To address the issue of a large two-stroke marine diesel engine having higher fuel consumption due to adopting the exhaust gas recirculation (EGR) to meet the Tier Ⅲ emissions regulations

the influence of split injection and injection angle on the fuel-air mixture

combustion and emissions were studied by using three dimensional numerical simulation based on the single cylinder model of such engine with multiple injectors. The results show that 30% of EGR rate can meet Tier Ⅲ

and the injection angle directly determines the formation of fuel-air mixture in the cylinder. If the injection angle is too small

the tips of fuel sprays of the injectors overlaps in the central cylinder and forms local rich region

leading to insufficient utilization of the in-cylinder air. If the injection angle is overlarge

fuel sprays and flames collids on the cylinder wall and hence results in increased heat loss through the wall. With a moderate fuel injection angle of 20°

in contrast

optimal mixing and heat release can be achieved with improved power output and reduced fuel consumption. In the presence of EGR

synergistically optimizing split injection and injection angle can reduce NOx by 65.5% with fuel consumption increasing only by 1.24% when using 30% of EGR rate

10.0% of fuel fraction in pilot injection

15° of interval between pilot and main injections and 20° of injection angle. Adopting three-time injection can effectively improve the compromise between fuel consumption and NOx emissions

but with a small room for a further optimization.