Mathematical modelling of catalytic exhaust systems for EURO-3 and EURO-4 emissions standards
The application of computer simulation in the development of catalytic exhaust aftertreatment systems for cars is over thirty years old. However, ever-increasingly stringent exhaust emissions legislation requires an ever-increasing degree of accuracy and complexity in the mathematical models applied. Traditionally, the Langmuir-Hinshelwood kinetics were applied in the majority of the models available, with a small number of representative chemical reactions. In this paper it is proved, by means of typical case studies, that the above modelling approach, with the necessary refining, can be brought to the level of accurately predicting the behaviour of advanced catalyst systems employed in EURO-3 and EURO-4 emissions homologation. An essential characteristic that was introduced to this end is the computer-aided selection (best fit) of the tunable parameters representing the apparent chemical kinetics and oxygen storage and release properties of each different catalyst-washcoat combination. Other modelling improvements are also discussed in the present paper, setting the scene for high accuracy simulations in view of the current and future emissions standards for spark-ignited, diesel and gasoline direct injection (GDI)-engined vehicles. These include the modelling of the aged catalyst, as well as taking into account the effect of precious metal loading variation on the apparent kinetics.