Demonstration of SCR on a Diesel Particulate Filter System on a Heavy Duty Application

Selective Catalytic Reduction (SCR) catalysts have been demonstrated as an effective solution for controlling NOx emissions from diesel engines. Typical 2013 Heavy Duty Diesel emission control systems include a DOC upstream of a catalyzed soot filter (CSF) which is followed by urea injection and the SCR sub-assembly. There is a strong desire to further increase the NOx conversion capability of such systems, which would enable additional fuel economy savings by allowing engines to be calibrated to higher engine-out NOx levels. One potential approach is to replace the CSF with a diesel particulate filter coated with SCR catalysts (SCRF^® technology, hereafter referred to as SCR-DPF) while keeping the flow-through SCR elements downstream, which essentially increases the SCR volume in the after-treatment assembly without affecting the overall packaging. This could enable higher NOx reduction efficiency hence allowing the engine to operate at higher engine out NOx while still achieving the same emission targets and potentially improving the engine fuel economy. In this work, a system consisting of a SCR-DPF unit was evaluated in the field on a truck using a 1998 engine certified at 4.0g/hp-hr engine out NOx. The SCR-DPF based system exhibited very high NOx reduction efficiency during normal on-road operation, even after reducing the flow through SCR element volume by more than half. The soot oxidation activity of this system was also evaluated. The system exhibited a very stable backpressure during 1300 hours of field operation without any active regeneration. This indicated that the system is capable of passive regeneration in a real HDD application. The results of this work demonstrated that using SCR-DPF systems could meet very high NOx reduction required for future applications and thus improve fuel economy for heavy duty diesel vehicles by allowing them to operate at higher engine out NOx conditions.