Expanding high ammonia energy ratios in an ammonia-diesel dual-fuel engine across wide-range rotational speeds

Ammonia (NH3), as a hydrogen carrier and carbon -free fuel, has garnered increasing attention for its potential to reduce carbon emissions in transportation. Due to the poor ignition characteristics of ammonia, the ammoniadiesel dual -fuel combustion mode is one of the pathways for achieving low carbon emissions in compression ignition engines. This study compared the combustion and emission characteristics of an ammonia -diesel dualfuel engine at various speeds, ranging from 900 to 1800 rpm, with an extended ammonia energy ratio of 88 %. The results showed that advancing Start of Injection (SOI) moderately could reduce NH3 emissions. Higher engine speeds showed increased indicated thermal efficiency, reaching approximately 47 % at 1800 rpm. However, maintaining the ammonia energy ratio above 80 % at higher speeds became challenging. As the ammonia energy ratio increased, unburned ammonia emissions rose, while Nitrogen Oxides (NOx) emissions gradually decreased. Furthermore, a principal component analysis (PCA) was employed to integrate control parameters and combustion/emission characteristics of ammonia combustion, comparing correlations among different parameters. The results indicated that the control elements for unburned ammonia emissions primarily involve the diesel SOI and ammonia energy ratio.