Search Results (7,035)

Studies on the use of LPG in maritime applications mostly evaluate emissions, engine performance, or system safety separately; approaches that integrate experimental findings with ship-level risks remain limited. This study aims to evaluate the trade-offs between the environmental advantages of LPG and energy performance and safety requirements within a common decision support framework. In the experimental phase, a single-cylinder gasoline–LPG spark-ignition engine was tested at five LPG mixture ratios and six load levels between 500–3000 W; specific fuel consumption, thermal efficiency, CO, CO₂, and HC were measured. Using legislation, the literature, and engineering evaluation, 38 failure types were identified from the experimental findings and prioritized using FMEA and entropy-weighted multi-criteria decision-making methods. The final ranking was obtained using the Borda method, and inter-method agreement and ranking stability were validated with sensitivity analyses. The results showed that increasing the LPG ratio reduced CO, CO₂, and HC emissions, but higher ratios increased fuel consumption and decreased thermal efficiency. Specific fuel consumption, gas detection error, and thermal efficiency were identified as the three most prioritized risks. The findings reveal that the emission benefits of LPG in maritime applications should be evaluated in conjunction with sensing, insulation, emergency stop reliability, and energy performance. This integrated approach provides a scientific basis for balanced and transparent fuel decisions. Full article

Hybrid-electric powertrains offer a solution to significantly reduce aircraft emissions in flight. This study presents a method that couples the generative design of hybrid-electric architectures with reinforcement learning for the optimization of their control parameters. The application proposed is the retrofitting of an ATR-72 with the objective of identifying an optimal green architecture. The results show that a promising candidate is a dual fuel powertrain combining a gas turbine and fuel cells. Compared with a conventional architecture, this concept reduces ${\mathrm{CO}}_2$ and ${\mathrm{NO}}_x$ emissions by up to 74% and 86%, respectively, incurring a payload mass penalty of only 24%. Full article

The growing deterioration of water resources and the energy requirements of conventional wastewater treatment technologies have increased interest in systems that combine organic matter removal with bioelectrochemical conversion. This study evaluated a laboratory-scale dual-chamber microbial fuel cell (MFC) operated with real wastewater using Scenedesmus acutus (S. acutus) and a native microbial consortium as anodic biocatalysts at 25 and 30 °C. The system was assessed through continuous monitoring of voltage, pH, temperature, and CH₄, H₂, and CO₂ signals in the anodic headspace, together with physicochemical characterization and chemical oxygen demand (COD) removal. COD removal efficiencies of 33.7 and 30.3% were obtained for S. acutus at 25 and 30 °C, respectively, whereas the native microbial consortium achieved 29.8 and 43.4% removal under the same conditions. The consortium at 30 °C showed the most favorable combination of COD removal and electrical response, whereas S. acutus at 30 °C reached the highest maximum voltage and stored energy, although with greater signal variability. The CH₄, H₂, and CO₂ signals differed among conditions and were consistent with the possible participation of fermentative and methanogenic processes alongside electrogenic activity, although gas production rates and the contribution of individual pathways were not quantified. Overall, the results demonstrate the operational feasibility of the proposed MFC for coupling wastewater treatment with a measurable electrical response and support further evaluation of native microbial consortia as anodic biocatalysts. Full article

Park-level integrated energy systems with high shares of wind and photovoltaic power face pronounced seasonal source–load mismatches, renewable energy curtailment, and low-carbon operation challenges. This paper proposes a capacity planning method considering seasonal salt-cavern hydrogen storage and adaptive representative days. An electricity–heat–cooling–hydrogen coupled system is established by integrating renewable generation, conventional conversion units, short-term storage, electrolyzers, fuel cells, and salt-cavern hydrogen storage, together with waste-heat recovery and tiered carbon trading. To represent interseasonal hydrogen transfer under representative-day modeling, a seasonal hydrogen inventory formulation based on weighted net hydrogen changes is developed, considering cushion gas, storage bounds, injection and withdrawal efficiencies, and flow-rate limits. A season-specific adaptive K-medoids method based on CRITIC evaluation is further proposed to determine the number of representative days, while zero-weight extreme days are introduced to verify capacity feasibility under boundary conditions. The optimization objective is to minimize annualized total cost. Case studies show that removing seasonal hydrogen storage increases total system cost by 23.63%, raises wind and photovoltaic curtailment from 1.81% to 13.09%, and increases carbon emissions by 13.74%. The proposed method improves economic, renewable-energy-utilization, and low-carbon performance. Full article

As fossil fuels are being replaced by lower-carbon alternatives, the EU renewable energy directives RED II/III mandate increases in the proportion of advanced biofuels within liquid fuels, aiming to reduce greenhouse gas emissions over first-generation biofuels. It is crucial to study how these fuels affect engine performance to ensure they also meet emissions standards of relevance to air quality. Advanced biofuels, mainly from lignocellulosic feedstocks, are promising options. This work tested model butanolysis-derived blends using hydrotreated vegetable oil (HVO) as the base fuel, due to its lower carbon footprint, favourable combustion properties, and potential to replace diesel without engine modifications, along with ultra-low sulphur diesel (ULSD). Physical properties such as density and flash point were tested on the butyl-based biofuel blends. The measured densities fell between those of pure HVO and ULSD, while the measured flash points exceeded the minimum standards required for fuels. This study examines the use of such blends with a EU Stage V emission compliant Yanmar L100V compression ignition (CI) engine as part of a generator set, using model butanolysis biofuel mixtures blended with HVO at various ratios. A CI engine was chosen because generators, off-road machinery, heavy-duty vehicles, and marine vessels will continue to rely on CI engines for the foreseeable future. Ignition delays (IDs), brake-specific fuel consumption (BSFC), gaseous and particulate matter (PM_2.5) emissions were determined. Gaseous emissions were measured with a Horiba MEXA7100D, and PM_2.5 was collected on filters for gravimetric analysis. All blends, including pure HVO, had shorter IDs than diesel. Emissions of nitrogen oxides (NOx = NO + NO₂), carbon monoxide (CO), and total hydrocarbons (THC) decreased compared to diesel. PM_2.5 levels dropped with the additions of advanced biofuels relative to pure HVO and ULSD. CO emission factors were below EU Stage V limits, but slight exceedances occurred for THC and NOx. Full article

Electric vehicles are rapidly reshaping global transportation, emerging as a central pillar of efforts to cut greenhouse gas emissions and end dependence on fossil fuels. This review provides a critical and integrative synthesis of recent advances in electric vehicle technologies, focusing on three interconnected domains: battery innovations, charging strategies, and grid integration. Progress in high-energy-density lithium-ion chemistries, emerging solid-state and sodium-ion batteries, and advanced battery management systems is examined with respect to their implications for driving range, safety, and lifecycle sustainability. Charging infrastructure developments, including fast and ultra-fast charging, wireless charging, and battery-swapping networks, are evaluated in terms of technical feasibility, grid impact, and user adoption. The evolving role of EVs in enhancing energy system flexibility is further analyzed through vehicle-to-grid (V2G) and smart grid interactions, with emphasis on control algorithms, grid stability, and renewable energy integration. By critically analyzing recent literature, this review identifies key technological, infrastructural, and system-level challenges, as well as emerging research directions that require coordinated optimization across domains. The insights presented aim to guide future research, technology development, and policy design toward the realization of a resilient, efficient, and scalable electric mobility ecosystem. Full article

Ammonia, as a hydrogen carrier and carbon-free alternative fuel, shows great potential in future low-carbon energy systems. This study uses dimethyl ether (DME) as a combustion promoter for ammonia to enhance the combustion performance of ammonia-fueled engines. To address the issue of unburned ammonia emissions, the original combustion chamber geometry was optimized by removing the squish area to enhance flame propagation. At an ammonia energy ratio (AER) of 60%, the modified combustion chamber (MCC) reduces unburned ammonia (uNH₃) emissions by up to 85.46% and improves indicated thermal efficiency (ITE) by 1.93% compared to the original combustion chamber (OCC). Furthermore, to achieve higher thermal efficiency and lower pollutant emissions, the DME injection strategy was redesigned based on the MCC. The results show that adjusting the single injection timing (SIT) and injection angle (INA) of DME can effectively improve the homogeneity of the in-cylinder combustible mixture and enhance combustion efficiency; however, overly concentrated injection can lead to rapid heat release and increase the risk of knock. The split injection strategy enables more controllable combustion phasing, significantly reduces the maximum pressure rise rate (MPRR) and ringing intensity (RI), and mitigates knocking tendency. When the main injection timing (MIT) is −5 °CA ATDC, pilot injection timing (PIT) is −30 °CA ATDC, and the pilot injection ratio (PIR) is 60%, the ITE reaches 49.98%, which is 3.53% higher than that of the pure diesel mode. Greenhouse gas (GHG) and NO_x emissions are reduced by 45.94% and 62.49%, respectively, with uNH₃ emissions as low as 4.16 g/kW·h. Full article

This study evaluates the effects of hydrogen enrichment of compressed natural gas (HCNG, CNG) on particle number emissions and particle size distribution in a dual-fuel compression-ignition (CI) engine. The experiments were conducted using a Fiat 1.3 MultiJet engine operated with conventional diesel fuel, diesel–CNG, and diesel–hydrogen-enriched CNG. Measurements were performed over a range of engine speeds, loads, and energy-substitution conditions. The hydrogen volume fraction in the gaseous fuel ranged from 5–10 vol.% to 53 vol.%. Particle size distributions were measured using an ELPI+ impactor. The use of CNG and hydrogen generally reduced soot-particle emissions in the accumulation mode, particularly within the particle-diameter range of approximately 0.03–0.2 µm. However, under some operating conditions, the number of ultrafine particles increased, particularly in the sub-23 nm range. This finding indicates a transition from a particle-formation mechanism dominated by soot formation and agglomeration to one dominated by nucleation and condensation. This phenomenon is associated with suppressed soot-precursor formation, enhanced soot oxidation by OH radicals, and a reduction in the surface area available for the condensation of volatile components. The effect of hydrogen depended on the engine operating point (EOP) and did not always scale linearly with hydrogen concentration. The results confirm that evaluating alternative fuels solely on the basis of particulate mass is insufficient. Particle number, particle size distribution, and the sub-23 nm fraction must also be considered. Full article

Taxi fleets operate intensively, accumulate high annual mileage, and contribute disproportionately to urban greenhouse gas emissions, making them attractive candidates for transport electrification. Despite growing interest in electric mobility, integrated evaluations of the environmental, energy, and economic implications of taxi fleet electrification remain limited, particularly for medium-sized cities in Türkiye. This research examines the replacement of the commercial taxi fleet operating in the central districts of Denizli with battery electric vehicles (BEVs) through a framework that integrates operational emission estimation, electricity demand, charging infrastructure, and life-cycle cost analysis (LCCA). Operational emissions were quantified using the IPCC Tier 1 fuel-based approach together with a distance-based consistency check. Under the adopted assumptions, electrification reduced annual operational CO₂ emissions by 4217.48 tCO₂ (57.9%). The electrified fleet required 18.36 MWh of electricity per day (6.70 GWh annually), while estimated peak charging demand varied between 1.22 MW and 5.57 MW, depending on the charging strategy. Economic evaluation showed a positive net present value (NPV) of 1.32 million TL per vehicle, an internal rate of return (IRR) of 80.86%, and a discounted payback period (DPP) of 1.37 years. Although profitability varied with energy prices, vehicle costs, and annual mileage, fleet electrification remained economically feasible across all scenarios considered. These results suggest that electrifying commercial taxi fleets can support urban decarbonization while remaining financially attractive when accompanied by appropriate charging infrastructure and coordinated transport planning. Full article

Maritime transport is a major component of global supply chains, but reducing its atmospheric emissions remains essential to improving the environmental sustainability of shipping. This study analyzes onboard emission data reported for the MV Ilshin Green Iris under real-world operating conditions to assess how fuel selection affects the direct-emission performance of a dual-fuel marine propulsion system. The vessel is equipped with a MAN B&W 6G50ME-C9.5-GI engine employing high-pressure dual-fuel (HPDF) technology. A quantitative comparison between heavy fuel oil (HFO) and liquefied natural gas (LNG) was performed at 50% of the maximum continuous rating (MCR). At 50% MCR, LNG reduced CO₂ emissions by 27.0%, NOx emissions by 20.7%, and CO emissions by 18.2% relative to HFO, while PM showed an indicative reduction of approximately 69%; its precise magnitude remains uncertain because a complete PM uncertainty budget was unavailable. Over the 900 s measurement period, the estimated reduction in CO₂ mass was 154 kg. During LNG operation, the specific CH₄ emission at 50% MCR was approximately 0.6 g/kWh. Using a 100-year global warming potential of 29.8 for fossil CH₄, this corresponds to approximately 17.9 g CO₂-eq/kWh, equivalent to about 10.5% of the direct CO₂ reduction between HFO and LNG at this operating point. The results are representative of the analyzed stabilized operating point rather than of the vessel’s complete operational profile. The main contribution of this study is a structured matched-load analysis of HFO and LNG emissions from the same HPDF marine engine. The analysis combines measurement-derived specific emissions with energy-based mass estimates, methane-related limitations, data-quality considerations, and regulatory and sustainability implications. Because both fuels were evaluated in the same engine at the same 50% MCR operating point, the study provides a consistent basis for assessing fuel-related differences within the limits of the available dataset. Full article

Reactivity-controlled compression ignition (RCCI) enhances engine performance while mitigating the diesel soot–NO_x tradeoff. In this work, natural gas (NG) RCCI combustion was investigated on a heavy-duty single-cylinder research engine with three different pilot fuels: diesel, an 80/20 (% v/v) blend of n-butanol and diesel (80B20D), and dipropyl oxymethylene ether (P1P). The experiments were performed at a constant speed of 1339 rev/min, a fixed load (IMEP_g = 5 bar), and 1.5 bar boost pressure. Initially, NG RCCI combustion was studied under identical operating conditions, and subsequently with constant combustion phasing (CA50) for all pilot fuel–NG combinations for a levelized comparison. The results revealed that CA50 profoundly impacted the efficiency and unburned hydrocarbon (HC) emissions for all pilot fuels. Maintaining an optimal CA50 of 363 ± 1 CAD, high fuel conversion efficiencies (~40%) and HC emission reductions (~38–49%) were achieved across pilot fuels. The pilot fuel reactivity significantly affected combustion and emissions. The apparent heat release histories transformed from a two-stage to a single-stage Gaussian profile at a much-retarded start of injection (SOI~30 bTDC) for 80B20D-NG compared to diesel–NG and P1P-NG (40 bTDC), leading to significantly lower NO_x emissions. More advanced SOIs and lower NO_x emissions were possible with diesel–NG and P1P-NG compared to 80B20D-NG. Full article

Geopolitical disruptions of natural gas supply have repeatedly forced importing countries to reorganize their electricity systems, yet it remains unclear whether such disruptions are followed by movement of structurally different economies toward comparable energy-security and sustainability outcomes. This study compares Germany, a high-income economy exposed to the 2022 curtailment of Russian pipeline gas, with Jordan, a developing import-dependent economy exposed to the repeated sabotage of the Arab Gas Pipeline after 2011, using harmonized generation-mix and carbon intensity data for Germany over 1985–2024 and Jordan over 2000–2022, supplemented by weekly German market data. The generation fuel mix concentration is measured with a Herfindahl-based Supply Concentration Index (SCI), structural change is estimated with segmented interrupted time series (ITS) regressions inferred through Newey–West heteroskedasticity- and autocorrelation-consistent standard errors, and the joint security–sustainability position of each country is summarized with a newly proposed Energy Vulnerability–Transition Index (EVTI) that combines diversification, renewable penetration, and carbon intensity performance. The results show that Jordan’s 2011 disruption was associated with a baseline estimated change in its carbon intensity trajectory from +3.32 to −12.63 gCO₂/kWh per year and with renewable growth of +2.39 percentage points per year from a near-zero base, while Germany’s 2022 disruption was associated with a temporary carbon intensity shock, visible in a coal reactivation index that peaked at 1.26 and a sixfold wholesale price increase, followed by a policy-supported return to the pre-existing decarbonization pathway. The Germany–Jordan EVTI ratio narrowed from 6.5× in 2014 to 1.8× in 2022, and this convergence is robust to alternative component weightings. The findings indicate that geopolitical gas disruptions, despite their high short-run costs, were followed in both contexts by measurable movement toward more diversified and lower-carbon electricity systems, with direct implications for Sustainable Development Goal (SDG) 7. Full article

Carbon capture is more and more often seen as a component of an integrated carbon-management system than as a stand-alone separation phase. The practical utility of capture technology depends on the chemical state in which the carbon dioxide is held, the energy and material needs for regeneration, the compatibility of the caught species with downstream catalysis and the lifetime of the resulting carbon-containing product. This paper offers an in-depth framework for integrated CO₂ capture and circular carbon use, including catalytic conversion, bio-integrated processes, biomass-derived materials and fuels, hydrogen-enabled routes, mineralization, and artificial intelligence-assisted process design. Reactive capture techniques that convert carbonate, bicarbonate, carbamate, dissolved CO₂ or surface-bound intermediates without first generating a purified gas stream are contrasted with sequential capture, purification, compression, transport and conversion. The thermocatalytic, electrochemical, photoelectrochemical and biological conversion pathways are compared against common parameters such as working capacity, conversion rate, selectivity, carbon efficiency, regeneration energy, stability and life-cycle greenhouse gas performance. Special emphasis is given on dual-functional materials, interfacial reactors, bio-integrated methanation, carbon mineralization in construction materials and coupling with renewable hydrogen. The review also discusses how machine learning, molecular screening, process simulation, graph-based data architecture, and digital monitoring could speed up material selection and system optimization. Across all pathways, the central design requirement is not maximum capture capacity alone, but a balanced match among binding strength, transport, catalytic reactivity, product separation, durability, and carbon permanence. A reporting framework and research agenda are proposed to guide credible scale-up and comparison of integrated carbon-management technologies. Full article

Green hydrogen is a key energy carrier in Power-to-Liquid (PtL) pathways for the production of sustainable synthetic fuels, contributing to the decarbonization of the industrial and transport sectors. However, the intermittent nature of renewable energy sources and the variable hydrogen requirements needed to maintain the appropriate stoichiometric ratio for synthesis processes necessitate regulating hydrogen production according to process demand, rather than maximizing its generation. This article proposes an intelligent control strategy for alkaline water electrolysis, in which the hydrogen production target is determined from the stoichiometric requirements of synthetic methanol production, based on available carbon dioxide. ANN models were developed using the experimental data, incorporating both classical and conformable activation functions in the hidden layer. Based on the selected models, the ANNi was formulated, and PSO and GA were used to determine the required feed current according to hydrogen demand. The proposed methodology was evaluated under a dynamic hydrogen-demand profile derived from the stoichiometric requirements of methanol synthesis. The results show that the proposed controllers closely track changes in hydrogen demand. After each change in the setpoint, the H₂/CO₂ ratio returned to a $\pm 2\%$ band around the stoichiometric setpoint in approximately 0.98 s for ICANNi-PSO and 0.96 s for ICANNi-GA. Furthermore, some conformable activation functions achieved performance comparable to that of classical activation functions while using fewer neurons in the hidden layer. Both optimization algorithms provided comparable tracking performance under the evaluated conditions. Full article

The imperative to mitigate climate change has accelerated the development of Carbon Capture, Utilization, and Storage (CCUS) technologies, particularly CO₂ hydrogenation into high-value chemicals and alternative fuels. This work evaluates the fundamental thermodynamic limitations and the primary directions of CO₂ conversion, with a primary focus on methanation, alongside related pathways such as methanol synthesis and the reverse water-gas shift (RWGS) reaction. To overcome the high kinetic barriers of CO₂ activation, various catalytic systems are analyzed. While noble metal catalysts exhibit high catalytic performance, nickel-based catalysts serve as a viable and cost-effective alternative. To overcome nickel’s susceptibility to thermal sintering and coking, advanced bimetallic and multimetallic formulations are being developed to enhance structural stability and selectivity. These advancements are crucial for producing Synthetic Natural Gas (SNG) and sustainable aviation fuels (SAF). Ultimately, the objective of this comprehensive review is to systematically summarize recent advancements in catalyst design, critically analyze the advantages and fundamental bottlenecks of distinct catalytic systems, and outline prospective paths for the efficient industrial-scale production of sustainable alternative fuels. Full article