Fuels, Volume 7, Issue 3 (September 2026) – 23 articles

An integrated power-to-low-carbon hydrogen process is proposed in which a natural gas–fired Allam–Fetvedt (AF) supercritical carbon dioxide (CO₂) cycle supplies electricity and process water to low- and high-temperature electrolyzers based on proton exchange membrane (PEM), anion exchange membrane (AEM), and solid oxide electrolyzer (SOE) technologies. The novelty of this study is the development of a unified process-level framework that combines Aspen HYSYS simulation, techno-economic analysis, and multidimensional sustainability assessment to compare AF-integrated PEM, AEM, and SOE hydrogen production pathways under the same 437 MW-net power basis. Detailed steady-state simulations were carried out in Aspen HYSYS for an AF cycle producing approximately 795 MW of gross electrical power and 437 MW of net electrical power after internal and auxiliary power consumption. The resulting 437 MW net output was used as the fixed electrical input for the PEM, AEM, and SOE configurations to ensure a consistent comparison among the three electrolysis pathways. The resulting mass and energy balances were coupled with a methodological sustainability assessment framework that aggregates 44 indicators grouped into four dimensions: material, energy, environmental, and economic performance. Techno-economic analysis included capital expenditure (CAPEX), operating expenditure (OPEX), levelized cost of hydrogen (LCOH), and 25-year cash-flow metrics at a 10% discount rate with oxygen (O₂) by-product credit. All integrated schemes achieved high material and environmental efficiencies, with normalized scores exceeding 95% and approximately 97%, respectively. The AF–electrolyzer system was internally water self-sufficient, while the O₂ by-product supplied approximately 25–30% of the AF cycle oxygen demand. Energy efficiency was moderate but technology-dependent, with AF+SOE outperforming AF+PEM and AF+AEM due to higher electrolysis efficiency and stronger heat-integration potential. The main limitation was economic, as LCOH varied between approximately 4.3 and 7.3 $ kg⁻¹ hydrogen (H₂) across optimistic and pessimistic CAPEX/OPEX scenarios. Overall sustainability scores of 81.4%, 80.3%, and 83.0% for AF+PEM, AF+AEM, and AF+SOE, respectively, show that all three pathways are viable low-carbon hydrogen options, while AF+SOE provides the strongest combined energy, environmental, and techno-economic performance. Full article

The transition to renewable energy is essential for mitigating greenhouse gas emissions and advancing carbon neutrality. Lignocellulosic biomass offers an abundant and sustainable feedstock for biofuel production, but its inherent recalcitrance demands effective pretreatment to enable enzymatic saccharification. This study evaluated five commercial organic acids typical of anaerobic digestion (AD) effluents, namely acetic, propionic, butyric, valeric, and caproic acids, for corncob pretreatment. Compared with untreated corncob, which gave a glucose yield of only 23%, all acid pretreatments substantially enhanced enzymatic hydrolysis. A strong correlation between xylan removal and total sugar yield (R² = 0.98) confirmed that hemicellulose solubilization is the primary factor governing digestibility in typical AD-derived organic acid pretreatment. Among the conditions tested, pretreatment with 2.5% butyric acid at 180 °C for 45 min was optimal, removing 91.84% xylan and 53.10% lignin while retaining 75.24% glucan, which led to a near-complete glucose release during subsequent enzymatic hydrolysis at 2% solid loading with cellulase (15 FPU/g substrate). Fermentation of the butyric acid-pretreated hydrolysate via separate hydrolysis and fermentation produced 43.32 g/L ethanol with ~99% glucose consumption. In this case, the final ethanol yield from consumed sugars was 79.8% of the theoretical yield. These findings demonstrate that typical AD-derived pure organic acids serve as effective pretreatment agents, offering a promising route for lignocellulose valorization and biofuel production within a circular biorefinery framework. Full article

Raw and torrefied faeces from four zoo animals (giraffe, deer, camel, reindeer) and a sample of zebra manure pellets were studied to assess their energy potential using combustion calorimetry and thermoanalytical (TG/DTA) methods. Marked differences (ca 12%) in the torrefaction yield of the faeces were found depending on the animal species. Using the standard deviation of torrefaction yield, the heterogeneity of the droppings within one animal species was estimated to be up to 4%. Torrefied faeces demonstrated an increase in higher heating values by about 30% compared to raw samples. The differences between the higher heating values of samples torrefied at 300 °C and 250 °C were found to be relatively insignificant, both leading to completely comparable values of the energy densification ratio. According to elemental composition, higher heating value and combustion characteristics, torrefied faeces proved to be quite comparable to these parameters of lignite. Full article

Microalgae-based wastewater treatment represents a sustainable approach for simultaneous nutrient removal and biodiesel feedstock production. This study evaluated the growth, total organic carbon (TOC) removal, FAME productivity, fatty acid composition, and predicted biodiesel properties of Chlorella vulgaris and Scenedesmus obliquus cultivated in urban wastewater and synthetic medium under photoautotrophic and mixotrophic conditions, with and without nitrogen limitation using a two-stage cultivation strategy. S. obliquus showed greater adaptability to urban wastewater, with better growth and the highest TOC removal efficiency (92%) under mixotrophic cultivation with nitrogen limitation. Nitrogen limitation significantly enhanced FAME productivity in both species, with increases of 43.06–79.35% for C. vulgaris and 48.11–69.98% for S. obliquus relative to the corresponding photoautotrophic cultures. Fatty acid analysis revealed higher saturated fatty acid contents in C. vulgaris and higher polyunsaturated fatty acid levels in S. obliquus. Based on the fatty acid composition, C. vulgaris showed lower predicted iodine values and greater predicted oxidative stability than S. obliquus. The predicted cetane numbers were below the minimum values cited in international biodiesel specifications, while predicted kinematic viscosity was within the ranges reported by ASTM D6751 and EN 14214. However, the predicted cold filter plugging point (CFPP) values of 14.9–15.0 °C indicated limited suitability for low-temperature applications, and oxidative stability met the cited EN 14214 threshold only for some C. vulgaris treatments. These results indicate the potential of urban wastewater as a culture medium for sustainable microalgal FAME production and as a feedstock source for biodiesel applications, particularly when combined with fatty acid profile optimization or blending strategies. Full article

Lithium-ion batteries are widely used in electric mobility, renewable energy integration, portable electronics, and renewable–hydrogen hybrid energy systems. Despite significant advances in battery materials and design, long-term degradation remains a major challenge that affects system reliability, efficiency, and economic viability. In renewable–hydrogen hybrid architectures, battery degradation influences not only energy storage performance but also hydrogen production stability, electrolyzer operation, fuel cell utilization, and overall system efficiency. Major degradation mechanisms include solid electrolyte interphase (SEI) growth, electrolyte decomposition, lithium inventory loss, transition-metal dissolution, particle cracking, and structural phase transformations. This review provides a comprehensive assessment of degradation mechanisms affecting lithium-ion battery components and their implications for renewable–hydrogen hybrid systems. Advanced characterization techniques, including in situ and operando X-ray diffraction, electron microscopy, spectroscopy, electrochemical impedance spectroscopy, cyclic voltammetry, and differential capacity analysis, are examined for their ability to reveal chemical, structural, and morphological changes during battery operation. Particular emphasis is placed on the effects of dynamic load variations, partial state-of-charge cycling, temperature fluctuations, and intermittent renewable energy inputs that accelerate degradation in hybrid systems. The review further discusses mitigation strategies such as surface engineering, electrolyte optimization, material doping, thermal management, intelligent energy management systems, predictive maintenance, and machine learning-based prognostics. Key challenges associated with battery–hydrogen integration, including efficiency trade-offs, component ageing, hydrogen production stability, and lifecycle costs, are critically analysed. The adaptability of hybrid systems under varying operating conditions is also explored, highlighting the importance of degradation-aware control strategies, digital twins, and real-time diagnostics. Finally, future research directions are identified, including multiscale characterization, physics-informed machine learning, techno-economic optimization, and life-synergy modelling. These approaches are essential for developing reliable, adaptive, and cost-effective renewable–hydrogen hybrid energy systems capable of supporting long-term decarbonization objectives. Full article

Elemental mercury (Hg⁰) removal in coal combustion flue-gas over commercial V-based SCR catalysts is still limited by insufficient low-temperature activity and the complex interference of gas components. In this work, V₂O₅/TiO₂, V₂O₅⁻MoO₃/TiO₂, and V₂O₅⁻MoS₂/TiO₂ catalysts were comparatively investigated for Hg⁰ removal under simulated coal combustion flue-gas conditions. Among them, V₂O₅⁻MoS₂/TiO₂ exhibited the best performance over the whole temperature window of 200–400 °C, reaching a Hg⁰ removal efficiency of 73.3% at 200 °C, which was markedly higher than those of V₂O₅/TiO₂ and V₂O₅⁻MoO₃/TiO₂. Under multicomponent SCR atmospheres in coal-fired plants, the catalyst also showed the highest Hg⁰ oxidation efficiency of 72.9%, indicating that MoS₂ modification was more effective than oxide promotion in enhancing low-temperature mercury removal. XRD and FT-IR results showed that MoS₂ and vanadia were successfully incorporated onto TiO₂ as dispersed surface phases, while the MoS₂-modified catalyst exhibited a distinct and persistent terminal V=O feature, implying the formation of a coupled Mo-S-V interfacial environment. H₂-TPR and NH₃-TPD demonstrated that MoS₂ modification simultaneously stabilized the redox structure and moderated the surface acidity, suppressing excessively strong NH₃ retention while maintaining a tunable oxidation-active surface. XPS analysis further revealed atmosphere-dependent redistribution of O_α/O_β species, sulfur oxidation to SO₃²⁻/SO₄²⁻ species, and dynamic V⁵⁺/V⁴⁺ interconversion, confirming that MoS₂ acted not only as a sulfur-containing component but also as an interfacial electronic regulator. Post-reaction Hg 4f XPS showed that retained mercury mainly existed as Hg²⁺ species, while Hg-TPD indicated that MoS₂ modification provided a more diverse and thermally stable mercury-binding environment. These results demonstrate that Hg⁰ removal over V₂O₅⁻MoS₂/TiO₂ proceeds through oxidation-retention coupling rather than simple oxidation alone. The enhanced performance originates from the synergistic effects of active oxygen migration, vanadium redox cycling, sulfur-assisted stabilization, and interfacial Mo-S-V electronic coupling. This work provides a promising strategy for designing multifunctional SCR catalysts in coal-fired plants for efficient Hg⁰ control under practical coal combustion flue-gas conditions. Full article

The present study experimentally investigates the influence of n-octanol addition to Jet-A fuel on the combustion performance and emission behavior of a micro-turboprop-based hybrid UAV (“Unmanned Aerial Vehicle”) power system. The experiments were conducted on a dedicated hybrid propulsion test bench equipped with a KingTech micro-turboprop engine mechanically coupled to a T-Motor electric generator and supplying a regulated 48 V DC bus. The system is capable of delivering approximately 3 kW of continuous electrical power, with peak values reaching 3.5 kW. Jet-A and three n-octanol/Jet-A blends containing 10%, 20%, and 30% n-octanol by volume, denoted O10, O20, and O30, respectively, were tested under four operating regimes ranging from idle to 2500 W electrical load. Exhaust gas temperature, carbon monoxide, sulfur dioxide, nitrogen oxides, electrical output, and near-field pollutant dispersion were evaluated. The results show that n-octanol addition affects engine behavior in a strongly load-dependent manner. At idle, the O10 blend reduced CO concentration from approximately 2520 ppm for Jet-A to approximately 2270 ppm, corresponding to a reduction of about 9.9%. At the same operating condition, O10 reduced exhaust gas temperature from approximately 498.3 °C to 463.2 °C, while O20 and O30 produced stronger cooling effects. At intermediate regimes, the oxygenated molecular structure of n-octanol contributed to lower CO formation in selected cases, indicating improved combustion-completeness behavior. At high load, however, exhaust gas temperatures converged toward or exceeded those of Jet-A, particularly for O30, showing that higher octanol fractions may introduce additional thermal constraints. Among the tested fuels, O10, corresponding to 10% n-octanol by volume, provided the most balanced behavior across the investigated operating range, from idle to 2500 W electrical load. The dispersion measurements performed at 30 m from the source further showed that ambient pollutant concentrations are strongly influenced by wind speed, wind direction, and plume transport. These findings support moderate n-octanol blending as a promising transitional strategy for small-scale hybrid UAV propulsion systems, while highlighting the need for future repeated testing, direct fuel-flow measurement, and numerical dispersion modeling. Full article

Supercritical CO₂ injection can mitigate depletion-induced deterioration of shale oil, but the relationship between laboratory-scale fluid-property changes and field-scale recovery remains insufficiently understood. This study integrates time-lapse produced-oil characterization, high-pressure PVT experiments, whole-hydrocarbon gas chromatography, and compositional reservoir simulation for the Mabei shale oil reservoir. From October 2023 to October 2025, the viscosity of dehydrated and degassed produced oil at 80 °C increased from 20.93 to 56.8 mPa·s, accompanied by depletion of light hydrocarbons and enrichment of heavy components, indicating progressive compositional deterioration during depletion. At 106.75 °C and 65.07 MPa, increasing the added CO₂/oil molar ratio from 0 to 80% reduced live-oil viscosity from 9.7841 to 3.8470 mPa·s and density from 0.8326 to 0.7897 g/cm³. Most viscosity, density, and oil-phase compositional changes occurred within the first 6 h in the closed, continuously stirred PVT cell. CO₂ contact preferentially transferred C3–C7 hydrocarbons out of the analyzed oil-rich phase, resulting in relative enrichment of C15–C37 components in the residual oil. The history-matched compositional model showed that CO₂ improved reservoir pressure maintenance and expanded low-viscosity regions primarily along fracture-connected flow paths, although the incremental response became limited between the 20 and 25% cases. Regional compositional analysis further demonstrated that strongly CO₂-contacted residual oil became heavier, whereas the produced oil was enriched in mobilized light and intermediate hydrocarbons. These results establish a consistent laboratory-to-field interpretation of CO₂-induced compositional redistribution and provide a basis for optimizing CO₂-assisted development in deeply buried shale oil reservoirs. CO₂-induced asphaltene precipitation/deposition and the associated permeability impairment were not measured or represented in the numerical model. Therefore, the reported recovery response reflects CO₂–oil property and transport effects in the absence of solid-phase formation damage. Full article

This study presents a comparative thermochemical and combustion analysis of biomass pellets derived from softwood, hardwood, sunflower husks, wheat straw, and lavender residues. This investigation was performed using thermogravimetric analysis (TG), derivative thermogravimetric analysis (DTG), and differential scanning calorimetry (DSC) to evaluate the thermal degradation behavior, combustion reactivity, heat-release characteristics, and ash-forming tendencies of the investigated biomass types. The results revealed substantial differences between woody biomass and agricultural residues in terms of thermal stability, thermal degradation behavior, and energy output. Softwood pellets exhibited the highest thermal reactivity, the most intense devolatilization process, and the highest heat release during combustion, indicating higher thermal reactivity and favorable fuel properties. Hardwood pellets demonstrated improved thermal stability due to increased lignin content, resulting in broader thermal decomposition regions and more gradual heat release. In contrast, sunflower husk and wheat straw pellets showed lower thermal reactivity and significantly higher residual mass, indicating elevated ash content and reduced thermal decomposition behavior. Lavender pellets exhibited intermediate thermochemical behavior associated with the presence of volatile extractives and moderate thermal stability. The integrated TG-DTG-DSC approach enabled a direct comparison of woody biomass and agricultural residues under identical experimental conditions and expanded the available thermochemical data for lavender-derived pellets. The results provide a comparative framework for assessing biomass resources intended for energy applications. Full article

Addressing the safety limitations and operational challenges associated with online particulate matter sampling in high-pressure natural gas pipelines, this paper proposes and systematically investigates a non-intrusive, safe sampling alternative utilizing existing pressure gauge tapping ports. Through experimental and Computational Fluid Dynamics (CFD) numerical analyses, the influence of velocity ratio R (ratio of sampling velocity to pipeline gas velocity), pipeline flow velocity V₀, and port orientation on sampling efficiency η (ratio of sampled concentration to true concentration) was examined. Results show that sampling via a pressure gauge port exhibits a trend contrary to traditional isokinetic sampling: efficiency increases significantly with R. At R = 2, particles below 10 μm are effectively collected, with notably improved capture for larger particles. Flow field analysis reveals that efficiency enhancement originates from a recirculation zone upstream, expansion of the high-pressure zone downstream, and a “wall impaction–bounce–recapture” mechanism under high R conditions. An empirical efficiency formula was established based on experimental data, with prediction errors below 15%. In field tests at a gas transmission station, applying this correction increased the evaluated filtration efficiency from 9.4% to 50.2%, effectively restoring true operating conditions. This study provides a reliable theoretical basis and practical technical solution for safe, convenient, and accurate particulate monitoring in natural gas pipelines. Full article

Coal-fired power plants equipped with selective catalytic reduction (SCR) and wet flue-gas desulfurization (WFGD) can co-control mercury, but performance is limited by incomplete upstream Hg⁰ oxidation and downstream re-emission. This study evaluated a 660 MW unit using gas-, liquid-, and solid-phase measurements and coordinated single-factor and coupled operating tests. Under baseline conditions, SCR Hg⁰ oxidation was 31.66%, WFGD Hg²⁺ capture was 73.79%, and net mercury removal was 31.08%, with a stack Hg^T concentration of 4.70 µg/Nm³. Coupled optimization increased SCR Hg⁰ oxidation to 69.76% and WFGD Hg²⁺ capture to 96.05%, reduced the re-emission index from 0.596 to 0.250, and raised net removal to 70.83%. SCR inlet temperature, equivalent space velocity, and catalyst health were the dominant upstream factors, while S(IV), oxidation–reduction potential (ORP), slurry pH, and oxidation air supply governed downstream stabilization. A practical operating window was identified near 340 °C, with a normalized stoichiometric ratio (NSR) of approximately 1.0, high ammonia injection uniformity, pH of 5.5–6.0, ORP of approximately 200 mV, and S(IV) of approximately 2 mmol/L. The results show that coordinated operation of existing SCR–WFGD equipment can substantially reduce stack mercury without dedicated mercury-control hardware, provided that NH₃ slip, SO₃-related risk, catalyst condition, and absorber stability are simultaneously constrained. Full article

Child-well stimulation design has become a central challenge in mature unconventional reservoirs, where infill wells are commonly completed in reservoirs that have already been modified by parent-well production. Prior depletion changes pore pressure, stress distribution, and fracture-propagation pathways, causing child-well treatments to behave differently from parent-well completions. As a result, increasing fluid volume, proppant loading, stage density, or pump rate does not necessarily produce proportional gains in recovery. This review synthesizes the comprehensive literature on child-well stimulation intensity with emphasis on well performance, fracture-driven interactions, pad-scale economics, diagnostics, and resource-use considerations. The analysis shows that the production response is highly conditional: larger treatments can enhance reservoir contact when fractures access underdrained rock; however they may lose effectiveness when depletion-induced stress changes redirect fracture growth toward parent-well drainage areas or pre-existing fracture networks. In such cases, higher nominal intensity can increase interwell communication, reduce completion efficiency, impair parent-well performance, and weaken pad-level economic value. A key outcome of this review is the distinction between nominal stimulation intensity, represented by the treatment pumped, and effective stimulation intensity, represented by the fraction of that treatment that creates incremental productive fracture area. This distinction reframes child-well optimization from a treatment-size problem to a depletion-aware fracture-placement problem. Diagnostics, coupled modeling, production analysis, and mitigation strategies are therefore necessary to determine whether added stimulation intensity improves recovery or primarily redistributes production within the pad. From an economic perspective, the pad rather than the individual child well is the correct unit for evaluating stimulation-intensity decisions, since pad-level net present value integrates incremental child-well recovery, parent-well degradation, protection costs, spacing effects, and completion capital. Produced-water reuse and lifecycle emission benchmarking represent practical tools for reducing the environmental footprint of child-well development programs while simultaneously lowering freshwater demand and disposal volumes. These economic and environmental dimensions are inseparable from the technical optimization of stimulation intensity and are addressed explicitly in this review. This review concludes that child-well stimulation intensity should be optimized within a pad-scale framework that integrates depletion state, spacing, landing-zone selection, parent-well management, and long-term value rather than being uniformly maximized. Full article

This study employs numerical simulations to systematically investigate the combustion characteristics of methane/ethanol blended fuel–air mixtures under non-premixed turbulent conditions. The effects of the methane blending ratio on the flow-field structure, flame morphology, NO emissions, and combustion efficiency are analyzed. The results show that, with increasing methane blending ratio, the recirculation mechanism gradually shifts from near-field local entrainment to far-field transport, accompanied by a reduction in local shear intensity. Methane addition enhances flame intensity, accelerates combustion, shortens flame length, mitigates heat transfer limitations, and reduces combustion delay. At the initial 10% and the final 20% of the methane blending range, the combustion process exhibits pronounced instability. Methane addition significantly suppresses NO formation, with temperature being the dominant controlling factor, while fuel composition also plays an important role. The overall combustion efficiency is improved. However, a slight decrease is observed at low blending ratios (0–0.1), and the enhancement becomes marginal when the methane blending ratio exceeds 0.6. Full article

Improving gasoline octane quality is essential for modern spark-ignition engines, as increased knock resistance supports better efficiency, optimized combustion, and reduced fuel consumption. Environmental concerns have increased the demand for cleaner organic alternatives instead of conventional metallic octane boosters. This study evaluated selected organic octane improvers for commercial gasoline fuels, focusing on isopropanol (IPA), N-ethylaniline (NEA), and their binary blends. Fuel samples were prepared by controlled dosing of additives into base gasoline, followed by homogenization and determination of octane number using a portable fuel analyzer. Both additives increased gasoline octane rating, but their effectiveness depended on chemical type and dosage. NEA showed stronger octane-enhancing performance, whereas IPA provided a moderate improvement and potential combustion benefits associated with oxygenated fuel components. The investigated IPA–NEA binary blends increased the research octane number by up to 3.5 units at 3 vol.% additive concentration. Engine bench testing demonstrated reductions in CO emissions of up to 60%, in HC emissions of up to 40.8%, and in fuel consumption of up to 4.7% under selected operating conditions. Distillation characteristics remained within acceptable gasoline quality limits, indicating that the investigated additives did not adversely affect fuel volatility. Full article

The increasing interest in carbon-free fuels has positioned ammonia as a promising energy carrier for Internal Combustion Engines (ICEs), particularly in hard-to-abate sectors such as Heavy-Duty (HD) transport and maritime applications. However, its low reactivity, narrow flammability limits, and intrinsic nitrogen content pose significant challenges for stable combustion and emissions control. This work presents a predictive Quasi-Dimensional (QD) combustion model applied to simulate ammonia-fueled engines operating under both Spark Ignition (SI) and Reactivity Controlled Compression Ignition (RCCI) modes. The proposed framework couples a turbulent premixed combustion sub-model with a diffusive combustion sub-model, including a dedicated fuel-NO_x mechanism to capture nitrogen oxide formation pathways associated with fuel-bound nitrogen. The model accounts for key physical and chemical processes governing combustion, such as ignition delay, mixture stratification, and heat release dynamics, while maintaining computational efficiency suitable for parametric studies. The model is validated against experimental data from a Single-Cylinder Engine (SCE) over a wide range of operating conditions, including variations in equivalence ratio, spark timing, Ammonia Energy Fraction (AEF), and injection strategy. Results demonstrate good agreement in terms of in-cylinder pressure evolution, Apparent Heat Release Rate (AHRR), and NO_x emissions, with peak-pressure errors below 4 bar and peak-pressure locations predicted within 2 crank angle degrees. Notably, the dedicated fuel-NO_x sub-model substantially improves emission predictions, revealing that fuel-bound nitrogen is the dominant source of NO_x in ammonia combustion. Overall, the proposed QD model represents a robust and efficient tool for the analysis and optimization of ammonia-fueled engines, supporting the development of low-carbon combustion strategies for future energy systems. Full article

Effective management of dairy manure is crucial for reducing environmental and public health risks. This waste material can serve as a viable source of bioenergy via anaerobic digestion. The recalcitrance of lignocellulosic fiber in manure presents challenges for its efficient conversion to methane. Hydrothermal pretreatment of manure fiber improves process performance by deconstructing the lignocellulosic structure. Low-temperature hydrothermal treatment (90–180 °C) of lignocellulosic biomass optimally enhances the AD process performance by limiting the formation of inhibitory compounds such as furfurals. The integration of an optimal hydrothermal pretreatment within an anaerobic digestion system can improve the homogeneity, miscibility, and digestibility of dairy manure, thereby enhancing biogas yield. This review examines the hydrothermal treatment of lignocellulosic biomass, with a focus on dairy manure, the water chemistry involved in pretreatment, relevant process parameters, and the challenges faced in anaerobic digestion. Full article

In this work, the use of biodiesel derived from Acacia sieberiana (commonly referred to as “Bagaruwa”) seed oil is presented as a potential renewable fuel for compression ignition engines. The biodiesel was produced using transesterification and characterized using Fourier transform infrared spectroscopy (FTIR) and gas chromatography–mass spectrometry (GC–MS). The FTIR analysis confirmed the presence of functional groups, including C=O stretching at 1740 cm⁻¹, and C–O ester bands at 1244 and 1170 cm⁻¹. The GC–MS analysis showed that linoleic acid methyl ester was the dominant compound (54.77%), followed by 11-octadecenoic acid methyl ester (22.91%) and palmitic acid methyl ester (11.71%). The physicochemical properties of biodiesel–diesel blends were evaluated according to the ASTM standards. Increasing the biodiesel content reduced the density, viscosity, cetane number, and calorific value, while the flash point was found to increase. B10 and B15 blends showed the highest density values within ASTM limits. The results indicated that Acacia sieberiana seed oil is a promising non-edible feedstock for sustainable biodiesel production and applications. Full article

The lower flammability limit (LFL) is critical for assessing ignition and explosion risks associated with lithium-ion battery thermal runaway gases. In this study, a primary experimental LFL database containing 58 data points for H₂–CO–CH₄–C₂H₄–CO₂–N₂–O₂ mixtures was compiled from the first author’s publicly available doctoral dissertation. Le Chatelier’s rule was first evaluated as a baseline model, and its prediction residuals were then corrected using a five-coefficient data-driven model based on physically interpretable variables, including total diluent fraction, CO₂ fraction in diluent gases, oxygen fraction, and the interaction between highly reactive fuels and dilution. Results showed that Le Chatelier’s rule provided a useful first-order estimate but systematically underestimated LFL under high-dilution and CO₂-rich conditions. The proposed correction model reduced the mean absolute error from 2.40% to approximately 1.00% while retaining an explicit mathematical form. This experimental-data-driven framework provides a preliminary and interpretable tool for rapid LFL estimation of multicomponent gases relevant to battery thermal runaway risk assessment. Full article

Filter cake is a nutrient-rich solid byproduct generated during sugarcane juice clarification, representing both a challenge and an opportunity for the sugar–energy industry. This study presents a systematic bibliometric analysis of global research on filter cake valorization, with a particular focus on its potential for bioenergy and biofuel production. Data were retrieved from the Scopus database and analyzed using VOSviewer, resulting in a dataset of 530 publications up to 2024, of which 485 address recycling and reintegration pathways. The results identify Brazil and India as leading contributors, with research traditionally concentrated on agricultural applications. However, emerging trends highlight the growing interest in thermochemical and biochemical conversion routes, including its use as a substrate for biogas, bioethanol, and other biofuels. The findings demonstrate that filter cake is a promising feedstock for integrated biorefinery systems, contributing to renewable energy generation and resource recovery. Despite this potential, the transition toward advanced biofuel production and high-value energy applications remains limited. This review provides a comprehensive overview of research trends, identifies key gaps, and outlines strategic directions to support the shift from conventional waste management to energy-oriented valorization within a circular bioeconomy framework. Full article

Traditional hypergolic propellants, such as hydrazine derivatives combined with nitrogen tetroxide, present severe toxicity, operational, and environmental hazards. High-test peroxide has emerged as a leading green oxidiser replacement due to its low volatility, high density, and benign decomposition products. This review comprehensively analyses recent advancements in HTP-based hypergolic fuel formulations, categorising them into three major emerging families: catalytically-promoted, reactive, and ionic liquid-based systems. By evaluating key parameters such as ignition delay times, specific impulse and toxicity, this work identifies a clear technological shift from fundamental chemical screening to increasingly more mature solutions. While historical targets defined hypergolicity below 100 ms, recent advanced formulations routinely achieve it under 10 ms requiring minimal additive concentrations (<5 wt%), directly competing with legacy systems. Furthermore, this review highlights critical open challenges that limit commercial adoption, including the long-term storage stability of catalytic blends, high toxicity of reactive systems, and the lifecycle toxicity and high cost of frequently employed ionic liquids. Ultimately, it is concluded that rather than a single universal replacement, the future of green hypergolic propulsion lies in a plurality of solution, where each family is tailored to specific niches defined by mission requirements and cost structures. Full article

Underground coal gasification (UCG) requires rigorous geological suitability evaluation to reduce project risks, and scientific site selection is critical for success. Taking the No. 15 coal seam in the Yushe–Wuxiang Block (Qinshui Basin) as the focus, this study evaluates the feasibility of deep UCG using a multi-criteria decision-making framework. A hierarchical evaluation model comprising four primary and 10 secondary geological indicators (e.g., coal thickness, parting coefficient, fault fractal dimension, roof lithology) was constructed. Subjective weights were derived from the Analytic Hierarchy Process (AHP) and combined with objective weights from the coefficient of variation method. The TOPSIS (Technique for Order Preference by Similarity to an Ideal Solution) method was then applied to rank seven development units. Results indicate that the No. 15 coal seam has reasonable potential for UCG implementation. The most favorable areas (Blocks II and VII) are characterized by thick coal seams (>5 m), low parting coefficients (<8%), simple fault networks (fractal dimension ≤0.5–1.05), and competent mudstone roofs. Blocks III, V, and VI are moderately favorable, while Blocks I and IV are marginally favorable. These findings provide a prioritized roadmap for pilot-scale UCG testing in the Yushe–Wuxiang Block. Full article

The Lantana genus, especially L. camara, has emerged as a potential yet underutilized lignocellulosic feedstock for various catalytic thermochemical conversion products and advanced carbon materials. This study reviews recent developments in the valorization of Lantana biomass to generate biofuels, bio-oil, syngas, and engineered biochar materials through pyrolysis, gasification, hydrothermal processing, and integrated biorefinery processes, in a critical manner. Particular focus will be on nanocomposite-modified, metal-doped biochar with catalytic elements such as ZSM-5, Fe₃O₄, TiO₂, and Ni-, Co-, and Zn-based oxides to enhance deoxygenation, catalytic cracking, tar reforming, pollutant remediation, and energy storage. Recent developments in catalyst synthesis techniques, such as impregnation, hydrothermal deposition, and in situ functionalization, are reviewed, along with characterization methods including BET, XRD, SEM/TEM, Raman spectroscopy, and XPS. The review further examines the impact of pore structure, surface chemistry, the presence of redox-active centers, and catalyst stability on product selectivity, syngas quality, and upgrading bio-oil performance. The effects of biochar on microbial immobilization, anaerobic digestion, and integrated biochemical conversion are discussed in detail, excluding thermochemical effects. The challenges of catalyst deactivation, biomass heterogeneities, scalability, techno-economic viability, and decentralized biomass logistics are also discussed. In summary, the development and implementation of catalytic reaction engineering, the design of nanocomposite biochar, and circular bioeconomy strategies have great potential to facilitate the conversion of invasive Lantana biomass into renewable fuels, multifunctional carbon materials, and environmentally friendly bioeconomy products. Full article

The standardized copper strip corrosion test is commonly used to assess the corrosive effects of automotive gasoline and diesel fuels on metallic materials. This test relies on visual evaluation of copper strip discoloration, which may introduce subjectivity and limit quantitative interpretation. The aim of this study was to compare the conventional visual evaluation with a colorimetric approach as a quantitative alternative. Copper strip corrosion tests were performed according to EN ISO 2160 using gasoline and diesel fuel samples. While all samples were visually classified within corrosion Class 1, colorimetric analysis revealed measurable differences in surface discoloration, with ΔE*_ab values ranging from 0.4 to 11.1, and highest values observed for aged fuels. These results demonstrate that colorimetric evaluation provides additional quantitative information beyond conventional visual classification and enables differentiation between fuels within the same acceptance category. Full article