Numerical Study and Optimization of Combustion and Emissions of Ammonia/Diesel Dual-Fuel Engines Under Heavy Load

Ammonia fuel is expected to emerge as an effective alternative to fossil fuels due to its zero-carbon nature, high-efficiency storage and transportation advantages, and extensive industrial manufacturing infrastructure. This study discussed the impacts of compression ratio and injection timing on combustion and emission characteristics of an ammonia/diesel dual-fuel (ADDF) engine using numerical simulation. Results indicated that the corresponding optimal indicated thermal efficiency (ITE) continuously increases with an increasing compression ratio. When the compression ratio is 15:1, the injection timing corresponding to the maximum indicated thermal efficiency is −18 °CA after top dead center (ATDC). When the compression ratio ranged from 16:1 to 19:1, the corresponding optimal ITE was achieved at a retarded injection timing of −12 °CA ATDC. At a compression ratio of 19:1, the optimal ITE reached 47.9%. The in-cylinder formation regions of nitrous oxide (N₂O) are closely correlated with NH₃, NO, and temperature distributions, being primarily located at the interface between high-concentration regions of unburned NH₃ and NO. Under the comprehensive impact of increased compression ratio and advanced injection timing, both N₂O and unburned NH₃ emissions show a tendency of increasing first and then decreasing, while NO_x emissions demonstrated a monotonically increasing behavior.