How to assess the state of exhaust catalyst systems in driving vehicles?

Future emission legislation will focus even further on real driving emissions. With Euro VId there will be a shift of assessed driving profiles to lower load operation. A further step to include cold start emissions in the evaluation is presently discussed. To meet these requirements it will be necessary to understand better the behaviour of catalyst systems under real driving conditions, including the factors that drive the deterioration of such systems. To ensure this, it will not be sufficient to have a limited analysis on very selected missions e.g. by using a PEMS equipment. Instead, a more comprehensive approach by analysing long term data of various different vehicles will be needed. Such data can be gathered by on-board sensors.Umicore and the Institute for Internal Combustion Engines and Powertrain Systems of the Technical University of Darmstadt are developing a corresponding methodology to assess the long-term state of the exhaust gas aftertreatment system under real driving conditions. In order to access real driving data, a heavy-duty truck of the 13 l class is equipped with a data-logger, which records specific vehicle and exhaust aftertreatment parameters and additional NOx-sensor values during daily use. Data has been gathered over a period of more than 16 months. The challenge is to assess the actual state of the catalyst system in an always changing environment of different driving situations as well as flow and temperature conditions in the exhaust system. With such insights it will be possible to determine long term poisoning and ageing of the exhaust gas aftertreatment system and to potentially correlate it to specific driving modes.To achieve this, sophisticated methods of analysis are required. One approach is to define classes of recurring quasi-stationary operation conditions. The measurement data is then sorted according to those predefined classes. Each class is separately analysed for its catalyst performance as a function of operation time.As a result, this method enables the assessment of the state of the exhaust gas aftertreatment system isolated from other influences. The method reveals the state of poisoning and ageing of the catalyst system at each point of operation and striking changes in the deterioration curve can be identified to look for potential triggers for deactivation or activation.