Ammonia Combustion Emissions: Study Reveals Concerns for Fuel Decarbonization

A recent study published in the Journal of Engineering for Gas Turbines and Power has shed light on the potential emissions issues associated with ammonia combustion in internal combustion engines. Researchers from the University of Minnesota investigated particulate emissions from NH3-H-2-air combustion in a single-cylinder engine, finding that elevated particle number concentrations occur as the ammonia fraction rises. This suggests that combustion with ammonia leads to higher particulate emissions compared to hydrogen combustion.

Key Takeaways:

• The study found that ammonia combustion in internal combustion engines may form nitrogen-containing ultrafine particulate matter, despite not containing carbon.
• The research, supported by the U.S. State of Minnesota Session Law, Chapter 4, Article 2, Section 4, investigated particulate emissions from NH3-H-2-air combustion in a single-cylinder Waukesha cooperative fuel research (CFR) octane engine.
• The study utilized a Scanning Mobility Particle Sizer (SMPS) to quantify particle size distributions and a dual-stage dilution sampling system to reduce unburned ammonia concentration.
• Modeling suggests that NH3 and NO2 in the combustion chamber have the potential to form gas-phase ammonium nitrate, which later condenses to form particles in the exhaust system.
• The study found that 100% hydrogen-fueled experiments produced lower particulate emissions compared to ammonia-fueled experiments.
• Various ammonia-hydrogen fuel blends were tested to quantify the contribution of ammonia-based particulate matter in the exhaust.
• The study concluded that ammonia combustion in internal combustion engines may have higher particulate emissions compared to hydrogen combustion.

Statistics:

• The study found elevated particle number concentrations as the ammonia fraction rises, with a maximum concentration occurring at 50% ammonia fraction.
• The presence of both unburned ammonia and NO2 in the exhaust indicates that the measured particles may consist of ammonium nitrate.
• The study utilized a Scanning Mobility Particle Sizer (SMPS) to quantify particle size distributions.
• The dual-stage dilution sampling system was used to reduce unburned ammonia concentration and maintain particle concentration within instrument limits.
• The engine was motored to measure crankcase particle emissions from lubricant oil atomization.

Sources:

• Experimental Investigation of Particulate Emissions From an Ammonia-fueled Internal Combustion Engine. Journal of Engineering for Gas Turbines and Power, 2025;147(10).
• U.S. State of Minnesota Session Law, Chapter 4, Article 2, Section 4, NH3-fueled power generation research and development.