12th DOE Crosscut Workshop
on Lean Emissions Reduction SimulationApril 28th - 30th, 2009University of Michigan - Dearborn, 4901 Evergreen Road, Dearborn, Michigan 48128
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HC-SCR for Diesel NOx Reduction on Supported Metal Catalysts
Richard Blint, GM R & D Center
Richard Blint, Steven J. Schmieg and Michael B. Viola
General Motors R&D Center, Chemical and Environmental Sciences Laboratory
General Motors R&D Center
30500 Mound Rd
Warren, MI 48090-9055
The SCR of NO using hydrocarbons (HC-SCR) has been studied extensively as a potential alternative method for the removal of NOx under oxygen-rich conditions . HC-SCR utilizes the fuel on board the vehicle as the NOx reductant, and does not require the complex engine control and large amounts of expensive platinum-group metal catalysts employed in NOx storage catalyst systems. While the conversion efficiencies reported in the literature are commonly > 80% over various temperature ranges, the adaptability of these results to the reduction of NOx from light-duty diesel exhaust is difficult. A unique catalyst developed using high-throughput discovery techniques in collaboration with BASF Corporation was investigated at General Motors under simulated diesel engine exhaust feed conditions for the selective catalytic reduction of NOx as part of a Department of Energy (DOE) supported cooperative project (DE-FC26-02NT41218). Consequently the effects of NOx (as NO or NO2), hydrocarbon concentration level (HC:NOx ratio), oxygen concentration, NO concentration, catalyst space velocity, catalyst temperature, and the co-presence of hydrogen on steady-state NOx reduction activity were measured in a laboratory flow reactor system. NOx reduction over Ag/Al2O3 catalysts in a laboratory flow reactor system using a simulated diesel fuel mixture will be presented at the temperatures, flow rates, and inlet NOx concentrations likely to be encountered by a HC-SCR catalyst system on a light-duty compression ignition direct injection (diesel) vehicle under the FTP, US06, and HWYFET test schedules. In addition, using a V6 turbo charged diesel engine connected to a dynamometer running light-duty transient test cycles, NOx efficiency was evaluated as a function of catalyst volume, the hydrocarbon to NOx ratio (HC/NOx), and space velocity.
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Analytical solutions for convection, diffusion and chemical reaction in Diesel Particulate Filters
Athanasios Konstandopoulos, APT Lab, CPERI/CERTH
The goal of the present work is to derive analytical solutions for the problem of convection, diffusion and chemical reaction in wall-flow monoliths. The advantage of having an analytical solution instead of solving numerically is obvious as it not only brings full scale simulations of diesel particulate filters to the real time domain, but also enables efficient implementations on computationally limited ECUs for on-board management and control of emission control systems. The presentation depicts the mathematical problem formulation, the governing dimensionless parameters and the corresponding assumptions. Then the analytical solution is derived and several asymptotic (for limiting values of the parameters) and approximating solutions are developed, corresponding to different physical situations. Reactant distributions in the filter are presented and discussed for several values of the parameters. The conclusion is that the classic single channel model for DPF simulation can for all practical conditions accommodate diffusive phenomena with no added computational cost and without significantly altering the structure of existing code implementations.
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Passive Ammonia SCR for Lean SIDI Engines: Experiments
Wei Li, GM R&D Center
Wei Li, Kevin L. Perry, Kushal Narayanaswamy, Chang H. Kim, and Paul Najt
In this talk we present a new concept for lean NOx aftertreatment system for stratified SIDI engines. This new concept offers significant cost advantage over the conventional LNT or urea SCR systems. Steady state and transient dynamometer test results will be presented and the potential and limitations of this new concept will be discussed.
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Development of Real Time Hybrid Neural Network Catalyst Model for Engine & Powertrain Control Design
Syed Wahiduzzaman, Gamma Technologies
Development of Real Time Hybrid Neural Network Catalyst Model for Engine & Powertrain Control Design
Dr. Syed Wahiduzzaman
Gamma Technologies Inc.
ABSTRACT
Engines and vehicle systems are becoming increasing complex partly due to the incorporation of emission abatement components as well as control strategies that are technologically evolving and innovative to keep up with emissions requirements. This makes the testing and verification with actual prototypes prohibitively expensive and time-consuming. Consequently, there is an increasing reliance on Software-In-the-Loop (SIL) and Hardware-In-the-Loop (HIL) simulations for design evaluation of system concepts.
This paper introduces a methodology in which detailed chemical kinetic models of catalytic converters are transformed into fast running models for control design, calibration or real time ECU validation. The proposed methodology is based on the use of a hybrid, structured, semi-automatic scheme for reducing high-fidelity models into fast running models. The resulting hybrid model consists of a set of neural network-based static sub-models that account for the large non-linearity of the system, concatenated with physical sub-models that account for the dynamics and hysteresis that are inherent in the processes being modeled.
A model of DOC-SCR catalyst system was chosen as the surrogate for this methodology. In this regards, the paper will describe procedures involving identification of relevant parameters using experimental data and design of experiment (DOE) optimization. The DOE results were used to train hybrid-NN Model. The hybridization is achieved by incorporation of physical sub-models for coverage and catalyst warm-up within NN model. The comparison of the results show that the methodology conserves accuracy and achieves computational efficiency, thus making advanced engine control design, calibration and ECU validation (involving coupled engine, aftertreatment and vehicle models) in some cases simply feasible, and in other cases more secure, faster and easier.
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NOx Storage-Reduction Characteristics of Lean NOx Trap Catalysts Subjected to Simulated Road Aging
Mark Crocker, University of Kentucky
NOx Storage-Reduction Characteristics of Lean NOx Trap Catalysts Subjected to Simulated Road Aging
Yaying Ji1, Courtney Fisk1, Vence Easterling 1, Mark Crocker1*,
Jae-Soon Choi2, William Partridge2
1 Center for Applied Energy Research, University of Kentucky,
2540 Research Park Drive, Lexington, KY 40511-8479
2 Fuels, Engines, and Emissions Research Center, Oak Ridge National Laboratory,
2360 Cherahala Blvd., Knoxville, TN 37932-1563
Although Lean NOx Trap (LNT) catalyst technology has made significant strides in recent years, the issue of LNT durability remains problematic. Following on from our previous research concerning the effect of ceria addition on LNT performance, in this study we focus on the role of ceria in ameliorating the deterioration of Ba-based LNT catalysts during aging. Indeed, we have observed that spectacular improvements in LNT durability can be achieved through the incorporation of CeO2-ZrO2 into the LNT formulation, and, to a lesser extent, La-stabilized ceria.
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NOx Storage-Reduction Characteristics of Lean NOx Trap Catalysts Subjected to Simulated Road Aging
Yaying Ji, University of Kentucky
Although Lean NOx Trap (LNT) catalyst technology has made significant strides in recent years, the issue of LNT durability remains problematic. Following on from our previous research concerning the effect of ceria addition on LNT performance, in this study we focus on the role of ceria in ameliorating the deterioration of Ba-based LNT catalysts during aging. Indeed, we have observed that spectacular improvements in LNT durability can be achieved through the incorporation of CeO2-ZrO2 into the LNT formulation, and, to a lesser extent, La-stabilized ceria.
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Development of a 1-D CPF Model to Simulate Active Regeneration of a Diesel Particulate Filter
Kiran Premchand, Michigan Tech University
A quasi-steady 1-dimensional computer model of a catalyzed particulate filter (CPF) has been developed at MTU. This model is capable of simulating the processes that are associated with the flow, filtration, gas-phase kinetics and particulate matter (PM)-related kinetics that take place in the particulate filter during active regeneration via fuel injection upstream of a diesel oxidation catalyst placed upstream of the particulate filter or other means of elevating the filter inlet gas temperature. By doing so, the model is able to predict overall pressure drop across the particulate filter and its components during various stages of the active regeneration experiments such as loading, active regeneration and post-loading, PM mass balance (and its location-wise distribution), gaseous species concentrations, filtration efficiency, gas temperature and velocities as functions of axial location in the CPF and time. In this presentation, an overview of the development of this model from the governing equations is shown. Results from calibrating the model to data obtained from a set of experiments conducted at MTU are also presented.
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Dual SCR Aftertreatment for Lean NOx Reduction
Galen Fisher, Delphi Powertrain Systems
Galen B. Fisher*, Craig L. DiMaggio, Ken M. Rahmoeller, Mark Sellnau
Delphi Powertrain Systems
3000 University Drive, Auburn Hills, MI 48326
(*Presently at the Dept. of Chemical Engineering, University of Michigan, gbfisher@umich.edu)
Low-cost lean NOx aftertreatment is one of the main challenges facing high efficiency gasoline and diesel engines operating with lean exhausts. While there are many candidate technologies, they all offer tradeoffs. We have investigated a multi-catalyst Dual SCR aftertreatment system that is capable of obtaining NOx reduction efficiencies of greater than 90% under lean conditions, without the use of platinum group metals (PGMs) or urea injection into the exhaust. This Dual SCR approach uses an Ag/Al2O3 HC-SCR catalyst followed by an NH3-SCR catalyst. In bench reactor studies from 150 °C to 500 °C with modest C/N ratios, NOx reacts over the first catalyst to predominantly form nitrogen. In addition, it also forms ammonia in sufficient quantities to react on the second NH3-SCR catalyst to improve overall performance. The operational window and the formation of NH3 are improved in the presence of small quantities of hydrogen (0.1-1.0%). The response of the system to other factors such as exhaust oxygen content and space velocity has also been explored. In addition, we have begun to develop a model in GT Power for the HC-SCR reaction to combine with a model of the NH3-SCR reaction to be able to cover the Dual SCR system. This Dual SCR technology for lean NOx reduction is especially well matched for use with pre-mixed low-temperature diesel combustion. It has the potential to be a low-cost, non-urea enabler for satisfying Tier2/Bin5 and Tier2/Bin2 emissions standards.
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Spatially-Resolved Reactant Species Concentrations in a Model Diesel Oxidation Catalyst
William Epling, University of Waterloo
Authors: Bill Epling, Karishma Irani and Dick Blint
Oxidation reactions over a model monolith-supported Pt-Pd/Al2O3 diesel oxidation catalyst were characterized as a function of temperature and position within the catalyst using spatially resolved capillary-inlet mass spectrometry (SpaciMS). The data obtained demonstrate that H2 and CO are oxidized prior to C3H6 and C12H26 and clearly show back-to-front ignition of the reductant species. NO oxidation was observed to light-off at the same time as the dodecane, and high NO conversions were observed, likely related to dodecane partial oxidation products.
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Elucidating the Mechanism of NOx Storage and Reduction
Michael Harold, University of Houston
NOx storage and reduction (NSR) is a complex catalytic process involving periodic operation, multi-functional catalysts, multiple products, and strong coupling between adsorption, reaction, and transport processes. Bench reactor experiments reveal the existence of traveling concentration and thermal fronts. In order to carry out a rational design of the lean NOx trap (LNT), a comprehensive understanding of the reaction pathways and kinetics is essential. Towards this goal, we are conducting a combination of atmospheric flow reactor experiments and high vacuum pulsing experiments in a TAP (temporal analysis of products) reactor to build a predictive microkinetic model for NSR.
The TAP experiments employing isotopically labeled reactants provide insight about reaction pathways on the multi-functional catalyst. A typical experiment involved the pre-nitration of a Pt/BaO with 15NO so that the storage phase initially comprised Ba(15NO3)2. Subsequent exposure of the catalyst to a sequence of H2/NO pulses enabled the identification of the source of the N2 product. This experiment simulates the storage and reduction cycle in the LNT. The results reveal more than two routes to molecular nitrogen. The sustained production of 15N2 during the 15NO pulse suggests the direct decomposition of 15NO on clean Pt sites. These sites are continuously cleansed by scavenging of adsorbed O during the H2 pulse, and do not involve N species pre-stored on the BaO storage phase. On the other hand, both 15NN and N2 are produced during both the 15NO and H2 pulses. Their production clearly shows the involvement of NOx species that spillover from the Ba phase to the Pt. A third source of N2 is from NH3 formed during the H2 pulse (H2 being in excess). Additional data provide insight into the extent of gradients in the vicinity of the Pt crystallites.
Bench-scale reactor experiments were conducted to elucidate the role of Pt dispersion on the N-product distribution. The high dispersion catalyst (50%) leads to higher rates of NO oxidation and stored NOx reduction with high selectivity to N2. On the other hand, the low dispersion catalyst (3%) leads to significantly higher ammonia selectivity at high NOx conversion. These findings, which have implications for the design of hybrid LNT-SCR units, will be discussed in terms of a phenomenological model of the spatio-temporal behavior of the LNT.
A predictive LNT model has been developed that contains a microkinetic description of the NO/H2/O2 reaction system and NO oxidation and NOx storage processes, and that is consistent with the TAP findings. Comparisons will be made to selected model predictions and experimental results.
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Experimental Studies and Reactor Modeling for NOx Control in Diesel Engines using NH3 and HNCO
Maruthi Devarakonda, Pacific Northwest National Laboratory
Urea-SCR catalysts are regarded as the leading NOx aftertreatment technology to meet the 2010 NOx emission standards for on-highway vehicles running on heavy-duty diesel engines. Unfortunately, during low temperature engine operating conditions, urea droplets might not evaporate and thermolyze to form NH3 to reduce NOx in diesel exhaust. Since urea breaks up into NH3 and HNCO, there is a need to understand the reactions of both the species on an SCR catalyst. This talk presents a brief overview of modeling and experimental efforts using both NH¬3 and HNCO species, individually, on a Fe-zeolite monolith core for NOx aftertreatment. A brief overview of the test procedure involving surface isotherm and transient response tests using NH3 is presented, followed by a discussion on system identification and model validation. To investigate the NH3/NOx (alpha) effect on NOx conversion during the transient response tests, the inlet NH3 concentration is varied based on SCR reaction stoichiometry. In the second part of the talk, test procedure to generate HNCO is presented followed by data analysis and a few observations on possible reaction pathways involving NO, NO2, NH¬3 and HNCO species.
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Technical Challenges in the Integration of DPF and SCR Aftertreatment – Review from a Systems Perspe
Maruthi Devarakonda, Pacific Northwest National Laboratory
Urea-SCR catalysts and diesel particulate filters (DPFs) are proven technologies in reducing the NOx and particulate emissions from diesel engines respectively. These are being considered as the technologies to meet the US 2010 emission standards of NOx (0.2 gm/bhp-hr) and particulate matter (PM - 0.01 gm/bhp-hr). To decrease the overall volume of the catalysts and the costs of the precious metals in the catalysts to burn the harmful pollutants (CO, HC, NOx and PM) in the exhaust, researchers have been investigating to develop an integrated NOx/PM aftertreatment system on a single substrate. One such technology involves the combination of urea-SCR and DPF catalytic converters for a heavy duty application. Though considerable knowledge is attained in understanding the catalyst components from a steady state perspective, more fundamental understanding is necessary through laboratory/engine testing to develop an integrated system. This talk presents a review on SCR and DPF catalysts individually, while looking at other technologies that were researched in the past for simultaneous NOx/PM control in diesel engines. Technical observations on the integrated system from a systems and modeling perspective will be summarized and recommendations for the future will be presented.
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Low-dimensional Models for Real Time Simulations of Catalytic After-treatment Systems
Vemuri Balakotaiah, University of Houston
In the first part of this work, we present accurate low-dimensional (LD) models for real time simulation, control and optimization of catalytic after-treatment systems (TWC, DOC, LNT and SCR). 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 or internal diffusional effects without using the concept of the effectiveness factor. The models reduce to the classical two-phase models only in the limit of vanishingly thin washcoat. The models are validated by simulating the transient behavior for various test cases and comparing the predictions with detailed solutions. It is shown that these new LD 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 various catalytic after-treatment systems.
In the second part of this work, we combine the low-dimensional models with micro as well as global kinetic models of NOx storage and reduction on a Pt/BaO/Al2O3 catalyst to examine the operation of a LNT with hydrogen as reductant. The spatiotemporal patterns (adsorption, reduction and thermal front properties) and product distributions predicted by the model are compared with our recent experimental data [Applied Cat. B: 84, 616-630 (2008)]. The use of the LD models to estimate kinetic parameters using bench scale data will also be discussed.
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Intersting dynamics of soot combustion on a planar diesel particulate filter
Dan Luss, University of Houston
The dynamic features of soot combustion on a single layer, planar diesel particulate filter (DPF) were studied using IR imaging. At low oxygen concentrations and feed temperature of 635 oC the soot combustion rate was uniform all over the surface . At higher oxygen concentrations local ignition occurred at either one or several locations. The maximum temperature of the moving fronts, that bound the ignited zones was much higher (>100 oC) than those attained during uniform combustion. The maximum temperature of a downstream moving front exceeded that of the one moving upstream. At soot loading of 10 g/L a hot zone formed close to the end of the DPF and the bounding temperature front propagated upstream until it conquered the whole surface. At soot loading of 20 g/L the position and number of the hot zones strongly depended on the oxygen concentration. As the flow rate per unit filter surface area was increased, the maximum temperature rise attained first a local maximum and later a local minimum. A sudden change from normal to idle conditions can lead to an transient temperature rise higher than that attained under either one of these two states. This behavior has some similarity to the wrong-way behavior known to exist in packed bed reactors
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Computational method for determining kinetic rate constants for an SCR model
Praveen Chavannavar, Caterpillar
Overview of a computational method based on genetic algorithms to determine the appropriate kinetic reaction rates and other calibration constants in an SCR model to enable the model to appropriately describe the SCR catalyst behavior, including a discussion on identifying and selecting appropriate data for calibration and validation of the model.
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Kinetic modelling of sulphur poisoning and regeneration of Lean NOx traps
Louise Olsson, Chalmers
Kinetic modelling of sulphur poisoning and regeneration of Lean NOx traps
Louise Olsson1, Marielle Fredriksson1 and Richard J. Blint1
1Competence Centre for Catalysis, Chemical Reaction Engineering, Chalmers University of Technology, 412 96 Göteborg, Sweden
2General Motors R&D Center, Chemical and Environmental Sciences Laboratory
30500 Mound Rd, Warren, MI 48090-9055
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Passive Ammonia SCR for Lean SIDI Engines: Modeling Overview
Kushal Narayanaswamy, General Motors R&D
Co-authors: Wei Li, Paul M. Najt, Chang H. Kim and Kevin L Perry
Passive Ammonia SCR operation is a low-cost promising alternative for lean NOx aftertreatment in SIDI engines. This talk provides an overview of system level analysis as a compliment to experimental testing in the development of a passive SCR based afterteratment system.
The size and location of the lean NOx aftertreatment device was determined to achieve the best trade-off between engine back-pressure, catalyst warm-up and acceptable thermal aging under high speed/load conditions. In addition, various aftertreatment architecture (SCR type, the order of the catalysts) were efficiently evaluated and screened, requirements for aftertreatment components and exhaust thermal management devices were defined, and promising technologies were recommended for further development and testing.
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Microkinetic modeling development and use in exhaust gas after-treatment technologies
Dion Vlachos, Univ. of Delaware
The introduction of microkinetic modeling in catalysis more than ten years ago promised to improve our understanding of the chemistry and eventually lead to better catalysts and reactors. However, this promise has been met with limited success only, despite several research efforts. A major obstacle in microkinetic model development is the huge number of parameters that need to be extracted from experimental data or to be estimated. First principles density functional theory (DFT) emerges as a powerful tool to assist with parameter estimation. However, the common materials and pressure gaps along with the uncertainty of parameter values make direct use of DFT a daunting task. Furthermore, the computational burden associated with parameter estimation for large reaction networks renders use of DFT impractical. Even if parameters are estimated, the reliability of a microkinetic model in extrapolation is questionable. Examples on catalytic oxidation of CO and H2 on noble metals will be given to illustrate these points.
In this talk, we propose a hierarchical multiscale simulation framework for development of microkinetic models. The idea of hierarchical multiscale modeling and simulation is to start with the simplest possible “sound” model at each scale and identify the important scales and (‘active’) model parameters at each scale. Once this is accomplished, one assesses the model accuracy by comparison with data and potentially improves the model of the important scale(s) and the associated active parameters using a higher-level model or theory. For example, the simplest identification tool employed extensively and successfully in chemical kinetics is local sensitivity analysis. Upon improvement of models and parameters, another iteration is taken until convergence is achieved, i.e., the important scales and parameters do not change between successive iterations. We will demonstrate the power of the approach with the specific examples of water gas shift, preferential oxidation, and steam reforming reactions on noble metals.
In order for these models to become useful, we discuss multiscale model-based design of experiments to optimize the chemical information content of a reaction mechanism in order to improve the fidelity and accuracy of reaction models. Extension of this framework to catalyst design will be touched upon. We illustrate the use of such detailed and reduced kinetic models using the examples of catalytic combustion of hydrogen, carbon monoxide, and hydrocarbons, NO oxidation on Pt/Al2O3, and reduction of cold startup emissions of CO via H2 addition.
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Modeling of multi-layer catalysts and application in deNOx system
Grigorios Koltsakis, Aristotle University Thessaloniki
The combined use of a lean-NOx trap with a passive NH3-SCR system has already been proposed as an elegant technology to meet the stringent deNOx requirements without the hardware investment associated to external reductant supply. The LNT-SCR combination may be realized either via in-series installation of two separate devices or by applying a two washcoat layers on the same substrate. The presentation will deal with the problem of modeling such combined LNT-SCR concepts, starting from model calibration examples and continuing with exemplary simulation results. Special focus is given to the importance of “internal” diffusion modeling within the washcoat, which is a critical model feature especially in the case of multi-layer LNT-SCR technologies.
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Simulation Supporting the Exhaust Aftertreatment Development Process - 1D Concept and Control Design, 3D Detail Optimization
Johann Christian Wurzenberger, AVL List GmbH
This presentation discusses a comprehensive simulation framework using
1D and 3D simulation tools to investigate diesel exhaust
aftertreatment on both system and component level. On the component
level 3D simulations are performed to investigate the impact of mixing
devices on ammonia uniformity and wall film formation. A 3D detail
analysis is performed on DPF channel flow of open filters. On the
system level, advanced 1D DPF and injector models are presented.
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|
Overview |
Agenda |
Abstracts |
Presentations |
Local Info |
