GB2508485A

GB2508485A - Honeycomb particulate filter with intermediate plugs

Info

Publication number: GB2508485A
Application number: GB1317235.8A
Authority: GB
Inventors: Romain Demory; Peter Graham Eastwood
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2012-10-08
Filing date: 2013-09-30
Publication date: 2014-06-04
Anticipated expiration: 2033-09-30
Also published as: CN203532009U; DE102013111070A1; GB201317235D0; GB2506677A; GB2508485B; GB201217949D0

Abstract

A particulate filter 20 comprises a honeycomb body 21 having an inlet end, an outlet end, and a plurality of flow passages 23 separated by porous walls. Plugs 22F, 22M and 22R are formed in predetermined flow passages 23 for removing particulate matter from an exhaust gas flow passing through the porous walls. The plugs include plugs 22F at the inlet end, plugs 22R at the outlet end, and plugs 22M positioned and distributed in a configuration that increases the regeneration efficiency of the particulate filter 20. The intermediate plugs may be located towards the inlet end of the honeycomb body, and/or they may be outlet end plugs that have been repositioned towards the inlet end. A motor vehicle may comprise an engine and the particulate filter, which may be a diesel particulate filter (DPF). The position of the intermediate plugs may be optimised using flow modeling, such as computational flow dynamics (CFD).

Description

A Method for Improving the Regeneration Efficiency of a Particulate Filter This invention relates to an improved particulate filter for an engine of a motor vehicle and in particular to a method and apparatus for improving the regeneration efficiency of such a filter.

It is known from, for example and without limitation, US Patent Number 7,691,167 to provide a ceramic honeycomb filter constituted by a ceramic honeycomb body comprising a peripheral wall and porous partition walls inside the peripheral wall. Plugs are used to alternately seal open ends of the flow paths formed between the porous partition walls such that some ends of the flow paths at an inlet end of the honeycomb body are sealed and some ends of the flow paths at an outlet end of the honeycomb body are sealed.

Exhaust gas containing particulate matter flows into the open inlet ends, passes through the porous partition walls into the adjacent flow paths and is discharged as a cleaned gas from the exit open ends. While passing through the porous partition walls the particulate matter contained in the exhaust gas is captured in fine pores in the porous partition walls. The ceramic honeycomb filter therefore acts as an exhaust gas cleaning filter.

It is a problem with such an arrangement that the distribution of soot is uncontrolled. During regeneration of the particulate filter it is relatively quick and requires only a small amount of additional fuel to regenerate or burn off the soot captured near the inlet side of the honeycomb body but a considerable amount of energy in the form of additional fuel has to be used to burn off the captured soot near to the exit end of the honeycomb body.

In addition, beoause the inlet side of the honeycomb body heats up rapidly during regeneration but the outlet end of the honeycomb body heats up more slowly, a significant thermal gradient is produced in the honeycomb body resulting in high thermal stresses being generated in the honeycomb body during regeneration.

It is a first object of the invention to provide a method for improving the regeneration efficiency of a diesel particulate filter.

It is a second object of the invention to provide a diesel particulate filter with improved regeneration efficiency.

According to a first aspect of the invention there is provided a method for improving the regeneration efficiency of a particulate filter wherein the method comprises providing a honeycomb body having an inlet end, an outlet end and porous internal walls defining a number of exhaust gas flow passages, forming plugs in predetermined flow passages for removing particulate matter from an exhaust gas flow passing through the porous walls including plugs located at the inlet end of the honeycomb body, plugs located at the outlet end of the honeycomb body and plugs located at an intermediate position between the inlet end and the outlet end of the honeycomb body and modelling the flow of exhaust gas through the honeycomb body to optimise the positioning and distribution of the intermediate plugs.

The flow of exhaust gas though the honeycomb body may be modelled using computational fluid dynamics.

Increasing the regeneration efficiency of the particulate filter may comprise at least one of reducing the fuel required to regenerate the filter, reducing the time taken for the regeneration event and increasing the percentage of soot captured by the filter that is removed by the regeneration event.

The method may further comprise repositioning outlet plugs to a position nearer to the inlet end to form the intermediate plugs.

The positioning of the intermediate plugs may be optimised to increase the amount of soot captured by the porous walls near to the inlet end of the honeycomb body.

According to a second aspect of the invention there is provided a particulate filter for an engine comprising a honeycomb body having an inlet end, an outlet end and porous internal walls defining a number of exhaust gas flow passages and plugs formed in predetermined flow passages for encouraging the flow of exhaust gas through the porous walls wherein the diesel particulate filter includes plugs located at the inlet end of the honeycomb body, plugs located at the outlet end of the honeycomb body and, in order to increase the regeneration efficiency of the diesel particulate filter, plugs located at an intermediate position between the inlet end and the outlet end of the honeycomb body so as to increase the amount of soot captured by the porous walls near the inlet end of the honeycomb body and the intermediate plugs are outlet end plugs that are repositioned to a position nearer to the inlet end of the honeycomb body.

The particulate filter may be a diesel particulate filter.

The intermediate plugs may be positioned so as to optimise the distribution of soot captured by the diesel particulate filter.

The intermediate plugs may be located towards the inlet end of the honeycomb body.

Increasing the regeneration efficiency of the diesel particulate filter may comprise at least one of reducing the fuel required to regenerate the filter, reducing the time taken for the regeneration event and increasing the percentage of soot captured by the filter that is removed by the regeneration event.

According to a third aspect of the invention there is provided a motor vehicle having an engine and a particulate filter arranged to receive an exhaust gas flow from the engine wherein the particulate filter is a particulate filter constructed in accordance with said second aspect of the invention.

The invention will now be described by way of example with reference to the accompanying drawing of which:-Fig.1 is a schematic view of a motor vehicle having a particulate filter according a first aspect of the invention; Fig.2 is a transverse cross section through a honeycomb body forming part of the particulate filter shown in Fig.1; Fig.3 is a partial longitudinal cross-section of the particulate filter including a cross-section through the honeycomb body on the line X-X on Fig.2; Fig.4 is a cross-section on the line Y-Y on Fig.3 showing the distribution of numerous intermediate plugs.

Fig.5a is a graph showing changes in temperature at inlet and outlet ends of the honeycomb body during a regeneration event for a prior art diesel particulate filter; and Fig.5b is a graph showing changes in temperature at inlet and outlet ends of the honeycomb body during a regeneration event for a particulate filter optimised in accordance with this invention.

With reference to Fig.1 there is shown a motor vehicle 1 having four road wheels 2 and a diesel engine 5 controlled by an electronic controller 10.

Air is admitted to the engine 5 via an inlet manifold (not shown) and fuel is injected to the various cylinders of the engine 5 by a number of fuel injector (not shown) . The products of combustion in the form of exhaust gas leave the engine 5 via an exhaust manifold 6 and flow along an exhaust pipe 7 to a diesel particulate trap or filter (DPF) 20. The exhaust gas flows through the DPE 20 where partioulates of combustion are removed and then flows from the DPF 20 to atmosphere via a tailpipe 8. It will be appreciated that other exhaust gas after-treatment devices such as a catalyst may be included in the exhaust gas flow path from the engine to atmosphere. Furthermore, one or more noise suppressors such as a silencer may be included in the exhaust gas flow path downstream of the DPF 20.

With reference to Figs.2 to 4 the DPF 20 comprises a honeycomb body 21 having an outer wall 25. The honeycomb body 21 and the outer wall 25 are sometimes referred to in the art as a filter brick' or simple a brick' . The honeycomb body 21 can be made from various materials able to withstand the high temperatures found in an exhaust stream from an engine. For example and without limitation the material could be Silicon Carbide, Cordierite or Aluminium-Titanate.

The cuter wall 25 of the honeycomb body 21 is fastened within a central portion 27 of a metal casing that also includes an inlet end cap 20a and an cutlet end cap 20b.

The inlet cap 20a is ccnnected to the exhaust pipe 7 and the outlet end cap 20b is connected to the tailpipe 8. The exhaust gas from the engine 5 flows into the honeycomb body 21 at an inlet end as indicated by the arrow A' and flows out of the honeycomb body 21 at an outlet end as indicated by the arrow B' The honeycomb body 21 defines a number of flow paths or passages 23 of which only one is referenced on Figs.2 to 4.

Each of the flow passages 23 is separated from adjacent flow passages 23 by porous walls 24 (of which only two are referenced on Fig.3) through which exhaust gas can flow.

The porous walls 24 trap particulate matter flowing therethrough so as to clean the exhaust gas.

Some of the flow passages 23 are sealed off at the inlet end of the honeycomb body 21 by & respective inlet end sealing plug 22F and some of the flow passages 23 are sealed off at the outlet end of the honeycomb body 21 by a respective outlet end sealing plug 22R. The distribution of the end plugs 22F, 22R is such that most of the flow passages 23 are sealed in an alternate pattern at their inlet and outlet ends respectively, this encourages the flow of exhaust gas through the porous walls 24 as indicated by the arrows F on Fig.3.

However, in the case of a DPF constructed in accordance with this invention, some of the flow passages 23 that would normally be sealed off at the exit end of the honeycomb body 21 are instead sealed by a respective intermediate sealing plug 22F4 at a position between the inlet and outlet ends of the honeycomb body 21.

The distribution in terms of number and positioning of these intermediate sealing plugs 22M is determined based upon modelling of the exhaust gas flow and distribution of soot in the honeycomb body 21. Such modelling is often referred to as Computational fluid dynamics' (CFD) and involves the use of numerical methods and algorithms to solve and analyse the fluid flow through an object.

In this case CFD is used to determine the number and most appropriate positioning for the intermediate plugs 22M in order to improve the regeneration efficiency of the DPE 20.

Regeneration efficiency will be improved if at least one of the total amount of fuel used to regenerate the DPF is reduced, the time taken to regenerate the DPF 20 is reduced and the percentage of soot removed during the regeneration is increased without increasing fuel usage.

In order to regenerate a diesel particulate filter the temperature within the diesel particulate filter must be increased in order to burn off or oxidise the soot trapped in the porous walls 24 of the honeycomb body 21. To do this it is usual to use late or post injection of fuel to increase the temperature of the exhaust gases and/or as a source of additional heat when unburnt fuel enters the DPF where it combusts. It is also common to use a fuel borne catalyst or use heating of the exhaust gas in an upstream oxidation catalyst to assist with regeneration.

In all cases the temperature in the DPF is increased and causes an exothermic reaction in the soot thereby burning off the stored soot. The use of late or post injection of fuel into the engine 5 is undesirable for several reasons. Firstly, it has a negative effect on fuel usage/ engine fuel efficiency because the post injected fuel is not being used to create power from the engine 5.

Secondly, it is disadvantageous because it can result in dilution of the lubricating oil and hence potentially increased mechanical wear.

By using intermediate plugs 2204 positioned towards the inlet end of the honeycomb body 21 more soot is stored near to the inlet end of the honeycomb body 21. Therefore, during the early stages of regeneration a stronger exothermic reaction takes place due to the increased volume of scot being combusted and so more heat is generated. The increased heat particularly at the beginning of regeneration is transferred through the honeycomb body 21 by the flow of exhaust gas through the flow passages 23. The additional heat helps to heat up the honeycomb body 21 particularly towards the outlet end of the honeycomb body 21 so that the outlet end more rapidly reaches the temperature required for regeneration of the soot. In this way less fuel is required to regenerate the DPF 20 and the time taken to regenerate the DPF 20 is reduced because the outlet end of the honeycomb body 21 heats up quicker. In addition the amount of soot removed is increased because a larger percentaqe of the captured soot is captured near to the inlet end of the honeycomb body 21 which experiences a strong exotherrnic reaction at the commencement of the regeneration event and continues to receive fuel until the regeneration event is terminated. That is to say, regeneration will potentially take place at the inlet end of the honeycomb body 21 for the entire regeneration event whereas at the outlet end there is a delay before regeneration commences. That is to say regeneration takes place for a longer period of time at the inlet end of the honeycomb body 21 than it does at the outlet end.

With particular reference to Figs.5a and 5b there is shown two temperature versus time charts for a regeneration event showing temperatures for prior art DPF during the event and temperatures for a DPF oonstructed in accordance with this invention during the event.

It can be seen that at the beginning of the regeneration event the temperature at the inlet end of the honeycomb body 21 is increased in accordance with this invention compared to the prior art due to the very strong exothermic reaction that takes place. However, the temperature at the outlet end of the honeycomb body 21 at the end of the regeneration event is reduced compared to the prior art. The very high temperatures which can occur at the end of a prior art regeneration are undesirable because they increase thermal stress in the honeycomb body 21 and also result in very high temperature exhaust gas travelling downstream through the tailpipe 8.

Although the temperature difference between the inet and outlet ends of the PDF 20 at the beginning of the regeneration event is greater than the temperature difference i-between the inlet and outlet ends of the prior art PDF at the beginning of the regeneration event it is smaller than the temperature difference L2 between the inlet and outlet ends of the prior art PDF at the end of the regeneration event. Therefore the peak thermal stress within the honeycomb body 21 is reduced. Also the temperature differences At: and A1 at the beginning and end of the regeneration event are both smaller than the temperature difference A-2 confirming that the thermal stress with the honeycomb body 21 is reduced.

The exact location and number of intermediate plugs 22F4 reguired to optimise regeneration will depend upon the specific design of the DPE 20 and the invention is not limited to the distribution of intermediate plugs 2214 shown.

For example, although all of the intermediate plugs 2214 are shown aligned on a single transverse plane indicated by -10 -the line Y-Y this need not be the case and some of the intermediate plugs 22M could be located nearer the inlet end of the honeycomb body than others.

Furthermore, although all of the intermediate plugs 22M are in the example shown, outlet end plugs 22R that have been replaced in the respective flow passage 23 by an intermediate plug 2214, this need not be the case and the intermediate plugs 22M could be inlet end plugs 22F that have been replaced in the respective flow passage 23 or a combination of replaced inlet and outlet end plugs 22F and 22R.

Therefore in summary, by locating some of the plugs used to block off flow passages within a honeycomb body of a diesel particulate filter to positions where the deposition of more soot near to an inlet end of the honeycomb body is achieved, the inventors have found that the regeneration efficiency of the particulate filter can be increased.

Although the invention has been described by way of example to a diesel particulate filter it will be appreciated that it is not limited to such a use and could be applied with benefit to a gasoline engine having a particulate filter.

It will be appreciated by those skilled in the art that although the invention has been described by way of example with reference to one or more embodiments it is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined by the appended claims.

Claims

-11 -Claims 1. A method for improving the regeneration efficienoy of a particulate filter wherein the method comprises providing a honeycomb body having an inlet end, an outlet end and porous internal walls defining a number of exhaust gas flow passages, forming plugs in predetermined flow passages for removing particulate matter from an exhaust gas flow passing through the porous walls including plugs located at the inlet end of the honeycomb body, plugs located at the outlet end of the honeycomb body and plugs located at an intermediate position between the inlet end and the outlet end of the honeycomb body and modelling the flow of exhaust gas through the honeycomb body to optimise the positioning and distribution of the intermediate plugs.
2. A method as claimed in claim 1 wherein the flow of exhaust gas though the honeycomb body is modelled using computational fluid dynamics.
3. A method as claimed in claim 1 or in claim 2 wherein increasing the regeneration efficiency of the particulate filter comprises at least one of reducing the fuel required to regenerate the filter, reducing the time taken for the regeneration event and increasing the percentage of soot captured by the filter that is removed by the regeneration event.
4. A method as claimed in any of claims 1 to 3 wherein the method further comprises repositioning outlet plugs to a position nearer to the inlet end to form the intermediate plugs.
5. A method as claimed in any of claims 1 to 4 wherein the positioning of the intermediate plugs is optimised to increase the amount of soot captured by the porous walls near to the inlet end of the honeycomb body.

-12 -
6. A particulate filter for an engine comprising a honeycomb body having an inlet end, an outlet end and porous internal walls defining a number of exhaust gas flow passages and plugs formed in predetermined flow passages for encouraging the flow of exhaust gas through the porous walls wherein the diesel particulate filter includes plugs lccated at the inlet end of the honeycomb body, plugs located at the outlet end of the honeycomb body and, in order to increase the regeneration efficiency of the diesel particulate filter, plugs located at an intermediate position between the inlet end and the outlet end of the honeycomb body so as tc increase the amount of soot captured by the pcrous walls near the inlet end of the honeycomb bcdy and the intermediate plugs are outlet end plugs that are repositioned to a position nearer to the inlet end of the honeycomb body.
7. A filter as claimed in claim 6 wherein the intermediate plugs are pcsiticned so as to optimise the distribution of soct captured by the diesel particulate filter.
8. A filter as claimed in claim 6 or in claim 7 wherein the intermediate plugs are located towards the inlet end of the honeycomb body.
9. A filter as claimed in any of claims 6 to 8 wherein increasing the regeneraticn efficiency of the diesel particulate filter ccmprises at least one of reducing the fuel reguired to regenerate the filter, reducing the time taken for the regeneration event and increasing the percentage of soot captured by the filter that is removed by the regeneration event.
10. A motor vehicle having an engine and a particulate filter arranged to receive an exhaust gas flow from the -13 -engine wherein the particulate filter is a particulate filter as claimed in any of claims 6 to 9.
11. A method for improving the regeneration efficiency of a particulate filter substantially as described herein.
12. A particulate filter substantially as described herein with reference to Figs.l to 4 and 5b of the accompanying drawing.
13. A motor vehicle substantially as described herein with reference to Figs.l to 4 and 5b of the accompanying drawing.