Daniel Chatterjee

Detailed surface reaction mechanism in a three-way catalyst

Monolithic three-way catalysts are applied to reduce the emission of combustion engines. The design of such a catalytic converter is a complex process involving the optimization of different physical and chemical parameters (in the simplest case, e.g., length, cell densities or metal coverage of the catalyst). Numerical simulation can be used as an effective tool for the investigation of the catalytic properties of a catalytic converter and for the prediction of the performance of the catalyst. To attain this goal, a two-dimensional flow-field description is coupled with a detailed surface reaction model (gas-phase reactions can be neglected in three-way catalysts). This surface reaction mechanism (with C3H6 taken as representative of unburnt hydrocarbons) was developed using sub-mechanisms recently developed for hydrogen, carbon monoxide and methane oxidation, literature values for C3H6 oxidation, and estimates for the remaining unknown reactions. Results of the simulation of a monolithic single channel are used to validate the surface reaction mechanism. The performance of the catalyst was simulated under lean, nearly stoichiometric and rich conditions. For these characteristic conditions, the oxidation of propene and carbon monoxide and the reduction of NO on a typical Pt/Rh coated three-way catalyst were simulated as a function of temperature. The numerically predicted conversion data are compared with experimentally measured data. The simulation further reveals the coupling between chemical reactions and transport processes within the monolithic channel.

Natural Gas Conversion in Monolithic Catalysts: Interaction of Chemical Reactions and Transport Phenomena

Abstract The interaction of transport and kinetics in catalytic monoliths used for natural gas conversion is studied experimentally and numerically. The paper focuses on a precise flow field agreement between experiment and model. Therefore, we use extruded monoliths with rectangular channel cross-section and a three-dimensional Navier-Stokes simulation including detailed reaction mechanisms and a heat balance. Latter also accounts for heat conducting channel walls and external heat loss. If a washcoat is used, a set of one-dimensional reaction-diffusion equations is additionally applied for modeling the transport and heterogeneous reactions in the washcoat. Partial oxidation of methane to synthesis gas on rhodium coated monoliths has been studied as example.

Three-Dimensional Simulation of the Transient Behavior of a Three-Way Catalytic Converter

The ultimate goal in the numerical simulation of automotive catalytic converters is the prediction of exhaust gas emissions as function of time for varying inlet conditions, i.e. the simulation of a driving cycle. Such a simulation must include the calculation of the transient three-dimensional temperature-field of the monolithic solid structure of the converter, which results from a complex interaction between a variety of physical and chemical processes such as the gaseous flow field through the monolith channels, the catalytic reactions, gaseous and solid heat transport, and heat transfer to the ambience. This paper will discuss the application of the newly developed CFD-code DETCHEM MONOLITH for the numerical simulation of the transient behavior of three-way catalytic converters that have a monolithic structure. The code combines the two-dimensional simulations of the reactive flows in a representative number of monolith channels with a transient simulation of the three-dimensional temperature field of the solid structure of the converter including insulation and canning. The chemical reactions are modeled by a multi-step heterogeneous reaction mechanism, which is based on the elementary processes on the platinum and rhodium catalysts used. The integration over the chemical conversion in the single channels leads to the total conversion in the converter as function of time. This paper presents a numerical simulation of the startup phase of an automotive catalytic converter for temporally varying inlet conditions. The variation of the temperature distribution in the solid structure and in the single channels as well as the species profiles are described. The numerically predicted time-dependent conversion of the combustion pollutants is compared with experimental data. The potentials and limitations of the models and computational tools are discussed.

Influence of Physical and Chemical Parameters on the Conversion Rate of a Catalytic Converter: A Numerical Simulation Study

Monolithic three-way catalysts are applied to reduce the emission of combustion engines. The design of such a catalytic converter is a complex process involving the optimization of different physical and chemical parameters. Simple properties such as length, cell densities or metal coverage of the catalysts influence the catalytic performance of the converter. Numerical simulation is used as an effective tool for the investigation of the catalytic properties of a catalytic converter and for the prediction of the performance of the catalyst. To attain this goal, a two-dimensional flow field description is coupled with a detailed chemical reaction model. In this paper, results of the simulation of a monolithic single channel are shown. In a first step, the steady state flow distribution was calculated by a two dimensional simulation model. Subsequently, the reaction mechanism of the chemical species in the exhaust gas was added to the simulation process. The performance of the catalyst was simulated under lean, nearly stoichiometric and rich conditions. For these characteristic conditions, the oxidation of propen and CO and the reduction of NO on a typical Pt/Rh coated three-way catalyst were simulated as a function of temperature. The numerically predicted conversion data are compared with experimentally measured data. The simulation further reveals the coupling between chemical reactions and transport processes within the monolithic channel.

Modeling of Exhaust-Gas After-Treatment

This special issue of the International Journal of Emission Control Science and Technology presents a selection of the best papers given at the 5th International Symposium on Modeling of Exhaust-Gas After-Treatment (MODEGAT V) held in Bad Herrenalb/Karlsruhe, Germany, on September 3–5, 2017. The purpose of this biannual symposium is to support the exchange of state-of-the-art modeling and simulation techniques and new approaches among researchers, scientists, and engineers from industry and academia. The location, program, and low conference fee is set up to boost open discussions and new collaborations. Therefore, the number of attendees is limited to 100; as always, a good mix from participants was reached, this time 55% were from industry. In total, 56 contributions were presented at MODEGAT V in oral and poster presentations in subsequent sessions, each of them focusing on a special exhaust-gas after-treatment system and reaching from three-way catalysts (TWC), oxidation catalysts (DOC), selective catalytic-reduction (SCR), NOx storage catalysts (NSC), and particulate filters (DPF) to after-treatment systems. Individual topics were introduced by keynote lectures, which also served as tutorials for newcomers in the field. We wish to express our appreciation to those keynote speakers: A. Yezerets (Cummins Inc., USA) on SCR, G. Groppi (Politecnico di Milano, Italy) on CH4 oxidation, M. Votsmeier (Umicore, Germany) on TWC, and W. P. Partridge Jr. (Oak Ridge National Laboratory, USA) on the spatial resolution of reactions inside honeycomb monoliths. Tremendous reduction of hydrocarbons, carbon monoxide, nitric oxides, and particulates emitted from internal combustion engines is today achieved by the application of automotive catalytic converters and particulate filters, respectively. The systems commonly consist of monolithic structures of many parallel channels, each of which is coated with a porous catalytic active material or the porous walls serve as filter. The zcatalysts, commonly very expensive noble metals such as platinum, palladium, and rhodium, guarantee high conversion but also significantly contribute to high production costs of the automobile exhaust-gas after-treatment system; those costs are meanwhile on the order of the costs of the engine itself. Reduction of the amount of noble metal content without scarifying performance as well as overall optimization of the design and operational conditions of the exhaust-gas aftertreatment system demand a detailed understanding of the complex processes in the converter under varying inlet conditions, i.e., exhaust-gas compositions, flow rate, and temperature. Design and optimization of a catalytic converter is challenging due to the complex interaction between chemical reactions and mass and heat transfer. Experimental test bench measurements are finally needed but they also are expensive and time-consuming and, therefore, should be limited. Furthermore, those experiments are difficult to be interpreted concerning the details of the different chemical and physical processes inside the catalytic structure. Therefore, reliable models and numerical simulations can serve as a powerful method to investigate and eventually optimize the performance of emission control devices. The models and simulations tools, however, can only be of practical relevance if they are developed in close collaboration with the technical * Olaf Deutschmann deutschmann@kit.edu

SCR Technology for Off-highway (Large Diesel Engine) Applications

The term Off-Highway includes a great variety of diesel engine applications like propulsion of ships, mining trucks, harvesters, trains, power generation and pump drives, e.g. for hydraulic fracturing.