Influence analysis of monolith structure on regeneration temperature in the process of microwave regeneration in the diesel particulate filter

Based on models A, B, and C of three kinds of diesel particulate filter (DPF) with microwave regeneration, a DPF microwave regeneration model is established according to the laws of conservation of mass, momentum, and energy. The trends of internal temperature under different velocities of exhaust gas in channels are simulated and analyzed. The results show that: (1) Regeneration temperature in the process of microwave regeneration will begin to increase from the front to the rear end of along the axial direction, and the maximum temperature value will appear in the rear end of the monolith. (2) The internal flow velocity in the DPF of model C is the most uniform and the temperature gradient is the smallest among the three models. Therefore, it is the most useful for DPF regeneration. (3) The minimal thermal stress is exerted on the DPF of model C. Therefore, this model is most useful for prolonging the service life of a DPF.     

Emissions from a diesel car during regeneration of an active diesel particulate filter

The California Air Resources Board (CARB) and the Joint Research Center of the European Commission (JRC) have collaborated on emissions testing of a light duty diesel vehicle, which is Euro 4 compliant and comes equipped with a diesel particulate filter (DPF). The California testing included an investigation of the regeneration of the DPF over cruise conditions and NEDC test cycles. DPF regeneration is caused by the buildup of soot in the filter, and for the present test vehicle the regeneration process is assisted by a fuel borne catalyst. Regulated exhaust emissions increased substantially during the regeneration events; however, PM emissions levels were below California LEVII emissions standards. There was a very large increase of volatile particles between 5 and 10 nm, and these volatile particles were generated during all of the observed regeneration events. It appears that the particle number instruments that use the PMP methodology do not capture the PM mass increase during DPF regeneration; however, for one regeneration event there was an apparent large increase in solid particles below the PMP size limit. The PM mass increase associated with regeneration appears to be due to semi-volatile particles collected on filters. During the testing, the regeneration events exhibited considerable variations in the time for regeneration as well as the amount of PM emissions. From this investigation, several questions have been posed concerning the emission of very small (<20 nm) volatile and solid particles during DPF regeneration that need further investigation.     

Evidences of the Cerium Oxide-Catalysed DPF Regeneration in a Real Diesel Engine Exhaust

The active phase Ce_0.5Pr_0.5O₂ has been loaded on commercial substrates (SiC DPF and cordierite honeycomb monolith) to perform DPF regeneration experiments in the exhaust of a diesel engine. Also, a powder sample has been prepared to carry out soot combustion experiments at laboratory. Experiments performed in the real diesel exhaust demonstrated the catalytic activity of the Ce–Pr mixed oxide for the combustion of soot, lowering the DPF regeneration temperature with regard to a counterpart catalyst-free DPF. The temperature for active regeneration of the Ce_0.5Pr_0.5O₂-containing DPF when the soot content is low is in the range of 500–550 °C. When the Ce_0.5Pr_0.5O₂-containing DPF is saturated with a high amount of soot, pressure drop and soot load at the filter reach equilibrium at around 360 °C under steady state engine operation due to passive regeneration. The uncoated DPF reached this equilibrium at around 440 °C. Comparing results at real exhaust with those at laboratory allow concluding that the Ce_0.5Pr_0.5O₂-catalysed soot combustion in the real exhaust is not based on the NO₂-assisted mechanism but is most likely occurring by the active oxygen-based mechanism.     

Effect of Exhaust Gas Temperature on Oxidation of Marine Diesel Emission Particulates with Nonthermal-Plasma-Induced Ozone

Because the regulations governing diesel engine emissions are becoming more stringent, effective aftertreatment is needed for particulate matter. Although diesel particulate filters (DPFs) are a leading technology used in automobiles, there remains a problem with DPF regeneration for marine diesel engines that use heavy oil fuel. In the present study, pilot-scale experiments were conducted to develop a particulate oxidation technology for marine diesel engine emissions using DPF regeneration by nonthermal-plasma-induced ozone injection. It has been shown that particulate oxidation depends on the exhaust gas temperature, and regeneration can be performed most effectively at a temperature of approximately 300 °C.     

Numerical simulation of soot filtration and combustion within diesel particulate filters

The numerous benefits offered by diesel engines, compared to gasoline ones, are balanced by a drawback of increasing concern, namely soot emissions. Nowadays, soot emissions can be reduced by physically trapping the particles within on-board diesel particulate filters (DPF). The filter gets progressively loaded by filtering the soot laden flue gases, thus causing an increasing pressure drop, until regeneration takes place. The aim of this work is to develop a fully predictive three-dimensional mathematical model able to accurately describe the soot deposition process into the filter, the consequent gradual modification of the properties of the filter itself (i.e. permeability and porosity), the formation of a soot filtration cake, and the final regeneration step. The commercial computational fluid dynamics (CFD) code Fluent 6.2.16, based on a finite-volume numerical scheme, is used to simulate the gas and particulate flow fields in the DPF, whereas particle filtration sub-models and regeneration kinetics are implemented through user-defined-subroutines (UDS).Model predictions highlight uneven soot deposition profiles in the first steps of the filtration process; however, the very high resistance to the gas flow of the readily formed cake layer determines the evolution into an almost constant layer of soot particles. The ignition of the loaded soot was simulated under different operating conditions, and two regeneration strategies were investigated: a “mild regeneration” at low temperature and oxygen concentration, that operated a spatially homogeneous ignition of the deposited soot, and a “fast regeneration”, with an uneven soot combustion along the axial coordinate of the filter, due to strong temperature gradients inside the filter itself. These findings are supported by comparison and validation with experimental data.     

Hot zones formation during regeneration of diesel particulate filters

A diesel particulate filter (DPF) is used to remove particulate matter (PM) from the diesel engine exhaust. The accumulated PM is periodically removed by combustion, which sometimes leads to excessive temperature excursions that melt the ceramic filter. This behavior cannot be explained by operation under stationary feed conditions. We propose that these temperature excursions are a dynamic effect following a rapid change in the driving mode while the DPF is being regenerated. Specifically, a rapid decrease in the exhaust temperature can lead to a counterintuitive large transient temperature rise above that which would exist under a higher stationary feed temperature. This unexpected behavior is similar to the well‐known wrong‐way behavior in packed‐bed reactors, even though the axial‐dependent flow through the filter in a DPF is rather different from the constant axial flow through a packed bed. We present simulations that provide insight about the dependence of the amplitude of this wrong‐way temperature rise on the filtration velocity, the PM loading, dimensions of the DPF, and the amplitude of the rapid temperature decrease and when it occurs after the start of the regeneration. The insight provided by these simulations will help develop operation and control protocols that circumvent or at least decrease the probability of the occurrence of the destructive melting of the DPF. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Multi-channel simulation of regeneration in honeycomb monolithic diesel particulate filters

In recent years advanced computational tools of diesel particulate filter (DPF) regeneration have been developed to assist in the systematic and cost-effective optimization of next generation particulate trap systems.In the present study, we employ a previously validated, state-of-the-art multichannel DPF simulator to study the regeneration process over the entire spatial domain of the filter. Particular attention is placed on identifying the effect of inlet cones and boundary conditions, filter can insulation and the dynamics of “hot spots” induced by localized external energy deposition. Lateral heat losses through the insulation and the periphery of the filter can, as captured by the magnitude of the Nusselt number, Nu, are detrimental to the effectiveness of the regeneration process. A filter can Nu number less than 10 and preferably less than 5 is a good design target for high regeneration efficiency. For the case studied, insulation of the inlet cones can lead to a gain of 30% in regeneration efficiency by eliminating radial temperature gradients at the inlet filter face. The multichannel simulator provides an instructive illustration of the well-appreciated effects of localized hot spot on filter regeneration: hot spots play a more significant role (spread over) when located near the entrance of the filter.     

Impact of Biodiesel-Based Na on the Selective Catalytic Reduction of NOx by NH3 Over Cu–Zeolite Catalysts

A single-cylinder diesel engine was used to investigate the impact of Na on Cu–zeolite SCR catalysts using 20 % bio- and petrol-diesel fuel blend (B20) with elevated levels of Na. The Na exposure was performed on light-duty (DOC–SCR–DPF) and heavy-duty (DOC–DPF–SCR) configurations of the diesel emissions control devices. The accelerated Na aging is achieved by exposing the system to elevated levels of Na that represent full useful life exposure (700,000 km) and periodically increasing the exhaust temperature to replicate DPF regeneration. After aging, the NO_x performance and relevant chemistry of the SCR catalysts were evaluated in a bench flow reactor. The SCR in the DOC–SCR–DPF configuration was found to be severely affected by Na contamination, especially when NO was the only NO_x species in the simulated exhaust gases. In the DOC–DPF–SCR configuration, no impact is observed in the SCR NO_x reduction activity. Electron microprobe analysis (EPMA) reveals that Na contamination on the SCR samples in the DOC–SCR–DPF configuration is present throughout the length of the catalysts.     

Detailed investigation of non‐catalytic DPF regeneration

The present investigation concerns the phenomena that occur during the non‐catalytic regeneration of Diesel Particulate Filters (DPFs). The temperature evolution in the filter has been correlated to the emissions of CO, HC, NO, and NO₂ during the loading and regeneration process. The emissions were assessed over both the diesel oxidation catalyst (DOC) and the DPF, in order to characterise the chemical species evolution inside the after‐treatment line. Different regeneration temperatures, which have been found to have a strong impact on the evolution of the soot oxidation rate, have been assessed. Finally, the particulate emissions during regeneration have been measured on a number and size basis.     

New Tool for Experimental Analysis of Diesel Particulate Filter Loading

The loading of a diesel particulate filters (DPFs) entails the need of trap regeneration by particulate combustion, whose efficiency and frequency are somehow affected by the way soot is deposited along the channels. Great efforts are thus spent to improve the understanding of the filtration process of DPFs, aimed at obtaining a deeper insight into the relationship between engine performance and filter loading so as to take advantage of this insight for DPF design and optimization purposes. Small lab-scale 300 cpsi DPF samples were loaded downstream the Diesel oxidation catalyst (DOC) in an ad hoc designed reactor capable of hosting five samples with part of the entire flow produced by an automotive diesel engine at the 2500 × 8 BMEP operating condition, selected to be representative as one of the critical engine points of the New European Driving Cycle (NEDC). Soot layer thickness was estimated by means of Field emission scanning electron microscope (FESEM) observations after sample sectioning at progressive locations, obtained through a procedure defined not to affect the distribution of the soot inside the filter and to enable estimation of the actual soot thickness along the channel length. This is a pre-requisite to get suitable data for the validation of the DPF models required for trap design and optimisation.     

Counter‐intuitive temperature excursions during regeneration of a diesel particulate filter

A major technological challenge in the regeneration of diesel particulate filters (DPFs) is that sometimes local high temperature excursions melt the cordierite ceramic filter. The cause of this melting is still an open question as the highest temperature attained under stationary (constant feed) combustion of the accumulated particulate matter is too low to cause this melting (melting temperature ～1250°C). We recently conjectured that the high temperature excursions are a counterintuitive response to a rapid deceleration, which decreases the exhaust gas temperature and flow rate and increases the oxygen concentration. Infrared measurements of the spatiotemporal temperature during soot combustion on a single‐layer DPF showed that a simultaneous step change of the feed temperature, flow rate, and oxygen concentration can lead to a transient temperature that exceeds the highest attained for stationary operation under either the initial or the final operation conditions. The experiments revealed that the magnitude of the temperature rise depends in a complex way on several factors, such as the direction of movement of the propagating temperature front. The amplitude of the temperature rise is a monotonic decreasing function of the distance that the temperature front moved before the step change. The rapid response to the feed oxygen concentration increases initially the moving front temperature. The slow response of the ceramic DPF to a decrease in the feed temperature may eventually decrease the moving front temperature and even lead to premature extinction and partial regeneration. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

In-Operation Monitoring of the Soot Load of Diesel Particulate Filters: Initial Tests

Diesel particulate filters (DPF) are indispensable parts of modern automotive exhaust gas aftertreatment systems due to the stringent emissions legislation. For a fuel-efficient control strategy, it would be beneficial to determine directly and in-operation their actual trapped soot mass. Two novel approaches—based on the electrical conductivity of trapped soot particles—emerged recently. By measuring the electrical resistance between different single walls inside the filter, the soot load is determined with local resolution. The microwave-based technique is a contactless approach that gives an integral value depending on the soot mass in the DPF. We present investigations on loading and regeneration of DPFs in a dynamometer test bench applying both methods. The results are compared with each other and correlated with the differential pressure and the soot mass. Especially the microwave-based technique has a potential for serial application.     

RECP: A Reactor Designed to Test the Effect of a Catalyst on Soot Oxidation in a Diesel Particulate Filter

A new reactor designed to test soot combustion on a filter coated with an oxidation catalyst is described. It is designed to achieve screening investigations of catalysts in realistic conditions, i.e., close to those prevailing in a diesel particulate filter (DPF). In a DPF a soot layer is formed at the surface of a porous wall (filtration area) which may or may not be covered with a catalytic layer. In this new setup, the soot is deposited on a sample of a DPF which can be easily impregnated with oxidation catalysts. A model soot (commercial carbon black) is used for the investigation, and different procedures for the soot „deposit on the filter are tested.     

Effect of Biofuels on Catalyzed Diesel Particulate Filter Regeneration

Under the terms of the Renewable Energy Directive, EU member states are required to use 10 % of transport energy sourced from renewable sources, mainly biofuels, by 2020. The purpose is to reduce greenhouse gas (GHG) emissions from the transport sector. However, biodiesel used as fuel has a significant impact on emissions, as related by most of the literature on the subject. In particular, nitric oxides (NOx) and particulate matter (PM) emissions from current diesel technologies are critical factors because they are already close to the limits permitted by regulations and both limits will be even more stringent in the near future. Soot particles are trapped on a diesel particulate filter (DPF). If the DPF is catalyzed like in this study, the soot is then burned by reaction with NO₂ (CDPF continuous regeneration) which occurs at lower temperatures than reaction with O₂ (active regeneration). Tests of ultra-low sulfur diesel blended with rapeseed-biodiesel at 30 % (B30) and Fischer–Tropsch diesel (FT30) were conducted. The Fischer–Tropsch diesel was chosen to represent a biomass-to-liquid fuel. This work investigated the impact of these two biofuels on engine polluting emissions and the resulting CDPF ability to regenerate. When compared with similar inlet conditions on a synthetic gas bench, an impact of fuel was observed on soot reactivity: the CDPF loaded with FT30 soot regenerated slightly faster. Engine bench tests were also performed to combine the effects of fuel on engine emissions and soot reactivity and to evaluate the CDPF. The increase in NOx and decrease in PM emissions observed for B30 appeared to significantly improve CDPF continuous regeneration by NO₂.     

In Situ Formation of Silicon Carbide Nanofibers on Cordierite Substrates

Twenty-five years of diesel particulate filter (DPF) developments have shown that high-volume ceramic materials are well suited for the harsh requirements of exhaust after treatment. Nevertheless, problems regarding filter reliability and durability associated with the regeneration of the filter have limited their serious application until only recently. To extend useful filter life, the present study has examined the growth of silicon carbide (SiC) nanofibers by a simple carbothermal reduction process on cordierite support surfaces using cheap raw materials such as kaolin, talc, and carbon black. Transmission electron microscopy confirms the crystalline (β - SiC) nature of the nanofibers (10–20 nm diameter). The growth of these nanofibers increases the support-specific surface area restricting the agglomeration of noble metal catalyst particles that otherwise occurs in wash-coat sintering. As a result, fewer particles are needed to perform the catalyst role (at reduced cost) and the support structure can host the catalyst for prolonged times at higher temperatures. As the future will see increasing economic competition in filter fabrication routes and materials, this new design of catalytic DPF promises to play a significant role.     

Characteristics of the simultaneous removal of PM and NOx using CuNb-ZSM-5 coated on diesel particulate filter

The purpose of this study is to investigate the characteristics of the simultaneous removal of PM and NOx on the CuNb-ZSM-5 SCR/DPF catalysts coated onto DPF substrate. NOx conversion by the CuNb-ZSM-5 catalyst was higher than those by Cu- or Fe-ZSM-5 catalysts. NOx conversion of the SCR/DPF catalyst with a wall-flow (plugged) was considerably lower under 450 °C than that of the SCR/DPF catalyst with a channel-flow (unplugged). The de-NOx performance of the SCR/DPF catalyst coated with CuNb-ZSM-5 was highest among the catalysts examined. SCR/DPF catalyst coated with CuNb-ZSM-5 had superior PM oxidation performance compared to the other SCR/DPF catalysts.     

Evaluation of Performance of Diesel Particulate Filters Through Integrated Multi-Scale Computer Calculations

Wall-flow channel models and soot deposition models based on micro scale considerations are integrated into global 3D diesel particulate filter simulations. In addition, transient and steady-state simulations are combined to understand at the same time short- and long-time behaviour of the diesel particulate filter (DPF). The functionality of the simulation tool is achieved and correlations with measured data encourage the use of the model as a tool to predict DPF behaviour.     

Behavior features of soot combustion in diesel particulate filter

Infra-red measuremnts of the combustion of particular matter (PM) deposited on the surface of a single layer diesel particulate filter (DPF) showed that it may proceed in three different modes: either by a moving hot zone emanating from a single ignition point, or hot zones generated at several different ignition points or uniform combustion all over the surface. The velocity of the downwards moving temperature front exceeds that of the upstream front bounding the hot zone. The number of ignition points increases as the PM loading is decreased. The highest temperature rise is obtained by a downward moving hot zone. Avoiding this mode of combustion decreases the probability of excessive hot zone formation during the PM regeneration.     

DPF520型淀粉分离机设计及样机带物料应用试验

DPF520型淀粉分离机的设计与样机带物料应用试验作了介绍,并与DPX445型淀粉分离机在主要性能参数上作了对比,通过样机的实际应用试验,证明该型机满足了顾客提出的技术指标,设计是成功的,产品开发达到了目的。     

Comparison of Exhaust Particle Number Measured by EEPS,CPC, and ELPI

An Engine Exhaust Particle Sizer (EEPS) Spectrometer, a Condensation Particle Counter (CPC) and an Electrical Low Pressure Impactor (ELPI) were used to determine the exhaust particle number of a Diesel engine on steady speeds and on the New European Driving Cycle (NEDC), upstream and downstream several Diesel Particulate Filters (DPF). In order to obtain different particle numbers, five DPFs with different porosity were used. The above three instruments give quite similar total particle numbers on steady speeds and on the NEDC for the tests upstream DPF. Downstream DPF, EEPS reaches its limit of measurement; however, the total particle numbers obtained by this instrument are still close to the particle numbers obtained by CPC and ELPI. The particle number versus time of the three instruments are quite close in the case of the NEDC measurements upstream DPF. Downstream DPF, CPC, and ELPI give quite similar signals, but EEPS reached its limits of detection. Upstream DPF, ELPI, and EEPS determine quite similar median diameters in the case of steady speeds, despite their different shape in particle size distribution.