Design and thermodynamics analysis of marine dual fuel low speed engine with methane reforming integrated high pressure exhaust gas recirculation system

The carbon-neutral target leads to the development of low-carbon\zero-carbon marine fuels. Natural gas is currently one of the most competitive low-carbon fuels, however, the low compression ratio used to control knock combustion limits the improvement of thermal efficiency of natural gas engines. Meanwhile, low-pressure injection natural gas engines also suffer from methane slip. In this paper, a system including a fuel reformer and a natural gas engine with a high-pressure EGR of 20% was proposed. EGR could reduce NOx emission and control methane slip but it will decrease the thermal efficiency. Fuel reforming could improve engine thermal efficiency and increase flame propagation speed but it will increase NOx emission. Moreover, EGR could also provide higher temperature energy for fuel reforming. Therefore, the proposed system was designed to achieve the complementary advantages between EGR and fuel reforming. The results showed that the thermal efficiency of the proposed system was 49.3% at the reforming ratio of 5%, which is 2% higher than the original engine and 4.7% higher than the EGR engine. In addition, the methane slip was reduced by 20% and the NOx emission was 2.93 g/kWh, which can meet the IMO Tier III. Finally, the thermo-economic analysis of the system and the EEDI calculation were carried out. The results showed that the annual fuel cost saved by installing the system on the ship was approximately US $151,726 and the EEDI was reduced by 3.75%

Automated summary

This paper proposes a system consisting of a fuel reformer and a high-pressure EGR natural gas engine to achieve a balance between fuel efficiency and emission control. Through this system, engine efficiency can be improved while reducing methane slip and controlling NOx emissions, saving costs and meeting the IMO Tier III standards.