Testing functionality of catalyst, e.g. nitrogen oxide storage catalyst, comprises carrying out regeneration test to remove reversible functionality losses, and testing and assessing functionality

摘要

A regeneration test removes reversible functionality losses. Functionality is then tested and assessed. Preferred Features: Functionality is first tested. Regeneration testing is only carried out should functionality be insufficient. Following this, functionality is re-tested, on the basis of which, functionality is assessed. To test regeneration, exhaust gas reductants are increased ahead of the catalyst. In addition the exhaust gas temperature is raised ahead of the catalyst. To raise the reductants, the air-fuel ratio is varied and/or ignition is retarded. During determination of functionality, a sensor after the catalyst is caused to vary its signal output, by changing exhaust gas properties. The delay in signal output change is used for diagnosis. The perturbation is determined ahead of the catalyst by a sensor. Mixture composition is alternated periodically between weak and rich operation. The delay of reaction to change, exhibited at the rear sensor, is used to assess functionality. A nitrogen oxide (NOx) sensor is used. The interval between sulfur regeneration and the second diagnosis does not exceed a predetermined threshold, or else the second diagnosis is not carried out.