Search Results (462)

Hydrotreated ester and fatty acids to jet (HEFA-tJ) is presently the most developed and economically attractive pathway to produce sustainable aviation fuel (SAF). An ongoing systematic study of the critical variables of different pathways to SAF has revealed significantly lower greenhouse gas (GHG) reduction potential for the HEFA-tJ pathway compared to competing markets using the same resources for road diesel production. Moderate yield variations between air and road pathways lead to several hundred thousand tons less GHG reduction per project, which is generally not evaluated thoroughly in standard environmental assessments. This work demonstrates that, although the HEFA-tJ market seems to have more attractive features than biodiesel/renewable diesel, considerable viability risks might manifest as HEFA-tJ fuel market integration rises. The need for more transparent data and effort in this regard, before envisaging making decisions regarding the volume of HEFA-tJ production, is emphasized. Overall, reducing the carbon intensity of road diesel appears to be less capital-intensive, less risky, and several times more efficient in reducing GHG emissions. Full article

A computational fluid dynamics (CFD) numerical simulation methodology was implemented to model transient heating processes in steel industry reheating furnaces, targeting combustion efficiency optimization and carbon emission reduction. The effects of oxygen concentration (O₂%) and different fuel types on the flow and heat transfer characteristics were investigated under both oxygen-enriched combustion and MILD oxy-fuel combustion. The results indicate that MILD oxy-fuel combustion promotes flue gas entrainment via high-velocity oxygen jets, leading to a substantial improvement in the uniformity of the furnace temperature field. The effect is most obvious at O₂% = 31%. MILD oxy-fuel combustion significantly reduces NOx emissions, achieving levels that are one to two orders of magnitude lower than those under oxygen-enriched combustion. Under MILD conditions, the oxygen mass fraction in flue gas remains below 0.001 when O₂% ≤ 81%, indicating effective dilution. In contrast, oxygen-enriched combustion leads to a sharp rise in flame temperature with an increasing oxygen concentration, resulting in a significant increase in NOx emissions. Elevating the oxygen concentration enhances both thermal efficiency and the energy-saving rate for both combustion modes; however, the rate of improvement diminishes when O₂% exceeds 51%. Based on these findings, MILD oxy-fuel combustion using mixed gas or natural gas is recommended for reheating furnaces operating at O₂% = 51–71%, while coke oven gas is not. Full article

Combustion of aviation jet fuel emits a complex mixture of pollutants linked to adverse health outcomes among airport personnel and nearby communities. While epidemiological studies showed the detrimental effects of aviation-derived air pollutants on human health, the molecular mechanisms of the interactions of these pollutants with cellular biomolecules like proteins that drive the adverse health effects remain poorly understood. In this study, we performed molecular docking simulations of 272 pollutant–protein complexes using AutoDock Vina 1.2.7 to characterize the binding strength of the pollutants with the selected proteins. We selected 34 aviation-derived pollutants that constitute three chemical categories of pollutants: volatile organic compounds (VOCs), polyaromatic hydrocarbons (PAHs), and organophosphate esters (OPEs). Each pollutant was docked to eight proteins that play critical roles in endocrine, metabolic, transport, and neurophysiological functions, where functional disruption is implicated in disease. The effect of binding of multiple pollutants was analyzed. Our results indicate that aliphatic and monoaromatic VOCs display low (<6 kcal/mol) binding affinities while PAHs and organophosphate esters exhibit strong (>7 kcal/mol) binding affinities. Furthermore, the binding strength of PAHs exhibits a positive correlation with the increasing number of aromatic rings in the pollutants, ranging from nearly 7 kcal/mol for two aromatic rings to more than 15 kcal/mol for five aromatic rings. Analysis of intermolecular interactions showed that these interactions are predominantly stabilized by hydrophobic, pi-stacking, and hydrogen bonding interactions. Simultaneous docking of multiple pollutants revealed the increased binding strength of the resulting complexes, highlighting the detrimental effect of exposure to pollutant mixtures found in ambient air near airports. We provide a priority list of pollutants that regulatory authorities can use to further develop targeted mitigation strategies to protect the vulnerable personnel and communities near airports. Full article

Driven by stringent emission regulations, advanced combustion modes utilizing turbulent jet ignition technology are pivotal for enhancing the performance of marine low-speed natural gas dual-fuel engines. This review focuses on three novel combustion modes, yielding key conclusions: (1) Compared to the conventional DJCDC mode, the TJCDC mode exhibits a significantly higher swirl ratio and turbulence kinetic energy in the main chamber during initial combustion. This promotes natural gas jet development and combustion acceleration, leading to shorter ignition delay, reduced combustion duration, and a combustion center (CA50) positioned closer to the Top Dead Center (TDC), alongside higher peak cylinder pressure and a faster early heat release rate. Energetically, while TJCDC incurs higher heat transfer losses, it benefits from lower exhaust energy and irreversible exergy loss, indicating greater potential for useful work extraction, albeit with slightly higher indicated specific NOx emissions. (2) In the high-compression ratio TJCPC mode, the Liquid Pressurized Natural Gas (LPNG) injection parameters critically impact performance. Delaying the start of injection (SOI) or extending the injection duration degrades premixing uniformity and increases unburned methane (CH₄) slip, with the duration effects showing a load dependency. Optimizing both the injection timing and duration is, therefore, essential for emission control. (3) Increasing the excess air ratio delays the combustion phasing in TJCPC (longer ignition delay, extended combustion duration, and retarded CA50). However, this shift positions the heat release more optimally relative to the TDC, resulting in significantly improved indicated thermal efficiency. This work provides a theoretical foundation for optimizing high-efficiency, low-emission combustion strategies in marine dual-fuel engines. Full article

Sustainable aviation fuels (SAFs) are vitally important for aviation decarbonization. The laminar burning velocity (LBV), a key parameter reflecting the combustion behavior of fuel/oxidizer mixtures, serves as a fundamental metric for evaluating SAF performance. This paper systematically reviews and evaluates the LBV experiment method and the performance of traditional aviation fuel, SAFs produced via different pathways, and individual components (n-alkanes, iso-alkanes, cycloalkanes, and aromatic hydrocarbons, as well as the impacts of isomers and homologues) in aviation fuels. It is found that LBV values of different SAFs exhibit significant fluctuations, approaching or slightly deviating from those of conventional aviation fuels. Carbon number, branching degree, substituent types, and testing methods in the components all affect LBV performance. Specifically, increased branching in iso-alkanes reduces LBV, cyclohexane and benzene show higher LBV than their methylated counterparts (methylcyclohexane and toluene), and n-alkylcyclohexanes/benzenes with short (C1–C3) side chains demonstrate minimal LBV variation. Spherical flame methods yield more consistent (and generally lower) LBV values than stagnation flame techniques. These findings provide insights for optimizing SAF–conventional fuel blends and enhancing drop-in compatibility while ensuring operational safety and usability. Full article

The generation of fine coal particles during mining and processing presents significant environmental and logistical challenges, particularly in coal-dependent, developing countries like South Africa (SA). This review critically evaluates the technical viability of fine coal briquetting as a sustainable waste-to-energy solution within a SA context, while drawing from global best practices and comparative benchmarks. It examines abundant feedstocks that can be used for valorization strategies, including fine coal and agricultural biomass residues. Furthermore, binder types, manufacturing parameters, and quality optimization strategies that influence briquette performance are assessed. The co-densification of fine coal with biomass offers a means to enhance combustion efficiency, reduce dust emissions, and convert low-value waste into a high-calorific, manageable fuel. Attention is also given to briquette testing standards (i.e., South African Bureau of Standards, ASTM International, and International Organization of Standardization) and end-use applications across domestic, industrial, and off-grid settings. Moreover, the review explores socio-economic implications, including rural job creation, energy poverty alleviation, and the potential role of briquetting in SA’s ‘Just Energy Transition’ (JET). This paper uniquely integrates technical analysis with policy relevance, rural energy needs, and practical challenges specific to South Africa, while offering a structured framework for bio-coal briquetting adoption in developing countries. While technical and economic barriers remain, such as binder costs and feedstock variability, the integration of briquetting into circular economy frameworks represents a promising path toward cleaner, decentralized energy and coal waste valorization. Full article

Sustainable aviation fuels (SAFs) are currently considered a key element in the decarbonization of the aviation sector, offering a feasible solution to reduce life cycle greenhouse gas emissions without requiring fundamental changes in aircraft or infrastructure. This article provides a comprehensive overview of the current state of SAFs, including their classification, production technologies, economic aspects, and environmental performance. The analysis covers both currently certified SAF pathways, such as HEFA and FT-SPK, and emerging technologies like alcohol-to-jet and power-to-liquid, assessing their technological maturity, feedstock availability, and scalability. Economic challenges related to high production costs, investment risks, and policy dependencies are discussed, alongside potential mechanisms to support market deployment. Furthermore, the article reviews SAFs’ emission performance, including CO₂ and non-CO₂ effects, based on existing life cycle assessment (LCA) studies, with an emphasis on variability caused by feedstock type and production method. The findings highlight that, while SAFs can significantly reduce aviation-related emissions compared to fossil jet fuels, the magnitude of benefits depends strongly on supply chain design and sustainability criteria. There are various certified pathways for SAF production, as well as new technologies that can further contribute to the development of the industry. Properly selected biomass sources and production technologies can reduce greenhouse gas emissions by more than 70% compared to conventional fuels. The implementation of SAFs faces obstacles related to cost, infrastructure, and regulations, which hinder its widespread adoption. The study concludes that although SAFs represent a promising pathway for aviation climate mitigation, substantial scaling efforts, regulatory support, and continued technological innovation are essential to achieve their full potential. Full article

The research and development of the next generation of supersonic transports (SSTs) meets economic and environmental problems. An SST encounters critical challenges, including the need for low fuel consumption, low noise, and low gas emissions. Currently, the feasibility of developing SSTs is increasing through the application of cutting-edge technologies, such as composite materials, advanced electric systems, sustainable aviation fuel, and innovative design methodologies. The object of this study was to perform the conceptual design of a 50-seat supersonic transport utilizing general conceptual design methods. In estimating weight and flight performance, statistical formulae were correlated with data from civil supersonic and subsonic jet transports. For wing sizing, carpet plots were created to explore the optimal combination of wing aspect ratio and wing loading. The results suggested that by utilizing advanced technologies, such as the use of a composite material for the structure, the maximum takeoff weight can potentially be reduced while still meeting design requirements. The constraint of climb gradient largely affects the maximum takeoff weight, and it is anticipated that flight performance at low speeds will be improved. Full article

The growing interest in alternative fuels stems from the need to reduce greenhouse gas emissions and promote sustainable development. Despite the dominance of fossil fuels in aviation, pulsejet engines offer a promising platform for testing new fuels due to their simple design and fuel versatility. This study presents a multi-criteria analysis of alternative fuels for use in pulsejet engines, emphasizing environmental impacts. Both gaseous (biogas, ethyne, LPG, and natural gas) and liquid fuels (methanol, ethanol, biodiesel, Jet A-1, and SAF) were examined. Exhaust emissions (CO₂, H₂O, CO) were simulated in Ansys 2025 based on literature data and chemical calculations. Additional factors analyzed included calorific value, production cost, thermal expansion, density, life cycle emissions (LCA), CO₂ emissions per fuel mass, and renewable energy content. Using the zero-unitization method, results were normalized into a single aggregate variable for each fuel. The highest values were recorded for biogas and methanol, respectively, indicating their potential as alternative fuels. The findings support further development of sustainable fuels for pulsejet engines. Future research should address combustion optimization and noise reduction, enhancing viability in aviation and other transport sectors. Integration with the current fuel infrastructure is also recommended to facilitate broader implementation. Full article

The application of fluidized bed reactors to biomass fast pyrolysis is regarded as a promising technology for enabling high-value utilization of biomass. This work established a three-dimensional numerical model of an industrial-scale fluidized bed reactor for biomass catalytic pyrolysis, employing the multiphase particle-in-cell method (MP-PIC) and coupling catalytic pyrolysis kinetics. Primary gas flow rate and biomass–catalyst injection modes were optimized to further improve the performance of the reactor. The model received additional validation from experimental data, primarily to ensure prediction accuracy. The results revealed that an optimal primary gas flow rate of 4 kg/s achieved a peak catalytic efficiency of 71.3%. Using maximum high-quality liquid fuels and adopting a relatively dispersed inlet mode with opposite jetting for biomass and catalyst promoted uniform particle distribution and thermal homogeneity in the dense phase zone, further increasing the catalytic efficiency to 75.6%. With the integration of the multiphase particle-in-cell (MP-PIC) method with catalytic pyrolysis kinetics at the industrial-scale, this work could provide theoretical guidance for designing fluidized bed catalytic pyrolysis reactors and optimizing biomass catalytic pyrolysis processes. Full article

The increasing global demand for sustainable energy solutions has intensified the need to replace fossil fuels in gas turbines, particularly in aviation and power generation where alternatives to gas turbines are currently limited. This review explores the feasibility of utilizing sustainable liquid and gaseous fuels in gas turbines by evaluating their environmental impacts, performance characteristics, and technical integration potential. The study examines a broad range of alternatives, including biofuels, hydrogen, alcohols, ethers, synthetic fuels, and biogas, focusing on their production methods, combustion behavior, and compatibility with existing turbine technology. Key findings indicate that several bio-derived and synthetic fuels can serve as viable drop-in replacements for conventional jet fuels, especially under ASTM D7566 standards. Hydrogen and other gaseous alternatives show promise for industrial applications but require significant combustion system adaptations. The study concludes that a transition to sustainable fuels in gas turbines is achievable through coordinated advancements in combustion technology, fuel infrastructure, and regulatory support, thus enabling meaningful reductions in greenhouse gas emissions and advancing global decarbonization efforts. Full article

This study investigates the impact of circumferential angle (φ) and interaction angle (θ) between hydrogen jets and diesel sprays in a co-axial hydrogen–diesel injector on combustion and emissions in a hydrogen–diesel dual-fuel engine using 3D CFD simulations. The results demonstrate that a co-axial dual-layer nozzle design significantly enhances combustion performance by leveraging hydrogen jet kinetic energy to accelerate fuel–air mixing. Specifically, a co-axial alignment (φ = 0°) between hydrogen and diesel sprays achieves optimal combustion characteristics, including the highest in-cylinder pressure (20.92 MPa), the earliest ignition timing (−0.3° CA ATDC), and the maximum indicated power of the high-pressure cycle (47.26 kW). However, this configuration also results in elevated emissions, with 29.6% higher NOx and 34.5% higher soot levels compared to a φ = 15° arrangement. To balance efficiency and emissions, an interaction angle of θ = 7.5° proves most effective, further improving combustion efficiency and increasing indicated power to 47.69 kW while reducing residual fuel mass. For applications prioritizing power output, the φ = 0° and θ = 7.5° configuration is recommended, whereas a φ = 15° alignment with a moderate θ (5–7.5°) offers a viable compromise, maintaining over 90% of peak power while substantially lowering NOx and soot emissions. Full article

Addressing the urgent need to decarbonise aviation and valorise agricultural waste, this paper investigates the production of Sustainable Aviation Fuel (SAF) from corn stover. A preliminary evaluation based on a literature review indicates that among various conversion technologies, fast pyrolysis (FP) emerged as the most promising option, offering the highest fuel yield (22.5%) among various pathways, a competitive potential minimum fuel selling price (MFSP) of 1.78 USD/L, and significant greenhouse gas savings of up to 76%. Leveraging Aspen Plus simulation, SAF production via FP was rigorously designed and optimised, focusing on the heat integration strategy within the process to minimise utility consumption and ultimately the total cost. Consequently, the produced fuel exceeded the American Society for Testing and Materials (ASTM) limit for the final boiling point, rendering it unsuitable as a standalone jet fuel. Nevertheless, it achieves regulatory compliance when blended at a rate of up to 10% with conventional jet fuel, marking a practical route for early adoption. Energy optimisation through pinch analysis integrated four hot–cold stream pairs, eliminating external heating, reducing cooling needs by 55%, and improving sustainability and efficiency. Economic analysis revealed that while heat integration slashed utility costs by 84%, the MFSP only decreased slightly from 2.35 USD/L to 2.29 USD/L due to unchanging material costs. Sensitivity analysis confirmed that hydrogen, catalyst, and feedstock pricing are the most influential variables, suggesting targeted reductions could push the MFSP below 2 USD/L. In summary, this work underscores the technical and economic viability of corn stover-derived SAF, providing a promising pathway for sustainable aviation and waste valorisation. While current limitations restrict fuel quality during full substitution, the results affirm the feasibility of SAF blending and present a scalable, low-carbon pathway for future development. Full article

Hydrogen is a promising fuel in the current transition to zero-net CO₂ emissions. However, most practical combustion equipment is not yet ready to burn pure hydrogen without adaptation. In the meantime, blending hydrogen with natural gas is an interesting option. This work reports a computational study of the performance of swirl-stabilized natural gas/hydrogen flames in a novel combustion chamber design. The combustor employs an air-staging strategy, introducing secondary air through a top-mounted plenum in a direction opposite to the fuel jet. The thermal load is fixed at 5 kW, and the effects of fuel composition (hydrogen molar fraction ranging from zero to one), excess air coefficient (λ = 1.3, 1.5 or 1.7), and primary air fraction (α = 50–100%) on the velocity, temperature, and emissions are analysed. The results show that secondary air changes the flow pattern, reducing the central recirculation zone and lowering the temperature in the primary reaction zone while increasing it further downstream. Secondary air improves the performance of the combustor for pure hydrogen flames, reducing NO emissions to less than 50 ppm for λ = 1.3 and 50% primary air. For natural gas/hydrogen blends, a sufficiently high excess air level is required to keep CO emissions within acceptable limits. Full article

With increasing energy demand and depletion of fossil fuels, the search for renewable energy sources has become imperative. Among them, biomass energy has attracted significant attention as it is clean, renewable, and abundant. This review summarizes recent advances in the electroreduction of the biomass-derived platform compound furfural (FF) for producing high-value fuels and chemicals. First, the principles and mechanisms of electrocatalysis are introduced, followed by a detailed analysis of reaction pathways for electrocatalytic hydrogenation, hydrogenolysis, and dimerization. Subsequently, the review highlights the research progress on the electrochemical reduction of FF to hydrofuroin (HDF, a precursor for jet fuel), analyzing its reaction mechanisms and summarizing the effects of catalytic materials and reaction conditions on product selectivity and faradaic efficiency. Additionally, it provides an overview of catalyst selection for both hydrogenation and hydrogenolysis processes. Studies indicate that Cu-based catalysts exhibit superior performance in hydrogenation and hydrogenolysis, with the latter being more favorable under low pH. In contrast, metal-doped carbon catalysts demonstrate enhanced activity in dimerization reactions. Reaction conditions also significantly influence product distribution, with lower reduction potentials generally favoring dimerization. Finally, the challenges and future directions in FF electroreduction are discussed, including the need for deeper understanding of competing pathways, improved electrode stability, and scalable reactor design. The integration of electrocatalytic with renewable energy offers a green and sustainable approach for the efficient utilization of biomass-derived compounds, holding substantial research significance and application potential. Full article