Development of a Methodology to Separate Thermal From Oil Aging of a
Inclusive Dates: 10/01/00 - 09/30/01
Background - Catalytic converters became part of the vehicle exhaust system in the mid-1970s to meet EPA-mandated emission regulations. 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 very expensive and time consuming, and not very practical during the design and development of products. 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/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 ratio (AFR) to create a condition that accelerates the aging of the test part. Engine/dynamometer systems are expensive, exhibit variation in operation due to a number of factors, consume oil at an inconsistent rate, and require a substantial amount of maintenance. An equivalent alternative that is less costly, potentially more accurate and repeatable, does not confound the thermal aging with oil poisoning, and requires less maintenance would be very attractive.
The objective of this work is to develop a control method for a burner system that would allow the burner to simulate exhaust temperature, flow, and AFR created by an engine during accelerated thermal aging. Validation of the methodology will be achieved through comparison of the differences (or similarities) between engine- and burner-induced accelerated thermal aging. If the burner system provides thermal aging comparable to an engine, an alternative oil-free (or oil consumption controlled, if desired) aging system that is less expensive, and requires less maintenance, will be identified.
Accomplishments - The burner system used in this program is an SwRI-designed and built, gasoline-fueled burner (FOCAS® rig) designed to operate with a near stoichiometric AFR (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. The simulated cycle was part of a published aging protocol known as the Rapid Aging Test A. Three catalysts have been aged on the FOCASŪ rig, and three on the engine. The final performance evaluations are near completion.