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Enhancing Oil Recovery Through Vibration-Stimulated Waterflooding: Experimental Insights and Mechanisms
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Evaluation of N,N,N′,N′-Tetramethylethylenediamine (TMEDA) as an Alternative Fuel for a Hypergolic Bipropellant Rocket Engine
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Environmentally Sustainable and Energy-Efficient Nanobubble Engineering: Applications in the Oil and Fuels Sector
Journal Description
Fuels
Fuels
is an international, peer-reviewed, open access journal on fuel science, published quarterly online by MDPI. The Institute of Energy and Fuel Processing Technology (ITPE) is affiliated to Fuels and their members receive a discount on the article processing charges.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within ESCI (Web of Science), EBSCO, Ei Compendex, and other databases.
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 24.7 days after submission; acceptance to publication is undertaken in 8.8 days (median values for papers published in this journal in the first half of 2025).
- Recognition of Reviewers: APC discount vouchers, optional signed peer review, and reviewer names published annually in the journal.
- Journal Cluster of Energy and Fuels: Energies, Batteries, Hydrogen, Biomass, Electricity, Wind, Fuels, Gases, Solar, ESA and Methane.
Impact Factor:
2.8 (2024);
5-Year Impact Factor:
3.1 (2024)
Latest Articles
Optimizing the Powertrain of a Fuel Cell Electric Bus: A Sizing and Hybridization Analysis
Fuels 2025, 6(4), 78; https://doi.org/10.3390/fuels6040078 - 8 Oct 2025
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In this study, the impact of the electric motor size and the hybridization ratio of a Fuel Cell Electric Bus on its vehicle performance (i.e., gradeability and acceleration) and fuel consumption was investigated using the ADVISOR software. The investigation first involved a parametric
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In this study, the impact of the electric motor size and the hybridization ratio of a Fuel Cell Electric Bus on its vehicle performance (i.e., gradeability and acceleration) and fuel consumption was investigated using the ADVISOR software. The investigation first involved a parametric analysis with different electric motor and fuel cell sizes for the dynamic performance metrics, specifically the 0–60 km/h vehicle acceleration and the maximum gradeability (%) at a constant speed of 20 km/h. The results revealed that the acceleration is most sensitive to fuel cell power. Regarding gradeability, a more complex relationship was observed: when the electric motor power was below 215 kW, gradeability remained consistently low regardless of the fuel cell size. However, for motors exceeding 215 kW, fuel cell power then became a significant influencing factor on the vehicle’s climbing capability. Subsequently, the analysis focused on the effect of the hybridization ratio, which represents the power balance between the fuel cell and the energy storage system, varied between 0 and 0.8. Results showed that increasing the hybridization ratio decreases gradeability and acceleration performance and increases total energy consumption. This trade-off is quantitatively illustrated by the results over the Central Business District (CBD) driving cycle. For instance, the pure battery-electric configuration (a hybridization ratio of 0), featuring a 296 kW battery system, recorded a gradeability of 12.4% and an acceleration time of 16.3 s, while consuming 28,916 kJ. At an intermediate hybridization ratio of 0.4 (composed of a 118.4 kW fuel cell and a 177.6 kW battery), performance remained high with a gradeability of 12.2% and an acceleration of 17.3 s, but the energy consumption increased to 43,128 kJ. Finally, in the fuel-cell-dominant configuration with a hybridization ratio of approximately 0.8 (a 236.8 kW fuel cell and a 59.2 kW battery), gradeability dropped to 8.4%, acceleration time deteriorated to 38.9 s, and total energy consumption increased further to 52,678 kJ over the CBD driving cycle.
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Open AccessArticle
Comprehensive Petrophysical Assessment of Carbonate Reservoirs in the Shanul Gas Field (SW Iran): A Case Study with Implications for Hydrocarbon Exploration and Production
by
Pariya Zendehdel, Amir Karimian Torghabeh, Hossein Jowkar and Nuno Pimentel
Fuels 2025, 6(4), 77; https://doi.org/10.3390/fuels6040077 - 6 Oct 2025
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This study presents an integrated petrophysical workflow for the comprehensive characterization of the Upper Dalan and Kangan carbonate gas reservoirs in the Shanul Field, southwest Iran. By combining advanced cross-plot techniques (including M-N, MID, and RHOma-Uma plots) with probabilistic porosity modeling calibrated to
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This study presents an integrated petrophysical workflow for the comprehensive characterization of the Upper Dalan and Kangan carbonate gas reservoirs in the Shanul Field, southwest Iran. By combining advanced cross-plot techniques (including M-N, MID, and RHOma-Uma plots) with probabilistic porosity modeling calibrated to core data, this work achieves a higher-resolution discrimination of lithology and more robust estimation of fluid properties compared to conventional single-log approaches. The results reveal significant heterogeneity within both formations but demonstrate the superior reservoir quality of the Upper Dalan, particularly within the UD2 subzone, and in the Ka-2a subzone of the Kangan. The improved workflow enables more accurate zonation and identification of high-quality, productive intervals, supporting optimized field development strategies. These findings provide methodological advances for challenging and heterogeneous carbonate systems, offering a reference framework for similar reservoirs in the Zagros Basin and beyond.
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Open AccessArticle
Tuning Chemical Looping Steam Reforming of Methane Performance via Ni-Fe-Al Interaction in Spinel Ferrites
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Jun Hu, Hongyang Yu and Yanan Wang
Fuels 2025, 6(4), 76; https://doi.org/10.3390/fuels6040076 - 3 Oct 2025
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The chemical looping steam reforming of methane (CLSR) employing Fe-containing oxygen carriers can produce syngas and hydrogen simultaneously. However, Fe-based oxygen carriers exhibit low CH4 activation ability and cyclic stability. In this work, oxygen carriers with fixed Fe content and different Fe/Ni
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The chemical looping steam reforming of methane (CLSR) employing Fe-containing oxygen carriers can produce syngas and hydrogen simultaneously. However, Fe-based oxygen carriers exhibit low CH4 activation ability and cyclic stability. In this work, oxygen carriers with fixed Fe content and different Fe/Ni ratios were synthesized by the sol–gel method to investigate the effects of Ni-Fe-Al interactions on CLSR performance. Ni-Fe-Al interactions promote the growth of the spinel structure and regulate both the catalytic sites and the available lattice oxygen, resulting in the CH4 conversion and CO selectivity being maintained at 96–98% and above 98% for the most promising oxygen carrier, with an Fe2O3 content of 20 wt% and Fe/Ni molar ratio of 10. The surface, phase, and particle size were kept the same over 90 cycles, leading to high stability. During the CLSR cycles, conversion from Fe3+ to Fe2+/Fe0 occurs, along with transformation between Ni2+ in NiAl2O4 and Ni0. Overall, the results demonstrate the feasibility of using spinel containing earth-abundant elements in CLSR and the importance of cooperation between oxygen release and CH4 activation.
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Open AccessArticle
A Prudent Approach to Reduce CO2 Emissions While Enhancing Oil Recovery
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Mohammad Al-Ghnemi, Erdal Ozkan and Hossein Kazemi
Fuels 2025, 6(4), 75; https://doi.org/10.3390/fuels6040075 - 2 Oct 2025
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Emissions of carbon dioxide (CO2) resulting from steam-driven enhanced oil recovery (EOR) operations present an environmental challenge as well as an opportunity to further enhance oil recovery. Using numerical simulations with realistic input data from field and laboratory measurements, we demonstrate
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Emissions of carbon dioxide (CO2) resulting from steam-driven enhanced oil recovery (EOR) operations present an environmental challenge as well as an opportunity to further enhance oil recovery. Using numerical simulations with realistic input data from field and laboratory measurements, we demonstrate a prudent approach to reduce CO2 emissions by capturing CO2 from steam generators of a steam-driven enhanced oil recovery (EOR) project and injecting it in a nearby oil field to improve oil recovery in this neighboring field. The proposed use of CO2 as a water-alternating-CO2 (WAG-CO2) EOR project in a small, 144-acre, sector of a target limestone reservoir would yield 42% incremental EOR oil while sequestering CO2 with a net utilization ratio (NUR) of 3100 standard cubic feet CO2 per stock tank barrel (SCF/STB) of EOR oil in a single five-spot pattern consisting of a central producer and four surrounding injectors. This EOR application sequesters 135,000, 165,000, and 213,000 metric tons of CO2 in five, ten, and twenty years in the single five spot pattern (i.e., our sector target), respectively. As a related matter, the CO2 emissions from nearby steam oil recovery project consisting of ten 58-ton steam/hr boilers amounts to 119,000 metric tons of CO2 per year with an estimated social cost of USD 440 million over 20 years. Upscaling the results from the single five-spot pattern to a four-pattern field scale increases the sequestered amount of CO2 by a factor of 4 without recycling and to 11 with recycling produced CO2 from the EOR project. Furthermore, the numerical model indicates that initiating CO2 injection earlier at higher residual oil saturations improves EOR efficiency while somewhat decreases sequestration per incremental EOR barrel. The most significant conclusion is that the proposed venture is an economically viable EOR idea in addition to being an effective sequestration project. Other sources of CO2 emissions in oil fields and nearby refineries or power generators may also be considered for similar projects.
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Open AccessArticle
Effect of Hot Water Extraction of Lignocellulosic Biomass on Fuel Pellet Properties
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Autumn Elniski and Biljana M. Bujanovic
Fuels 2025, 6(4), 74; https://doi.org/10.3390/fuels6040074 - 23 Sep 2025
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Pelletizing enhances competitiveness of lignocellulosic biomass (LCB) as a fuel by increasing its bulk and energy density. However, LCB pellets are prone to degradation from moisture, have high ash, and pose safety risks due to carbon monoxide (CO) emissions during storage. Hot water
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Pelletizing enhances competitiveness of lignocellulosic biomass (LCB) as a fuel by increasing its bulk and energy density. However, LCB pellets are prone to degradation from moisture, have high ash, and pose safety risks due to carbon monoxide (CO) emissions during storage. Hot water extraction (HWE), a mild hydrothermal treatment particularly effective for angiosperms, removes most hemicelluloses (xylans), reduces ash, and increases lignin content in remaining HWE-LCB. Based on the current understanding of CO formation, these changes suggested that HWE could reduce CO emissions. In this study, we evaluated the effects of HWE on pellets made from shrub willow, miscanthus, and wheat straw. A statistical analysis was conducted on ash, energy content, bulk density, durability, pellet length and density, moisture absorption, and CO emissions. All HWE-LCB pellets demonstrated significant increases in energy content (up to 3.54%) and reductions in moisture absorption (up to 23.84%). Although not all effects reached statistical significance, HWE generally had positive effects on ash content, bulk density, durability, and average pellet length and density. Contrary to expectations, HWE-LCB pellets emitted significantly more CO under both ambient and isothermal temperature conditions (up to 4.25 times overall increase), although still less than commercial hardwood/softwood blend pellets (<200 ppm in HWE-LCB vs. >300 ppm).
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Open AccessArticle
Comparative Morphological and Thermal Analysis of Biochar from Oak, and from Oak, Pine and RDF Blends, in a Downdraft Gasifier
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Paul C. Ani, Hasan J. Al-Abedi, Joseph D. Smith and Zeyad Zeitoun
Fuels 2025, 6(3), 73; https://doi.org/10.3390/fuels6030073 - 22 Sep 2025
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This study investigates the influence of feedstock blending on the structural and thermal properties of biochar produced via downdraft gasification at 850 °C. Biochars from 100% oak, a 1:1 oak-–pine blend, and a ternary blend of 50% oak, 30% pine, and 20% RDF
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This study investigates the influence of feedstock blending on the structural and thermal properties of biochar produced via downdraft gasification at 850 °C. Biochars from 100% oak, a 1:1 oak-–pine blend, and a ternary blend of 50% oak, 30% pine, and 20% RDF were analyzed using SEM, BET, TGA, XRD, Raman spectroscopy, and CHN elemental analysis. The oak biochar exhibited the highest surface area (107.7 m2/g) and fixed-carbon content (79.94%), while the RDF-based biochar showed a 99.2% decrease in surface area (0.86 m2/g) and a 19.7% reduction in fixed carbon. These findings underscore RDF’s detrimental impact on porosity and stability, despite its waste valorization potential, suggesting its limited use in applications requiring high adsorption or structural integrity. Further studies should optimize RDF preprocessing and blending ratios to balance sustainability with functional performance.
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Open AccessArticle
Granular Activated Carbon and Organic Loading Interactions in Methane Fermentation: An Inverse Load-Dependent Relationship and Absolute Microbial Abundance Analysis
by
Hikaru Kaneko, Yusuke Ozaki, Jun Takezaki and Hiroyuki Daimon
Fuels 2025, 6(3), 72; https://doi.org/10.3390/fuels6030072 - 22 Sep 2025
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This study addresses volatile fatty acid (VFA) accumulation, a key issue limiting methane fermentation under high organic loading rate (OLR) conditions. Batch experiments were conducted with GAC (0–10%) under various OLRs (1:0.5–1:10) to investigate its effect on biogas yield, methane purity, and microbial
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This study addresses volatile fatty acid (VFA) accumulation, a key issue limiting methane fermentation under high organic loading rate (OLR) conditions. Batch experiments were conducted with GAC (0–10%) under various OLRs (1:0.5–1:10) to investigate its effect on biogas yield, methane purity, and microbial interactions. Higher GAC levels (7.5% and 10%) significantly enhanced biogas production (750–800 mL/g VS) and methane concentration (–70%) while shortening stabilization time. A continuous system with 10% GAC showed suppressed VFA accumulation, stable pH (7.0–8.1), and improved organic matter degradation. This work quantitatively evaluates the link between GAC dosage, DIET induction, and microbial community shifts under high OLR. These findings highlight GAC as an operationally simple and potentially cost-beneficial strategy for stabilizing methane fermentation, particularly in decentralized or small-scale applications.
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Open AccessArticle
Biochar Surface Chemistry Modification by Blending Hardwood, Softwood, and Refuse-Derived Fuel: Insights from XPS, FTIR, and Zeta Potential Analysis
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Paul C. Ani, Hasan J. Al-Abedi, Joseph D. Smith and Zeyad Zeitoun
Fuels 2025, 6(3), 71; https://doi.org/10.3390/fuels6030071 - 22 Sep 2025
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This study investigates how the inclusion of refuse-derived fuel (RDF) alters the surface chemistry and electrostatic behavior of oak-based biochar. Biochars were produced using downdraft gasification at 850 °C from 100% oak (HW) and a ternary blend comprising 50% oak, 30% pine, and
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This study investigates how the inclusion of refuse-derived fuel (RDF) alters the surface chemistry and electrostatic behavior of oak-based biochar. Biochars were produced using downdraft gasification at 850 °C from 100% oak (HW) and a ternary blend comprising 50% oak, 30% pine, and 20% RDF (HW/SW/RDF). Characterization using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), zeta potential, pH, and electrophoretic mobility was conducted to assess surface functionality and colloidal behavior. The RDF-containing biochar exhibited a 43.3% increase in surface nitrogen content (from 0.24% to 0.90%) and a 6.6% rise in calcium content (from 2.07% to 2.27%) alongside the introduction of chlorine (0.20%) and elevated silicon levels (0.69%) compared to RDF-free counterparts. A concurrent reduction in oxygen-containing functional groups was observed, as O1s decreased from 15.75% in HW to 13.37% in HW/SW/RDF. Electrokinetic measurements revealed a notable decrease in zeta potential magnitude from −31.5 mV in HW to −24.2 mV in HW/SW/RDF, indicating diminished surface charge and colloidal stability. Moreover, the pH declined from 10.25 to 7.76, suggesting a loss of alkalinity and buffering capacity. These compositional and electrostatic shifts demonstrate that RDF inclusion significantly modifies the surface reactivity of biochar, influencing its performance in catalysis, ion exchange, and nutrient retention. The findings underscore the need for tailored post-treatment strategies to enhance the functionality of RDF-modified biochars in environmental applications.
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Open AccessArticle
Engine Response and Emission Optimization of Ceramic-Oxide-Doped Diesel Blends with Reclaimed Waste Energy
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K. Sudha Madhuri, Syed Altaf Hussain, Rohit Kumar, Upendra Rajak and Tikendra Nath Verma
Fuels 2025, 6(3), 70; https://doi.org/10.3390/fuels6030070 - 19 Sep 2025
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Without changing any of its constituents, tyre pyrolysis oil energy (TPOE) has frequently been subjected to Diesel-RK (D-RK) analyses in diesel engines in an effort to serve as a substitute for diesel fuel. Environmentally beneficial TPOE features, such as biodegradability, renewability, and ease
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Without changing any of its constituents, tyre pyrolysis oil energy (TPOE) has frequently been subjected to Diesel-RK (D-RK) analyses in diesel engines in an effort to serve as a substitute for diesel fuel. Environmentally beneficial TPOE features, such as biodegradability, renewability, and ease and safety of handling, are highly sought after. In addition to its beneficial aspects, TOPE also has drawbacks. The BTE and SFC of performance metrics, as well as the smoke and NOx of emission parameters of alternative fuel, do not meet the emission limits specified by regulatory authorities. Nano-additions have been shown to be effective for boosting fuel quality for improved performance and production characteristics. In this study, TPOE–diesel blends are blended with ceramic oxide (CeO2 of 50 and 100 ppm) nanoparticles and subjected to a performance and production investigation of engine working physiognomies in diesel engines. For the blend TPOE10CDF80 + D, the numerical results show a positive outcome of a 1.0% rise in BTE, a 2.0% decrease in SFC, a 17.7% decrease in smoke emission, and an 18.2% increase in NOx emission as compared to diesel fuel (CDF).
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Open AccessReview
Mapping Research Trends in Pulsed Electric Field Technology Applied to Biogas Production: A Comprehensive Bibliometric Analysis
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Đurđica Kovačić
Fuels 2025, 6(3), 69; https://doi.org/10.3390/fuels6030069 - 19 Sep 2025
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This study provides a comprehensive review of the application of pulsed electric field (PEF) technology as a pretreatment method for enhancing biogas production from various organic substrates. A comparative bibliometric analysis was conducted using four databases, Web of Science Core Collection, Scopus, Dimensions,
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This study provides a comprehensive review of the application of pulsed electric field (PEF) technology as a pretreatment method for enhancing biogas production from various organic substrates. A comparative bibliometric analysis was conducted using four databases, Web of Science Core Collection, Scopus, Dimensions, and Google Scholar, to evaluate research activity, interdisciplinarity, and geographic distribution of PEF-related literature. The results show that, although biomass pretreatment research has grown considerably over the past two decades, the number of studies focused specifically on PEF remains extremely low, accounting for less than 0.5% in each database. A detailed overview of 66 studies further confirms PEF’s potential to improve methane yield through substrate disintegration and microbial community enhancement, yet highlights the need for standardization and scalability. Optimization studies reveal promising outcomes, particularly for sludge and algal substrates, though most were limited to laboratory scale. Two full-scale studies demonstrated economic feasibility, yet long-term stability, energy balance, and integration into existing anaerobic digestion systems remain underexplored. The analysis of author countries and institutions shows that research is concentrated in China, Sweden, and France. Overall, this review identifies major research gaps and outlines future directions aimed at including a more diverse range of substrates, improving comparability, and validating PEF in real-scale biogas production systems.
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Open AccessArticle
Towards Net-Zero: Comparative Analysis of Hydrogen Infrastructure Development in USA, Canada, Singapore, and Sri Lanka
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Myo Myo Khaing, Chuck Hookham, Janaka Ruwanpura and Shunde Yin
Fuels 2025, 6(3), 68; https://doi.org/10.3390/fuels6030068 - 18 Sep 2025
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This paper compares national hydrogen (H2) infrastructure plans in Canada, the United States (the USA), Singapore, and Sri Lanka, four countries with varying geographic and economic outlooks but shared targets for reaching net-zero emissions by 2050. It examines how each country
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This paper compares national hydrogen (H2) infrastructure plans in Canada, the United States (the USA), Singapore, and Sri Lanka, four countries with varying geographic and economic outlooks but shared targets for reaching net-zero emissions by 2050. It examines how each country approaches hydrogen production, pipeline infrastructure, policy incentives, and international collaboration. Canada focuses on large-scale hydrogen production utilizing natural resources and retrofitted natural gas pipelines supplemented by carbon capture technology. The USA promotes regional hydrogen hubs with federal investment and intersectoral collaboration. Singapore suggests an innovation-based, import-dominant strategy featuring hydrogen-compatible infrastructure in a land-constrained region. Sri Lanka maintains an import-facilitated, pilot-scale model facilitated by donor funding and foreign collaboration. This study identifies common challenges such as hydrogen embrittlement, leakages, and infrastructure scalability, as well as fundamental differences based on local conditions. Based on these findings, strategic frameworks are proposed, including scalability, adaptability, partnership, policy architecture, digitalization, and equity. The findings highlight the importance of localized hydrogen solutions, supported by strong international cooperation and international partnerships.
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Open AccessArticle
Influence of EGR and Acoustic Waves on Particles and Other Emissions of IC Engine Powered with Diesel and RME Fuels
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Sai Manoj Rayapureddy and Jonas Matijošius
Fuels 2025, 6(3), 67; https://doi.org/10.3390/fuels6030067 - 17 Sep 2025
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To achieve the goal of climate neutrality set by the European Union, it is important to find an efficient strategy to simultaneously lower nitrogen oxide, carbon monoxide, and particle emissions. When a portion of exhaust gas is reintroduced back into the combustion chamber,
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To achieve the goal of climate neutrality set by the European Union, it is important to find an efficient strategy to simultaneously lower nitrogen oxide, carbon monoxide, and particle emissions. When a portion of exhaust gas is reintroduced back into the combustion chamber, it reduces the combustion temperature. This reduces NOX emissions but has a negative impact on CO and particle emissions due to the lower concentration of O2. Reducing the combustion temperature can also indirectly influence particle formation. By including an oxygen-rich alternative fuel, CO emissions are reduced by 28% and 33% at 60 and 90 Nm, respectively. To further reduce particle emissions, which have significant health risks, acoustic waves are introduced to achieve better filtration through conventional DPFs that filter particles with larger diameters. With 21 kHz of acoustic frequency and 0% EGR, a 6% increase in large particles is observed. With moderate rise in the recirculation percentage, a higher combined efficiency of EGR and acoustic waves is observed. With 21 kHz acoustic frequency and 10% EGR, a 73% increase in larger particles is observed at lower loads and a 32% increase at higher loads is observed. Simultaneous emission reduction can be achieved by combining the benefits of using oxygen-rich fuel, acoustics, and EGR at a moderate rate.
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Open AccessArticle
Opportunities for Emission Reduction in the Transformation of Petroleum Refining
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Emilio Seijo-Bestilleiro, Ignacio Arias-Fernández, Diego Carro-López and Manuel Naveiro
Fuels 2025, 6(3), 66; https://doi.org/10.3390/fuels6030066 - 13 Sep 2025
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Crude oil accounts for approximately 40% of global energy consumption, and the refining sector is a major contributor to greenhouse gas (GHG) emissions, particularly through the production of hard-to-abate fuels such as aviation fuel and fuel oil. This study disaggregates the refinery into
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Crude oil accounts for approximately 40% of global energy consumption, and the refining sector is a major contributor to greenhouse gas (GHG) emissions, particularly through the production of hard-to-abate fuels such as aviation fuel and fuel oil. This study disaggregates the refinery into its key process units to identify decarbonization opportunities along the entire production chain. Units are categorized into combustion-based processes—including crude and vacuum distillation, hydrogen production, coking, and fluid catalytic cracking—and non-combustion processes, which exhibit lower emission intensities. The analysis reveals that GHG emissions can be reduced by up to 60% with currently available technologies, without requiring major structural changes. Electrification, residual heat recovery, renewable hydrogen for desulfurization, and process optimization through digital twins are identified as priority measures, many of which are also economically viable in the short term. However, achieving full decarbonization and alignment with net-zero targets will require the deployment of carbon capture technologies. These results highlight the significant potential for emission reduction in refineries and reinforce their strategic role in enabling the transition toward low-carbon fuels.
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Open AccessArticle
A Geothermal-Driven Zero-Emission Poly-Generation Energy System for Power and Green Hydrogen Production: Exergetic Analysis, Impact of Operating Conditions, and Optimization
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Guy Trudon Muya, Ali Fellah, Sun Yaquan, Yasmina Boukhchana, Samuel Molima, Matthieu Kanyama and Amsini Sadiki
Fuels 2025, 6(3), 65; https://doi.org/10.3390/fuels6030065 - 28 Aug 2025
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Since the hydrogen-production process is not yet fully efficient, this paper proposes a poly-generation system that is driven by a geothermal energy source and utilizes a combined Kalina/organic Rankine cycle coupled with an electrolyzer unit to produce, simultaneously, power and green hydrogen in
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Since the hydrogen-production process is not yet fully efficient, this paper proposes a poly-generation system that is driven by a geothermal energy source and utilizes a combined Kalina/organic Rankine cycle coupled with an electrolyzer unit to produce, simultaneously, power and green hydrogen in an efficient way. A comprehensive thermodynamic analysis and an exergetic evaluation are carried out to assess the effect of key system parameters (geothermal temperature, high pressure, ammonia–water concentration ratio, and terminal thermal difference) on the performance of concurrent production of power and green hydrogen. Thereby, two configurations are investigated with/without the separation of turbines. The optimal ammonia mass fraction of the basic solution in KC is identified, which leads to an overall optimal system performance in terms of exergy efficiency and green hydrogen production rate. In both configurations, the optimal evaluation is made possible by conducting a genetic algorithm optimization. The simulation results without/with the separation of turbines demonstrate the potential of the suggested cycle combination and emphasize its effectiveness and efficiency. Exemplary, for the case without the separation of turbines, it turns out that the combination of ammonia–water and MD2M provides the best performance with net power of 1470 kW, energy efficiency of 0.1184, and exergy efficiency of 0.1258 while producing a significant green hydrogen amount of 620.17 kg/day. Finally, an economic study allows to determine the total investment and payback time of $3,342,000 and 5.37 years, respectively. The levelized cost of hydrogen (LCOH) for the proposed system is estimated at 3.007 USD/kg H2, aligning well with values reported in the literature.
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(This article belongs to the Special Issue Sustainability Assessment of Renewable Fuels Production)
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Open AccessArticle
Microalgae Grown in Hydroponic Greenhouse Wastewater Towards Biofuels: An Environmental Assessment
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Loukia P. Chrysikou, Vasiliki Dagonikou and Stella Bezergianni
Fuels 2025, 6(3), 64; https://doi.org/10.3390/fuels6030064 - 27 Aug 2025
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This study conducts a life cycle assessment (LCA) of a microalgae-based biorefinery producing biofuels, using a well-to-tank approach. Microalgae were cultivated using greenhouse wastewater, while the extracted lipids were converted to biofuels via catalytic hydrotreatment. Experimental data supported an Aspen Plus model to
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This study conducts a life cycle assessment (LCA) of a microalgae-based biorefinery producing biofuels, using a well-to-tank approach. Microalgae were cultivated using greenhouse wastewater, while the extracted lipids were converted to biofuels via catalytic hydrotreatment. Experimental data supported an Aspen Plus model to generate inventory data for the LCA. The assessment incorporated multiple environmental metrics, including global warming potential (GWP), net energy ratio (NER) etc., under variant energy sources scenarios. Results show a low GWP (0.86 kg CO2-eq/MJ) and a NER (3.7), indicating favorable environmental performance, while the downstream processes were identified as the most energy-intensive. Sensitivity analysis highlighted the critical role of energy sources, with renewable energy improving the sustainability compared to fossil-based inputs. Overall, the results support the viability of wastewater-grown microalgae for sustainable biofuel production, particularly when integrated with low-impact energy sources.
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(This article belongs to the Special Issue Sustainability Assessment of Renewable Fuels Production)
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Open AccessArticle
Characterization of Perfluoro Sulfonic Acid Membranes for Potential Electrolytic Hydrogen Production and Fuel Cell Applications for Local and Global Green Hydrogen Economy
by
Lihle Mdleleni, Sithenkosi Mlala, Tobeka Naki, Edson L. Meyer, Mojeed A. Agoro and Nicholas Rono
Fuels 2025, 6(3), 63; https://doi.org/10.3390/fuels6030063 - 20 Aug 2025
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Fuel cells have become a fundamental technology in the development of clean energy systems, playing a vital role in the global shift toward a low-carbon future. With the growing need for sustainable hydrogen production, perfluoro sulfonic acid (PFSA) ionomer membranes play a critical
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Fuel cells have become a fundamental technology in the development of clean energy systems, playing a vital role in the global shift toward a low-carbon future. With the growing need for sustainable hydrogen production, perfluoro sulfonic acid (PFSA) ionomer membranes play a critical role in optimizing green hydrogen technologies and fuel cells. This study aims to investigate the effects of different environmental and solvent treatments on the chemical and physical properties of Nafion N−115 membranes to evaluate their suitability for both hydrogen production in proton exchange membrane (PEM) electrolyzers and hydrogen utilization in fuel cells, supporting integrated applications in the local and global green hydrogen economy. To achieve this, Nafion N−115 membranes were partially dissolved in various solvent mixtures, including ethanol/isopropanol (EI), isopropanol/water (IW), dimethylformamide/N-methyl-2-pyrrolidone (DN), and ethanol/methanol/isopropanol (EMI), evaluated under water immersion and thermal stress, and characterized for chemical stability, mechanical strength, water uptake, and proton conductivity using advanced electrochemical and spectroscopic techniques. The results demonstrated that the EMI-treated membrane showed the highest proton conductivity and maintained its structural integrity, making it the most promising for hydrogen electrolysis applications. Conversely, the DN-treated membrane exhibited reduced stability and lower conductivity due to solvent-induced degradation. This study highlights the potential of EMI as an optimal solvent mixture for enhancing PFSA membranes performance in green hydrogen production, contributing to the advancement of sustainable energy solutions.
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Open AccessArticle
Elemental Composition Analysis of Major Refined Petroleum Fuel Products in Ghana
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Robert Wilson and Calvin Kwesi Gafrey
Fuels 2025, 6(3), 62; https://doi.org/10.3390/fuels6030062 - 19 Aug 2025
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Samples of refined petroleum fuels from the three major oil-marketing companies (GOIL Company Limited, Total Energies Ghana Limited and Shell Vivo Ghana Limited) in Ghana have been analysed for elemental concentrations using an X-ray fluorescence facility at the National Nuclear Research Institute, Ghana
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Samples of refined petroleum fuels from the three major oil-marketing companies (GOIL Company Limited, Total Energies Ghana Limited and Shell Vivo Ghana Limited) in Ghana have been analysed for elemental concentrations using an X-ray fluorescence facility at the National Nuclear Research Institute, Ghana Atomic Energy Commission. The samples were acquired from seven different fuel service stations where customers directly purchase refined petroleum fuels such as diesel, petrol and kerosene. The X-ray fluorescence method was considered for the study because sample preparation does not require the addition of reagents, and the fluorescence measurements involve a direct electron transition effect. The fluorescence study was carried out to estimate the concentrations of sulphur and other contaminants in the major refined petroleum fuel products patronised in Ghana. The average sulphur concentration in the samples of diesel products were 17.543, 25.805 and 26.813 ppm in DFS, DE and DXP samples compared to 22.258, 22.623 and 15.748 ppm in petrol samples of PE, PXP and VP. Also, the sulphur concentration of sample KE, kerosene products, is 33.250 ppm. Among the diesel samples, DE and DXP recorded the highest but most comparable average concentration of elemental contaminants, and DFS the least, while PXP recorded the least among the petrol samples. The study estimated the concentrations of four heavy metal elements that are toxic to biological life (Hg, Pb, Cr and Mn) to be less than 10.0 ppm, except Cr. The study concluded that most of the elemental contaminants of heavy metals in the samples were relatively less than ultra-low levels. Therefore, exhaust emissions may have little impact on the environment. Also, the content of the ash-producing metal elements in each sample of the seven refined fuel products is between 10.0 and 50.0 ppm. Since the concentration of sulphur and a few other elemental contaminants could not meet the internationally accepted standard (<10.0 ppm), the imported refined fuel products used in Ghana may be considered relatively good but not environmentally safe.
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Open AccessArticle
Solvent Extraction of Rare-Earth Elements (REEs) from Lignite Coal In Situ
by
Ian K. Feole and Bruce C. Folkedahl
Fuels 2025, 6(3), 61; https://doi.org/10.3390/fuels6030061 - 19 Aug 2025
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Plugs of lignite coal from multiple formations were subjected to a series of tests to determine the amount of rare-earth elements (REEs) to be extracted from coal in an in situ mining operation. These tests were used to determine if extraction of REEs
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Plugs of lignite coal from multiple formations were subjected to a series of tests to determine the amount of rare-earth elements (REEs) to be extracted from coal in an in situ mining operation. These tests were used to determine if extraction of REEs and other critical minerals in an in situ environment would be possible for future attempts as an alternative to extraction mining. The tests involved subjecting whole lignite coal plugs from the Twin Butte coal seams in North Dakota to flow-through tests of water, and concentrations of 1.0 M ammonium nitrate, 1.0 M and 1.5 M sulfuric acid, and 1.0 M and 1.5 M hydrochloric acid (HCl) solvents at different concentrations and combinations. The flow-through testing was conducted by alternating the solvent and water flow-through to simulate an in situ mining scenario. The samples were analyzed for their concentrations of REEs (lanthanum [La], cerium [Ce], praseodymium [Pr], neodymium [Nd], samarium [Sm], europium [Eu], gadolinium [Gd], terbium [Tb], dysprosium [Dy], holmium [Ho], erbium [Er], thulium [Tm], ytterbium [Yb], lutetium [Lu], yttrium [Y], and scandium [Sc], as well as germanium [Ge] and cobalt [Co], manganese [Mn], nickel [Ni], and barium [Ba]). Results from the testing showed that REEs were extracted in concentrations that were on average higher using sulfuric acid (8.9%) than with HCl (5.8%), which had a higher recovery than ammonium nitrate. Tests were performed over a standard time interval for comparison between solvents, while a second set of testing was done to determine recovery rates of REEs and critical minerals under certain static and constant flow-through times to determine extraction in relation to time. Critical minerals had a higher recovery rate than the REEs across all tests, with a slightly higher recovery of light REEs over heavy REEs.
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Open AccessArticle
Utilization of Iron Foam as Structured Catalyst for Fischer–Tropsch Synthesis
by
Yira Victoria Hurtado, Ghazal Azadi, Eduardo Lins de Barros Neto and Jean-Michel Lavoie
Fuels 2025, 6(3), 60; https://doi.org/10.3390/fuels6030060 - 14 Aug 2025
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This work focuses on the fabrication, characterization, and performance of a structured iron catalyst to produce hydrocarbons by the Fischer–Tropsch synthesis (FTS). The structured catalyst enhances the heat and mass transfer and provides a larger surface area and lower pressure drop. Iron-based structured
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This work focuses on the fabrication, characterization, and performance of a structured iron catalyst to produce hydrocarbons by the Fischer–Tropsch synthesis (FTS). The structured catalyst enhances the heat and mass transfer and provides a larger surface area and lower pressure drop. Iron-based structured catalysts indicate more activity in lower H2/CO ratios and improve carbon conversion as compared to other metals. These catalysts were manufactured using the sponge replication method (powder metallurgy). The performance of the structured iron catalyst was assessed in a fixed-bed reactor under industrially relevant conditions (250 °C and 20 bar). The feed gas was a synthetic syngas with a H2/CO ratio of 1.2, simulating a bio-syngas derived from lignocellulosic biomass gasification. Notably, the best result was reached under these conditions, obtaining a CO conversion of 84.8% and a CH4 selectivity of 10.4%, where the catalyst exhibited a superior catalytic activity and selectivity toward desired hydrocarbon products, including light olefins and long-chain paraffins. The resulting structured catalyst reached a one-pass CO conversion of 84.8% with a 10.4% selectivity to CH4 compared to a traditionally produced catalyst, for which the conversion was 18% and the selectivity was 19%, respectively. The results indicate that the developed structured iron catalyst holds considerable potential for efficient and sustainable hydrocarbon production, mainly C10–C20 (diesel-range hydrocarbons), via Fischer–Tropsch synthesis. The catalyst’s excellent performance and improved stability and selectivity offer promising prospects for its application in commercial-scale hydrocarbon synthesis processes.
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Open AccessArticle
Thermo-Kinetic Assessment of Ammonia/Syngas Combustion: Experimental and Numerical Investigation of Laminar Burning Velocity at Elevated Pressure and Temperature
by
Mehrdad Kiani, Ali Akbar Abbasian Arani, Ehsan Houshfar, Mehdi Ashjaee and Pouriya H. Niknam
Fuels 2025, 6(3), 59; https://doi.org/10.3390/fuels6030059 - 12 Aug 2025
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The utilization of ammonia as a fuel for gas turbines involves practical challenges due to its low reactivity, narrow flammability limits, and slow laminar flame propagation. One of the potential solutions to enhance the combustion reactivity of ammonia is co-firing with syngas. This
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The utilization of ammonia as a fuel for gas turbines involves practical challenges due to its low reactivity, narrow flammability limits, and slow laminar flame propagation. One of the potential solutions to enhance the combustion reactivity of ammonia is co-firing with syngas. This paper presents an experimental and numerical investigation of the laminar burning velocity (LBV) of ammonia/syngas/air mixtures under elevated pressures (up to 10 bar) and temperatures (up to 473 K). Experiments were conducted in a constant-volume combustion chamber with a total volume of 11 L equipped with a dual-electrode capacitive discharge ignition system. A systematic sensitivity analysis was conducted to experimentally evaluate the system performance under various syngas compositions and equivalence ratios from 0.7 to 1.6 and ultimately identify the factors with the most impact on the system. As a complement to the experiments, a detailed numerical simulation was carried out integrating available kinetic mechanisms—chemical reaction sets and their rates—to support advancements in the understanding and optimization of ammonia/syngas co-firing dynamics. The sensitivity analysis results reveal that LBV is significantly enhanced by increasing the hydrogen content (>50%). Furthermore, the LBV of the gas mixture is found to increase with the use of a rich flame, higher mole fractions of syngas, and higher initial temperatures. The results indicate that higher pressure reduces LBV by 40% but at the same time enhances the adiabatic flame temperature (by 100 K) due to an equilibrium shift. The analysis was also extended to quantify the impact of syngas mole fractions and elevated initial temperatures. The kinetics of the reactions are analyzed through the reaction pathways, and the results reveal how the preferred pathways vary under lean and rich flame conditions. These findings provide valid quantitative design data for optimizing the combustion kinetics of ammonia/syngas blends, offering valuable design data for ammonia-based combustion systems in industrial gas turbines and power generation applications, reducing NOₓ emissions by up to 30%, and guiding future research directions toward kinetic models and emission control strategies.
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