Search Results (2,047)

The engine system requirements for different engine cycles significantly influence the design of the mixing head. A literature review of fuel-injection technology for hydrogen and methane is presented. The literature review aimed to answer proposed questions specific to the liquid rocket engine fuel injector design. The current review methodology accounts for the engine system effect. Thus, a comprehensive literature review of the working principles of startup-staged-combustion-cycle engines based on original patents is provided. At the end of the review, the research gaps and suggestions for further work are summarised. At high mass flow rate and injection pressure in the supercritical regime (>50 MPa), experience is limited to the staged-combustion cycle developed in Russia and the US. It is necessary to consider a fluid-dynamic heat transfer coupling study for the multi-injection element design in the supercritical state. Cryogenic spray atomisation experiments need to be designed with research significance in mind. It is still needed to study how the similarity of the spray flow field to the combustion performance affects a liquid rocket engine problem. Moreover, scaling stoichiometric mixing theory needs to be expanded to different injector types, such as tricoaxial and pintle injectors, to validate the correlation between the non-reactive mixing length and flame length. Full article

In a bid to investigate the optimum transportation method for offshore wind-produced hydrogen (H₂) and assess the feasibility of repurposing the existing oil and gas infrastructure for H₂ transmission, this paper assesses the existing H₂ transportation methods with a comprehensive review of the H₂ impact on the existing natural gas pipeline infrastructure. To establish the possibility of repurposing the existing natural gas (NG) pipelines for H₂ gas transport, this paper reviews the influential technical measures—composition, pressure, temperature, volumetric energy density, density, and pressure drop—to assess whether the characteristics of hydrogen gas are compatible with the natural gas pipeline infrastructure. Based on these reviews, it was found that the current NG pipeline pressure exacerbates the H₂ embrittlement; for the existing NG pipelines to be repurposed, the operating pressure should be reduced, and the pipeline material should be revised. It was found that higher strength steels can be re-used with major modifications, or the pipeline should be constructed from material grade X52 or below. Nevertheless, the fitness of the existing NG pipelines for H₂ transmission should be assessed on a case-by-case basis and other factors such as erosion, leakage, pressure cycling, monitoring (e.g., distributed fiber-optic sensing technology) and a rigorous assessment of welds and joints should also be considered. Full article

Sustainable hydrogen production in water-scarce regions poses critical environmental challenges due to limited freshwater availability and the energy intensity of seawater treatment. This study examines the environmental trade-offs of providing water for hydrogen production via seawater desalination (with or without brine treatment) or freshwater purification, using a comprehensive life cycle assessment (LCA) framework. The assessment centers on three water-stressed countries: the United Arab Emirates (UAE), Spain, and Australia. Results reveal clear trade-offs between freshwater conservation and marine environmental pressures. Brine treatment reduces nutrient-related marine impacts but increases energy-related burdens, particularly under fossil-dominated electricity systems. Water sourcing for electrolysis coupled with energy-intensive desalination systems generally exhibits higher environmental pressures than alternative configurations, whereas freshwater-based supply for hydrogen production pathways shows lower burdens in several impact categories but raise concerns regarding freshwater resource use. Sensitivity analysis confirms that system performance is strongly influenced by water demand and electricity characteristics, highlighting the importance of aligning hydrogen deployment strategies with regional energy and water conditions. Overall, the findings demonstrate that water sourcing decisions play a critical role in shaping the environmental sustainability of hydrogen systems in water-stressed regions and must be evaluated through integrated water–energy planning. Full article

This paper proposes a collaborative energy management strategy based on power prediction and deep reinforcement learning (DRL) to address the trade-offs among economic efficiency, durability, and dynamic performance in fuel cell hybrid power systems (FCHPS) under dynamic driving conditions. First, a hybrid prediction model termed LSTM-LSSVM with Cascade Correction (LSTM-LSSVM-CC) is developed. The cascade correction (CC) mechanism adopts a hierarchical structure to capture both low-frequency steady-state trends and high-frequency dynamic fluctuations, which are typically challenging for single models to represent. By integrating an online residual correction mechanism, this model generates accurate future power demand sequences. Second, a Dynamic Spatio-Temporal Fusion (DSTF) method is introduced to construct a high-dimensional DRL state space. This approach integrates predicted data, historical residuals, and real-time system states, enabling the agent to perform anticipatory decision-making. Third, a Dynamic Hierarchical Adaptive Multi-Objective Optimization Framework (DHAMOF) is designed. This framework dynamically adjusts objective weights and constraint boundaries based on real-time operating characteristics, enabling adaptive switching of optimization priorities across diverse scenarios. Furthermore, a closed-loop control architecture comprising “prediction–decision–execution–feedback” is established. By incorporating rolling horizon optimization and a proportional-integral (PI) residual compensation mechanism, the proposed architecture effectively suppresses prediction error accumulation and mitigates communication delays. Simulation results under combined CLTC-P and WLTP driving cycles demonstrate that, compared to conventional fixed-weight strategies, the proposed method achieves an 11.3% reduction in hydrogen consumption, a 30.9% decrease in $SOC$ fluctuation range, and a 55.3% reduction in power tracking error. Moreover, under disturbance scenarios involving prediction errors, sensor noise, and a 200 ms communication delay, the system exhibits superior robustness: the increase in hydrogen consumption is limited to within 8.3 g/100 km, and the power tracking error is reduced by 65.6% relative to uncorrected baselines. This collaborative optimization approach overcomes the limitations of traditional open-loop prediction and fixed-weight control, offering a novel technical pathway for the high-efficiency and stable operation of fuel cell hybrid power systems. Full article

As the global imperative for climate neutrality intensifies, hydrogen (H₂) from fossil fuels remains central to decarbonizing hard-to-abate sectors. Conventional production via steam methane reforming (SMR), however, is carbon-intensive and, even with carbon capture and storage (CCS), incurs energy penalties and long-term storage constraints. This review develops a harmonized well-to-gate, market-oriented framework to evaluate methane pyrolysis (MP) relative to SMR and autothermal reforming (ATR), with or without CCS, moving beyond reactor-focused assessments toward system-level commercialization analysis. MP decomposes methane into hydrogen and solid carbon, avoiding direct CO₂ formation and the need for CCS infrastructure. Integrating with the reverse water–gas shift (RWGS) reaction enables flexible syngas production with adjustable H₂:CO ratios for methanol and chemical synthesis. A central finding is the dominant role of the “carbon lever”: MP generates approximately 3 kg of solid carbon per kg of H₂, making the carbon market’s absorptive capacity the primary scalability constraint. While carbon monetization can reduce levelized hydrogen costs, large-scale deployment would rapidly saturate existing carbon black and specialty carbon markets. Techno-economic evidence indicates that carbon prices above $500/ton are required to achieve parity with gray hydrogen, whereas $150–200/ton enables competitiveness with blue hydrogen. Lifecycle assessments further show that climate superiority over SMR or ATR with CCS requires upstream methane leakage below 0.5% and very low-carbon electricity. Commercial readiness varies, with plasma MP at TRL 8–9 and thermal, catalytic, and molten-media pathways remaining at the pilot or demonstration stage. Parametric decision-space analysis under harmonized boundary assumptions shows that MP is not a universal substitute for reforming but a conditional pathway competitive only under aligned conditions of low-leakage gas supply, low-carbon electricity, credible carbon monetization, and supportive policy incentives. The review concludes with a roadmap that highlights standardized carbon certification, end-of-life accounting, and long-duration operational data as priorities for commercialization. Full article

Wind–solar coupled hydrogen production DC microgrids have significant potential for improving renewable energy utilization and reducing the cost of hydrogen production. However, the randomness of wind–solar power causes frequent electrolyzer start–stop operations, accelerating lifetime degradation, while a single energy storage system cannot simultaneously suppress power fluctuations and regulate energy. Therefore, this study proposes a two-stage day-ahead energy scheduling optimization framework. A DBSCAN–K-means hybrid clustering method generates representative wind–solar power scenarios. A supercapacitor-based strategy mitigates high-frequency power fluctuations using empirical mode decomposition. Furthermore, a dual-scenario-driven electrolyzer scheduling strategy adapted to different wind–solar output conditions is developed, where power allocation is determined by battery state-of-charge and electrolyzer operating states, enabling stepwise power compensation and dynamic operating-state optimization. Case studies comparing wind–solar-only supply, a conventional strategy, and the proposed strategy demonstrate that the proposed strategy balances hydrogen production and economic objectives, and reduces annual electrolyzer start–stop cycles by 73%, thereby prolonging electrolyzer lifetime. Furthermore, the proposed framework enhances renewable energy utilization, reduces curtailment, and lowers lifecycle costs, thereby contributing to the development of sustainable hydrogen production systems. Full article

The storage quality of fresh-cut peach fruit is compromised by weight loss and chromatic aberration. In this experiment, taurine at 30 mg L⁻¹ was applied to fresh-cut peaches to evaluate its effect on storage quality. Changes in weight loss, chromatic aberration, antioxidant system, endogenous nitric oxide (NO) metabolism, endogenous hydrogen sulfide (H₂S) metabolism, and phenylpropanoid metabolism were studied. The results indicated that 30 mg L⁻¹ taurine effectively improved the ability to scavenge ROS, including •OH, O₂^•−, MDA, and H₂O₂, by inhibiting the decrease in the activities of SOD and CAT, enhancing POD activity, reducing PPO activity, and maintaining the AsA-GSH cycle. Moreover, taurine treatment increased the activities of 4CL and PAL and retarded the decrease in the activities of SKDH and C4H, thereby improving the accumulation of total phenols, flavonoids, and lignin. These findings showed that taurine mitigated oxidative damage in fresh-cut peaches by enhancing the antioxidant defense system. Exogenous taurine consistently enhanced NOS-like activity while decreasing NR activity in the early storage phase, and elevated the contents of L-Arginine, nitrite, and endogenous NO. Taurine treatment up-regulated the activities of SAT, L-CD, and OAS-TL, thus promoting endogenous H₂S content in fresh-cut peaches. Taurine alleviated weight loss and chromatic aberration in fresh-cut peaches during storage by enhancing the antioxidant system and modulating NO, H₂S and phenylpropanoid metabolism. Full article

While green hydrogen is vital for sustainable energy transitions, the volatility of renewable power adversely affects the dynamic operation and service life of electrolyzers in integrated energy systems (IESs). To mitigate these effects while minimizing operational costs and extending the service life of electrolyzers, this paper proposes an optimization method for the operation of IESs that considers the dynamic operating characteristics and lifetime degradation of multiple types of electrolyzers. Firstly, detailed models for alkaline (ALK) electrolyzer and proton exchange membrane (PEM) electrolyzer are developed, and their start–stop characteristics and lifetime degradation characteristics are analyzed. Secondly, an optimal operation model for IES is established, taking economy as the optimization objective and considering the dynamic operating characteristics and lifetime degradation of multiple types of electrolyzers. By piecewise linearizing the hydrogen production rate of the electrolyzer, the original model is transformed into a mixed-integer linear programming model for solution. The results indicate that the proposed method can reduce the operational costs of IES, increase the proportion of stable operation time for the electrolyzer, decrease the number of startups and shutdowns, subsequently reduce the cost associated with the lifetime degradation of the electrolyzer, and specifically extend the actual lifetime of the PEM electrolyzer by 12.17% versus its rated life. Ultimately, this approach not only improves the economic viability of the system but also ensures the long-term sustainability of green hydrogen projects by minimizing equipment replacement cycles and maximizing renewable energy accommodation. Full article

The electrochemical reduction of carbon dioxide (CO₂RR) into value-added chemicals using renewable electricity is a pivotal strategy for achieving a sustainable carbon cycle. However, this process is plagued by intrinsic challenges, including poor product selectivity, competing hydrogen evolution, and catalyst instability. Metal–organic frameworks (MOFs), with their highly designable periodic structures, atomically dispersed active sites, and tunable pore microenvironments, have emerged as a uniquely versatile platform to address these issues. This review articulates a multi-scale design philosophy that enables precise steering of the CO₂RR pathway. We systematically elaborate on hierarchical tuning strategies, beginning with molecular-scale engineering of active sites (metal nodes and organic ligands) to define intrinsic activity and intermediate binding. This is synergistically integrated with the optimization of electronic structure and charge transport to overcome conductivity bottlenecks, meso-scale modulation of crystal morphology and defects to enhance mass transport and site accessibility, and the construction of heterogeneous interfaces for tandem catalysis and synergistic effects. Through this coherent, cross-scale design framework, MOF-based catalysts demonstrate exceptional capability in the precise control of reaction pathways, leading to remarkably selective synthesis of target high-value products, from C₁ compounds (CO, HCOOH, CH₄, CH₃OH) to C₂⁺ species (C₂H₄, C₂H₅OH) and urea. Finally, we outline future directions centered on dynamic mechanistic understanding, electrode engineering for industrial current densities, and stability enhancement, thereby providing a comprehensive material design guideline to advance CO₂RR technology. This work positions MOFs as a quintessential tunable catalytic platform for the sustainable conversion of CO₂. Full article

The increasing discharge of synthetic dyes into industrial wastewater necessitates sustainable and low-cost treatment strategies. This study valorizes orange seed powder (OSP), an abundant agro-food residue, as a novel biosorbent for Congo red (CR) removal through a combined experimental and molecular simulation approach. Raw OSP was prepared solely by drying and grinding, without chemical activation, emphasizing its practical applicability and environmental sustainability. Physicochemical characterization using FTIR, SEM, and EDX confirmed adsorption-induced structural and compositional changes. Batch experiments evaluated the effects of initial dye concentration, adsorbent dosage, pH, temperature, and contact time. Equilibrium data were well fitted by the Langmuir and Freundlich isotherm models (R² ≈ 0.99), with a maximum adsorption capacity of 258.39 mg g⁻¹ at 25 °C and pH 4, and a removal efficiency exceeding 99.55%. The adsorption kinetics followed a pseudo-second-order model, while intraparticle diffusion contributed to the rate-controlling mechanism, as indicated by the Weber–Morris model. OSP demonstrated excellent regeneration performance over five adsorption–desorption cycles, retaining more than 96% of its initial CR removal efficiency when regenerated with methanol. Grand Canonical Monte Carlo (GCMC) simulations revealed that adsorption is primarily driven by electrostatic interactions, hydrogen bonding, and π–π stacking interactions, in good agreement with the experimental findings. Overall, raw OSP represents an efficient, regenerable, and sustainable biosorbent, highlighting the originality of integrating experimental investigations with GCMC simulations for wastewater treatment applications. Full article

The proton exchange membrane (PEM) electrolyzer is vital for converting surplus renewable energy (RE) into hydrogen, underpinning the efficient and stable operation of the electric–hydrogen system. However, frequent start–stop cycles and load variations accelerate the degradation of proton exchange membranes and catalyst layers, incurring significant lifetime costs that existing studies ignore. To explore how the PEM electrolyzer’s dynamic traits impact system performance, we introduce an optimized operation approach for the electricity–hydrogen integrated energy system (IES) that incorporates these dynamic features and the novel Loss of Life Cost (LLC) model. Initially, to rectify the inadequacy in modeling the PEM electrolyzer within the current electricity–hydrogen IES operational framework, we integrate its dynamic characteristics based on electrochemical properties and establish a quantitative relationship between operational cycles and degradation costs. This enhanced model accurately reflects how operational conditions affect the electrolyzer’s hydrogen production efficiency and lifetime consumption, enabling precise performance simulation and economic assessment. This, in turn, promotes high-quality renewable energy utilization via hydrogen production while ensuring asset longevity, meeting the rising demand for hydrogen energy applications. Building on this, we further factor in constraints related to diverse energy conversion and safe operation within the electricity–hydrogen IES, as well as the operational limits of hydrogen fuel cells, various energy storage (ES) options, cogeneration units, and other pertinent equipment, aiming to minimize the system’s total daily costs (operational plus degradation costs). Consequently, we develop an optimization operation model for the electricity–hydrogen IES that accounts for the PEM electrolyzer’s dynamic characteristics and degradation economics. Finally, through simulation examples validated against published experimental data, we comprehensively analyze how the PEM electrolyzer’s dynamic traits influence system operation, confirming the effectiveness of our proposed model and methodology. Simulation findings reveal that, under varying electrolyzer capacities, ignoring the PEM electrolyzer’s dynamic characteristics can result in a deviation in system operating. Compared with the proposed method, it can reduce the equipment degradation speed by a maximum of 5.78 times. Full article

Remote off-grid microgrids are often locked into diesel-backed operation because renewable variability creates multi-day and seasonal energy gaps that short-duration batteries cannot economically bridge. This work examines how renewable hydrogen can complement batteries and dispatchable biomass to push an existing hybrid microgrid toward near-autonomous, low-carbon operation, while remaining robust under future electrification demands. The analysis is based on real operational load insights from a remote off-grid system, combined with techno-economic optimization in HOMER Pro. The examined architecture includes PV panels, battery energy storage, a biomass CHP unit, and a diesel generator as backup; the hydrogen pathway additionally incorporates an electrolysis, storage and a PEMFC. Three scenarios are considered: a baseline PV/BAT configuration, an intermediate PV/BAT/BIO configuration that strengthens dispatchable renewable supply and short-term flexibility, and a PV/BAT/BIO/H₂ configuration targeting an increase in renewable energy penetration (REP). Results show that hydrogen integration shifts the system from curtailment-limited, diesel-supported operation to storage-enabled operation: surplus renewable production that would otherwise be curtailed is converted into hydrogen and later dispatched during prolonged deficits, enabling deep diesel displacement without compromising reliability. Hydrogen-enabled configurations achieve 90–99% REP, reduced diesel consumption, and lower CO₂ emissions, primarily by converting curtailed surplus into storable hydrogen. A rule-based EMS highlights technology complementarity across timescales, with batteries providing diurnal balancing and hydrogen covering longer deficits, which also reduces battery cycling stress. Overall, the study clarifies key design trade-offs, especially the need for coordinated PV expansion and storage sizing, and illustrates how a multi-storage portfolio can support high renewable penetration in such systems. Full article

This study proposes a CO₂ re-liquefaction system utilizing the cold energy of LNG and liquid hydrogen (LH₂) to efficiently manage boil-off gas in alternative fuel-based CO₂ carriers. Process simulations using Aspen HYSYS V11 under 100% and 70% propulsion loads evaluated the Specific Energy Consumption (SEC), Coefficient of Performance (COP), UA of heat exchangers, and Specific Life Cycle Cost (SLCC). The results demonstrate that under both 100% and 70% propulsion load conditions, the utilization of cold energy decreases the SEC by 24.5% and improves the COP by approximately 34% compared to the reference model without cold energy utilization. Sensitivity analysis on the minimum temperature approach indicates limited impact on performance. The UA of the heat exchangers decreased by up to 83% (LNG) and 87% (LH₂), offering significant downsizing advantages. Economically, SLCC was reduced by up to 14.8% and 15.9% for the LNG and H₂ models, respectively, due to lower Capital Expenditure (CAPEX) and Operating Expenditure (OPEX). Consequently, this study demonstrates that exploiting the cold energy of alternative fuels significantly improves both the thermodynamic performance and economic feasibility of CO₂ re-liquefaction systems, providing foundational data for future optimization. Full article

Hydrogen is increasingly adopted as a clean energy carrier for storing and transporting low-carbon energy. Achieving a practical volumetric energy density for real-world deployment typically requires compression to several hundred bar, which in turn demands dedicated high-pressure infrastructure. Because valves are indispensable for isolation and flow control within this infrastructure, durable sealing valve materials become a key reliability and safety requirement. This assembly-level screening study compares two valve configurations with different polymer assemblies: EPDM O-rings with PEEK seats/bushing and NBR O-rings with POM seats/bushing. Four new identical 500-bar ball valves were tested (two EPDM/PEEK and two NBR/POM). For each seal configuration, one valve was cycled 5000 times at 500 bar in helium (inert baseline), and a second identical valve was cycled 5000 times at 500 bar in hydrogen to isolate hydrogen effects from mechanical/metallic wear. Leakage was tracked during cycling, and seals were analyzed by SEM/EDX after testing. The EPDM/PEEK configuration remained leak-tight in both gases, with no cracking observed in the elastomer or thermoplastic components. The NBR/POM configuration exhibited POM bushing fracture during cycling and minor external leakage at the stem during the hydrogen phase, accompanied by micro-fissures on the NBR O-ring surface. EDX indicated composition changes after cycling, including oxygen and fluorine enrichment and occasional metallic transfer species, consistent with surface films and deposits. Under the present valve geometry and cycling protocol, EPDM/PEEK provided robust sealing, whereas NBR/POM showed failure modes relevant to high-pressure service. These findings are intended as configuration-level screening evidence to be used in valves rather than as a full qualification of the individual materials. Full article

The development of efficient, stable, and sustainably fabricated photocatalysts for solar-driven hydrogen evolution remains a critical challenge in the field. Herein, we report a novel green coprecipitation strategy to synthesize calcium-doped zinc oxide (Ca-ZnO) nanosheets, utilizing cactus juice as a natural, multifunctional medium for the coprecipitation process. This method enables the in situ, tunable incorporation of 3–7% Ca²⁺ ions into the wurtzite ZnO lattice without the use of harsh chemical reagents. Comprehensive characterization confirms that Ca²⁺ substitutionally replaces Zn²⁺, which preserves the intrinsic crystal structure of ZnO well while inducing the formation of uniform nanosheet morphology. This doping strategy effectively modulates the electronic band structure, progressively narrowing the bandgap from 3.19 eV to 2.90 eV and significantly enhancing visible-light absorption. Crucially, the incorporation of Ca²⁺ also generates oxygen vacancies, which serve as efficient electron traps to suppress photogenerated charge carrier recombination. The optimized 5%Ca-ZnO photocatalyst demonstrates a favorable hydrogen evolution rate of 889 μmol·g⁻¹·h⁻¹ under full-spectrum irradiation, with stability, retaining 94.8% of its activity after four cycles. This work not only provides a high-performance material but also establishes a generalizable, sustainable paradigm for the design of advanced semiconductor photocatalysts. Full article