Simulation Research on the Injection Strategy of a Diesel-Ammonia Dual-Fuel Marine Engine

Abstract

Currently, most ships still rely on fossil fuels as the main source for marine engines. However, diesel as a fuel for marine engines is no longer sufficient to meet the economic requirements of shipping and emission restrictions imposed by regulations as a result of the depletion of fossil fuels and the pollution generated by their burning. This research examined the viability of employing hydrogen-carrying fuel ammonia (NH3) in marine engines to develop a low-carbon combustion technology, to address the carbon emission problem of marine diesel engines. The results demonstrate that a greater proportion of ignition fuel must be injected into the burning of ammonia due to its higher ignition energy requirements. And ammonia has a high evaporation rate, so it is important to properly extend the injection duration to lower the combustion rate and keep the maximum explosion pressure in the cylinder under control. If the injection duration of the original engine’s diesel mode is maintained in dual-fuel mode, the explosion pressure in the cylinder can increase by more than 5 MPa, exceeding the limit of the original engine. However, by extending the original engine duration, the maximum explosion pressure returned to the original engine level. The starting point of the in-cylinder combustion can be efficiently regulated by changing the injection timing. Under typical injection intervals, the heat released rate (HRR) curve shifted with ammonia injection time, and rough combustion occurred only when the injection interval between the ignition fuel and ammonia was too short. According to the simulation, with all other conditions held constant, the optimal fuel injection strategy maintains the in-cylinder pressure of the engine at the diesel engine’s original level in the dual-fuel mode. Additionally, it reduced carbon emissions by over 90% and NOx emissions by approximately 70% compared with the original diesel engine.