DAAAC Protocol for Durability Demonstration of Diesel Aftertreatment Systems: Emissions Performance Validation 2022-01-1015

Aftertreatment durability demonstration is a required validation exercise for on-road medium and heavy-duty diesel engine certification. The demonstration is meant to validate emissions compliance for the engine and aftertreatment system at full useful life or FUL. Current certification practices allow engine manufacturers to complete partial aging and then extrapolate emissions performance results to FUL. While this process reduces the amount of service accumulation time, it does not consider changes in the aftertreatment deterioration rate. Rather, deterioration is assumed to occur at a linear rate, which may lead to false conclusions relating to emissions compliance.

With CARB and EPA’s commitment to the reduction of criteria emissions, emphasis has also been placed on revising the existing certification practices. The updated practices would require engine manufacturers to certify with an aftertreatment system aged to FUL. By utilizing an application-specific field cycle, this approach could, theoretically, generate FUL field representative parts. Thus, the requirement would validate field emissions compliance with higher certainty. Establishing a more stringent certification requirement also brings challenges to engine manufacturers. For example, a heavy-duty on-road application would require 9,800 hours of service accumulation time or 14 months. This time commitment poses several issues for engine manufacturers, which include reduced development cycle scheduling and an increased cost burden.

To address manufacturer challenges, regulators are proposing accelerated aging as an acceptable alternative to conventional aging. The Diesel Aftertreatment Accelerated Aging Cycle protocol, or DAAAC, is an accelerated aging methodology that considers primary catalyst deterioration mechanisms. This includes exposure to hydrothermal aging, sulfur, and lubricant-derived poisons at accelerated rates. The methodology utilizes application-specific information to derive the aging cycle modes and deterioration mechanism exposure rates. The following work will consider tailpipe emission results from a conventionally aged aftertreatment system and two accelerated aged systems utilizing the DAAAC protocol. The objective of the work was to validate the DAAAC approach on two accelerated aging platforms. The results will consider the performance deterioration utilizing certification cycles like the HD-FTP and RMC.