A new method for on-vehicle detection of catalyst malfunction based upon measurement of non-equilibrated gas mixtures

Abstract Legislation is shortly to be enacted that will require the on-vehicle detection of catalyst malfunction. This is not straightforward for several reasons, such as uncertainty over which parameters would give the best indication of catalyst condition, the unavailability of suitable sensors, the passive nature of the catalyst and the need to avoid false fault detection. It is proposed here that measurement of the degree of non-equilibration in the exhaust gases as they exit a faulty catalyst could be used as a suitable criterion for the assessment of catalyst condition. In order to demonstrate the concept, we have prepared several resistive-type SnO 2 thin-film sensors with differing amounts of surface Pt doping. The sensors are exposed to CO/O 2 /CO 2 gas mixtures at varying levels of non-equilibration. The highest sensitivities to the level of non-equilibration are shown by the undoped sensors. This is an accordance with our theory that increasing the catalytic activity of the sensor itself decreases the available signal. This is in opposition to all currently available exhaust gas sensors, whose high catalytic activity is necessary for unambiguous indication of the stoichiometric air/fuel ratio, which also discards the non-equilibrated parameter.