The goal of this thesis is to characterise diesel-ammonia combustion using a mean value first principle approach, and to implement this characterisation of diesel-ammonia combustion in a time domain two-stroke engine model. This model will be used to indicate the technical feasibility of diesel-ammonia as a marine fuel. The main research question of this project is: How does the performance of the main engine of a deep-sea cargo vessel fuelled with diesel-ammonia compare to one fuelled by diesel only? The TU Delft engine B model is chosen to model the behaviour of an engine of an ocean going cargo vessel. The model has been adapted to simulate the behaviour of diesel-ammonia engines. The adapted model is used to compare the performance of a diesel only engine with a diesel-ammonia engine. The main conclusion from this study is that diesel-ammonia engine compared to diesel only engines have a higher specific fuel consumption because of the lower heating value of ammonia. Newly designed diesel-ammonia engines can potentially be more power dense because of stoichiometric air-fuel ratio of ammonia. However, the combustion efficiency could be a limiting factor. The diesel-ammonia engine emits significantly less CO2 and SOx emissions. However, ammonia emissions, caused by incomplete combustion, and an increase in NOx emissions, caused by the nitrogen in ammonia, are a concern. Furthermore, diesel-ammonia engines operate at lower maximum pressures and temperatures, therefore the mechanical limits of the engine are not exceeded. Lastly, diesel-ammonia engines do not require a different turbo charger system.