Effect of the Injector Nozzle Hole Diameter and Number on the Spray Characteristics and the Combustion Performance in Medium-Speed Diesel Marine Engines

Experiments and numerical simulations have been carried out to investigate the NOx formation and fuel consumption according to various fuel injection nozzle geometry in medium-speed marine diesel engines. The spray visualization was performed experimentally in a constant-volume high-pressure chamber to verify numerical simulation results on the spray characteristics of the spray angle. A time-resolved spray behavior was captured by high-speed digital camera. We modified the coefficient in the correlation of spray penetration suggested by Hiroyasu et al.[1] and the f(T) of the correlation of spray angle suggested by Reitz et al.[2][3] The behavior of spray and combustion phenomena in diesel engine was examined by FIRE code. Wave breakup model and Zeldovich model were adopted to describe the atomization characteristics and the NOx formation. In case of breakup model, we modified the model constant C₂ with respect to breakup time and spray angle as a function of mean density of the combustion chamber to consider the variation of density for the combustion duration. The fuel injection rate was also measured by Rig-test to use as an input data for the combustion analysis. The combustion analysis results for the given nozzle configurations were verified with the experimental data such as the cylinder pressure, RoHR(Rate of Heat Release) and the NOx formation through adjustment of some model constants at 50 and 100% load. Finally, we investigated the effects of fuel injection nozzles on the engine performance through the NOx vs. fuel consumption trade-off curves.