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.
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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