Research on the ammonia post-injection strategy for in-cylinder NO_x abatement via SNCR in an ammonia/diesel dual-fuel direct-injection engine

This research establishes a numerical simulation model of an ammonia/diesel dual-fuel (ADDF) direct-injection engine to investigate the effect of in-cylinder nitrogen oxide (NO_x) reduction via triggering selective non-catalytic reduction (SNCR) reactions through ammonia post-injection strategy. It explores the effects of ammonia post-injection timing (PIT) and energy proportion of ammonia post-injection (PIP) on combustion and emission characteristics under a high-premixed combustion condition. The results show that delaying PIT reduces indicated thermal efficiency (ITE), and increasing PIP exacerbates this reduction, with a maximum reduction of 2.4%. NO_x emissions decrease with the increase of PIP. When PIT = 60 °CA and PIP = 3%, the reduction effects of nitric oxide (NO) and nitrogen dioxide (NO₂) are optimal, with reductions of 97.73% and 82.76%, respectively, but at the cost of a significant increase in nitrous oxide (N₂O) and unburned ammonia (NH₃) emissions; when PIT is advanced to 40 °CA, the reduction effect of NH₃ weakens, the NO_x emissions reduction amplitude decreases, while N₂O and unburned NH₃ emissions remain almost unchanged.