Accelerated aging of automotive gasoline emissions catalysts has been performed on bench engines for decades. The EPA regulations include an accelerated aging cycle called the Standard Bench Cycle (SBC) that is modeled on the RAT-A cycle developed by GM Corp. and published in 1988. However, this cycle cannot be used for diesel aftertreatment components because it is based on stoichiometric operation, whereas diesel engines typically operate under excess air (lean) conditions.
The need for accelerated aging cycles for diesel emissions systems can be illustrated by considering that the full useful life (FUL) requirement in the United States for an on-highway truck is 435,000 miles, and an off-road application may be 8,000 hours. With the recent CARB Omibus legislation, the durability duration will be increasing for on-road applications by as much as 80 percent in the next decade. Additionally, regulators have implemented much more stringent durability demonstration requirements which include generating and evaluating FUL equivalently aged aftertreatment components for certification. Aging under normal operating conditions is time-consuming and expensive. This need was recognized, and the Diesel Aftertreatment Accelerated Aging Cycles (DAAAC) Protocol was developed to provide accelerated aging cycles for diesel emissions system applications.
The DAAAC Protocol is a diesel aftertreatment accelerated aging procedure that results in catalytic system deterioration similar to that observed in field-aged components. This protocol includes primary aging deactivation mechanisms observed on diesel engine aftertreatment systems such as hydrothermal, chemical exposure, and deposit deposition. The procedures that were developed aimed to shorten durability testing times dramatically, with a reduction in durability testing time goal of ≥ 90 percent. This paper describes the DAAAC Protocol that is being considered for emissions system certification use in the US.