Ammonia-diesel dual fuel substitute for marine diesel engine utilizing combustion modelling
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Date
2026-10-19
Authors
Κουραντής, Αντώνιος
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Abstract
Due to environmental pollution, increasingly stringent regulations pressure the maritime sector to develop new ways of reducing emissions while minimizing potential performance sacrifices. One of the primary ways this objective can be achieved is through engine optimization and the adoption of carbon-free alternative fuels. In this thesis, a three-dimensional sector model of a four-stroke marine engine is developed, utilizing computational fluid dynamics (CFD) and detailed chemical kinetics to accurately capture the complex in-cylinder phenomena occurring during combustion. Simulations play a pivotal role in engine optimization, development, and control, serving as a robust and cost-effective alternative to expensive physical experiments.
Specifically, a single cylinder-piston system of the medium-speed MAN 32/40 marine engine—widely used in medium-sized vessels for both propulsion and auxiliary power generation—is modeled using ANSYS Forte. Due to the engine's multiple commercial configurations (varying in cylinder count and inline or V-type layouts), modeling a single cylinder sector provides computational efficiency while allowing results to be extrapolated to full multi-cylinder configurations. The governing mathematical equations and sub-models utilized by the solver are formulated, and the model development methodology is explained step by step alongside all necessary engineering assumptions.
The study is divided into two main phases. First, a baseline pure diesel model (referred to as the foundational model) is developed. To compensate for the lack of experimental test-rig data, a parametric study is conducted by varying the initial intake pressure between 2.5 and 5.0 bar, validating the model's power output, fuel consumption, and thermodynamic behavior against official manufacturer data. Second, dual-fuel ammonia-diesel combustion models are developed by introducing ammonia premixed with the intake air at intake valve closing (IVC), ignited by a direct-injected diesel pilot spray. These dual-fuel models are categorized by their energy replacement ratio into energy-balanced mixtures (50% ammonia / 50% diesel energy), ammonia-rich mixtures (75% ammonia / 25% diesel), and diesel-rich mixtures (25% ammonia / 75% diesel), and are further subjected to parametric variations in intake pressure, intake temperature, and pilot fuel mass.
Comparing the in-cylinder pressure and temperature profiles, chemical heat release rates (CHRR), gross indicated power, and exhaust emissions (NOx, CO, CO2, soot, UHC, and unburnt NH3) against the diesel baseline reveals the distinct combustion characteristics of ammonia. Because ammonia exhibits a lower lower heating value (LHV), slower laminar flame speed, and higher auto-ignition temperature than diesel, ammonia-rich mixtures suffer from incomplete combustion, reduced thermal efficiency, and significant unburnt ammonia slip. Energy-balanced mixtures demonstrate high sensitivity to initial intake conditions, showing that careful optimization of boost pressure, intake preheating, and pilot injection ratio can yield viable combustion. Finally, in diesel-rich mixtures, ammonia addition substantially reduces both carbon-based (CO2, soot) and thermal NOx emissions (due to lower peak cylinder temperatures) with minimal penalties to indicated power output, confirming ammonia's strong potential as a transitional and long-term marine fuel.
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Keywords
Dual-fuel, Combustion models, Ammonia-diesel fuel, Emissions, Four stroke diesel engines