Experimental and Numerical Study on the Effect of Nozzle Number on Large-Bore Marine Engine Performance

The experimental and numerical research, based on a large-bore marine single-cylinder engine, on the influence of the number of nozzle holes on the engine performance was carried out. Two injectors, which have identical structural parameters except the nozzle hole number, were investigated in the experiment. The pressure difference between inlet and exhaust was altered for studying the effect of the number of injector holes on the performance and emission of the diesel engine under different conditions. The experimental results show that the fuel consumption, NOx emission, and SOOT emission of the 8-hole injector are lower than those of the 7-hole injector under the same pressure-difference boundary and same maximum combustion pressure, in which the fuel consumption is reduced by 2-7g/kWh, NOX emission and SOOT emission are reduced by 50-100ppm and 0.2-0.4FSN respectively. The CFD calculation was carried out to explain the experimental results. The simulation shows that the flow rate of the injector with 7 holes is smaller, and the center of combustion is far away from the top dead center, which results in increased fuel consumption. The single-hole fuel jet of the 7-hole injector has larger momentum because of the longer injection duration. After hitting the wall, the fuel jet develops along the wall and in the opposite direction of the injection, and the interference of the fuel jet itself and adjacent jets is strengthened, resulting in more high-temperature zones, and thus the increase of NOx. The strengthened interference of the fuel jet itself and adjacent jets results in high fuel concentration zones, which leads to higher SOOT formation rate and lower SOOT oxidation rate, so that SOOT emission is increased. The experimental and numerical research conducted in this paper can provide guidance for further energy conservation and emission reduction of large-bore marine diesel engines.