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Technical Paper

Applications of Multi-layer Catalyst Modeling in deNOx and DPF Systems

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.
Technical Paper

Optimization Methodologies for DPF Substrate-catalyst Combinations

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.
Technical Paper

Development of Metal Foam Based Aftertreatment System on a Diesel Passenger Car

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.
Technical Paper

Model-based Optimization of Catalyst Zoning in Diesel Particulate Filters

Catalyzed wall-flow particulate filters are increasingly applied in diesel exhaust after-treatment for multiple purposes, including low-temperature catalytic regeneration, CO and hydrocarbon conversion, as well as exothermic heat generation during forced regeneration. In order to optimize Precious Metals usage, it may be advantageous to apply the catalytic coating non-uniformly in the DPF, a technology referred to as “catalyst zoning”. In order to simulate the behavior of such a filter, one has to consider coupled transport-reaction modeling. In this work, a previously developed model is calibrated versus experimental data obtained with full-scale catalyzed filters on the engine dynamometer. In a next step, the model is validated under a variety of operating conditions using engine experiments with zoned filters. The performance of the zoned catalyst is analyzed by examining the transient temperature and species profiles in the inlet and outlet channels.
Technical Paper

Model-based optimization methods of combined DPF+SCR Systems

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.
Technical Paper

Metal Foam Substrate for DOC and DPF Applications

A new metal foam material for diesel particulate filtration, trademarked as INCOFOAM® HighTemp, was recently presented. Extensive tests showed the potential of achieving filtration efficiencies of the order of 85% or more at low pressure drop using a radial flow design concept with graded foam porosity. By applying a catalytic washcoat, the foam exhibits enhanced gas mixing and thus higher conversion efficiencies at high space velocities. In addition, due to an excellent soot-catalyst contact, the washcoated foam exhibited high catalytic regeneration rates. The present paper focuses on a novel “cross-flow” design concept for a better filtration/pressure drop trade-off as well as application of the foam as an oxidation catalyst substrate. The experimental testing starts from small-scale reactors and proceeds to real exhaust testing on the engine bench as well as vehicle tests on the chassis dynamometer and on-road testing.
Technical Paper

Development and Experimental Validation of a NOx Trap Model for Diesel Exhaust

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.
Technical Paper

Filtration and Regeneration Performance of a Catalyzed Metal Foam Particulate Filter

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.
Technical Paper

Performance of Catalyzed Particulate Filters without Upstream Oxidation Catalyst

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.
Technical Paper

Study of Catalytic Regeneration Mechanisms in Diesel Particulate Filters Using Coupled Reaction-Diffusion Modeling

Diesel particulate filters are today widely accepted as a viable technology for drastically reducing particulate emissions from diesel engines. Current applications are based on some form of catalytic assistance for the filter regeneration purposes, either in the form of a fuel borne catalyst or by employing catalyzed filters. This paper presents an experimental and computational study of the prevailing reaction mechanisms in the catalyst supported DPF systems. The knowledge of the soot reaction kinetics in uncatalyzed filters with O2 and NO2 is a prerequisite in this respect. Next, the reaction rates in the case of using a Ce-based fuel-borne catalyst are evaluated. Emphasis is given on the importance of oxygen diffusion effects during uncontrolled regeneration. Finally, the regeneration mechanisms in a catalyst coated filter are studied.
Technical Paper

Modeling and Experimental Study of Uncontrolled Regenerations in SiC Filters with Fuel Borne Catalyst

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.
Technical Paper

Computer Aided Engineering in the Development of Diesel Exhaust Aftertreatment Systems

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.
Technical Paper

Computer Aided Assessment of Catalyst Ageing Cycles

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.
Technical Paper

Transient Modeling of 3-Way Catalytic Converters

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.