CFD investigation the combustion characteristic of ammonia in low-speed marine engine under different combustion modes

As a carbon-free hydrogen-carrying fuel, ammonia can effectively solve the problem of greenhouse gas emissions and has great application potential in marine engines. At present, low pressure and high pressure injection are the two main combustion modes of low-speed marine engine, and the former is closer to the Otto cycle, while the latter is closer to the Diesel cycle. In this study, a low pressure direct injection natural gas/diesel dual fuel engine was converted to an ammonia/diesel engine (LP). High pressure direct injection ammonia/diesel engine was converted by a diesel-only engine (HP). The application of ammonia was compared in above two combustion modes. Results show that using ammonia in HP mode can easier get high power, but LP's IMEP, efficiency performance is better. However, LP mode has a large risk of ammonia escape (2.79%) and unburning (5.49%), and N2O in the emission is also worthy of attention and further research. In addition, due to the difference in N2O, the greenhouse effect of LP mode is also greater. For ignition, LP mode is not only affected by diesel injection, but also in-cylinder swirl and equivalent ratio due to the influence of premix mode. Currently, the HP mode has more potential for marine engine.