In this system, the SCR-A refers to a brick with only SCR catalyst coating, whereas SCR-B is a SCR brick
with AMOX coating in the last 10% of the brick length.
Information of the Aftertreatment System used for demonstration of T2B5 comparable emissions levels Catalyst Substrate Type Catalyst Catalyst Aging Function Dimensions DOC Cordierite 5.66" x 4" 700 C/24 Hours SCRonDPF Silicon Carbide 5.66" x 6" 700 C/ 24 Hours SCR Brick
A Cordierite 4.66" x 3" 650 C/ 24 Hours SCR Brick
B Cordierite 5.66" x 4" 650 C/ 24 Hours Table 3.
An SCR brick
, placed downstream of an engine which was operated with ULSD, was used for analysis.
After taken out, it was found that the SCR brick was plugged with black materials in its inlet faces, as shown in Figure 5.
Plausible root cause scenario is likely to be this way: Gradually increasing urea deposition blended with black particulate matter sitting at the catalyst inlet face, leading to high backpressure, causing an engine abnormal behavior, so miss-firing could happen and a temperature excursion occurred in the catalyst brick by high temperature soot combustion which in the end caused the SCR brick to melt down.
Nevertheless, to achieve additional NOx reduction over an SCR behind the SCR-DPF, optimized urea dosing will be needed so that there is enough N[H.sub.3] at the SCR-DPF outlet to allow NOx reduction to occur on the SCR brick
. As shown in Figure 2, sufficient N[H.sub.3] slip was obtained in these tests which will allow the NOx reduction reaction to occur on the SCR behind the SCR-DPF.