Identifying the extra nanoparticles from SCR-equipped diesel engines and reducing them via regulating surface tension...

Urea selective catalytic reduction (SCR) has been widely used on lean-burn engines for its good de-NO_x performance; however, concerns from industry over the aqueous urea solution (AUS) injection-derived particle generation are arising as the global regulations on particle number (PN) are ever tightening, with the formation mechanisms yet to be fully explained. This study collected and analyzed exhaust particle samples with and without AUS injection and therefore managed to affirm the contribution of AUS injection to extra inorganic particle formation and shows dependence upon the surface tension of AUS. Multiple analysis methods have been applied to the collected particle samples, X-ray photoelectron spectroscopy (XPS) reported nitrogen element in 2.7% mass; lattice ablation noticed in crystallographic analysis combined with spacing information confirmed the contribution of urea and cyanuric acid (CYA) to AUS-derived particles, which increased the exhaust particle size via surface growth mechanism. Exhaust PN concentrations were found negatively corresponding to increased surface tension of AUS. The addition of surfactants, which reduced the surface tension, caused a remarkable PN surge of roughly 20 times. Changes in the spray shape and size distribution of the droplets were deemed the underlying reasons. It is hence force necessary to set up AUS standards enrolling surface tension as a control item to benefit the reduction of nanoparticle emissions from road vehicles.