Effect of hydrogen direct injection timing on ammonia combustion in a marine engine: A numerical study

The injection timing of hydrogen in an ammonia-hydrogen fueled marine engine significantly affects combustion performance and emissions. This study aims to identify the optimal hydrogen direct injection timing window. Three-dimensional CFD simulations are conducted to evaluate the effects of different injection timings on in-cylinder pressure, heat release rate, temperature distribution, IMEP, and emissions. Delaying hydrogen injection reduces peak cylinder pressure, but excessive delay (e.g., 630°CA) leads to incomplete combustion and power loss, while overly early injection may cause the peak pressure to exceed the limit. Considering combustion process, engine power output, fuel consumption, and emission targets, an injection timing between 550°CA and 590°CA is identified as effective. Flame development is optimal at 550°CA, whereas at 590°CA, ammonia injection timing should be adjusted to improve NH₃ emissions. To ensure complete combustion, the hydrogen injection timing should not be later than 590°CA, and under other engine loads, the operable range can be appropriately extended based on the behavior of the hydrogen injector.