Understanding effect of ammonia introduction method on characteristics of formation and combustion of in-cylinder combustible-mixture and emissions for a marine ammonia/diesel dual-fuel engine

For ammonia/diesel dual-fuel engines, the ammonia introduction method critically influences combustion and emissions. This study established four fuel organization modes for an ammonia/diesel engine through three-dimensional simulation: intake-port premixed homogeneous charge of ammonia (PHC), intake-port premixing ammonia by annular mixer (PBM), and side and central in-cylinder pilot injection of ammonia (SPI and CPI, respectively). Then differences and underlying mechanisms in engine combustion and emission characteristics across these modes were investigated. The result shows that the ammonia introduction method primarily acts by altering the positional coupling between NH 3 distribution and diesel spray as well as the propagating flames. Specifically, the CPI mode yields minimal unburned loss and NH 3 and N 2 O emissions despite maximal cooling loss, achieving relatively high thermal efficiency. Conversely, the SPI mode shows markedly increased unburned loss and peak NH 3 and N 2 O emissions, resulting in the lowest thermal efficiency. The PHC mode delivers intermediate combustion and emission performance.