Potential of thermal methods for catalyst on-board diagnosis

Abstract

Reductions in vehicle-related air pollution are expected to be supported by improved and efficient monitoring strategies. The on-board detection of catalyst failure is a key issue in this respect and is already fully prerequisite by the US and European legislation. Despite the progress made in the field so far, more efforts are required to develop simple and reliable on-board diagnosis (OBD) and on-board measurement systems for catalytic converters. This paper presents an OBD concept and methodology based on the measurement of catalyst exotherm. After a review of the main existing OBD systems, the theoretical approach of the method is analysed. The characterization of the catalyst condition is made by a specially defined performance index, which is continuously calculated on board. The capabilities of the presented technique are displayed on the basis of experiments performed with two catalysts of different ageing levels, as well as a simulation of a large number of aged catalysts. The results indicate that the presented methodology may be successfully applied to conventional underbody as well as to alternative catalyst systems (pre-converters and electrically heated catalysts) for OBD purposes.