Exhaust emission control device

Abstract

To provide an exhaust emission control device capable of determining each of NOx concentration and ammonia concentration downstream of a reduction catalyst by using a detection value obtained by an NOx sensor that reacts with both of NOx and ammonia.SOLUTION: An exhaust emission control device 3 includes: a main exhaust pipe extending from an internal combustion engine 1 and serving as a flow passage for a discharge gas in which a reduction catalyst 20 and a first NOx sensor 31 are provided from the upstream side in this order; and a bypass pipe 12 that connects a first opening part 14 provided in the main exhaust pipe between the reduction catalyst and the first NOx sensor and a second opening 16 part provided in the exhaust pipe downstream of the first NOx sensor. The bypass pipe has an ammonia slip catalyst 22 and a second NOx sensor 32 that are disposed from the upstream side in this order. In the exhaust emission control device, the ammonia slip catalyst can convert all of a maximum flow rate of ammonia flowing in the bypass pipe into NOx.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an exhaust gas purification device that causes a reduction reaction of NOx in exhaust gas.

Background Art

[0002] Exhaust gas discharged from an internal combustion engine such as a diesel engine contains nitrogen oxides (hereinafter referred to as "NOx") that may affect the environment. As an exhaust gas purification device used to purify this NOx, an exhaust gas purification device is known in which a reducing agent such as an aqueous urea solution is injected and supplied upstream of a reduction catalyst disposed in an exhaust pipe, and the NOx in the exhaust gas is caused to undergo a reduction reaction in the reduction catalyst.

[0003] In such an exhaust gas purification device, if the injection amount of the reducing agent is insufficient with respect to the amount of NOx contained in the exhaust gas, there is a risk that NOx will flow out to the downstream side of the reduction catalyst. On the other hand, if the injection amount of the reducing agent becomes excessive, ammonia generated by hydrolysis of urea may exceed the saturation adsorption amount of the reduction catalyst, and there is a risk that ammonia will flow out to the downstream side of the reduction catalyst.

[0004] In order to make the injection amount of the reducing agent appropriate, it is conceivable to attach a NOx sensor to the downstream side of the reduction catalyst and control the injection amount of the reducing agent based on the signal of the NOx sensor. Here, since a known NOx sensor reacts to both NOx and ammonia, the detection value of the NOx sensor includes a detection value based on the amount of NOx and a detection value based on the amount of ammonia. Therefore, when NOx and ammonia are contained in the exhaust gas, the amounts of NOx and ammonia cannot be determined from the detection value of the NOx sensor. And it is not possible to accurately determine the injection amount of the reducing agent based on the detection value of the NOx sensor.

[0005] Patent Document 1 discloses a control device for a urea SCR system (exhaust gas purification device) capable of performing feedback control of the addition amount (injection amount of the reducing agent) of aqueous urea using the detection value of a NOx sensor.

Prior Art Documents

Patent Document

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The control of the exhaust gas purification device disclosed in Patent Document 1 uses a model that calculates the concentration of ammonia derived from the results of experiments and simulations conducted in advance. Therefore, if there is a difference between the exhaust gas purification device used in the experiment and the exhaust gas purification device actually used, that difference will affect the calculated ammonia concentration and also affect the determined amount of urea water to be added. In addition, experiments and simulations are required for each specification of the exhaust gas purification device, and it takes time to determine the model. Also, when there is a change in the specification of the exhaust gas purification device, it may be necessary to remake the model.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to use the detection values of a NOx sensor that reacts with both NOx and ammonia, and without using an arithmetic model as disclosed in Patent Document 1, to provide an exhaust gas purification device capable of determining the accurate NOx concentration and ammonia concentration on the downstream side of the reduction catalyst, respectively. And it is to provide an exhaust gas purification device capable of controlling the injection amount of the reducing agent based on the NOx concentration and the ammonia concentration.

Means for Solving the Problems

[0009] The exhaust gas purification device according to the present invention is a main exhaust pipe (10) which is a flow path for exhaust gas that extends from an internal combustion engine (1) and in which a reduction catalyst (20) and a first NOx sensor (31) are provided in order from the upstream side, A bypass pipe (12) that connects a first opening (14) provided in the main exhaust pipe (10) between the reduction catalyst (20) and the first NOx sensor (31), and a second opening (16) provided in the main exhaust pipe (10) on the downstream side of the first NOx sensor (31). Comprising The bypass pipe (12) has, in order from the upstream side, an ammonia slip catalyst (22) and a second NOx sensor (32). An exhaust gas purification device (3), The ammonia slip catalyst (22) can convert all of the ammonia at the maximum flow rate flowing through the bypass pipe (12) into NOx. It is an exhaust gas purification device (3).

Advantages of the Invention

[0010] According to the present invention, it is possible to provide an exhaust gas purification device capable of determining the accurate NOx concentration and ammonia concentration on the downstream side of the reduction catalyst by using the detection values of a NOx sensor that reacts to both NOx and ammonia. And it is possible to provide an exhaust gas purification device capable of controlling the injection amount of the reducing agent based on the NOx concentration and ammonia concentration.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0012] Hereinafter, embodiments of the reducing agent supply device and its control method according to the present invention will be specifically described with reference to the drawings as appropriate. In each of the drawings, members denoted by the same reference numerals represent the same members unless otherwise specified, and the description thereof will be omitted as appropriate.

[0013] Hereinafter, an exhaust gas purification device according to an embodiment of the present invention will be described.

[0014] <Overall Configuration of Exhaust Gas Purification Device> FIG. 1 is a schematic diagram for explaining an example of the overall configuration of the exhaust gas purification device 3. This exhaust gas purification device 3 is a device for purifying NOx in the exhaust gas discharged from the internal combustion engine 1. The internal combustion engine 1 is, for example, a diesel engine.

[0015] The exhaust gas purification device 3 includes a main exhaust pipe 10 extending from the internal combustion engine 1 and a bypass pipe 12 that branches from the main exhaust pipe 10 and rejoins.

[0016] In the main exhaust pipe 10, a reducing agent injection valve 42, a reduction catalyst 20, and a first NOx sensor 31 are provided in order from the upstream side.

[0017] A first opening 14, which is one end of the bypass pipe 12, opens onto the main exhaust pipe 10 between the reduction catalyst 20 and the first NOx sensor 31. A second opening 16, which is the other end of the bypass pipe 12, opens onto the main exhaust pipe 10 downstream of the first NOx sensor 31. In the bypass pipe 12, an ammonia slip catalyst 22 and a second NOx sensor 32 are provided in order from the upstream side.

[0018] Further, an additional ammonia slip catalyst (not shown) may be provided in the main exhaust pipe 10 downstream of the second opening 16.

[0019] The reduction catalyst 20 is a catalyst having a function of promoting the reduction reaction of NOx in the exhaust gas. It adsorbs the reduction components generated from the reducing agent and selectively reduces the NOx in the exhaust gas flowing into the reduction catalyst with the reduction components. An aqueous urea solution is used as the reducing agent. Ammonia is generated as a reduction component by the decomposition of the aqueous urea solution in the main exhaust pipe 10.

[0020] The ammonia slip catalyst 22 is formed by supporting an oxidation catalyst component or the like on the surface of a ceramic carrier such as a honeycomb structure, and has a function of decomposing (oxidizing) the ammonia in the bypass pipe 12. Here, the ammonia in the bypass pipe 12 is the ammonia that has slipped from the reduction catalyst 20 and has flowed into the bypass pipe 12 through the first opening 14.

[0021] The ammonia slip catalyst 22 is configured to be able to convert all of the ammonia at the maximum flow rate assumed to flow into the bypass pipe 12 into NOx. In order to use an inexpensive and small ammonia slip catalyst 22, it is preferable to use a bypass pipe 12 with a small flow path cross-sectional area. The flow path cross-sectional area of the bypass pipe 12 is preferably selected to be small enough that there is no difference in the gas flow in the bypass pipe 12 compared to the gas flow in the main exhaust pipe 10. For example, the flow path cross-sectional area of the bypass pipe 12 is preferably 10% or more and 50% or less of the flow path cross-sectional area of the main exhaust pipe 10.

[0022] The first NOx sensor 31 and the second NOx sensor 32 are sensors that detect the concentration of NOx. However, the first NOx sensor 31 and the second NOx sensor 32 react not only to NOx but also to ammonia. Therefore, the first NOx sensor 31 and the second NOx sensor 32 detect the combined concentration of the NOx concentration and the ammonia concentration. For example, the first NOx sensor 31 detects the combined concentration of the NOx concentration and the ammonia concentration in the exhaust gas flowing through the location where the first NOx sensor 31 is installed in the main exhaust pipe 10.

[0023] The reducing agent injection valve 42 is connected to the supply module 44 through the reducing agent passage 48. The supply module 44 pumps out the aqueous urea solution, which is the reducing agent, from the tank 46 and supplies it to the reducing agent injection valve 42 through the reducing agent passage 48. The reducing agent injection valve 42 injects and supplies the reducing agent into the main exhaust pipe 10 on the upstream side of the reduction catalyst 20.

[0024] The exhaust gas purification device 3 further includes a control device 100. The reducing agent injection valve 42 and the supply module 44 are electrically connected to the control device 100 and are controlled by the control device 100. The control device 100 controls the supply module 44 so that the pressure in the reducing agent passage 48 is within a predetermined pressure range, and controls the reducing agent injection valve 42 so as to supply the amount of reducing agent required for the reduction action into the main exhaust pipe 10.

[0025] <Control device> FIG. 2 shows a configuration example in which a part related to the control of the present invention in the control device 100 is represented by functional blocks. This control device 100 is mainly configured around a known microcomputer and has an acquisition unit 103, a control unit 105, and a determination unit 107. Specifically, each of these units is realized by executing a program by the microcomputer.

[0026] In addition, the control device 100 is provided with storage elements (not shown) such as a RAM (Random Access Memory) and a ROM (Read Only Memory), a timer counter, and a drive circuit for controlling the energization of the reducing agent injection valve 42 and the supply module 44.

[0027] The acquisition unit 103 acquires the detection value SIG1 of the first NOx sensor 31 and the detection value SIG2 of the second NOx sensor 32. The acquisition unit 103 may be configured to acquire information from other devices. The acquired information is sent to the control unit 105 and / or the determination unit 107.

[0028] Based on the detection value SIG1 of the first NOx sensor 31 and the detection value SIG2 of the second NOx sensor 32, the control unit 105 calculates the NOx concentration and ammonia concentration in the exhaust gas at the outlet of the reduction catalyst 20, respectively. Further, based on the calculated NOx concentration and ammonia concentration, the control unit 105 calculates the amount of reducing agent to be supplied from the reducing agent injection valve 42 into the main exhaust pipe 10, and controls the reducing agent injection valve 42 and the supply module 44 to supply the amount of reducing agent.

[0029] The calculation method by which the control unit 105 calculates the NOx concentration and ammonia concentration in the exhaust gas at the outlet of the reduction catalyst 20 is as follows.

[0030] Assuming that the NOx concentration at the outlet of the reduction catalyst 20 is CNOx and the ammonia concentration is CNH3, the detection value SIG1 of the first NOx sensor 31 is, SIG1 = K1 * CNOx + K2 * CNH3 ··· (Equation 1) where K1 is the sensitivity coefficient of the first and second NOx sensors 31 and 32 with respect to the NOx concentration, and K2 is the sensitivity coefficient of the first and second NOx sensors 31 and 32 with respect to the ammonia concentration. Note that the detection value (output value) of an actual NOx sensor may have a constant term, but here, for simplicity, the constant term is set to zero. Also, although the first and second NOx sensors 31 and 32 may have different sensitivity coefficients from each other, here, for simplicity, they are assumed to have the same sensitivity coefficient.

[0031] Since the NOx concentration and ammonia concentration at the inlet of the ammonia slip catalyst 22 are the same as the NOx concentration and ammonia concentration at the outlet of the reduction catalyst 20, at the inlet of the ammonia slip catalyst 22, the NOx concentration is CNOx and the ammonia concentration is CNH3. On the other hand, at the outlet of the ammonia slip catalyst 22, all the ammonia that has entered the ammonia slip catalyst 22 is converted to NOx. Therefore, the detection value SIG2 of the second NOx sensor 32 is, SIG2 = K1 * (CNOx + K3 * CNH3) ··· (Equation 2) This results in. Here, K3 is the conversion coefficient from ammonia to NOx. Since all of the ammonia that has passed through the ammonia slip catalyst 22 is converted to NOx, the NOx concentration detected by the second NOx sensor 32 is the sum of CNOx and K3*CNH3.

[0032] From Equation 1 and Equation 2, the NOx concentration CNOx at the outlet of the reduction catalyst 20 is CNOx = (K3 / (K1 * K3 - K2)) * (SIG1 - (K2 * SIG2) / (K1 * K3)) ··· (Equation 3) This is the case. Also, the ammonia concentration CNH3 at the outlet of the reduction catalyst 20 is obtained by substituting the calculation result of Equation 3 into the following Equation 4. CNH3 = (SIG1 - K1 * CNOx) / K2 ··· (Equation 4)

[0033] Thus, according to the exhaust gas purification device according to the embodiment of the present invention, by using a NOx sensor that reacts not only with NOx but also with ammonia, the NOx concentration and the ammonia concentration at the outlet of the reduction catalyst 20 can be accurately determined respectively. Furthermore, by using this NOx concentration and ammonia concentration, the amount of the aqueous urea solution to be supplied to the reduction catalyst 20 can be accurately determined. Therefore, according to the exhaust gas purification device according to the embodiment of the present invention, NOx in the exhaust gas can be accurately reduced. Also, although not described in detail here, the NOx concentration CNOx and the ammonia concentration CNH3 may be determined in consideration of the time difference in the detection of the first and second NOx sensors 31 and 32.

[0034] The operations of the acquisition unit 103, the control unit 105, and the determination unit 107 will be further described below.

[0035] The operation of the exhaust gas purification device 3 according to the embodiment of the present invention will be described using the flowchart of FIG. 3.

[0036] In step S10, the flowchart is started and the process proceeds to step S20.

[0037] In step S20, the acquisition unit 103 acquires the detection value SIG1 of the first NOx sensor 31, sends it to the control unit 105, and proceeds to step S30.

[0038] In step S30, the acquisition unit 103 acquires the detection value SIG2 of the second NOx sensor 32, sends it to the control unit 105, and proceeds to step S40.

[0039] In step S40, the control unit 105 calculates the NOx concentration CNOx and ammonia concentration CNH3 at the outlet of the reduction catalyst 20 based on Formula 3 and Formula 4.

[0040] In step S50, the control unit 105 determines the supply amount of the aqueous urea solution to the reduction catalyst 20 based on the NOx concentration CNOx and ammonia concentration CNH3 at the outlet of the reduction catalyst 20.

[0041] For example, the determination unit 107 determines whether the NOx concentration CNOx and ammonia concentration CNH3 at the outlet of the reduction catalyst 20 are within the allowable ranges respectively. And when the NOx concentration CNOx exceeds the allowable range, the control unit 105 may determine the supply amount of the aqueous urea solution to increase. When the ammonia concentration CNH3 exceeds the allowable range, the control unit 105 may determine the supply amount of the aqueous urea solution to decrease.

[0042] In step S60, the control unit 105 controls the reductant injection valve 42 and the supply module 44 so that the supply amount determined in step S50 is supplied to the reduction catalyst 20. After step S60, it returns to step S10.

[0043] As described above, according to the exhaust gas purification device according to the embodiment of the present invention, by using a NOx sensor that reacts not only with NOx but also with ammonia, the NOx concentration and ammonia concentration at the outlet of the reduction catalyst 20 can be accurately determined. Further, by using this NOx concentration and ammonia concentration, the amount of aqueous urea solution to be supplied to the reduction catalyst 20 can be accurately determined. Therefore, according to the exhaust gas purification device according to the embodiment of the present invention, NOx in the exhaust gas can be accurately reduced.

[0044] As described above, the embodiments of the present invention have been described in detail with reference to the drawings, but the present invention is not limited to such examples. It is obvious that those having ordinary knowledge in the technical field to which the present invention pertains can conceive of various modification examples or correction examples within the scope of the technical idea described in the claims, and it is naturally understood that these also belong to the technical scope of the present invention.

Explanation of Reference Numerals

[0045] 1 Internal combustion engine, 3 Exhaust gas purification device, 10 Main exhaust pipe, 12 Bypass pipe, 14 First opening, 16 Second opening, 20 Reduction catalyst, 22 Ammonia slip catalyst, 31 First NOx sensor, 32 Second NOx sensor, 42 Reducing agent injection valve, 44 Supply unit, 46 Tank, 48 Reducing agent passage, 100 Control device, 103 Acquisition unit, 105 Control unit, 107 Judgment unit

Claims

1. A main exhaust pipe (10) which is a flow path for exhaust gas extending from an internal combustion engine (1) and having a reduction catalyst (20) and a first NOx sensor (31) provided in order from the upstream side, A bypass pipe (12) connecting a first opening (14) provided in the main exhaust pipe (10) between the reduction catalyst (20) and the first NOx sensor (31) and a second opening (16) provided in the main exhaust pipe (10) on the downstream side of the first NOx sensor (31), comprising, The bypass pipe (12) has an ammonia slip catalyst (22) and a second NOx sensor (32) in order from the upstream side, An exhaust gas purification device (3), The ammonia slip catalyst (22) can convert all the ammonia at the maximum flow rate flowing through the bypass pipe (12) into NOx, Exhaust gas purification device (3).

2. The exhaust gas purification device (3) further includes a control device (100), The control device (100) determines the NOx concentration and the ammonia concentration in the exhaust gas discharged from the reduction catalyst (20) based on the detection value of the first NOx sensor (31) and the detection value of the second NOx sensor (32), The exhaust gas purification device (3) according to claim 1.

3. The exhaust gas purification device (3) further includes a reducing agent injection valve (42) attached to the upstream side of the reduction catalyst (20) for supplying a reducing agent to the main exhaust pipe (10), The control device (100) determines the amount of the reducing agent supplied from the reducing agent injection valve (42) based on the calculated NOx concentration and the ammonia concentration, The exhaust gas purification device (3) according to claim 2.

4. The flow path cross-sectional area of the bypass pipe (12) is smaller than the flow path cross-sectional area of the main exhaust pipe (10), The exhaust gas purification device (3) according to any one of claims 1 to 3.

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