Catalyst Accelerated Thermal Aging Using the SwRI^® R-FOCAS^® Rig – A Joint Industry Program, 03-9441

Principal Investigator
Cynthia C. Webb

Inclusive Dates:  11/01/03 – 02/01/05

Background - Catalytic converters became part of the vehicle exhaust system in the mid-1970s to meet emission regulations mandated by the U.S. Environmental Protection Agency (EPA). Since that time, engineers and scientists have worked to optimize the performance and durability of these devices to meet increasingly stringent emissions and durability standards. As catalysts age, their ability to convert exhaust pollutants decreases. Research continues to focus on understanding thermal deactivation; formulate improvements to increase the stabilization of the washcoat and the substrate at higher temperatures; and improve long-term durability. 

Current vehicle catalyst durability requirement is 100,000 miles, with future proposed durability extending to 150,000 miles. To expose a component to actual engine aging would be expensive, time consuming, and not very practical during product design and development. However, thermal aging can be efficiently accelerated because the rate of the mechanism by which thermal deactivation occurs can be increased by operating at higher catalyst temperature. Accelerated thermal aging is generally performed using an engine and dynamometer test stand. 

Approach - Typically, an engine/dynamometer thermal aging cycle contains combinations of elevated catalyst inlet temperatures, chemical reaction-induced thermal excursions (simulating misfire events), and average air/fuel ratios (AFRs) to create a condition that accelerates the aging of the test part. Engine/dynamometer systems are expensive, exhibit variation in operation as a result of a number of factors, consume oil at an inconsistent rate, and require a substantial maintenance. FOCAS® provides an equivalent alternative that is potentially more accurate and repeatable, does not confound the thermal aging with oil poisoning, and requires less maintenance. A comparison of test stand setup for catalyst aging between the two types of aging is shown in the illustration below.

There are two objectives for this work. The first is to improve catalyst inlet temperature control during thermal aging on the R-FOCAS® rig. The second and main objective is to demonstrate that a catalyst aged on an accelerated thermal aging cycle, using a burner (R-FOCAS®), is equivalent to one aged on an engine. 

Accomplishments - The burner system used in this program was a SwRI-designed and built, gasoline-fueled burner (FOCAS® rig) designed to operate around a stoichiometric air/fuel ratio (a chemically balanced mix of fuel and air). During this work, the burner operation was modified to simulate the temperature and flow of an engine running a thermal aging cycle, and the system was upgraded to allow the burner to be run at 80 SCFM and to provide catalyst aging temperature control. Since the completion of this work, the burner has again been upgraded to allow operation up to 160 SCFM. The thermal aging portion of the work demonstrated that burner aging produces substantially equivalent aging results to an engine aging test stand.

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