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Robust on-board diagnosis of emission catalyst performance requires the development of artificially damaged "threshold" catalysts that accurately mimic the performance of damaged catalysts in customer use. The threshold catalysts are used by emissions calibrators to determine fore-aft exhaust oxygen sensor responses that indicate catalyst failure. Rather than rely on traditional trial-and-error processes to generate threshold catalysts, we have used a DFSS (Design For Six-Sigma) approach that explores, at a research level, the relationship between oxygen storage capacity (OSC) of the catalyst (i.e., the fundamental property dictating the response of the aft oxygen sensor) and key process input variables: high-temperature exposure, phosphorus poisoning, and catalyst "recovery."

Phosphorus is known to reduce effectiveness of the three-way catalysts (TWC) commonly used by automotive OEMs. This phenomenon is referred to as catalyst deactivation. The process occurs as zinc dialkyldithiophosphate (ZDDP) decomposes in an engine creating many phosphorus species, which eventually interact with the active sites of exhaust catalysts. This phosphorous comes from both oil consumption and volatilization. Novel low-volatility ZDDP is designed in such a way that the amounts of volatile phosphorus species are significantly reduced while their antiwear and antioxidant performances are maintained. A recent field trial conducted in New York City taxi cabs provided two sets of “aged” catalysts that had been exposed to GF-4-type formulations. The trial compared fluids formulated with conventional and low-volatility ZDDPs. Results of field test examination were reported in an earlier paper (1).

Newly developed, low volatility zinc dialkyldithiophosphate (ZDDP) technology significantly reduces the amounts of volatile phosphorus (P) species while retaining their antiwear protective behavior and antioxidant performances. In the past researchers gathered a variety of engine data supporting the hypothesis that P volatility can have a significant impact on catalytic converter efficiency, but corresponding field performance results were limited. A recent field trial was conducted with New York City taxi cabs that provided extended sets of engine and drain performance parameters data. This trial compared side-by-side performance of oils formulated with conventional and low volatility ZDDPs. Following completion of the test, the extensive engine inspections and used oil analysis revealed excellent antiwear control and oxidation inhibition with both types of ZDDP technologies.

Catalyst poisoning from engine oil additives is a complicated process that depends in part on the pathway by which the oil is consumed in the engine. Engine studies were conducted to assess the relative impact of three major modes of oil consumption - through the PCV system, past the piston rings, and through the valve guides. Minimal phosphorus poisoning was observed with oil consumed through the PCV system and piston rings, whereas oil consumed through the intake valve guides demonstrated severe catalyst poisoning. The former produces effects characteristic of complete combustion of the ZDDP additive previously shown to produce relatively innocuous washcoat overlayers of porous zinc phosphate. In contrast, the latter produces effects characteristic of incomplete combustion (i.e., spray of oil additive into the exhaust and, most notably a washcoat pore-plugging effect accompanied by a marked decrease in washcoat surface area.

The relationship between engine oil formulations and catalyst performance was investigated by comparatively testing five engine oils. In addition to one baseline production oil with a calcium plus magnesium detergent system, the remaining four oils were specifically formulated with different additive combinations including: one worst case with no detergent and production level zinc dialkyldithiophosphate (ZDTP), one with calcium-only detergent and two best cases with zero phosphorus. Emissions performance, phosphorus loss from the engine oil, phosphorus-capture on the catalyst and engine wear were evaluated after accumulating 100,000 miles of taxi service in twenty vehicles. The intent of this comparative study was to identify relative trends.

The pulse flame combustor was adapted by researchers at Ford Motor Company in the early 1970s in order to produce exhaust gas simulating the combustion products of the internal combustion engine for the evaluation of automotive catalysts. Over the years, the pulse flame combustor has found application in a wide variety of research oriented tasks associated with automotive catalysts and emissions. More recent research and development efforts which have resulted due to elevated demands toward lower vehicle emission levels have prompted continuing refinements of the apparatus and effected innovative approaches to the study of emerging automotive catalyst and emission control issues with the pulse flame combustor. This report provides an overview of the operation and design evolution of the pulse flame combustor. In addition, recent applications of this laboratory device for studying automotive catalysts, alternative fuels, and other automotive emission control topics are reviewed.

This paper provides an overview of the dual EGO sensor method for OBD-II catalyst efficiency monitoring. The processes governing the relationship between catalyst oxygen storage, HC conversion efficiency, and rear EGO sensor response are reviewed in detail. A simple physical model relating catalyst oxygen storage capacity and rear EGO sensor response is constructed and used in conjunction with experimental data to provide additional insight into the operation of the catalyst monitor. The effect that the catalyst washcoat formulation has in determining the relationship between catalyst oxygen storage capacity and HC conversion efficiency and its impact on the catalyst monitor is also investigated. Lastly, the effects of catalyst failure mode, fuel sulfur, and the fuel additive MMT on the catalyst monitor's ability to properly diagnose catalyst function are discussed.

The effect of MMT on the OBD-II catalyst efficiency monitor has been investigated. The results conclusively show that manganese which is deposited onto the catalyst during the combustion of MMT- containing fuel provides for an increased level of catalyst oxygen storage capacity. This added oxygen storage was found to result in a reduced rear EGO sensor response and caused malfunctioning catalysts to be incorrectly diagnosed by the OBD-II catalyst efficiency monitor.