US20140208724A1

US20140208724A1 - Aftertreatment system

Info

Publication number: US20140208724A1
Application number: US14/228,674
Authority: US
Inventors: Andrew M. Denis; James D. Peltier; Kevin J. Weiss
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2014-03-28
Filing date: 2014-03-28
Publication date: 2014-07-31

Abstract

An aftertreatment system of an engine is disclosed. The aftertreatment system includes a housing. The aftertreatment system also includes a Selective Catalytic Reduction (SCR) catalyst provided within the housing. The aftertreatment system further includes an exhaust duct associated with the SCR catalyst. The aftertreatment system includes a sampling flute provided within the exhaust duct. The aftertreatment system also includes a NOx sensor at least partly enclosed by a first end of the sampling flute. The aftertreatment system further includes a spring member. The spring member is joined to the sampling flute and the exhaust duct.

Description

TECHNICAL FIELD

The present disclosure relates to an aftertreatment system, and more specifically to a mounting arrangement for a sampling flute of the aftertreatment system.

BACKGROUND

Engines generate exhaust gas as a byproduct of combustion. The exhaust gas includes nitrogen oxides (NOx) among other components. An aftertreatment system is used to treat an exhaust gas flow. Some aftertreatment systems may include a Selective Catalytic Reduction (SCR) catalyst. Typically in such systems, a reductant is injected into the exhaust gas flow upstream of the SCR catalyst. Thereafter, the NOx is reduced to diatomic nitrogen (N₂) and water with the help of the SCR catalyst.
One or more nitrogen oxide sensors (NOx sensor) may be positioned at various locations in an engine system in order to measure a concentration of nitrogen oxides in the exhaust gas flow. For example, the NOx sensors may be present upstream and/or downstream of the SCR catalyst with respect to a direction of the exhaust gas flow. The NOx sensors located upstream and downstream of the SCR catalyst may be provided within respective ducts. A reading provided by each of the NOx sensors is based on a portion of the exhaust gas flowing thereover. However, in some situations, each of the NOx sensors may contact with a relatively small portion of the exhaust gas flow due to its position within the duct of the exhaust system. Known designs include providing a sampling flute within the duct in order to direct a portion of the exhaust gas flow over the NOx sensor.
In such known designs, the sampling flute is attached to the duct. The duct typically has a large diameter compared to the sampling flute. Therefore, heat capacities of the duct and the sampling flute are different due to the differences in thermal mass. Also contributing to potentially differential thermal characteristics, the material of the sampling flute may also differ from a material of the duct. Both the duct and the sampling flute get heated and undergo thermal expansion due to exposure to heated exhaust gas. However, a differential thermal expansion may be caused by different temperatures of the sampling flute and the duct due to different heat transfer rates to the sampling flute and the duct, and/or the different heat capacities. This may lead to a high thermal stress in a joint between the sampling flute and the duct.

SUMMARY OF THE DISCLOSURE

In one aspect of the present disclosure, an aftertreatment system of an engine is disclosed. The aftertreatment system includes a housing configured to receive an exhaust gas flow from the engine. The aftertreatment system also includes a Selective Catalytic Reduction (SCR) catalyst provided within the housing. The aftertreatment system further includes an exhaust duct associated with the SCR catalyst. The exhaust duct is configured to discharge the exhaust gas flow out of the housing. The aftertreatment system includes a sampling flute provided within the exhaust duct. The sampling flute includes a plurality of holes configured to allow passage of the exhaust gas flow therethrough. Further, a first end of the sampling flute is coupled to the exhaust duct. The aftertreatment system also includes a NOx sensor at least partly enclosed by the first end of the sampling flute. The aftertreatment system further includes a spring member. The spring member is joined to the sampling flute and the exhaust duct.
Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary aftertreatment system of an engine, according to an embodiment of the present disclosure;

FIG. 2 is a sectional view of an exhaust duct, according to an embodiment of the present disclosure;

FIG. 3 is a partial perspective view of the exhaust duct, according to an embodiment of the present disclosure;

FIG. 4 is a perspective view of a spring member, according to an embodiment of the present disclosure;

FIG. 5A is a rear view of the spring member within the exhaust duct, according to another embodiment of the present disclosure;

FIG. 5B is a top view of the spring member within the exhaust duct, according to the embodiment of FIG. 5A;

FIG. 6A is a perspective view of the spring member within the exhaust duct, according to yet another embodiment of the present disclosure;

FIG. 6B is a top view of the spring member within the exhaust duct, according to the embodiment of FIG. 6A; and

FIG. 7 is a perspective view of the spring member within the exhaust duct, according to a further embodiment of the present disclosure.

DETAILED DESCRIPTION

Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or the like parts. Referring to FIG. 1, an aftertreatment system 100 of an engine (not shown) is illustrated. The aftertreatment system 100 includes a housing 102 in the accompanying figures. A Selective Catalytic Reduction (SCR) catalyst (not shown) is provided within the housing 102. The SCR catalyst may include one or more catalyst modules. The aftertreatment system 100 includes a reductant injector (not shown) configured to introduce a reductant into an exhaust gas flow of the engine. The exhaust gas flow may contain one or more constituents, such as, carbon monoxide (CO), sulfur dioxide (SO2), nitrogen oxides (NOx) and other similar compositions in a gaseous state. In one embodiment, the aftertreatment system 100 may introduce the reductant to reduce and/or convert an amount of NOx present in the exhaust gas flow into other compounds using one or more chemical reactions and/or processes. The reductant and/or decomposition byproducts thereof may react with NOx present in the exhaust gas flow, in the presence of the SCR catalyst, to form water (H₂O) and diatomic nitrogen (N₂).
The aftertreatment system 100 may include a number of components therein. An inlet duct (not shown) of the aftertreatment system 100 may be fluidly coupled to an exhaust manifold (not shown) of the engine. The inlet duct may be configured to receive the exhaust gas flow from the engine. Further, the housing 102 may be configured to receive the exhaust gas flow from the inlet duct of the aftertreatment system 100.
The aftertreatment system 100 further includes an exhaust duct 104 in fluid communication with an outlet of the SCR catalyst. In an embodiment, an Ammonia Oxidation (AMOX) catalyst (not shown) may be provided between the exhaust duct 104 and the outlet of the SCR catalyst. The exhaust duct 104 is provided downstream of the SCR catalyst and is configured to discharge the exhaust flow out of the housing 102 via an outlet 106. In one embodiment, the exhaust duct 104 may be fluidly coupled to an exhaust stack (not shown). The exhaust stack may be open to atmosphere. In another embodiment, the exhaust duct 104 may be further fluidly coupled to another module (not shown) of the aftertreatment system 100. The exhaust duct 104 illustrated in the accompanying figures has a hollow cylindrical configuration defining a longitudinal axis X-X′. The exhaust duct 104, as shown in FIG. 1 is exemplary in nature, and the exhaust duct 104 may have any other configuration, such as, a rectangular configuration, an elliptical configuration and other similar configurations.
The exhaust duct 104 may include a NOx sensor 108 disposed therein. In the illustrated embodiment, the NOx sensor 108 is located on a surface of the exhaust duct 104 to extend substantially perpendicularly thereto. However, alternative exemplary embodiments include configurations wherein the NOx sensor 108 may be disposed in a manner such that the NOx sensor 108 protrudes into the exhaust duct 104 at an angle relative to the longitudinal axis X-X′. In such various alternative embodiments, the angle between the NOx sensor 108 and the longitudinal axis X-X′ may be up to about 10 degrees. The NOx sensor 108 may be affixed to the exhaust duct 104 by any fastening method known in the art including, but not limited to, bolting, welding, adhesion, and the like. The NOx sensor 108 may be configured to measure a concentration of NOx in the exhaust gas flow. Further, the NOx sensor 108 may be connected to an engine control module (not shown) via one or more electrical connections (not shown).
The exhaust duct 104 further includes a sampling flute 110 provided in cooperation with the NOx sensor 108. In the illustrated embodiment, the sampling flute 110 is disposed within the exhaust duct 104 substantially perpendicular to the longitudinal axis X-X′ of the exhaust duct 104. Alternative exemplary embodiments include configurations wherein the sampling flute 110 may be inclined at an angle relative to the longitudinal axis X-X′. The sampling flute 110 may extend across at least a portion of a width of the exhaust duct 104. In the illustrated embodiment, the sampling flute 110 is provided extending diametrically within the exhaust duct 104. The sampling flute 110 may be configured to sample the exhaust gas flow by channeling a portion of the exhaust gas flow towards the NOx sensor 108. The sampling flute 110 may also be configured for increasing fills per measurement of the sampled exhaust gas flow. The fills per measurement may refer to a volume of the exhaust gas flow which is in contact with the NOx sensor 108 for providing a value indicative of the NOx concentration. Therefore, any increase in the fills per measurement may be regarded as an increase in the amount of exhaust gas flow sampled by the NOx sensor 108. Additionally, the sampling flute 110 may also homogenize the exhaust gas flowing towards the NOx sensor 108. Further, another set of the NOx sensor 108 and the sampling flute 110, as described above, may be provided upstream of the of the SCR catalyst. This set of the NOx sensor 108 and the sampling flute 110 may measure a concentration of NOx present in the exhaust gas flow before being treated by the SCR catalyst.
FIG. 2 shows a sectional view of the exhaust duct 104, according to an embodiment of the present disclosure. Various components of the aftertreatment system 100, as shown in FIG. 1, have been removed for clarity. As shown in FIG. 2, the sampling flute 110 has a first end 202, and a second end 204 distal to the first end 202. The sampling flute 110 further has an elongated, hollow, cylindrical configuration defining a conduit 206. In alternative embodiments, the sampling flute 110 may have a non-circular cross-section, for example, polygonal, elliptical, and the like, without deviating from the scope of the present disclosure. The sampling flute 110 includes multiple holes 208 opening into the conduit 206. The holes 208 may be provided collinearly between the first and second ends 202, 204 of the sampling flute 110 in a spaced apart arrangement with respect to each other. The holes 208 are configured to receive a portion of the exhaust gas flow, indicated by arrows ‘A’, into the conduit 206. The exhaust gas flow may therefore enter the exhaust duct 104 in a direction substantially parallel to the longitudinal axis X-X′. A portion of the exhaust gas flow then enters the conduit 206 through the holes 208. The exhaust gas flow inside the conduit 206 may be substantially perpendicular to the longitudinal axis X-X′. In one embodiment, the plurality of holes 208 may have a generally similar shape and size. Alternatively, the plurality of holes 208 may vary in shape and dimension. It will be apparent to one of ordinary skill in the art that the shape, number and dimensions of each of the plurality of holes 208 provided on the sampling flute 110 may vary as per system design and requirements.
Further, as shown in FIG. 2, the first end 202 of the sampling flute 110 is coupled to an inner surface of the exhaust duct 104. In various embodiments, the first end 202 of the sampling flute 110 may be attached to the exhaust duct 104 by, for example, but not limited to, welding, brazing, fasteners, and the like. The first end 202 of the sampling flute 110 also at least partly encloses the NOx sensor 108. In an embodiment, as shown in FIG. 2, the NOx sensor 108 is shown to be completely enclosed by the first end 202 of the sampling flute 110. The sampling flute 110 also includes an exhaust outlet 210 provided in cooperation with the NOx sensor 108. In the illustrated embodiment, the exhaust outlet 210 is provided on the first end 202 of the sampling flute 110. Further, the exhaust outlet 210 may be provided diametrically opposite to the holes 208. The exhaust outlet 210 is configured to allow the exhaust gas flow in the conduit 206 to exit out of the sampling flute 110 after contacting the NOx sensor 108. The location of the NOx sensor 108 relative to the first end 202 of the sampling flute 110 is purely exemplary in nature and various alternative configurations are possible without deviating from the scope of the present disclosure. For example, the NOx sensor 108 may extend partly (not shown) from the exhaust outlet 210.
FIG. 2 also shows a magnified view of the second end 204 of the sampling flute 110 for clarity. The second end 204 of the sampling flute 110 is attached to a spring member 212. The spring member 212 includes a first portion 214, a second portion 216 and a third portion 218. The second end 204 of the sampling flute 110 is attached to the first portion 214. The second portion 216 extends from the first portion 214 and is inclined at an angle 220 to the first portion 214. In various embodiments, the angle 220 may vary between 0 and 90 degrees. Moreover, the third portion 218 extends from the second portion 216. The third portion 218 is attached to the inner surface of the exhaust duct 104. Further, the third portion 218 may be substantially parallel to the first portion 214. In the illustrated embodiment, the spring member 212 extends in a direction substantially opposite to the outlet 106 of the exhaust duct 104. Further, the spring member 212 may also be disposed substantially parallel to the longitudinal axis X-X′. However, in an alternative embodiment (not shown), the spring member 212 may extend towards the outlet 106. In a further embodiment (not shown), the spring member 212 may be oriented obliquely relative to the longitudinal axis X-X′.
FIG. 3 shows a detailed partial perspective view of the exhaust duct 104, according to an embodiment of the present disclosure. As shown in FIG. 3, the second end 204 of the sampling flute 110 is received within an aperture 302 of the first portion 214 of the spring member 212. In various embodiments, a diametrical gap (not shown) between an outer surface of the sampling flute 110 and an inner surface of the aperture 302 may lie in a range from about 0.5 mm to about 2.7 mm. In an alternative embodiment (not shown), the second end 204 of the sampling flute 110 may be joined to the first portion 214 of the spring member 212 by a butt weld. In such a case, the aperture 302 may not be present in the first portion 214. Further, the second end 204 of the sampling flute 110 is joined to the first portion 214 by a weld 304. Moreover, the third portion 218 of the spring member 212 is joined to the inner surface of the exhaust duct 104 by welds 306. In various embodiments, each of the welds 304, 306 may have a thickness of about 2 mm. The spring member 212 may be joined to the sampling flute 110 and the exhaust duct 104 by various welding processes known in the art, for example, but not limited to, arc welding, gas welding, resistance welding, laser welding, and the like.
FIG. 4 illustrates a perspective view of the spring member 212, according to an embodiment of the present disclosure. As shown in FIG. 4, the first, second and third portions 214, 216 and 218 have substantially planar shapes. Further, the first, second and third portions 214, 216, 218 have lengths 402, 404, and 406, respectively. In various embodiments, a sum of the lengths 402, 404 and 406 may lie in a range from about 60 mm to about 180 mm. The length 402 of the first portion 214 may be greater than the length 406 of the third portion 218. Moreover, the length 406 of the third portion 218 may be greater than the length 404 of the second portion 216. A thickness 408 of the spring member 212 may lie in a range from about 0.95 mm to about 2.78 mm. A width 410 of the spring member 212 may lie in a range from about 45 mm to about 90 mm. A diameter 412 of the aperture 302 may vary according to an outer diameter of the sampling flute 110 (shown in FIGS. 1-3) and a diametrical gap between the inner surface of the aperture 302 and the outer surface of the sampling flute 110. In alternative embodiments (not shown), the sampling flute 110 and/or the aperture 302 may have a cross-section other than circular, for example, polygonal, elliptical, and the like. Also, alternative embodiments include configurations wherein the aperture 302 may be omitted entirely and the sampling flute 110 may have the second end 204 thereof directly welded to the first portion 214.
The various dimensions, as expressed above, are purely exemplary in nature, and the dimensions the spring member 212 may vary as per system design and requirements. The material of the spring member 212 may also vary according to design. The spring member 212 be made of any metal or metal alloy, for example, but not limited to, spring steel, aluminum/aluminum alloy, and the like. The shape of the spring member 212 may also vary. For example, the third portion 218 may be inclined obliquely relative to the first portion 214. One or more of the first, second and third portions 214, 216 and 218 may have a curvilinear shape. Moreover, a width and/or thickness of each of the first, second and third portions 214, 216, 218 may vary. Further, in alternative embodiments (not shown), the spring member 212 have an overall planar or curvilinear shape without any inclined portion.
FIGS. 5A and 5B illustrate rear and top views, respectively, of the spring member 502 within the exhaust duct 104, according to another embodiment of the present disclosure. The spring member 502 includes a first portion 504 and a second portion 506. The first portion 504 and the second portion 506 are oriented substantially perpendicular to one another. Further, the first portion 504 includes an aperture 508. The first portion 504 and the second portion 506 may be substantially rectangular. Moreover, a width 510 of the first portion 504 may be lower than a width 512 of the second portion 506. In various embodiments, the first portion 504 and the second portion 506 may be attached to one another by welding, adhesives, and the like. The first portion 504 may be provided substantially parallel to the longitudinal axis X-X′ of the exhaust duct 104. Further, the second portion 506 may be provided substantially perpendicular to the longitudinal axis X-X′ of the exhaust duct 104. The aperture 508 of the first portion 504 receives the second end 204 of the sampling flute 110. Further, the first portion 504 may be joined to the second end 204 by a weld 514. Two ends of the second portion 506 may be joined to the exhaust duct 104 by welds 516.
FIGS. 6A and 6B illustrate perspective and top views, respectively, of the spring member 602 within the exhaust duct 104, according to yet another embodiment of the present disclosure. The spring member 602 has a substantially trapezoidal shape with a wide end 604 and a narrow end 606. The spring member 602 further includes an aperture 608 proximate the narrow end 606. The aperture 608 receives the second end 204 of the sampling flute 110. Further, the second end 204 of the sampling flute 110 is joined to the spring member 602 by a weld 610. The wide end 604 is joined to the exhaust duct 104 by welds 612. In an embodiment, the spring member 602 may be inclined relative to the longitudinal axis X-X′ of the exhaust duct 104 such that the wide end 604 is positioned at a lower height relative to the narrow end 606.
FIG. 7 illustrates a perspective of the spring member 702 within the exhaust duct 104, according to a further embodiment of the present disclosure. The spring member 702 includes an aperture 704 in a central portion 705. The aperture 704 is joined to the sampling flute 110 via a weld 706. The spring member 702 may be joined to any region of the sampling flute 110 between the first end 202 (shown in FIG. 2) and the second end 204. Two end portions 708 of the spring member 702 are joined to the exhaust duct 104 via welds 710. The spring member 702 is illustrated as substantially rectangular. However, a width of the spring member 702 may increase from the central portion 705 towards each of the end portions 708. Further, one or more stepped portions (not shown) may be provided between the central portion 705 and each of the end portions 708.

INDUSTRIAL APPLICABILITY

An aftertreatment system may be used to treat an exhaust gas flow of an engine. An aftertreatment system may include an SCR catalyst which aids a reductant, injected into the exhaust gas flow, to reduce nitrogen oxides in the exhaust gas flow to diatomic nitrogen (N₂) and water. A NOx sensor may be provided upstream and/or downstream of the SCR catalyst in an exhaust duct of the aftertreatment system. A sampling flute may be attached to the exhaust duct in order to direct a portion of the exhaust gas flow over the NOx sensor. The exhaust duct may have a large diameter compared to the sampling flute. Therefore, heat capacities of the exhaust duct and the sampling flute are different due to the size difference. A material of the sampling flute may also differ from a material of the exhaust duct. Both the exhaust duct and the sampling flute may get heated and undergo thermal expansion due to a high temperature of the exhaust gas. However, a differential thermal expansion may be caused by different temperatures of the sampling flute and the exhaust duct due to different heat transfer rates to the sampling flute and the exhaust duct and/or the different heat capacities. The differential thermal expansion may also result due to a difference in material thermal expansion coefficient between the exhaust duct and the sampling flute. This may lead to a high thermal stress in a joint between the sampling flute and the exhaust duct.
Referring to FIGS. 1 to 4, the aftertreatment system 100 of the present disclosure includes the exhaust duct 104. The NOx sensor 108 and the sampling flute 110 are provided within the exhaust duct 104. The first end 202 of the sampling flute 110 is coupled to the inner surface of the exhaust duct 104. The second end 204 of the sampling flute 110 is received within the aperture 302 of the first portion 214 of the spring member 212. Further, the second end 204 is joined to the first portion 214 by the weld 304.
During operation of the engine, the exhaust flow may result in a thermal expansion of the sampling flute 110 and the exhaust duct 104 due to a high temperature. However, due to a size difference between the sampling flute 110 and the exhaust duct 104, the sampling flute 110 may undergo higher thermal expansion as compared to the exhaust duct 104. The thermally expanded state of the sampling flute 110 is shown by dashed lines in FIG. 2.
As shown in FIG. 2, the second end 204 of the sampling flute 110, in the expanded state, may extend downwards as the first end 202 is fixedly coupled to the exhaust duct 104. Consequently, the first portion 214 of the spring member 212 may deform downwardly along with the second end 204 of the sampling flute 110. The second portion 216 may also deform in order to account for the movement of the first portion 214. However, the third portion 218, which is fixedly coupled to the exhaust duct 104, may not deform substantially. The sampling flute 110 may be therefore secured at both the first and second ends 202, 204. Further, the spring member 212 may permit an expansion of the second end 204 of the sampling flute 110 in order to account for differential thermal expansion between the sampling flute 110 and the exhaust duct 104. This is turn may prevent a buildup of thermal stress in an interface between the first end 202 of the sampling flute 110 and the exhaust duct 104. The spring member 212 may also provide for varying degrees of differential thermal expansion.
The various parameters of the spring member 212, including the lengths 402, 404, and 406 of the first, second and third portions 214, 216 218, respectively; the angle 220 between the first and second portions 214, 216; the thickness 408 and the width 410 of the spring member 212; the thicknesses of the welds 304, 306; and the diameter 412 of the aperture 302 may be varied as per requirements of the aftertreatment system 100. For example, an overall length and/or the thickness 408 of the spring member 212 may be increased in order to cater to a larger size of the exhaust duct 104, and hence higher differential thermal expansion and thermal stress.
Though the operation of the spring member 212 is described above, it may be apparent that the spring members 502, 602 and 702 may also deform and permit an expansion of the second end 204 of the sampling flute 110. Therefore, the spring members 502, 602 and 702 may accommodate differential thermal expansion between the sampling flute 110 and the exhaust duct 104. The spring member 702 may also provide support to the sampling flute 110 at any desired region between the first and second ends 202, 204.
While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.

Claims

What is claimed is:

1. An aftertreatment system of an engine, the aftertreatment system comprising:

a housing configured to receive an exhaust gas flow from the engine;

a Selective Catalytic Reduction (SCR) catalyst provided within the housing;

an exhaust duct associated with the SCR catalyst;

a sampling flute provided within the exhaust duct, wherein the sampling flute comprises a plurality of holes configured to allow passage of the exhaust gas flow therethrough, and wherein a first end of the sampling flute is coupled to the exhaust duct;

a NOx sensor at least partly enclosed by the first end of the sampling flute; and

a spring member joined to the sampling flute and the exhaust duct.