Fuel最新文献

{"title":"Kinetic and thermodynamic analyses of multigranular low-rank coal: Synergistic effect of particle size on reactivity and coke properties","authors":"Xiaowei Gan ,&nbsp;Zhengjie Chen ,&nbsp;Wenhui Ma ,&nbsp;Yakun Zhang ,&nbsp;Junyu Qu ,&nbsp;Chenguang Han ,&nbsp;Zirui Li","doi":"10.1016/j.fuel.2025.137065","DOIUrl":"10.1016/j.fuel.2025.137065","url":null,"abstract":"<div><div>This study performed kinetic and thermodynamic analyses on samples of multigranular low-rank unbound coal (LNC) with three different particle size ranges: 40–80 mesh, 80–150 mesh, and 150–300 mesh. The study investigated the pyrolytic coke yield of multigranular LNC and its reaction characteristics under a CO₂ atmosphere. The synergistic effect of particle size and coke properties on the reactivity was highlighted using a combination of characterization techniques (BET, SEM, XRD, Raman, and FTIR) and the Friedman, Kissinger-Akahira-Sunose, Flynn-Wall-Ozawa, and Starink methods. The results showed that reducing the particle size significantly increased the specific surface area and pore volume of the coal samples. Upon increasing the pyrolysis temperature, the coke yield decreased from 91.2–93.64 wt% at 300 °C to 64.8–66.92 wt% at 900 °C. The fine-grained samples had slightly lower yields because they underwent more thorough volatilization. At the same temperature, the <em>I</em>_D/<em>I</em>_G values of the fine-grained samples (150–300 mesh) were significantly higher than those of the coarse-grained samples, and they also exhibited greater reactivity. Their gasification reaction index (GRI), comprehensive pyrolysis index (CPI), and comprehensive gasification characteristic index (S) values were respectively 0.77 %, 20.21 %, and 31.36 % higher than those of the coarse-grained samples (40–80 mesh). The kinetic analysis indicated that the average activation energy (<em>E</em>_a) of the fine-grained samples was 169.19 kJ/mol, which was significantly lower than that of the coarse-grained samples. The reaction mechanism was dominated by diffusion and nucleation, and Δ<em>H</em>, Δ<em>G</em>, and Δ<em>S</em> confirmed that the fine-grained samples were more reactive. This study provides guidance for optimizing the particle size during the classification and utilization of low-rank coal to regulate the coke yield for the large-scale application of CO₂.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"406 ","pages":"Article 137065"},"PeriodicalIF":7.5,"publicationDate":"2025-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145263711","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Selective deoxygenation of lignite with microwave torrefaction and its action mechanisms on pyrolysis process","authors":"Wei He ,&nbsp;Bin Tian ,&nbsp;Shuolin Wang ,&nbsp;Long Xu ,&nbsp;Xiaoxun Ma ,&nbsp;Xingbao Wang","doi":"10.1016/j.fuel.2025.137082","DOIUrl":"10.1016/j.fuel.2025.137082","url":null,"abstract":"<div><div>Thermal torrefaction is an important tool for lignite deoxygenation, but traditional thermal torrefaction either causes an obvious loss of aliphatic structures. This work proposed a novel approach to selectively remove oxygenated functional groups of lignite by microwave torrefaction. The fuel properties, changes of chemical structure, and the pyrolysis processes of Zhaotong lignite (ZTL) during torrefaction were investigated coupled with quantitative analysis and pyrolysis experiments for revealing the role of microwave torrefaction. It was found that the deoxygenation of microwave torrefaction was superior to traditional furnace torrefaction, especially for C=O and COO. Microwave torrefaction was not expected to destroy the alkyl side chains, but had the positive role of activating and relaxing the compact structures of ZTL. The CH₂/CH₃ ratio for ZTL increased from 3.390 to 4.167 during microwave torrefaction so that the torrefied lignite was more prone to decompose. Besides, all oxygen containing gases in the pyrolysis of ZTL before 400 °C were reduced after torrefaction, while hydrocarbon gases increased. The increased activated energy of ZTL during torrefaction confirmed that the strong bonds in ZTL were not influenced by torrefaction. Phenolic compounds and hydrocarbon moieties in the volatile of ZTL have increased significantly after microwave torrefaction, while the groups of ethers/alcohols and ketones/aldehydes were all decreased in this process. These results are expected to give better understand about pyrolysis mechanisms of lignite pretreated by microwave torrefaction.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"406 ","pages":"Article 137082"},"PeriodicalIF":7.5,"publicationDate":"2025-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145263715","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A comprehensive review of system-level integration for ammonia engines","authors":"Wenyao Zhao ,&nbsp;Junheng Liu ,&nbsp;Qian Ji ,&nbsp;Chengcheng Ao ,&nbsp;Lidong Zhang","doi":"10.1016/j.fuel.2025.137012","DOIUrl":"10.1016/j.fuel.2025.137012","url":null,"abstract":"<div><div>With the intensifying threat of global warming and the growing demand for sustainable development, the transportation sector, which relies on conventional internal combustion engines, is increasingly pressured to transition to low-carbon and even zero-carbon fuels. Ammonia, as a carbon–neutral energy carrier with high hydrogen content and well-established production and distribution infrastructure, is regarded as a promising alternative to fossil fuels. However, its application in engines is associated with several technical challenges, including pseudo-zero carbon emissions, slow flame propagation, high auto-ignition temperature and material corrosion. To address these challenges, a systematic review is conducted on the life cycle environmental impact, subsystem parameter optimization and technological innovations related to ammonia-fueled engines, with the goal of achieving efficient and clean combustion, minimizing unburned ammonia and harmful emissions, and ensuring long-term system reliability. Additionally, the effects of combustion strategy optimization on engine performance are investigated, encompassing high-reactivity fuel supplementation, combustion chamber design, injection strategy refinement, intake parameter control and artificial intelligence combustion prediction. These strategies have been found to improve combustion stability and thermal efficiency by enhancing fuel mixing uniformity, strengthening the thermally active atmosphere and promoting flame propagation. This review also emphasizes that current aftertreatment efforts should focus on improving real-time monitoring of ammonia escape and developing N₂O specific catalysts to mitigate high levels of unburned ammonia and N₂O emissions. Through the coordinated optimization of engine subsystems, combustion strategies and aftertreatment systems, ammonia engines are considered to have significant potential for commercial deployment and are capable of supporting the achievement of carbon neutrality.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"406 ","pages":"Article 137012"},"PeriodicalIF":7.5,"publicationDate":"2025-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145263289","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ammonia-fueled internal combustion engines: a review of research trends","authors":"Shitu Abubakar ,&nbsp;Yuqiang Li","doi":"10.1016/j.fuel.2025.137016","DOIUrl":"10.1016/j.fuel.2025.137016","url":null,"abstract":"<div><div>This study conducts a qualitative and quantitative bibliometric analysis of 978 scholarly records retrieved from the Scopus database from 1943 to 2025. The study analyses publication trends, citations, collaborations, bursts, keywords and clusters using VOSviewer (v1.6.19), CiteSpace (v6.3.R1), and Microsoft Excel. The <em>Fuel</em> and <em>International Journal of Hydrogen Energy</em> dominate in terms of both document output and citations. China, the US, and the UK lead in both publication number and citations. The challenges of ammonia combustion, including high ignition energy, low flame speed, and slow reactivity, are currently being addressed using ignition enhancement techniques and dual fuel combustion, which reflect the research hotspots identified through temporal keyword co-occurrence network visualisation. Burst detection analysis of authors indicates that ammonia–diesel dual-fuel engines have emerged as a major research focus in ammonia-fueled internal combustion engines (ICEs), driven by the growing demand for heavy-duty vehicles. Pure ammonia in SI engines needs enhanced ignition including multi-spark, plasma, or laser, high compression ratios, optimised spark timing, and intake boosting to offset poor combustibility. Studies indicate that stable ammonia combustion can be achieved with co-fuel energy shares as low as 5–30%, using a range of fuels including hydrogen, methane, diesel, gasoline, methanol, ethanol, ethers, and biodiesel. Future work on ammonia-fueled engines should focus on advanced control strategies using artificial intelligence (AI), simultaneous emissions reduction, the use of ternary blends to leverage the strengths of individual fuels, optimisation of ammonia energy ratio, ammonia-fed fuel cells for hybrid electric vehicles, the use of nonadditives for enhanced combustion.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"406 ","pages":"Article 137016"},"PeriodicalIF":7.5,"publicationDate":"2025-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145263721","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Synergistic effects in FeP4-NPC-CP Nanocomposites electrocatalysts for Boosted nitrate reduction to ammonia","authors":"Ya-Fei Guo ,&nbsp;Sajid Mahmood ,&nbsp;Anum Bilal ,&nbsp;Ali Bahadur ,&nbsp;Shahid Iqbal ,&nbsp;Ali Hussain ,&nbsp;Muhammad Sajjad ,&nbsp;Syed Kashif Ali ,&nbsp;Salah Knani","doi":"10.1016/j.fuel.2025.137067","DOIUrl":"10.1016/j.fuel.2025.137067","url":null,"abstract":"<div><div>An electrocatalytic reduction of NO₃⁻ to NH₃ operates as a promising methodology both for sustainable nitrogen cycle management and ammonia industrial production. Herein, an advanced NO₃⁻RR electrocatalyst based on iron phosphide-nitrogen-phosphorus doped carbon (FeP₄-NPC) nanoparticle is prepared, which shows exceptional performance for nitrate reduction reactions, exhibiting an ammonia yield of 0.500 mmol h⁻¹mg⁻¹_cat. and Faradaic efficiency of 86.18 % at an optimized potential of −1.655 V vs. SCE under neutral conditions due to improved charge transfer capabilities and active site availability. The electrochemical tests also demonstrate both superior longevity and recyclability because the catalyst maintains its current density output as well as solution integrity across numerous operational cycles without deterioration. Moreover, based on detailed mechanistic studies by different characterizations and theoretical calculations, the super hydrophilic and electrophilicity (Fe) properties of FeP₄-NPC heterostructure interface synergistically promote to build better interfacial charge transfer and reactivity and contribute to the easy and fast accessibility of reactant species, which in turn help to reduce energy barrier of rate-determining step (*NO→*NHO) significantly and to inhibit the side reaction of hydrogen evolution. This investigation offers a deep understanding of the design of promising electrocatalysts for electrochemical ammonia production.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"406 ","pages":"Article 137067"},"PeriodicalIF":7.5,"publicationDate":"2025-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145263716","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental investigation on dynamic diffusion characteristics and mechanism of liquid kerosene jet in supersonic high-enthalpy inflow","authors":"Junlong Zhang ,&nbsp;Naigang Cui ,&nbsp;Guangjun Feng ,&nbsp;Hongchao Qiu ,&nbsp;Jiarui Zhang ,&nbsp;Bohao Yan ,&nbsp;Wen Bao","doi":"10.1016/j.fuel.2025.137040","DOIUrl":"10.1016/j.fuel.2025.137040","url":null,"abstract":"<div><div>This study investigates the dynamic diffusion characteristics and mechanisms of liquid kerosene jets in supersonic high-enthalpy flows. Experiments were conducted on the ground directly connected scramjet combustor test rig with a high-speed schlieren system at injection pressures of 0.44 MPa, 0.60 MPa, and 0.78 MPa. The dynamic development of kerosene diffusion was analyzed based on the grayscale values of schlieren images, further revealing the underlying diffusion mechanisms. Results show that kerosene diffusion in supersonic high-enthalpy flows involves two stages: diffusion development and steady-state oscillation. Increasing injection pressure significantly accelerates diffusion and expands its range. Higher inertia lowers the main oscillation frequency but increases oscillation energy by enhancing turbulent energy exchange and phase-change disturbances. The oscillation mode shifts from small-scale, high-frequency fluctuations near the nozzle, caused by gas–liquid shear instability, to large-amplitude, low-frequency oscillations downstream due to phase-change expansion. The diffusion process and distribution result from the dynamic interplay of jet momentum, aerodynamic heating, and phase-change effects. These findings are significant for improving fuel mixing and combustion efficiency.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"406 ","pages":"Article 137040"},"PeriodicalIF":7.5,"publicationDate":"2025-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145263375","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental investigation of common rail direct injection engine operated on hydrogen fumigation and mango seed biodiesel-diesel blend dosed with graphene oxide nanoparticle employing exhaust gas recirculation for NOx control strategy","authors":"Amol Pitale,&nbsp;Pramod Walke,&nbsp;Vivek Khond","doi":"10.1016/j.fuel.2025.136998","DOIUrl":"10.1016/j.fuel.2025.136998","url":null,"abstract":"<div><div>In this study, replacement of diesel with mango seed biodiesel (MSBD) with enrichment of hydrogen to reduce carbon emission was explored. Also, the effect of exhaust gas recirculation was investigated with graphene oxide nanoparticles (20 ppm) on the MSBD −diesel blend with varying hydrogen fumigation composition is investigated on a compression ignition (CI) engine in a dual-fuel mode. Biodiesel is produced from Mango seed oil, and blend of 15 % (v/v) with 85 % of diesel fuel was made and 20 ppm Graphene oxide particles are dosed and ultrasonicated to form stable blends. The samples are tested on diesel engine as a primary fuel and hydrogen is fumigated through intake manifold with variable volume flow rates. The effects of fuel blends and hydrogen fuel enrichment with and without exhaust gas recirculation on combustion, performance, and emissions of diesel engine are investigated at varying load condition. It is observed that maximum cylinder pressure is 58.09 bar for B15GO20H4 compared to 57.82 bar for B15 blend. The maximum net heat release rate was 67.74 J/⁰CA for B15GO20H8EG5 compared to 50.99 J/ ⁰CA for B15 blend. The maximum percentage increase in brake thermal efficiency was 8.75 % and decreases in brake-specific fuel consumption by 19.35 % at full load for B15GO20H8 blend when compared to the biodiesel–diesel blend. The decrease in carbon monoxide, smoke opacity and carbon dioxide emissions by 66.66 %, 56.55 % and 25.58 % for B15GO20H8 blend respectively, at 100 percent load when compare to B15. However, the Hydrocarbon increased by 29.41 % at a higher load as compare to B15. NOx emission was decreases for all samples compared to B15 and maximum reduction (79.04 %) was observedin B15GO20H8EG5. It is concluded that exhaust gas recirculation is more effective for reduction of NOx in hydrogen enriched CI engine.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"406 ","pages":"Article 136998"},"PeriodicalIF":7.5,"publicationDate":"2025-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145263717","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"From NMR signals to fluid volumes: accurate quantification of shale fluids via a multi-component/nanopore-coupled framework","authors":"Xinbin Zhao ,&nbsp;Min Wang ,&nbsp;Junyang Chen ,&nbsp;Yu Sun ,&nbsp;Min Wang ,&nbsp;Junliang Li ,&nbsp;Xiaohao Li","doi":"10.1016/j.fuel.2025.137045","DOIUrl":"10.1016/j.fuel.2025.137045","url":null,"abstract":"<div><div>Nuclear Magnetic Resonance (NMR) technology serves as a critical tool for fluid evaluation in shale reservoirs; however, its accuracy relies on reliable conversion of relaxation signals to fluid volume. Current research predominantly focuses on identifying hydrogen-containing components while neglecting systematic calibration of quantitative conversion relationships. This study establishes a free-state/nano-pore coupled calibration method, constructing a comprehensive calibration framework using multiple hydrogen-nucleus-density fluids (crude oil + formation water + crude oil components). Validation was achieved through fluid dynamic loss experiments on sealed core samples and distillation–extraction tests. Key findings include: (1) Free-state calibration reveals that the crude oil-formation water combination better replicates in-situ characteristics. The calibration coefficient k-value increases from 3,590.9 to 6,027.1 (a 68 % rise) with thermal maturity (R₀: 0.7 %–1.67 %), yet decreases from 4,350.8 to 3,816.5 (a 12.3 % reduction) with increasing salinity, showing statistically high consistency (R² = 0.89) with the crude oil component calibration model; (2) Under shale nano-pore confinement, the calibration conversion coefficient (k) for crude oil decreases slightly (6.5 %), while that for formation water increases modestly (5.29 %); (3) Quantitative results from this calibration system demonstrate high consistency between NMR and distillation–extraction evaluations. This research overcomes prior limitations in free-state fluid calibration, elucidates quantitative regulatory patterns of thermal maturity and salinity on k-values, quantifies nano-pore confinement effects on conversion coefficients, and ensures accuracy via a dedicated calibration coefficient verification model. The framework advances shale fluid quantification from “empirical estimation” to in-situ precision quantification, providing technical support for target zone optimization.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"406 ","pages":"Article 137045"},"PeriodicalIF":7.5,"publicationDate":"2025-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145263288","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pore characterization of coal cuttings based on low-field nuclear magnetic resonance: A new method","authors":"Hongda Wen ,&nbsp;Cheng Zhai ,&nbsp;Jizhao Xu ,&nbsp;Yong Sun ,&nbsp;Fei Wu ,&nbsp;Hexiang Xu ,&nbsp;Yu Wang","doi":"10.1016/j.fuel.2025.137066","DOIUrl":"10.1016/j.fuel.2025.137066","url":null,"abstract":"<div><div>Coal reservoir pore complexity governs coalbed methane occurrence and migration, making core analysis essential for pore architecture characterization. However, obtaining intact cores from soft, low-permeability coal seams with weak mechanical strength and dense fractures is challenging. Consequently, drilling cuttings are often used for pore structure evaluation, necessitating assessment of their substitutability for porosity and pore size distribution analysis. To address this, we developed a low-field nuclear magnetic resonance (LF-NMR) methodology for cuttings porosity measurement. Bituminous coal samples from Shenmu’s Zhangminggou Mine were analyzed using a 1H probe and 5 % CuSO4 centrifugation. Comparative testing employed two artificial crushing methods to prepare cuttings particles. Porosity and pore size distributions across varying particle sizes were compared with intact core data. Key findings indicate: (1) Cutting and core T2 spectra exhibit high similarity, with micropores (&lt;2 nm) and mesopores (2–50 nm) dominating pore structures; (2) Maximum porosity deviation is 3.03 %, minimized at &gt; 3.35 mm particle sizes, confirming cuttings reliability for basic reservoir characterization; (3) Fragmentation intensity critically affects measurements—total porosity increases from 10.13 % to 14.26 % as particle size decreases from 3.35 mm to 0.85 mm due to exposed occluded pores and semi-closed pore transformation, while micropore proportion rises from 53.84 % to 58.00 %. We propose a ≥ 1 mm particle size threshold, with optimal accuracy at 1.7–2.36 mm cuttings, balancing precision and closed-pore preservation. This non-destructive method enables efficient unconsolidated coal reservoir evaluation with significant engineering applicability.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"406 ","pages":"Article 137066"},"PeriodicalIF":7.5,"publicationDate":"2025-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145263368","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evolution of molecular structure during coalification and graphitization: Evidence from multiple characterization methods","authors":"Peng Qiao ,&nbsp;Lei Xiao ,&nbsp;Liru Tao ,&nbsp;Jin Qian ,&nbsp;Kun Yu ,&nbsp;Mingna Ge","doi":"10.1016/j.fuel.2025.136990","DOIUrl":"10.1016/j.fuel.2025.136990","url":null,"abstract":"<div><div>The molecular structure of coal plays a critical role in coalbed methane enrichment, carbon capture, utilization and storage (CCUS), as well as in the preparation of coal-based carbon materials. However, few studies have examined the continuous, overall evolution of coal molecular structure throughout coalification and graphitization. In this work, ultimate analysis, X-ray diffraction (XRD), Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectroscopy (FTIR) were employed to characterize the molecular structure of coals ranging from low-rank to coaly graphite. The results reveal distinct spectral features corresponding to different coal maturities. During the elimination of heteroatoms, deoxidation occurs primarily in the early stage of coalification, as evidenced by the disappearance of C=O structure from low-rank to medium-rank coals. Dehydrogenation proceeds throughout both coalification and graphitization, especially at high maturity stage, marked by the loss of aliphatic side chains and aromatic C–H bonds. The evolutionary trends of L_a, L_c and d₀₀₂ parameters derived from XRD as a function of R_{o, m} indicate that aromatic layers begin forming in low-rank coals, with vertical stacking continuing through the medium-rank stage and accompanied by a decrease in d₀₀₂. Re-stacking of aromatic layers and re-reduction of d₀₀₂ occur during the early stage of graphitization. Polycondensation of naphthalene and 3 × 3, 4 × 4 aromatic rings proceed continuously during coalification and graphitization, increasing the lateral size of crystallites. The trends in G-FWHM from Raman data and alignment degree derived from HRTEM with increasing R_{o, m} suggest that the molecular structure become progressively more directionally aligned from graphitized coal to coaly graphite. The stepwise evolution of multiple parameters obtained from XRD, HRTEM and Raman indicates that coal graphitization is limited to R_{o, m} values between 4.0 % and 5.0 %. Overall, the results enhance the theoretical framework of coalification and graphitization, and have indicative significance for coal-to-oil, CCUS and preparation of coal-based carbon materials.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"406 ","pages":"Article 136990"},"PeriodicalIF":7.5,"publicationDate":"2025-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145263666","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}