Effect of multiple injection strategies on emissions and performance in the Wärtsilä 6L 46 marine engine. A numerical approach

The present paper proposes a Computational Fluid Dynamics model to analyze the operation cycle and exhaust gas composition in a four-stroke marine diesel engine, the Wärtsilä 6L 46. Once validated, the numerical model was employed to study the influence of several pre-injection parameters such as pre-injection rate, duration, starting instant and number of pre-injections. The purpose is to reduce consumption and emissions, especially nitrogen oxides, due to the current increasingly restrictive legislation. It was found that the fuel injection is a critical factor influencing combustion and emission characteristics. Important nitrogen oxides emission reductions were obtained for the parameters analyzed. Particularly, a 31.9% nitrogen oxides reduction was obtained using 20% pilot injection, 65.7% advancing 4° the pre-injection start angle, 20.1% shorting 4° the pre-injection duration and 36.7% using 4 pre-injections. A slight increment of hydrocarbons, carbon monoxide and consumption was obtained, lower than 5% for almost all the cases analyzed, and a negligible effect on carbon dioxide emissions.