11th DOE Crosscut Workshop
on Lean Emissions Reduction SimulationMay 13th - 15th, 2008University of Michigan - Dearborn, 4901 Evergreen Road, Dearborn, Michigan 48128
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In Silico Assessment of Diesel Emission Control Materials: Vision, Status and Roadmap
Athanasios Konstandopoulos, APT Lab, CPERI/CERTH
In Silico Assessment of Diesel Emission Control Materials:
Vision, Status and Roadmap
Monolithic reactors such as honeycomb flow-through converters (FTC) and wall-flow filters (WFF) continue to be important components of diesel emission control systems, and include functionalities such as gas species oxidation (such as CO, hydrocarbons and NO) storage phenomena (such as NOx and NH3 storage) and soot nanoparticle filtration and oxidation. An in depth understanding of the coupled transport – reaction phenomena occurring inside the microstructure of the coated walls of FTCs and WFFs can provide useful guidance for catalyst placement and improved accuracy over idealized models, without a detailed treatment of the microstructure.
In the present work we describe the implementation of a research program for the in silico assessment of diesel emission control materials of the future, based on realistic representations of all “actors” active in the emission control “theater of operations”: nano and microstructured porous substrates, filters, catalyst coatings and dispersions, soot nanoparticle aggregates and ash residues. Trade-offs between true-to-geometry representations and finite computational resources are addressed and novel subgrid resolution enhancement approaches will be presented. These developments make possible the detailed description of the coupled transport and reaction phenomena taking place in the microstructure of emission control devices, supporting the vision of their use as surrogate “experiments” that allow the calibration of coarse-grained/effective medium type models that are inevitably needed for practical, day-to-day use. A roadmap for the incorporation of these results, convoluted with rational/analytical approximations, in efficient large scale simulations of diesel emission control devices as well as implementations on computationally limited ECUs is also outlined.
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Development and Application of a Fast Quasi-Steady Solver for Integrated Modeling of Exhaust Aftertreatment Systems
Syed Wahiduzzaman, Gamma Technologies
Syed Wahiduzzaman, Weiyong Tang and Seth Wenzel
Gamma Technologies, Westmont, Illinois
Engines/vehicle systems are becoming increasing complex partly due to the incorporation of emission abatement components that are technologically evolving 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. However, it is frequently the case that the numerical burden of the aftertreatment system model involving is the main bottleneck in SIL/HIL compatible system model. In this study implementation and use of fast Quasi-steady (QS) solver will be demonstrated. This new approach is capable of simulating AT systems at speeds of 10-100 times faster than real time. To demonstrate the applicability of this method, several case studies have been conducted: (a) development of an intrinsic SCR mechanistic model from micro-reactor measurements with V2O5-WO3/TiO2 catalysts; (b) kinetic calibration and emissions prediction for a green and aged DOC; and (c) simulation of a system level AT model consisting of a fuel reformer, a LNT, a DPF and a SCR for NOx control. Kinetic analyses, simulation results and comparisons to experiments are presented and discussed.
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Kinetic models for NH3 SCR over Cu-ZSM-5
Louise Olsson, Chalmers University of Technology
Kinetic models for NH3 SCR over Cu-ZSM-5
Louise Olsson (a), Hanna Sjövall (a), Richard J. Blint (b) and Ashok Gopinath (c)
(a) Competence Centre for Catalysis, and Chemical Reaction Engineering, Chalmers University of Technology, SE-412 96 Göteborg, Sweden
(b) General Motors R&D Center, Chemical and Environmental Sciences Laboratory,30500 Mound Rd, Warren, MI 48090-9055
(c) General Motors R&D India Science Lab, Creator Building, International Tech Park, Whitefield Road, Bangalore 560 066, INDIA
We have developed both global [1] and detailed [2-4] kinetic models for ammonia SCR over copper zeolites. These models were developed for use in predicting NOx emissions from urea SCR automotive catalytic converters. The kinetics described in these models were developed using experimental data from coated monolith cores in flow reactor experiments, FTIR and TPD experiments. In addition two monolith samples (11 wt% washcoat and 23 wt.% washcoat) were used to evaluate the mass-transfer limits in the wash-coat. When holding the ratio between the total flow rate and the wash-coat amount constant, there were no differences in outlet NOx and NH3 concentrations indicating no significant mass-transfer limitations in the wash-coat layer. Ammonia temperature programmed desorption (TPD) experiments were used for investigating the adsorption and desorption of ammonia from the catalyst, which is crucial for simulating transient experiments. Further, the NO oxidation and NH3 oxidation submodels were examined separately. The global kinetic model also contains three steps for NH3 SCR: standard SCR (NO + O2 + NH3), rapid SCR (NO + NO2 + NH3) and NO2 SCR (NO2 + NH3) and one additional step for the N2O formation. 5% water was used in all experiments for the global model and the detailed model was developed both for dry and wet conditions. The global model was validated with six separate experiments including long steady state and short transient measurements. The NH3 concentration, NO concentration, and NO to NO2 ratio were varied and the model successfully predicted all the validation experiments. All global kinetic parameters and their 95% linearized confidence regions have recently been published [1].
[1] L. Olsson, H. Sjövall and R. J. Blint, Applied Catalysis B: Environmental, In press, 2008.
[2] H. Sjövall, R. J. Blint and L. Olsson, submitted, 2008.
[3] H. Sjövall, R. J. Blint and L. Olsson, submitted, 2008.
[4] L. Olsson, H. Sjövall, R. J. Blint, submitted, 2008.
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Fundamental Modeling and Experimental Studies of DPF Operation
Mark Stewart, PNNL
Even as widespread commercial deployment of diesel particulate filters takes place around the world, a continuing need exists for improved understanding of the principles that govern effective soot filtration and oxidation. Such understanding could help accelerate the optimization of soot filtration systems and help diagnose field operational issues as DPFs are exposed to countless combinations of engines, fuels and driving conditions.
Experiments and simulations have been conducted to help isolate various complexities associated with real DPF operation. Filtration experiments using artificial aerosols and lab-generated soot help to eliminate some of the variability and uncertainty associated with real diesel soot. Such techniques may also offer new possibilities for characterizing DPF behavior. Development continues on methods for performing simulations of filtration and regeneration at the scale of individual filter pores. Improvements in these modeling tools may allow better guidance of future substrate development.
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Effect of Ceria on the Sulfation and Desulfation Characteristics of Lean NOx Trap Catalysts
Mark Crocker, University of Kentucky
Y. Ji (a), V. Easterling (a), M. Crocker (a), T.J. Toops (b), J. Theis (c), J. Ura (c), R.W. McCabe (c)
(a) University of Kentucky Center for Applied Energy Research, Lexington, KY 40511, USA;
(b) Fuels, Engines and Emissions Research Center, Oak Ridge National Laboratory, Knoxville, TN 37932, USA;
(c) Chemical Engineering Department, Ford Research and Innovation Center, Dearborn, MI 48121, USA
Several years ago, Theis and co-workers reported that the addition of ceria to lean NOx trap (LNT) catalysts improved their sulfur tolerance [1]. It is well known that ceria is able to store sulfur (as sulfate), which may help to delay the poisoning of the main NOx storage components and thereby extend the time between desulfations. To better understand the role of ceria in alleviating the sulfur deactivation of LNTs, we have investigated the NOx storage capacity of ceria-containing and ceria-free powder LNT catalysts before and during sulfation. The desulfation behavior of the powder catalysts has also been studied and the results compared with those obtained for fully formulated monolithic LNTs.
[1] J. Theis, J. Ura, C. Jr. Goralski, H. Jen, E. Thanasiu, Y. Graves, A. Takami, H. Yamada, S. Miyoshi, SAE Technical Paper Series 2003-01-1160.
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MB E320 Emission Control System: Field Aging and Onboard Monitoring
Owen Bailey, Umicore
Up to now, agings and evaluations of advanced diesel emission control systems have been developed based on a variety of assumptions related to the architecture and placement of the components, their associated operating window and regeneration requirements, and engine performance features affecting exhaust composition and temperature. With this in mind, a production 2007 Tier 2 Bin 8 MB E320 Bluetec featuring a DOC+LNT+CDPF+SCR system was equipped with an onboard data logger system allowing a variety of exhaust system parameters to be studied during real world operation. The results of this investigation which includes LNT and CDPF regeneration conditions and frequencies, as well as the performance of the system on the chassis dynomometer will be discussed.
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Nanomaterials: Organic and Inorganic for Next Generation Diesel Technologies
Randy Vander Wal, USRA (non-profit)
Nanoscale materials are redefining the relation between material composition, size and properties. Chemical properties (e.g. reactivity) and physical properties (e.g. surface area) become a strong function of size at the nanoscale. This presentation will highlight applications of organic and inorganic nanomaterials to heavy-duty diesel trucks and include selected examples from the author’s work. Selected technologies include catalysis, composite materials, energy storage, sensors, thermal management, and tribology.
Catalysis is central to particulate and NOx after-treatment systems. A prime example of reducing materials to nanoscale and realizing new properties is catalysis by nanoscale gold. Au nanoparticles supported on oxides such as CeO2, TiO2 and Fe2O3 offer ambient temperature oxidation of CO, volatile organic compounds (VOCs) and potentially exhaust hydrocarbons.
Lightweight materials will reduce weight significantly yielding substantial benefits in fuel efficiency with reduced emissions. Composites with substantial gains in Young’s modulus, tensile strength, and EM shielding may be realized in polymeric composites using carbon nanotubes as an interfacial modifier rather than bulk filler.
Advances in energy storage include batteries, ultra-capacitors. These can support lighting, appliances, a starter, cooling fans, transmission and hydraulic systems, fuel and air handling systems and ultimately enable hybrid systems. Towards these goals, substantial gains in Li ion battery cathode and anode materials have been realized using carbon nanofibers, coating processes and including elements such as tin and silicon.
With regards to overall system integration and control, sensors will play a prominent role. With ultrahigh surface exposure relative to bulk material, nanoscale materials are exceedingly sensitive to gas adsorption. Exploitation of nanoscale properties will lead to new NOx sensors and in-cylinder oxygen sensors. Examples include catalyst coated metal oxide semiconductors capable of ambient temperature operation. In contrast SiC MOSFETs offer high temperature capability for measuring fuel/oxygen ratio.
Thermal management will benefit from nanofluids. Nanofluids can increase thermal conductivity and reduce radiator and heat exchanger size. Carbon-based nanofluids using nano-onions and carbon nanotubes have increased water conductivity by ~ 20%.
Lubrication is critical to many engine components and powertrain systems. Nanolubricants can bridge the gap between fluid and solid materials. As additives with liquids or greases, synergistic properties may be realized, particularly in boundary-phase lubrication. Improved coating formulations and properties can reduce or eliminate fretting and pitting. Results with nanocarbons show superior performance relative to graphite, diamond like carbon (DLC) and even Teflon
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Simulation Based Control System Analysis of a Urea-SCR Aftertreatment System Based on NH3 Sensing
Maruthi N. Devarakonda, Michigan Tech University
State-of-the-art NOx sensors are cross sensitive to NH3 and are a drawback for closed loop NOx control in urea-selective catalytic reduction (SCR) aftertreatment systems, if the cross sensitivity is not compensated. One way to overcome this limitation is to use an NH3 sensor for feedback purposes. NH3 sensors, relatively new to automotive applications, have been researched in Europe for NH3 feedback to meet the NOx emission regulations. This work presents preliminary control system simulation results in a urea-SCR catalyst based on NH3 sensor feedback. A four state control oriented lumped parameter model is used to analyze the controllability and observability properties of the urea-SCR plant. A model based estimator is designed in simulation and a control system based on sliding model control framework is developed. The control system based on NH3 sensor feedback is analyzed in simulation by comparing it to a control system based on NOx sensor feedback. Simulation results show that the NH3 sensor based strategy performs closely in comparison to a NOx sensor based strategy. The control system performance metrics in NOx index, urea index, urea usage and NH3 slip suggest that the NH3 sensor can be a potential alternative to a NOx sensor for urea-SCR control applications.
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X-Ray inspection of Diesel Particulate Filters
Jan Zandhuis, 3DX-Ray Ltd
Jan Zandhuis, 3DX-Ray Ltd;
Charles Finney, ORNL; Todd Toops, ORNL; Stuart Daw, ORNL
This presentation will describe novel results of research at Oak Ridge National Laboratory, using new commercially available non-destructive x-ray techniques to make engineering measurements on diesel particulate filters. We will present data showing the ability to visualize and measure flaws in substrates, quantify the distribution of individual or multiple wash-coats, and make through-the-can evaluations of the distribution of soot, ash, and thermal regeneration damage.
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1D/3D Simulation in the Development of DeNOx Aftertreatment Systems
for US10 Heavy Duty Application
Johann Christian Wurzenberger, AVL List GmbH
1D/3D Simulation in the Development of DeNOx Aftertreatment Systems
for US 2010 Heavy Duty Applications
J. C. Wurzenberger, R. Wanker, M. Schuessler
The fulfillment of significantly reduced US emission limits for heavy
duty diesel engines as imposed by US 2010 emission legislation
presents a great challenge for the next development period. The
individual technology elements necessary to achieve these stringent
targets (engine-related measures as well as aftertreatment systems)
are available on the market. However, the pre-requisite for future
business success will be an optimised combination of these elements to
fully cover the customers' needs and expectations.
From today's point of view a combination of DOCs, a wall flow DPF and
a urea SCR system seems to be the most promising aftertreatment
concept to meet future emission limits. The application of complex
aftertreatment systems requires not only highly effective
aftertreatment components but also a systematic approach for the
integration of entire systems. At early development stages,
computationally efficient 1D simulation models can be used not only to
deepen the insight into all physical and chemical effects but also to
investigate and optimize the layout of entire systems. At later
development stages especially highly resolved 3D simulations are used
to investigate more-dimensional effects given by e.g. the urea
injection system and to perform final design tuning.
This paper presents a comprehensive simulation framework using 1D and
3D simulations by the example of a heavy-duty exhaust system. The
deNOx performance of the entire exhaust gas line during a drive cycle
is investigated by a 1D model consisting of pipes, DOC, DPF, SCR and
a dosing control unit. The models of the individual components are
discussed and compared to experimental data. The impact of different
pipe wall insulations on the overall NOx reduction is compared for
different engine operating phases. A 3D model is applied to describe
the behavior of a urea injection system. The model covers injection of
urea-water droplets, evaporation of water, thermolysis of urea,
droplet wall interaction, build-up of wall-films and the influence of
mixing devices. The model is used to investigate the impact of the
urea injection system on ammonia formation and distribution in front
of the SCR converter. Due to the combined and systematic application
of 1D/3D simulation tools both the overall system and the detailed
urea injection performance can be calculated with sufficient physical
details and an appropriate computational effort.
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Temperature and Concentration Gradients During NOX Storage and Reduction Cycling
William Epling, University of Waterloo
William Epling, Alan Shaw, Khurram Aftab, Aleksey Yezerets and Neal Currier
In emissions catalyst applications, axial distributions of reaction rates, surface chemistry, and temperature all exist along the catalyst surface. To develop physically relevant models of such systems, understanding these distributions is required. IR thermography can be used to measure the temperature distributions on a monolith-supported catalyst, but can also be used to indirectly measure surface concentrations of sorbed species. This indirect method consists of measuring the temperature rise associated with an exothermic or endothermic reaction, with the target surface species as a reactant in such a reaction. IR thermography was used to measure the distribution of nitrate species on model and commercial diesel NOX adsorber catalysts. Axial distributions of the nitrate species as a function of lean-phase time, temperature and using NO2 and NO as NOX source were evaluated by measuring temperatures along the catalyst surface during the regeneration phase. With increasing lean-phase time, more NOX was trapped, and larger temperature rises were observed. This was also true of increasing rich-phase times since more NOX could be trapped with the more fully regenerated surface. The data indicate that with shorter trapping times, NOX is trapped near the front of the catalyst and the surface concentration of trapped NOX moves from back-to-front, as expected. The data also demonstrate quantitatively, the relative amounts as a function of axial position. With longer trapping times, more surface NOX species were still found at the front half of the catalyst, however within the front half, more NOX was trapped slightly downstream relative to the amounts at the very inlet. This indicates that there was not a smooth saturation wave that propagates simply from front-to-back as more NOX is trapped on the catalyst.
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NO Oxidation Rate as a Function of LNT Loading
Robert Middleton, University of Michigan
A method was developed to determine the rate of NO oxidation as a function of LNT precious metal loading and distribution. This method was applied to data reported in the literature. Due to inconsistent reporting in the literature no firm trends were observed. Based on this study several suggestions for the community are posed to standardize reporting of results for future use and collaboration.
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From zero to four-dimensional after-treatment models: needs and challenges
Grigorios Koltsakis, Aristotle University Thessaloniki
The presentation deals with simulation of catalytic converters and particulate filters starting from fundamentals and focusing on real application examples. Using multi-dimensional modeling concept, it is possible to study in detail phenomena not only in the macroscopic dimensions but also in the wall-scale. This is important for internal diffusion calculations in the washcoat. For DPF applications, this approach enables the prediction of DPF filtration efficiency, soot accumulation and pressure drop under transient and reacting conditions. Special emphasis is given on the effect of NO2 based passive regeneration which is studied using a transport-reaction modeling scheme. The model accuracy is demonstrated versus experimental data from critical regenerations under high soot loadings. The 3-d temperature field calculations can be subsequently used for thermal stress predictions and support design improvements.
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X-Ray inspection of Diesel Particulate Filters
Thomas Fox, X-Metrix
Jan Zandhuis, 3DX-Ray Ltd;
Charles Finney, ORNL; Todd Toops, ORNL; Stuart Daw, ORNL
This presentation will describe novel results of research at Oak Ridge National Laboratory, using new commercially available non-destructive x-ray techniques to make engineering measurements on diesel particulate filters. We will present data showing the ability to visualize and measure flaws in substrates, quantify the distribution of individual or multiple wash-coats, and make through-the-can evaluations of the distribution of soot, ash, and thermal regeneration damage.
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Effect of Mass Transfer on the Performance of SCR Systems
Tariq Shamim, University of Michigan-Dearborn
In addition to the heterogeneous chemical reactions between the exhaust gas and the monolith surface, the performance of an SCR catalyst is strongly influenced by the mass transport mechanism of the exhaust gases to the catalyst surface. Especially at higher temperatures, the mass transfer process becomes rate-limiting to an increasing extent. Hence, a correct description of the mass transfer process is important in catalyst models. Most studies modeled the mass transfer processes by using the simplified one-dimensional film model, which utilizes a dimensionless Sherwood (Sh) number to describe the mass transfer rate. Without being too much sophisticated, the film model is a good compromise to obtain a reasonable prediction of the converter efficiency. However, many uncertainties remain about the estimate of Sh number. This talk presents a computational investigation of the effect of mass transfer on the performance of an ammonia based SCR system for mobile applications
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Mechanistic Studies of the Reduction of NOx by Oxygenates
Eric Weitz, Northwestern University
Younghoon Yeom, Meijun Li, Aditya Savara, Wolfgang Sachtler and Eric Weitz
Institute for Catalysis in Energy Processes and Department of Chemistry
Northwestern University
Evanston, IL, USA 60208
Using principally FTIR spectroscopy we have elucidated the multi-step mechanisms for the reduction of NOx in the presence of acetaldehyde over BaNa/Y zeolite [1] as well as for NOx reduction in the presence of ethanol over silver exchanged Y zeolite (Ag/Y) [2]. Surface acetate ions, formed from the oxidation of acetaldehyde, react with NO2 to yield nitromethane: a critical intermediate in subsequent deNOx chemistry. Nitromethane, which is likely in equilibrium with its aci-anion, reacts with NO2. Our data indicate that this reaction leads to a dinitromethane intermediate, which then dissociates to form HNCO. HNCO can then be hydrolyzed to produce ammonia. The subsequent chemistry to form ammonium nitrite and then N2 by decomposition of ammonium nitrite is well known. The major qualitative difference in these systems is the temperature dependence of the reaction of acetate with NO2. Nitromethane is a critical intermediate in the pathway for NOx reduction with both ethanol and acetaldehyde. When introduced as a reductant, yields for the reduction of NO2 to N2 approach 100% at temperatures as low as 140 C [3]. The implications of these observations for the rate limiting step in the mechanism for NOx reduction in these systems will be discussed. If time permits, the role of NO in the reduction of NOx with added NH3 will also be discussed [4].
1. Yeom Y., Wen B., Sachtler W.M.H., and Weitz E. J. Phys. Chem., B, 108 5386 (2004)
2. Yeom. Y, M. Li, W. M.H. Sachtler, and E. Weitz, J. Catalysis 238 110-110 (2006)
3. Yeom. Y, M. Li, W. M.H. Sachtler, and E. Weitz,, Catalysis Letters 118, 173-179 (2007).
4. Yeom Y., Henao J., Li M., Sachtler W.M.H., and Weitz E. J. Cat. 231, 181-193 (2005)
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Thermal Transient Effects on the Performance of Catalysts for SCR of NOx
Jonathan Male, Pacific Northwest National Laboratory
In the development of catalysts for urea-selective catalytic reduction (SCR) of NOx there is a need to accelerate the transition from testing of powders under steady state conditions to transient test regimes. Pacific Northwest National Laboratory (PNNL) has developed a transient thermal cycle micro-reactor that emulates the thermal changes of an exhaust stream in the Federal Test Procedure (FTP) heavy-duty transient cycle used for emission testing of heavy-duty on-road diesel engines. Results from the testing of an industry supplied zeolite based urea-SCR catalyst will be discussed.
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Impact of Biodiesel on Advanced Aftertreatment Systems
Aaron Williams, NREL
The impact of biodiesel blended fuels on the short term performance of advanced aftertreatment systems, including Diesel Particulate Filters (DPF) and Selective Catalytic Reduction (SCR) systems, is explored. Engine testing with DPFs shows filter regeneration occuring at a lower temperature and faster rate with the use of biodiesel. Subsequent soot characterization work explains the difference in the soot particles which lead to this result. Further testing of a vehicle equiped with a DPF confirms that improvements are maintained under real world operating conditions. Engine testing with SCR systems explores the relative importance of catalyst temperature, exhaust chemistry and space velocity on overall NOx reduction efficiencies.
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Aftertreatment Options and Challenges for Lean-Burn Gasoline Engines
Robert McCabe, Ford Motor Company
The quest for improved fuel economy has rekindled interest in lean-burn gasoline engines. A direct injection engine with stratified-charge capability can provide leaner A/F ratios and consequently better fuel economy than those obtainable with a lean-burn port fuel injected (PFI) engine. Nevertheless, challenges remain to obtain benefits in emissions and/or fuel economy relative to those achievable with alternative combustion strategies such as EGR and variable cam and/or valve timing. In regards to emission control, the principal challenges are high engine-out NOx and HC emissions, the thermal durability requirements, and the need to achieve high NOx efficiencies over a broad temperature window. In this talk, we consider both the emission and fuel economy consequences of several potential aftertreatment options for lean gasoline engines, including lean NOx traps (LNT), urea-SCR, and LNT+in-situ SCR (i.e., LNT+SCR). While the main focus is on NOx emissions, we also briefly consider the challenges associated with hydrocarbon (HC) and particulate matter (PM) emissions – all with an eye toward comparing and contrasting lean gasoline emission challenges with those of diesel engines. Lean NOx traps do not require an extra reductant on-board, but the temperature window can be limited and the fuel penalty associated with the rich purges can cut significantly into the fuel economy benefits of lean operation. Urea-SCR technology eliminates the need for the rich purges and can potentially offer a broader temperature window, but it requires an additional reductant on-board (e.g., urea). Also, relative to its use on diesel engines, the application on lean-burn gasoline engines presents new challenges in the dynamic control of urea injection as well as SCR catalyst durability. The LNT+SCR concept eliminates the need for the additional reductant on-board and can expand the temperature window relative to the LNT alone, but the purge fuel penalty still reduces the fuel economy benefit of lean operation. The strong interactions between lean combustion characteristics, engine controls, and aftertreatment system durability and efficiency point to a need for model-driven system selection and optimization.
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Spatio-Temporal Behavior of NOx Storage and Reduction Monolith Catalysts
Michael Harold, University of Houston
Robert Clayton
Ashok Kumar
Jin Xu
Michael P. Harold
Vemuri Balakotaiah
University of Houston
Department of Chemical and Biomolecular Engineering
Houston, TX 77204
Lean-burn gasoline and diesel-powered vehicles require significant reductions in emissions of nitrogen oxides (NOx) and particulate soot. NOX Storage and Reduction (NSR) involves the sequential periodic reactive trapping of NOx and rapid reduction on multi-functional catalysts containing precious metal and storage components. While NSR is effective in achieving high NOX conversion, elucidation of the selectivity of NOx reduction to desired product N2 and byproducts such as NH3 and N2O is paramount in optimizing the lean NOx trap (LNT) or hybrid LNT/SCR systems. A combination of Temporal Analysis of Products (TAP), and bench-scale reactor experiments, and microkinetic modeling is being carried out to elucidate the spatio-temporal features of NSR on monolithic Pt/Ba catalysts.
The regeneration of a model Pt/BaO/Al2O3 monolith catalyst was studied with hydrogen as the reductant to elucidate the reaction pathways. Our results reveal that H2 is very effective in achieving a high time-averaged NOx conversion on Pt/Ba catalysts but the product distribution (N2, NH3, N2O) is a sensitive function of the operating conditions. Storage and reduction cycles are identified that maximize the NOx conversion and minimize reductant requirements. Experiments with series of monoliths of a range of lengths enabled the construction of spatio-temporal profiles of reactant and product concentrations. The results show that there are two primary competing routes to the desired N2 product; a direct route from the reduction of stored NOx by H2 (H2 + NOx ? N2) or by a sequential route through NH3 (H2 + NOx ? NH3; NH3 + NOx ? N2). The results revealed H2 is the superior reductant, especially for temperatures below 230 oC. At higher temperatures the reduction is feed-limited and the difference between the reductants H2 and NH3 is small. The findings are pieced together to establish a phenomenological picture of the spatio-temporal features of the LNT and microkinetic-based description of the regeneration chemistry.
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Thermokinetic Analysis of Ethylene Soot and Diesel Engine Soot
Khalid Al-Qurashi, Penn State Univ.
Soot oxidative reactivity is dependent upon its physico-chemical properties. These properties can be manipulated by altering the fuel source or soot formation conditions. Recent studies in our laboratories showed that soot oxidation reactivity can be enhanced by changing the combustion conditions. We used the exhaust gas recirculation (actual and simulated) to alter the conditions under which soot is formed. The soot samples are (1) ethylene flame soot generated with and without CO2 addition to the oxidizer stream (2) diesel soot generated from a single cylinder engine with and without CO2 addition to the intake air and (3) diesel soot generated from a 4-cylinder DI common rail turbocharged diesel engine with and without EGR. The kinetic parameters of interest are the activation energy (Ea), the pre-exponential factor (A), and the reaction order with respect to the soot (n). Knowledge about these parameters is a prerequisite for successive modeling and design of diesel particulate filters (DPF) and the regeneration strategy for the DPF. These parameters were determined based on multiple nonisothermal TGA experiments. The results show that the CO2 or EGR addition leads to an increase in the reaction rate of soot oxidation. These diluents do not affect the activation energy of the soot from the same origin but increase the pre-exponential factor significantly. It is concluded that the rate-determining step (RDS) in the soot oxidation is the same for all soot samples and that the soot follows the same oxidation mechanism irrespective of its formation history. The kinetic analysis conforms to the TGA reactivity measurements and suggests that the enhanced oxidation of the soot is ascribed solely to the increase of active sites which are incorporated implicitly in the pre-exponential factor. Based on these data, a simplified thermokinetic model that predicts soot conversion with temperature was developed.
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StarCD es-aftertreatment: Shared library interface for third
Michael Weaver, CD-adapco
This presentation will describe an interface that is being developed in StarCD for third party models. The physics incorporated in the interface will be
covered in detail and the mechanics of performing aftertreatment simulations with 1-D models in Star-CD will be reviewed.
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