1. Field of the Invention
The present invention relates to the configuration of a reducing agent injection nozzle which injects a reducing agent added to an exhaust gas of an internal combustion engine and the configuration of a nitrogen oxide purification system with the reducing agent injection nozzle.
2. Description of the Related Art
As an example of a nitrogen oxide purification system which purifies nitrogen oxide (NOx) contained in the exhaust gas of a diesel engine, a urea selective reduction system (urea SCR system) which uses an aqueous urea solution as a reducing agent may be exemplified. For example, as disclosed in Japanese Patent Application Laid-Open No. 2005-113688, a urea SCR system includes a reducing catalyst which is provided in an exhaust pipe and a reducing agent injection nozzle which is disposed on the upstream side of the reducing catalyst and injects an aqueous urea solution into the exhaust pipe. The reducing catalyst causes a reaction of nitrogen oxide contained in the exhaust gas with ammonia (NH3) produced from the aqueous urea solution injected into the exhaust pipe, and reduces it into harmless nitrogen (N2) and water (H2O) thereby purifying the nitrogen oxide. Further, the reducing agent injection nozzle is inclined at a predetermined angle with respect to the flow of the exhaust gas so that the reducing agent may be injected toward the reducing catalyst.
In order to improve the purification efficiency of the nitrogen oxide using the reducing catalyst, there is a need to supply the aqueous urea solution to the entire surface of the reducing catalyst so as to be a uniformly distributed. However, since the reducing agent injection nozzle generally injects the aqueous urea solution in a conical shape, in order to widely spread the aqueous urea solution on the entire surface of the reducing catalyst, there is a need to ensure some distance between the reducing agent injection nozzle and the reducing catalyst so that the injection range of the aqueous urea solution is sufficiently widened. On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 2005-113688, for example, an oxidation catalyst or the like which is different from the reducing catalyst is generally provided on the upstream side of the reducing catalyst and the reducing agent injection nozzle. When the distance between the catalysts is lengthened, problems such as vehicle mountability is degraded due to an increase in the size of the entire system or increases in pressure loss arise. That is, in the case that the reducing agent injection nozzle disclosed in Japanese Patent Application Laid-Open No. 2005-113688 is used, as the points of improving in the purification efficiency of nitrogen oxide and decreasing the distance between the catalysts are contrary to each other, the problem arises that it is difficult to achieve both these things at once.
The present invention has been made to solve these problems, with the aim of providing a reducing agent injection nozzle which injects a reducing agent at a wide angle at a short distance and a nitrogen oxide purification system which shortens the distance between catalysts while improving the purification efficiency of nitrogen oxide.
According to one aspect of the invention, there is provided a reducing agent injection nozzle including: a nozzle body which is provided with a plurality of injection apertures, a reducing agent being injected from the plurality of injection apertures, wherein in the nozzle body, a pair of the injection apertures arranged along one direction are formed, and wherein a pair of injection apertures are formed so that the reducing agent injected from one injection aperture and the reducing agent injected from the other injection aperture collide with each other.
Hereinafter, preferred embodiments of the invention will be described by referring to the accompanying drawings.
An exhaust pipe 2 is connected to a diesel engine 1 which is an internal combustion engine, and an exhaust gas discharged from the diesel engine 1 passes in the exhaust pipe 2 in a direction indicated by the arrow A in a state where the side of the diesel engine 1 is set as the upstream side. An oxidation catalyst 3 is provided in the course of the exhaust pipe 2 so as to oxidize carbon monoxide (CO), hydrocarbon (HC), or the like contained in the exhaust gas. Further, an SCR catalyst 4 which is a reducing catalyst is provided on the downstream side of the oxidation catalyst 3 so as to purify nitrogen oxide (NOx) contained in the exhaust gas.
The SCR catalyst 4 is a catalyst which purifies NOx by the reaction of a reaction gas with ammonia (NH3) which is produced from an aqueous urea solution added to the exhaust gas as a reducing agent. A reducing agent injection nozzle 5 which injects the aqueous urea solution into the exhaust pipe 2 is provided between the oxidation catalyst 3 and the SCR catalyst 4. An aqueous urea solution tank 5a which stores the aqueous urea solution therein and an aqueous urea solution addition system 5b which supplies the aqueous urea solution in the aqueous urea solution tank 5a to the reducing agent injection nozzle 5 are connected to the reducing agent injection nozzle 5 through a connection pipe 5c. Furthermore, the portion of the exhaust pipe 2 which is positioned between the oxidation catalyst 3 and the SCR catalyst 4 has approximately the same diameter as those of the catalysts, and is connected to the oxidation catalyst 3 and the SCR catalyst 4 without throttling the area of the flow passage of the exhaust gas.
A filter 6 which traps particulate materials (PM) contained in the exhaust gas is provided on the downstream side of the SCR catalyst 4. Further, a slip catalyst 7 which eliminates ammonia passing through the SCR catalyst 4 without any reaction, for example, when the amount of ammonia is excessively larger than the amount of NOx contained in the exhaust gas is provided on the downstream side of the filter 6. A muffler (not illustrated) is connected to the downstream side of the slip catalyst 7, and the exhaust gas passing through the slip catalyst 7 is discharged into the atmosphere after reducing the exhaust noise inside the muffler.
Further, NOx sensors 8a and 8b which detect the amount of NOx contained in the exhaust gas are respectively provided on the upstream side and the downstream side of the SCR catalyst 4. The aqueous urea solution addition system 5b and the NOx sensors 8a and 8b are electrically connected to an ECU 9 which controls the operations of the diesel engine 1 and the nitrogen oxide purification system. The ECU 9 determines the injection amount and the injection timing of the aqueous urea solution based on the amount of NOx detected by the NOx sensors 8a and 8b, and outputs a signal based on the determined result to the aqueous urea solution addition system 5b, thereby controlling the injection of the aqueous urea solution using the reducing agent injection nozzle 5.
Here, the configuration of the reducing agent injection nozzle 5 will be described in detail by referring to
First,
As illustrated in
Further, the reducing agent injection nozzle 5 includes a needle valve 14 which is configured to be slidable inside the reducing agent passageway 11a of the nozzle body 11. The needle valve 14 is a member which opens and closes the communication aperture 13 by a tip end portion 14a at the lower side, and is configured to be movable up and down inside the reducing agent passageway 11a by the driving of a solenoid (not illustrated) which is provided at the upper side of the nozzle body 11. The needle valve 14 has a passage (not illustrated) which allows to flow the aqueous urea solution from the reducing agent passage way 11a to the seat portion 11b. When the needle valve 14 is moved downward, the tip end portion 14a comes into contact with the seat portion 11b, so that the communication aperture 13 is blocked, and the supply of the aqueous urea solution from the reducing agent passageway 11a to the space 12 is stopped. On the other hand, when the needle valve 14 is moved upward, the tip end portion 14a is separated from the seat portion 11b, so that the communication aperture 13 is opened, and the supply of the aqueous urea solution from the reducing agent passageway 11a to the space 12 is started.
In the reducing agent injection nozzle 5 with such a configuration, the lower end portion of the nozzle body 11 is provided with two flat surfaces, that is, opening surfaces 15 and 16 which are inclined at an angle α so as to face different directions, and the opening surfaces 15 and 16 are exposed in the exhaust pipe 2. Further, as illustrated in
The pair of injection apertures 21a and 21b which are opened to the opening surface 15 are arranged along the direction indicated by the arrow A of
As illustrated in
Next, the operations of the nitrogen oxide purification system and the reducing agent injection nozzle 5 according to Embodiment 1 of the invention will be described.
As illustrated in
When the signal for opening the valve of the reducing agent injection nozzle 5 is output from the ECU 9, as illustrated in
Here, as illustrated in
Further, as illustrated in
On the other hand, as illustrated in
Returning to
As described above, since the pair of injection apertures 21a and 21b and the pair of injection holes 22a and 22b which generate the fan-like impinging jets are formed in the nozzle body 11 of the reducing agent injection nozzle 5, the entire injection range of the aqueous urea solution may be widened in the direction indicated by the arrow B while being maintained so as to be substantially flat in the direction indicated by the arrow A. That is, it is possible to disperse more aqueous urea solution within a range of a short distance in the direction of the arrow A than aqueous urea solutions of an equivalent amount injected in a taper shape. Accordingly, in the reducing agent injection nozzle 5, the reducing agent may be injected at a wide angle in a short distance.
Further, since the nozzle body 11 is provided with the opening surface 15 to which the injection apertures 21a and 21b are opened and the opening surface 16 to which the injection apertures 22a and 22b are opened and the opening surfaces 15 and 16 are inclined by the angle α so as to face different directions, an inclination of the angle α is also formed between the fan-like injection from the injection apertures 21a and 21b and the fan-like injection from the injection apertures 22a and 22b, and the aqueous urea solution may be injected with a wider angle.
Furthermore, as described above, since the reducing agent injection nozzle 5 is configured to inject the aqueous urea solution at a wide angle in a short distance, the aqueous urea solution may be broadly supplied to the entire surface of the SCR catalyst 4 even when the SCR catalyst 4 and the reducing agent injection nozzle 5 are arranged adjacent to each other. Accordingly, since the distance L necessary between the oxidation catalyst 3 and the SCR catalyst 4 is shortened, it is possible to decrease the size of the entire system by shortening the distance L between the catalysts while improving the purification efficiency of NOx or reduce the pressure loss between the catalysts.
Further, since there are a plurality of injection apertures formed in the nozzle body 11 (in the embodiment, four injection apertures 21a, 21b, 22a, and 22b), it is possible to reduce the injection pressure and more uniformly inject the reducing agent compared to the case where the reducing agents of the equivalent amount are injected from a single injection aperture.
Next, a reducing agent injection nozzle according to Embodiment 2 of the invention will be described.
In the reducing agent injection nozzle according to Embodiment 2, three opening surfaces are formed compared to the reducing agent injection nozzle of Embodiment 1 having two opening surfaces to which the injection apertures are opened. Furthermore, in the respective embodiments to be described below, since the same reference numerals of
As illustrated in
As described above, even when three opening surfaces 33 to 35 are formed in the nozzle body 32 of the reducing agent injection nozzle 31, the same effect as that of the reducing agent injection nozzle 5 of Embodiment 1 may be obtained. Furthermore, when the number of opening surfaces is increased as in the case of the reducing agent injection nozzle 31, the pressure necessary for injecting the aqueous urea solution from each injection aperture decreases. Accordingly, it is possible to widely inject the aqueous urea solution at a pressure lower than when aqueous urea solutions of an equivalent amount are injected from the small number of opening surfaces.
Next, a nitrogen oxide purification system according to Embodiment 3 of the invention will be described.
In the nitrogen oxide purification system according to Embodiment 3, an SCR catalyst 51 to be described below is used instead of the SCR catalyst 4 as the reducing catalyst in the nitrogen oxide purification system according to Embodiment 1.
As shown in
As described above, even when the nitrogen oxide purification system is configured so as to use the SCR catalyst 51, the same effect as that of Embodiment 1 may be obtained. Further, since the reducing agent injection nozzle 5 injects the aqueous urea solution so as to be widened in the other direction while being maintained so as to be substantially flat in one direction, the injection range has an oval shape or an ellipsoidal shape as seen from a top view. That is, since the aqueous urea solution which is injected from the reducing agent injection nozzle 5 is supplied to the end surface 51a of the SCR catalyst 51 with higher efficiency, it is possible to further improve the purification efficiency of NOx using the SCR catalyst 51.
Although the nitrogen oxide purification systems according to Embodiments 1 to 3 are configured as a urea SCR system which purifies NOx with an SCR catalyst in a state where the aqueous urea solution is used as the reducing agent, the invention is not limited to a urea SCR system. For example, the invention may be applied to a purification system with a NOx absorption reducing catalyst which absorbs and purifies NOx in accordance with the air/fuel ratio of the exhaust gas, and in this case, the reducing agent is gas oil.
Further, in the nitrogen oxide purification systems according to Embodiments 1 to 3, the SCR catalyst is provided directly behind the downstream side of the oxidation catalyst, but the arrangement order of the catalysts is not limited. For example, as shown in
In the second Embodiment, the lower portion of the nozzle body 32 is provided with three pairs of injection apertures 41a, 41b, 42a, 42b, 43a and 43b, but injection apertures 41a, 41b, 42a and 42b may be omitted. In this case, the same effect of Embodiment 1 may be obtained. A reducing agent injection nozzle 131 with a nozzle body 132 according to the above Embodiment is shown in
Further, although the reducing agent injection nozzles according to Embodiments 1 to 3 are provided so that the injection range is maintained so as to be substantially flat without being thickened along the plane perpendicular to the circulation direction of the exhaust gas, but may be maintained so as to be substantially flat without being thickened along the plane which is not perpendicular to the circulation direction of the exhaust gas. For example, the direction of the injected reducing agent may be inclined so as to inject the reducing agent toward the SCR catalyst, and the reducing agent may be injected toward a dispersing member or a so-called mixer or swirler separately provided inside the exhaust pipe.
Number | Date | Country | Kind |
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2011-133296 | Jun 2011 | JP | national |