Low-dimensional Models for Real Time Simulations of Catalytic After-treatment Systems

Vemuri  Balakotaiah, University of Houston

In the first part of this work, we present accurate low-dimensional (LD) models for real time simulation, control and optimization of catalytic after-treatment systems (TWC, DOC, LNT and SCR). These are derived directly by averaging the governing equations and using the concepts of internal and external mass transfer coefficients. They are expressed in terms of three concentration and two temperature modes and include washcoat or internal diffusional effects without using the concept of the effectiveness factor. The models reduce to the classical two-phase models only in the limit of vanishingly thin washcoat. The models are validated by simulating the transient behavior for various test cases and comparing the predictions with detailed solutions. It is shown that these new LD models are robust and accurate with practically acceptable error, speed up the computations by orders of magnitude, and can be used with confidence for the real time simulation and control of various catalytic after-treatment systems.
In the second part of this work, we combine the low-dimensional models with micro as well as global kinetic models of NOx storage and reduction on a Pt/BaO/Al2O3 catalyst to examine the operation of a LNT with hydrogen as reductant. The spatiotemporal patterns (adsorption, reduction and thermal front properties) and product distributions predicted by the model are compared with our recent experimental data [Applied Cat. B: 84, 616-630 (2008)]. The use of the LD models to estimate kinetic parameters using bench scale data will also be discussed.

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