Pathways to maritime decarbonisation: analysing alternative fuels across vessel classes

The quality of biomass briquettes is largely determined by the type of raw material and the manufacturing process, especially in efforts to develop waste-based alternative fuels. This research analyzes the effect of the combination of coconut shells with cassava skins and corn husks on the physical properties and burning rate of briquettes using tapioca flour adhesive. Test results show that variations in biomass produce significantly different combustion characteristics. Cassava husk–coconut shell based briquettes showed a higher combustion rate (0.24 g/minute), while corn husk–coconut shell briquettes produced more stable combustion with a lower rate (0.17 g/minute). Even though the water content of the two briquettes is still within acceptable limits, the high ash content (>25%) is the main limiting factor because it does not meet the SNI 01-6235-2000 standard and has the potential to reduce energy efficiency. These findings confirm that the selection of biomass type and control of the carbonization process play a crucial role in determining the performance of briquettes. Optimizing production parameters is needed so that agricultural waste-based biomass briquettes can be developed as an alternative fuel that meets national quality standards and supports a sustainable energy transition.

With the increasing stringency of international decarbonization regulations, the maritime industry is accelerating the application of low-carbon alternative fuels. Among them, methanol is considered one of the most promising alternatives due to its low carbon content, clean combustion and easy-storage characteristics. When applied to marine engines, methanol is typically used in combination with a certain amount of diesel to ensure stable ignition and combustion, resulting in a methanol/diesel dual fuel engine configuration. For methanol/diesel dual fuel engines operating under port injection (PI) mode, abnormal combustion phenomena—such as misfire at low loads and knock at high loads—often occur, which limit further increases in the methanol substitution ratio (MSR). In this study, a three-dimensional simulation model was developed and validated by using experiment data from a natural gas/diesel dual fuel engine, which is then modified to a methanol/diesel dual fuel engine model considering the differences in fuel property and combustion reaction kinetics mechanism. The modified engine model is employed to investigate the effects of MSR on the combustion and emission characteristics under various operating conditions. The characteristics of abnormal combustion phenomenon—misfire and knock—were analyzed, whilst the maximum MSR under various engine operating loads were predicted. Additionally, the effects of three knock-related factors, that is, initial gas temperature (IGT), exhaust gas recirculation (EGR), and start of injection (SOI), were analyzed under the commonly used 85% operating load. Subsequently, a multi-objective optimization was performed to determine the optimal combination of the abovementioned three factors. Results indicate that the optimal performance was achieved when EGR = 12%, SOI = 2.5°CA, and IGT = 348 K. Under this strategy, the ringing intensity (RI) was reduced by 95.07%, enabling stable combustion at 50% MSR. Simultaneously, NOx emissions were reduced by 73.95%. Although the output power of methanol/diesel dual fuel engine decreased by 6.89% compared to that before the optimization, it still showed an 11.75% improvement over the baseline output power of natural gas/diesel dual fuel engine at 85% load.

With the growing emphasis on developing clean fuels to reduce emissions, hydrogen has become a critical focus due to its potential for lowering environmental impact. However, the operational challenges in lean fuel systems, particularly combustion instability, highlight the necessity of parametric studies to ensure stable performance with alternative fuels. This study numerically examines the thermoacoustic instability of pure hydrogen and methane in a Rijke tube combustor using the Unsteady Reynolds-Averaged Navier-Stokes method. The investigation focuses on two distinct instability behaviors: beating and limit cycle oscillations. Key findings reveal that for both fuels, increasing the equivalence ratio toward richer mixtures tends to damp thermoacoustic instabilities. It was observed that a 20% increase in fuel flow rate caused a transition from beating to limit cycle oscillations. A comparative analysis shows that lean methane flames produce stronger fluctuations, whereas hydrogen has a wider instability range under fuel-rich conditions. Advanced modal analysis using Dynamic Mode Decomposition identifies the dominant longitudinal acoustic modes and localized oscillations near the fuel nozzle that influence flame structure. These results provide critical insights into the unique thermoacoustic characteristics of hydrogen and methane, which can inform the design of stable, next-generation combustion systems.

The development of high-performance gas sensors is crucial for ensuring safety and efficiency in the emerging hydrogen economy, particularly for detecting hydrogen (H2) and ammonia (NH3), which are essential for hydrogen storage, transportation, and energy applications. Hydrogen is highly flammable, with a lower explosive limit of 4%, while ammonia is toxic and can cause severe health hazards; thus, their early and accurate detection is critical to prevent accidents and ensure safe handling. However, most hydrogen sensors exhibit cross-sensitivity to ammonia, making it challenging to distinguish between the two gases. Additionally, blends of ammonia and hydrogen are considered as alternative fuels to achieve zero-carbon emissions. Detecting them in mixture form is essential, as the flammability and toxicity limits of the mixture differ from those of the individual gases, requiring precise monitoring for safety, process optimization, and efficient fuel utilization. In this study, we employ palladium (Pd) nanoparticle-decorated electrostatically formed nanowire (Pd-EFN) sensor for the selective detection of H2, NH3, and their mixtures at low concentrations. The EFN sensor, a multiple-gate depletion-mode field-effect transistor (FET) fabricated using complementary metal-oxide-semiconductor (CMOS)-compatible processes, provides unique multigate electrostatic control, enabling enhanced sensitivity and selectivity. Experimental results demonstrate a highly reversible response, with distinct "electrostatic fingerprints" observed across different back-gate voltages, allowing for improved gas differentiation. Using supervised machine learning techniques including Linear and Kernel Support Vector Machine, AdaBoost, Gradient Boosting, Extra Trees, Random Forest, Decision Tree, Linear Discriminant Analysis, and K-Nearest Neighbors, we achieved up to 94% classification accuracy in distinguishing H2 vs NH3 and H2 vs (NH3 + H2), respectively. Additionally, adopting a transfer learning approach using the VGG-19 neural network and leveraging sensor response maps as inputs, further improved accuracy to approximately 97 and 96%, respectively. Furthermore, the ability to discern the individual gases and the mixture (H2/NH3/(NH3 + H2)) was improved from 77 to 87% with the use of transfer learning. The ability to selectively identify individual gases and their mixtures using a single sensor with high accuracy, without the need for sensor arrays, paves the way for advanced, miniaturized, and cost-effective gas sensing platforms, demonstrating potential for real-world applications in hydrogen safety and environmental monitoring.

Future emissions assessment of mersin international port (MIP) with hydrogen fuel and the other alternative fuels

The need for energy and environmental concerns are driving the demand of efficient, sustainable fuels as transportation fuels. This article is an inquiry on energy efficiency improvement in internal combustion engines using alternative fuels under the scenario of Bangladesh. A Quantitative research design was adopted, primary data were obtained from 400 respondents through a structured questionnaire developed by applying Cochran’s sample size formula. The interviewers were vehicle owners, operators, drivers, and mechanics with first hand practice in fuel consumption and engine performance. Statistical analysis was performed by SPSS and descriptive statistics were utilized to analyze trends and associations. The results show that biofuels offer good options to improve fuel economy, engine performance and reduce pollutants when compared with conventional petroleum fuels. The engine optimization strategies include appropriate tuning and maintenance which were also identified as significant factors for achieving efficiency results. However, the research also highlighted some bottlenecks, such as high conversion costs, inadequate refueling infrastructure, fuel quality variation and a shortage of qualified repairmen that may limit the widespread use. The paper finds that there is potential for alternative fuels to contribute towards sustainable transport and energy efficiency in Bangladesh. Policy support, infrastructure development, technical capacity building, and regulatory oversight are suggested to smooth the transition towards cleaner fuel technologies and sustainable environment in the long run.

The depletion of petroleum reserves, rising fossil fuel demand, and increasing plastic waste pollution highlight the need for alternative fuels. This study investigated the performance and exhaust emissions of a direct-injection diesel engine fueled with waste cooking oil biodiesel blended with plastic pyrolysis oil at concentrations of 5%, 10%, 15%, and 20% (B+A5 to B+A20). Biodiesel was produced through degumming, esterification, and transesterification, while plastic pyrolysis oil was obtained via thermal cracking. Engine tests under a constant load across a range of engine speeds evaluated brake power, brake-specific fuel consumption (BSFC), brake thermal efficiency (BTE), and exhaust emissions. The results indicate that increasing the proportion of plastic pyrolysis oil improved engine performance compared to pure biodiesel. The B+A20 blend provided the best overall performance, with 44.4% higher power output, 39.6% higher BTE, and 30% lower BSFC than biodiesel, although performance remained below conventional diesel. Regarding emissions, B+A20 reduced CO by 16.3% relative to biodiesel and slightly reduced CO₂ (1%), while NOx increased by 59.7%, highlighting a trade-off between improved performance and NOx control. Overall, blending waste cooking oil biodiesel with plastic pyrolysis oil enhances renewable fuel performance and valorizes plastic waste, but further measures are needed to mitigate NOx emissions.

The International Maritime Organization's (IMO) decarbonization targets necessitate adopting alternative fuels. Liquefied Natural Gas (LNG), regulated by the International Code of Safety for Ships Using Gases or Other Low-Flashpoint Fuels (IGF Code), offers potential emission reductions but faces debates regarding methane slip and cost-effectiveness. This meta-analysis synthesized 48 peer-reviewed studies (2015–2024) following PRISMA guidelines. Random- effects models quantified LNG’s performance versus conventional fuels (HFO/MDO) in emissions (CO₂eq, SOₓ, NOₓ, PM), economics (CAPEX/OPEX), and safety. Heterogeneity was assessed via I² statistics. LNG reduces SOₓ by 98% (95% CI: 96–99), NOₓ by 25% (18–32), and PM by 93% (88–97). Net CO₂eq reduction is 12% (5–19) after methane slip adjustment (0.2–5%). CAPEX is 25% higher (SMD = 1.8; 1.5–2.1), but OPEX is 22% lower (SMD = -1.2; -1.8 to -0.6). Safety incidents are 1.8× more likely (OR = 1.8; 1.2–2.7), mitigated by IGF-compliant training (OR = 0.6; 0.4–0.9). LNG achieves immediate air quality benefits but requires methane slip abatement for climate goals. Policy priorities include bio-LNG blending and global bunkering standardization

The shipping industry is undergoing a critical phase of green transition, in which seafarers constitute the core driving force of decarbonization. As this transition deepens, seafarers’ roles are undergoing a dual transformation: from reliance on traditional mechanical labor to functions empowered by digital and intelligent technologies, and from exclusively shipboard operations to integrated cooperation with shore-based control and support. However, seafarers are confronted with multiple protection deficits throughout the green transition, with issues of energy justice becoming increasingly prominent. Specifically, complex combinations of alternative fuels intensify seafarers’ operational burdens, safety risks associated with clean fuels threaten their physical and mental health, and the fragmented landscape of global emissions regulations significantly heightens their exposure to legal liability. In response, this paper advocates for the Just Transition principle as the guiding framework: adopting fixed-route operation models to alleviate seafarers’ fuel-handling pressures, implementing specialized training schemes to mitigate health risks, and promoting a cautious application of criminal liability and reasonable exemptions for seafarers within evolving decarbonization-related liability regimes. This paper provides a valuable contribution to advancing the global shipping decarbonization process while balancing environmental sustainability with the protection of seafarers’ rights and interests.

Two of the most environmentally critical and operationally challenging maritime environments anywhere in the world are the Red Sea and the Arabian Gulf. The shallow waters and high salinity levels, along with unprecedented sea surface temperatures and growing traffic from commercial vessels, are presenting major challenges to conventional design concepts that are highly unlikely to overcome the challenges for ship designs. In addition, there are global environmental statutes and regional sustainability agendas, especially within the Middle East, which put a greater focus on greener and more efficient maritime practices. This paper presents an examination of sustainable ship design concepts, focusing specifically on the environment of the Red Sea and the Arabian Gulf. The present paper critically reviews major dimensions of ship design, such as ship optimization, propulsion systems, energy-efficient technologies, alternative fuels, and environmentally adaptable materials, through a comprehensive review of recent developments in naval architecture with an analytical synthesis of advances made in marine engineering and sustainable technologies. Furthermore, this research also identifies the applicability of new concepts of sustainable ship design regarding international maritime legislation and regional policy, considering sustainability factors involved with regional economic and environmental growth. The research shows that fuel efficiency, emission reduction, and consequently environmental protection could be substantially achieved with regionally tailored design approaches, along with improved ships' operational performance and reliability. A conceptual framework for sustainable ship design, incorporating environmental constraints, adopting technological advancement, and adhering to regulations, has been presented in the paper.

The present study investigates the formulation of surrogatesforJet-A and sustainable aviation fuel (SAF) by means of a chemical reactornetwork (CRN) to predict emissions in gas-turbine combustors. Themodeling framework is used to analyze the effects of fuel composition,specifically the replacement of Jet-A with SAF as well as the substitutionof aromatics in Jet-A with cycloalkanes. This approach enables theexamination of the effects of the fuel class and molecular structureindependently of global exhaust emission trends. A comprehensive chemicalkinetic mechanism incorporating 8478 species and 33,318 reactionswas used to model jet fuel surrogates. This mechanism, validated againstignition delay times, laminar flame speeds, and extinction strainrates, accurately predicted combustion characteristics for iso-cetaneand iso-dodecane, key components of SAF. Surrogate fuels for Jet-Aand alternative fuels were formulated targeting critical propertiessuch as density and cetane number. Surrogate simulation results showstrong alignment with experimental data on ignition delay and flamespeed, further confirming the reliability of the surrogates. The CRNmodel was developed using the CFM56 engine data and validated againstthe International Civil Aviation Organization emission benchmarks.After that, two different fuel replacement scenarios, involving Jet-A,are investigated. In the first one, Jet-A is compared to 100% SAF,which helps assess expected differences in combustion performanceif a fully renewable fueling supply is followed. Results show thatNOx emissions are unaffected by SAF, aligningwith previous experimental studies. Polycyclic aromatic hydrocarbons(PAH) decrease by 93% for SAF compared to Jet-A, while Jet-A producesmore CO due to its aromatic content. Substituting aromatics with cycloalkanesin Jet-A reduces PAH emissions by up to 96 or 92%, depending on whetherall aromatics are replaced or only diaromatics. In a second scenario,aromatics are removed from conventional Jet-A and replaced with cycloalkanespecies, which can still hold the swelling properties needed by thefueling system. In terms of combustion, cycloalkane substitution leadsto slightly increased CO emissions and reduced flame temperatures.These results demonstrate the potential of SAFs and cycloalkanes inreducing soot precursors while maintaining a highly similar performancein the combustion process. Overall, the proposed CRN framework providesa good example of how a predictive and computationally efficient toolcan help in the early evaluation of alternative aviation fuels underrealistic gas-turbine combustor conditions.

Abstract In April 2025, the International Maritime Organization approved the IMO Net-Zero Framework. If adopted in 2026, the IMO Net-Zero Framework is expected to raise more than USD 10 billion per year. This article is the first to provide an in-depth analysis of how revenues will be distributed under the IMO Net-Zero Framework, focusing on the implications for (i) the research, development, and availability of alternative fuels and technologies; (ii) addressing the disproportionately negative impacts on states; and (iii) the just transition of the maritime workforce. The analysis suggests that a narrow understanding of what projects or programmes can be financed by the IMO Net-Zero Fund increases the risks of not addressing effectively , cost-effectively, and comprehensively disproportionately negative impacts on states and support a just transition for the maritime workforce. A broad reading of what can be financed under the IMO Net-Zero Framework is also compatible with MARPOL and its Annexes.

With the intensification of global greenhouse effects and energy crises, zero-carbon and alternative fuels have become major development trends for internal combustion engines. Ammonia, as a potential clean fuel, is considered one of the most promising alternative engine fuels due to its widespread raw material availability, ease of storage and transportation, and carbon-free combustion products. However, ammonia-fueled engines produce significant NH3 and NOX emissions after combustion. In order to effectively reduce NH3 and NOX emissions from ammonia/diesel dual-fuel engines, engine combustion chamber models and DOC-coupled SCR after-treatment models were built using CONVERGE and GT-POWER. The control of NH3 and NOX emissions was then investigated by integrating these models with the response surface methodology. The results show that in the range of AER10% to AER40%, as the ammonia substitution rate increases, unburned NH3 emissions rise but decrease significantly after oxidation by the DOC. NOX emissions decrease. Advancing the main-injection timing reduces the unburned NH3 content at the exhaust valve opening, while NOX emissions increase. With an increase in injection pressure, unburned NH3 emissions decrease, while NOX emissions increase. Under the conditions of an engine speed of 1400 rpm and 50% load, with an ammonia substitution rate of 32%, main-injection timing of 2 °CA ATDC, and injection pressure of 140 MPa, along with a DOC carrier diameter of 119 mm, length of 80 mm, and cell density of 100 cpsi, the NH3 and NOX emissions of the ammonia/diesel dual-fuel engine can be effectively reduced.

The International Maritime Organization (IMO) committed at the 2015 Paris Climate Summit to reducing greenhouse gas (GHG) emissions from shipping. Many studies and classification society outlooks agree that meaningful decarbonisation of deep-sea shipping will require a shift to low- or zero-carbon fuels. This research systematically evaluates three leading alternative fuels—hydrogen, ammonia, and methanol—regarded as capable of helping the sector meet the IMO’s 2050 targets. Each fuel was assessed using technical, environmental, economic, and social criteria through a hybrid multi-criteria decision analysis (MCDA) approach combining the analytical hierarchy process (AHP) and TOPSIS (Technique for Order Preference by Similarity to Ideal Solution). Criteria weights were derived from an online survey of 57 maritime experts, while secondary data from existing literature informed the TOPSIS analysis. AHP results show that environmental performance is the most important factor in fuel selection, followed by technical, economic, and social considerations. The combined AHP and TOPSIS results show that ammonia is the most suitable alternative fuel to reach IMO 2050 goals. This study’s findings provide a structured and evidence-based comparison of the main deep-sea alternative fuels and offer practical guidance for maritime decision-makers seeking to identify the most suitable option for decarbonising their fleets in line with global GHG reduction goals for 2050 and beyond.

The use of sustainable carbon-free energy sources is becoming a priority in the field of transport so that it becomes sustainable. Sustainable transport can also be achieved with vehicles equipped with diesel engines fuelled by alternative fuels that do not contain carbon, like hydrogen. The paper presents an analysis of the experimental results obtained at the fuelling with diesel fuel and hydrogen of a modern diesel engine, operating at 50% partial load and 2500 rev/min speed. For H2 energy substitution degrees of up to 43%, the combustion process is improved: the specific energy consumption is reduced, the combustion duration is reduced, the heat release rate is increased, the maximum pressure is increased, the carbon-based pollutant emissions are decreased and the cyclic dispersion is reduced. For 33% H2 energy substitution degree, the maximum pressure increases by 16.4%, the indicated mean effective pressure increases by 7.5%, the specific energy consumption is reduced by 5.36% and the level of greenhouse gases emission is reduced by 34.5% for carbon dioxide. In case of pollutant emissions, the smoke level is reduced by 58.6% and the unburned hydrocarbons level is reduced with 18%. For higher percentages of H2, emissions reductions can be accentuated. At H2 use, the combustion cyclic variability is reduced, the values of the COV variability coefficients determined for the parameters of interest and the combustion duration being reduced. As a novelty aspect, the optimal adjustment between engine load-speed-diesel fuel flow-hydrogen flow-maximum combustion pressure-smoke emission level-exhaust temperature level is presented. The use of hydrogen at the diesel engines can provide the beginning of sustainable transportation solutions in the future.

Currently, the public interest is still quite high for fossil fuels as indicated by the increase in fuel consumption which requires imports to meet domestic fuel needs. the negative impact of the use of fossil fuels is the availability of crude oil that continues to decline and the problem of exhaust emissions is increasingly concerning. the use of fossil fuels must be reduced by substitution of alternative fuels, especially in diesel engines. One alternative fuel is biodiesel which can be used directly in diesel engines without having to modify engine components. Biodiesel is a fuel produced from the transesterification process. Biodiesel can be produced by utilizing vegetable oils, animal fats, used cooking oil, and algae so that biodiesel can be said to be a renewable, biodegradable, non-toxic, and environmentally friendly fuel because the exhaust emissions produced are relatively cleaner. In applications in everyday life diesel engines are often used to drive generators. In use in Indonesia, the government encourages to mix biodiesel with diesel oil. Now it has reached B30 biodiesel, which is 30% biodiesel and 70% diesel oil. Diesel motors or diesel engines are required to use B30 by the government. Therefore, this study aims to create a setup machine as a learning medium for biodiesel applications in diesel engines and to facilitate several types of research on diesel engines with biodiesel fuel, because the trainer form is simple but still has the same function. The method used in this research consists of 3 stages, namely design, manufacture, and performance testing using halogen lamps as an output. The results of this study is that this simple diesel engine design can work properly shown by halogen lamps which all 4 were lit during testing process.

Abstract The uptake of alternative fuels in maritime transport presents new environmental and safety risks. The IMO Legal Committee is investigating the suitability of the existing international liability and compensation regimes. CMI has already concluded that these regimes do not sufficiently cover these new risks. It is therefore likely that a new regime will need to be developed. This article examines what lessons can be drawn from the development and design of existing civil liability and compensation regimes for shaping a future framework suitable for alternative fuels. Using a mixed methods approach that combines literature and document analysis with semi-structured expert interviews, the study explores not only legal principles but also political, institutional, and practical factors that enabled or hindered regime development.

This paper presents an MAUT-based decision-support framework, developed within the NAVGREEN project, to enable the evaluation of alternative fuels and technologies in shipping decarbonization pathways toward zero-emission targets. The framework integrates stakeholder-derived weights elicited through the Analytic Hierarchy Process (AHP) and systematically evaluates alternatives across five criteria: cost, technological maturity, safety and regulatory compatibility, carbon footprint, and social acceptability. Alternatives are mapped into a common utility space through criterion-specific utility functions and aggregated into a composite utility score, enabling transparent and reproducible comparison of single and combined solutions. To strengthen applicability beyond a single illustrative application, the study incorporates a structured scenario and sensitivity analyses (policy stringency, infrastructure constraints, conservative regulatory environments, and weight and parameter perturbations) to assess ranking stability under plausible future conditions. A case study on an Ultramax bulk carrier is used solely to demonstrate the operability and workflow of the method, rather than to empirically validate technology choices across all ship types. Optional AI-assisted elicitation may be used as a supporting aid to harmonize indicative inputs when data are incomplete; however, validation of AI-generated estimates is outside the scope of the present study and is identified as future work.

The study explored the implications of fuel subsidy removal on the income of taxi drivers in Abuja metropolis, with the primary objective bound to Examines the Implications of fuel subsidy removal on the income of taxi drivers in Abuja metropolis,2010-2024. The study adopted Income Determinism to serve as it theoretical guide. To achieve the objectives of the study, a mixed research design which entails both qualitative and quantitative approaches were employed. The study revealed that removal of fuel subsidies in Nigeria has had a profound impact on the income of taxi drivers in Abuja Metropolis and negatively affected their livelihoods. The study concluded that the impact of fuel subsidy removal on taxi drivers is not just economic; it also has social and psychological implications. Many taxi drivers are breadwinners for their families, and the reduction in their income has led to increased stress, anxiety, and uncertainty. Base on the findings, the study recommended that government should establish well-structured support programs specifically designed for taxi drivers, including financial assistance, training, and access to affordable alternative fuels like CNG. This will help enhance their economic resilience and adaptability in the face of changing fuel prices.