GB2570450A

GB2570450A - Particulate filter

Info

Publication number: GB2570450A
Application number: GB1801127.0A
Authority: GB
Inventors: Cudmore Stephen; Hartland Jonathon
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2018-01-24
Filing date: 2018-01-24
Publication date: 2019-07-31
Anticipated expiration: 2038-01-24
Also published as: GB2570450B; GB201801127D0

Abstract

A particulate filter 20 for an exhaust system (52, fig 4) of a vehicle (50, fig 4) comprises an inlet channel 24 and an outlet channel 22, 26 separated by a porous wall 21, where a flow path from the inlet channel to the outlet channel passes through the porous wall. A particulate matter regeneration catalyst 29 for catalysing the regeneration of particulate matter retained by the filter is provided on a portion of a surface of the outlet channel and not on a surface of the inlet channel. There may be a plurality of outlet channels and inlet channels. The catalyst may be in the form of a washcoat, and may have a higher loading or higher concentration of active ingredients at an outlet end of the filter than at an inlet end. The invention also provides a method of manufacturing the particulate filter, and an exhaust system and a vehicle including the particulate filter.

Description

PARTICULATE FILTER

TECHNICAL FIELD

The present disclosure relates to a particulate filter and particularly, but not exclusively, to a diesel particulate filter. Embodiments of the invention relate to a particulate filter for reducing particulate matter emissions from diesel engine-powered vehicles, for example from diesel engine-powered cars. Aspects of the invention relate to a particulate filter, to a vehicle, to a method of manufacture, and to a product of the method.

BACKGROUND

Particulate filters are used to remove particulate matter from the exhaust flow of internal combustion engines and, in particular, from the exhaust flow of diesel engines. Particulate matter, often referred to as “soot”, accumulates in the particulate filter in use.

From time to time, accumulated particulate matter is burnt off during an active regeneration process involving subjecting a diesel particulate filter and the accumulated particulate matter to significantly higher temperatures than in normal operation. This involves operating the engine in a state which increases the temperature of the exhaust gases which in turn transfer increased heat to the DPF and accumulated particulate matter. The particulate matter is then burnt and converted to gases such as CO₂ and steam which are then released to the atmosphere. The engine operating state required to provide the increase in exhaust gas temperature for DPF regeneration requires increased fuel consumption and so is undesirable in terms of fuel economy. As such in some DPF designs, the DPF comprises a catalyst which lowers the temperature required to burn off the accumulated particulate matter. This means that a lower increase in exhaust gas, and hence a lower increase in fuel consumption of the engine, is required during a regeneration process. Typically, the catalyst is included in a coating applied to the DPF.

In some diesel particulate filter applications, the DPF may have the additional functionality of oxidising unburnt hydrocarbons and carbon monoxide in the exhaust gas in to water and carbon dioxide which are then released in to the atmosphere. This reaction is achieved through the use of a catalyst applied to the DPF. This catalyst may be the same catalyst which aids in regeneration of the DPF as described above. Alternatively, a separate catalyst may be provided for the purpose of regeneration.

Vehicles are usually tested for emissions levels. If the mass and count of particulate matter is high during a regeneration process, there may be a fail during a vehicle emissions test. The legislative trend is for tougher emission controls, requiring further development and refinement of particulate filters like DPFs.

A longitudinal cross section through a representative portion of a typical particulate filter 10 is shown in Figure 1. Specifically, Figure 1 shows a wall flow region of the particulate filter 10. As is well-known in the field of the invention, a particulate filter core 11 is made of an inert material such as cordierite, aluminium oxide, refractory metal oxides, mullite, or silicon carbide. Other suitable core materials are known to the skilled addressee. A number of elongate channels 12, 14, and 16 are formed through the porous core 11. Opposing ends of some of the channels are plugged by plugs 13, 15 and 17 to form inlet 14 and outlet 12, 16 channels in the particulate filter. In use, exhaust gas flows from an associated vehicle engine in the direction of arrow F into the inlet channels 14 and is forced through the walls of the inlet channel into the porous body of the core 11, and out through adjacent outlet channels 12, 16. Particulate matter accumulates on the walls of the inlet channels 14. The filtered exhaust gas then flows to the tail pipe of the vehicle’s exhaust system. A washcoat 19 including a catalyst for catalysing the oxidation of unburnt hydrocarbons and carbon monoxide in the exhaust gas is applied to the particulate filter core during manufacture. The washcoat 19 is applied to the walls of both the inlet 14 and outlet 12, 16 channels.

In use, a layer of particulate matter accumulates on the walls of the inlet channels. On regions of the walls to which the washcoat is applied, during a regeneration event as described above the increased temperatures in the particulate filter in combination with the catalyst in the washcoat will cause this layer of particulate matter to burn from the surface of the walls towards the centre of the respective inlet channel 14. This phenomenon also occurs during a partial regeneration event during which nitrogen dioxide in the exhaust gas converts the particulate matter in to carbon dioxide and nitrogen. When a driver rapidly depresses the accelerator pedal of the associated vehicle the flow rate of exhaust gases passing through the particulate filter rapidly increases. When a tip in event coincides with a regeneration or partial regeneration event, the small particles of partially burnt particulate matter adjacent to the surface of the walls of the inlet channels 14 pass through the porous core 11, in to the outlet channels 12,16 and out towards the exhaust system tailpipe as a large number of very fine particles. This is termed a “blow off” event and this release of very fine particles is undesirable. In contrast it is understood that, during a regeneration or partial regeneration event, layers of particulate matter accumulated on the surface of the walls of the inlet channels not coated with the washcoat will burn in the direction from the centre of the respective inlet channel 14 towards the surface of the walls. This means that any small particulate matter which is partially burnt is captured by the unburnt portion of the particulate matter layer during a blow off event.

It is known to apply a washcoat including a catalyst to specific areas of a particulate filter to minimise the risk of cracking of the filter in use due to localised heating causing thermal stresses within the filter core - typically in its centre. See for example US 2008/0047244 where not applying a washcoat to the central portion of a filter core is taught. It is also known to selectively coat regions of the inlet and outlet channels of a DPF with a washcoat in order to maximise contact of the exhaust gases with the catalyst as the exhaust gases flow through the DPF. Drops in the pressure of the exhaust gas as it flows through the DPF may affect the selection of the coated and uncoated regions.

It should be noted that although a diesel particulate filter is referred to throughout this description, the invention could also be applied to a gasoline particulate filter.

It is an aim of the present invention to address disadvantages associated with the prior art.

SUMMARY OF THE INVENTION

Aspects of the invention are defined in the appended claims.

According to an aspect of the invention there is provided a particulate filter for a vehicle, the particulate filter comprising an inlet zone separated from an outlet zone by a filtration zone, in which, in use, a gas flow including particulate matter passes through the inlet zone so that particulate matter is captured in the filtration area, the filter including a catalyst for catalysing regeneration of particulate material captured in the filter, in which the catalyst is present in the outlet zone and not in the inlet zone.

According to an aspect of the present invention there is provided a particulate filter for an exhaust system of a vehicle comprising an inlet channel and an outlet channel separated by a porous wall, wherein a flow path from the inlet channel to the outlet channel passes through the porous wall; and a particulate matter regeneration catalyst for catalysing the regeneration of particulate matter retained by the filter in use; wherein the particulate matter regeneration catalyst is provided on a portion of a surface of the outlet channel and not on a surface of the inlet channel.

It is noted that where a plurality of filter channels comprising an inlet channel and an outlet channel is referred to, this is not intended to limit the scope of the invention to filter channels comprising a single inlet channel and a single outlet channel. This is intended to define filter channels comprising at least one inlet channel and at least one outlet channel.

The particulate filter may comprise an inlet end at which exhaust gases enter the particulate filter in use and an outlet end at which exhaust gases exit the particulate filter in use. In this embodiment, the inlet channel is open at the inlet end of the particulate filter and closed at the outlet end of the particulate filter, and the outlet channel is closed at the inlet end of the particulate filter and open at the outlet end of the particulate filter.

The particulate filter may comprise a plurality of outlet channels. In this embodiment, the particulate matter regeneration catalyst may be provided on a portion of a surface of more than one of the outlet channels.

The particulate filter may comprise a plurality of inlet channels. In this embodiment, the particulate matter regeneration catalyst may not be provided on a surface of any of the inlet channels.

The particulate matter regeneration catalyst may be provided in the form of a coating. The coating may be in the form of a washcoat.

The particulate matter regeneration catalyst may be provided over more than half the length of the surface of the or each outlet channel. The particulate matter regeneration catalyst may be provided over the entire length of the surface of the or each outlet channel.

Where the particulate filter has an inlet end and an outlet end, there may be a higher loading of the particulate matter regeneration catalyst at the outlet end compared to the inlet end. Alternatively or additionally, there may be a higher concentration of active ingredients in the particulate matter regeneration catalyst at the outlet end compared to the inlet end.

According to another aspect of the invention, there is provided a method of manufacturing a particulate filter comprising: providing an inlet channel and an outlet channel separated by a porous wall, wherein a flow path from the inlet channel to the outlet channel passes through the porous wall; and applying a particulate regeneration catalyst for catalysing the regeneration of particulate matter retained by the filter in use; wherein the particulate matter regeneration catalyst is applied to a portion of a surface of the outlet channel and not to a surface of the inlet channel.

In this aspect of the invention, a plurality of outlet channels may be provided and the particulate matter regeneration catalyst may be applied to a portion of a surface of more than one of the outlet channels. Also in this aspect of the invention, a plurality of inlet channels may be provided, with the particulate matter regeneration catalyst not being applied to a surface of any of the inlet channels.

The particulate matter regeneration catalyst may be applied over more than half the length of the surface of the or each outlet channel. The particulate matter regeneration catalyst may be applied over the entire length of the surface of the or each outlet channel.

The particulate regeneration catalyst may be applied to the surface of the or each outlet channel in a washcoat. The washcoat may be drawn through the or each outlet channel. The washcoat may be drawn by a vacuum through the or each outlet channel.

The inlet channel may be open at an inlet end of the particulate filter and closed at an outlet end of the particulate filter, and the or each outlet channel may be closed at the inlet end of the particulate filter and open at the outlet end of the particulate filter. The washcoat may be drawn from the outlet end towards the inlet end such that the particulate matter regeneration catalyst is applied to a portion of a surface of the or each outlet channel and not to a surface of the or each inlet channel.

A higher loading of the particulate matter regeneration catalyst may be applied at the outlet end compared to the inlet end. Alternatively or additionally, a higher concentration of active ingredients may be provided in the particulate matter regeneration catalyst at the outlet end compared to the inlet end.

A higher loading of the particulate matter regeneration catalyst at the outlet end compared to the inlet end may be provided by repeatedly drawing the washcoat from the outlet end towards the inlet end.

According to another aspect of the invention there is provided a particulate filter obtained or, obtainable by a method of manufacture according to a previous aspect of the invention.

According to another aspect of the invention there is provided a vehicle including a particulate filter according to a previous aspect of the invention. The particulate filter may be included in the exhaust system of the vehicle. The vehicle may be a diesel engine-powered vehicle. For example, the vehicle may be a car.

According to a further aspect of the invention, there is provided an exhaust system including a particulate filter according to a previous aspect of the invention.

Throughout the description and claims of this specification, the words comprise and contain and variations of the mean including but not limited to, and they are not intended to exclude other moieties, additives, components, integers or steps. Throughout the description and claims of the specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in the specification, and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in the specification, or any novel one, or any novel combination, of the steps of any method or process so disclosed.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

The prior art has already been described with reference to Figure 1 which shows a longitudinal cross section through a representative portion of a known particulate filter.

One or more embodiments of the invention will now be described, by way of example only, with reference to the further accompanying drawings in which:

Figure 2 is a longitudinal cross-sectional view through a portion of a particulate filter in accordance with an embodiment of the invention;

Figure 2A is a schematic longitudinal cross-sectional view through the particulate filter of Figure 2;

Figure 3 is a schematic diagram illustrating a method of manufacture of a filter in accordance with an embodiment of the invention; and

Figure 4 is a side view of a vehicle in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

A wall flow region of a particulate filter 20, specifically a DPF, in accordance with an embodiment of the invention, is shown in Figure 2. As is well-known in the field of the invention, a particulate filter core 21 is made of an inert material such as cordierite, aluminium oxide, refractory metal oxides, mullite, or silicon carbide. Other suitable core materials are known to the skilled addressee. A number of elongate channels 22, 24 and 26 are formed through the porous core 21. The channels 22, 24 and 26 may be for example quadrilateral, hexagonal, or octagonal in cross-section. Other channel cross-sections such as an Asymmetrical Cell Technology arrangement are also contemplated. Opposing ends of some of the channels 22, 24 and 26 are plugged by plugs 23, 25 and 27 to form inlet 24 and outlet 22, 26 channels in the particulate filter. If the channels in the wall flow region have a quadrilateral cross-section, then channels which are plugged at the inlet end, are preferably adjacent on all four sides to channels which are plugged at the outlet end. In this way, the channels in the wall flow region form a chequerboard pattern.

In use, and as particularly shown in Figure 2A, exhaust flows from an associated vehicle engine in the direction of arrow F into the inlet channels 24 and is forced through the porous body of the core 21 and out through adjacent outlet channels 22, 26. A washcoat including a catalyst is applied to the filter core during manufacture. The wash coat may comprise for example aluminium oxide, titanium dioxide, silicon dioxide, and silica/ aluminium oxide mixtures. The catalyst may be for example a precious metal such as platinum. The washcoat is applied to the walls of outlet 22, 26 channels only. In the embodiment shown the washcoat extends along the length of the outlet channel.

In use, the particulate filter 20 is arranged in a vehicle exhaust system, such that exhaust gas flows through the particulate filter, as described above. Over time, particulate matter accumulates in the particulate filter. As explained above, during a regeneration or partial regeneration event, particulate matter which has accumulated on the walls of the inlet channels 14 burns in the direction from the centre of the respective inlet channel 14 towards the surface of the walls as there is no washcoat on the surface of the walls of the inlet channels 14. Any partially burnt particulate matter is captured in the particulate matter layer during a blow off event which reduces downstream loss of the particulate matter. This significantly reduces the amount of particulate matter released during a blow off event.

A method of making a DPF according to an embodiment of the invention, involves first producing a porous filter core 30. As previously discussed, the filter core 30 may be made for example from cordierite, aluminium oxide, silicon carbide, or other materials. The filter core 30 is formed with several longitudinal channels, which provide the inlet and outlet channels in the completed particulate filter. Ends of the inlet channels are stopped, plugged or otherwise closed on the outlet side 31 of the filter core 30. Conversely, ends of the outlet channels are stopped, plugged or otherwise closed on the inlet side of the filter core 32. Some channels may be left open at either end to allow free flow through the filter. As shown in Figure 3, liquid coating 33, or washcoat, including an appropriate catalyst is provided in a bath 34. During the method of manufacture, the outlet end 31 of the filter core 30 is dipped in the liquid coating 33. The liquid coating 33 is drawn partially through the open outlet channels of the filter core 30, but is excluded from the inlet channels which are plugged or otherwise closed at the outlet end 31, by applying a vacuum to one end of the filter core 30, in the direction of arrow V. The coated filter core 30 is then removed from the bath before drying.

The extent of coating of the outlet channels may be controlled during the method of manufacture. By way of example, this may be achieved by controlling the vacuum applied to the filter core, or by controlling the viscosity of the liquid coating to facilitate the coating process. In particular, the coating process may be adjusted to control the deposition of the washcoat on the filter surface to minimise clogging the porous structure of the filter core. The deposition of the washcoat may be arranged to maximise the washcoat on the filter channel surfaces. The washcoat may be applied to the whole of an outlet channel surface or to a significant portion of the surface.

Additionally, the extent of coating of the outlet channels may be controlled during the method of manufacture by controlling the number of times the liquid coating is drawn through the outlet channels. For example, a higher concentration of the particulate matter regeneration catalyst may be provided over part of the length of the outlet channel by drawing a first coating through the entire length of the channel and subsequently drawing further coatings over this part of the length of the channel.

In one embodiment, the plugging or closing of the inlet and/or outlet channels may be completed after the application of a catalyst-containing washcoat. In other words, coating the filter core as for a flow-through catalyst, but using a mask to block certain channels, which will become inlet channels in the final particulate filter so as not to coat inlet channels with catalyst-containing washcoat.

A vehicle 50 including an exhaust system 52 comprising a particulate filter 54 according to an embodiment of the invention is shown in Figure 4.

Many modifications may be made to the above examples without departing from the scope of the present invention as defined in the accompanying claims.

Claims

1. A particulate filter for an exhaust system of a vehicle comprising:

an inlet channel and an outlet channel separated by a porous wall, wherein a flow path from the inlet channel to the outlet channel passes through the porous wall; and a particulate matter regeneration catalyst for catalysing the regeneration of particulate matter retained by the filter in use; wherein the particulate matter regeneration catalyst is provided on a portion of a surface of the outlet channel and not on a surface of the inlet channel.

2. A particulate filter according to claim 1, comprising a plurality of outlet channels, wherein the particulate matter regeneration catalyst is provided on a portion of a surface of more than one of the outlet channels.

3. A particulate filter according to claim 1 or claim 2, comprising a plurality of inlet channels, wherein the particulate matter regeneration catalyst is not provided on a surface of any of the inlet channels.

4. A particulate filter according to any preceding claim, wherein the inlet channel is open at an inlet end of the particulate filter and closed at an outlet end of the particulate filter, and the or each outlet channel is closed at the inlet end of the particulate filter and open at the outlet end of the particulate filter.

5. A particulate filter according to any preceding claim, wherein the particulate matter regeneration catalyst is provided in the form of a coating.

6. A particulate filter according to claim 5, wherein the coating is in the form of a washcoat.

7. A particulate filter according to any preceding claim, wherein the particulate matter regeneration catalyst is provided over more than half the length of the surface of the or each outlet channel.

8. A particulate filter according to any preceding claim, wherein the particulate matter regeneration catalyst is provided over the entire length of the surface of the or each outlet channel.

9. A particulate filter according to any of claims 5 to 8, when dependent on claim

4, wherein there is a higher loading of the particulate matter regeneration catalyst at the outlet end compared to the inlet end.

10. A particulate filter according to any of claims 5 to 9, when dependent on claim 4, wherein there is a higher concentration of active ingredients in the particulate matter regeneration catalyst at the outlet end compared to the inlet end.

11. A method of manufacturing a particulate filter comprising:

providing an inlet channel and an outlet channel separated by a porous wall, wherein a flow path from the inlet channel to the outlet channel passes through the porous wall; and applying a particulate regeneration catalyst for catalysing the regeneration of particulate matter retained by the filter in use; wherein the particulate matter regeneration catalyst is applied to a portion of a surface of the outlet channel and not to a surface of the inlet channel.

12. A method according to claim 11, comprising providing a plurality of outlet channels, wherein the particulate matter regeneration catalyst is applied to a portion of a surface of more than one of the outlet channels.

13. A method according to claim 11 or claim 12, comprising providing a plurality of inlet channels, wherein the particulate matter regeneration catalyst is not applied to a surface of any of the inlet channels.

14. A method according to any one of claims 11 to 13, wherein the particulate matter regeneration catalyst is applied over more than half the length of the surface of the or each outlet channel.

15. A method according to any one of claims 11 to 14, wherein the particulate matter regeneration catalyst is applied over the entire length of the surface of the or each outlet channel.

16. A method according to any of claims 11 to 15, wherein the particulate regeneration catalyst is applied to the surface of the or each outlet channel in a washcoat.

17. A method of manufacture according to claim 16, wherein the washcoat is drawn through the or each outlet channel.

18. A method according to claim 17, wherein the washcoat is drawn by a vacuum through the or each outlet channel.

19. A method according to claim 17 or 18, wherein the inlet channel is open at an inlet end of the particulate filter and closed at an outlet end of the particulate filter, and the or each outlet channel is closed at the inlet end of the particulate filter and open at the outlet end of the particulate filter, and the washcoat is drawn from the outlet end towards the inlet end such that the particulate matter regeneration catalyst is applied to a portion of a surface of the or each outlet channel and not to a surface of the or each inlet channel.

20. A method according to claim 19, wherein a higher loading of the particulate matter regeneration catalyst is applied at the outlet end compared to the inlet end.

21. A method according to claim 20, wherein the higher loading of the particulate matter regeneration catalyst is provided by repeatedly drawing the washcoat from the outlet end towards the inlet end.

22. A method according to any of claims 19 to 21, wherein a higher concentration of active ingredients is provided in the particulate matter regeneration catalyst at the outlet end compared to the inlet end.

23. A particulate filter obtained or obtainable by a method of manufacture according to any one of claims 11 to 22.

24. An exhaust system for a vehicle, comprising a particulate filter according to any 5 one of claims 1 to 10.

25. A vehicle comprising a particulate filter according to any one of claims 1 to 10, or obtained by a method of manufacture according to any one of claims 11 to 22, or comprising an exhaust system according to claim 24.

26. A vehicle according to claim 25 which is a diesel engine-powered vehicle.