Fuels

The stability of hydrogen-fueled flames in afterburner systems is crucial for advancing clean energy technologies but is challenged by intense turbulence and flow variability. This study uniquely integrates advanced particle image velocimetry (PIV) techniques to investigate the flow dynamics around a V-gutter flame holder fueled with 100% hydrogen. Detailed velocity measurements were conducted to analyze the standard deviation of V_y, average V_y, average V, and uncertainty of V_y, as well as the mean swirling strength and mean vorticity profiles across multiple horizontal and vertical lines. The results reveal significant flow variability and turbulence intensity near the flame holder, with standard deviation peaks of up to 12 m/s, indicating zones of high turbulence and potential flame instability. The mean swirling strength, peaking at 850,000 [1/s²], and vorticity values up to 5000 [1/s] highlight intense rotational motion, enhancing fuel–air mixing and flame stabilization. The average V_y remained stable near the centerline, ensuring balanced flow conditions, while lateral deviations of up to −10 m/s reflect vortical structures induced by the flame holder geometry. Low uncertainty values, typically below 1 m/s, validate the precision of the PIV measurements, ensuring a reliable representation of the flow field. By providing a detailed analysis of turbulence structures and their impact on hydrogen combustion, this study offers novel insights into the interplay between flow dynamics and flame stability. These findings not only advance the understanding of hydrogen-fueled afterburner systems but also demonstrate the critical role of rotational flow structures in achieving stable and efficient combustion. By addressing key challenges in hydrogen combustion, this study provides a foundation for designing more robust and environmentally sustainable combustion systems, contributing to the transition toward clean energy technologies. Full article

The deployment of large installed power capacities from intermittent renewable energy sources requires balancing to ensure the steady and safe operation of the electrical grid. New methods of energy storage are essential to store excess electrical power when energy is not needed and later use it during high-demand periods, both in the short and long term. Power-to-Gas (P2G) is an energy storage solution that uses electric power produced from renewables to generate gas fuels, such as hydrogen, which can be stored for later use. Hydrogen produced in this manner can be utilized in energy storage systems and in transportation as fuel for cars, trams, trains, or buses. Currently, most hydrogen is produced from fossil fuels. Solid-oxide electrolysis (SOE) offers a method to produce clean hydrogen without harmful emissions, being the most efficient of all electrolysis methods. The objective of this work is to determine the optimal operational parameters of an SOE system, such as lower heating value (LHV)-based efficiency and total input power, based on calculations from a mathematical model. The results are provided for three different operating temperature levels and four different steam utilization ratios. The introductory chapter outlines the motivation and background of this work. The second chapter explains the basics of electrolysis and describes its different types. The third chapter focuses on solid-oxide electrolysis and electrolyzer systems. The fourth chapter details the methodology, including the mathematical formulations and software used for simulations. The fifth chapter presents the results of the calculations with conclusions. The final chapter summarizes this work. Full article

The aim of the present study was to clarify the influence of the thickness of the Pd/Cu membrane on the characteristics of biogas dry reforming (BDR) with aNi/Cr/Ru catalyst. We also clarified the impact of the reaction temperature, the molar ratio of CH₄:CO₂, the differential pressure between the reaction and sweep chambers, and the introduction of a sweep gas on the characteristics of a BDR reactor with a Pd/Cu membrane and a Ni/Cr/Ru catalyst. Through this study’s results, we clarify that the concentration of H₂ in the reaction chamber and the sweep chamber increases with the increase in the reaction temperature. In addition, this study clarifies that the highest concentration of H₂ in the reaction chamber and the sweep chamber can be obtained with a molar ratio of CH₄:CO₂ = 1.5:1. This study also clarifies that the highest concentration of H₂ can be obtained with a thickness of 40 μm, a molar ratio of CH₄:CO₂ = 1.5:1, and a differential pressure between the reaction chamber and the sweep chamber of 0 MPa without a sweep gas, which was 4890 ppmV in the reaction chamber and 38 ppmV in the sweep chamber. Under these conditions, CH₄ conversion, H₂ yield, and thermal efficiency were 75.0%, 0.214%, and 2.92%, respectively. Full article

This study examines the qualities and potential uses of various types of biomass as fuel, focusing on wood pellets, sunflower husk pellets and mixed pellets. The primary objective is to analyze the thermal and energy properties of these pellets in order to evaluate their efficiency and acceptance by consumers in the Bulgarian market. Thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) are employed, revealing that the processes of drying and volatile substance release are accompanied by energy absorption, with combustion being the main stage where most heat is generated. The results show that wood pellets have 7.31% moisture, 0.72% ash and a calorific value of 18.33 kJ/kg; sunflower husk pellets have 7.62% moisture, 2.42% ash and a calorific value of 19.63 kJ/kg; and mixed pellets have 7.07% moisture, 0.69% ash and a calorific value of 18.05 kJ/kg. These findings indicate that the pellets achieve efficient combustion with minimal mass loss. The conducted marketing research reveals that Bulgarian consumers prefer wood and mixed pellets for their efficiency, although sunflower husk pellets are more affordable. Key factors influencing consumer choice include price, which is important for 51% of the respondents, and quality, prioritized by 34%. The conclusion of this study is that pellets are a promising energy source with good environmental and economic characteristics, and the results can contribute to the development of more efficient fuels adapted to the needs of the market and consumers. Full article

The current investigation aims to offer fundamental, molecular- to microscopic-level descriptions of methane gas inside natural source clay minerals. Texas montmorillonite (STx-1), Georgia kaolinite (KGa-2), and Ca²⁺-saturated Texas montmorillonite (Ca-STx-1, Ca-bentonite) were utilized as subsurface model clay minerals for elucidating nano-confinement behaviors of ¹³C-labeled methane gas. High-pressure magic angle spinning (MAS) nuclear magnetic resonance (NMR) was used to describe the interactions between methane and the clays by varying temperature and pressure. Proton-decoupled ¹³C-NMR spectra were acquired at 28.2 bar at 307 K, 32.6 bar at 346 K, 56.4 bar at 307 K, 65.1 bar at 346 K, 112.7 bar at 307 K, and 130.3 bar at 346 K. In the pure state, no significant thermal effect on the behavior of methane was observed. However, there was a perceptible variation in the chemical shift position of confined methane in the mixtures with the clays up to 346 K. Conversely, the ¹³C-NMR chemical shift of methane altered by varying pressure in a pure state, and the mixtures with clays, attributed to the interaction of methane with the clay surfaces or the nanopore network of the clay–silica mixed phase. Pressure-induced shifts in methane peak positions were observed: 0.25 ppm (28.2–56.4 bar) and 0.47 ppm (56.4–112.3 bar) at 307 K. For methane in a montmorillonite mixture, shifts were 0.32 ppm for bulk-like methane and 0.20 ppm for confined methane under similar conditions. At 346 K, increasing pressure from 65.1 to 130.3 bar caused shifts exceeding 0.50 ppm, with bulk-like methane showing a 0.64 ppm shift and confined methane a 0.57 ppm shift. There was only one ¹³C-NMR methane peak in the mixture with either kaolinite (KGa-2) or Ca-bentonite with line broadening compared to that of pure methane. Still, two peaks were observed in the mixture with STx-1, explained by the imbibition and mobility of methane in the pore network. Full article

The development of alga-based biodegradable membranes represents a significant advancement in fuel cell technology, aligning with the need for sustainable material solutions. In a significant advancement for sustainable energy technologies, we have developed a novel biodegradable κ-carrageenan (KC) and boron nitride (BN) nanoparticle membrane, optimized with ammonium sulfate (NHS). This study employed a set of characterization techniques, including thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), where thermal anomalies were observed in the membranes around 160 °C and 300 °C as products of chemical decomposition. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) revealed the phases corresponding to the different precursors, whose value in the EDS measurements reached a maximum in the KC/BN/NHS5% membrane at 2.31 keV. In terms of the mechanical properties (MPs), a maximum tensile stress value of 10.96 MPa was achieved for the KC/BN sample. Using Fourier transform infrared spectroscopy (FTIR), the physicochemical properties of the membranes were evaluated. Our findings reveal that the KC/BN/NHS1% membrane achieves an exceptional ionic conductivity of 7.82 × 10⁻⁵ S/cm, as determined by impedance spectroscopy (IS). The properties of the developed membrane composite suggest possible broader applications in areas such as sensor technology, water purification, and ecologically responsive packaging. This underscores the role of nanotechnology in enhancing the functional versatility and sustainability of energy materials, propelling the development of green technology solutions. Full article

Microbial electrolysis cells (MECs) are receiving increasing scholarly recognition for their capacity to simultaneously remediate contaminated streams and generate renewable hydrogen. Within the realm of acid mine drainage (AMD) treatment, MECs demonstrate pronounced advantages by merging pollutant mitigation with hydrogen production, thereby attracting intensified research interest. Drawing on 1321 pertinent publications extracted from the Web of Science Core Collection (2004–2024), this bibliometric assessment systematically elucidates the current research landscape and prospective directions in MEC-based AMD remediation and H₂ synthesis. Key thematic areas encompass (1) a detailed appraisal of distinctive publication dynamics within this specialized domain; (2) insights into the principal contributing nations, institutions, journals, and academic fields; and (3) a synthesized overview of technological milestones, emerging investigative foci, and prospective developmental pathways. By critically reviewing extant knowledge, this evaluation offers meaningful guidance to researchers newly engaging with MEC-driven AMD treatment while illuminating the technological trajectories poised to shape the future of this evolving field. Full article

Currently, the key challenge of the oil-refining industry worldwide is to produce environmentally friendly fuel in large volumes to meet market demand, which is due to strict environmental standards governing the permissible sulfur content in fuel. Natural gas, refinery gas, and coal gas contain acid gases such as hydrogen sulfide and carbon dioxide. These compounds must be removed from the gas stream because of the toxicity of H₂S and to prevent the acid gas-induced corrosion of pipelines and facilities. Hydrogen sulfide is released as a result of various industrial processes, and its removal is critical because this compound can cause corrosion and environmental damage even at low concentrations. Sulfur compounds are also present in natural gas, biofuels and other fuel gases used in power plants. This article proposes new adsorbents of natural and waste origin and presents the results of their testing for the removal of acid gases. This paper also considers methods for the preparation of adsorbents from waste and procedures for the removal of sulfur-containing compounds. Using agricultural, industrial waste to produce activated sorbents not only solves the problem of waste disposal but also reduces the cost of desulfurization, contributing to the creation of sustainable and environmentally friendly technologies. The Review Section comprehensively summarizes current research on hydrogen sulfide removal in gas cleaning processes using agricultural and industrial waste as highly efficient adsorbents. In the Experimental Section, 10 composite materials based on natural raw materials and wastes, as well as 6 commercial adsorbents, were synthesized and tested under laboratory conditions. The choice of materials for the adsorbent production was based on the principles of environmental friendliness, availability, and cost-effectiveness. The developed materials based on modified sludge from water treatment plants of thermal power plants are effective sorbents for the purification of gas emissions from petrochemical enterprises. For industrial use, it is necessary to solve the problems of increasing the economic attractiveness of sorbents from waste, the ability of regeneration, the competitive adsorption of pollutants, the use of indicator sorbents, the optimization of operating conditions, and safe waste disposal. Full article

The reliance on fossil fuels for electricity production in insular regions creates critical environmental, economic, and logistical challenges, particularly for ecologically fragile islands. Transitioning to renewable energy is essential to mitigate these impacts, enhance energy security, and preserve unique ecosystems. This systematic review addresses key research questions: what practical strategies have proven effective in reducing fossil fuel dependency in island contexts, and what barriers hinder their widespread adoption? By applying the PRISMA methodology, this study examines a decade (2014–2024) of research on renewable energy systems, highlighting successful initiatives such as the integration of solar and wind systems in Hawaii, energy storage advancements in La Graciosa, hybrid renewable grids in the Galápagos Islands, and others. Specific barriers include high upfront costs, regulatory challenges, and technical limitations, such as grid instability due to renewable energy intermittency. This review contributes by synthesizing lessons from diverse case studies and identifying innovative approaches like hydrogen storage, predictive control systems, and community-driven renewable projects. The findings offer actionable insights for policymakers and researchers to accelerate the transition towards sustainable energy systems in island environments. Full article

This research evaluates the mineral ions and their concentrations in formation water from five well samples of the Bibi Hakimeh oil field (Iran). The analysis reveals the presence of calcium (Ca²⁺), sodium (Na⁺), and magnesium (Mg²⁺) cations, as well as sulfate (SO₄²⁻), bicarbonate (HCO₃⁻), and chloride (Cl⁻) anions, which are soluble in water within the Bibi Hakimeh oil formation. Furthermore, mineral deposits of CaSO₄, CaSO₄.2H₂O, CaCO₃, and MgCO₃ are investigated and predicted using StimCADE 2 software. The findings highlight the significant chemical precipitation of calcium sulfate and calcium carbonate mineral deposits under the operating conditions of the Bibi Hakimeh oil well. The geochemical composition of the formation waters is discussed to understand the equilibrium conditions and possible influence of the physical parameters. Additionally, this study examines the interaction between rock and water of the Bibi Hakimeh formation, revealing a notable correlation between the concentration of calcium and magnesium ions and the water–rock reaction in this field. Full article

This research investigates the feasibility of utilizing anaerobic digestion to produce biogas from organic waste generated at an equestrian center, emphasizing energy savings and environmental sustainability. The biogas system produces an estimated 85,495 kWh annually, surpassing the center’s electricity consumption of 18,644 kWh. This reduces greenhouse gas emissions by 2753 kg of CO₂. Photovoltaic systems, which meet 70.77% of the energy demand, further contribute to a reduction of 1178 kg of CO₂. Substituting fossil fuels with biofuels and planting 1700 trees achieved reductions of 26,263 kg of CO₂ and 51,033 kg of CO₂, respectively, resulting in a 49% overall carbon footprint reduction. This study evaluates the economic viability of biogas systems in the equestrian sector and optimal feedstock characteristics for efficient production. Additionally, complementary strategies, including photovoltaic solar panels and water management systems, are analyzed for their roles in promoting sustainable resource management. These integrated solutions support a transition to a circular economy while reducing environmental impacts and fostering energy independence in the equestrian industry. Full article

The global shift towards clean energy has been driven by the need to address global warming, which is exacerbated by economic expansion and rising energy demands. Traditional fossil fuels, particularly coal, emit more pollutants than other fuels. Recent studies have shown significant efforts in using biomass as a replacement or co-firing it with coal. This is because biomass, being a solid fuel, has a combustion mechanism similar to that of coal. This study investigates the co-firing behavior of pulverized coal and biomass in a semi-combustion furnace with a 500 kW heat input, comprising a pre-chamber and a main combustion chamber. Using computational fluid dynamics (CFD) simulations with ANSYS Fluent 2020 R1, the study employs species transport models to predict combustion reactions and discrete phase models (DPM) to track fuel particle movement. These models are validated against experimental data to ensure accurate predictions of mixed fuel combustion. The research examines various biomass-to-coal ratios (0%, 25%, 50%, 75%, and 100%) to understand their impact on combustion temperature and emissions. Results show that increasing the biomass ratio reduces combustion temperature due to biomass’s lower heating value, higher moisture content, and larger particle size, leading to less efficient combustion and higher CO emissions. However, this temperature reduction also correlates with lower NO_x emissions. Additionally, biomass’s lower nitrogen and sulfur content contributes to further reductions in NO_x and SO₂ emissions. Despite biomass having higher volatile matter content, which results in quicker combustion, coal demonstrates a higher carbon burnout rate, indicating more efficient carbon combustion. The study concludes that while pure coal combustion efficiency is higher at 87.7%, pure biomass achieves only 77.3% efficiency. Nonetheless, increasing biomass proportions positively impacts emissions, reducing harmful NO_x and SO₂ levels. Full article

Fossil fuels drive global warming, necessitating renewable alternatives such as biomethane (or renewable natural gas). Biomethane, primarily produced through anaerobic digestion (AD), offers a cleaner energy solution but is limited by the slow AD process. Biomass gasification followed by syngas methanation has emerged as a faster alternative. This review examines advancements in these processes over the last decade (2015–2024), focusing on techno-economic and life cycle assessment (LCA) studies. Techno-economic analyses reveal that biomethane production costs are influenced by several factors, including process complexity, feedstock type and the scale of production. Smaller gasification units tend to exhibit higher capital costs (CAPEX) per MW capacity, while feedstock choice and process efficiency play significant roles in determining overall production costs. LCA studies highlight higher impacts for gasification and methanation due to energy demands and associated emissions. However, integrating renewable hydrogen production through electrolysis, along with innovations such as sorption-enhanced gasification (SEG), can enhance overall system efficiency and reduce environmental impacts. This review critically evaluates the technical and economic challenges, along with the opportunities for optimizing biomethane production, and discusses the potential for these technologies to contribute to sustainable bioenergy solutions in the transition to a low-carbon economy. Full article

The growing demand for chicken meat products has increased the amount of wastewater associated with their production; their treatment has increased the generation of sludge and oils trapped in the trap process treatment. This work presents a process for the valorization of this residual oil recovered through the production of biodiesel. An oil degumming process was applied, and the quality of the treated oil was evaluated. This was transesterified with alkaline conditions and a homogeneous catalyst (KOH); a 3^k experimental design was applied with two factors: the temperature at 50, 60, and 70 °C and the molar ratios of 5, 6, and 7 moles of methanol per mole of recovered chicken oil. The biodiesel quality parameters were evaluated based on the ASTM standard. The process achieved a yield of 90.2%. The biodiesel obtained met all the quality parameters; however, only the process conditions with a molar ratio of 6:1 and a temperature of 60 °C achieved a kinematic viscosity of 5.64 ± 0.15 mm² s⁻¹, meeting the limits of 1.9–6.0 mm² s⁻¹ of the ASTM regulation. The fluidity of this biodiesel in mixtures of 25, 50, and 75% v with petroleum diesel was also evaluated, and a better adjustment of the Bingham mixing rule model and rheological analysis revealed that the mixtures did not lose their Newtonian behavior. This allows for the application of this biodiesel in internal combustion engines, achieving the valorization of residual oil. Full article

This study investigates the combustion of hydrogen in supercritical gas turbines, emphasizing the optimization of combustor design through computational fluid dynamics (CFD) simulations. Key parameters analysed include the number of oxygen inlets, operating pressure, excess working fluid in oxygen inlets, power output, and the use of different working fluids: supercritical argon (sAr) and supercritical xenon (sXe). The results highlight how these parameters influence temperature distribution, flame stability, and overall combustion efficiency. Findings suggest that increasing the number of oxygen inlets can significantly affect temperature profiles, while higher operating pressures lead to shorter flames. The dilution of oxygen by argon reduces the peak temperatures, and the choice of working fluid impacts cooling efficiency and flame dynamics. This study provides valuable information on optimizing the design of supercritical combustion chambers for hydrogen combustion in novel supercritical gas turbine systems. Full article

This work shows a proposal for reducing emissions, fuel costs, and respiratory disease hospitalizations using environmental cost accounting principles for the production of biodiesel production from waste frying oil (WFO). PM₁₀, PM_2.5, and O₃ data from 2017 to 2022 were collected and correlated with the number of hospitalizations for respiratory diseases and their costs. WFO samples were collected locally from households and restaurants in the greater ABC region, Brazil, and biodiesel was produced using the samples. The results showed that throughout the studied period, one or more of the polluting gases showed a strong correlation with hospitalizations due to respiratory diseases, corroborating what has already been verified by other studies carried out by the WHO. WFO biodiesel was within the standard limits, and the total annual production was estimated to be 30,435 m³; moreover, the associated annual carbon credits would equal 67 tCO₂, as well as a decrease of 30% in total pollutant emissions. Environmental cost accounting revealed that the annual number of respiratory disease hospitalizations could decrease by 3093 and the associated healthcare cost would decrease by USD 838 thousand per year; moreover, the sale of biodiesel and byproducts can generate an annual profit of USD 19 million. The biodiesel plant project had an NPV of USD 172.5 million, a payback of 1 month, and a return on investment of more than 170 times the initial financing. In addition, the reputation and the quality of life of the greater ABC region’s residents could improve. Full article

Methane gas hydrate-bearing sediments hold substantial natural gas reserves, and to understand their potential roles in the energy sector as the next generation of energy resources, considerable research is being conducted in industry and academia. Consequently, safe and economically feasible extraction methods are being vigorously researched, as are methods designed to estimate site-specific reserves. In addition, the presence of methane gas hydrates and their dissociation have been known to impact the geotechnical properties of submarine foundation soils and slopes. In this paper, we advance research on gas hydrate-bearing sediments by theoretically studying the effect of the hydromechanical coupling process related to ocean wave hydrodynamics. In this regard, we have studied two geotechnically and theoretically relevant situations related to the oscillatory wave-induced hydromechanical coupling process. Our results show that the presence of initial methane gas pressure leads to excessively high oscillatory pore pressure, which confirms the instability of submarine slopes with methane gas hydrate accumulation originally reported in the geotechnical literature. In addition, our results show that neglecting the presence of initial methane gas pressure in gas hydrate-bearing sediments in the theoretical description of the oscillatory excess pore pressure can lead to improper geotechnical planning. Moreover, the theoretical evolution of oscillatory excess pore water pressure with depth indicates a damping trend in magnitude, leading to a stable value with depth. Full article

The increasing need for sustainable waste management and abundant availability of banana tree waste, a byproduct of widespread banana cultivation, have driven interest in biomass conversion through clean fuels. This study investigates the oxidative pyrolysis of banana tree waste to optimize process parameters and enhance bio-oil production. Experiments were conducted using a fluidized bed reactor at temperatures ranging from 450 °C to 550 °C, with oxygen to biomass (O/B) ratios varying from 0.05 to 0.30. The process efficiently converts this low-cost, renewable biomass into valuable products and aims to reduce energy intake during pyrolysis while maximizing the yield of useful products. The optimal conditions were identified at an O/B ratio of 0.1 and a temperature of 500 °C, resulting in a product distribution of 26.4 wt% for bio-oil, 20.5 wt% for bio-char, and remaining pyro-gas. The bio-oil was rich in oxygenated compounds, while the bio-char demonstrated a high surface area and nutrient content, making it suitable for various applications. The pyro-gas primarily consisted of carbon monoxide and carbon dioxide, with moderate amounts of hydrogen and methane. This study supports the benefits of oxidative pyrolysis for waste utilization through a self-heat generation approach by partial feed combustion providing the internal heat required for the process initiation that can be aligned with the principles of a circular economy to achieve environmental responsibility. Full article

This study aims to explore anaerobic co-digestion (AcoD) of cassava (EUM) and poultry (FP) effluents using one inoculum/substrate ratio (30%) and three EUM vs. FP substrate composition ratios (25:75, 50:50, and 75:25). The AcoD process was therefore designed for 20 L batch digesters, under mesophilic conditions, with less than 5% total solids for 66 days. The results showed that EUMs were highly resistant to degradation, while FPs were the most easily degradable. Kinetic analysis indicated specific organic matter (MO) reduction rates of 0.28% per day for EUM and 0.76% per day for FP. EUM alone produced 45.47 mL/g MO, while the 50:50 substrate produced 1184.60 mL/g MOV. The main factors contributing to EUM inefficiency were the inability to tame acidic conditions and the accumulation of volatile fatty acids. AcoD produced 23 to 50 times more methane than EUM alone, 2 to 5 times more than FP alone, and 2 to 4 times more than inoculum. As a result, the AcoD of both types of waste had a qualitative and quantitative effect on biogas production. CH₄ content increased from around 2 to 75%, depending on the amount of organic nitrogen added. The addition of nitrogen by AcoD, even under mesophilic conditions, improves the kinetics and quality of anaerobic digestion of low-nitrogen substrates. Its impact on thermophilic and psychrophilic conditions needs to be verified. Full article