Researchers from Tianjin University and Lund University have developed a pioneering in-cylinder active reduction strategy to combat the high NO x emissions that have long hindered the adoption of ammonia-fueled internal combustion engines (ICEs). By utilizing an ammonia post-injection (API) technique, the research team successfully reduced NO x emissions by 14.4% without compromising combustion efficiency.
Ammonia is widely recognized as a promising carbon-free fuel for the transportation and energy sectors. However, its fuel-bound nitrogen content leads to significant NO x emissions during combustion, posing a major challenge for meeting increasingly stringent environmental regulations, such as the Euro 7 standard.
In the study published in ENGINEERING Energy , the researchers demonstrated that ammonia can serve a dual purpose: as a fuel and as an agent for Selective Non-Catalytic Reduction (SNCR)—a chemical process that breaks down NO x into harmless nitrogen.
Key Research Highlights:
The researchers utilized a high-precision Computational Fluid Dynamics (CFD) model to visualize the combustion process. Their simulations showed that post-injected ammonia efficiently reacts with existing NO x in the cylinder. While the strategy effectively cuts NO x , the team also observed trade-offs, including increased N 2 O (a potent greenhouse gas) and unburned NH 3 emissions when the post-injection timing was excessively delayed.
"This study provides an innovative method for reducing NO x emissions from ammonia combustion," the authors noted. "Combined with the inherent low NO x emission characteristics of ammonia diffusion combustion, this approach holds great promise for achieving effective NO x emission control in future ammonia-fueled engines".
The team emphasizes that while the API strategy is highly effective, further optimization of combustion chamber geometry and ammonia injection hardware will be critical for practical, large-scale industrial application.
Journal: ENGINEERING Energy
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Cite this article: Yang, R., Yu, Z., Li, J. et al. In-cylinder NO x active reduction via ammonia post-injection in ammonia direct-injection engines. ENGINEERING Energy 20, 10798 (2026). https://doi.org/10.1007/s11708-026-1079-8
ENGINEERING Energy
In-cylinder NOx active reduction via ammonia post-injection in ammonia direct-injection engines
15-Jun-2026