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The present work describes the numerical modeling of medium-speed marine engines, operating in a fumigated dual-fuel mode, i.e. with the second fuel injected in the ports. This engine technology allows reducing engine-out emissions while maintaining the engine efficiency and can be fairly easily retrofitted from current diesel engines. The main premixed fuel that is added can be a low-carbon one and can additionally be of a renewable nature, thereby reducing or even completely removing the global warming impact. To fully optimize the operational parameters of such a large marine engine, computational fluid dynamics can be very helpful. Accurately describing the combustion process in such an engine is key, as the prediction of the heat release and the pollutant formation is crucial. Auto-ignition of the diesel fuel needs to be captured, followed by the combustion and flame propagation of the premixed fuel.

In this work, the possibility to perform a cold-flow simulation as a way to improve the accuracy of the starting conditions for a combustion simulation is examined. Specifically, a dual-fuel marine engine running on methanol/diesel and natural gas/diesel fueling conditions is investigated. Dual-fuel engines can provide a short-term solution to cope with the more stringent emission legislations in the maritime sector. Both natural gas and methanol appear to be interesting alternative fuels that can be used as main fuel in these dual-fuel engines. Nevertheless, it is observed that combustion problems occur at part load using these alternative fuels. Therefore, different methods to increase the combustion efficiency at part load are investigated. Numerical simulations prove to be very suitable hereto, as they are an efficient way to study the effect of different parameters on the combustion characteristics.

In the upcoming decade sustainable powertrain technologies will seek for market entrance in the transport sector. One promising solution is the utilization of dual-fuel engines using renewable methanol ignited by a pilot diesel fuel. This approach allows the displacement of a significant portion of fossil diesel, thereby reducing greenhouse gas emissions. Additionally, this technology is, next to newbuilds, suited for retrofitting existing engines, while maintaining high efficiencies and lowering engine-out emissions. Various researchers have experimentally tested the effects of replacing diesel by methanol and have reported different boundaries for substituting diesel by methanol, including misfire, partial burn, knock and pre-ignition. However, little research has been conducted to explore ways to extend these substitution limits.

The use of renewable fuels such as hydrogen and methanol in marine engines is a promising way to reduce greenhouse gas emissions from maritime transport. Hydrogen and methanol can be used as the main fuel in dual-fuel engines. However, the co-combustion of hydrogen-diesel and methanol-diesel needs to be carefully studied. In the present work, the ignition delay (ID) and laminar burning velocity (LBV) for pilot-ignited dual fuel engine operation with hydrogen or methanol are studied. A constant volume batch reactor numerical setup is used in the open source Cantera code to calculate the effect of the premixed fuel on the ID of the pilot fuel. Also, Cantera is used to simulate a freely-propagating, adiabatic, 1-D flame to estimate the laminar flame speed of either hydrogen or methanol and how it is affected by the presence of pilot fuel. First, suitable chemical kinetic schemes are selected based on experimental data collected from the literature.