|
|
Friday, September 10 |
| CLEERS Home > Workshops > Workshop 7> | Workshop 7 |
|
Cross-Cut Lean Exhaust Emissions Reduction Simulations Seventh DOE Crosscut Workshop Agenda | Overview | Abstracts | Summary | Notes | Presentations | Photos Modeling the effects of exhaust gas speciation on the efficiency of hydrocarbon SCRs Using our proprietary tool, Bistro, we have prepared reaction networks and catalyst models that capture the significant behavior of hydrogen, carbon monoxide and hydrocarbons in the selective catalytic reduction of NOx. We will present the salient features and sensitivities of the models. All Soot Deposits Are Not Created Equal: Variations on a Theme of Peclet Number It\'s been widely reported that backpressure of wall-flow filters is not an accurate representation of the quantity of soot deposit in the filter. It is shown here that this is due to the soot deposit microstructure changing according to exhaust flow conditions through the filter, namely flow rate and flow temperature. The exact deposition condition and hence soot microstructure depend on mass transfer Peclet number, a ratio of transport by convection vs. diffusion. Details and examples are provided, along with results from both light-duty and heavy-duty engine soot emission studies through filters. Applications of these findings in regeneration control are also demonstrated. Advantages of using ArvinMeritor's Plasma Fuel Reformer for desulfating a NOx Adsorber We present results and a strategy for performing desulfation of the traps using ArvinMeritor's Plasma fuel reformer. In contrast to vaporized diesel, which requires very high temperatures that fall outside the normal exhaust operating temperatures for diesel engines, desulfation was achieved at temperatures around 350°C using the Plasma Fuel Reformer. This is likely to provide substantial durability benefits for the NOx traps, a major hurdle remaining in the commercialization of that technology. A lower temperature that falls within the normal engine operating range also provides an effective desulfation strategy including the possibility of some desulfation occurring simultaneously with regeneration. We also present experimental results on the fuel reformer including hydrogen yield, soot production, start-up time and durability. The fuel reformer is capable of reaching up to 90% of the theoretically possible hydrogen yield at a range of fuel flow rates when used in conjunction with a downstream catalyst. The soot production is minimal both upstream (<20 mg/m3) and downstream (< 5 mg/m3) of the catalyst, while the start-up time required to reach 90% of the maximum hydrogen output is around 10 seconds. The system has been operated for more than 3000 cycles without any noticeable performance degradation. Quantum Chemistry Calculations of NOx Species on a NOx Trap Surface Quantum Chemistry Calculations of NOx Species on a NOx Trap Surface Christopher J. Mundy, I-feng W. Kuo and William J. Pitz Lawrence Livermore National Laboratory Thermal/fluid codes are being developed to model NOx trap aftertreatment devices. These codes require surface chemistry submodels to treat the adsorption and desorption of NOx species on the trap surface. To develop surface chemistry submodels, the controlling surface species and reactions must be identified. Ab initio molecular dynamics techniques allow the identification of important surface moieties that control the surface reactions. In this work, Car-Parrinello molecular dynamics is used to model important surface moieties on the NOx trap surface. For the first time, a much more realistic barium carbonate surface is modeled. In previous studies in the literature, only barium oxide surfaces have been attempted. Modelling of Diesel Particulate Filters Widespread market application of Diesel Particulate Filters (DPFs) has been accompanied by the introduction of new filter materials and configurations in terms of cell density, wall thickness, pore size, porosity, catalyst coatings etc. Given this state-of-affairs materials development, DPF design, system integration, regeneration control strategy optimization and ash aging assessment, based on a traditional design of experiments approach becomes very time consuming and costly, due to the high number of tests required. This provides a priviledged window of opportunity for the application of simulation tools. DPF behavior depends strongly on the coupling of phenomena occurring over widely disparate spatial and temporal scales and the simulation approach must recognize and exploit these facts. In this presentation we provide a review of our work on DPF simulation. Modelling of Diesel Particulate Filters I will accompany Dr. Athanasios G. Konstandopoulos who will give the presentation on Modelling of Diesel Particulate Filters (see separate submission) Fundamental Aspects of Lean-Burn Hydrocarbon Selective Catalytic Reduction The direct reduction of nitrogen oxides by hydrocarbons under lean-burn conditions is still an important target because of the inherent simplicity of the process as compared to NOx storage systems. This presentation will give an overview of our understanding of NOx reduction on noble metal catalysts by a range of hydrocarbons particularly at the lower temperatures found in some diesel emission systems. The dramatic effect of hydrogen as a co-reductant for hydrocarbon SCR with silver catalysts will be described. The lecture will attempt show how we can begin to identify the relevant reaction mechanisms from the interpretation of fast transient kinetic and isotope labelling experiments, combined with density functional theory calculations of some relevant molecular transformations on metal surfaces. Modeling an Ammonia SCR DeNOx Catalyst: Model Development and Validation A 1-D numerical model describing the ammonia selective catalytic reduction (SCR) de-NOx process has been developed based on data measured on a laboratory microreactor for a vanadia-titania washcoated catalyst system. Kinetics for various NH3-NOx reactions were investigated, as well as those for ammonia, CO and hydrocarbon oxidation. The model has been successfully validated against engine bench measurements, over light off and ESC tests, under a wide range of conditions, e.g. flow rate, temperature, NO2/NO ratio, and ammonia injection rate. A very good agreement between the experimental data and the model has been achieved. The model has now been used to predict the effect of NO2/NO ratio on NOx conversion, and the effect of different ammonia injection rates on the efficiency of the SCR process. Regeneration Characteristics of Diesel Particulate Filters under Transient Exhaust Conditions A major challenge in developing a diesel particulate filter (DPF) with wider applications is its lower durability. The filter durability may be increased by careful design of regeneration (soot oxidation) strategies. The regeneration characteristics of a DPF under steady state conditions are well known. However, during a typical driving cycle, a DPF is subjected to highly transient conditions due to changes in driving modes. These transients result in fluctuations of exhaust flow rate, gas composition and temperature. Such modulating exhaust conditions lead to variation in oxygen and NOx concentration and gas residence over the soot layer in the DPF. These transients make the DPF performance and regeneration characteristics differ significantly from that under steady state conditions. This talk will present the results of a computational investigation, which is conducted to determine the effect of temperature and exhaust flow modulations on the regeneration characteristics of a DPF. The study contributes to a better fundamental understanding of the DPF’s performance under actual driving conditions. Isostatic Strength of Extruded Honeycomb Ceramics Isostatic strength plays an important role in mechanical reliability of both the automotive substrates and diesel filters. This presentation will describe the test methods for measuring both 3D and 2D isostatic strengths. It will also relate the isostatic strength to cell shape, cell dimensions, skin thickness, structural stiffness and material strength. In this manner the predicted strength can be compared with measured strength. Once the isostatic strength model is verified by measured values, it can then be used to optimize honeycomb structure from strength point of view. However, other requirements such as heat capacity, thermal shock resistance and pressure drop must also be considered simultaneously. The trade-offs associated with such an optimization will be discussed. Relationship between Pressure Drop and Pore Microstructure for Diesel Particulate Filters from Experimentation and Capillary Pore Modeling The pressure drop of ceramic DPFs is important for fuel economy, engine performance, and regeneration control strategy. For a given filter geometry and flow condition, the pressure drop versus soot-loading behavior depends strongly upon the pore microstructure of the bare or catalyzed ceramic. Experimental pressure drop measurements as a function of flow rate and artificial soot loading for a wide variety of filter materials are used to derive quantitative relationships among clean and soot-loaded pressure drop, permeability of the clean and soot-containing wall, and the porosity and pore size distribution of the ceramic. These observations are supplemented with permeability and pressure drop calculations based upon theoretical models that approximate the ceramic pore microstructure by randomly oriented capillary pores of uniform diameter. Differences in pressure drop behaviors are interpreted in terms of the location and packing density of the soot within, and on the surface of, the filter walls. One-dimensional Catalyst Modeling and its Application to Urea SCR Devices As government regulatory agencies continue to decrease the tolerance level for problematic emissions, there is an overwhelming need to model aftertreatment devices in order to optimize their control and on-board placement. This is because experimental tests alone cannot solve the problem due to cost and time-constraints. In this talk, a brief history of one-dimensional catalyst modeling is presented to illustrate the pertinent processes that occur within the catalyst. Based on the appropriate source terms, a catalyst model was derived from the Euler equations of motion and expanded to account for an insulating layer and energy generation within the catalyst. Fast numerical solvers are described to allow for efficient numerical computation of all of the models including transient terms. A general framework was created in order to model any type of aftertreatment device. It was then used to simulate a Urea SCR device over a complete FTP-75 emission regulatory test. Ford/DOE SCR Program Update Ford Motor Company, with ExxonMobil and FEV, is participating in the Department of Energy's (DOE) Ultra-Clean Transportation Fuels Program with the goal to develop an innovative emission control system for diesel sport utility vehicles. The focus on diesel engine emissions is a direct result of the improved volumetric fuel economy (up to 50%) and lower CO2 emissions (up to 25%) over comparable gasoline engines shown in Europe. Selective Catalytic Reduction (SCR) with aqueous urea as the NOx reductant and a catalyzed Diesel Particulate Filter (DPF) were chosen as the primary emission control system components The program expects to demonstrate more than 90% reduction in particulate matter (PM) and NOx emissions on a light-duty truck/SUV application. Very low sulfur diesel fuel (~15 ppm) will enable lower PM emissions, reduced fuel economy penalty due to the emission control system and improved long-term system durability. The end result will allow vehicles with diesel engines to be Tier 2 emissions certified at a minimized cost to the consumer. Agenda | Overview | Abstracts | Summary | Notes | Presentations | Photos |
|
Disclaimers | Mailing Lists | Contact us | Feedback | Register for CLEERS News |
