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The effects of seven matching parameters of a fuel injector and combustion chamber geometries on nitrogen oxide (NOx), soot and specific fuel oil consumption (SFOC) were investigated by means of a parametric study. The study was carried out on four different engine loads, i.e. L25 (25%), L50 (50%), L75 (75%) and L100 (100%) loads. The injection-related parameters were found to have more prominent influences as opposed to the combustion chamber geometries. Then, a multi-objective genetic algorithm (MOGA) method was proposed in order to identify a set of optimal designs for the L100 load. The emissions and performance of these optimal designs were also examined and compared on the other three engine loads. Finally, an optimal design which meets the IMO (International Maritime Organization) Tier II NOx emissions regulations (research shows it is impossible to meet Tier III NOx emissions regulations solely on the basis of the optimisation of the combustion progress) and which has the best fuel economy was singled out

The structure and performance of the common-rail system for the marine diesel engine are different from those used for automobile applications, resulting from the larger accumulator volume and the single injection volume. According to the characteristics of the distributed structure of the accumulator volume, a novel optimisation idea to improve the steady-state performance of the high-pressure common-rail fuel injection system designed for a marine engine retrofitting is proposed. The study concentrates on the optimisation in the hydraulic layouts and the structure parameters to manage the energy stored in the pressure waves. First, the test rig was established to study and evaluate the steady-state performance of the high-pressure common-rail system. Second, the experiments of rail orders and injection sequences were carried out to study the influence of different hydraulic layouts on the energy distribution of pressure waves in the system. Meanwhile, a comprehensive and detailed model of the high-pressure common-rail system was built to investigate the structural parameters of a rail-to-injector pipe. Based on the high-pressure common-rail system model, the modified multi-objective genetic algorithm was employed to seek the trade-off between the consistency of the injection volume and the reduction of the rail pressure fluctuation. Results show that a uniform distribution of multiple rails in one cycle contributed to reducing the amplitude of the rail pressure oscillation. In the parameter ranges of this study, a longer length and larger diameter of the rail-to-injector pipe could reduce the standard deviation of the injection volume and the rail pressure fluctuation rate simultaneously.