“Abstract

Innovative marine propulsion systems play a pivotal role for decarbonising global maritime transportation. This study investigated an ammonia-fuelled hybrid powertrain system that integrates ammonia internal combustion engines with a battery energy storage system for a large containership, which were based on the credible and validated physical engine and battery models and real operation profiles of the case ship. A multi-objective optimisation framework based on the Non-Dominated Sorting Genetic Algorithm II (NSGA-II) is developed for component sizing and selection. In parallel, a rule-based Energy Management Strategy (EMS) is employed to optimize power distribution and improve operational efficiency. The proposed hybrid configuration is benchmarked against a real-world powertrain system powered by heavy fuel oil engines and a scenario powertrain solely powered by the same type of ammonia engines. The case study on the representative containership demonstrates that the ammonia-fuelled propulsion system has significantly lower carbon emissions than the conventional propulsion system, which achieves a 79.36 % reduction in CO₂ emissions. The hybrid ammonia-fuelled powertrain system has further 0.15 % CO₂ emission reductions with an Energy Efficiency Existing Ship Index (EEXI) of 0.8085 gCO₂/(t∗nmi). Nevertheless, fuel costs account for over 86 % of lifecycle expenditure, and high ammonia genset prices increase Capital Expenditure (CAPEX), resulting in higher overall costs of the ammonia-fuelled propulsion systems. These results indicate that ammonia as a marine fuel offers substantial decarbonisation potential and its economic feasibility depends on future ammonia cost reductions and optimal marine propulsion system design.”

 

The full report is accessible via: https://doi.org/10.1016/j.jclepro.2025.147145

For related publications please see Resources – UK National Clean Maritime Research Hub

“Abstract

Freight transport contributes 8 % of GHG emissions and requires propulsion systems that deliver both sustainability and high efficiency. This study introduces a novel system-level approach that links experimental data to modelling of a recuperated split cycle engine (RSCE) to identify a fuel-agnostic, high-efficiency pathway. The RSCE separates compression and expansion, enabling independent optimisation, intracycle heat recovery and combustion processes beyond the limits of conventional engines. While previous RSCE studies have demonstrated potential, they have typically focused on partial subsystems or idealised conditions, leaving key aspects of full-cycle thermodynamics underexplored. This work addresses those gaps by linking thermo-fluidic modelling with experimental results from a single-cylinder research engine (ESRE), representing the recuperation and expansion stages. Compression, recuperation, and expansion processes are analysed and integrated with AspenTech and Chemkin-Pro multizone simulations. Parameter studies evaluate the degree of isothermal compression (C), recuperator effectiveness (RE), expansion cylinder insulation, and compression to expansion volume ratios (CR:ER). Net system indicated efficiencies (η_{sys,indicated}) of up to 57 % are achieved under trade-off conditions (C = 0.4–0.5, RE = 0.85, CR:ER = 1:1.6–1.82), while maintaining initial temperatures high enough to enable autoignition, with peak temperature below the ≈2200 K thermal NO_x rapid formation. A comparative analysis of hydrogen and methane fuelling shows similar η_sys values to diesel, demonstrating the architecture’s fuel flexibility. These results provide a robust reference for future clean engine development by demonstrating the feasibility of RSCE architectures to exceed conventional efficiency limits and offering a validated modelling platform readily expandable to future sustainable propulsion strategies.”

 

The full report is accessible via: https://doi.org/10.1016/j.energy.2025.139158

For related publications please see Resources – UK National Clean Maritime Research Hub

“Abstract

Ammonia, a promising carbon-free fuel, offers practical advantages over hydrogen, such as liquid-phase storage, making it suitable for direct use in compression ignition engines. As a hydrogen carrier, ammonia has the potential to decarbonise internal combustion engines. However, its widespread adoption faces challenges, including high emissions of unburned ammonia and other pollutants. This study examines the effect of liquid injection timing of ammonia on the combustion, performance, and emissions of a rapeseed methyl ester (RME) dual-fuel compression ignition engine. Experiments were carried out on a single-cylinder diesel engine equipped with dual high-pressure injectors to evaluate ammonia injection timings between −25 and −7 CAD bTDC using a GDI injector. The results show that overlapping ammonia injection with RME significantly enhanced engine performance, with the optimal SOI of −17 CAD for both fuels achieving the highest indicated efficiency of 37.8 %. Moreover, injecting ammonia a few CADs after the RME effectively minimised emissions. Therefore, the lowest NH₃ emission of 453 ppm was recorded at SOI of −14 CAD. However, delaying the SOI of ammonia further to −7 CAD led to a rise in CO, N₂O, and PM emissions due to incomplete combustion of RME caused by liquid ammonia injection.”

 

The full report is accessible via: https://doi.org/10.1016/j.energy.2025.137919

For related publications, please see Resources – UK National Clean Maritime Research Hub

“Abstract

Global maritime shipping is an important driver to the global economy, accounting for 12.3 billion tonnes in maritime trade volume in 2023. Mainly driven by petroleum-based fuels, the sector emitted 706 Mt of CO2 in 2022, constituting 2 % of global CO2 emissions. The International Maritime Organization (IMO) have set greenhouse gas emissions (GHG) reduction targets with the ultimate goal of achieving net-zero by 2050 with short- and medium-term checkpoints in 2030 and 2040. Internal combustion engines shall continue to be the prime propulsion method for ships as it could meet the load requirements throughout the ship’s voyage. Therefore, meeting these targets and the increasingly strict regulations governing GHG and NOx from the exhaust must be the sole focus of future ship propulsion design. This can be achieved by adopting incrementally radical and advanced combustion technologies, from operational optimization towards retrofit of new technologies paving the way to radical redesign of thermodynamic cycles. In addition, moving away from long-chain carbon fuels towards zero-carbon fuels is the proposed pathway towards removing CO2 altogether from exhaust emission. This article proposes a roadmap towards achieving the 2050 IMO target and discusses the implementation and utilization of various fuel and engine technologies. Furthermore, this article discusses retrofit considerations, economic viability, and ports infrastructure preparedness in adopting these alternative fuels. It was reported that 36% of ships on order will adopt liquefied natural gas (LNG), signalling a promising shift to decarbonise, supported by ports around the world developing infrastructure for LNG, hydrogen, and ammonia bunkering.”

 

The full report is accessible via: https://doi.org/10.1016/j.ecmx.2025.101184

For related publications, please see Resources – UK National Clean Maritime Research Hub

“Abstract

This study proposes a retrofit energy system for a marine diesel oil (MDO) container vessel, integrating a methanol-fuelled internal combustion engine (ICE), molten carbonate fuel cell (MCFC), carbon capture system, and organic Rankine cycle (ORC). The main goal of the paper was to reduce a large container vessel’s greenhouse gas (GHG) emissions by retrofitting the traditional MDO ICE propulsion system. Comprehensive thermodynamic and economic analyses were conducted to evaluate its performance and feasibility. The system captures 93.2 % of CO₂, reducing the CO₂ emission intensity (EMI) from 358.7 to 32.1 kg/MWh. While carbon capture equipment lowers the electrical efficiency by 8.4 %, the system achieves overall electrical and exergy efficiencies of 49 % and 56 %, respectively. The system meets the vessel’s propulsion demand (39.9 MW) and supplies the required 4 MW auxiliary and 6 MW heating power. The levelised cost of energy (LCOE) is 0.16 $/kWh, with fuel costs accounting for 73.5 % of the LCOE. Annual revenues from CO₂ sales and carbon credits are projected at $12.35 million, surpassing carbon capture costs.”

 

The full report is accessible via: https://doi.org/10.1016/j.apenergy.2025.126504

For related publications please see Resources – UK National Clean Maritime Research Hub

“Abstract

Direction Injection Dual-Fuel (DIDF) engines fueled with ammonia and diesel are identified as a promising solution for decarbonizing large-scale Compression Ignition (CI) engines. This study addresses the research gap of missing a parametric model for simulating the combustion process in DIDF CI engines using ammonia and diesel. Multi-objective optimization and genetic algorithms are applied to generate a parametric Multi-Wiebe Combustion (MWC) model based on experimental results from a NH3-diesel DIDF CI engine. The innovative approach supports one-dimensional engine modeling with NH3-diesel combustion in GT-Power, enhancing the understanding of direct injection timings, fuel interactions, and combustion dynamics. Key findings include the impact of dual-fuel injection timings and fuel ratios on ignition delay, individual combustion phase durations, and heat release rate, providing a quantitative description of combustion behavior under varying conditions. The validation results show that with injection timing variations from −17.5 to −10 CAD aTDC and NH3 energy ratios ranging from 40 % to 60 %, relative errors remain below 5 % for key performance indicators such as pressure and efficiency. This study proposes a methodology to generate an accurate combustion model – the MWC model – for one-dimensional dual-fuel engine simulation, aiding in calibrating scaled-up DIDF CI engines and guiding further engine designs.”

 

The full report is accessible via: https://doi.org/10.1016/j.energy.2025.136181

For related publications, please see Resources – UK National Clean Maritime Research Hub