A Two Dimensional Numerical Soot Model for Advanced Design and Control of Diesel Particulate Filters

One of the most effective methods to control diesel particulate matter (PM) emissions from heavy duty diesel engines is to use wall flow diesel particulate filters (DPF). It is still a major challenge to get an accurate estimation of soot loading, which is crucial for the engine afterteratment assembly optimization. In the recent past, several advanced computational models of DPF filtration and regeneration have been presented to assess the cost effective optimization of future particulate trap systems. They are characterized by different degree of detail and computational costs, depending on the specific application (i.e diagnostics, control, system design, component design etc).;The objective of this study is to compare in detail a two dimensional (2-D) approach with a one dimensional (1-D) approach, thus giving a better insight of the variation of properties over the DPF length. This task has been archived by extending an in-house developed 1-D numerical soot model to the next dimension to understand the impact of 2-D representation to predict both steady state and transient behavior of a catalyzed diesel particulate filter (CDPF). Performance of the model was evaluated using three key parameters: pressure drop, filter outlet temperature and soot mass retained in the filter during both active and continuous regeneration events. Quasi-steady state conservation of mass, momentum and energy equations were solved numerically using finite difference methods adopting a spatially uniform mesh. The results obtained from the current model were compared with the 1-D code to evaluate the general validity of assumptions made in the latter, especially DPF loading status prediction.;The model was validated using the data gathered at the West Virginia University Engine and Emissions Research Laboratory (WVU-EERL) using a model year 2004 Mack MP7-355E Diesel engine coupled to a Johnson Matthey catalyzed diesel particulate filter (CDPF) exercised over a 13 mode European stationary cycle (ESC) followed by two federal transient cycles (FTP). A constant set of model tuning parameters were maintained for the sake of general validation of simplifying assumptions of the 1-D code.;The analysis shows that the predicted pressure drop across the DPF is in good agreement with the data obtained at EERL in both steady state and transient cycles. It is also shown that the soot accumulates mainly in the frontal and rear parts across the filter length under given soot concentrations. The model is capable of tracking DPF soot mass satisfactorily with a maximum discrepancy of 3.47g during steady state cycle. A 7.95% decrease in soot layer thickness can be seen in the front portion of the DPF during the transient cycle mainly due to O2 assisted regeneration at elevated temperatures. Both 1-D and 2-D models produce similar results during the loading phase. However, the current model is able to capture regeneration phase of the FTP cycle more descriptively than the 1-D model. The discrepancy of the reported total soot mass estimation between two models was 2.12%. The distribution corresponding to the 1-D model is representative of soot layer distribution given by the 2-D model at one tenth distance away from the DPF front face. 1-D model representation is effective towards PM prediction, although presenting considerable axial effects at higher DPF temperatures

Numerical Simulation of a Wall-Flow Particulate Filter Made of Biomorphic Silicon Carbide Able to Fit Different Fuel/Biofuel Inputs

To meet the increasingly strict emission limits imposed by regulations, internal combustion engines for transport applications require the urgent development of novel emission abatement systems. The introduction of biodiesel or other biofuels in the engine operation is considered to reduce greenhouse gas emissions. However, these alternative fuels can affect the performance of the post-combustion systems due to the variability they introduce in the exhaust particle distribution and their particular physical properties. Bioceramic materials made from vegetal waste are characterized by having an orthotropic hierarchical microstructure, which can be tailored in some way to optimize the filtration mechanisms as a function of the particle distribution of the combustion gases. Consequently, they can be good candidates to cope with the variability that new biofuel blends introduce in the engine operation. The objective of this work is to predict the filtration performance of a wall-flow particulate filter (DPF) made of biomorphic silicon carbide (bioSiC) with a systematic procedure that allows to eventually fit different fuel inputs. For this purpose; a well-validated DPF model available as commercial software has been chosen and adapted to the specific microstructural features of bioSiC. Fitting the specific filtration and permeability parameters of this biomaterial into the model; the filtration efficiency and pressure drop of the filter are predicted with sufficient accuracy during the loading test. The results obtained through this study show the potential of this novel DPF substrate; the material/microstructural design of which can be adapted through the selection of an optimum precursor.Ministerio de Economía y Competitividad de España (MINECO) MAT2013-41233-RMinisterio de Economía y Competitividad de España (MINECO) BES-2014-069023Ministerio de Economía y Competitividad de España (MINECO) EEBB-I-17-1233

A review on the catalytic combustion of soot in Diesel particulate filters for automotive applications: From powder catalysts to structured reactors

Abstract The current soot oxidation catalyst scenario has been reviewed, the main factors that affect the activity of powder catalysts have been highlighted and kinetic soot oxidation models have been examined. A critical review of recent advances in modelling approaches has also been presented in this work. The multiscale nature of DPFs lends itself to a hierarchical organization of models, over various orders of magnitude. Different observation scales (e.g., wall, channel, entire filter) have often been addressed with separate modelling approaches that are rarely connected to one another, mainly because of computational difficulties. Nevertheless, DPFs exhibit an intrinsic multi-scale complexity that is reflected by a trade-off between fine and large-scale phenomena. Consequently, the catalytic behavior of DPFs usually results in a non-linear combination of multi-scale phenomena

Lumped Approach for Flow-Through and Wall-Flow Monolithic Reactors Modelling for Real-Time Automotive Applications

[EN] The increasingly restrictive legislation on pollutant emissions is involving new homologation procedures driven to be representative of real driving emissions. This context demands an update of the modelling tools leading to an accurate assessment of the engine and aftertreatment systems performance at the same time as these complex systems are understood as a single element. In addition, virtual engine models must retain the accuracy while reducing the computational effort to get closer to real-time computation. It makes them useful for pre-design and calibration but also potentially applicable to on-board diagnostics purposes. This paper responds to these requirements presenting a lumped modelling approach for the simulation of aftertreatment systems. The basic principles of operation of flow-through and wall-flow monoliths are covered leading the focus to the modelling of gaseous emissions conversion efficiency and particulate matter abatement, i.e. filtration and regeneration processes. The model concept is completed with the solution of pressure drop and heat transfer processes. The lumped approach hypotheses and the solution of the governing equations for every sub-model are detailed. While inertial pressure drop contributions are computed from the characteristic pressure drop coefficient, the porous medium effects in wall-flow monoliths are considered separately. Heat transfer sub-model applies a nodal approach to account for heat exchange and thermal inertia of the monolith substrate and the external canning. In wall-flow monoliths, the filtration and porous media properties are computed as a function of soot load applying a spherical packed bed approach. The soot oxidation mechanism including adsorption reactant phase is presented. Concerning gaseous emissions, the general scheme to solve the chemical species transport in the bulk gas and washcoat regions is also described. In particular, it is finally applied to the modelling of CO and HC abatement in a DOC and DPF brick. The model calibration steps against a set of steady-state in-engine experiments allowing separate certain phenomena are discussed. As a final step, the model performance is assessed against a transient test during which all modelled processes are taking place simultaneously under highly dynamic driving conditions. This test is simulated imposing different integration time-steps to demonstrate the model’s potential for real-time applications.This research has been partially supported by FEDER and the Government of Spain through project TRA2016-79185-R and by the European Union’s Horizon 2020 Framework Programme for research, technological development and demonstration under grant agreement number 723976.Payri, F.; Arnau Martínez, FJ.; Piqueras, P.; Ruiz Lucas, MJ. (2018). Lumped Approach for Flow-Through and Wall-Flow Monolithic Reactors Modelling for Real-Time Automotive Applications. SAE Technical Papers. https://doi.org/10.4271/2018-01-0954

Packed bed of spherical particles approach for pressure drop prediction in wall-flow DPFs (diesel particulate filters) under soot loading conditions

The soot loading process in wall-flow DPFs (diesel particulate filters) affects the substrate structure depending on the filtration regime and produces the increase of pressure drop. Deep bed filtration regime produces the decrease of the porous wall permeability because of the soot particulates deposition inside it. Additionally, a layer of soot particulates grows on the porous wall surface when it becomes saturated. As soot loading increases, the pressure drop across the DPF depends on the porous wall and particulate layer permeabilities, which are in turn function of the substrate and soot properties. The need to consider the DPF pressure drop influence on engine performance analysis or DPF regeneration processes requires the use of low-computational effort models describing the structure of the soot deposition and its effect on permeability. This paper presents a model to describe the micro-scale of the porous wall and the particulate layer structure assuming them as packed beds of spherical particles. To assess the model s capability, it is applied to predict the DPF pressure drop under different experimental conditions in soot loading, mass flow and gas temperature.This work has been partially supported by the Vicerrectorado de Investigacion de la Universitat Politecnica de Valencia through grant number SP20120340-UPPTE/2012/96 and by the Conselleria de Educacio, Cultura i Esport de la Generalitat Valenciana through grant number GV/2013/043.Serrano Cruz, JR.; Arnau Martínez, FJ.; Piqueras Cabrera, P.; García Afonso, Ó. (2013). Packed bed of spherical particles approach for pressure drop prediction in wall-flow DPFs (diesel particulate filters) under soot loading conditions. Energy. 58:644-654. https://doi.org/10.1016/j.energy.2013.05.051S6446545

Catalyzed diesel particulate filter modeling

This is the published version.An increasing environmental concern for diesel particulate emissions has led to the development of efficient and robust diesel particulate filters (DPF). Although the main function of a DPF is to filter solid particles, the beneficial effects of applying catalytic coatings in the filter walls have been recognized. The catalyzed DPF technology is a unique type of chemical reactor in which a multitude of physicochemical processes simultaneously take place, thus complicating the tasks of design and optimization. To this end, modeling has contributed considerably in reducing the development effort by offering a better understanding of the underlying phenomena and reducing the excessive experimental efforts associated with experimental testing. A comprehensive review of the evolution and the most recent developments in DPF modeling, covering phenomena such as transport, fluid mechanics, filtration, catalysis, and thermal stresses, is presented in this article. A thorough presentation on the mathematical model formulation is given based on literature references and the differences between modeling approaches are discussed. Selected examples of model application and validation versus the experimental data are presented

The effects of soot properties on the regeneration behaviour of wall-flow diesel particulate filters

In recent years, significant effort has been put into studying the regeneration process of diesel particulate filters (DPFs) either through experiments or modelling. However, less attention is paid to understanding the important influence of soot properties on the regeneration process. In this paper, for the first time, five fundamental soot properties, namely activation energy, frequency factor of the reaction, soot bulk density, porosity and mean soot particulate diameter, are investigated. Sensitivity analyses are carried out for each of these parameters based on a one-dimensional generalized DPF regeneration model. It is found that activation energy is the most important factor in the regeneration process, followed by frequency factor, bulk density, porosity and mean particulate size. In addition, the results also indicate that the concentration of exhaust gas oxygen has a significant influence on the role played by each parameter. This clearly shows the importance of gas diffusion in the regeneration process

Modelling wall-flow diesel particulate filter regeneration processes

This research was aimed at providing a better understanding of regeneration processes in wall-flow diesel particulate filters (DPFs), with emphasis on the combustion of particulate matter (PM). A 1-D model was used to investigate the effects of inherent PM properties on DPF regeneration behaviour. These properties were mean particulate diameter, porosity and bulk density of the PM, as well as the kinetic parameters of PM oxidation, i.e. frequency factor and activation energy. A parametric study showed that the activation energy of the PM oxidation reaction was the most important parameter and this was followed by the associated frequency factor, bulk density and porosity and mean particulate diameter. Due to the importance of the kinetic parameters of the PM oxidation reactions, a new 1-D model with a multi-step reaction scheme that required no tuneable kinetic parameters for the PM oxidation reactions was developed. [Continues.

Optimisation of autoselective plasma regeneration of wall-flow diesel particulate filters

The increase in number of diesel powered vehicles has led to greater concern for the effects of their exhaust emissions. Engine manufacturers must now consider using diesel particulate filters to make their engines meet the legislated limits. Diesel particulate filters can remove more than 95% of the particulates from the exhaust flow but require cleaning, known as regeneration. This thesis describes the research and optimisation of the Autoselective regeneration system for cordierite wall flow diesel particulate filters. The novel Autoselective technology uses an atmospheric pressure glow discharge plasma to selectively oxidise particulate matter (soot) trapped within the filter. The aim of this research was to produce a regeneration system that can operate under all exhaust conditions with a low energy demand and no precious metal dependence to compete with the numerous pre-existing technologies. The effect of discharge electrode type and position on regeneration performance has been investigated in terms of regeneration uniformity, power requirement and regeneration rate. The results showed that the electrode orientation had a large effect on regeneration distribution and energy demand. The electrode capacitance and breakdown voltage was shown to affect the choice of power supply circuit because not all power supply topologies were suitable for powering electrodes with >100 pF capacitance. A number of power supplies were designed and tested, a voltage driven resonant transformer type supply was shown to be optimal when used in conjunction with a swept frequency. The current and frequency ranges of electrical discharges were continuously variable, and their effect on discharge regeneration performance was studied. The results showed that the discharge frequency had no effect on the regeneration process but did affect spatial distribution. An optimised resonant transformer power supply was designed that was ideally suited for the electrodes used. A novel power modulation strategy, which used a switching frequency phase locked to the ~ iii ~ modulating frequency, was employed which extended the operating range of the discharge to below 10 mA for electrode separations > 7.5 mm. The heat flows within the filter and discharge during regeneration were analysed and the filter damage process was linked to the heat released by the discharge inside the filter wall. Other filter materials were compared based on the findings and Mullite ceramic was identified as a potentially better filter material for Autoselective regeneration. The filtration efficiency is important and was observed to be affected by the Autoselective process. The effect of the discharge on filtration efficiency was studied and the mechanism of particulate re-entrainment was identified as a combination of electrostatic and electro-acoustic forces. The Autoselective technology was successfully implemented in both flow-rig and on-engine tests. Results showed significant reduction in back-pressure for power inputs of ~ 500 W. The understanding of the Autoselective regeneration system has been improved and the research resulted in a novel method of filter regeneration

Simulation of Diesel Particulate Filter regeneration using Lattice Boltzmann method

Lattice Boltzmann Method is a novel approach, which has shown promise in solving a wide variety of fluid flow problems including single and multi-phase flows in complex geometries. Volume elements of the fluid domain are considered to be composed of particles and these particles fall under a velocity distribution function at each grid point. Particles collide with each other under the influence of external forces and the rules of collision are defined so as to be compatible with the Navier-Stokes Equation. In the current work, LBM has been applied to Diesel Particulate filters which is a device used for reducing Particulate Matter emissions from diesel engines. Diesel Particulate Filtering (DPF) technologies as they are collectively known, have a two-step mechanism to them. First is the trapping of the particulate matter and second is the regeneration process, which is essentially the cleaning process applied to get rid of the trapped soot with or without the help of catalytic compounds. The deposited soot is oxidized during this regeneration process. This oxidation of soot has been modeled in the current work using LBM. An artificially created porous microstructure as used by authors in some earlier works has been used to simulate the flow of fluid, which is considered to have a specified mass fraction of soot for different runs of the simulation. The velocity and concentration fields have been modeled with a D2Q9 lattice arrangement and the temperature field with a D2Q4 arrangement. The numerical code is developed using C. Flow over a heated cylinder has been modeled as a benchmark case. The pressure, velocity, temperature and concentration contours for the disordered media are compared with published work