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The transient heat transfer behavior of an automotive catalytic converter has been simulated with OpenFOAM in 1D. The model takes into consideration the gas-solid convective heat transfer, axial wall conduction and heat capacity effects in the solid phase, but also the chemical reactions of CO oxidation, based on simplified Arrhenius and Langmuir-Hinshelwood approaches. The associated parameters are the results of data in literature tuned by experiments. Simplified cases of constant flow rates and gas temperatures in the catalyst inflow have been chosen for a comprehensive analysis of the heat and mass transfer phenomena. The impact of inlet flow temperatures and inlet flow rates on the heat up characteristics as well as in the CO emissions have been quantified. A dimensional analysis is proposed and dimensionless temperature difference and space-time coordinates are introduced.

In the last years, as a response to the more and more restrictive emission legislation, new devices (SRC, DOC, NOx-trap, DPF) have been progressively introduced as standard components of modern after-treatment system for Diesel engines. In addition, the adoption of electrical heating is nowadays regarded with interest as an effective solution to promote the light-off of the catalyst at low temperature, especially at the start-up of the engine and during the low load operation of the engine typical of the urban drive. In this work, a state-of-the-art 48 V electrical heated catalyst is considered, in order to investigate its effect in increasing the abatement efficiency of a standard DOC. The electrical heating device considered is based on a metallic support, arranged in a spiral layout, and it is heated by the Joule effect due to the passage of the electrical current.

Metallic open-cell foams have proven to be valuable for many engineering applications. Their success is mainly related to mechanical strength, low density, high specific surface, good thermal exchange, low flow resistance and sound absorption properties. The present work aims to investigate three principal aspects of real foams: the geometrical characterization, the flow regime characterization, the effects of the pore size and the porosity on the pressure drop. The first aspect is very important, since the geometrical properties depend on other parameters, such as porosity, cell/pore size and specific surface. A statistical evaluation of the cell size of a foam sample is necessary to define both its geometrical characteristics and the flow pattern at a given input velocity. To this purpose, a procedure which statistically computes the number of cells and pores with a given size has been implemented in order to obtain the diameter distribution.

Objective of this work is the incorporation of the flame stretch effects in an Eulerian-Lagrangian model for premixed SI combustion in order to describe ignition and flame propagation under highly inhomogeneous flow conditions. To this end, effects of energy transfer from electrical circuit and turbulent flame propagation were fully decoupled. The first ones are taken into account by Lagrangian particles whose main purpose is to generate an initial burned field in the computational domain. Turbulent flame development is instead considered only in the Eulerian gas phase for a better description of the local flow effects. To improve the model predictive capabilities, flame stretch effects were introduced in the turbulent combustion model by using formulations coming from the asymptotic theory and recently verified by means of DNS studies. Experiments carried out at Michigan Tech University in a pressurized, constant-volume vessel were used to validate the proposed approach.

Metallic foams or sponges are materials with a cell structure suitable for many industrial applications, such as reformers, heat catalytic converters, etc. The success of these materials is due to the combination of various characteristics such as mechanical strength, low density, high specific surface, good thermal exchange properties, low flow resistance and sound absorption. Different materials and manufacturing processes produce different type of structure and properties for various applications. In this work a genetic algorithm has been developed and applied to support the design of catalytic devices. In particular, two substrates were considered, namely the traditional honeycomb and an alternative open-cell foam type. CFD simulations of pressure losses and literature based correlations for the heat and mass transfer were used to support the genetic algorithm in finding the best compromise between flow resistance and pollutant abatement.

In this work a detailed model to simulate the transient behavior of catalytic converters is presented. The model is able to predict the unsteady and reacting flows in the exhaust ducts, by solving the system of conservation equations of mass, momentum, energy and transport of reacting chemical species. The en-gine and the intake system have not been included in the simulation, imposing the measured values of mass flow, gas temperature and chemical composition as a boundary condition at the inlet of the exhaust system. A detailed analysis of the diffusion stage triggering is proposed along with simplifications of the physics, finalized to the reduction of the calculation time. Submodels for water condensation and its following evaporation on the monolith surface have been taken into account as well as oxygen storage promoted by ceria oxides.

Nowadays a great attention is paid to the level and quality of noise radiated from the tailpipe end of intake and exhaust systems, to control the gas dynamic noise emitted by the engine as well as the characteristics of the cabin interior sound. The muffler geometry can be optimized consequently, to attenuate or remark certain spectral components of the engine noise, according to the result expected. Evidently the design of complex silencing systems is a time-consuming operation, which must be carried out by means of concurrent experimental measurements and numerical simulations. In particular, 1D and multiD linear/non-linear simulation codes can be applied to predict the silencer behavior in the time and frequency domain. This paper describes the development of a 1D-multiD integrated approach for the simulation of complex muffler configurations such as reverse chambers with inlet and outlet pipe extensions and perforated silencers with the addition of sound absorbing material.

The paper describes the experimental and simulation work recently carried out to investigate the effects of secondary air injection on the emission conversion in the exhaust after-treatment system of a S.I. automotive engine. The modeling of the 1D unsteady reacting flows in the complete exhaust system of a spark ignition engine, designed to satisfy the Euro IV limits, has been performed including the secondary air injection system, to predict the possible shortening of catalyst light-off time and the speed-up of the after-treatment system warm-up. The transport of chemical species with reactions in gas phase (post-oxidation of unburned HC in the exhaust manifold) and in solid phase (conversion of pollutants in the catalyst) with and without secondary air has been simulated by the 1D thermo-fluid dynamic model GASDYN, developed by the authors.

The paper describes the research work concerning the simulation of 1D unsteady reacting flows in s.i. engine pipe-systems, including pre-catalysts and main catalysts. The numerical model GASDYN has been developed to enable the concurrent prediction of the wave motion in the intake and exhaust ducts, the chemical composition of the gas discharged by the cylinder of a s.i. engine, the chemical and thermal behavior of catalytic converters. The effect of considering the transport of chemical species with reactions in gas phase (post-oxidation of unburned HC in the exhaust manifold) and in solid phase (conversion of pollutants in the catalyst) on the predicted wave motion is reported.

Nowadays 1D fluid dynamic models are widely used by engine designers, since they can give sufficiently accurate predictions in short times, allowing to support the optimization and development work of any prototype. According to the last requirements in terms of pollutant emission control, some enhancements have been introduced in the 1D code GASDYN, to improve its ability in predicting the composition of the exhaust gas discharged by the cylinders and the transport of the chemical species along the exhaust system. The main aspects of the methods adopted to model the combustion process and the related formation of pollutants are described in the paper. To account for the burnt gas stratification, two different approaches have been proposed, depending on the expected turbulence levels inside the combustion chamber. The reliability of the simulation of the pollutant formation process has been enhanced by the integration of the thermodynamic module with the Chemkin code.

This paper describes some recent advances of the research work concerning the 1D fluid dynamic modeling of unsteady reacting flows in s.i. engine pipe-systems, including pre-catalysts and main catalysts. The numerical model GASDYN developed in previous work has been further enhanced to enable the simulation of the catalyst. The main chemical reactions occurring in the wash-coat have been accounted in the model, considering the mass transfer between gas and solid phase. The oxidation of CO, C3H6, C3H8, H2 and reduction of NO, the steam-reforming reactions of C3H6, C3H8, the water-gas shift reaction of CO have been considered. Moreover, an oxygen-storage sub-model has been introduced, to account for the behavior of Cerium oxides. A detailed thermal model of the converter takes into account the heat released by the exothermic reactions as a source term in the heat transfer equations. The influence of the insulating mat is accounted.

This paper deals with some recent advances in the field of 1D fluid dynamic modeling of unsteady reacting flows in complex s.i. engine pipe-systems, involving a catalytic converter. In particular, a numerical simulation code has been developed to allow the simulation of chemical reactions occurring in the catalyst, in order to predict the chemical specie concentration in the exhaust gas from the cylinder to the tailpipe outlet, passing through the catalytic converter. The composition of the exhaust gas, discharged by the cylinder and then flowing towards the converter, is calculated by means of a thermodynamic two-zone combustion model, including emission sub-models. The catalytic converter can be simulated by means of a 1D fluid dynamic and chemical approach, considering the laminar flow in each tiny channel of the substrate.

The paper describes the 1-D fluid dynamic modeling of unsteady flows with chemical specie tracking in the ducts of a four-cylinder s.i. automotive engine, to predict the composition of the exhaust gas reaching the catalyst inlet. A comprehensive simulation model, based on classical and innovative numerical techniques for the solution of the governing equations, has been developed. The non-traditional shock-capturing CE-SE (Conservation Element-Solution Element) method has been extended to deal with the propagation of chemical species. A comparison of the MacCormack method plus FCT or TVD algorithms with the CE-SE method has pointed out the superiority of the latter scheme in the propagation of contact discontinuities. A realistic composition of the exhaust products in the cylinder, evaluated by a two-zone combustion model including emission sub-models, has been imposed at the opening of the exhaust valve, considering the effect of short-circuit of air during valve overlap.