US20080053070A1

US20080053070A1 - Apparatus and method for regenerating a particulate filter with a non-uniformly loaded oxidation catalyst

Info

Publication number: US20080053070A1
Application number: US11/469,674
Authority: US
Inventors: Andrew Hatton
Original assignee: Individual
Current assignee: Faurecia Emissions Control Technologies USA LLC
Priority date: 2006-09-01
Filing date: 2006-09-01
Publication date: 2008-03-06
Also published as: WO2008028061A3; WO2008028061A2

Abstract

An apparatus for removing particulate soot from an exhaust gas of an internal combustion engine includes a catalyst and a soot particulate filter positioned downstream of the catalyst for trapping soot particles therein. Atomized fuel is injected into the catalyst. The catalyst has a non-uniform catalytic loading such that the catalyst has an upstream region having a catalytic loading of a first concentration and a downstream region having a catalytic loading of a second concentration. The first concentration is greater than the first. The catalyst catalyzes an exothermic oxidation reaction between the hydrocarbon fuel and oxygen in the exhaust gas. Heat from this exothermic oxidation reaction is transferred to the soot particulate filter thereby igniting the soot particles trapped therein. A method for regenerating a particulate filter assembly having with a catalyst having a non-uniform catalytic coating is also disclosed.

Description

FIELD OF THE DISCLOSURE

The present disclosure relates generally to an emission abatement device, and more particularly to an emission abatement device using an oxidation catalyst having a non-uniformly distributed catalytic material.

BACKGROUND

Untreated internal combustion engine emissions include various effluents such as NO_X(oxides of nitrogen), hydrocarbons, and carbon monoxide, for example. Moreover, the untreated emissions from certain types of internal combustion engines, such as diesel engines, also include particulate carbon-based soot. Federal regulations relating to soot emission standards are becoming more and more rigid thereby furthering the need for devices and/or methods which remove soot from engine emissions. For example, the amount of soot produced and/or released by an engine system can be reduced by fuel injection rate shaping and/or by the use of an emission abatement device such as a filter or trap. Such a filter or trap is periodically regenerated in order to remove the soot therefrom. The filter or trap may be regenerated by use of a burner or electric heater to burn the soot off of the filter. An oxidation catalyst may serve as a burner when fuel is introduced therein, allowing an exothermic reaction to take place providing the heat necessary for regeneration.

SUMMARY

According to the present disclosure, an emission abatement device is provided for removing particulate soot from an exhaust gas of an internal combustion engine. The device includes a particulate filter assembly having a catalyst and a soot particulate filter positioned downstream of the catalyst for trapping soot particles therein. The catalyst includes a non-uniformly distributed catalytic material disposed thereon. Fuel is injected at a location upstream of the catalyst. The catalyst catalyzes an exothermic reaction between the fuel and a gas containing oxygen. Heat from this exothermic reaction is transferred to the soot particulate filter thereby igniting the soot particles trapped therein.
In one exemplary embodiment, the catalyst includes a substrate. The substrate has an upstream region having a first concentration of catalytic material disposed thereon. The substrate also has a downstream region having a second concentration of catalytic material disposed thereon. In this exemplary embodiment, the first concentration is greater than the second concentration.
Further according to the present disclosure, a method for regenerating a particulate filter is provided. The method includes injecting fuel into a catalyst having a non-uniformly distributed catalyst disposed thereon. The fuel is injected onto a first region of the oxidation catalyst having a catalytic material loading of a first concentration. A first portion of the injected fuel is oxidized by the first region. A second portion of the fuel is oxidized by a second region of the oxidation catalyst having a second catalytic loading concentration less than the first concentration. Heat generated during the oxidation steps is transferred to a particulate filter positioned downstream from the oxidation catalyst to regenerate the particulate filter.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the accompanying figures in which:

FIG. 1 is a diagrammatic cross sectional view of a emission abatement device; and

FIG. 2 is a diagrammatic cross sectional view of an oxidation catalyst.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to FIG. 1, there is shown an exemplary embodiment of an emission abatement device 10 for removing soot particles from the exhaust gases of an internal combustion engine. In this exemplary embodiment, the emission abatement device 10 is configured for use with a diesel engine (not shown).
The emission abatement device 10 includes an oxidation catalyst 14 and a soot particulate filter 12, which are housed in an interior chamber 18 of a housing 16. The soot particulate filter 12 is configured to filter soot produced during engine combustion. The oxidation catalyst 14 assists in burning off the soot trapped in the soot particulate filter. In particular, the emission abatement device 10 is disposed in the exhaust path of a diesel engine as illustrated in FIG. 1. The housing 16 has a first end 19 coupled to an exhaust pipe 22, and a second end 21 coupled to either another exhaust pipe 23 that is open to the atmosphere or coupled to an additional exhaust system component (not shown) positioned downstream of the emission abatement device 10. The first end 19 defines an exhaust gas inlet 20, whereas the second end of the housing 16 defines an exhaust gas outlet 28. Hence, exhaust gases 24 from the diesel engine enter the housing 16 through the exhaust gas inlet 20, are advanced through the oxidation catalyst 14 and the soot particulate filter 12, and then are exhausted from the housing 16 via the exhaust gas outlet 28. As the untreated exhaust gases 24 flow through the soot particulate filter 12, the soot is trapped therein allowing the filtered exhaust gases 26 to flow out of the housing 16 through exhaust gas outlet 28.
The oxidation catalyst 14 is positioned upstream of the soot particulate filter 12. The oxidation catalyst 14 may be spaced apart from the soot particulate filter 12 by a predetermined distance, may be positioned in contact with the soot particulate filter 12, or may even be fabricated as a common structure with the soot particulate filter 12 (e.g., a common structure having a catalyst portion positioned upstream of a filter portion). The soot particulate filter 12 traps soot or other particulates present in the untreated exhaust gases 24 from the diesel engine. The soot particulate filter 12 may be embodied as any known exhaust particulate filter such as a “deep bed” or “wall flow” filter. Deep bed filters may be embodied as metallic mesh filters, metallic or ceramic foam filters, ceramic fiber mesh filters, and the like. Wall flow filters, on the other hand, may be embodied as a cordierite or silicon carbide ceramic filter with alternating channels plugged at the front and rear of the filter thereby forcing the gas advancing therethrough into one channel, through the walls, and out another channel.
The oxidation catalyst 14 is configured to catalyze an oxidation reaction between a gaseous component containing oxygen and hydrocarbon fuel, such as diesel fuel. Specifically, when hydrocarbon fuel is advanced into contact with the oxidation catalyst 14 in the presence of a gaseous component containing oxygen, the oxidation catalyst 14 catalyzes an oxidation reaction, which converts the hydrocarbon fuel and a portion of the oxygen into, amongst other things, water.
This oxidation reaction is highly exothermic, and, as a result, produces heat that is transferred to the downstream-positioned soot particulate filter 12. The heat, which may illustratively be in the range of 600-650 degrees Celsius, raises the temperature of the soot particles trapped in the soot particulate filter 12 to a temperature sufficient to ignite the particles thereby regenerating the soot particulate filter 12. It should be appreciated that such regeneration of the soot particulate filter 12 may be self-sustaining once initiated by heat from the exothermic reaction catalyzed by the oxidation catalyst 14. Specifically, once the soot particulate filter 12 is heated to a temperature at which the soot particles trapped therein begin to ignite, the ignition of an initial portion of soot particles trapped therein can cause the ignition of the remaining soot particles much in the same way a cigar slowly burns from one end to the other. In essence, as the soot particles “burn,” an amount of heat is released in the “burn zone.” Locally, the soot layer (in the burn zone) is now much hotter than the immediate surroundings. As such, heat is transferred to the as yet un-ignited soot layer downstream of the burn zone. The energy transferred may be sufficient to initiate oxidation reactions that raise the un-ignited soot to a temperature above its ignition temperature. As a result of this, heat from the oxidation catalyst 14 may only be required to commence the regeneration process of the soot particulate filter 12 (i.e., begin the ignition process of the soot particles trapped therein).
In this illustrative embodiment a fuel line 30 supplies hydrocarbon fuel from a source such as a fluidly-coupled diesel fuel tank (not shown) to oxidation catalyst 14 allowing for heat to regenerate the soot particulate filter 12 to be produced. It should be appreciated that a control system can be configured to control when the fuel is supplied through fuel line 30 to the emission abatement device 10. Fuel line 30 is disposed through inlet 31 to supply fuel within the exhaust path. The inlet may be configured as an orifice that is defined in the walls of the housing 16, or, alternatively, may include a tube, coupling assembly, or other structure which extends through the wall of the housing 16. A fuel injector can inject the fuel into the housing allowing the fuel to reach the oxidation catalyst 14 to produce the exothermic reaction. In this exemplary embodiment, the fuel is injected using a fuel atomizer 36, which atomizes the atomized fuel 38 to enhance the exothermic reaction when reaching oxidation catalyst 14. Such atomizing fuel injector assemblies are commercially available.
Oxidation catalyst 14 includes a substrate having a precious metal or other type of catalytic material disposed thereon. Such a substrate may be constructed of ceramic, metal, or other suitable material. The catalytic material may be, for example, embodied as platinum, palladium, rhodium, including combinations thereof, along with any other similar catalytic materials.
The oxidation catalyst 14 in this exemplary embodiment includes an upstream portion 32 and a downstream portion 34. The upstream portion 32 contains a catalytic material loading of a concentration greater than that of the downstream portion 34. The different concentrations of the upstream portion 32 and the downstream portion 34 is represented in FIG. 1 by the line densities shown in the illustration of oxidation catalyst 14.
When hydrocarbon fuel enters an oxidation catalyst, most of the oxidation reaction typically occurs in the upstream portion of an oxidation catalyst with respect to the longitudinal length the oxidation catalyst 34. Using an oxidation catalyst having a catalytic material loading of greater concentration in the upstream portion enhances the efficiency of the oxidation reaction. A lower concentration can be used in the downstream region because less of the reaction is expected to take place in that region.
It should be appreciated that in addition to the aforedescribed use of the oxidation catalyst 14 to regenerate the soot particulate filter 12, the oxidation catalyst 14 may also function as an oxidation catalyst for removing certain compounds from the exhaust gases of the engine. In particular, the oxidation catalyst 14 may be configured to catalyze, in the presence of heat supplied by the exhaust gasses (e.g., 250 degrees Celsius), an oxidation reaction which converts, for example, hydrocarbons (HC) and carbon monoxide (CO) into water vapor, carbon dioxide, and other less toxic gases. Hence, the emission abatement device 10 may be used to not only remove soot from the engine's exhaust gases, but also other compounds as well (e.g., HC, CO).
As described above, the oxidation catalyst 14 catalyzes an exothermic reaction between a gaseous component containing oxygen and hydrogen. Generally, exhaust gases from an internal combustion engine may function as the source of oxygen. In particular, suitable amounts of oxygen for sustaining such an oxidation reaction exist in the exhaust gases of an internal combustion engine without the introduction of additional oxygen. However, to fit the needs of a given design or implementation, supplemental oxygen may be introduced into the engine's exhaust gases prior to advancement thereof into the emission abatement device 10. One way to do this is by use of an air inlet (not shown) positioned upstream of the oxidation catalyst 14 for introducing a desired amount of air into the engine's exhaust gases prior to advancement thereof into contact with the oxidation catalyst 14.
It should be appreciated that while the specific exemplary embodiment described in regard FIG. 1 has significant advantages, this embodiment is merely descriptive in nature, and should not be construed as limiting to the claims in any way absent specific language in the claims to the contrary.
Referring now to FIG. 2, an oxidation catalyst 40 having varying catalytic material loading throughout is shown. This representation illustrates a first region 42 of oxidation catalyst 40 having a first catalytic material loading and a second region 44 having a second catalytic material loading. The concentration of the loading of the first region 42 is greater than that of the second region 44 in this exemplary embodiment providing a “step” change in concentration from the first region 42 to the second region 44.
The oxidation catalyst 40 has a longitudinal length 46 and the first region 42 of oxidation catalyst occupies a portion 48 along the longitudinal length 46. In this exemplary embodiment, the portion 48 is approximately 15% of the longitudinal length 46. It should be appreciated that the dimension of portion 48 can be selected according to the needs of a particular emission abatement device being implemented.
Various concentrations of catalytic material can be used to be disposed on the first region 42 and the second region 44 of oxidation catalyst 40. In the exemplary embodiment of FIG. 2, platinum can be used as the catalytic material disposed on oxidation catalyst 40. The first region 42 can have a platinum concentration of 75 g/ft³and the second region can have a platinum concentration of 10 g/ft³. The oxidation catalyst 40 can be prepared by dipping the first region 42 into a mixture to coat the oxidation catalyst 40 with platinum in the desired concentration. The oxidation catalyst 40 is dipped until the desired portion 48 is reached. The second region 44 can be dipped into a mixture to apply the desired catalytic material concentration.
In another exemplary embodiment, the oxidation catalyst 40 can be used in an emission abatement device, such as emission abatement device 10 shown in FIG. 1. In this exemplary embodiment, the oxidation catalyst is cylindrically shaped having a longitudinal length 46 of approximately 12 inches. The cross-section dimension of the oxidation catalyst 40 in this exemplary embodiment is approximately 10.5 inches. The first region 42 includes approximately 15% of the longitudinal length 46, or 1.8 inches. It is to be appreciated that the first region 42 may include more or less of the longitudinal length than that disclosed in this exemplary embodiment. Also, the concentrations of the catalytic material loading of the first region 42 and second region 44 can be varied from the 75 g/ft³and 10 g/ft³, respectively, disclosed above.
There are a plurality of advantages of the present disclosure arising from the various features of the apparatus and methods described herein. It will be noted that alternative embodiments of the apparatus and methods of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations of an apparatus and method that incorporate one or more of the features of the present disclosure and fall within the spirit and scope of the present disclosure.

Claims

1. An emission abatement device comprising:

a particulate filter,

an oxidation catalyst positioned upstream from the particulate filter, the oxidation catalyst comprising a substrate including (i) an upstream region having a catalytic material loading of a first concentration, and (ii) a downstream region having a catalytic material loading of a second concentration that is less than the first concentration, and

a fuel injector configured to inject fuel into the upstream region of the oxidation catalyst.

2. The emission abatement device of claim 1, wherein the fuel injector is a fuel atomizer configured to inject atomized fuel into the upstream region of the substrate.

3. The emission abatement device of claim 1, wherein the substrate has a longitudinal length, and the upstream region of the substrate is less than 50% of the longitudinal length.

4. The emission abatement device of claim 3, wherein the upstream portion of the substrate is less than 25% of the longitudinal length.

5. The emission abatement device of claim 4, wherein the upstream portion of the substrate is less than 10% of the longitudinal length.

6. The emission abatement device of claim 1, wherein the substrate is impregnated with a precious metal.

7. The emission abatement device of claim 6, wherein the precious metal is platinum.

8. The emission abatement device of claim 6, wherein the precious metal is palladium.

9. An oxidation catalyst for oxidizing atomized fuel in the exhaust path of an internal combustion engine, the oxidation catalyst comprising:

a substrate including (i) a first region having a catalytic material loading of a first concentration, and (ii) a second region having a catalytic material loading of a second concentration that is less than the first concentration.

10. The oxidation catalyst of claim 1, wherein the substrate has a longitudinal length, and the first region of the substrate is less than 50% of the longitudinal length.

11. The oxidation catalyst of claim 10, wherein the first portion of the substrate is less than 25% of the longitudinal length.

12. The oxidation catalyst of claim 11, wherein the first portion of the substrate is less than 10% of the longitudinal length.

13. The emission abatement device of claim 9, wherein the substrate is impregnated with a precious metal.

14. The emission abatement device of claim 13, wherein the precious metal is platinum.

15. The emission abatement device of claim 13, wherein the precious metal is palladium.

16. A method of regenerating a particulate filter comprising the steps of:

injecting fuel into a first region of an oxidation catalyst, the first region having a catalytic material loading of a first concentration,

oxidizing a first portion of the injected fuel in the first region of the oxidation catalyst,

oxidizing a second portion of the injected fuel in a second region of the oxidation catalyst, the second region having a catalytic material loading of a second concentration that is less that the first concentration, and

transferring heat generated during the oxidation steps to a particulate filter positioned downstream from the oxidation catalyst to regenerate the particulate filter.