抄録
Numerical simulations and experiments have been carried out to meet the next IMO(International Maritime Organization) Tier2 NO_x regulations, which would be determined to reduce about 19-21% of the current limit for medium-speed diesel engine. The selected parameters in this study are piston bowl shape, fuel injection nozzle configuration and fuel injection rate. The behavior of spray and combustion phenomena in diesel engine was examined by the three-dimensional FIRE code. As a droplet breakup model, the wave breakup model was used. In order to predict spray characteristics accurately in the wide range of ambient gas density, the model constant B_1 with respect to breakup time was set as a function of ambient gas density ρ, B_1=1.4239×ρ+0.2093. The spray visualization experiment was performed in the constant-volume high-pressure chamber to clarify the numerical results on the spray characteristics of the spray angle and penetration. The fuel injection rig test was performed to know the fuel injection rate profile as an input data for the numerical analysis by using Bosch-tube injection rate metes. The computational results for the two different nozzle configurations were verified with the experimental data on the cylinder pressure, fuel consumption and NO_x formation through adjustment of some model constants at 50% load. The effects of fuel injection nozzle, piston bowl and fuel injection rate on the engine performance were investigated to find the optimum parameters on NO_x control. Finally, 23.7% NO_x reduction could be achieved with 0.71% deterioration in fuel consumption to meet the next IMO Tier2 regulations.
