We use a one-dimensional two phase transient model with position dependent heat and mass transfer coefficients for the case of laminar flow to predict the performance of a catalytic monolith converter. Shape normalized effective length scales have been used so that the model described here is applicable to any channel shape and washcoat profiles. We consider washcoat diffusional limitations in the model (model 1) to obtain the concentration profiles within the washcoat for the typical exhaust gases. Another model (model 2) which does not consider washcoat diffusional limitations has also been proposed. We simulate the transient response of concentrations and temperature using both models for the same set of parameters and analyze the difference in the results. We observe that the predicted time required for ignition depends on the model used because of the difference in reaction rates predicted by both the models. Also, the kind of ignition (front, back or middle) may be predicted differently by both the models. Neglecting diffusional limitations in the washcoat can also lead to a prediction of incorrect steady state behavior, thus necessitating their inclusion in the calculations.

The typical reactions occurring in a TWC have been considered and global rate expressions have been used to study the temperature profiles and conversion of various reactants. Periodic cycling between lean and rich conditions for a gasoline engine is studied with ceria added to the TWC catalyst. When ceria is not present, the achieved conversion fluctuates with the inlet conditions (lean or rich). On addition of ceria, a higher conversion of various species is achieved for lean as well as rich conditions because of oxygen storage during lean conditions. Also, early ignition is achieved which leads to reduced cold start emissions. The effect of axial variation of catalyst loading has also been studied and it has been found that an appropriate distribution of catalyst in the monolith can lead to a decrease in the total amount of catalyst used to achieve the same performance. We simulate the urban dynamometer driving schedule of the FTP (Federal Test Procedure) test with varying inlet concentrations of reactants, temperature and inlet velocities. We estimate the cumulative emissions of the various exhaust gases during the FTP cycle and found that a large percentage of the total emissions are during the initial few minutes of the FTP cycle.