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In recent years, the importance of engine performance at part load has gradually increased in marine generator engines because they are generally operated at part load. So, various studies were carried out to reduce fuel oil consumption at part load for a medium speed diesel engine, HiMSEN Engine, which is generally used as a marine generator, in order to satisfy the needs of customers. The basic concept for the improvement of fuel oil consumption at part load is increasing maximum cylinder pressure and fuel injection pressure. In this study, the air waste-gate system is introduced and evaluated through the performance simulation. The main performance parameters of the combustion system such as fuel cam shape, fuel injection nozzle, turbocharger specification and engine compression ratio are also evaluated and optimized by using performance and combustion simulations.

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.