Dynamic Response of Automotive Catalytic Converters to Modulations in Engine Exhaust Compositions

This paper presents a computational investigation of the effect of composition modulations on an automotive catalytic converter. The objective is to develop a better fundamental understanding of the converter’s performance under actual driving conditions. Such an understanding will be beneficial in devising improved emission control methodologies by exploiting the catalyst transient behavior. The study employs a single-channel based, one-dimensional, non-adiabatic model. Two types of imposed transients (sinusoidal and step changes) are considered. The results show that composition modulations cause a significant departure in the catalyst behavior from its steady behavior, and modulations have both favorable and harmful effects on pollutant conversion. The departure is relatively significant for catalyst CO and HC conversion performance. The operating conditions and the modulating gas composition have substantial influence on catalyst behavior. Near stoichiometric condition, modulations of HC concentration have relatively greater effect and result in increased CO and HC conversions. Modulations of CO, on the other hand, result in a decrease of CO conversion. The effect of CO modulations on HC conversion is slightly positive. For the conditions studied, NO modulations generally do not result in any significant change in catalyst performance.