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The modeling of transient phenomena occurring inside an automotive 3-way catalytic converter poses a significant challenge to the emissions control engineer. Since the significant progress that has been observed with steady-state models cannot be directly exploited in this direction, it is necessary to develop a fully transient model and computer code incorporating dynamic behaviour of the three way catalytic converter in a relatively simple and effective way. The Laboratory of Applied Thermodynamics (LAT), Aristotle University Thessaloniki, is cooperating with the Engine Direction of FIAT Research Center, in the development of a computer code fulfilling these objectives, within the framework of an EEC Brite EuRam cost shared project. The CRF and LAT modeling approaches, along with the underlying philosophy and experimental work, are presented in this paper.

The objective of this study is to explain the physical and chemical mechanisms involved in the operation of a catalyzed diesel particulate filter. The study emphasizes on the coupling between reaction and diffusion phenomena (with emphasis on NO2 “back-diffusion”), based on modeling and experimental data obtained on the engine dynamometer. The study is facilitated by a novel multi-dimensional mathematical model able to predict both reaction and diffusion phenomena in the filter channels and through the soot layer and wall. The model is thus able to predict the species concentration gradients in the inlet/outlet channels, in the soot layer and wall, taking into account the effect of NO2 back diffusion. The model is validated versus engine dyno measurements. Two sets of measurements are employed corresponding to low-temperature “controlled” regenerations as well as high-temperature “uncontrolled” conditions.

The possibility to employ a single-brick system with a catalyzed filter (CDPF) for the after-treatment of diesel engines is potentially a promising and cost-effective solution. In the first part of this paper, the effectiveness of a single brick CDPF system towards reducing the gaseous CO and HC emissions is investigated experimentally and computationally. The second part of the paper deals with the behavior of single brick catalyzed filters compared with two brick systems comprising an upstream oxidation catalyst. The main differences of the two systems are highlighted in terms of regeneration efficiency and thermal loading, based on simulation results. The modeling work is based on a 3-dimensional model of the catalyzed filter and an axi-symmetric model of the oxidation catalyst. Model validations are presented based on engine bench testing.

As the Diesel Particulate Filter (DPF) technology is nowadays established, research is currently focusing on meeting the emission and durability requirements by proper system design. This paper focuses on the optimum combination between the catalytic coating and substrate structural properties using experimental and simulation methodologies. The application of these methodologies will be illustrated for the case of SiC substrates coated with innovative sol-gel coatings. Coated samples are characterized versus their uncoated counterparts. Multi-dimensional DOC and DPF simulation models are used to study several effects parametrically and increase our understanding on the governing phenomena. The comparative analysis of DOC/DPF systems covers filtration – pressure drop characteristics, CO/HC/NO oxidation performance, effect of washcoat amount and catalyst dispersion on oxidation activity and finally passive regeneration performance.

The objective of this paper is to study the parameters affecting the evolution of “uncontrolled” regeneration in diesel particulate filters with fuel-borne catalyst (FBC) support with emphasis on the development of thermal stresses critical for filter durability. The study is based on experiments performed on engine dynamometer, corresponding to “worst-case” scenario, as well as on advanced, multi-dimensional mathematical modeling. A new 2-dimensional mathematical model is presented which introduces an additional dimension across the soot layer and wall. With this dimension it is possible to take into account the variability of catalyst/soot ratio in the layer and to compute intra-layer composition gradients. The latter are important since they induce interesting O2 diffusion phenomena, which affect the regeneration evolution.

The design of integrated exhaust lines that combine particulate and NOx emission control is a multidimensional optimization problem. The present paper demonstrates the use of an exhaust system simulation platform which is composed of well-established multidimensional mathematical models for the transient thermal and chemical phenomena in DOC, DPF and SCR systems as well as connecting pipe heat transfer effects. The analysis is focused on the European Driving Cycle conditions. Illustrative examples on complete driving cycle simulations with and without forced regeneration events are presented for alternative design approaches. The results illustrate the importance of DOC and DPF heat capacity effects and connecting pipe heat losses on the SCR performance. The possibility of combining DPF and SCR functionality on a single wall-flow substrate is studied.

This paper focuses on some of the DPF system design issues where 3-dimensional modeling is necessary. The study is based on an existing 3-dimensional DPF model (axitrap) which is coupled to a commercial CFD code (Star-CD, CD-Adapco). The main focus is the effect of the inlet pipe geometry on soot distribution in the filter during loading and regeneration mode. The results show that due to the self-balancing effect, the resulting soot distribution in the filter under typical loading modes with low flow rates is quite uniform. With the assumption of adiabatic inlet pipe, the effect of non-symmetric inlet pipe is also negligible even during regeneration. However, under the realistic assumption of a non-adiabatic inlet pipe, the effect of inlet pipe geometry becomes very significant. Especially, for the case of a bent-shaped inlet pipe, the risk of impartial regeneration of the filter increases significantly.

The objective of this study is to present a particulate filter concept, based on a new porous material: INCOFOAM® HighTemp, a Ni-based superalloy foam. The paper examines the filtration and pressure drop characteristics as well as the regeneration performance of different filter configurations, based on experimental data and modeling. A number of different foam structures with variable pore characteristics are studied. The experimental testing covers flow and pressure drop behavior with air and exhaust gas, filtration efficiency measurements as function of particle size and regeneration rate measurements. The testing starts from mini-scale reactors and proceeds to real exhaust testing on the engine bench as well as vehicle tests on the chassis dynamometer and on-road. In parallel, a previously developed mathematical model is applied to study and understand the filtration and pressure drop mechanisms in the case of clean and soot loaded filters.

An alternative metal foam substrate for exhaust aftertreatment applications has been recently presented and characterized. The present paper focuses on the potential of the metal foam technology as an efficient DOC and CDPF substrates on real-world conditions. The target platform is a mid-size passenger car and the methodology includes both modeling and experiments. The experimental testing starts from small-scale reactor characterization of the basic heat/mass transfer properties and chemical kinetics. The results show that the foam structure exhibits excellent mass-transport properties offering possibilities for precious metal and catalyst volume savings for oxidation catalyst applications. These results are also used to calibrate an advanced 2-dimensional model which is able to predict the transient filtration and reaction phenomena in axial and radial flow systems.

This paper presents a mathematical model for the simulation of NOx traps during the storage and the regeneration phases. The objective is to validate the model under realistic exhaust gas conditions during NOx storage and release phases. The model is based on a previous modeling platform developed by Aristotle University which simulates the behavior of 3-way catalysts. The previous model is extended to include the additional reactions taking place on a NOx trap, with particular emphasis on the calculation of thermodynamic equilibrium effects. Moreover, the model includes the necessary reactions to simulate catalyst sulfation and de-sulfation processes. In parallel, a set of measurements are conducted under well controlled conditions with real diesel exhaust to study the storage and release phenomena under various operating conditions. The experimental data are used to calibrate the reaction kinetics and validate the model.

This paper presents experimental and modeling results related to the application of a novel material as a diesel particulate filter substrate. The material, trademarked as INCOFOAM® HighTemp, is a Ni-based superalloy foam. The material can be produced in sheet form with a large range of microstructure parameters. Thanks to the mechanical properties of the sheets, they can be flexibly shaped in various forms. The foam can be washcoated with active catalytic material to promote regeneration. The experimental testing covers flow and pressure drop behavior with air and exhaust gas, filtration efficiency measurements as function of particle size and regeneration rate measurements. The testing starts from mini-scale reactors and proceeds to real exhaust testing on the engine bench as well as vehicle tests with legislated driving cycles. Special emphasis is given to the characterization of the foam as a catalyst substrate.

Computer Aided Engineering (CAE) Methodologies are increasingly being applied to assist the design of SI-engine exhaust aftertreatment systems, in view of the stage III and IV emissions standards. Following this trend, the design of diesel exhaust aftertreatment systems is receiving more attention in view of the capabilities of recently developed mathematical models. The design of diesel exhaust systems must cope with three major aftertreatment categories: (i) diesel oxidation catalysts, (ii) diesel particulate filters and (iii) de-NOx catalytic converters. An integrated CAE methodology that could assist the design of all these classes of systems is described in this paper.

The design of a diesel particulate trap system to fit a specific vehicular application requires significant expenditure, due to the high degree of interaction between the vehicle operation and trap behavior. The assistance of modeling in the design process is already well established. This paper presents the basic principles of a Computer Aided Engineering methodology aimed to assist the selection of the basic parameters of a Diesel Particulate Trap System by reducing the number of the necessary experimental tests. The computational modules currently supporting the CAE methodology are based on fundamental mathematical models, incorporating a small number of semi-empirical relations derived by experimental data on trap loading and catalytic regeneration, exhaust system heat transfer and trap backpressure effect on fuel consumption.

In view of recent and future US and european regulations the design optimization of 3-way catalytic converters (3WCC) should also account for catalyst durability. The purpose of this paper is to extend the authors' approach for 3WCC modeling and evaluation in the direction of covering some aspects of ageing behavior. After a brief examination of the commonly accepted ageing mechanisms, a new methodology for the assessment of catalyst durability is formulated. This methodology takes into account the effect of thermal loading, high-temperature oxidation and poisoning of the catalyst. Based on the approach presented, along with the 3WCC and other related models and computer codes already in-use by the authors, a comparative assesment of engine bench ageing cycles may be computationally supported. Correlation of vehicle ageing cycles with engine bench cycles may also be accomplished as illustrated by a case study.

Due to the increasing pressure to develop small-size and low-cost after-treatment systems meeting the legislative demands it is desirable to integrate multiple functionalities and exploit any possible synergies. Typical examples include DPFs catalyzed with deNOx catalysts, as well as LNT-SCR combinations using layered coating technology. The present paper deals with the modeling challenges involved for the proper simulation of such advanced concepts. Key role in such advanced simulation attempts has the coupling between diffusion-reaction phenomena, which is captured through intra-layer modeling. All investigations in this paper deal with the application of possible combined LNT-SCR system configurations. The simulation results show that a dual bed LNT- passive SCR configuration offers substantial NOx emissions reductions compared to a single LNT catalyst and effectively controls secondary NH3 emissions produced during LNT regeneration phases.

In order to use modeling as a predictive tool for real-world particulate filter designs (segmented filters, non-axisymmetric designs), it is necessary to develop reliable 3-dimensional models. This paper presents a 3 d modeling approach, which is validated against engine-bench measurements with both FBC and CDPF systems. Special emphasis is given to the prediction of the transient inlet flow distribution, which is realized without resorting to external CFD software. The experimental and modeling results illustrate the 3-d nature of the problem, induced by the heat capacity and conductivity effects of the cement layers. It is possible to predict the localization of regeneration in certain areas of the filter (partial regeneration), as a result of poor heat transfer to thermally isolated regions in the filter. The accuracy of the model was validated by extensive comparisons with temperature measurements in 30 positions inside the filters and at various operating conditions.