Study on effects of EGR and injection strategies on the combustion and emission characteristics of ammonia/diesel dual-fuel engine

Ammonia, as a carbon-neutral fuel that contains nitrogen itself, makes the ammonia-fueled engines emit more NOX emissions. While exhaust gas recirculation (EGR) is an effective means to decrease NOX emissions, the effectiveness of its application in ammonia-fueled engines is not clear. In this study, the effects of EGR on the ammonia/diesel dual-fuel combustion (ADDC) mode are deeply investigated, and the combustion process is further improved by injection strategy optimization. The results show the introduction of EGR leads to a reduction in the indicated thermal efficiency (ITE) of the ADDC engine but is effective in controlling NOX emissions. Compared to the pure diesel combustion mode, the ADDC mode is less tolerant to high EGR rates, but the introduction of EGR has a more significant suppression effect on NOX emissions, in which the NO emissions respectively decreased by 58.4 % and 67.87 % after increasing the EGR rate from 0 % to 30 % under 0 % and 70 % ammonia ratios. In addition, when high EGR rates are used in ADDC engines, appropriate advanced injection or increased injection pressure can improve ITE and combustion stability, while effectively reducing carbonbased pollutant emissions with a small increase in NOX emissions.