Parametric investigation of hydrogen-diesel combustion for a marine medium-speed dual fuel engine

Zero carbon fuels are expected to catalyse the decarbonisation of the maritime industry with hydrogen being considered a long-term solution. However, hydrogen combustion limitations must be addressed for marine engines, to accommodate the use of higher hydrogen energy fractions whilst maintaining knock-free conditions, minimise unburnt hydrogen, and reduce NOx emissions. Although hydrogen port injection can become an attractive solution to retrofit marine engines, studies in the pertinent literature are limited. This study aims to investigate a marine dual fuel engine operating with hydrogen as secondary fuel with 20% hydrogen energy fraction. A large marine four-stroke engine with nominal power output of 10.5 MW at 500 rpm is investigated considering hydrogen port injection. A CFD model is set up in CONVERGE for both the diesel and the diesel-hydrogen operating modes to investigate the effects of on the engine performance, emissions, and combustion characteristics. This model is validated against experimental data for the diesel mode and reported data for a smaller engine operating with diesel and hydrogen. The mesh characteristics are selected to compromise between the prediction error and computational effort. Case studies with varying in-cylinder temperature at inlet valve close are considered to identify the envelope for stable combustion. The results provide guidance to optimise the investigated engine settings considering the contradictory objectives of high efficiency, low NOx emissions and knock-free operation. This study contributes to the identification of efficient and reliable combustion conditions for diesel-hydrogen dual fuel marine engines.