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Selective Catalytic Reduction (SCR) diesel exhaust aftertreatment systems are virtually indispensable to meet NOx emissions limits worldwide. These systems generate the NH3 reductant by injecting aqueous urea solution (AUS-32/AdBlue®/DEF) into the exhaust for the SCR NOx reduction reactions. Understanding the AUS-32 injector spray performance is critical to proper optimization of the SCR system. Specifically, better knowledge is required of the formation of near-nozzle deposits that have been observed on existing underfloor SCR systems. The current work presents in-situ time lapse imaging of an underfloor mounted AUS-32 exhaust-mounted urea dosing unit. The operating conditions under examination are representative of low-load low speed urban driving interspersed with high temperature exposures typical of periodic DPF regeneration.

The impact of fuel composition (ethanol and aromatic content) and injector design on particulate number generation was studied in a 1.0L displacement direct injection spark ignition engine. Two types of engine tests that mimic real-life vehicle operation were carried out using a matrix of eight fuels and two injectors. It was found that the DISI injector design had the biggest impact on the extent of particulate number generation. An injector prototype designed to meet Euro 6c specifications for PN (6*1011 particles/km) resulted in much lower PN values compared to those obtained using a production injector currently available in the market. The impact of fuel composition on PN was apparent only during engine operation with the production injector. Overall, qualitative trends were observed but no statistically significant differences were observed for the impact of ethanol (E10 fuel match-blended for aromatics and octane quality) and aromatic content (19-28%) variation.