Numerical study of HTJI on combustion characteristics of neat ammonia engine under atmospheric intake conditions

Abstract

Low-carbon life is spreading to every corner of the world, but also offers new challenges to the internal combustion engine (ICE). Ammonia (NH3), as a hydrogen carrier and carbon-free fuel, is the key for ICE to being zero-carbon. Hydrogen turbulent jet ignition (HTJI) is thought as an optimal method to overcome the poor combustion performance of ammonia. In this study, the combustion characteristics of a neat ammonia engine with HTJI are numerically studied by addressing the orifice diameter and pre-chamber reactivity. The results show that an optimal orifice diameter is needed to maximize the promoting effect of HTJI on ammonia combustion. The jet flame quenches under small orifice conditions, and no jet flame products under large orifice conditions. When considering the pre-chamber reactivity, the scavenging process leads to a low degree of H2 in the pre-chamber during the compression, which results in low-efficiency ammonia combustion. By increasing the pre-chamber reactivity (hydrogen quantity) of the pre-chamber, the jet flame is advanced and much stronger, resulting in better engine performance. For nitrogen-based emissions, the unburned NH3 emissions mainly depend on combustion efficiency, while NO emissions show an opposite trend. The current results can help find the optimization method of the ammonia engine with HTJI.