Investigation in impact of ammonia energy ratio and operating parameters on combustion process and multi-objective optimization in an ammonia-diesel dual-fuel engine

As a carbon-free fuel, ammonia can effectively mitigate the greenhouse effect caused by transportation. However, its low reactivity necessitates diesel assistance for ignition in compression-ignition engines. This study investigated the combustion and emission characteristics of ammonia–diesel dual-fuel (ADDF) engines using a validated three-dimensional numerical model. The effects of ammonia energy fraction and intake strategies were systematically analyzed. Results revealed that elevated intake temperature (IT) improved ammonia ignition and reduced the emissions of unburned ammonia, but promoted nitrogen oxide formation. Moderately increasing the intake pressure (IP) could reduce the in-cylinder temperature and increase the emissions of nitrous oxide (N 2 O) and unburned ammonia. Furthermore, a response surface optimization (RSM) model was developed with IT, swirl ratio, IP, and diesel injector nozzle diameter as decision variables. The model aimed to optimize targets such as N 2 O emissions and the emissions of unburned ammonia from the engine. The optimized best matching result was obtained with an IT of 360 K, a swirl ratio of 2.1, an IP of 148.7 kPa and a diesel injection nozzle diameter of 0.2 mm. Compared to the original data, N 2 O emissions and the emissions of unburned ammonia had decreased by 11.43 % and 20.13 %, respectively, while the peak cylinder pressure (PCP) increased by 29.5 %.