed gas of a high energy density, a typical unstart oblique detonation wave system is observed due to the ignition on the front wedge of the projectile, and the detonation waves move downstream to the shoulder as the energy density decreases. In the start range of the overdrive factor, the wave position also shows a tendency to move downstream as the projectile velocity increases, accompanied by oscillations of the wave surface and thrust. As the throat width increases, the wave standing position changes non-monotonously, with an interval of upstream movement and Mach reflection. The typical wave structure of a ram accelerator in super-detonative mode is identified, as well as the unstart stable wave features and the unstable process for choking, which can provide theoretical guidance for avoiding unstart issues in ram accelerators and optimizing their performance. Full article

Because the surface of MDF is not aesthetically pleasing, it usually needs to be veneered and then painted, but such a board releases harmful VOCs, among which Benzene Series is the most harmful. Benzene and its series are a group of carcinogenic compounds. With the diluents of nitrocellulose (NC)-lacquered MDF as the research objects, the release of the Benzene Series was studied to provide a scientific basis for pollution control and a reference for eco-friendly paint production. The attenuant of NC paint, anhydrous ethanol, ethyl acetate and solvents mixed with different alcohol ester ratios were used as diluents in NC lacquer. Two kinds of wood-veneered MDF with different thickness (18 mm and 8 mm) were coated with NC lacquer and analyzed in the experiment. The gas was collected using a small environmental chamber and the Benzene Series was analyzed using GC-MS. The concentration of Benzene Series released by MDF was 316.24 μg·m⁻³, and that of the NC-lacquered MDF with thicknesses of 18 mm and 8 mm were 284.44 μg·m⁻³ and 281.06 μg·m⁻³, respectively. The MDF released 14 kinds of Benzene Series, and the NC-lacquered MDF with two thicknesses released 18 kinds of it. The release concentration order of Benzene Series in NC-lacquered MDF with different diluents of the 18 mm thick panel was NC-M, NC-A, and NC-E from high to low. The lowest concentration of it occurred when the ratio of anhydrous ethanol to ethyl acetate was 1:3, and the lowest amount of components were at the ratio of 1:2. The concentration of Benzene Series released by MDF is higher than that released by the NC-lacquered MDF. Thickness has no effect on the type of release. The thicker MDF was, the higher the concentration was. The alcohol and ester thinner can control the release of Benzene Series from the source, and the optimal mixing ratio was 1:3. Full article

The direct activation of diluted CO₂ in argon was studied in a co-axial dielectric barrier discharge (DBD) reactor powered by photovoltaic energy. The influence of the initial CO₂ and argon concentration on the CO₂ decomposition to form CO was investigated using a copper-based catalyst in the discharge zone. It was observed that the CO₂ conversion was higher at lower CO₂ concentrations. The presence of the diluent gas (argon) was also studied and it was observed how it has a high influence on the decomposition of CO_2, improving the conversion at high argon concentrations. At the highest observed energy efficiency (1.7%), the CO₂ conversion obtained was 40.2%. It was observed that a way to enhance the sustainability of the process was to use photovoltaic energy. Taking into account a life cycle assessment approach (LCA), it was estimated that within the best-case scenario, it would be feasible to counterbalance 97% of the CO₂ emissions related to the process. Full article

A series of TiO₂-SiC supported Ni-based catalysts with and without ceria doping were prepared by a traditional impregnation method. CeO₂ was introduced into the catalyst in different steps of the impregnation process. All the samples were characterized by N₂ physisorption, XRD, TPR, and TGA, and were tested for the performance of CO methanation in a fixed-bed reactor under atmospheric conditions through the steam of H₂/CO = 3 without diluent gas. All the Ni-based catalysts supported by TiO₂-SiC exhibited the property of anti-sintering and could efficiently avoid carbon deposition occurring on catalysts. The experimental results show that the performance of all CeO₂ doping samples (more than 80% of CO conversion) was better than the sample without CeO₂ (around 20% of CO conversion). Introducing CeO₂ after the dry step of impregnation achieved complete CO conversion at a lower temperature compared with its introduction through doping at the co-impregnation and step-impregnation methods. The results of further characterization indicate that the addition of CeO₂ in different impregnation steps affected the dispersion of nickel on support, made the size of metal particles smaller, and changed the reducibility of catalysts. Full article