Search Results (113)

Amidst the escalating global greenhouse effect, the shipping industry faces mounting pressure to decarbonize. Consequently, ammonia has emerged as a promising zero-carbon fuel for marine engines. This review systematically categorizes current research on ammonia-fueled marine engines into compression ignition (CI) and spark ignition (SI) types. CI engines, including homogeneous charge compression ignition (HCCI), partially premixed combustion (PPC), and in-cylinder high-pressure direct-injection dual-fuel (HPDF) configurations, face challenges such as limited operating ranges, difficulties in emission control (particularly NO_x and NH₃ slip), and power constraints. Conversely, SI engines encompass conventional spark plug and pre-chamber jet ignition systems. While conventional SI engines suffer from limited power output and rely heavily on reactive fuel blending, such as hydrogen, pre-chamber jet ignition shows potential to enhance combustion stability and flame speed. Despite notable progress, widespread application of ammonia fuel in marine engines is hindered by persistent technical bottlenecks, including low reactivity, slow combustion kinetics, and the formation of fuel-bound NO_x and unburned NH₃ emissions. A key unresolved technical gap is the lack of an integrated combustion–after-treatment control strategy capable of dynamically maintaining an appropriate engine-out NH₃/NO_x balance under variable marine operating conditions while simultaneously suppressing NO_x, NH₃ slip, and secondary N₂O formation, thus accelerating the practical implementation of ammonia-powered marine propulsion. Full article

Solar-driven hydrogen evolution is limited by the poor ability of conventional photocatalysts to utilize the visible–near-infrared (Vis–NIR) region, which accounts for ~95% of the solar spectrum. Here, we design an upconversion-plasmonic Fabry–Pérot cavity (Al/NaYF₄:Yb³⁺,Tm³⁺/Au/TiO₂) to achieve cascaded photon upcycling for efficient solar hydrogen production. In this architecture, the NaYF₄:Yb³⁺,Tm³⁺ layer serves as the dielectric medium of the cavity, enabling multiple light reflections and enhanced NIR-to-UV/Vis upconversion. The upconverted photons, together with the incident light, are further concentrated by the adjacent Au layer via surface plasmon resonance, promoting hot-electron generation and injection into TiO₂. As a result, the optimized structure achieves a broadband absorption efficiency of 60.57% and a hydrogen evolution rate of 19.86 mmol·g⁻¹·h⁻¹ from polylactic acid wastewater, 124 times higher than that of pristine TiO₂. This work provides a scalable strategy for broadband solar harvesting and plastic-waste-to-hydrogen conversion. Full article

In the current context of developing strategies to mitigate global warming driven by anthropogenic greenhouse gas emissions, hydrogen and ammonia have emerged as critical vectors for the decarbonization of the transportation, energy, and industrial sectors. Ammonia, specifically, serves as a highly effective hydrogen carrier, possessing three times the volumetric energy density of hydrogen. In this study, the authors present experimental findings from a compression ignition (CI) engine operating at a constant speed across two distinct loads. A dual-fuel strategy was employed, wherein ammonia was injected into the intake manifold to partially displace conventional diesel fuel. The results demonstrate that optimizing ammonia injection leads to a significant smoke reduction of up to 73.43% and a decrease in CO₂ emissions of approximately 15.7%, albeit with a relative BTE penalty of 9.14% and an NO_x increase of 9.30% at the lower load setting. These findings strongly align with earlier research, providing further evidence that ammonia effectively mitigates soot and carbon-based emissions while simultaneously reducing fuel consumption and smoke opacity. Full article

Gas blending with hydrogen represents a core research direction for present and future energy transport systems. The throttling of natural gas and hydrogen mixtures through pressure-regulating valves inevitably induces thermodynamic temperature variations. Theoretical analyses and simulated thermal profiles demonstrate that hydrogen blending effectively counteracts the extreme expansion temperature drop post-throttling. This thermodynamic shift alleviates the localized microclimatic thermal conditions favorable to ice-plugging, validating the feasibility of hydrogen injection as a systematic thermal mitigation strategy for high-pressure pipeline networks. This study utilizes computational fluid dynamics software to model the flow field variations in pure hydrogen and gas–hydrogen mixtures under the influence of pressure-regulating valves. Employing a real gas equation of state across varying operational temperatures and pressure conditions, this research calculates and analyzes the flow field variations driven by the Joule–Thomson effect for pure hydrogen and mixtures with varying hydrogen blending ratios. The objective is to inform temperature regulation strategies for long-distance hydrogen–natural gas pipeline networks and to establish an empirical temperature fitting relationship for pure hydrogen. The numerical evaluation indicates a maximum relative error of 6.02% and a maximum absolute error of 0.06877 K. Furthermore, guided by the localized temperature variation patterns, the temperature rise results from 75 pure hydrogen simulation cases were extracted. A Multilayer Perceptron artificial intelligence algorithm was utilized to perform inverse calculation iterations on the thermal data and regulation results. Through the stochastic selection of initial parameters and repeated training iterations referencing the fitting formula, an optimized regulation sequence was obtained. This process drives the fluid temperature to approach the practical regulation target. Following the network training phase, the maximum absolute error between the calculated temperature regulation result and the target regulation temperature is recorded at 0.0556 K, providing a methodological reference for subsequent high-pressure hydrogen applications. Full article

Carbon capture, utilization, and storage (CCUS) is critical for carbon neutrality, and deep saline aquifers are promising reservoirs for CO₂ sequestration. CO₂ diffusion in brine directly affects dissolution trapping efficiency and is strongly influenced by salt ions. Molecular dynamics simulations were employed to investigate CO₂ diffusion in NaCl brines under varying concentrations (0.1–5.0 mol/L), temperatures (298–353 K), and pressures (3–40 MPa). Diffusion coefficients were derived from mean square displacement, and radial distribution functions combined with hydrogen bond analysis were used to elucidate microscopic mechanisms. Results show that as NaCl concentration increases from 0.1 to 5.0 mol/L, the diffusion coefficient decreases by ~50%, reflecting the kinetic consequence of the salting-out effect. Raising temperature from 298 to 353 K enhances diffusion by ~149%, following Arrhenius behavior, while pressure shows negligible influence below 30 MPa but causes a 15% drop at 40 MPa. RDF analysis reveals that higher salinity densifies the CO₂ hydration shell without changing its coordination number, and ions do not accumulate near CO₂. Hydrogen bond analysis indicates that slower diffusion arises primarily from increased viscosity and steric hindrance from hydrated ions rather than disruption of hydrogen bonds. These molecular-level insights can guide site selection and injection strategy optimization for CO₂ geological storage in saline aquifers. Full article

Hydrogen is a promising carbon-neutral fuel for future internal combustion engines due to its wide flammability range, high flame speed, and absence of carbon-based emissions. However, its high reactivity significantly increases susceptibility to abnormal combustion phenomena such as knock and pre-ignition, which can compromise engine efficiency, durability, and operational stability. Accurate detection and characterization of knock in hydrogen-fueled spark-ignition engines remain challenging due to the highly transient, broadband, and cycle-dependent nature of abnormal combustion-induced pressure oscillations. Conventional knock indicators based solely on time-domain pressure oscillations or fixed-band frequency analysis are limited in their ability to capture transient resonance behavior and cyclic variability. This study presents an integrated frequency- and time–frequency-domain methodology for knock detection using high-resolution in-cylinder pressure data acquired from a single-cylinder research engine operating under hydrogen port fuel injection (PFI). A discrete Fast Fourier Transform (DFFT) approach applied at stationary points of dynamically windowed pressure signals enables accurate identification of dominant resonance modes while minimizing spectral leakage. A Gaussian-based adaptive windowing strategy is introduced to capture combustion-driven cyclic variations more effectively. Short-Time Fourier Transform (STFT) and sum-based spectral analysis further provide detailed time–frequency localization of transient knock events. The proposed methodology demonstrates a clear separation between normal combustion and knock conditions, enabling reliable cycle-by-cycle identification of abnormal combustion events under varying operating conditions. The experimentally observed resonance frequencies are validated against theoretical predictions using Draper’s acoustic resonance equation, supporting the physical interpretation of knock-induced pressure oscillations. The results demonstrate that the proposed adaptive spectral methodology significantly improves knock detection accuracy compared to conventional indicators and provides a robust framework for advanced knock diagnostics, engine calibration, and combustion control in hydrogen-fueled engines. Full article

The global push for low-carbon electricity generation has made hydrogen-enriched natural gas an attractive near-term decarbonization option. This paper combines experimental and thermodynamic analyses of H₂–CH₄ combustion in gas turbine combustion chambers. Experiments were conducted on a patented two-stage swirl burner across 240 operating conditions. The effects of hydrogen fraction (γ = 0–40%), swirler vane angle (30°, 45°, 60°), equivalence ratio (φ = 0.17–1.00), and fuel injection strategy were measured against NOx and CO emissions and lean blowout stability. Each 10% increase in hydrogen content raised NOx by 23–24% via the Zel’dovich thermal mechanism, while CO fell by up to 28.5% at φ = 0.3 and 60° due to enhanced OH-radical activity. The minimum recorded NOx was 12.08 ppm (Type 2 injection, 30°, γ = 0%, φ = 0.3). Hydrogen addition improved lean blowout stability by 32–46% per 10% H₂. A parallel thermodynamic analysis showed that integrating an organic Rankine cycle (ORC) and supplementary H₂–CH₄ firing in the heat recovery steam generator cuts specific CO₂ emissions by 7.5–10% and raises net efficiency by 0.79–4.0 percentage points. Critical comparison with 28 published studies identified an optimal operating window: γ = 20–30%, φ = 0.5–0.7, 45° vane angle (SW = 0.8). Full article

Self-healing materials have attracted increasing attention as a strategy to enhance durability, extend service life, and reduce maintenance in advanced material systems. Among these, cellulose-based self-healing materials represent a sophisticated intersection between sustainable macromolecular chemistry and adaptive materials science. This review provides a synthesis of recent advancements in the field, systematically categorizing materials derived from cellulose raw materials. We evaluate the fundamental chemical strategies employed to achieve autonomous repair, distinguishing between extrinsic mechanisms—utilizing cellulose-based micro/nano-capsules to sequester healing agents—and intrinsic mechanisms governed by dynamic covalent chemistry (Schiff-base, boronic ester, Diels–Alder) and supramolecular interactions (hydrogen bonding, metal–ligand coordination, and host–guest assemblies). The analysis highlights how cellulose’s hierarchical structure and abundant surface functionality are leveraged to overcome the traditional trade-off between mechanical toughness and healing efficiency. Particular emphasis is placed on the transition from simple structural hydrogels to sophisticated multifunctional systems. These include ultra-stretchable strain and pressure sensors for e-skin applications, biocompatible and injectable matrices for chronic wound management and stem cell delivery, and advanced anti-freezing eutectogels for performance in extreme environments. Furthermore, we explore the integration of cellulose into traditional sectors, such as self-healing concrete utilizing microbe-induced calcification and smart, eco-friendly coatings for corrosion protection. Finally, we discuss critical challenges, including environmental stability, scalability, and the development of standardized evaluation protocols, providing a roadmap for the next generation of bio-derived, sustainable and intelligent materials. Full article

The use of hydrogen direct injection (DI) plays a crucial role in decarbonizing internal combustion engine (ICE) technology. However, a suitable characterization of the injection process is required to control the mixture preparation before combustion, especially in the case of late injection timing. CFD modeling represents a useful tool to support experiments in addressing this goal. This study presents a numerical investigation of hydrogen DI using a swirled-type injector, seated in a constant-volume vessel. First, the selected numerical setup is validated against optical measurements of the jet penetration, demonstrating the reliability of the approach. Then, the analysis compares swirling and non-swirling configurations under different nozzle pressure ratios (nPRs) to evaluate the interaction between swirl-induced mixing and under-expanded jet structures. Results show that at lower nPR, swirl significantly alters the momentum distribution, reducing axial penetration. Instead, at higher nPR, where the H2 jets exhibit strong shock structures, the effects of swirl become negligible, with penetration and plume morphology nearly identical to non-swirling conditions. Analysis of the scalar dissipation rate showed the presence of a redistribution of mixing characteristics at low nPR due to swirl, while shock structures dominate at high nPR. This could have a significant impact on combustion and NO_x emissions in ICE operated with late injection strategies, where lower nPR are found. Full article

In global navigation satellite systems (GNSS), the system time reference is maintained by the ground control segment and kept traceable to UTC, enabling inter-system compatibility and interoperability. Advances in onboard atomic-clock stability and inter-satellite time transfer accuracy make it feasible for a constellation to autonomously realize a space-based time reference, with periodic traceability updates and steering via satellite–ground links to enhance resilient time maintenance. BeiDou-3 (BDS-3) carries high-performance onboard hydrogen masers and Ka-band inter-satellite links (ISL) for time transfer, providing stable frequency sources and high-precision time transfer capability for establishing a space-based time reference. Using in-orbit BDS-3 clock offset data, we propose a space-based autonomous timekeeping approach that combines high-precision ISL synchronization with timekeeping by a small ensemble of hydrogen masers, together with a space–ground cooperative strategy with BeiDou time (BDT). The approach first performs constellation-wide synchronization using ISL, then selects a timekeeping ensemble based on in-orbit clock performance to generate a space-based ensemble atomic timescale, denoted TA(SPACE); when satellite–ground links are available, TA(SPACE) is steered to BDT to maintain consistency with the ground time reference. Based on this space-based time reference, satellite clock offsets are predicted to generate clock-parameter products. Experiments show that, in the autonomous mode, the time offset between TA(SPACE) and BDT is kept within 25.06 ± 41.47 ns over 90 days, whereas in the space–ground cooperative mode, satellite–ground steering stabilizes the offset within 10 ns. The proposed approach provides a practical solution for constellation time maintenance under disruptions such as anomalous ground injection, improving the resilience and reliability of GNSS services. Full article

Liquid hydrogen (LH₂) fuel system architectures for aviation remain at low Technology Readiness Levels (TRLs) due to limited experimental data and the challenges of modelling cryogenic hydrogen’s behavior. This paper presents a computationally efficient framework for sensitivity analysis that integrates cryogenic thermodynamics, tank geometry, external heat ingress, engine mass flow demands, and pressurization control strategies. A set of operational scenarios was modeled to demonstrate how tank pressure and temperature evolve under various control and geometric conditions, delivering five key insights: (1) Passive tank self-pressurization leads to continuous pressure rise and subcooled liquid. (2) LH₂ withdrawal alone may not fully stop pressurization with high heat ingress. (3) Gaseous hydrogen (GH₂) injection stabilizes pressure only up to moderate heat ingress during LH₂ extraction. (4) The addition of venting enables full pressure control. (5) Tank geometry and heat flux govern transient behavior. Spherical tanks show slower pressure and temperature rise than cylindrical ones, and both geometries maintain near-constant pressure at low heat flux. These insights offer practical guidance for designing reliable and thermally stable LH₂ storage systems for future aircraft applications, paving the way towards sustainable and zero-emission aviation. Full article

Hydrogen is recognized as a promising energy vector for the decarbonization of energy production. Besides the undoubted benefits, its utilization poses some technological challenges in the generation, transportation, storage and utilization phases, which must be carefully assessed. The aim of this work is to assess the effect of methane substitution with hydrogen in a dual-fuel diesel/methane engine on fuel conversion efficiency and pollutant emission levels. Therefore, an extensive experimental campaign has been designed in which a hydrogen/methane mixture with variable composition is ignited with a pilot injection of diesel fuel. The engine was operated in naturally aspirated or supercharged conditions, and conventional or alternative combustion strategies were implemented, spanning a pilot injection timing over a broad range of values. The results show that the effect of a variation in H₂ percentage of up to 20% strongly depends on air intake pressure and pilot injection timing. In particular, engine efficiency and HC and CO emissions are penalized as H₂ percentage increases; however, this penalty can be mitigated in naturally aspirated conditions if a late pilot SOI strategy is adopted. In terms of NO_x, a reduction is observed as H₂ percentage increases. Late SOIs determine the lowest levels of NO_x emissions in both naturally aspirated and supercharged conditions. Full article

This article provides a comprehensive review of current state of knowledge regarding the ongoing development of hydrogen-fueled internal combustion engines (H₂ICE). It describes the key challenges, the resolution of which will determine further progress in the development, practical application, and popularization of H₂ICE. The article details the problems associated with creating and optimizing the fuel mixture in the H₂ICE cylinder. It also highlights directions for development of hydrogen injection, ignition, and boosting processes. The risks resulting from abnormal combustion processes and the related optimization of combustion strategies in H₂ICE are extensively discussed. Problems and difficulties associated with adapting existing engine designs to hydrogen fueling are also considered. Attention is paid to the different degradation patterns and the requirements placed on engine lubricating oil when fueling engines with hydrogen. The article then describes emissions from hydrogen-fueled engines, with particular emphasis on high NOx emissions and methods for reducing those emissions. The last part of the article discusses the influence of hydrogen admixture in various hydrocarbon fuels on combustion processes, engine performance and harmful exhaust emissions into the atmosphere. The article stands out in that it identifies and describes the most important challenges that determine the further development of H₂ICE engines. It also provides a comprehensive overview of the current state of knowledge in the field of ongoing development of hydrogen-powered internal combustion engines (H₂ICE). Full article

Aviation heavy-fuel piston engines are widely used in UAVs, general aviation, and military platforms due to their fuel efficiency and adaptability. However, emissions of NO_x, PM, and other pollutants pose significant environmental challenges. This paper reviews emission-reduction strategies, including combustion-chamber optimization, fuel-injection control, alternative fuels, and exhaust after-treatment technologies. Research indicates that optimizing combustion-chamber geometry, high-pressure common-rail injection, and turbulence enhancement improve combustion efficiency and reduce emissions. Biofuels, synthetic aviation fuels (SAF), and hydrogen-based fuels demonstrate strong potential for low-carbon emissions, while after-treatment technologies such as SCR, DPF, and EGR effectively mitigate NO_x and PM emissions. Despite technological advancements, challenges remain in balancing combustion efficiency with NO_x control and ensuring compatibility between EGR and combustion stability. Future advancements in intelligent combustion control, novel catalytic materials, low-temperature combustion, and high-efficiency after-treatment systems will drive aviation diesel engines toward lower emissions, higher efficiency, and greater intelligence, contributing to the green and sustainable transformation of aviation propulsion systems. Full article

The development of multifunctional, mechanically robust, and sustainable hydrogels from renewable biomaterials has attracted increasing attention for advanced biomedical applications; however, achieving an optimal balance between mechanical stability, biofunctionality, and infection control remains challenging. In this work, collagen (COL) extracted from raw trimming wastes from a tannery is used to fabricate COL/PAA/Fe composite hydrogels via the ammonium persulfate (APS)-initiated polymerization of acrylic acid (AA) coupled with Fe³⁺-mediated coordination cross-linking. The resulting hydrogel network is stabilized by synergistic COL-poly(acrylic acid) (PAA) hydrogen bonding and dynamic Fe³⁺–carboxylate coordination, imparting enhanced mechanical strength and elasticity. The optimized hydrogel exhibited maximum tensile and compressive strengths of ~0.176 MPa at 751% elongation and ~1.945 MPa at a strain of 80%, respectively. In addition, a high ionic conductivity of 4.11 S·m⁻¹ is achieved, enabling structural integrity under deformation and suitability for flexible electronic interfaces. The prepared hydrogel also displayed rapid autonomous self-healing behavior and substantial antibacterial properties against both Gram-positive and Gram-negative bacteria. Overall, COL is employed herein as a sustainable precursor, highlighting an eco-conscious approach to biomaterial design. This work presents a versatile strategy for producing mechanically stable and biofunctional hydrogels with strong potential for wound dressing, tissue engineering, and injectable biomedical applications. Full article