A NEW METHOD FOR ON-VEHICLE DETECTION OF CATALYST MALFUNCTION BASED UPON MEASUREMENT OF NON-EQUILIBRATED GAS-MIXTURES

Legislation is shortly to be enacted that will require the on-vehicle detection of catalyst malfunction. This is not straightforward for sev eral 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 fal se fault detection. It is proposed here that measurement of the degree of non-equilibration in the exhaust gases as they exit a faulty catal yst could be used as a suitable criterion for the assessment of cataly st condition. In order to demonstrate the concept, we have prepared se veral resistive-type SnO2 thin-film sensors with differing amounts of surface Pt doping. The sensors are exposed to CO/O-2/CO2 gas mixtures at varying levels of non-equilibration. The highest sensitivities to t he level of non-equilibration are shown by the undoped sensors. This i s in accordance with our theory that increasing the catalytic activity of the sensor itself decreases the available signal. This is in oppos ition to all currently available exhaust gas sensors, whose high catal ytic activity is necessary for unambiguous indication of the stoichiom etric air/fuel ratio, which also discards the non-equilibrated paramet er.