Study for improving ammonia combustion and emissions using different hydrogen addition strategies in pre-chamber turbulent jet ignition mode

Abstract

The turbulent jet ignition (TJI) mode is a viable strategy to achieve high thermal efficiency and low nitrogen oxide (NO_x) emissions for ammonia (NH₃). In this study, the combustion behavior and NO_x emissions were comprehensively compared under lean-burn condition for active TJI mode with pure NH₃, active TJI mode with pre-chamber H₂ addition, and passive TJI mode with NH₃/H₂ blend. The results indicated that the active TJI mode with the equivalence ratio (ER) of the pre-chamber increased from 0.6 to 0.9 by H₂ addition produces a higher velocity jet flame that rebounds into the main chamber, substantially shortening ignition delay and initial flame duration while avoiding excessive peak heat release rates. Increasing the ER or the H₂ energy ratio in the main chamber raises the flame temperature and radical concentrations. This reduces the final fuel NO and NO₂ emissions while increasing thermal+prompt NO and NO₂ emissions, which become dominant. In all TJI cases in this study, total N₂O emissions are dominated by fuel N₂O. During the early combustion stage, fuel NO_x is concentrated at the flame front. In the later stage, fuel NO and NO₂ are mainly distributed near the chamber wall, while fuel N₂O remains close to zero. Thermal+prompt NO_x is generated in high-temperature regions during the later combustion stage, declining slowly after peaking.