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Technical Paper

Microkinetic Modelling for Propane Oxidation in Channel Flows of a Silver-Based Automotive Catalytic Converter

Computational Fluid Dynamics (CFD) is used to simulate chemical reactions and transport phenomena occurring in a single channel of a honeycomb-type automotive catalytic converter under lean burn combustion. Microkinetic analysis is adopted to develop a detailed elementary reaction mechanism for propane oxidation on a silver catalyst. Activation energies are calculated based on the theory of the Unity Bond Index-Quadratic Exponential Potential (UBI-QEP) method. The order-of-magnitude of the pre-exponential factors is obtained from Transition State Theory (TST). Sensitivity analysis is applied to identify the important elementary steps and refine the pre-exponential factors of these reactions. These pre-exponential factors depend on inlet temperatures and propane concentration; therefore optimised pre-exponential factors are written in polynomial forms. The results of numerical simulations are validated by comparison with experimental data.
Technical Paper

Development and Validation of a Cu-Zeolite SCR Catalyst Model

A one-dimensional numerical model for a Cu-zeolite SCR catalyst has been developed. The model is based on kinetics developed from laboratory microreactor data for the various NH₃-NOX reactions, as well as for NH₃ oxidation. The kinetic scheme used is discussed and evidence for it presented. The model is capable of predicting the conversion of NO and NO₂, NH₃ slip and the formation of N₂O, as well as effects associated with NH₃ storage and desorption. To obtain a good prediction of catalyst temperature during cold start tests, it was found necessary to include storage and desorption of H₂O in the model; storage of H₂O is associated with a sizable exotherm and the subsequent desorption of this water produces a correspondingly large endotherm.
Technical Paper

Strategies for Gasoline Particulate Emission Control - A “Foresight Vehicle” Project

The health threat from sub-100 nm particulates, emitted in significant numbers from gasoline vehicles, and anticipated changes in legislation to address this, have prompted investigation of techniques capable of trapping and oxidizing particulates from gasoline engines. Numerical studies have indicated that cooling to encourage particle capture by thermophoresis is less effective than use of electrostatic fields. A laboratory wire-cylinder electrostatic trap is under development, showing promising initial results. As an alternative trapping technique, the effectiveness of a cordierite wall-flow filter has been demonstrated, in simulation experiments and on a GDI-engined vehicle. Catalysts have been identified for particulate oxidation at typical exhaust temperatures, using water vapour and carbon dioxide as the oxygen source and retaining activity after short-term high-temperature aging.
Journal Article

The Effect of Pt:Pd Ratio on Light-Duty Diesel Oxidation Catalyst Performance: An Experimental and Modelling Study

This paper presents a two-part study on the effect of Pt:Pd ratio (at a constant total Pt+Pd loading of 120 g ft−3) on the catalytic performance of a Diesel Oxidation Catalyst (DOC) intended for light-duty applications, covering ratios across the full range from 100% Pd to 100% Pt. (Work on a heavy-duty DOC is presented in SAE 2015-01-1052). The first part of this paper presents a reactor study on the effect of Pt:Pd ratio on the catalytic activity of key reactions occurring individually over the DOC, including the oxidation of CO, C3H6, n-C10H22, CH4 and NO. For some reactions, activity increases continuously with Pt content (oxidation of n-C10H22 and NO); in contrast the activity for CH4 oxidation increases with decreasing Pt content (increasing Pd content), while CO and C3H6 oxidation exhibit more complicated dependencies. The second part presents the development of a one-dimensional model capable of predicting the effect of Pt:Pd ratio on DOC performance.