Investigation of particle emissions from homogeneous NH3 combustion in a spark ignition engine

Ammonia (NH3) presents a promising alternative fuel for spark ignition (SI) and compression ignition (CI) combustion engines, thus contributing to the decarbonization of mobile sources. Recent research demonstrates that neat NH3 operation is feasible, but there is a lack of comprehensive information on particle formation with neat NH3 combustion. This study investigates particle emissions of an SI engine running on neat NH3, focusing on the understanding of the particle physical characteristics and the evaluation of techniques for the removal of volatile components. Particle number emissions from the engine were measured using different sampling/conditioning systems, and various operating points were examined. Particle emissions of NH3 were compared to those of neat methane (CH4) combustion, used as the reference baseline. Additionally, the use of a catalytic stripper in the particle sampling system was evaluated. Results indicate that both total PN10 and PN23 emissions from NH3 were higher than those from CH4. The APC system, equipped with catalytic stripper, achieved the greatest particle removal, while the minimal effect on 23 nm particles suggests they are likely solid. The catalytic stripper did not seem to produce new particles despite NH3 slip from the engine. Based on species availability and formation conditions, sulfate from sulfur in lubricating oil and nitrate salts with ammonium were identified as potential sources of the new particles formed.