Title:
EXHAUST EMISSION CONTROL DEVICE WITH ADDITIVE INJECTOR
Kind Code:
A1


Abstract:
An exhaust emission control apparatus is provided which is equipped with an additive injector to inject additive such as a urea aqueous solution into an exhaust pipe through which exhaust emissions flow. The exhaust pipe includes a straight section and a bent section. A catalyst such as a SCR (Selective Catalytic Reduction) catalyst is disposed downstream of the straight section. A hollow protrusion is formed on an outer peripheral wall of the bent section substantially in parallel to a longitudinal center line of the straight section. The protrusion has an opening formed in one of opposed ends thereof which communicates with inside the bent section. The additive injector is designed to produce a cone-shaped spray of additive and installed on the other end of the protrusion to inject the cone-shaped spray of additive into the exhaust pipe without interfering with at least a downstream edge of the opening.



Inventors:
Maruyama, Masatoshi (Kariya-shi, JP)
Ohshima, Keiji (Gamagoori-shi, JP)
Application Number:
11/957980
Publication Date:
07/03/2008
Filing Date:
12/17/2007
Assignee:
DENSO CORPORATION (Kariya-city, JP)
Primary Class:
Other Classes:
60/303
International Classes:
F01N3/10
View Patent Images:
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Primary Examiner:
BOGUE, JESSE SAMUEL
Attorney, Agent or Firm:
NIXON & VANDERHYE, PC (ARLINGTON, VA, US)
Claims:
What is claimed is:

1. An exhaust emission control apparatus comprising: an exhaust pipe through which exhaust emission flow, said exhaust pipe including a straight section and a bent section extending from the straight section in an upstream direction of a flow of the exhaust emissions; a catalyst disposed downstream of the straight section of said exhaust pipe in connection therewith; a hollow protrusion having a length extending outside the said exhaust pipe from a peripheral wall of the bent section substantially in parallel to a longitudinal center line of the straight section, said protrusion having a first end and a second end opposed to the first end, said protrusion having an opening formed in the first end which communicates with inside the bent section of said exhaust pipe; and an additive injector designed to produce a cone-shaped spray of additive, said additive injector being installed in the second end of said protrusion and oriented to inject the cone-shaped spray of additive into said exhaust pipe through the opening of said protrusion without interfering with at least a downstream edge of the opening, the additive being carried by the flow of the exhaust emissions downstream to said catalyst and used in a given exhaust emission purification reaction, as induced by said catalyst, to purify the exhaust emissions.

2. An exhaust emission control apparatus as set forth in claim 1, wherein said additive injector is so oriented by said protrusion as to avoid interference of the cone-shaped spray of additive with an entire edge of the opening of said protrusion.

3. An exhaust emission control apparatus as set forth in claim 1, wherein said protrusion has a cylindrical inner wall.

4. An exhaust emission control apparatus as set forth in claim 1, wherein said additive injector has a head in which a spray hole is formed, and wherein a distance between the downstream edge of the opening of said protrusion and the head of said additive injector is so selected as a function of an angle of spread of the additive, as sprayed from said additive injector, as to avoid interference of the cone-shaped spray of the additive with the downstream edge of the opening of said protrusion.

5. An exhaust emission control apparatus as set forth in claim 1, wherein said additive injector is oriented in alignment of an axis thereof with that of the straight section of said exhaust pipe.

6. An exhaust emission control apparatus as set forth in claim 1, wherein said additive injector is oriented in alignment of an axis with that of said catalyst.

7. An exhaust emission control apparatus as set forth in claim 4, wherein said additive injector is designed to change the angle of spread of the additive, and wherein said additive injector is oriented to avoid interference of the cone-shaped spray of additive with at least the downstream edge of the opening when the angle of spread of the additive is maximized.

8. An exhaust emission control apparatus as set forth in claim 1, wherein said exhaust pipe also includes a second bent section through which the exhaust gas flows, said second bent section communicating with the bent section and the straight section at a branch joint, and wherein the opening of said protrusion leading inside said exhaust pipe through a wall of the branch joint, said protrusion extending outside said exhaust pipe substantially in parallel to the longitudinal center line of the straight section.

9. An exhaust emission control apparatus as set forth in claim 1, wherein the bent section is curved.

10. An exhaust emission control apparatus as set forth in claim 1, wherein the bent section is flexed to a right angle.

Description:

CROSS REFERENCE TO RELATED DOCUMENT

The present application claims the benefit of Japanese Patent Application No. 2006-342319 filed on Dec. 20, 2006, the disclosure of which is totally incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates generally to an exhaust emission control device equipped with an additive injector which may be used with an SCR (Selective Catalytic Reduction) system working to induce an exhaust gas purification reaction using additive such as a urea aqueous solution.

2. Background Art

Urea SCR systems designed as exhaust emission control devices for use in electric power plants, factories, or automobiles especially equipped with diesel engines are now being developed and partially put in practical use.

FIG. 5 illustrates a typical one of the urea SCR systems.

The urea SCR system includes generally an SCR catalyst 51, an exhaust pipe 52 extending between an exhaust emission source (i.e., an automotive diesel engine) and the catalyst 51, and a urea solution injection valve 53. The catalyst 51 works to induce NOx reduction to purify exhaust gas flowing thereinto through the exhaust pipe 52. The urea solution injection valve 53 is installed in the exhaust pipe 52 to inject or spray an aqueous urea (i.e., a urea aqueous solution) to a flow of the exhaust gas within the exhaust pipe 52 as a reducing agent. Specifically, the urea solution injection valve 53 is, as clearly illustrated in FIG. 5, inclined to the length of the exhaust pipe 52 at a given angle to have a spray hole 53a facing the catalyst 51 so as to orient the spray of the aqueous urea toward the catalyst 51.

In operation, the urea solution injection valve 53 sprays the aqueous solution into the exhaust pipe 52. The aqueous solution is then carried by the flow of exhaust gas to the catalyst 51 located downstream of the urea solution injection valve 53, so that the exhaust gas is purified through NOx reduction taken place on the catalyst 51. In the reduction of NOx emissions, the urea aqueous solution is hydrolyzed by the thermal energy of the exhaust gas to produce ammonia (NH3) which is, in turn, added to the NOx emissions, as selectively adsorbed by the catalyst 51, so that the NOx emissions react with the ammonia on the surface of the catalyst 51 and are converted into harmless products.

The exhaust pipe 52 is sometimes shaped to have a bend depending upon the layout of component parts of the vehicle. There are known urea solution injection valves disposed in such a bend of the exhaust pipe. For instance, Japanese Patent First Publication Nos. 2001-3737 and 2003-293739 and Translated PCT Publication No. 2001-516635 teach such a type of urea solution injection valve.

It is preferable that urea SCR systems having the urea solution injection valve installed in the bend of the exhaust pipe are designed to orient a stream of urea aqueous solution in the same direction as the flow of exhaust gas in order to mix the urea aqueous solution with the exhaust gas passing through the bend homogeneously and supply it to the catalyst. However, the urea solution injection valves, as disclosed in the above second and third publications, are so disposed as to be exposed inside the bend, so that they are subjected to intense heat of the exhaust gas.

The urea solution injection valve, as disclosed in the above first publication, is mounted in a protrusion extending outside the bend of the exhaust pipe in a direction opposite to the catalyst in order to minimize the exposure of the urea solution injection valve to the intense heat of exhaust gas. This structure is, however, needed to select the length of the protrusion from the outer surface of the bend or regulate the angle of a cone-shaped spread of urea aqueous solution accurately in order to avoid the adhesion of a spray of the urea aqueous solution to an inner wall of the protrusion, which may result in instability in mixing the urea aqueous solution with the exhaust gas homogeneously.

SUMMARY OF THE INVENTION

It is therefore a principal object of the invention to avoid the disadvantages of the prior art.

It is another object of the invention to provide an exhaust emission control device equipped with an additive injector which is designed to protect the additive injector from intense heat of exhaust gas and ensure the stability in an exhaust gas purification reaction using additive injected into exhaust gas.

According to one aspect of the invention, there is provided an exhaust emission control apparatus which may be used as a urea SCR (Selective Catalytic Reduction) system for automotive internal combustion engines which works to convert harmful emissions into less harmless substances. The exhaust emission control apparatus comprises: (a) an exhaust pipe through which exhaust emissions flow, the exhaust pipe including a straight section and a bent section extending from the straight section in an upstream direction of a flow of the exhaust emissions; (b) a catalyst disposed downstream of the straight section of the exhaust pipe in connection therewith; (c) a hollow protrusion having a length extending outside the exhaust pipe from a peripheral wall of the bent section substantially in parallel to a longitudinal center line of the straight section, the protrusion having a first end and a second end opposed to the first end, the protrusion having an opening formed in the first end which communicates with inside the bent section of the exhaust pipe; and (d) an additive injector designed to produce a cone-shaped spray of additive, the additive injector being installed in the second end of the protrusion and oriented to inject the cone-shaped spray of additive into the exhaust pipe through the opening of the protrusion without interfering with at least a downstream edge of the opening. The additive is carried by the flow of the exhaust emissions downstream to the catalyst and used in a given exhaust emission purification reaction, as induced by the catalyst, to purify the exhaust emissions.

Specifically, the protrusion extends outside the exhaust pipe. The additive injector is retained by the protrusion without being exposed directly to the exhaust emissions flowing through the exhaust pipe, thereby minimizing the transmission of intense heat of the exhaust emissions to the additive injector. Additionally, the additive injector is also so held by the protrusion as to avoid the interference of the cone-shaped spray of the additive with at least the downstream edge of the opening that is a portion of the opening located farthest away from the additive injector. Further, the protrusion is formed to extend substantially parallel to the longitudinal center line of the straight section of the exhaust pipe. The additive injector is secured to the second end of the protrusion. In other words, the center axis of the cone-shaped spray, that is, a path along which the additive is sprayed from the additive injector is aligned with the longitudinal center line of the straight section of the exhaust pipe, thereby minimizing the adhesion of the additive to an inner wall of the protrusion and mixing the additive to the exhaust emissions homogeneously which are, then, carried to the catalyst.

In the preferred mode of the invention, the additive injector is so oriented by the protrusion as to avoid interference of the cone-shaped spray of additive with an entire edge of the opening of the protrusion.

The protrusion has a cylindrical inner wall, thereby facilitating machining of the protrusion and also minimizing the adhesion of the spray of additive thereto.

The additive injector has a head in which a spray hole is formed. The distance between the downstream edge of the opening of the protrusion and the head of the additive injector is so selected as a function of an angle of spread of the additive, as sprayed from the additive injector, as to avoid interference of the cone-shaped spray of the additive with the downstream edge of the opening of the protrusion.

The additive injector is oriented in alignment of an axis thereof with that of the straight section of the exhaust pipe, thereby resulting in a uniform distribution of the spray of additive over the straight section of the exhaust pipe and carrying a homogeneous mixture of the additive and the exhaust emissions to the catalyst.

The additive injector may also be oriented in alignment of an axis with that of the catalyst.

The additive injector may be designed to change the angle of spread of the additive. The additive injector is oriented to avoid interference of the cone-shaped spray of additive with at least the downstream edge of the opening when the angle of spread of the additive is maximized.

The exhaust pipe may also include a second bent section through which the exhaust gas flows. The second bent section communicates with the bent section and the straight section at a branch joint. The opening of the protrusion leads inside the exhaust pipe through a wall of the branch joint. The protrusion extends outside the exhaust pipe substantially in parallel to the longitudinal center line of the straight section.

The bent section is curved smoothly or flexed to a right angle.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only.

In the drawings:

FIG. 1 is a schematic view which shows an exhaust emission control apparatus according to the invention;

FIG. 2 is a partially enlarged sectional view of FIG. 1;

FIG. 3 is a side view which shows a first modification of installation of a urea solution injection valve installed in the exhaust emission control apparatus of FIG. 1;

FIG. 4(a) is a side view which shows a second modification of installation of a urea solution injection valve installed in the exhaust emission control apparatus of FIG. 1;

FIG. 4(b) is a side view which shows a third modification of installation of a urea solution injection valve installed in the exhaust emission control apparatus of FIG. 1; and

FIG. 5 is a partially sectional view which shows installation of a urea solution injection valve used in a conventional urea SCR systems

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, particularly to FIG. 1, there is shown a urea SCR (Selectively Catalytic Reduction) system according to the invention which is engineered, like the one in FIG. 5, as an exhaust emission control device to convert NOx emissions contained in exhaust gas from an automotive diesel engine (not shown) into harmless products.

The urea SCR system includes a DOC (Diesel Oxidation Catalyst) 21, an exhaust pipe 10, and a SCR (Selectively Catalytic Reduction) catalyst 20, and a urea solution injection valve 50. The exhaust gas, as emitted from the diesel engine, flows through the exhaust pipe 10 in a direction A.

The urea solution injection valve 50 is installed in a portion the exhaust pipe 10 between the DOC 21 and the SCR catalyst 20. The urea solution injection valve 50 is controlled in operation by a controller (not shown) to inject or spray a urea aqueous solution as a reducing agent (also called reducer) to the exhaust gas flowing from the DOC 21 to the SCR catalyst 20. The urea aqueous solution is then carried by the stream of exhaust gas to the SCR catalyst 20 and used in NOx reduction.

Specifically, the SCR catalyst 20 works to induce the NOx reduction, that is, induce, for example, reactions below.


4NO+4NH3+O24N26H2O (1)


6HO2+8NH27N2+12H2O (2)


NO+NO2+2NH32N2+2H2O (3)

The ammonia (NH3) that is used as a reducing agent for the NOx reduction in the above reaction formulas is supplied by the urea solution injection valve 50 disposed upstream of the SCR catalyst 20.

The urea solution injection valve 50 is of a known structure similar to typical fuel injectors and works to produce, as indicated by an arrow F in FIG. 2, a cone-shaped spray of urea aqueous solution through a spray hole 75 formed in a head thereof. The urea solution injection valve 50 is supplied with the urea aqueous solution from a urea solution tank (not shown) through a urea solution supply pipe.

The exhaust pipe 10 is, as can be seen from FIG. 1, made up of three sections: a hollow cylindrical straight section 11 joined directly to the SCR catalyst 20, a curved section 12 extending from the straight section 11, and a curved section 13 joined to the DOC 21. The curved section 13 is bent in a direction opposite to the curved section 12 and connected thereto to define an S-shaped portion of the exhaust pipe 10. The curved section 12 has formed thereon a protrusion 14 in which the urea solution injection valve 50 is installed.

The protrusion 14 is hollow cylindrical and opens into the curved section 12 of the exhaust pipe 10, as illustrated in FIG. 1, in alignment of a longitudinal center line (i.e., an axis) 25 thereof with a longitudinal center line of the straight section 11. The protrusion 14 extends from an outer peripheral wall of the curved section 12 away from the straight section 11. The protrusion 14 may be machined to have a cylindrical inner wall. The SCR catalyst 20 is disposed in alignment of a longitudinal center line thereof with the longitudinal center line of the straight section 11.

The protrusion 14 has an end wall 18 to which the urea solution injection valve 50 is secured. Specifically, the urea solution injection valve 50 is joined to the end wall 18 of the protrusion 14 through a heat insulator 22 to have the head (i.e., the spray hole 75) thereof exposed inside the protrusion 14. The spray hole 75 is, as can be seen in FIG. 2, formed in the center of a top end wall of the head of the urea solution injection valve 50 to align a jet of urea aqueous solution with the SCR catalyst 20.

The urea solution injection valve 50 is so retained by the end wall 18 as to orient the cone-shaped spray F of urea aqueous solution to an oval opening 65, as defined by a joint between the curved section 12 of the exhaust pipe 10 and the protrusion 14, without physically interfering with a lower edge 15 of the oval opening 65 (i.e., the most downstream portion of the joint between the curved section 12 and the protrusion 14 in a direction of flow of the exhaust gas). In other words, the angle θ of spread of the urea aqueous solution and the distance L between the lower edge 15 of the opening 65 and the top end (i.e., the spray hole 75) of the urea solution injection valve 50 are so selected as to avoid the adhesion of the urea aqueous solution to the lower edge 15 of the opening 65. In this embodiment, the angle θ and the distance L are also selected so as to avoid the interference of the cone-shaped spray F of urea aqueous solution with an upper edge 16 of the oval opening 65 (i.e., the most upstream portion of the joint between the curved section 12 and the protrusion 14 in the direction of flow of the exhaust gas). It is also advisable that the angle θ and the distance L be selected so as to avoid the interference of the cone-shaped spray F of urea aqueous solution with an entire edge of the oval opening 65. The urea solution injection valve 50 may be designed to change the angle θ of spread of the urea aqueous solution in response to a change in operating condition of the engine. In this case, it is advisable that the urea solution injection valve 50 be installed in the protrusion 14 so that the spray of urea aqueous solution does not interfere with at least the lower edge 15 of the opening 65 when the angle θ is maximized.

The beneficial advantages of the urea SCR system will be described below.

The urea solution injection valve 50 is, as described above, secured to the end wall 18 of the protrusion 14, so that it is not exposed directly to the intense heat of the exhaust gas flowing, as indicated by an arrow A, in the exhaust pipe 10. The use of the heat insulator 22 further minimizes the transmission of the heat to the urea solution injection valve 50.

The urea solution injection valve 50 is oriented in alignment of the longitudinal center line thereof with that of the straight section 11 of the exhaust pipe 10 (i.e., the SCR catalyst 20), thereby directing the cone-shaped spray F of the urea aqueous solution uniformly over the entire inlet surface of the SCR catalyst 20. Specifically, the urea aqueous solution and the exhaust gas which are mixed homogeneously reach the entire surface of the SCR catalyst 20.

The location where the urea solution injection valve 50 is mounted on the protrusion 14 and the structure of the protrusion 14 are so determined that the urea aqueous solution is injected into the curved section 12 of the exhaust pipe 10 without interfering with at least the lower edge 15 of the opening 65 of the exhaust pipe 10, thus mixing the urea aqueous solution with the exhaust gas within the exhaust pipe 10 without the adhesion thereof to the inner wall of the protrusion 14.

FIG. 3 illustrates the first modification of the installation of the urea solution injection valve 50 to the exhaust pipe 10.

Specifically, the exhaust pipe 10 includes an L-shaped section 12a instead of the curved section 12 of FIG. 1. The L-shaped section 12a is bent at right angles and connected between the sections 11 and 13. The protrusion 14 extends from the L-shaped section 12a away from the straight section 11. The urea solution injection valve 50 is installed in the protrusion 14 in alignment of the longitudinal center line thereof with that of the straight section 11.

FIG. 4(a) illustrates the second modification of the installation of the urea solution injection valve 50.

The exhaust pipe 10 includes two curved sections 12b and 12c each of which is joined to one of DOCs (not shown). The curved sections 12b communicate with the SCR catalyst 20 through the straight section 11. The protrusion 14 is formed on a branch joint 19 of the curved sections 12b and 12c. The urea solution injection valve 50 is disposed in the protrusion 14 in alignment of the longitudinal center line thereof with that of the straight section 11 (i.e., the SCR catalyst 20).

FIG. 4(b) illustrates the third modification of the installation of the urea solution injection valve 50.

The exhaust pipe 10 includes a T-shaped section 12e joined at two inlets thereof to DOCs (not shown), respectively. The T-shaped section 12e is also joined at an outlet thereof to the SCR catalyst 20 through the straight section 11. The protrusion 14 is formed on the outer surface of the T-shaped section 12e in alignment with the outlet of the T-shaped section 12e. The urea solution injection valve 50 is disposed in the protrusion 14 in alignment of the longitudinal center line thereof with that of the straight section 11 (i.e., the SCR catalyst 20).

The urea SCR system may be used with engines other than diesel engines such as gasoline engines (e.g., spark ignition engines) or another type of exhaust emission control device. The urea SCR system may also be designed to use a reducing agent other than urea.

While the present invention has been disclosed in terms of the preferred embodiments in order to facilitate better understanding thereof it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modifications to the shown embodiments witch can be embodied without departing from the principle of the invention as set forth in the appended claims.