Search Results (577)

Molecular structural disparities between maceral components are intrinsic factors governing their reactivity and physicochemical behaviors during storage and transportation. To investigate the molecular structural differentiation between vitrain and durain in low- to medium-rank coals (R_o,max = 0.65–1.71%), this study selected samples of long-flame coal and gas coal from the Huanglong Coalfield, coking coal from the Hedong Coalfield, and fat coal from the Weibei Coalfield. The microstructural variations in macroscopic coal components during coalification were analyzed using Fourier transform infrared spectroscopy (FTIR), ¹³C nuclear magnetic resonance (¹³C-NMR), and X-ray photoelectron spectroscopy (XPS). The results indicated that the aromatic structures of vitrain are predominantly trisubstituted, with their proportion consistently exceeding that in durain. In contrast, durain exhibits a progressive transition from trisubstituted to pentasubstituted aromatics with increasing coal rank, accompanied by higher aromaticity, condensation degree, and aromatic carbon content. The d₀₀₂ size of the vitrain decreased from 3.82 to 3.47, while that of the durain decreased from 3.52 to 3.40. Both values showed a gradual decline, with the vitrain exhibiting a larger reduction than the durain. This indicates that the lateral extension of the microcrystalline structure in the durain is more developed, resulting in tighter molecular connections. ¹³C-NMR analysis further reveals that durain possesses higher f_al^H/f_al^* and bridge carbon ratios (X_BP), along with a lower f_a^S/f_a^’ ratio, reflecting a greater degree of aromatic ring condensation. XPS analysis revealed that durain generally contains a higher oxygen-functional group content but lower C-C/C-H content compared to vitrain. Collectively, these findings confirm significant structural divergence between vitrain and durain during coalification, with durain exhibiting more developed aromaticity, structural condensation, and organizational order. Full article

The transition toward sustainable energy systems necessitates innovative solutions that reduce greenhouse gas emissions while improving fuel efficiency in existing combustion technologies. Hydrogen has emerged as a promising clean energy carrier; however, its widespread deployment is limited by challenges associated with large-scale transportation and storage. This study investigates a practical alternative in which hydrogen-rich syngas produced via steam methane reforming (SMR) is directly integrated into the diesel engine intake, thereby eliminating the need for fuel transport, storage, and separation while supporting a more sustainable fuel pathway. A validated computational fluid dynamics (CFD) model was developed to examine the effects of varying SMR gas mixture ratios (0–20%) on engine combustion, performance, and emissions. The findings reveal that increasing the SMR fraction enhances in-cylinder pressure by up to 15.7%, heat release rate by 100%, and engine power output by 102.5% compared to conventional diesel operation. Additionally, under SMR20 conditions, CO₂ emissions are reduced by approximately 12%, demonstrating the potential contribution of this approach to decarbonization and climate mitigation efforts. However, the rise in in-cylinder temperatures was found to increase NO_x formation, indicating the necessity for complementary emission control strategies. Overall, the results suggest that direct SMR syngas integration offers a promising pathway to improve the environmental and performance characteristics of conventional diesel engines while supporting cleaner energy transitions. Full article

The aviation industry, responsible for approximately 2.5–3.5% of global greenhouse gas emissions, faces increasing pressure to adopt sustainable energy solutions. Hydrogen, with its high gravimetric energy density and zero carbon emissions during use, has emerged as a promising alternative fuel to support aviation decarbonization. However, its large-scale implementation remains hindered by cryogenic storage requirements, safety risks, infrastructure adaptation, and economic constraints. This study aims to identify and evaluate the primary technical and operational risks associated with hydrogen utilization in aviation through a comprehensive Monte Carlo Simulation-based risk assessment. The analysis specifically focuses on four key domains—hydrogen leakage, cryogenic storage, explosion hazards, and infrastructure challenges—while excluding economic and lifecycle aspects to maintain a technical scope only. A 10,000-iteration simulation was conducted to quantify the probability and impact of each risk factor. Results indicate that hydrogen leakage and explosion hazards represent the most critical risks, with mean risk scores exceeding 20 on a 25-point scale, whereas investment costs and technical expertise were ranked as comparatively low-level risks. Based on these findings, strategic mitigation measures—including real-time leak detection systems, composite cryotank technologies, and standardized safety protocols—are proposed to enhance system reliability and support the safe integration of hydrogen-powered aviation. This study contributes to a data-driven understanding of hydrogen-related risks and provides a technological roadmap for advancing carbon-neutral air transport. Full article

This study focuses on the development and physicochemical evaluation of an alternative liquid carrier for coal dust combustion modifiers containing solid catalyst particles. A commercially used acrylic-polymer-based carrier, whose viscosity is regulated by sodium hydroxide addition, was investigated and compared with a proposed safer substitute based on an aqueous sodium carboxymethyl cellulose (Na-CMC) solution. Rheological properties were measured in the shear-rate range relevant to industrial transport and injection systems, while sedimentation behavior was assessed using image-based analysis. The results show that the Na-CMC carrier exhibits shear-thinning behavior and viscosity levels comparable to the commercial formulation, enabling stable suspension of catalyst particles without the need for alkali additives. Unlike the reference system, the alternative carrier does not generate gas during storage, eliminating potential safety hazards associated with hydrogen evolution. Although no direct combustion experiments were performed, the obtained rheological and stability characteristics indicate that the proposed Na-CMC-based carrier is suitable for short-term storage and injection of catalyst-containing modifiers in coal dust combustion systems. Direct validation of combustion performance is planned in future work. Full article

The heterogeneity of pore structure in deep coal reservoirs is a critical factor controlling the storage and transport capacity of coalbed methane (CBM). However, the fundamental control exerted by macrolithotypes remains inadequately quantified. This study systematically investigates the No. 8 coal seam of the Taiyuan Formation in the Daniudi gas field, Ordos Basin, using an integrated multi-technique approach including high-pressure mercury intrusion (HPMI), low-temperature N₂ adsorption (LTGA-N₂), and low-pressure CO₂ adsorption (LPGA-CO₂). Results reveal a consistent bimodal pore structure across all samples, dominated by well-developed micropores and macropores, whereas mesopores are relatively underdeveloped. More importantly, a clear macrolithotype control is established: as coal brightness decreases from bright to dull coal, the proportions of micropores and macropores decline significantly, leading to a substantial reduction in total pore volume and specific surface area. Fractal analysis further indicates that dull and semi-dull coals exhibit larger fractal dimensions, reflecting more complex pore structures and stronger heterogeneity compared to bright and semi-bright coals. This heterogeneity shows a positive correlation with ash and mineral contents, but a negative correlation with vitrinite and fixed carbon contents, suggesting that coal composition plays a primary governing role. These findings underscore that bright and semi-bright coals, with their superior micropore storage capacity and well-connected macropore networks, represent the most favorable targets for deep CBM exploration. This work establishes macrolithotype as a practical key indicator for reservoir quality assessment and production strategy optimization in deep CBM plays. Full article

Ammonia (NH₃) is a zero-carbon fuel and an attractive hydrogen (H₂) carrier for gas turbine power generation due to its high energy density, ease of storage, and transportation. This study numerically investigates NH₃/air combustion using a hybrid Well-Stirred Reactor (WSR) and Plug Flow Reactor (PFR) model in Cantera at pressures of 1–20 atm, temperatures of 1850–2150 K, and equivalence ratios (ϕ) of 0.7–1.2. The effects of pressure, equivalence ratio, and temperature on NH₃ conversion and NO formation are examined. Results show that NH₃ exhibits a non-monotonic conversion curve with pressure after the WSR, reaching a minimum near 5 atm, whereas NO formation decreases monotonically from 1 to 20 atm. Equivalence ratio sweeps show that NO decreases steeply as ϕ increases from 0.7 to ~1.1 as nitrogen is redirected toward N₂ and oxidizer availability declines; residual NH₃ increases rapidly for ϕ > 1.0, especially at high pressure. Increasing temperature accelerates NH₃ oxidation and raises NO formation, most strongly at low pressure where thermal and NH/OH pathways are least inhibited. These results indicate that co-tuning pressure and equivalence ratio near rich operation enables low-NO_x ammonia combustion suitable for advanced gas turbine applications. Full article

Coalbed methane development is constrained by reservoir characteristics including high gas adsorption, high salinity, and high closure pressure, which impose significant limitations on conventional polymer fracturing fluids regarding viscosity enhancement, proppant transport, and fracture maintenance. In this study, a novel polymer fracturing fluid system, Z-H-PAM, was designed and synthesized to achieve strong salt tolerance, low adsorption affinity, and high elasticity to withstand closure pressure. This was accomplished through the molecular integration of a zwitterionic monomer ZM-1 and a hydrophobic associative monomer HM-2, forming a unified structure that combines rigid hydrated segments with a hydrophobic elastic network. The results indicate that ZM-1 provides a stable hydration layer and low adsorption tendency under high-salinity conditions, while HM-2 contributes to a high-storage-modulus, three-dimensional physically cross-linked network via reversible hydrophobic association. Their synergistic interaction enables Z-H-PAM to retain viscoelasticity that is significantly superior to conventional HPAM and to achieve rapid structural recovery in high-mineralization environments. Systematic evaluation shows that this system achieves a static sand-suspension rate exceeding 95% in simulated flowback fluid, produces broken gel residues below 90 mg/L, and results in a core damage rate of only 10.5%. Moreover, it maintains 88.8% of its fracture conductivity under 30 MPa closure pressure. Notably, Z-H-PAM can be prepared directly using high-salinity flowback water, maintaining high elasticity and sand-carrying capacity while enabling fluid recycling and reducing reservoir damage. This work clarifies the multi-scale mechanisms of strongly hydrated and highly elastic polymers in coalbed methane reservoirs, offering a theoretical and technical pathway for developing efficient and low-damage fracturing materials. Full article

The solidified natural gas (SNG) technology presents a prospective strategy for CH₄ storage and transportation. Low gas storage capacity and slow formation rate remain the key challenges for its field applications. This study suggested a compound system of cyclopentane (CP) + graphite nanoparticle (GNP) nanofluid to enhance the formation kinetics of CH₄ hydrate. Results indicated that both gas consumption and hydrate formation rate were higher at a higher CP concentration, peaking at 14 wt%, where t₉₀ (the time to reach 90% of the final gas uptake) was 65.7 min, and the gas uptake reached 0.1346 mol/mol. However, an excessive CP (21 wt%) negatively affected CH₄ hydrate generation kinetics due to the excessive cage occupancy of CP in 5¹²6⁴ cavities. A lower temperature was determined to be more favorable for CH₄ hydrate formation within nanofluids, which was visually demonstrated by the denser hydrate crystals formed at 275.15 K. Moreover, storage stability analysis revealed that CH₄ hydrate formed in CP + GNP nanofluids can be preserved at atmospheric pressure and 268.15 K without significant decomposition. This work provides a superior scheme for hydrate-based CH₄ storage, offering great contributions to SNG technology advancement. Full article

Supercritical CO₂ pipeline transportation is a crucial link in Carbon Capture, Utilization, and Storage (CCUS). Compared with traditional oil and gas pipelines, if a supercritical CO₂ pipeline is shut down for an excessively long time, the phase state of CO₂ may transform into a gas–liquid two-phase state. It is urgently necessary to conduct research on the phase change mechanism and safety control during the restart process of gas–liquid two-phase CO₂ pipelines. Based on a certain planned supercritical carbon dioxide pipeline demonstration project, this paper proposes a new pipeline safety restart scheme that actively seeks the liquefaction of gaseous CO₂ inside the pipeline by injecting liquid-phase CO₂ at the initial station. Through numerical simulation and experimental methods, the co-variation laws of parameters such as temperature, pressure, density, and phase state during the pipeline restart process were revealed. It was found that the pipeline shutdown and restart process could be subdivided into four stages: shutdown stage, liquefaction stage, pressurization stage, and displacement stage. The phase transition line would form a closed curve that is approximately trapezoidal. It is suggested to optimize the restart scheme from aspects such as reducing the restart time, controlling the pressure rise rate, and saving CO₂ consumption. It is proposed that the liquid holdup of CO₂ fluid in the pipe at the initial moment of restart and the mass flow rate of CO₂ injected at the initial station during the restart process are the main controlling factors affecting the evolution of the phase path of pipeline restart. For the demonstration project, the specific critical threshold values are given. The research results can provide a certain theoretical guidance and reference basis for the safe restart method of supercritical CO₂ pipelines. Full article

Cryogenic technologies are a crucial field of modern engineering, with applications in liquefied gas transport, renewable energy, aerospace, and high-precision medicine. Their advancement relies heavily on the performance and reliability of cryogenic tanks, which ensure the safe storage and handling of fluids at extremely low temperatures. This paper presents a concise review of recent engineering innovations, focusing on fluid behavior in single- and two-phase regimes, boil-off mechanisms, advanced thermal insulation, and energy loss control strategies. Recent numerical and experimental studies indicate that optimized insulation configurations, such as the placement of a low-emissivity intermediate layer near the cold wall, can reduce radiative heat loads by approximately 40–60%, thereby significantly mitigating cryogenic liquid boil-off. Developments in structural materials, functional coatings, and numerical simulations are also discussed, as they contribute to enhancing tank efficiency under demanding operational conditions. Particular emphasis is placed on material selection and surface engineering solutions aimed at reducing corrosion, improving cryogenic resistance, and extending service life. These approaches not only lower maintenance costs but also strengthen safety and sustainability in cryogenic applications. In addition, current industry trends are highlighted, including equipment miniaturization, integration into mobile platforms, and the adoption of international standards for safety and efficiency. The paper aims to provide an interdisciplinary synthesis that supports both academic research and the development of durable, high-performance cryogenic systems. Full article

Compressed air energy storage in aquifers presents a promising approach for large-scale energy storage, yet its implementation is complicated by geochemical reactions, such as pyrite oxidation, which can impact reservoir integrity and operational efficiency. This study numerically investigates the evolution of reservoir characteristics and geochemical processes during CAESA operations to address these challenges. Using the TOUGHREACT simulator, we developed one-dimensional and two-dimensional reactive transport models based on the Pittsfield aquifer field test parameters to simulate coupled thermal-hydrological–chemical processes under varying injection rates, temperatures, reservoir depths, and operational cycles. The results demonstrate that higher injection rates induce greater near-well pressure buildup and extended thermal zones, while deeper reservoirs exhibit abrupt declines in pressure and gas saturation due to formation constraints. Geochemical analyses reveal that pyrite oxidation dominates, leading to oxygen depletion, groundwater acidification (pH reduction), and secondary mineral precipitation, such as goethite and hematite. These findings underscore the critical interplay between operational parameters and geochemical reactions, highlighting the need for optimized design to ensure long-term stability and efficiency of aquifer-based energy storage systems. Full article

Maritime transport accounts for approximately 80–90% of global trade and nearly 3% of global greenhouse gas (GHG) emissions. In response, the International Maritime Organization (IMO) adopted an ambitious strategy for net-zero emissions by 2050, critically mandating a Well-to-Wake (WtW) life-cycle assessment for fuels. This framework invalidates fuels produced with high carbon intensity, regardless of their emissions at the point of use, thereby compelling the industry to focus on truly clean and sustainable alternatives. This push positions green hydrogen and ammonia as leading solutions, though they present a distinct trade-off. Hydrogen is an ideal fuel with zero-carbon emission in fuel cells but faces significant storage challenges due to its extremely low volumetric energy density and cryogenic requirements. In contrast, ammonia offers superior energy density and easier handling but contends with issues of toxicity and potentially harmful emissions like nitrous oxide. This paper provides a comprehensive review of this complex landscape, analyzing the production, utilization, and associated techno-economic and geopolitical challenges of using hydrogen and ammonia as future marine fuels, with environmental aspects briefly considered. Full article

Decarbonization of transport is a key element of the energy transition and of achieving the Sustainable Development Goals. Integration of renewable energy into transport systems is assessed together with the potential of electric, hybrid, hydrogen, and biofuel-based propulsion to enable low emission mobility. Literature published from 2019 to 2025 is synthesized using structured searches in Scopus, Web of Science, and Elsevier and evidence is integrated through a thematic comparative approach focused on energy efficiency, life cycle greenhouse gas emissions, and technology readiness. Quantitative findings indicate that battery electric vehicles typically require about 18 to 20 kWh per 100 km, compared with about 60 to 70 kWh per 100 km in energy equivalent terms for internal combustion cars. With higher renewable shares in electricity generation, life cycle CO₂ equivalent emissions are reduced by about 60 to 70 percent under average European grid conditions and up to about 80 percent when renewables exceed 50 percent. Energy storage and smart grid management, including vehicle to grid operation, are identified as enabling measures and are associated with peak demand reductions of about 5 to 10 percent. Hydrogen and advanced biofuels remain important for heavy duty, maritime, and aviation segments where full electrification is constrained. Full article

Renewable methanol is considered a promising carrier for sustainable hydrogen due to its convenience in storage and transportation. Methanol steam reforming (MSR) using exhaust heat from industrial boilers can further enhance energy efficiency. However, existing methanol reforming systems still face challenges in terms of matching with industrial boilers, heat exchanger compactness, and adaptability to fluctuations in exhaust gas conditions. To address these issues, this study proposes the design of a modular methanol reforming system driven by the exhaust heat of small industrial boilers and develops a three-dimensional multiphysics simulation model to investigate the heat transfer and reaction characteristics within the reactor. The results indicate that, within the ranges of exhaust heat temperature (220–270 °C), flow rate (0.4–1.2 g/s), and channel spacing (60–100 mm), increasing the exhaust heat temperature enhances the endothermic reforming process, while decreasing the channel spacing improves heat transfer and increases methanol conversion. The reactor with a 60 mm channel spacing achieves a conversion ratio of up to 95.3% at a flow rate of 0.4 g/s. Although the hydrogen yield increases with flow rate, the single-pass conversion ratio decreases due to shorter residence time and increased load per unit volume. Compared to traditional fixed-structure reactors, the proposed modular system allows flexible matching of scale and heat exchange capacity through adjustable channel configurations, enhancing adaptability to fluctuations in industrial exhaust temperature and load. This design improves the utilization efficiency of low-grade waste heat and offers a practical engineering solution for sustainable distributed hydrogen production. Full article

Molten salt heat exchangers are crucial components in systems requiring high-temperature heat transfer and energy storage, especially in renewable energy and advanced nuclear technologies. Their ability to operate efficiently at high temperatures while offering significant energy storage capacity makes them highly valuable in modern energy systems. They have high thermal stability. In the framework of this research, a computational fluid dynamics (CFD) simulation model of the HITEC molten salt cooling system has been developed. HITEC molten salt is a specialized heat transfer and thermal energy storage medium primarily used in industrial processes and solar thermal power plants. It is a eutectic blend of sodium nitrate, sodium nitrite, and potassium nitrate. COMSOL multi-physics code has been employed in this research. It simultaneously solves the fluid flow, energy, and heat conduction transport equations. Two cases have been investigated in this paper: a water flowing velocity of 1 [m/s] and a water flowing velocity of 10 [m/s]. The results indicate that the maximal surface temperature of the Crofer^®22 H reached 441.2 °C in the first case. The maximal surface temperature of the Crofer^®22 H reached 500 °C in the second case. Crofer^®22 H alloy provides excellent steam oxidation, high corrosion resistance, and thermal creep resistance. The proposed HITEC molten thermal system may be applied in the oil and gas industries and in power plants (such as the Organic Rankine Cycle). Full article