Researchers from Tianjin University and Lund University have developed a pioneering in-cylinder active reduction strategy to combat the high NOx 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 NOx 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 NOx 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 NOx into harmless nitrogen.
Key Research Highlights:
- Innovative NOx Control: The study reveals the NOx evolution and reduction mechanisms induced by ammonia post-injection, providing a robust theoretical and experimental basis for in-cylinder emission control.
- Mechanistic Insights: Detailed chemical kinetics analysis identifies that NH2 radicals play the overwhelmingly dominant role in reducing both NO and NO2 within the combustion chamber.
- Effective Emission Reduction: Engine experiments confirmed that by appropriately delaying the post-injection timing, a 14.4% reduction in NOx emissions was achieved while maintaining high combustion efficiency.
- Reaction Pathways: The study elucidates the SNCR reaction pathways, showing that NO is primarily reduced to N2 via three distinct pathways involving NH and NH2 radicals.
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 NOx in the cylinder. While the strategy effectively cuts NOx, the team also observed trade-offs, including increased N2O (a potent greenhouse gas) and unburned NH3 emissions when the post-injection timing was excessively delayed.
"This study provides an innovative method for reducing NOx emissions from ammonia combustion," the authors noted. "Combined with the inherent low NOx emission characteristics of ammonia diffusion combustion, this approach holds great promise for achieving effective NOx 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
