Pub Date : 2026-02-03DOI: 10.1016/j.fuel.2026.138644
Dian Jiao , Gaige Liu , Zhisheng Liu , Tianzhen Feng , Xiangkun Li , Xiangjun Li
Polystyrene (PS) is a common microplastic can have toxic effects on the anaerobic digestion system of sludge by affecting the secretion of organic matter and volatile fatty acid, the activity of related enzymes, and the structure of microbial communities. Magnetite is a common conductive magnetic material can enhance anaerobic digestion of sludge. For the purpose to investigate the improvement of magnetite to an anaerobic digestion system inhibited by high quantity of PS microplastics, for anaerobic digestion of sludge were built and run with different conditions. The results demonstrated that high concentration microplastic stress of 300 particles/gTS initially inhibit VFAs synthesis, followed by further inhibition of protease and coenzyme F420 functions, ultimately leading to the accumulation of propionic acid/butyric acid and inhibiting anaerobic digestion for methane production, and an appropriate amount of magnetite (1 g/L) can effectively alleviate the methane production inhibition induced by microplastics (from 6.41 mlCH4/gVS∙d to 9.24 mlCH4/gVS∙d) through enhanced butyrate kinase activity and coupled with selective enrichment of Methanospirillum to optimize VFAs utilization. The microbial community reorganization supplemented by magnetite increased bacterial abundance and promoted the surface oxidation and fragmentation degree of PS. The findings reveal the addition of magnetite can alleviate the toxic effects of PS particles on the system and enhance its running performance.
{"title":"Improving anaerobic sludge digestion system combined with high quantity of polystyrene microplastics through adding magnetite","authors":"Dian Jiao , Gaige Liu , Zhisheng Liu , Tianzhen Feng , Xiangkun Li , Xiangjun Li","doi":"10.1016/j.fuel.2026.138644","DOIUrl":"10.1016/j.fuel.2026.138644","url":null,"abstract":"<div><div>Polystyrene (PS) is a common microplastic can have toxic effects on the anaerobic digestion system of sludge by affecting the secretion of organic matter and volatile fatty acid, the activity of related enzymes, and the structure of microbial communities. Magnetite is a common conductive magnetic material can enhance anaerobic digestion of sludge. For the purpose to investigate the improvement of magnetite to an anaerobic digestion system inhibited by high quantity of PS microplastics, for anaerobic digestion of sludge were built and run with different conditions. The results demonstrated that high concentration microplastic stress of 300 particles/gTS initially inhibit VFAs synthesis, followed by further inhibition of protease and coenzyme F420 functions, ultimately leading to the accumulation of propionic acid/butyric acid and inhibiting anaerobic digestion for methane production, and an appropriate amount of magnetite (1 g/L) can effectively alleviate the methane production inhibition induced by microplastics (from 6.41 mlCH<sub>4</sub>/gVS∙d to 9.24 mlCH<sub>4</sub>/gVS∙d) through enhanced butyrate kinase activity and coupled with selective enrichment of Methanospirillum to optimize VFAs utilization. The microbial community reorganization supplemented by magnetite increased bacterial abundance and promoted the surface oxidation and fragmentation degree of PS. The findings reveal the addition of magnetite can alleviate the toxic effects of PS particles on the system and enhance its running performance.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"417 ","pages":"Article 138644"},"PeriodicalIF":7.5,"publicationDate":"2026-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146102739","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}
Pub Date : 2026-02-03DOI: 10.1016/j.fuel.2026.138586
Gen-Wang Ma , Xiao-Han Guo , Wei-Zhuo Gai , Yang Yang , Jie Zhang , Zheng-hui Pan , Zhen-Yan Deng
Aluminum (Al) is an active metal with a redox potential as low as of −1.66 V, but its surface passive oxide film prevents inner Al from contacting outside. In the past twenty years, Al surface modification by covering nanometer oxides was successfully used to activate Al so that it can rapidly generate hydrogen with water. However, the underlying mechanism is controversial so far. In this work, a model experiment was done by soaking and heat-treating Al sheet and powder so that a layer of porous nanometer γ-Al2O3 or Al(OH)3 covers on Al surfaces. It was found that there is a sharp wettability transition from hydrophobic on pristine Al surfaces to hydrophilic on modified Al. The contact angle of water droplet decreases from ∼ 90° to 30-40° and underwater hydrogen bubble contact angle increases from ∼ 125° to ∼ 180° after Al surface modification. Nanometer porous structures on modified Al surfaces push water towards inner Al such that the hydration process of Al surface passive oxide film is speeded up, and hydrogen bubble adhesion force decreases from > 100 μN on pristine Al surfaces to almost zero on modified Al, leading to a shorter induction time for the beginning of Al-water reaction to generate hydrogen. Cyclic voltammetry tests and electrochemical impedance spectroscopy showed that Al surface modification enhances the current density and reduces the charge transfer resistance, which are beneficial to Al reduction reaction. The present study provides a new mechanism and route for Al activation in hydrogen generation.
{"title":"Improvement of surface hydrophilicity by nanometer oxides to promote aluminum-water reaction to generate hydrogen","authors":"Gen-Wang Ma , Xiao-Han Guo , Wei-Zhuo Gai , Yang Yang , Jie Zhang , Zheng-hui Pan , Zhen-Yan Deng","doi":"10.1016/j.fuel.2026.138586","DOIUrl":"10.1016/j.fuel.2026.138586","url":null,"abstract":"<div><div>Aluminum (Al) is an active metal with a redox potential as low as of −1.66 V, but its surface passive oxide film prevents inner Al from contacting outside. In the past twenty years, Al surface modification by covering nanometer oxides was successfully used to activate Al so that it can rapidly generate hydrogen with water. However, the underlying mechanism is controversial so far. In this work, a model experiment was done by soaking and heat-treating Al sheet and powder so that a layer of porous nanometer γ-Al<sub>2</sub>O<sub>3</sub> or Al(OH)<sub>3</sub> covers on Al surfaces. It was found that there is a sharp wettability transition from hydrophobic on pristine Al surfaces to hydrophilic on modified Al. The contact angle of water droplet decreases from ∼ 90° to 30-40° and underwater hydrogen bubble contact angle increases from ∼ 125° to ∼ 180° after Al surface modification. Nanometer porous structures on modified Al surfaces push water towards inner Al such that the hydration process of Al surface passive oxide film is speeded up, and hydrogen bubble adhesion force decreases from > 100 μN on pristine Al surfaces to almost zero on modified Al, leading to a shorter induction time for the beginning of Al-water reaction to generate hydrogen. Cyclic voltammetry tests and electrochemical impedance spectroscopy showed that Al surface modification enhances the current density and reduces the charge transfer resistance, which are beneficial to Al reduction reaction. The present study provides a new mechanism and route for Al activation in hydrogen generation.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"417 ","pages":"Article 138586"},"PeriodicalIF":7.5,"publicationDate":"2026-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146102749","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}
Pub Date : 2026-02-03DOI: 10.1016/j.fuel.2026.138542
Haihong Zhang, Chongchong Wu, Huiling Zhang, Ning Wang, Yu Song, Longnian Han, Siran Zhang, Mengjun Su, Jian Liu, Zhanggui Hou
The tightening of global environmental regulations and the growing emphasis on carbon neutrality have driven the petroleum industry to pursue ultra-clean fuels. Diesel, as a dominant transportation fuel, faces particularly stringent sulfur limits due to the adverse environmental and operational impacts of sulfur oxides. Hydrodesulfurization (HDS) remains the most mature and efficient industrial technology for producing low-sulfur diesel; however, the escalating demands for ultra-deep desulfurization and low-carbon operation have placed unprecedented challenges on catalyst performance. Despite significant advances in catalyst formulation, systematic reviews dedicated specifically to HDS catalyst development remain scarce. This review provides a comprehensive overview of recent progress in HDS catalysis, emphasizing strategies for modulating active phases, supports, and novel unsupported catalysts. The fundamental mechanisms governing desulfurization pathways are briefly summarized to establish the theoretical foundation for subsequent discussions. Recent advances in tuning metal–support interactions, tailoring acidity, and employing heteroatom or promoter modifications to enhance catalytic activity are critically analyzed. Support regulation strategies—including compositional modification of γ-Al2O3 and zeolite-based systems—are examined with attention to structure–performance correlations and industrial applicability. The review further explores the emerging class of unsupported catalysts, highlighting template-assisted synthesis and three-dimensional framework designs as promising directions. Finally, key scientific challenges and future prospects are outlined, aiming to provide guidance for the rational design of next-generation HDS catalysts that enable sustainable production of ultra-clean diesel.
{"title":"Hydrodesulfurization catalysts for ultra-clean diesel: Recent progress, modulation strategies, and emerging alternatives","authors":"Haihong Zhang, Chongchong Wu, Huiling Zhang, Ning Wang, Yu Song, Longnian Han, Siran Zhang, Mengjun Su, Jian Liu, Zhanggui Hou","doi":"10.1016/j.fuel.2026.138542","DOIUrl":"10.1016/j.fuel.2026.138542","url":null,"abstract":"<div><div>The tightening of global environmental regulations and the growing emphasis on carbon neutrality have driven the petroleum industry to pursue ultra-clean fuels. Diesel, as a dominant transportation fuel, faces particularly stringent sulfur limits due to the adverse environmental and operational impacts of sulfur oxides. Hydrodesulfurization (HDS) remains the most mature and efficient industrial technology for producing low-sulfur diesel; however, the escalating demands for ultra-deep desulfurization and low-carbon operation have placed unprecedented challenges on catalyst performance. Despite significant advances in catalyst formulation, systematic reviews dedicated specifically to HDS catalyst development remain scarce. This review provides a comprehensive overview of recent progress in HDS catalysis, emphasizing strategies for modulating active phases, supports, and novel unsupported catalysts. The fundamental mechanisms governing desulfurization pathways are briefly summarized to establish the theoretical foundation for subsequent discussions. Recent advances in tuning metal–support interactions, tailoring acidity, and employing heteroatom or promoter modifications to enhance catalytic activity are critically analyzed. Support regulation strategies—including compositional modification of γ-Al<sub>2</sub>O<sub>3</sub> and zeolite-based systems—are examined with attention to structure–performance correlations and industrial applicability. The review further explores the emerging class of unsupported catalysts, highlighting template-assisted synthesis and three-dimensional framework designs as promising directions. Finally, key scientific challenges and future prospects are outlined, aiming to provide guidance for the rational design of next-generation HDS catalysts that enable sustainable production of ultra-clean diesel.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"417 ","pages":"Article 138542"},"PeriodicalIF":7.5,"publicationDate":"2026-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146102829","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}
Pub Date : 2026-02-03DOI: 10.1016/j.fuel.2026.138552
Mohamed Salah Eddine Salah , M. Mustafa Kamal , Lyes Tarabet , Alessandro Parente
Biogas is a renewable and infrastructure-compatible fuel for distributed power generation, but its high CO2 content lowers heating value and flame speed, complicating flame stabilization and narrowing the flammability range. Hydrogen enrichment widens this range, accelerates ignition, and promotes full oxidation, enabling efficient, low-CO operation. This experimental study investigates hydrogen-enriched biogas combustion in a stagnation-point reverse-flow (SPRF) combustor, a practical configuration featuring internal flue gas recirculation (iFGR). Experiments were performed at 18 kW thermal power under various operating conditions in terms of biogas composition (0–40% CO2 by v/v.), hydrogen fraction (0–50% by v/v.), air-inlet diameters (40 and 24 mm), air preheating (500–900 K), and equivalence ratio (0.4–0.6). The dataset comprises 108 test cases combining dual-camera, two-line imaging of OH*, CH*, C2*, and broadband CO2* (100 Hz) with exhaust CO/NO measurements. Results show that OH* intensity increases monotonically with H2 and serves as a robust tracer of reactivity, while CH* and C2* exhibit non-monotonic behaviour due to competing thermal and carbon-depletion effects. The OH*/CH* and OH*/ C2* ratios track H2 enrichment in the wider-inlet geometry, whereas enhanced mixing in the compact inlet compresses their dynamic range. Comparison with published premixed and diffusion flame studies indicates that OH* intensity and the OH*/CH* ratio exhibit consistent trends, whereas other chemiluminescence signals and ratios are strongly configuration-dependent and require validation for each specific combustor geometry. Flame hysteresis occurs between attached and detached modes: the attached regime yields higher CO and NO due to incomplete oxidation, while the detached regime achieves low-CO operation through intensified air–fuel–recirculation interactions. Finally, Gaussian Process Regression (GPR) models trained on chemiluminescence intensities accurately predict emissions, illustrating the potential of virtual sensing for hydrogen-biogas combustors.
沼气是一种可再生和基础设施兼容的分布式发电燃料，但其高二氧化碳含量降低了热值和火焰速度，使火焰稳定变得复杂，并缩小了可燃性范围。氢富集扩大了这个范围，加速点火，促进充分氧化，实现高效，低co操作。本实验研究了富氢沼气在停滞点逆流（SPRF）燃烧器中的燃烧，这是一种具有内部烟气再循环（iFGR）的实用配置。在18 kW的热功率下，对不同工况下沼气组成（0-40% CO2 /v）、氢气含量（0-50% CO2 /v）、进气直径（40和24 mm）、空气预热（500-900 K）和等效比（0.4-0.6）进行了实验。该数据集包括108个测试用例，结合双摄像头、OH*、CH*、C2*和宽带CO2* (100 Hz)的两线成像，以及废气CO/NO测量。结果表明，OH*的强度随着H2的增加而单调增加，可以作为反应活性的稳健示踪剂，而CH*和C2*由于热效应和碳耗尽效应的竞争而表现出非单调行为。OH*/CH*和OH*/ C2*比值在宽进气道中跟踪H2富集，而在紧凑进气道中增强混合会压缩它们的动态范围。与已发表的预混火焰和扩散火焰研究的对比表明，OH*强度和OH*/CH*比值呈现出一致的趋势，而其他化学发光信号和比值则强烈依赖于构型，需要对每个特定燃烧室的几何形状进行验证。附着和分离模式之间存在火焰滞后：附着模式由于不完全氧化产生较高的CO和NO，而分离模式通过加强空气-燃料再循环相互作用实现低CO运行。最后，基于化学发光强度训练的高斯过程回归（GPR）模型准确预测了排放，说明了氢气-沼气燃烧器虚拟传感的潜力。
{"title":"Interpreting chemiluminescence signals and ratios in hydrogenated biogas flames in a micro gas turbine combustor","authors":"Mohamed Salah Eddine Salah , M. Mustafa Kamal , Lyes Tarabet , Alessandro Parente","doi":"10.1016/j.fuel.2026.138552","DOIUrl":"10.1016/j.fuel.2026.138552","url":null,"abstract":"<div><div>Biogas is a renewable and infrastructure-compatible fuel for distributed power generation, but its high CO<sub>2</sub> content lowers heating value and flame speed, complicating flame stabilization and narrowing the flammability range. Hydrogen enrichment widens this range, accelerates ignition, and promotes full oxidation, enabling efficient, low-CO operation. This experimental study investigates hydrogen-enriched biogas combustion in a stagnation-point reverse-flow (SPRF) combustor, a practical configuration featuring internal flue gas recirculation (iFGR). Experiments were performed at 18 kW thermal power under various operating conditions in terms of biogas composition (0–40% CO<sub>2</sub> by v/v.), hydrogen fraction (0–50% by v/v.), air-inlet diameters (40 and 24 mm), air preheating (500–900 K), and equivalence ratio (0.4–0.6). The dataset comprises 108 test cases combining dual-camera, two-line imaging of OH*, CH*, C<sub>2</sub>*, and broadband CO<sub>2</sub>* (100 Hz) with exhaust CO/NO measurements. Results show that OH* intensity increases monotonically with H<sub>2</sub> and serves as a robust tracer of reactivity, while CH* and C<sub>2</sub>* exhibit non-monotonic behaviour due to competing thermal and carbon-depletion effects. The OH*/CH* and OH*/ C<sub>2</sub>* ratios track H<sub>2</sub> enrichment in the wider-inlet geometry, whereas enhanced mixing in the compact inlet compresses their dynamic range. Comparison with published premixed and diffusion flame studies indicates that OH* intensity and the OH*/CH* ratio exhibit consistent trends, whereas other chemiluminescence signals and ratios are strongly configuration-dependent and require validation for each specific combustor geometry. Flame hysteresis occurs between attached and detached modes: the attached regime yields higher CO and NO due to incomplete oxidation, while the detached regime achieves low-CO operation through intensified air–fuel–recirculation interactions. Finally, Gaussian Process Regression (GPR) models trained on chemiluminescence intensities accurately predict emissions, illustrating the potential of virtual sensing for hydrogen-biogas combustors.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"417 ","pages":"Article 138552"},"PeriodicalIF":7.5,"publicationDate":"2026-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146102702","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}
Pub Date : 2026-02-03DOI: 10.1016/j.fuel.2026.138625
Sifan Cao , Yong-Chen Han , Huqe Farhana , Xiaochang C. Wang , Rong Chen , Yu-You Li , Bao-Shan Xing
Pretreatment methods are prominently used to enhance methane production from any raw materials, with hydrolysis remaining a key bottleneck among such energy-environment balance pretreatment methodologies. This research explored the comparative potency of ozone (solid–liquid ratio-time-ozone dose), hydrothermal (solid–liquid ratio-time–temperature) and super-alkali (superalkali dose-time–temperature) pretreatment on corn straw by employing the required optimizing parameters. Response Surface Methodology (RSM) for each pretreatment processes were corroborated for batch and semi-continuous reactors. Comparing the three pretreatment methods, ozone pretreatment was leading to the utmost amount of methane production of 160.18 mL CH4/g VS, which was 85.72% higher than that of the untreated group. The results demonstrated that the process leverages ozone’s strong oxidizing capacity to break down lignin, achieving a high delignification rate of 74.2% while retaining substantial fractions of cellulose and hemicellulose. No significant accumulation of phenol was observed following ozone pretreatment, with the system concentration remaining below the inhibitory threshold of 100 mg/L. In semi-continuous reactor, the tolerance to inhibitors and process stability were investigated simultaneously. The ozone-pretreated group exhibited a 7.8% increase in average biogas production, indicating microbial capability to degrade exogenously added inhibitory derivatives. An economic analysis was reviewed to strengthen the lucrative influence of ozone, ozone pretreatment of corn straw resulted in a 56.7% improvement in net profit. These findings indicate that ozone pretreatment can effectively recover resources from waste and improve the value conversion efficiency of waste.
预处理方法主要用于提高任何原料的甲烷产量，而水解仍然是这种能量-环境平衡预处理方法中的关键瓶颈。本研究采用所要求的优化参数，探讨了臭氧（固液比-臭氧剂量）、水热（固液比-时间-温度）和超碱（超碱剂量-时间-温度）预处理玉米秸秆的效果对比。响应面法（RSM）对间歇反应器和半连续反应器各预处理工艺进行了验证。对比三种预处理方法，臭氧预处理最大产甲烷量为160.18 mL CH4/g VS，比未处理组提高85.72%。结果表明，该工艺利用臭氧的强氧化能力分解木质素，达到74.2%的高脱木质素率，同时保留了大量纤维素和半纤维素。臭氧预处理后未观察到苯酚的显著积累，系统浓度保持在100 mg/L的抑制阈值以下。在半连续反应器中，同时考察了对抑制剂的耐受性和工艺稳定性。臭氧预处理组的平均沼气产量增加了7.8%，表明微生物有能力降解外源添加的抑制衍生物。对加强臭氧效益效应的经济分析进行了综述，臭氧预处理玉米秸秆的纯利润提高了56.7%。研究结果表明，臭氧预处理可有效回收废弃物资源，提高废弃物价值转化效率。
{"title":"Application of optimized hydrothermal, ozone and superalkali pretreatment techniques for qualitative biogas production from corn straw: A comparative assessment","authors":"Sifan Cao , Yong-Chen Han , Huqe Farhana , Xiaochang C. Wang , Rong Chen , Yu-You Li , Bao-Shan Xing","doi":"10.1016/j.fuel.2026.138625","DOIUrl":"10.1016/j.fuel.2026.138625","url":null,"abstract":"<div><div>Pretreatment methods are prominently used to enhance methane production from any raw materials, with hydrolysis remaining a key bottleneck among such energy-environment balance pretreatment methodologies. This research explored the comparative potency of ozone (solid–liquid ratio-time-ozone dose), hydrothermal (solid–liquid ratio-time–temperature) and super-alkali (superalkali dose-time–temperature) pretreatment on corn straw by employing the required optimizing parameters. Response Surface Methodology (RSM) for each pretreatment processes were corroborated for batch and semi-continuous reactors. Comparing the three pretreatment methods, ozone pretreatment was leading to the utmost amount of methane production of 160.18 mL CH<sub>4</sub>/g VS, which was 85.72% higher than that of the untreated group. The results demonstrated that the process leverages ozone’s strong oxidizing capacity to break down lignin, achieving a high delignification rate of 74.2% while retaining substantial fractions of cellulose and hemicellulose. No significant accumulation of phenol was observed following ozone pretreatment, with the system concentration remaining below the inhibitory threshold of 100 mg/L. In semi-continuous reactor, the tolerance to inhibitors and process stability were investigated simultaneously. The ozone-pretreated group exhibited a 7.8% increase in average biogas production, indicating microbial capability to degrade exogenously added inhibitory derivatives. An economic analysis was reviewed to strengthen the lucrative influence of ozone, ozone pretreatment of corn straw resulted in a 56.7% improvement in net profit. These findings indicate that ozone pretreatment can effectively recover resources from waste and improve the value conversion efficiency of waste.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"417 ","pages":"Article 138625"},"PeriodicalIF":7.5,"publicationDate":"2026-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146102741","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}
Pub Date : 2026-02-03DOI: 10.1016/j.fuel.2026.138643
Yu-Da Hsiao
Direct carbon dioxide (CO2) methanation is one of the most attractive technologies for realizing practical and sustainable carbon capture and utilization schemes. Among various engineering designs, multi-stage adiabatic reactor is still the major option due to its simplicity and flexibility. However, the drastic and rapid temperature increase along the first reactor due to reactive exothermicity makes it necessary to incorporate internal gas recirculating (IGR) designs, which however results in a massive amount of compression work for gas recirculation, which thus lowers its economic feasibility. Most studies adopted the IGR design by recirculating outlet gas from the first reactor, while other potentially viable alternatives by recirculating the ones from other downstream stages have never been systematically investigated. Therefore, in this study, several multi-stage adiabatic reactors with innovative IGR configurations were quantitatively assessed by analyzing their potentials of performance improvements. It was found that by recirculating the outlet gases from downstream reactors, the CO accumulation effect within the IGR loop may be effectively eliminated, which thus in thermodynamics prompts the forward proceedings of endothermic CO-forming reactions and offsets the exothermic effect by the methanation reactions. The results showed that the internal recirculating flowrates of non-condensable gases may be effectively reduced by 48.1–66.4%, and the accumulation of CO within the IGR loop may also be eliminated to facilitate the enhancement of CO2 conversion and CH4 yield by more than 2%. Also, the H2/CO2 ratio may be well maintained at around 4 over the entire process to prevent carbon deposition.
{"title":"Exploring alternative internal gas recirculating designs of multi-stage adiabatic reactors for direct CO2 methanation from thermodynamic insights","authors":"Yu-Da Hsiao","doi":"10.1016/j.fuel.2026.138643","DOIUrl":"10.1016/j.fuel.2026.138643","url":null,"abstract":"<div><div>Direct carbon dioxide (CO<sub>2</sub>) methanation is one of the most attractive technologies for realizing practical and sustainable carbon capture and utilization schemes. Among various engineering designs, multi-stage adiabatic reactor is still the major option due to its simplicity and flexibility. However, the drastic and rapid temperature increase along the first reactor due to reactive exothermicity makes it necessary to incorporate internal gas recirculating (IGR) designs, which however results in a massive amount of compression work for gas recirculation, which thus lowers its economic feasibility. Most studies adopted the IGR design by recirculating outlet gas from the first reactor, while other potentially viable alternatives by recirculating the ones from other downstream stages have never been systematically investigated. Therefore, in this study, several multi-stage adiabatic reactors with innovative IGR configurations were quantitatively assessed by analyzing their potentials of performance improvements. It was found that by recirculating the outlet gases from downstream reactors, the CO accumulation effect within the IGR loop may be effectively eliminated, which thus in thermodynamics prompts the forward proceedings of endothermic CO-forming reactions and offsets the exothermic effect by the methanation reactions. The results showed that the internal recirculating flowrates of non-condensable gases may be effectively reduced by 48.1–66.4%, and the accumulation of CO within the IGR loop may also be eliminated to facilitate the enhancement of CO<sub>2</sub> conversion and CH<sub>4</sub> yield by more than 2%. Also, the H<sub>2</sub>/CO<sub>2</sub> ratio may be well maintained at around 4 over the entire process to prevent carbon deposition.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"417 ","pages":"Article 138643"},"PeriodicalIF":7.5,"publicationDate":"2026-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146102748","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}
Pub Date : 2026-02-03DOI: 10.1016/j.fuel.2026.138538
Vadim A. Kuznetsov , Martin Gräbner , Ronny Schimpke. , Dirk Uhrlandt , Andreas Richter
The study overviews gasifiers driven by thermal and microwave plasma which primarily produce hydrogen and carbon monoxide. Industrially available plasma generation methods are described. Analysis of plasma gasification systems revealed eight distinct designs and their features. Counter current systems matured to industrial scale (up to 7000 kg/h of municipal solid waste), though tar cracking is not forced by plasma integration. The cold gas efficiency (∼61%) is similar to the autothermal industrial systems. Cross current systems reached technology readiness levels of 4–5 (up to 60 kg/h) but require long-term testing for stationary state balancing. In co-current downdraft systems wood and low-ash, plastic-rich municipal solid waste were processed (<110 kg/h). The drawback is that plasma temperature is limited by ash melting. A horizontal co-current design was proven at feeding rates of 400 kg/h in a 12 months’ run on municipal solid waste with slagging ash discharge, whereas cold gas efficiencies of ∼ 53% were reached that are comparable to conventional gasifiers. Entrained flow designs require good plasma-feedstock mixing, which is hard to ensure at throughputs far below 90 kg/h of coal. Arc and microwave discharge integrated solutions suffer from the feeding-caused instabilities of the discharge and require high energy consumption (>10 kWh/kg). The furnace-like designs, which have a throughput of up to 437 kg/h, also suffer from arc instabilities resulting in energy consumptions of > 4 kWh/kg due to a poor energy distribution. A counter current design was determined to be the most mature one, while horizontal co-current designs promise better performance.
{"title":"Systematic evaluation of gasifiers driven by the high-enthalpy plasma supply","authors":"Vadim A. Kuznetsov , Martin Gräbner , Ronny Schimpke. , Dirk Uhrlandt , Andreas Richter","doi":"10.1016/j.fuel.2026.138538","DOIUrl":"10.1016/j.fuel.2026.138538","url":null,"abstract":"<div><div>The study overviews gasifiers driven by thermal and microwave plasma which primarily produce hydrogen and carbon monoxide. Industrially available plasma generation methods are described. Analysis of plasma gasification systems revealed eight distinct designs and their features. Counter current systems matured to industrial scale (up to 7000 kg/h of municipal solid waste), though tar cracking is not forced by plasma integration. The cold gas efficiency (∼61%) is similar to the autothermal industrial systems. Cross current systems reached technology readiness levels of 4–5 (up to 60 kg/h) but require long-term testing for stationary state balancing. In co-current downdraft systems wood and low-ash, plastic-rich municipal solid waste were processed (<110 kg/h). The drawback is that plasma temperature is limited by ash melting. A horizontal co-current design was proven at feeding rates of 400 kg/h in a 12 months’ run on municipal solid waste with slagging ash discharge, whereas cold gas efficiencies of ∼ 53% were reached that are comparable to conventional gasifiers. Entrained flow designs require good plasma-feedstock mixing, which is hard to ensure at throughputs far below 90 kg/h of coal. Arc and microwave discharge integrated solutions suffer from the feeding-caused instabilities of the discharge and require high energy consumption (>10 kWh/kg). The furnace-like designs, which have a throughput of up to 437 kg/h, also suffer from arc instabilities resulting in energy consumptions of > 4 kWh/kg due to a poor energy distribution. A counter current design was determined to be the most mature one, while horizontal co-current designs promise better performance.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"417 ","pages":"Article 138538"},"PeriodicalIF":7.5,"publicationDate":"2026-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146102830","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}
Pub Date : 2026-02-03DOI: 10.1016/j.fuel.2026.138337
Yifan Jia, Liangjuan Gao
Molten carbonate fuel cells (MCFCs), an important type of high-temperature fuel cell, have received much more attention due to their high efficiency and fuel flexibility. However, the problems of component stability, electrode reaction efficiency, and electrolyte loss associated with high-temperature operation have become key factors limiting their lifetime. This review summarizes the research progress on the electrode reactions of MCFCs from the aspects of materials and electrochemical mechanisms. The molten carbonate electrolytes are modified with alkaline-earth metal carbonates to improve their interfacial wetting with electrodes and high-temperature stability. The anodic reaction is the fuel oxidation reaction, such as H2, C, and CO. The cathodic reaction is the oxygen reduction reaction (ORR), which is more complicated than that of anodic reaction since more intermediate species are involved during the reaction. For anodic reaction mechanisms, the synergistic roles of hydrogen adsorption–oxidation, and participation pathways are systematically discussed, together with the influence of temperature, pressure, gas composition, and anode microstructure. For cathodic reaction mechanisms, the peroxide, superoxide, percarbonate and peroxodicarbonate pathways are analyzed, with emphasis on the identification of active oxygen species (, , and C2) and their dependence on electrolyte composition, PCO2/PO2 ratio, and cathode microstructure. Furthermore, future research orientations on the MCFC electrode reactions and MCFC technology are proposed.
{"title":"Electrode reactions in molten carbonate fuel cells: A review","authors":"Yifan Jia, Liangjuan Gao","doi":"10.1016/j.fuel.2026.138337","DOIUrl":"10.1016/j.fuel.2026.138337","url":null,"abstract":"<div><div>Molten carbonate fuel cells (MCFCs), an important type of high-temperature fuel cell, have received much more attention due to their high efficiency and fuel flexibility. However, the problems of component stability, electrode reaction efficiency, and electrolyte loss associated with high-temperature operation have become key factors limiting their lifetime. This review summarizes the research progress on the electrode reactions of MCFCs from the aspects of materials and electrochemical mechanisms. The molten carbonate electrolytes are modified with alkaline-earth metal carbonates to improve their interfacial wetting with electrodes and high-temperature stability. The anodic reaction is the fuel oxidation reaction, such as H<sub>2</sub>, C, and CO. The cathodic reaction is the oxygen reduction reaction (ORR), which is more complicated than that of anodic reaction since more intermediate species are involved during the reaction. For anodic reaction mechanisms, the synergistic roles of hydrogen adsorption–oxidation, and <span><math><mrow><msup><mi>OH</mi><mo>-</mo></msup></mrow></math></span> participation pathways are systematically discussed, together with the influence of temperature, pressure, gas composition, and anode microstructure. For cathodic reaction mechanisms, the peroxide, superoxide, percarbonate and peroxodicarbonate pathways are analyzed, with emphasis on the identification of active oxygen species (<span><math><mrow><msubsup><mi>O</mi><mn>2</mn><mrow><mn>2</mn><mo>-</mo></mrow></msubsup></mrow></math></span>, <span><math><mrow><msubsup><mi>O</mi><mn>2</mn><mrow><mo>-</mo></mrow></msubsup></mrow></math></span>, <span><math><mrow><msubsup><mi>CO</mi><mn>4</mn><mrow><mn>2</mn><mo>-</mo></mrow></msubsup></mrow></math></span> and C<sub>2</sub><span><math><mrow><msubsup><mi>O</mi><mn>6</mn><mrow><mn>2</mn><mo>-</mo></mrow></msubsup></mrow></math></span>) and their dependence on electrolyte composition, P<sub>CO</sub><sub>2</sub>/P<sub>O2</sub> ratio, and cathode microstructure. Furthermore, future research orientations on the MCFC electrode reactions and MCFC technology are proposed.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"417 ","pages":"Article 138337"},"PeriodicalIF":7.5,"publicationDate":"2026-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146102828","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}
Pub Date : 2026-02-03DOI: 10.1016/j.fuel.2026.138635
Bassam S. Aljohani , Jianguo Du , Hao Wu , Moez Ben Houidi , William L. Roberts
While Spray and combustion characteristics have been extensively characterized at low ambient densities (14.8–22.8 kg/m3), limited understanding exists under ultra-high ambient density (∼50 kg/m3) representative of high-pressure or supercritical combustion conditions, particularly with multiple injection strategies. This knowledge gap arises from experimental challenges in controlling extreme thermodynamic conditions. The present study investigates the spray and combustion characteristics of real fuels and their surrogates operated with single, double, triple, and quadruple injection strategies under ultra-high ambient density conditions. This work is motivated by recent advances in isobaric combustion, where maintaining constant pressure combustion through multiple injections has shown improved efficiency over conventional diesel combustion. A high-pressure constant-volume combustion chamber (CVCC) capable of achieving pressures up to 300 bar was employed to reproduce engine-relevant isobaric combustion conditions. The study focused on achieving vessel pressure of 150 bar with ambient temperature of 1000 K, corresponding to ultra-high ambient bulk density of 50 kg/m3. A high-speed chemiluminescence imaging is employed to analyze the combustion characteristics, examining parameters such as ignition delay time (IDT), mixing period, flame natural luminosity (NL), rate of heat release (ROHR), and flame lift-off lengths (FLOL). Conventional gasoline and diesel were used alongside fuel surrogates, iso-octane and n-heptane, to emulate the behavior of real fuels. The findings indicate that the variations in IDTs among the tested fuels are negligible, whereas increasing the number of injections significantly prolongs the mixing period, nearly doubling from single to quadruple injections. The maximum FLOL decreases by over 20%, indicating earlier flame stabilization under multiple-injection operation. Diesel exhibited the longest effective combustion duration, exceeding other fuels by approximately 0.25 ms across all injection strategies, indicating diffusion-controlled combustion. Among the surrogates, n-heptane showed strong ROHR sensitivity to injection phasing under multiple injections, reflecting its pronounced low-temperature chemistry. Comparisons between real and surrogate fuels revealed that simplified surrogates cannot fully reproduce the ROHR and soot-formation behavior of real fuels under multiple injection strategies. Overall, this work provides insight into the fundamental understanding of multiple-injection combustion at high pressures and underscores the need for complementary numerical simulations to further elucidate the complex mechanisms governing high-pressure combustion.
{"title":"Spray and combustion characteristics under ultra-high-ambient density: a comparison of fuels and number of injections","authors":"Bassam S. Aljohani , Jianguo Du , Hao Wu , Moez Ben Houidi , William L. Roberts","doi":"10.1016/j.fuel.2026.138635","DOIUrl":"10.1016/j.fuel.2026.138635","url":null,"abstract":"<div><div>While Spray and combustion characteristics have been extensively characterized at low ambient densities (14.8–22.8 kg/m<sup>3</sup>), limited understanding exists under ultra-high ambient density (∼50 kg/m<sup>3</sup>) representative of high-pressure or supercritical combustion conditions, particularly with multiple injection strategies. This knowledge gap arises from experimental challenges in controlling extreme thermodynamic conditions. The present study investigates the spray and combustion characteristics of real fuels and their surrogates operated with single, double, triple, and quadruple injection strategies under ultra-high ambient density conditions. This work is motivated by recent advances in isobaric combustion, where maintaining constant pressure combustion through multiple injections has shown improved efficiency over conventional diesel combustion. A high-pressure constant-volume combustion chamber (CVCC) capable of achieving pressures up to 300 bar was employed to reproduce engine-relevant isobaric combustion conditions. The study focused on achieving vessel pressure of 150 bar with ambient temperature of 1000 K, corresponding to ultra-high ambient bulk density of 50 kg/m<sup>3</sup>. A high-speed chemiluminescence imaging is employed to analyze the combustion characteristics, examining parameters such as ignition delay time (IDT), mixing period, flame natural luminosity (NL), rate of heat release (ROHR), and flame lift-off lengths (FLOL). Conventional gasoline and diesel were used alongside fuel surrogates, iso-octane and n-heptane, to emulate the behavior of real fuels. The findings indicate that the variations in IDTs among the tested fuels are negligible, whereas increasing the number of injections significantly prolongs the mixing period, nearly doubling from single to quadruple injections. The maximum FLOL decreases by over 20%, indicating earlier flame stabilization under multiple-injection operation. Diesel exhibited the longest effective combustion duration, exceeding other fuels by approximately 0.25 ms across all injection strategies, indicating diffusion-controlled combustion. Among the surrogates, n-heptane showed strong ROHR sensitivity to injection phasing under multiple injections, reflecting its pronounced low-temperature chemistry. Comparisons between real and surrogate fuels revealed that simplified surrogates cannot fully reproduce the ROHR and soot-formation behavior of real fuels under multiple injection strategies. Overall, this work provides insight into the fundamental understanding of multiple-injection combustion at high pressures and underscores the need for complementary numerical simulations to further elucidate the complex mechanisms governing high-pressure combustion.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"417 ","pages":"Article 138635"},"PeriodicalIF":7.5,"publicationDate":"2026-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146102747","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}
Pub Date : 2026-01-31DOI: 10.1016/j.fuel.2026.138579
Gökçe Güner Karaali, İbrahim Kaba, Atıf Koca
Hydrogen technologies are expected to replace fossil fuels, which currently meet a large portion of our energy needs. In this context, research on efficient hydrogen production is rapidly advancing, and water splitting methods are emerging as an environmentally friendly and sustainable alternative. Extensive research is available in the literature on electrocatalysts designed to minimize energy consumption and maximize process efficiency. The exceptionally superior properties of graphene derivatives, such as high surface area, conductivity, structural flexibility, and thermal and mechanical properties, have led to their widespread use in hydrogen production processes from water electrolysis. Furthermore, numerous studies have been published in the literature on electrocatalysts whose performance is enhanced by methods such as doping and metal integration, thanks to graphene’s modifiable chemical structure. Derivatives can be presented as graphene-based electrocatalysts, heteroatom-doped metal-free graphene electrocatalysts, precious metal-free transition metal graphene electrocatalysts, and precious metal graphene electrocatalysts. Our review reveals through a critical literature review that electrocatalysts produced from graphene derivatives in recent years may offer effective solutions to challenges such as low stability and high overpotentials in hydrogen evolution reactions (HER) and may also be important for future research aiming to increase efficiency and reduce costs.
{"title":"Graphene derivative based electrocatalytic hydrogen evolution reaction of water splitting processes","authors":"Gökçe Güner Karaali, İbrahim Kaba, Atıf Koca","doi":"10.1016/j.fuel.2026.138579","DOIUrl":"10.1016/j.fuel.2026.138579","url":null,"abstract":"<div><div>Hydrogen technologies are expected to replace fossil fuels, which currently meet a large portion of our energy needs. In this context, research on efficient hydrogen production is rapidly advancing, and water splitting methods are emerging as an environmentally friendly and sustainable alternative. Extensive research is available in the literature on electrocatalysts designed to minimize energy consumption and maximize process efficiency. The exceptionally superior properties of graphene derivatives, such as high surface area, conductivity, structural flexibility, and thermal and mechanical properties, have led to their widespread use in hydrogen production processes from water electrolysis. Furthermore, numerous studies have been published in the literature on electrocatalysts whose performance is enhanced by methods such as doping and metal integration, thanks to graphene’s modifiable chemical structure. Derivatives can be presented as graphene-based electrocatalysts, heteroatom-doped metal-free graphene electrocatalysts, precious metal-free transition metal graphene electrocatalysts, and precious metal graphene electrocatalysts. Our review reveals through a critical literature review that electrocatalysts produced from graphene derivatives in recent years may offer effective solutions to challenges such as low stability and high overpotentials in hydrogen evolution reactions (HER) and may also be important for future research aiming to increase efficiency and reduce costs.</div></div>","PeriodicalId":325,"journal":{"name":"Fuel","volume":"416 ","pages":"Article 138579"},"PeriodicalIF":7.5,"publicationDate":"2026-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146075903","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}
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