Monolithic Catalytic Converter Research Articles

Prediction of Heat Transfer and Fluid Flow Effects on Entropy Generation in a Monolithic Catalytic Converter Using Large-Eddy Simulation.

In the present work, heat transfer and fluid flow and their effects on entropy generation in a realistic catalytic converter of a Lada Niva 21214 vehicle are studied using large eddy simulation. At first, the pressure drop over the catalytic converter is measured for dry air at constant temperature ( K), different volumetric flow rates, and extrapolated to large volumetric flow rates for dry air ( K) and for the exhaust gas under realistic engine conditions ( K) using the Darcy–Forchheimer relation. Then, coupled heat and fluid flow phenomena inside the catalytic converter are analyzed for nonreacting isothermal conditions and nonreacting conditions with conjugate heat transfer by using the large-eddy simulation. The predicted pressure drop agrees well with the measured and extrapolated data. Based on the obtained numerical results, the characteristic flow features are identified, namely: the impinging flow with stagnation, recirculation, flow separation and laminarization within the fine ducts of the monolith, which depends on the heat transfer through temperature-dependent thermophysical properties of exhaust gas. Moreover, due to high-velocity gradients at the wall of the narrow ducts in the monolith, entropy production by viscous dissipation is observed predominantly in the monolith region. In contrast, entropy production due to heat transport is relatively small in the monolith region, while it overwhelms viscous dissipation effects in the pipe regions.

Design and analysis of exhaust manifold for multi-cylinder diesel engine with monolith catalytic converter using CFD

This paper discusses the challenges in converting the existing multi-cylinder diesel ventilation system into an innovative model of the manifold with monolithic. Reactant gases after treatment of car engines are increasingly being used for the benefit of environmental quality, especially in the large metropolitan region of the country, through the use of exhaust systems to bring an end to their main pollutants. A well-conditioned exhaust system increases the performance of the engine. The performance of the manifold has a significant impact on engine efficiency. With the accelerated growth of modern technology and numerical methods, computer simulation has become a valuable method for research and development of fluid flow systems. The industrial CFD (Computational Fluid Dynamics) software was used to analyze the exhaust manifold system. In order to enhance the fundamental understanding of manifold operations, extensive knowledge was obtained on the flow property distribution and heat transfer. Various calculations were performed to research the parametric impacts of working conditions and math on the exhibition of manifolds. Proposals were made to improve complex plan and execution.

INVESTIGATION OF PERFORMANCE AND EMISSION CHARACTERISTICS OF AN SI ENGINE FITTED WITH ZEOLITE-COATED CATALYTIC CONVERTER FOR VARIOUS ETHANOL-GASOLINE BLENDS

Ethanol blended in gasoline will produce more NOx emissions, compared to the conventional engine working under a stoichiometric air-fuel ratio. But, the emission control regulatory bodies tightened the emission level year by year. So, in our present work, a new metal-doped zeolite (as a catalyst)-coated monolith catalytic converter (CC) is developed and tested in the twin-cylinder multipoint fuel injection (MPFI) petrol engine using ethanol-gasoline blended fuels (P100, P95, P90, P85, and P80) (the numbers following P indicate percentage of the volumetric amount of gasoline). Initially, the engine was tested without a catalytic converter at various designated speed levels (2200, 2400, 2600, 2800, and 3000 rpm) and the emissions such as CO, HC, NOx, CO2, and O2 were calculated by an AVL 444 Di-gas analyzer at each speed level. The emission levels were compared and it was found that P80 blended fuel gives less emission. So, P80 blended fuel alone was taken for further investigation. Then, the market available catalytic converter was linked immediately to the exhaust gas outflow and a similar procedure was continued. Likewise, the testing was conducted with a new in-house-made Cu-ZSM5 zeolite catalytic converter. Outcomes from these experiments revealed that Cu-ZSM5 zeolite-based catalytic converter reduces NOx emission by 29% more effective than the market available catalytic converter for all the speeds.

Mathematical modeling of automotive catalytic converter for catalytic combustion of the volatile organic compound (voc) methane

Monolithic catalytic converters are used to minimize the emission of air pollutants to the environment. Volatile organic compounds (VOCs) are seen to be released in considerable amounts from these catalytic converters during the warm-up period. In this paper, the conversion of a slow oxidizing volatile organic compound (VOC) methane is analysed with numerical simulation using a noble metal catalyst (Pt/δ-Al2O3) and metal oxide catalyst CuO/δ-Al2O3. The transient, one-dimensional monolith model is developed using gas-phase energy balance, solid-phase energy balance, and gas-phase mass balance. The unsteady state analysis consists of a system of partial differential equations (PDEs). These equations are solved using an Implicit Scheme with the help of Matlab software. The conversion of methane is analysed with reaction temperature for both Pt/δ-Al2O3 catalyst and CuO/δ-Al2O3 catalyst. Also, the effect of the ageing of catalysts on catalytic converter performance was analysed.

An Investigation on the Performance of an Oxidation Catalyst Using Two-dimensional Simulation with Detailed Reaction Mechanism

Abstract The advent of stricter emission standards has increased the importance of aftertreatment devices and the role of numerical simulations in the evolution of better catalytic converters in order to satisfy these emission regulations. In this paper, a 2-D numerical simulation of a single channel of the monolith catalytic converter is presented by using detailed surface reaction kinetics aiming to investigate the chemical behaviour inside the converter. The model has been developed to study the conversion of carbon monoxide (CO) in the presence of propene (C3H6) for low-temperature combustion (LTC) engine application. The inhibition effect of C3H6 over a wide range of CO inlet concentrations is investigated. Considering both low and high levels of CO concentration at the inlet, the 2-D model predicted better results than their corresponding 1-D counterparts when compared with the experimental data from literature. It was also observed that C3H6 inhibition at high temperatures was significant, particularly for high concentrations of CO compared to low concentrations of CO at the inlet.

Modeling the combustion of volatile organic compound (VOC) ethane in monolithic catalytic converter

Air pollution a potential environmental problem is caused mostly by the burning of fuels both in the transport sectors and industrial sectors. Motor vehicles are one of the significant growing air pollution contributors who produce a considerable amount of volatile organic compounds (VOCs) and other pollutants. The rising concern about the environmental effect of the exhaust emission pollutants has led to the need for the development of progressively efficient catalytic converters and exhaust gas after-treatment systems. Mathematical modeling is an essential way to understand the processes occurring in the catalytic converter, and it plays a critical part in improving and designing the existing models. A mathematical model has been formed for both non-catalytic and catalytic reactions based on mass and heat transfer for the oxidation of VOC ethane. Modeling equations have been solved with an implicit scheme, and numerical calculations have carried out using Matlab software. The results have been compared, obtained from the two reactions mechanisms.

Hybrid FEM and FDM Approach for Monolithic Catalytic Converters with Pore Diffusion

A transient, three-dimensional model is developed for monolith catalytic converters with washcoat pore diffusion. Due to the unique configuration of monolith converters, the flow within the channel can be considered fully developed laminar flow, and one-dimensional transport equations can be formulated for the flow and species. On the other hand, a three-dimensional equation is necessary for the monolith solid temperature to capture the effects of significant external heat loss or flow maldistribution. The proposed model employs a three-dimensional finite-element method (FEM) for the solid temperature equation and a one-dimensional finite-difference method (FDM) for the flow and species equations. A recently developed asymptotic approach (Bissett, Emiss. Control Sci. Technol. 1(1), 3–16, 2015, Bissett, Emiss. Control Sci. Technol. 5(1), 45–54, 2019) is utilized to solve the washcoat pore diffusion and surface coverages equations. The three-dimensional FEM meshes are chosen so the nodes also serve for the one-dimensional transport equations. All equations are solved fully coupled, without lagging or reliance upon external tools. The developed solver can efficiently simulate general cross-section geometries (circle, oval, rectangle, etc.) for a catalytic monolith under nonuniform inlet distribution and detailed washcoat pore diffusion. The solver is verified by comparing the simulation results to the one-dimensional simulation results for a simple geometry under uniform inlet conditions. The model can be applied to flow through general monolith catalytic reactors with single or dual washcoat layers and a wide range of kinetics.

A case study in multi‐scale model reduction: The effect of cell density on catalytic converter performance

One of the challenges of full‐scale computer simulation of a catalytic reactor is to consider the different scales involved in the problem in a practical fashion. In a monolith catalytic converter, these scales range from the molecular scale for the reactions, through the pore scale, washcoat scale, channel scale, and finally the full converter scale. This paper describes the implementation of a model reduction methodology using look‐up tables to perform a consistent comparison of six different catalytic converters used for the catalytic combustion of methane. A detailed mechanistic model for methane combustion is used. Diffusion in the non‐uniform washcoat is considered. The converters have different cell densities and wall thicknesses. Steady state and transient light‐off simulations are performed. Efficient computational speed is achieved by successive model reduction, which allows the preservation of detailed small‐scale information. The results obtained show that there is a non‐intuitive relationship between the various operating parameters, which can only be deduced from a comprehensive model.

Towards the simulation of the catalytic monolith converter using discrete channel-scale models

Over the past twenty years, several computer models for structured catalytic reactors such as the monolith converter have been developed with various levels of complexity and accuracy. Despite the availability of faster and faster computers, no reports have been made yet on the successful simulation of transport phenomena in every channel of a monolith catalytic converter by means of a full three-dimensional discrete model. The purpose of this work is to show the potential of such a model, based on the lattice Boltzmann method (LBM), for simulating fluid flow in an elliptical shaped honeycomb monolith reactor comprising a total of 7539 parallel channels. This example of industrial relevance will serve to evidence the progress made in computer modeling in recent years, but also to bring up aspects that need to be further improved, such as the use of LBM to simulate efficiently turbulent flow and heat and mass transfer in this type of structured catalytic reactors.

One + One‐Dimensional Modeling of Monolithic Catalytic Converters

AbstractThe inclusion of a washcoat model into monolithic catalyst simulations in order to create a one + one‐dimensional framework using a minimum number of parameters is reviewed. All assumptions and numerical methods are presented while ensuring the prevention of excessive temperature excursions. Parametric studies illustrate the influence of model parameters (porosity, wall thickness, pore diameter) on the conversion of carbon monoxide during a light‐off experiment using a uniform washcoat. Moreover, simulating a layered washcoat of dissimilar catalytic materials demonstrates a significant influence on conversion characteristics depending on the order of the layers. As a result, employing a washcoat requires careful consideration of the advection of the gas, the reactions occurring in each catalytic material, material layering, the diffusion properties of the different species, and the characteristics of the washcoat.

Numerical Investigation of Radiation Effects in Monolithic Catalytic Combustion Reactors

In modeling catalytic combustion in a monolithic catalytic converter, it is generally assumed that the gas within the individual monolith channels does not interfere with thermal radiation. To date, no quantitative study has been undertaken to validate this assumption. Past studies for carbon monoxide combustion also appear to indicate that the emissivity of the washcoat has little effect on the thermal radiation field. In order to investigate these two issues, methane-air combustion on platinum is modeled inside a single channel of a monolith using a detailed surface reaction mechanism comprised of 24 reactions between 19 species. Radiation transport is modeled using the Discrete Ordinates Method and a gray formulation. Planck-mean absorption coefficients of the gases, calculated from the HITEMP and HITRAN databases, are used to investigate participating medium effects. All calculations were performed using the commercial CFD code, CFD-ACE+™, supplemented by user-subroutines for calculating the radiative properties of the gas mixture. Results show that the conversion percentages and temperature distributions are unaltered by the inclusion of participating medium radiation effects, verifying the commonly held belief, stated earlier. However, in strong contrast with carbon monoxide combustion, the emissivity of the washcoat was found to significantly affect flammability limits in the case of methane combustion—the flame being hotter and more stable for smaller values of emissivity.

Numerical Investigation of Radiation Effects in Monolithic Catalytic Combustion Reactors

In modeling catalytic combustion in a monolithic catalytic converter, it is generally assumed that the gas within the individual monolith channels does not interfere with thermal radiation. To date, no quantitative study has been undertaken to validate this assumption. Past studies for carbon monoxide combustion also appear to indicate that the emissivity of the washcoat has little effect on the thermal radiation field. In order to investigate these two issues, methane-air combustion on platinum is modeled inside a single channel of a monolith using a detailed surface reaction mechanism comprised of 24 reactions between 19 species. Radiation transport is modeled using the Discrete Ordinates Method and a gray formulation. Planck-mean absorption coefficients of the gases, calculated from the HITEMP and HITRAN databases, are used to investigate participating medium effects. All calculations were performed using the commercial CFD code, CFD-ACE+™, supplemented by user-subroutines for calculating the radiative properties of the gas mixture. Results show that the conversion percentages and temperature distributions are unaltered by the inclusion of participating medium radiation effects, verifying the commonly held belief, stated earlier. However, in strong contrast with carbon monoxide combustion, the emissivity of the washcoat was found to significantly affect flammability limits in the case of methane combustion—the flame being hotter and more stable for smaller values of emissivity.

Adaptation and application of the In Situ Adaptive Tabulation (ISAT) procedure to reacting flow calculations with complex surface chemistry

In this article, the In Situ Adaptive Tabulation (ISAT) procedure, originally developed for the efficient computation of homogeneous reactions in chemically reacting flows, is adapted and demonstrated for reacting flow computations with complex heterogeneous (or surface) reactions. The treatment of heterogeneous reactions within a reacting flow calculation requires solution of a set of nonlinear differential algebraic equations at boundary faces/nodes, as opposed to the solution of an initial value problem for which the original ISAT procedure was developed. The modified ISAT algorithm, referred to as ISAT-S, is coupled to a three-dimensional unstructured reacting flow solver, and strategies for maximizing efficiency without hampering accuracy and convergence are developed. These include use of multiple binary tables, use of dynamic tolerance values to control errors, and periodic deletion and/or re-creation of the binary tables. The new procedure is demonstrated for steady-state catalytic combustion of a methane–air mixture on platinum using a 24-step reaction mechanism with 19 species, and for steady-state three-way catalytic conversion using a 61-step mechanism with 34 species. Both reaction mechanisms are first tested in simple 3D channel geometry with reacting walls, and the impact of various ISAT parameters is investigated. It is found that the temperature of the reacting wall dictates the retrieval rate from the ISAT table. As a final step, the catalytic combustion mechanism is demonstrated in an laboratory-scale monolithic catalytic converter geometry with 57 channels discretized using 354,300 control volumes (4.6 million unknowns) after employing quarter symmetry. For this particular case, the use of ISAT-S resulted in reduction of the overall CPU time from 19.3 to 13.6 h. For all of the cases considered, the reduction in the time taken to perform surface chemistry calculations alone was found to be a factor of 5–11.

Toward simulation of full-scale monolithic catalytic converters with complex heterogeneous chemistry

Computational fluid dynamic (CFD) modeling of full-scale catalytic converters with realistic chemistry has remained elusive primarily due to the extreme computational requirements. In this work, a new low-memory coupled implicit solver, based on the conservative unstructured finite-volume method, was utilized to simulate laboratory-scale catalytic converters with implicit coupling between fluid flow, heat transfer (including conjugate heat transfer), mass transfer, and heterogeneous chemical reactions. Steady-state calculations were performed for a catalytic methane–air combustion process with 24 reaction steps and 19 species (8 gas-phase species, 11 surface-adsorbed species), and for a three-way catalytic conversion process with 61 reaction steps and 31 species (8 gas-phase species, 23 surface-adsorbed species). Both calculations were conducted on a single processor for a monolith with 57 channels discretized using 354,300 control volumes. The catalytic combustion simulation was completed in 19 h and required 900 MB of memory, while the three-way conversion simulation required 6 days and 1 GB of memory, indicating that the complexity of the surface reaction mechanism dominates the overall CPU time requirements. Subsequently, the solver was parallelized, and the same catalytic combustion case was simulated for a monolith with 293 channels discretized using 1.27 million control volumes. A 4-node cluster was utilized for the parallel computations, and the parallelization efficiency was found to be about 80%.

Low‐dimensional models for real time simulations of catalytic monoliths

AbstractWe present accurate low‐dimensional models for real time simulation, control, and optimization of monolithic catalytic converters used in automobile exhaust treatment. 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 diffusional effects without using the concept of the effectiveness factor. The models reduce to the classical two‐phase models in the limit of vanishingly thin washcoat. The models are validated by simulating the transient behavior of a three‐way converter for various cases and comparing the predictions with detailed solutions. It is shown that these new 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 monolithic and other catalytic reactors. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Optimal design of axial noble metal distribution for improving dual monolithic catalytic converter performance

In practical applications, monolithic catalytic converters are operated at non-isothermal conditions. In this case, the active metal distribution along the length of the converter may influence its performance. Indeed, better conversions can be achieved by controlling the distribution of the same quantity of active material. In this study, we used a one-dimensional catalyst model to predict the transient thermal and conversion characteristics of a dual monolithic catalytic converter with Platinum/Rhodium (Pt/Rh) catalysts. The optimal design of a longitudinal noble metal distribution of a fixed amount of catalyst is investigated to obtain the best performance of a dual monolithic catalytic converter. A micro-genetic algorithm with considering heat transfer, mass transfer, and chemical reactions in the monolith during the FTP-75 cycle was used. The optimal design for the optimal axial distribution of the catalyst was determined by solving multi-objective optimization problems to minimize both the CO cumulative emissions during the FTP-75 cycle, and the difference between the integral value of a catalyst distribution function over the monolith volume and total catalytic surface area over the total monolith volume.

Comparison of Unsteady State and Quasi Steady State Modeling for Hydrocarbons in a Monolithic Catalytic Converter

In this study numerical solutions are obtained using quasi steady state and unsteady state conditions to predict the reduction in concentrations of polluting hydrocarbons. Before their release to the atmosphere these gases undergo catalytic after-treatment in a converter, causing a decrease in their concentrations. Both homogenous as well as heterogeneous reactions are considered for hydrocarbons propylene and propane. Quasi steady and unsteady state models are developed to simulate heat and mass transfer between the exhaust gas and the catalyst surface, convective heat and mass transport, chemical reactions and the related heat release along with heat conduction in the substrate.

Modeling the Effect of Temperature on Propylene Conversion during Warm-Up in a Monolithic Converter

In order to improve air quality, catalytic converters have been extensively employed throughout the world. These monolithic catalytic converters are very effective in reducing pollution only after they have heated up. The catalyst warming-up process takes some time and during this period a considerable amount of pollutants, especially hydrocarbons, is released into the atmosphere. In this paper, a one-dimensional model for the hydrocarbon propylene was developed, taking into account heat and mass transfer between the exhaust gas and the catalyst surface and the catalytic reaction. The equations so formed are a set of ordinary differential equations (ODEs) and a partial differential equation (PDE). The ODEs are solved using the Runge-Kutta method of fourth order and the PDE by backward implicit scheme. The effect of varying the inlet gas temperature and initial catalyst solid temperatures on conversion of propylene was analysed.

Editorial: Special Issue Contributed by CITICOMS 2007 - International Conference on Modeling and Simulation, Selected Papers

Coimbatore Institute of Technology, India, organized an International Conference on Modeling and Simulation (CITICOMS 2007) during August 27–29, 2007. The conference covered research works on modeling & simulation in a large number of diverse disciplines viz., biotechnology, chemical engineering, mechanical engineering, civil engineering, mathematics and nanotechnology, electrical engineering, electronic engineering and computer engineering.This special issue presents a set of nine selected research papers, which have undergone the peer-review process of the journal of Chemical Product and Process Modeling. Although these papers do not cover the entire gamut of modeling and simulation activities, they certainly present interesting and useful topics. In particular these topics include the black box modeling approach for identification of nonlinear systems, kinetic modeling of the adsorptive removal of toxic and hazardous pollutants from wastewaters, analysis and modeling of homogeneous tubular reactors, monolithic catalytic converters, and a constitutive model equation for the rheological behaviour of three phase polymer blends or so called double emulsions.

Modeling Catalytic and Homogenous Combustion of Hydrocarbons in Monolithic Converters

In order to meet the strict future emission standards monolithic catalytic converters play a very important role. Although they have been extensively studied, still there are some areas that need to be further explored like the warm up period, during which the hydrocarbon emissions are relatively high. A single channel one-dimensional model can help evaluate the physicochemical processes occurring in the converter. In this study a decrease in the level of hydrocarbon emissions for propylene and propane during cold start are analysed taking into consideration the effect of both catalytic and homogenous reactions. The model proposed accounts for the combined effect of heat transfer, mass transfer and exothermic chemical reactions which are all strongly coupled.