Post-Mortem Analysis of DAAAC and Conventionally Aged Aftertreatment Systems

Upcoming regulations from CARB and EPA will require diesel engine manufacturers to validate aftertreatment durability with full useful life aged components. To this end, the Diesel Aftertreatment Accelerated Aging Cycle (DAAAC) protocol was developed to accelerate aftertreatment aging by accounting for hydrothermal aging, sulfur, and oil poisoning deterioration mechanisms. Two aftertreatment systems aged with the DAAAC protocol, one on an engine and the other on a burner system, were directly compared to a reference system that was aged to full useful life using conventional service accumulation. After on-engine emission testing of the fully aged components, DOC and SCR catalyst samples were extracted from the aftertreatment systems to compare the elemental distribution of contaminants between systems. In addition, benchtop reactor testing was conducted to measure differences in catalyst performance. Sulfur was deposited uniformly on the aftertreatment components while the oil derived phosphorous deposited more heavily at the system inlet. Consistent with on-engine emission testing results, the reference system SCR had worse overall NO_X conversion performance, though the performance was still within the specification of commercially available aftertreatment systems. High levels of oil-derived phosphorous deposited on the DAAAC-Engine SCR inlet greatly inhibited NO_X conversion but improved as the phosphorous levels decreased axially along the SCR, suggesting more volatile oil was introduced into the DAAAC-Engine system. Improvements to the DAAAC protocol to better represent real world aging are discussed.