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A correlation between engine dynamometer- and vehicle-aged catalysts has been established for novel lean-burn applications. A lean-burn, 1.8-L Ford Mondeo with a close-coupled three-way catalyst and an underfloor lean-NOx trap was used for this study. Vehicle aging of the emissions control system was done using a prescribed driving schedule. Engine dynamometer aging was done using a four-event aging cycle modified for lean-burn applications. The two aging methods were compared using maximum NOx conversion efficiencies measured during a two-mode dynamometer evaluation cycle. It was found that 75 h of four-event dynamometer aging is equivalent to 80,500 km of prescribed vehicle driving.

Two types of exhaust sensors have been studied from the point of view of applying them in feedback systems to control the air/fuel (A/F) operating point of automotive engines. The particular sensors studied were zirconia (ZrO2) sensors and titania (TiO2) sensors. Both sensors were without built-in heaters and designed to indicate when engine A/F passes through stoichiometry. The paper includes results obtained from engine dynamometers and test vehicles; but the major experimental results are from laboratory tests specifically designed to establish advantages or limitations of a specific sensor and its associated circuitry when used in engine A/F control systems. Calibration data were measured for the zirconia sensors in order to plot curves of sensor output voltage versus A/F with temperature (T) as a parameter. The zirconia sensor was found to be especially sensitive to the presence of hydrogen (H2) in exhaust gas. Data establishing this sensitivity are presented.

The resistivity of titania (TiO2) ceramic depends upon the partial pressure of oxygen (PO2) in the atmosphere surrounding the ceramic. Because there is a functional relationship between the PO2 of the equilibrated exhaust gas and the air to fuel ratio (A/F) operating point of the internal combustion engine, the resistance of a TiO2 ceramic sensor, when temperature controlled, can be used to determine quantitatively the A/F. TiO2 sensors utilizing these principles have been built and found to work particularly well in the region rich of stoichiometry. Control of the A/F in the region rich of stoichiometry is desirable for engine/catalyst systems designed to meet low NOx emission levels. This paper reports on the design details and operating features of an experimental TiO2 sensor and its associated electronic controller.