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Natural gas-fueled vehicles impose unique requirements on exhaust aftertreatment systems. Methane conversion, which is very difficult for conventional automotive catalysts, may be required, depending on future regulatory directions. Three-way converter operating windows for simultaneous conversion of HC, CO, and NOx are considerably more narrow with gas engine exhaust. While several studies have demonstrated acceptable fresh converter performance, aged performance remains a concern. This paper presents the results of a durability study of eight catalytic converters specifically developed for natural gas engines. The converters were aged for 300 hours on a natural gas-fueled 7.0L Chevrolet engine operated at net stoichiometry. Catalyst performance was evaluated using both air/fuel traverse engine tests and FTP vehicle tests. Durability cycle severity and a comparison of results for engine and vehicle tests are discussed.

One of the central points of debate in the discussion of whether oxidation catalysts are capable of working with leaded-fuel is the simulation of in-use mileage accumulation. Various catalyst ageing cycles have been proposed. Some engine cycles have been shown to only slightly deactivate catalysts, while road ageing experience typically produces significant catalyst deactivation. This paper will report the influence of three different engine ageing cycles on oxidation catalyst durability when a typical 0.15 g Pb/liter European fuel is used. Steady-state ageing at either 370°C or 590°C inlet temperatures were compared to a multi-mode cycle with a maximum catalyst inlet temperature of 760°C. The multi-mode cycle was developed as a simulation of the CCMC cycle requirements based on information obtained from characterizing a vehicle driven according to the recommendations of the CCMC.