Search Results (143)

The increasing adoption of high-aspect-ratio wings to improve aerodynamic efficiency introduces significant structural flexibility, necessitating the integration of aeroelastic considerations into the earliest design stages. While critical, existing frameworks often lack the multi-fidelity modeling capabilities and automated workflows required to bridge conceptual design and high-fidelity verification. This paper presents the Flexible Aero-Structural Toolbox (FAST), a modular framework supporting both beam and shell structural modeling and integrated with MSC NASTRAN for industry-standard aeroelastic simulation. The toolbox’s capabilities are demonstrated through modal, flutter, and static aeroelastic analyses across three distinct configurations: the P-FLEX UAV, the Ventus sailplane, and an A320-like transport aircraft, including its hydrogen-powered derivative. Results show that FAST accurately captures the aeroelastic characteristics of high-aspect-ratio wings and effectively predicts loads for large-scale flexible airframes. Notably, analysis of the hydrogen configuration reveals a significant 25% increase in wing bending moments for the “dry” wing condition compared to standard kerosene configurations. Furthermore, the tool’s ability to model unconventional mass distributions, such as cryogenic fuel tanks, highlights its adaptability for disruptive aircraft technologies. The study concludes that FAST provides a versatile, physics-based decision-making environment that significantly improves efficiency in the aeroelastic analysis process without compromising simulation fidelity. Full article

This review synthesizes recent progress in modern energy storage technologies and proposes a selection-oriented comparison for power-system stabilization. Technologies are grouped into electrochemical, mechanical, chemical, and thermal storage, and evaluated using harmonized criteria (power and energy capability, response time, round-trip efficiency, lifetime, cost proxies, and maturity level). A comparative dataset and use-case mapping are used to link technology characteristics to grid services, with emphasis on voltage support, operational durability, and waste-heat utilization. The analysis highlights pumped-storage hydropower as the most robust option for long-duration, high-capacity applications, while battery energy storage systems are best suited for fast ancillary services, provided that cycle life, safety, and system integration constraints are met. Finally, the review discusses current technology trends (e.g., LFP and sodium-ion deployment, solid-state development, and commercialization barriers for lithium-sulfur) and identifies evidence-based directions for future research and deployment. Full article

Aviation is currently facing one of its greatest challenges: reconciling growing traffic demand with the need to drastically reduce climate-altering emissions. Hydrogen has emerged as one of the most promising alternatives to decarbonize air transport. However, it poses significant challenges related to cryogenic storage, safety, and the adaptation of the airport infrastructure. Aprons represent a critical issue, as the increased volume of fuel tanks and different refueling protocols directly impact airport operational capacity. This research fits within this framework by analyzing a Code 4E Italian airport over three time horizons: 2025, with an all-kerosene fleet; 2035, with a 25% penetration of hydrogen-powered class A and B aircraft; and 2045, with a further increase in the hydrogen share (75% class A and B and 15% class C). The study evaluates apron capacity using fast-time simulation and compares the outcomes with an analytical model. The results show good consistency between theoretical and simulated capacity. The 2035 and 2045 scenarios with the introduction of hydrogen-powered aircraft show a reduction in apron capacity between 16% and 5% compared to conventional scenarios. Full article

Renewable hydrogen purification is a critical yet often underemphasised step in enabling its use as a clean energy carrier. Hydrogen produced from biomass-based thermochemical and biological routes typically contains CO₂, CO, CH₄, H₂S, and other impurities that must be removed to meet stringent requirements for fuel cell, industrial, and grid-injection applications. This review provides a critical and up-to-date assessment of renewable hydrogen purification technologies, focusing on their suitability for variable and impurity-rich renewable hydrogen streams. Established benchmark technologies, including pressure swing adsorption and cryogenic separation, are described, with emphasis on their operating principles, material innovations, and process integration strategies. Recent advancements in inorganic, polymeric, and mixed-matrix membranes are highlighted, with particular focus on how advanced porous materials enhance selectivity, permeability, and flexibility. Additionally, a comparative techno-economic assessment is presented, evaluating each purification method based on technology readiness level, capital and maintenance costs, energy efficiency, and operational lifespan. By incorporating recent research trends, this approach facilitates the selection and design of purification systems that are not only efficient and scalable but also cost-effective, tailored to both decentralised and centralised renewable hydrogen production. Full article

The maritime shipping industry faces the challenge of decarbonising its operations while maintaining economic viability. We present a comprehensive techno-economic review of four alternative energy carriers, liquid hydrogen (LH₂), ammonia (NH₃), liquefied natural gas (LNG), and methanol, evaluating their suitability for maritime applications within the context of global decarbonisation policy. Through the comparative assessment of physicochemical properties, hazard profiles, storage requirements, and regulatory compliance mechanisms, this review demonstrates that fuel selection is highly route-dependent, with methanol emerging as the most practical near-term solution for short-sea corridors, ammonia emerging as the primary pathway for long-term deep-sea decarbonisation, leveraging existing production infrastructure to achieve up to 90% lifecycle GHG reduction when produced from renewable hydrogen, and hydrogen serving as an alternative option pending cryogenic infrastructure maturation. The integration of digital twin technologies and port call optimisation provides a realistic pathway to achieving International Maritime Organisation (IMO) decarbonisation targets by 2030 and beyond. The findings are contextualised within current and emerging regulatory frameworks, including MARPOL Annex VI and FuelEU Maritime, to support evidence-based fuel selection and infrastructure investment decisions. Full article

The aviation industry aims to reduce environmental impact by adopting alternative propulsion systems, including hydrogen-based, hybrid-electric, and all-electric architectures, requiring a new Thermal Management System (TMS). In addition, new design methods are needed for the TMS, at the system and component levels, to handle various fluids and varying fluid properties. Within the TMS, heat exchangers are critical components that may require significant space and must be considered early in the design process. This paper presents a parametric sizing methodology for heat exchangers suitable for early design phases within a Multidisciplinary Design Analysis and Optimization (MDAO) framework, specifically for cryogenic heat transfer. The method combines physical equations with validated empirical relationships, using iterative solver algorithms for sizing. To address multi-variable design challenges, the methodology integrates discretization schemes for fluid properties, temperature, and energy calculations, and constraint-based optimization with a weighted-sum approach for solution selection. The methodology is validated with a commercial heat exchanger, and cross-validated with a cryogenic Heat Exchanger (HX). A case study for an all-electric hydrogen fuel cell aircraft architecture with a 7.6 MW propulsion system is presented to demonstrate the effectiveness of the methodology. The presented heat exchanger performance can be predicted across multiple conditions quickly enough to enable large design space exploration. Overall, the presented model is a crucial element for the design of a TMS for future aircraft with hydrogen-based propulsion systems. Full article

The maritime sector is under growing pressure to decarbonize, driving the adoption of alternative fuels such as methane, methanol, ammonia, and hydrogen. This study evaluates their thermal behavior and associated risks using Engineering Equation Solve software for heat transfer modeling and Areal Locations of Hazardous Atmospheres software for dispersion and explosion analysis in pipelines and storage scenarios. Results indicate that methane presents moderate and predictable risks, mainly from thermal effects in fires or Boiling Liquid Expanding Vapor Explosion events, with low toxicity. Methanol offers the safest operational profile, stable at ambient temperature and easily manageable, though it remains slightly flammable even when diluted. Ammonia shows the greatest toxic hazard, with impact distances reaching several kilometers even when emergency shutoff systems are active. Hydrogen, meanwhile, poses the most severe flammability and explosion risks, capable of autoignition and generating destructive overpressures. Thermal analysis highlights that cryogenic fuels require complex insulation systems, increasing storage costs, while methanol and gaseous hydrogen remain thermally stable but have lower energy density. The study concludes that methanol is the most practical transition fuel, when comparing thermal behavior and associated risks, while hydrogen and ammonia demand further technological and regulatory development. Proper insulation, ventilation, and automatic shutoff systems are essential to ensure safe decarbonization in maritime transport. Full article

The aviation industry, responsible for approximately 2.5–3.5% of global greenhouse gas emissions, faces increasing pressure to adopt sustainable energy solutions. Hydrogen, with its high gravimetric energy density and zero carbon emissions during use, has emerged as a promising alternative fuel to support aviation decarbonization. However, its large-scale implementation remains hindered by cryogenic storage requirements, safety risks, infrastructure adaptation, and economic constraints. This study aims to identify and evaluate the primary technical and operational risks associated with hydrogen utilization in aviation through a comprehensive Monte Carlo Simulation-based risk assessment. The analysis specifically focuses on four key domains—hydrogen leakage, cryogenic storage, explosion hazards, and infrastructure challenges—while excluding economic and lifecycle aspects to maintain a technical scope only. A 10,000-iteration simulation was conducted to quantify the probability and impact of each risk factor. Results indicate that hydrogen leakage and explosion hazards represent the most critical risks, with mean risk scores exceeding 20 on a 25-point scale, whereas investment costs and technical expertise were ranked as comparatively low-level risks. Based on these findings, strategic mitigation measures—including real-time leak detection systems, composite cryotank technologies, and standardized safety protocols—are proposed to enhance system reliability and support the safe integration of hydrogen-powered aviation. This study contributes to a data-driven understanding of hydrogen-related risks and provides a technological roadmap for advancing carbon-neutral air transport. Full article

Temperature Swing Absorption (TSA) is the primary candidate for the Isotope Rebalancing and Protium Removal (IRPR) system within the envisioned EU-DEMO fusion reactor fuel cycle. TSA separates a mixed hydrogen isotope stream into two product streams using a semi-continuous process. One stream, enriched in heavy isotopes, is used to re-establish the required deuterium-to-tritium fuel ratio. The second, enriched in protium, is stripped off from the fuel cycle to counteract the protium build-up. Separation is achieved by cycling an isotope mixture between two columns filled with metallic absorption materials that have opposite isotope effects of metal hydride formation. The selection of these materials, the operation parameters and the column geometry allow for adjusting the resulting enrichments. To identify suitable operation parameters, a TSA process model is developed which depicts the process dynamics and interactions between the columns. A modified process operation mode is introduced, which enables higher system throughputs and non-cryogenic operation, i.e., operational temperatures between 0 to 130 °C, while reducing the tritium inventory due to shorter cycling times by reduced amplitudes of the temperature swings. Finally, simulations of a TSA system at relevant scale confirm the suitability of TSA technology for the separation task of the EU-DEMO IRPR system. Full article

Due to its high energy density, liquid Hydrogen is an essential fuel for both terrestrial energy systems and space propulsion. However, uncontrolled evaporation poses a challenge for cryogenic storage and transport technologies. Accurate modeling of evaporation remains difficult due to the multiscale menisci formed by the wetting liquid phase. Thin liquid films form near the walls of containers, ranging from millimeters to nanometers in thickness. Heat conduction through the solid walls enables high evaporation rates in this region. Discrepancies in the reported values of the accommodation coefficients (necessary inputs to models) further complicate evaporation calculations. In this study, we present a novel multiscale model for CFD simulations of evaporating Hydrogen menisci. Film profiles below 10 $\mu$m are computed by a subgrid model using a lubrication-type thin film equation. The microscale model is combined with a macroscale model above 10 $\mu$m. Evaporation rates are computed using a kinetic phase change model combined with in situ calculations of the accommodation coefficient using transition state theory. The submodels are implemented in Ansys Fluent^TM using User-Defined Functions (UDFs), and a method to establish two-way coupling is detailed. The modeling results are in good agreement with cryo-neutron experiments and show improvement over prior models. The model, including UDFs, is made available through a public repository. Full article

Fibre-reinforced polymer (FRP) composites are key materials used in the fabrication of lightweight and high-performance structures. Thus, a comprehensive understanding of material performance is required to ensure the safe and reliable operation of FRPs across a broad range of temperatures. For example, the application of FRPs in cryogenic environments, especially for lightweight cryogenic fuel storage, is gaining considerable attention. However, obtaining accurate tensile property measurements for FRPs can be challenging, as failure of the test specimen near the grips is common, even at room temperature. Under cryogenic conditions, the increased complexity of the experimental setup further reduces the accuracy and reproducibility of the tensile properties. This paper reviews standard test methods for tensile testing of FRPs and discusses the challenges of performing tensile tests in both room and cryogenic environments. Key experimental design considerations and directions for future research are identified to support the development of reliable tensile test methods that yield accurate and consistent measurements of FRP material properties. Full article

Hydrogen, a promising alternative to conventional fuels, presents significant combustion hazards due to its low minimum ignition energy (MIE) and wide flammability range (4–75 vol.%). The risks are amplified with liquid hydrogen (LH₂), which has an extremely low boiling point (20.3 K) and high diffusivity. Once released, LH₂ vaporizes rapidly and mixes with ambient air. This process forms a cryogenic and highly flammable cloud, which significantly increases ignition and explosion hazards. Therefore, a comprehensive understanding of the MIE of cryogenic hydrogen–air mixtures is crucial for quantitative risk assessment. This work develops and validates a numerical algorithm for predicting the MIE of hydrogen–air mixtures at cryogenic temperatures (down to 93 K) across a wide range of hydrogen concentrations (10~50 vol.%) and oxygen concentration ratios [O₂/(O₂ + N₂) = 21~52%]. By coupling a detailed H₂/O₂ reaction mechanism with a large eddy simulation (LES) turbulence model, this algorithm demonstrates high reliability and accuracy. The results indicate (1) an exponential increase in MIE with decreasing initial temperature; (2) a U-shaped dependence of MIE on hydrogen concentration, with the minimum occurring near 25% hydrogen concentration; (3) an asymptotic dependence of MIE on oxygen concentration ratio, particularly at 40% hydrogen concentration. The initial temperature has the greatest influence on MIE; hydrogen concentration is the second; and the oxygen concentration ratio has the weakest influence. This study provides a theoretical framework and a practical computational tool for assessing and mitigating cryogenic ignition associated with LH₂ leakage, thereby enabling safer application of liquid hydrogen technologies. Full article

Maritime transport accounts for approximately 80–90% of global trade and nearly 3% of global greenhouse gas (GHG) emissions. In response, the International Maritime Organization (IMO) adopted an ambitious strategy for net-zero emissions by 2050, critically mandating a Well-to-Wake (WtW) life-cycle assessment for fuels. This framework invalidates fuels produced with high carbon intensity, regardless of their emissions at the point of use, thereby compelling the industry to focus on truly clean and sustainable alternatives. This push positions green hydrogen and ammonia as leading solutions, though they present a distinct trade-off. Hydrogen is an ideal fuel with zero-carbon emission in fuel cells but faces significant storage challenges due to its extremely low volumetric energy density and cryogenic requirements. In contrast, ammonia offers superior energy density and easier handling but contends with issues of toxicity and potentially harmful emissions like nitrous oxide. This paper provides a comprehensive review of this complex landscape, analyzing the production, utilization, and associated techno-economic and geopolitical challenges of using hydrogen and ammonia as future marine fuels, with environmental aspects briefly considered. Full article

Biogas upgrading and bottling represent essential processes in transforming raw biogas produced via the anaerobic digestion of organic waste into high-purity biomethane (≥95% CH₄), a renewable energy source suitable for applications in cooking, transportation, and electricity generation. Upgrading technologies, such as membrane separation, pressure swing adsorption (PSA), water and chemical scrubbing, and emerging methods, like cryogenic distillation and supersonic separation, play a pivotal role in removing impurities like CO₂, H₂S, and moisture. Membrane and hybrid systems demonstrate high methane recovery (>99.5%) with low energy consumption, whereas chemical scrubbing offers superior gas purity but is limited by high operational complexity and cost. Challenges persist around material selection, safety standards, infrastructure limitations, and environmental impacts, particularly in rural and off-grid contexts. Bottled biogas, also known as bio-compressed natural gas (CNG), presents a clean, portable alternative to fossil fuels, contributing to energy equity, greenhouse gases (GHG) reduction, and rural development. The primary aim of this research is to critically analyze and review the current state of biogas upgrading and bottling systems, assess their technological maturity, identify performance optimization challenges, and evaluate their economic and environmental viability. The research gap identified in this study demonstrates that there is no comprehensive comparison of biogas upgrading technologies in terms of energy efficiency, price, scalability, and environmental impact. Few studies directly compare these technologies across various operational contexts (e.g., rural vs. urban, small vs. large scale). Additionally, the review outlines insights into how biogas can replace fossil fuels in transport, cooking, and electricity generation, contributing to decarbonization goals. Solutions should be promoted that reduce methane emissions, lower operational costs, and optimize resource use, aligning with climate targets. This synthesis highlights the technological diversity, critical barriers to scalability, and the need for robust policy mechanisms to accelerate the deployment of biogas upgrading solutions as a central component of a low-carbon, decentralized energy future. Full article

The hydrogen drive is a promising zero-emission solution in transportation that can be realised through hydrogen internal combustion engines or hydrogen fuel cells. The hydrogen combustion engine’s advantage lies in the simplicity and greater maturity of the technology. At the same time, these solutions require appropriate fuel storage systems. The publication presents an overview of the currently used and developed hydrogen storage technologies. The main focus is placed on hydrogen tanks intended for vehicles powered by hydrogen internal combustion engines. The manuscript describes physical storage, including popular pressurised and cryogenic tanks. Additionally, technologies which can lead to improvements in the future, such as metallic and non-metallic hydrides and sorbents, are presented. The characteristics of the storage technologies in connection with the combustion engines are shown, as well as the outlook for the future of these solutions and their recent uses in vehicles. When focusing on vehicular and combustion applications, their specifics make physical storage methods the leading technology for now. Hydrogen storage today is still not competitive with fossil fuels; however, there are promising developments than can lead to achieving the requirements needed for its viable storage and use. Full article