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The long-term durability of a vehicle's exhaust catalyst is essential for emission control. Catalyst durability can be affected by a variety of factors including engine oil consumption. During normal engine operation, some of the lubricating oil is combusted. The deposition of combustion products from phosphorus containing lubricant additives on the catalyst can adversely affect catalyst durability. In an attempt to minimize the impact of oil consumption on additive performance, engines have been designed to reduce oil consumption and oils are being formulated with lower concentrations of phosphorus compounds. However, these phosphorus compounds protect the engine from excessive wear and cannot be easily removed from lubricant oil due to concerns over engine durability. The use of a phosphorus scavenger is an approach that works together with engine design to minimize catalyst deterioration.

Greenhouse gas emissions (GHG) from light-duty vehicles have received attention recently because of increased focus on global warming and climate change. Relative to emissions of regulated pollutants like hydrocarbons and nitrogen oxides, nitrous oxide (N2O) emissions from all vehicles are generally very low. However, N2O is a powerful greenhouse gas, and small emissions of N2O can contribute substantially to total GHG inventories. Two fleets of different vehicle models, both meeting the current US Tier 1 emission standard, were evaluated in an effort to develop a better understanding of N2O emissions from modern three-way catalyst-equipped vehicles. Nine 1997 Ford Crown Victoria vehicles operating on clean-burning US Federal Phase 2 Reformulated Gasolines were assessed over 60,000 miles. For additional comparison, testing was also conducted with catalysts from six 1994 Toyota Camry vehicles, which had previously undergone 110,000 miles of controlled mileage accumulation.

The Clean Air Act of 1990 requires on-board diagnostics (OED) capabilities on all new vehicles. These diagnostic systems monitor the performance of engine and emission system components and inform the vehicle operator when component or system degradation could significantly impact emissions. Acceptable operation of the monitor requires proper treatment of system variables. Fuel composition is one of many possible variables that must be considered for monitoring components directly in the exhaust stream. Recently, the octane enhancing, emissions reducing additive methylcyclopentadienyl manganese tricarbonyl (MMT) was reintroduced into unleaded gasoline in the U.S. Prior to reintroduction, the additive underwent extensive testing to demonstrate that use of MMT does not adversely affect vehicle emissions or the operation of emission systems such as OBD. However, questions have been raised about the influence of the additive on OBD systems.

Extensive vehicle fleet testing has demonstrated that use of MMT can reduce net tailpipe out emissions. The use of fuel containing the octane-enhancing, emission-reducing fuel additive leads to manganese oxide deposits in the vehicle exhaust system. Studies of the physical and chemical effects of manganese oxide deposits on the performance of catalytic converters conclusively demonstrated that MMT does not adversely affect catalytic converters and, in fact, protected the converters from phosphorus and zinc. Despite the overwhelming evidence that MMT is compatible with catalytic converters and vehicle emission control systems, concerns have recently been raised about the effect of manganese oxides on OBD-II catalytic converter monitoring.

Ethyl has conducted extensive fleet testing to investigate the effect of a manganese-based antiknock additive (MMT) on exhaust emissions from production cars. The fleet consisted of 48 cars - six cars each of eight models representing more than 50% of 1988 U.S. sales. Three of each model were tested for 75,000 miles using the base fuel. The other three used the base fuel plus 0.03125 gram manganese per gallon as MMT. Results of this testing show that use of the additive will not cause or contribute to the failure of emission control systems. Exhaust back pressure data for the 48-car fleet as well as a test of a close-coupled catalyst at 80 mph showed no indication of catalyst distress or plugging. Catalyst conversion efficiency was generally higher for units aged on the MMT fuel. Particulate emission data showed that less than 0.5% of the input manganese was exhausted as airborne for the FTP cycle.