Effect of Accelerated Aging Rate on the Capture of Fuel-Borne Metal Impurities by Emissions Control Devices

Small impurities in the fuel can have a significant impact on the emissions control system performance over the lifetime of the vehicle. Of particular interest in recent studies has been the impact of sodium, potassium, and calcium that can be introduced either through fuel constituents, such as biodiesel, or as lubricant additives. In a collaboration between the National Renewable Energy Laboratory and the Oak Ridge National Laboratory, a series of accelerated aging studies have been performed to understand the potential impact of these metals on the emissions control system. This paper explores the effect of the rate of accelerated aging on the capture of fuel-borne metal impurities in the emission control devices and the subsequent impact on performance. Aging was accelerated by doping the fuel with high levels of the metals of interest. Three separate evaluations were performed, each with a different rate of accelerated aging. The aged emissions control systems were evaluated through vehicle testing and then dissected for a more complete analysis of the devices. Results from these experiments show that increasing the rate of acceleration impacts the amount of fuel-borne metals that are captured by the catalyst, which subsequently impacts the catalyst performance. Beyond a certain threshold, the acceleration rate creates an artificial mechanism for catalyst deactivation. In the range of acceleration rates that were examined in this study, these effects were primarily isolated to the inlet of the catalyst whereas performance further down the length of the catalyst was mostly unaffected.