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Improved understanding and compact descriptions of the pressure drop evolution of Particulate Filters (both for diesel and gasoline powered vehicles) are always in demand for intelligent implementations of exhaust emission system monitoring and control. In the present paper we revisit the loading process of a particulate filter focusing on a parametric description of the deep bed-to-cake transition in the light of recent progress in the understanding of soot deposit structure, growth dynamics and evolution. Combining experimental data, simulation models and information theoretic concepts we provide a closed-form representation of the entire evolution of pressure drop (from the initial clean state up to the evolving linear cake growth regime) parameterized in terms of the physical parameters of the system (filter and particle structure/geometry and flow properties).

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).

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.

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.

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.

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.

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).

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.

Direct catalytic soot oxidation is expected to become an important component of future diesel particulate emission control systems. The development of advanced Catalytic Diesel Particulate Filters (CDPFs relies on the interplay of chemistry and geometry in order to enhance soot-catalyst proximity. An extensive set of well-controlled experiments has been performed to provide direct catalytic soot oxidation rates in CDPFs employing small-scale side-stream sample exposure. The experiments are analyzed with a state-of-the-art diesel particulate filter simulator and a set of kinetic parameters are derived for direct catalytic soot oxidation by fuel-borne catalysts as well as by catalytic coatings. The influence of soot-catalyst proximity, on catalytic soot oxidation is found to be excellently described by the so-called Two-Layer model, developed previously by the authors.

Diesel Particulate Filters (DPFs) need to be periodically regenerated in order to achieve efficient and safe vehicle operation. Under typical diesel exhaust conditions, this invariably requires the raising of the exhaust gas temperature by active means, up to the point that particulate (soot) oxidation can be self-sustained in the filter. In the present work the development path of an advanced catalytic filter technology is presented. Full scale optimized Catalytic Diesel Particulate Filters (CDPFs) are tested in the exhaust of a light-duty modern diesel engine in line with a Diesel Oxidation Catalyst (DOC). The management of the DOC-CDPF emission control system is facilitated by a virtual soot sensor in order to ensure energy-efficient operation of the emission control system.

The pore structure of DPF (Diesel Particulate Filter) is one of the key factors in contributing the fuel consumption and the emission control performance of a vehicle. The pressure loss of mini samples (1 in. in diameter, 2 in. in length) with various pore structures was measured at relatively low filtration velocity (< 5 cm/sec). Then the obtained data were evaluated by using an index of “permeability”. As a result, among the parameters which characterize the pore structure, it was found that the size of the pore diameter and the sharpness of pore distribution were the most contributing factors in reducing pressure loss which in turn is related to the fuel consumption performance when the cell structure was fixed. On the other hand, it was found that the gas permeability was not affected significantly by any parameter when the catalyst was coated because the coating caused a broadening of the pore distribution.

A computational lumped parameter model (MTU-Filter-Lumped) was developed to describe the performance of diesel particulate filters (DPFs) during loading and regeneration processes. The model was formulated combining three major sub-models: a filtration model, a pressure drop model, and a mass and an energy balance equation for the total filter volume. The first two sub-models have been widely validated in the literature, while the third sub-model is introduced and combined with the first two sub-models in the present study. The three sub-models combined can give a full description of diesel particulate filter behavior during loading and regeneration processes, which was the objective of the present work. The total combined lumped parameter model was calibrated using experimental data from the literature covering a range of experimental conditions, including different catalytic regeneration means and engine operating conditions.

Compliance with future emission standards for diesel powered vehicles is likely to require the deployment of emission control devices, such as particulate filters and DeNOx converters. Diesel emission control is merging with powertrain management and requires deep knowledge of emission control component behavior to perform effective system level integration and optimization. The present paper focuses on challenges associated with a critical component of diesel emission control systems, namely the diesel particulate filter (DPF), and provides a fundamental description of the transient filtration/loading, catalytic/NO2-assisted regeneration and ash-induced aging behavior of DPF's.