EXHAUST GAS TREATMENT APPARATUS

Abstract

A gasoline particulate filter for an exhaust system of a gasoline internal combustion engine includes a substrate and a catalytic coating disposed on the substrate. The catalytic coating has a carrier and at least one catalytically active ingredient. The catalytic coating has a carrier loading less than or equal to 0.5 g/in.sup.3 (0.03 g/cm.sup.3), and a catalytically active ingredient loading greater than or equal to 0.01 g/ft.sup.3 (0.35 g/m.sup.3) and less than 2 g/ft.sup.3 (70.63 g/m.sup.3).

Claims

1. A gasoline particulate filter for an exhaust system of a gasoline internal combustion engine, the gasoline particulate filter comprising: a substrate; and a catalytic coating disposed on said substrate, the catalytic coating comprising a carrier and at least one catalytically active ingredient; wherein the catalytic coating has a catalytically active ingredient loading greater than or equal to 0.01 g/ft.sup.3 (0.35 g/m.sup.3) and less than 2 g/ft.sup.3 (70.63 g/m.sup.3), and wherein the catalytic coating has a carrier loading less than or equal to 0.5 g/in.sup.3 (0.03 g/cm.sup.3).

2. The gasoline particulate filter as claimed in claim 1, wherein the catalytically active ingredient loading is less than or equal to 1 g/ft.sup.3 (0.35 g/m.sup.3).

3. The gasoline particulate filter as claimed in claim 1, wherein the catalytically active ingredient loading is greater than or equal to one or more of the following: 0.1 g/ft.sup.3 (3.53 g/m.sup.3), 0.25 g/ft.sup.3 (8.83 g/m.sup.3), 0.5 g/ft.sup.3 (17.66 g/m.sup.3), 0.75 g/ft.sup.3 (26.49 g/m.sup.3) and 1 g/ft.sup.3 (35.31 g/m.sup.3).

4. The gasoline particulate filter as claimed in claim 1, wherein the at least one catalytically active ingredient consists of one or more oxidation catalyst.

5. The gasoline particulate filter as claimed in claim 4, wherein the one or more oxidation catalyst comprises a platinum-group metal.

6. The gasoline particulate filter as claimed in claim 5, wherein the oxidation catalyst consists of Platinum and/or Palladium.

7. (canceled)

8. The gasoline particulate filter as claimed in claim 6, wherein the carrier loading is 0.2 g/in.sup.3 (0.01 g/cm.sup.3).

9. The gasoline particulate filter as claimed in claim 1, wherein the catalytic coating comprises a stabiliser and/or a promoter.

10. An exhaust system having an aftertreatment system comprising one or more gasoline particulate filter as claimed in claim 1.

11. A system comprising an internal combustion engine and the exhaust system as claimed in claim 10.

12. The system as claimed in claim 11, wherein the internal combustion engine is configured to operate at stoichiometric conditions.

13. The system as claimed in claim 11, wherein, in use, the gasoline particulate filter is regenerated during a fuel-cut event or an overrun event.

14. A vehicle comprising the gasoline particulate filter as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:

[0037] FIG. 1 shows a schematic representation of a vehicle incorporating an aftertreatment system in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

[0038] A vehicle 1 in accordance with an embodiment of the present invention is illustrated in FIG. 1. The vehicle 1 comprises an internal combustion engine 2 having an exhaust system 3 for conveying exhaust gas from the internal combustion engine 2. The vehicle 1 in the present embodiment is an automobile, but the present invention may usefully be implemented in other types of vehicle.

[0039] The internal combustion engine 2 is a gasoline engine which combusts gasoline in one or more combustion chamber (not shown). In the present embodiment, the internal combustion engine 2 is a gasoline light duty engine adapted to operate at stoichiometric conditions. Exhaust gases from the combustion cycle are expelled from the internal combustion engine 2 into the exhaust system 3 for treatment by aftertreatment systems (denoted by the reference numeral 4) comprising a gasoline particulate filter (GPF) 6. The GPF 6 collects carbonaceous particulate material from the exhaust gas. The carbonaceous particulate material may comprise or consist of soot. The GPF 6 is regenerated by oxidising the trapped carbonaceous particulate material. The oxidation process requires oxygen and a high temperature.

[0040] The vehicle 1 comprises an engine control unit 7 for controlling operation of the internal combustion engine 2. The engine control unit 7 comprises a processor 8 connected to a memory device 9. The processor 8 is configured to implement a set of non-transitory computational instructions stored on said memory device 9. When executed, the computational instructions cause the processor to implement an engine control strategy for controlling operation of the internal combustion engine 2. The processor 8 is configured to output a lambda control signal CON1 for controlling lambda () of the internal combustion engine 2. Lambda () is the ratio of the actual air/fuel ratio (AFR) to the stoichiometric air/fuel ratio (AFR.sub.stoich) and is defined by the following equation:

[00001]$=\frac{\mathrm{AFR}}{\mathrm{AFRstoich}}$

[0041] As outlined above, the internal combustion engine 2 is configured to operate at stoichiometric conditions, i.e. lambda () is at least substantially equal to one (1). The lambda control signal CON1 may increase or decrease lambda () of the internal combustion engine 2. By varying lambda (), the content of the exhaust gas expelled from the internal combustion engine 2 may be selectively controlled. In order to maintain efficient operation of the aftertreatment systems 4, the engine control unit 7 is configured to adjust lambda () to control the oxygen content of the exhaust gas introduced into the exhaust system 3.

[0042] The engine control unit 7 is configured to control fuelling of the internal combustion engine 2 to maintain stoichiometric operation (=1). There is typically a small amount of oxygen available in the exhaust gas which enables oxidation of carbonaceous particulate material trapped in the GPF 6, provided the temperature of the GPF 6 is high enough. It will be understood that carbon monoxide (CO) and/or unburned hydrocarbons (UHC) may also be oxidised in the GPF 6. However, if there is insufficient oxygen available and/or the temperature of the GPF 6 is not high enough, there may be a build-up of carbonaceous particulate material in the GPF 6 over time. In order to regenerate the GPF 6, the engine control unit 7 is configured to perform an active regeneration event to promote oxidation of the carbonaceous particulate material. The active regeneration event comprises controlling the internal combustion engine 2 to increase the temperature of the exhaust gas introduced into the exhaust system 3 such that the temperature of the GPS 6 is increased. The engine control unit 7 is configured also to increase lambda () of the internal combustion engine 2 resulting in the application of a lean bias. This results in an increase in the oxygen content of the exhaust gas which means that more oxygen is available for oxidation of the carbonaceous particulate material in the GPF 6.

[0043] The GPF 6 comprises a substrate, for example a ceramic or metal core. A catalytic coating is applied to the substrate. In accordance with an aspect of the present invention the catalytic coating comprises a carrier and at least one catalytically active ingredient. The catalytic coating is an oxidative coating and the at least one catalytically active ingredient consists of one or more oxidation catalyst. The one or more oxidation catalyst promote oxidation of the carbonaceous particulate material during lean operation of the internal combustion engine 2. In the present embodiment the catalytic coating does not include a reduction catalyst. The catalytic coating does not promote reduction during rich operation of the gasoline internal combustion engine. The GPF 6 is not provided with a reductive coating or equivalent. Thus, the catalytic coating applied to the substrate does not function as a three-way catalyst (TWC).

[0044] The carrier is in the form of a washcoat for dispersing the oxidation catalyst over a large surface area of the substrate. The washcoat may, for example, comprise aluminium oxide, titanium dioxide, silicon dioxide, or a mixture of silica and alumina. The one or more oxidation catalyst may comprise a precious metal, for example a platinum-group metal (PGM). The platinum-group metals comprise Ruthenium (Ru), Rhodium (Rd), Palladium (Pd), Osmium (Os), Iridium (Ir), and Platinum (Pt). The oxidation catalyst in the present embodiment comprises or consists of Platinum (Pt) and/or Palladium (Pd). In alternative embodiments the oxidation catalyst may comprise or consist of Gold (Au) and/or Silver (Ag). The one or more oxidation catalyst promotes oxidation of the trapped carbonaceous particulate material. At least in certain embodiments the catalytic coating may enable oxidation of the trapped carbonaceous particulate material at a temperature of approximately 600 C. An equivalent GPF 6 without an oxidation catalyst would have to be heated to a temperature in the range 630 C. to 650 C. in order to perform oxidation at an equivalent rate. It will be understood, therefore, that the catalytic coating enables regeneration of the GPF 6 at a lower temperature. By lowering the temperature at which the carbonaceous particulate material is oxidised, there are increased opportunities to regenerate the GPF 6. The accumulation of carbonaceous particulate material in the GPF 6 may be partially or completely reduced over a wider range of duty cycles, thereby reducing the requirement/frequency of active regeneration events may also be reduced. Moreover, at least in certain embodiments, the active regeneration event may be performed more efficiently due to the lower temperature required for effective oxidation of carbonaceous particulate material in the GPF 6.

[0045] The catalytic coating applied to the GPF 6 in accordance with the present embodiment has a low loading. The carrier loading is low and/or the catalytically active ingredient loading is low. The carrier loading is less than or equal to 0.5 g/in.sup.3. More particularly, the carrier loading in the present embodiment is approximately 0.2 g/in.sup.3. The catalytically active ingredient loading is in the range 0.1 g/ft.sup.3 to 5 g/ft.sup.3, inclusive. More particularly, the catalytically active ingredient loading in the present embodiment is in the range 1 g/ft.sup.3 to 2 g/ft.sup.3, inclusive. By reducing the carrier loading and/or the catalytically active ingredient loading, any increase in backpressure in the exhaust system 3 may be reduced or minimised.

[0046] The engine control unit 7 is configured to control the internal combustion engine 2 during an active regeneration event to raise the temperature of the GPF 6 to approximately 600 C. The provision of the one or more oxidation catalyst helps to ensure that this temperature is sufficient for regeneration of the GPF 6 since the carbonaceous particulate material is oxidised.

[0047] It will be appreciated that various changes and modifications may be made to the engine control unit 7 described herein without departing from the scope of the present invention. The present invention has been described with particular reference to a gasoline light duty engine 2 adapted to operate at stoichiometric conditions. It will be understood that the present invention can be used in conjunction with spark-ignition internal combustion engines 2 which combust fuels other than gasoline under stoichiometric conditions. For example, the internal combustion engine 2 could be adapted to use compressed natural gas (CNG), alcohol or liquefied petroleum gas (LPG) as a fuel source.