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Technical Paper

The Effect of Diesel Exhaust Fluid Dosing on Tailpipe Particle Number Emissions

Introduction of modern diesel aftertreatment, primarily selective catalytic reduction (SCR) designed to reduced NOx, has increased the presence of urea decomposition byproducts, mainly ammonia, in the aftertreatment system. This increase in ammonia has been shown to lead to particle formation in the aftertreatment system. In this study, a state of the art diesel exhaust fluid (DEF)-SCR system was investigated in order to determine the influence of DEF dosing on solid particle count. Post diesel particulate filter (DPF) particle count (> 23 nm) is shown to increase by over 400% during the World Harmonized Transient Cycle (WHTC) due to DEF dosing. This increase in tailpipe particle count warranted a detailed parametric study of DEF dosing parameters effect on tailpipe particle count. Global ammonia to NOx ratio, DEF droplet residence time, and SCR catalyst inlet temperature were found to be significant factors in post-DPF DEF based particle formation.
Technical Paper

Experimental Study of Impact of Ash and Soot on Tail Pipe Particle Number

PN requirements have been implemented as part of the Euro 5b and Euro 6 emission standards and off hwy Stage V standards. The PN compliance is established by relying on creating soot layer on the DPF which has very high PN filtration efficiency. Off highway Stage V cycles are significantly higher in temperature than their on highway counterparts, leading to difficulty in the DPF to create and maintain a soot cake. Hence for these applications the meeting Particle Number Requirement is challenging. To meet PN on off highway engines, we will have to rely on DPF. This presents a challenge, since to meet the high filtration efficiency requirements the DPF will have to reduce mean pore size, pore standard deviation, and increase wall thickness, increasing backpressure, which results in a fuel consumption penalty. The other option is to evaluate ASH layer as a filtration mechanism to help in meeting PN regulation. This paper discusses the ability of ash to improve PN filtration.