Experimental Investigation of Particulate Emissions From an Ammonia-Fueled Internal Combustion Engine

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Abstract
Ammonia combustion is a topic of active research due to the need for fuel decarbonization. Although ammonia does not contain carbon, its use in internal combustion engines (ICEs) may still form nitrogen-containing ultrafine particulate matter. This work investigates particulate emissions from NH3–H2–air combustion in a single-cylinder Waukesha cooperative fuel research (CFR) octane engine under a range of hydrogen blending and engine load. Particle size distributions were quantified using a Scanning Mobility Particle Sizer (SMPS). A dual-stage dilution sampling system was used to reduce unburned ammonia concentration and maintain particle concentration within the instrument limits. The engine was motored to measure crankcase particle emissions from lubricant oil atomization. Additionally, 100% hydrogen-fueled experiments were conducted to evaluate the effect of combustion on particulate emissions from lubricant oil atomization without NH3-based particulate formation. Various ammonia–hydrogen fuel blends were tested to quantify the contribution of ammonia-based particulate matter in the exhaust. The elevated particle number concentration as the ammonia fraction rises suggests that combustion with ammonia leads to higher particulate emissions compared to hydrogen combustion at the equivalent peak in-cylinder pressure. Additionally, the presence of both unburned ammonia and NO2 in the exhaust indicate that the measured particles may consist of ammonium nitrate based on known chemical mechanisms. Modeling suggests that NH3 and NO2 found in cold regions of the combustion chamber have the potential to form gas-phase ammonium nitrate that later condenses to form particles in the exhaust system.

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