A Numerical Study on Combustion and Emission Characteristics of Marine Engine through Miller Cycle Coupled with EGR and Water Emulsified Fuel

The combustion in low-speed two-stroke marine diesel engines can be characterized as large spatial and temporal scales combustion. One of the most effective measures to reduce NOx emissions is to reduce the local maximum combustion temperature. In the current study, multi-dimensional numerical simulations have been conducted to explore the potential of Miller cycle, high compression ratio coupled with EGR (Exhaust Gas Recirculation) and WEF (water emulsified fuel) to improve the trade-off relationship of NOx-ISFC (indicated specific fuel consumption) in a low-speed two-stroke marine engine. The results show that the EGR ratio could be reduced combined with WEF to meet the Tier III emission regulation. The penalty on fuel consumption with EGR and WEF could be offset by Miller cycle and high geometric compression ratio. NOx can be reduced by 81.1% without penalty on fuel economy by using retarded exhaust valve closing timing (20°CA later) combined with 20% EGR and 40% W/F (the ratio of water and fuel), which can meet the Tier III emission regulation.