Parametric investigation of pre-injection on the combustion, knocking and emissions behaviour of a large marine four-stroke dual-fuel engine

This study aims at the parametric investigation of a large marine four-stroke dual-fuel engine in order to identify the pre-injection effects on the engine combustion, knocking and emissions parameters. A model was employed that was developed by integrating a 1-D engine model in AVL-BOOST and a 3-D CFD model in CONVERGE. The MAN 51/60DF marine engine is modelled and the simulation results were validated against experimental data. Subsequently, parametric runs for various pre-injection timings and mass ratios are performed and the simulation results are analysed and discussed. The derived in cylinder pressure oscillations at determined points are employed to calculate the knock index (KI), which was used as an evaluation indicator for the knocking intensity. A number of pre-injection strategies with varying timing and fuel mass ratios are studied. This study results reveal that a lower knock trend and NOX emissions can be achieved by early pre-injection timing and increasing pre-injection fuel mass ratio. In addition, the medium pre-injection interval increases the engine IMEP while reducing the NOX and total hydrocarbon emissions. Larger pre-injection mass ratio reduce the KI and NOX emissions, but reduces IMEP and causes the wetted-wall phenomenon. Besides, the excessive pre-injection intervals and pre-injection mass ratio result in a change in combustion mode from the conventional diesel compression ignition mode to a two-stage auto-ignition mode. This study provides a better understanding of the underlying interactions of involved parameters and proposes pre-injection solutions to improve the engine performance, emissions and knocking behaviour.