Diesel engines are widely used for propulsion on large ships, which has the undesired characteristic of generating large amounts of harmful emissions. To reduce these emissions, some alternative fuel was developed and used in a marine diesel engine. In this study, an experiment was carried out on a 6-cylinder turbocharged direct-injection marine diesel propulsion engine. A small proportion blend of biodiesel-diesel was used, aimed at exploring the emission characteristics and emission reduction mechanism for diesel propulsion engines. The results show that the high oxygen content of biodiesel blend is crucial for inhibiting the formation of particulate matter (PM) and reducing the formation of total unburned hydrocarbon (THC) and carbon monoxide (CO), which reduces the emission of harmful gases. At the same time, the number of particles (PN) has also decreased. However, the rapid burn rate of biodiesel was found to reduce brake thermal efficiency (BTE), resulting in an increase of fuel consumption and exhaust gas temperature (EGT), which can promote the formation of nitrogen oxides (NO x). More carbon dioxide (CO 2) is released due to the increased fuel consumption. The emission characteristics of the biodiesel blend and diesel fuel are discussed in this work.

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For reducing soot and NOx emissions, an effective method is to apply split injection strategies. In this research, characteristics of split injection were investigated by applying the pilot-main injection strategy and main-post injection strategy. The injection mass of fuel with the two strategies was measured by an in-house fuel injection rate test system based on the Bosch method. The development of spray tip and tail penetrations, as well as the evolvement of the spray angle when applying these two injection strategies, were explored by employing the high speed shadowgraphy at various injection pressures and surrounding gas densities. The results indicate the tail penetration rate of spray has no relation to the fuel injection pressure. However, the increased injection pressure causes a faster penetration development in the spray tip position. It was also found that the spray tip penetration rate of the second spray is slightly slower than that of the first spray at the beginning stage of injection, but it was significantly larger than the first one at the later stage.

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Particulate matter (PM) emissions from ships are increasingly posing health risks to population living along coastal areas. However, studies on the characteristics of particulate emissions from ships fueled with heavy fuel oil (HFO) are quite rare. In this paper, the characteristics of the PM sampled from the exhaust of a low-speed two-stroke common-rail marine diesel engine fueled with HFO are investigated at different loads. The thermal/optical carbon analyzer was employed to discriminate the elemental and organic carbons (EC and OC), the combustion-based elemental analysis was performed to obtain the C/H ratio, and the nuclear magnetic resonance spectrometer was used to analyze the molecular structure of the sample. With increasing loads, the EC/OC and C/H mass ratios and the mole ratio of polycyclic aromatic hydrocarbons to aliphatic hydrocarbons increase. From transmission electron microscopy images, noticeable changes in nanostructure, size, morphology, and nanostructural parameters of soot particles were analyzed. Furthermore, the elemental spatial distribution in soot particles was observed by energy-dispersive X-ray spectroscopy mapping. The main elements were detected by point-analyzed spectra. These results are believed to be valuable references for hazard evaluation and building a strategy of reducing particulate emissions from low-speed marine diesel engines.

The use of alternative fuels in ships faces the dual challenge of emission regulations and cost of use. In this paper, the impact of biodiesel blends from cooking waste as a carbon-neutral fuel for inland waterway vessels was investigated. The software AVL FIRE was used to simulate the detailed chemical combustion process of a marine diesel engine running on D100 (pure diesel), B5 (5% biodiesel by volume), B10 (10% biodiesel by volume), and B15 (15% biodiesel by volume). The results showed that B5, B10, and B15 all provided a better air-fuel mixture and significantly reduced soot production. Based on the performance and emission values, B5, B10, and B15 cause relatively small differences in engine performance compared to diesel and are readily applicable in practice. Optimizing exhaust gas recirculation (EGR) and varying injection timing can further optimize biodiesel fuel combustion while reducing NOx and soot emissions. The results of this study are helpful for the application of waste cooking oil biodiesel fuel and reducing exhaust gas emissions from ships.