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As use of Particulate Filters (PFs) is growing not only for diesel but also for gasoline powered vehicles, the need for better understanding of deposit structure, growth dynamics and evolution arises. In the present paper we address a number of deposit growth and restructuring phenomena within particulate filters with the aim to improve particulate filter soot load estimation. To this end we investigate the dynamic factors that quantify the amount of particles that are stored within the wall and the restructuring of soot deposits. We demonstrate that particle accumulation inside the porous wall is dynamically controlled by the dimensionless Peclet number and provide a procedure for the estimation of parameters of interest such as the loaded filter wall permeability, the wall-stored soot mass at the onset of cake filtration.

Evolving marine diesel emission regulations drive significant reductions of nitrogen oxide (NOx) emissions. There is, therefore, considerable interest to develop and validate Selective Catalytic Reduction (SCR) converters for marine diesel NOx emission control. Substrates in marine applications need to be robust to survive the high sulfur content of marine fuels and must offer cost and pressure drop benefits. In principle, extruded honeycomb substrates of higher cell density offer benefits on system volume and provide increased catalyst area (in direct trade-off with increased pressure drop). However higher cell densities may become more easily plugged by deposition of soot and/or sulfate particulates, on the inlet face of the monolithic converter, as well as on the channel walls and catalyst coating, eventually leading to unacceptable flow restriction or suppression of catalytic function.

Catalysts that have been extensively investigated for direct soot oxidation in Catalyzed Diesel Particulate Filters (CDPFs) are very often based on mixed oxides of ceria with zirconia, materials known to assist soot oxidation by providing oxygen to the soot through an oxidation-reduction catalytic cycle. Besides the catalyst composition that significantly affects soot oxidation, other parameters such as morphological characteristics of the catalyst largely determined by the synthesis technique followed, as well as the reagents used in the synthesis may also contribute to the activity of the catalysts. In the present work, two ceria-zirconia catalyst samples with different zirconia content were subjected to different milling protocols with the aim to shift the catalyst particle size distribution to lower values. The produced catalysts were then evaluated with respect to their soot oxidation activity following established protocols from previous works.

Asymmetric and Variable Cell (AVC) geometry Diesel Particulate Filters (DPF) occupy an increasing portion of the DPFs currently offered by various DPF manufacturers, aiming at providing higher filtration area in the same filter volume to meet demanding emission control applications for passenger cars but also for heavy duty vehicles. In the present work we present an approach for designing and optimizing such DPFs by providing a quantitative description of the flow and deposition of soot in these structures. Soot deposit growth dynamics in AVC DPFs is studied computationally, primary and secondary flows over the inlet channels cross-sectional perimeters are analyzed and their interactions are elucidated. The result is a rational description of the observed growth of soot deposits, as the flow readjusts to transport the soot particles along the path of least resistance (which is not necessarily the shortest geometric path between the inlet and outlet channel, i.e. the wall thickness).

In this study, a DOC catalyst was experimentally studied in an engine test cell with a2010 Cummins 6.7L ISB diesel and a production aftertreatment system. The test matrix consisted of steady state, active regeneration with in-cylinder fuel dosing and transient conditions. Conversion efficiencies of total hydrocarbon (THC), CO, and NO were quantified under each condition. A previously developed high-fidelity DOC model capable of predicting both steady state and transient active regeneration gaseous emissions was calibrated to the experimental data. The model consists of a single 1D channel where mass and energy balance equations were solved for both surface and bulk gas regions. The steady-state data were used to identify the activation energies and pre-exponential factors for CO, NO and HC oxidation, while the steady-state active regeneration data were used to identify the inhibition factors. The transient data were used to simulate the thermal response of the DOC.

Despite the great effort devoted to the modeling of the operation of catalytic DPFs, even today very simple expressions are used for the soot oxidation rate. In the relevant to DPF operation case of a gas phase rich in oxygen, the structure of the soot-catalyst geometry and its evolution during oxidation determines the reaction rate. An extensive set of controlled experiments (isothermal or with linear temperature increase) using fuel borne catalysts and catalytic coatings has been performed in order to obtain corresponding soot oxidation rate-conversion curves. The shape of the resulting curves cannot be described by the typical theories for solid phase reactions posing the need for microstructural models for the micromechanics of soot catalyst interactions.

In the present work we derive analytical solutions for the problem of convection, diffusion and chemical reaction in wall-flow monoliths. The advantage of having analytical instead of numerical treatments is clear as the analytical solutions not only can be exploited to bring full scale simulations of diesel particulate filters to the real time domain, but also they enable efficient implementations on computationally limited engine control units (ECUs) for on-board management and control of emission control systems. The presentation describes 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.

A laboratory flow reactor study was utilized to determine the durability impact of alkali metal (Na and K) exposure on three Pt/Pd-based diesel oxidation catalysts (DOC), two vanadium-based selective catalytic reduction (SCR) catalysts, and two Cu/zeolite-based SCR catalysts. All catalyst samples were contaminated by direct deposition of Na or K by an incipient wetness technique. The activity impact on the contaminated DOCs was accomplished by evaluating for changes in CO and HC light-off. The activity impact on the contaminated SCR catalysts was accomplished by evaluating for changes in the Standard SCR Reaction, the Fast SCR Reaction, the Ammonia Oxidation Reaction, and the Ammonia Storage Capacity. Contamination levels of 3.0 wt% Na was found to have a higher negative impact on Pt-based and zeolite containing DOCs for T-50 CO and HC light-off.

Urea selective catalytic reduction (SCR) catalysts have the capability to deliver the high NOx conversion efficiencies required for future emission standards. However, the potential for the occasional over-temperature can lead to the irreversible deactivation of the SCR catalyst. On-board diagnostics (OBD) compliance requires monitoring of the SCR function to make sure it is operating properly. Initially, SCR catalyst performance metrics such as NOx conversion, NH3 oxidation, NH3 storage capacity, and BET surface area are within normal limits. However, these features degrade with high temperature aging. In this work, a laboratory flow reactor was utilized to determine the impact on these performance metrics as a function of aging condition. Upon the completion of a full time-at-temperature durability study, four performance criteria were established to help determine a likely SCR failure.

Future diesel emission control systems have to effectively operate under non-conventional low-temperature combustion engine operating conditions. In this work the research and development efforts for the realization of a Multi-Functional catalyst Reactor (MFR) for the exhaust of the upcoming diesel engines is presented. This work is based on recent advances in catalytic nano-structured materials synthesis and coating techniques. Different catalytic functionalities have been carefully distributed in the filter substrate microstructure for maximizing the direct and indirect (NO2-assisted) soot oxidation rate, the HC and CO conversion efficiency as well as the filtration efficiency. Moreover, a novel filter design has been applied to enable internal heat recovery capability by the implementation of heat exchange between the outlet and the inlet to the filter flow paths.

Establishing a certain maintenance-free time period regarding modern diesel exhaust emission control systems is of major importance nowadays. One of the most serious problems Diesel Particulate Filter (DPF) manufacturers face concerning system's durability is the performance deterioration due to the filter aging because of the accumulation of the ash particles. The evaluation of the effect of the ash aging on the filter performance is a time and cost consuming task that slows down the process of manufacturing innovative filter structures and designs. In this work we present a methodology for producing filter samples aged by accumulating ash produced by the controlled pyrolysis of oil-fuel solutions. Such ash particles bear morphological (size) and compositional similarity to ash particles collected from engine aged DPFs. The ash particles obtained are compared to those from real engine operation.

Diesel aftertreatment systems configured with a diesel oxidation catalyst (DOC) upstream of an urea selective catalytic reduction (SCR) catalyst run the risk of precious metal contamination. During active diesel particulate filter (DPF) regeneration events, the DOC bed temperature can reach up to 850°C. Under these conditions, precious metal (especially Pt) can be volatized and then deposited on a downstream SCR catalyst. In this paper, the impact of ultra-low contamination of platinum group metals (PGM) on the SCR catalyst was studied. A method based on precious metal volatilization of a Pt-rich DOC at 850°C and under lean gas conditions was employed to contaminate downstream FeSCR and CuSCR formulations. The contamination resulted in poor NOx conversion (via NOx remake) and excessive N2O formation. The precious metal volatilization method was employed to screen various Pt/Pd based DOCs to avoid contamination of the downstream FeSCR.

Catalyzed Diesel Particulate Filters (CDPFs) continue to be an important emission control solution and are now also expanding to include additional functionalities such as gas species oxidation (such as CO, hydrocarbons and NO) and even storage phenomena (such as NOx and NH3 storage). Therefore an in depth understanding of the coupled transport - reaction phenomena occurring inside a CDPF wall can provide useful guidance for catalyst placement and improved accuracy over idealized effective medium 1-D and 0-D models for CDPF operation. In the present work a previously developed 3-D simulation framework for porous materials is applied to the case of NO-NO2 turnover in a granular silicon carbide CDPF. The detailed geometry of the CDPF wall is digitally reconstructed and micro-simulation methods are used to obtain detailed descriptions of the concentration and transport of the NO and NO2 species in the reacting environment of the soot cake and the catalyst coated pores of the CDPF wall.

Passenger and light duty diesel vehicles will require up to 90% NOx conversion over the Federal Test Procedure (FTP) to meet future Tier 2 Bin 5 standards. This accomplishment is especially challenging for low exhaust temperature applications that mostly operate in the 200 - 350°C temperature regime. Selective catalytic reduction (SCR) catalysts formulated with Cu/zeolites have shown the potential to deliver this level of performance fresh, but their performance can easily deteriorate over time as a result of high temperature thermal deactivation. These high temperature SCR deactivation modes are unavoidable due to the requirements necessary to actively regenerate diesel particulate filters and purge SCRs from sulfur and hydrocarbon contamination. Careful vehicle temperature control of these events is necessary to prevent unintentional thermal damage but not always possible. As a result, there is a need to develop thermally robust SCR catalysts.

In this paper, a model-based linear estimator and a non-linear control law for an Fe-zeolite urea-selective catalytic reduction (SCR) catalyst for heavy duty diesel engine applications is presented. The novel aspect of this work is that the relevant species, NO, NO2 and NH3 are estimated and controlled independently. The ability to target NH3 slip is important not only to minimize urea consumption, but also to reduce this unregulated emission. Being able to discriminate between NO and NO2 is important for two reasons. First, recent Fe-zeolite catalyst studies suggest that NOx reduction is highly favored by the NO 2 based reactions. Second, NO2 is more toxic than NO to both the environment and human health. The estimator and control law are based on a 4-state model of the urea-SCR plant. A linearized version of the model is used for state estimation while the full nonlinear model is used for control design.

Novel catalytic coatings with a variety of methods based on conventional and novel synthesis routes are developed for Diesel Particulate Filters (DPFs). The developed catalytic composition exhibits significant direct soot oxidation as evaluated by reacting mixtures of diesel soot and catalyst powders in a thermogravimetric analysis apparatus (TGA). The catalyst composition was further deposited on oxide and non-oxide porous filter structures that were evaluated on an engine bench with respect to their filtration efficiency, pressure drop behavior and direct soot oxidation activity under realistic conditions. The effect of the catalyst amount on the filtration efficiency of non-oxide filters was also investigated. Evaluation of the indirect soot oxidation was conducted on non-oxide catalytic filters coated with precious metal.

Steady-state particulate loading experiments were conducted on an advanced production catalyzed particulate filter (CPF), both with and without a diesel oxidation catalyst (DOC). A heavy-duty diesel engine was used for this study with the experiments conducted at 20, 40, 60 and 75 % of full load (1120 Nm) at rated speed (2100 rpm). The data obtained from these experiments were used and are necessary for calibrating the MTU 1-D 2-Layer CPF model. These experimental and modeling results were compared to previous research conducted at MTU that used the same engine but an earlier development version of the combination of DOC and CPF. The motivation for the comparison of the two systems was to determine whether the reformulated production catalysts performed as good or better than the early development catalysts. The results were compared to understand the filtration and oxidation differences between the two DOC+CPF and the CPF-only aftertreatment systems.

A new platform of advanced ceramic composite filter materials for diesel particulate matter and exhaust gas emission control has been developed. These materials exhibit high porosity, narrow pore-size distribution, robust thermo-mechanical strength, and are extruded into high cell density honeycomb structures for wall-flow filter applications. These new high porosity filters provide a structured filtration surface area and a highly connected wall pore space which is fully accessible for multi-phase catalytic reactions. The cross-linked microstructure (CLM™) pore architecture provides a large surface area to host high washcoat/catalyst loadings, such as those required for advanced multi-functional catalysts (4-way converter applications).

Model-based control strategies are important for meeting the dual objective of maximizing NOx reduction and minimizing NH3 slip in urea-SCR catalysts. To be implementable on the vehicle, the models should capture the essential behavior of the system, while not being computationally intensive. This paper discusses the adequacy of two different reduced order SCR catalyst models and compares their performance with a higher order model. The higher order model assumes that the catalyst has both diffusion and reaction kinetics, whereas the reduced order models contain only reaction kinetics. After describing each model, its parameter identification and model validation based on experiments on a Navistar I6 7.6L engine are presented. The adequacy of reduced order models is demonstrated by comparing the NO, NO2 and NH3 concentrations predicted by the models to their concentrations from the test data.

Following the successful market introduction of diesel particulate filters (DPFs), this class of emission control devices is expanding to include additional functionalities such as gas species oxidation (such as CO, HC and NO), storage phenomena (such as NOx and NH3 storage) to the extent that we should today refer not to DPFs but to Multifunctional Reactor Separators. This trend poses many challenges for the modeling of such systems since the complexity of the coupled reaction and transport phenomena makes any direct general numerical approach to require unacceptably high computing times. These multi-functionalities are urgently needed to be incorporated into system level emission control simulation tools in a robust and computationally efficient manner. In the present paper we discuss a new framework and its application for the computationally efficient implementation of such phenomena.