“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