WO2007010664A1

WO2007010664A1 - Exhaust purification apparatus

Info

Publication number: WO2007010664A1
Application number: PCT/JP2006/309600
Authority: WO
Inventors: Hiroki Ueno
Original assignee: Nissan Diesel Motor Co., Ltd.
Priority date: 2005-07-15
Filing date: 2006-05-12
Publication date: 2007-01-25
Also published as: JP4698314B2; JP2007023872A

Abstract

Not only is a reduction catalyst capable of reduction purification of NOx disposed in an engine exhaust pipe but also in two pipes branched from the exhaust pipe positioned in the exhaust upstream, there are respectively disposed plural oxidation catalysts differing from each other in the capacity of oxidation of NO to NO2. A control unit appropriately controls a flow rate control valve capable of independent and multistaged control of exhaust flow rates to the branched pipes on the basis of exhaust volume flow rate and oxidation catalyst temperature so that the ratio between NO and NO2 in the exhaust led to the reduction catalyst approaches a given ratio.

Description

Specification

Exhaust purification device

Technical field

TECHNICAL FIELD [0001] The present invention relates to an exhaust gas purification apparatus that reduces and purifies nitrogen oxides (NOx) in exhaust gas, and particularly relates to a technique for improving the NOx purification rate.

Background art

As a catalyst purification system for purifying NOx in engine exhaust, an exhaust purification device described in JP 2000-27627 A (Patent Document 1) has been proposed. The exhaust purifier is a catalyst that removes NOx and reducing agent in the exhaust gas by injecting and supplying a reducing agent according to the engine operating condition to the upstream side of the exhaust of the reducing catalyst installed in the engine exhaust pipe. A reduction reaction is performed to purify NOx into harmless components. Here, the reduction reaction uses ammonia having good reactivity with NOx, and as the reducing agent, an aqueous urea solution that generates ammonia by hydrolysis with exhaust heat and steam in the exhaust is used.

Patent Document 1: JP 2000-27627 A

Disclosure of the invention

Problems to be solved by the invention

[0003] By the way, in an exhaust gas purification apparatus using ammonia as a reducing agent, nitrogen monoxide (NO) and dioxygen nitrogen (NO) in the exhaust gas are used.

2) When the ratio of

It is known that the X rate is the best. For this reason, NO in the exhaust is oxidized by the acid catalyst installed upstream of the reduction catalyst, and the NO and NO in the exhaust introduced into the reduction catalyst are oxidized.

Technology to improve the ratio of 2 was developed.

[0004] However, the ratio of NO to NO in the exhaust gas varies greatly depending on the engine operating condition.

2

On the other hand, the oxidation ability to oxidize NO to NO by the oxidation catalyst does not change significantly

2

Therefore, it is difficult to bring the ratio of NO and NO close to the predetermined ratio in a wide range of operation.

2

It was. And in the operating range where the ratio of NO to NO in the exhaust is not a predetermined ratio,

2

The NOx purification rate due to the reduction catalyst decreased, and exhaust that was not sufficiently purified could be discharged into the atmosphere. In addition, light oil, gasoline, alcohol, and other fuels are used as reducing agents. However, there is a possibility that the same problem as in the exhaust gas purification device using an aqueous urea solution as a reducing agent may occur.

[0005] In view of the above-described conventional problems, the present invention controls the ratio of NO to NO in the exhaust gas introduced into the reduction catalyst by appropriately controlling the exhaust gas flow rate through which the oxidation catalyst passes.

2

An object of the present invention is to provide an exhaust purification device that is close to a predetermined ratio and has an improved NOx purification rate in a wide range of operation.

Means for solving the problem

[0006] For this reason, the exhaust emission control device according to the present invention is arranged in an engine exhaust pipe, and a reduction catalyst for reducing and reducing NOx, and each branch pipe branched into a plurality of exhaust pipes located upstream of the exhaust gas Plural acids with different oxidation capacities that are each arranged to oxidize NO to NO

2

A catalyst, a flow control valve capable of controlling the exhaust flow divided into each branch pipe independently and in multiple stages, an exhaust flow sensor for detecting the volume flow of the exhaust, a temperature sensor for detecting the catalyst temperature of the oxidation catalyst, and an exhaust Based on the volume flow rate of the catalyst and the catalyst temperature of the oxidation catalyst, the flow rate control valve is controlled so that the ratio of NO to NO in the exhaust gas introduced into the reduction catalyst approaches a predetermined ratio.

2

And a control unit to be controlled. Here, it is desirable that the predetermined ratio for effectively promoting the NOx reduction reaction in the reducing catalyst is a ratio suitable for the NOx reduction reaction by the reduction catalyst.

[0007] Further, instead of a configuration in which an oxidation catalyst is provided in each branch pipe, an oxidation catalyst is provided in one of the branch pipes branched into two exhaust pipes located upstream of the exhaust of the reduction catalyst. Alternatively, a plurality of acid catalysts having different acid capacities may be arranged on the branch pipes except at least one of the branch pipes.

The invention's effect

[0008] According to the exhaust emission control device of the present invention, the flow rate control valve is controlled based on the exhaust gas volume flow rate and the catalyst temperature of the oxidation catalyst, which are closely related to the oxidation capability of the oxidation catalyst, and each branch pipe The flow rate of the exhaust gas divided into two is controlled independently and in multiple stages. For this reason, the flow rate of exhaust gas passing through the oxidation catalyst is appropriately controlled, and exhaust gases with different ratios of NO and NO are mixed.

2

As a result, the ratio of NO to NO in the exhaust gas introduced into the reduction catalyst approaches the specified ratio.

2

The NOx purification rate can be improved in a wide range of operation. Brief Description of Drawings

[0009] FIG. 1 is a configuration diagram showing a first embodiment of an exhaust emission control device according to the present invention.

FIG. 2 is a flowchart showing the contents of control of the exhaust gas purification device.

FIG. 3 is a configuration diagram showing a second embodiment of the exhaust purification apparatus according to the present invention. Explanation of symbols

10 engine

12 Exhaust pipe

12A branch pipe

12B branch pipe

16 NOx reduction catalyst

20A flow control valve

20B Flow control valve

22A oxidation catalyst

22B oxidation catalyst

24 Exhaust temperature sensor

26 Air flow sensor

28: Pioneer roll tree

30 Engine control unit

32 Oxidation catalyst

34 Flow control valve

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1 showing the first embodiment of the present invention, an exhaust nozzle 12 connected to the engine 10 is supplied with an injection nozzle 14 for supplying an aqueous urea solution functioning as a reducing agent along the exhaust flow direction, and an aqueous urea solution. NOx reduction catalyst 16 for reducing and purifying NOx with ammonia obtained by hydrolyzing NOx, and ammonia oxidation catalyst 18 for oxidizing ammonia that has passed through NOx reduction catalyst 16 are provided, respectively. . The spray nozzle 14 is supplied with a urea aqueous solution corresponding to the engine operating state in a sprayed state mixed with air. NOx reduction catalyst 1 Each of the branch pipes 12A and 12B branching the exhaust pipe 12 located upstream of the six exhaust pipes 12A and 12B is an electromagnetic type whose exhaust passage area (opening) can be controlled in multiple stages along the exhaust flow direction. Flow control valves 20A and 20B and oxidation catalyst 22A that oxidizes NO in the exhaust to NO

2

And 22B, respectively. The oxidation catalysts 22A and 22B disposed in the branch pipes 12A and 12B have different acidifying capacities. For example, as the oxidation catalysts 22A and 22B located at the upper side and the lower side in the figure, A low-temperature oxidation catalyst that exhibits good oxidation ability at a low temperature where the catalyst temperature is less than a predetermined value, and a high-temperature oxidation catalyst that exhibits good oxidation ability at a high temperature where the catalyst temperature is higher than a predetermined value can be used.

[0012] On the other hand, as a control system for the exhaust gas purification device, an exhaust gas temperature sensor 24 that indirectly detects the catalyst temperature T from the exhaust gas temperature upstream of the oxidation catalysts 22A and 22B, and a mass flow rate Fi of the intake air are detected. And an air flow sensor 26 is provided. Each output signal from the exhaust temperature sensor 24 and the airflow sensor 26 is input to a control unit 28 with a built-in computer and introduced into the NOx reduction catalyst 16 by a control program stored in its ROM (Read Only Memory). The ratio of NO to NO in the exhaust gas is a predetermined ratio

2

The flow rate control valves 20A and 20B are controlled so as to approach In addition, the control unit 28 is connected to the engine control unit 30 that performs fuel injection control of the engine 10 via CAN (Controller Area Network) and the like so as to be able to communicate with each other, so that the fuel consumption rate C can be read appropriately. Has been. The exhaust flow sensor is configured by the cooperation of the air flow sensor 26, the control unit 28, and the engine control unit 30.

FIG. 2 shows the contents of a control program that is repeatedly executed at predetermined time intervals in the control unit 28.

In step 1 (abbreviated as “S1” in the figure, the same applies hereinafter), the catalyst temperature T of the acid catalyst 22A and 22B is read from the exhaust temperature sensor 24. Here, since the catalyst temperature T is indirectly detected from the exhaust gas temperature upstream of the exhaust gas, there is no need to attach a temperature sensor to the oxidation catalysts 22A and 22B. For example, the oxidation catalysts 22A and 22B are partially Even at high temperatures, it can be prevented from being affected by the heat.

In Step 2, the intake air mass flow Fi is read from the air flow sensor 26. In step 3, the engine control unit 30 power also reads the fuel consumption rate C. In step 4, based on the mass flow rate Fi of the intake air and the fuel consumption rate C, the volume flow rate Fe of the exhaust gas is calculated from a predetermined calculation formula. Here, since the exhaust volume flow rate Fe is indirectly detected from the intake mass flow rate Fi and the fuel consumption rate C, for example, the exhaust volume does not get dirty by the exhaust gas for many years. The flow rate Fe can be detected stably.

In step 5, a control value corresponding to the catalyst temperature T and the volume flow rate Fe is calculated with reference to a map in which control values corresponding to the exhaust volume flow rate and the catalyst temperature of the oxidation catalyst are set. Here, the control values can be the opening Θ and Θ of the flow control valves 20A and 20B.

1 2

wear. Since the control values of the flow control valves 20A and 20B are calculated with reference to the map, an increase in processing load related to the flow control can be suppressed.

[0016] In step 6, the flow control valves 20A and 20B are controlled according to the control value.

According to the construction, after the exhaust gas volume flow rate Fe is calculated from the intake mass flow rate Fi and the fuel consumption rate C, the exhaust volume flow rate Fe and the catalyst temperature T of the oxidation catalysts 22A and 22B are used as a map. The control value (opening) corresponding to the volume flow rate Fe and the catalyst temperature T is calculated. Then, the flow rate control valves 20A and 20B are controlled based on the control value, respectively, and the exhaust flow rate divided into the branch pipes 12A and 12B is controlled independently and in multiple stages. For this reason, if appropriate control values are set in the map through experiments, etc., NO and NO

The ratio of NO to NO in the exhaust can be determined by appropriately mixing the exhaust with different ratios to 2.

2

The fixed rate can be approached and the NOx purification rate can be improved in a wide range of operation.

[0017] Further, the urea aqueous solution injected and supplied together with air upstream of the NOx reduction catalyst 16 in the exhaust state is hydrolyzed by the exhaust heat and water vapor in the exhaust to become ammonia (NH).

Three

, Supplied to the NOx reduction catalyst 16. In the NOx reduction catalyst 16, NOx in the exhaust gas undergoes a reduction reaction with ammonia to form harmless water (H 2 O) and nitrogen (N 2) into the atmosphere.

twenty two

Discharged. At this time, the ammonia that has passed through the NOx reduction catalyst 16 is oxidized by the ammonia acid catalyst 18 disposed downstream of the exhaust gas, so that ammonia cannot be discharged as it is. Next, a second embodiment of the exhaust emission control device according to the present invention will be described. In the following description, for the purpose of eliminating redundant description, only the configuration different from the first embodiment will be described, and the common configuration will be denoted by the same reference numeral and the description thereof will be omitted or simplified. In FIG. 3 showing the configuration of the second embodiment of the present invention, an oxidation catalyst 32 that oxidizes NO in the exhaust to NO is disposed in the branch pipe 12A located in the upper part of the figure, while in the figure

2

The branch pipe 12B located below is provided with an electromagnetic flow control valve 34 capable of controlling the exhaust passage area (opening) in multiple stages. Here, as the oxidation catalyst 32, for example, a catalyst that exhibits a good acidity ability in a frequently used engine operating state can be used. Further, as the control program for controlling the flow control valve 34, the one shown in FIG. 2 can be used as it is, with only a slight change in the map in the first embodiment.

[0019] According to a powerful configuration, the exhaust gas in which NO is oxidized to NO through the acid catalyst 32 and NO

2

NO and NO in the exhaust gas are mixed appropriately with exhaust gas that has not been oxidized.

The ratio of 2 approaches the predetermined ratio, and the NOx purification rate can be improved in a wide range of operation. In the embodiment described above, the exhaust pipe is branched into two by two branch pipes. However, the present invention can also be applied to a configuration in which the exhaust pipe is branched into a plurality of branches by three or more branch pipes. In this way, the ratio of NO to NO in the exhaust introduced into the NOx reduction catalyst can be finely changed regardless of the engine operating condition.

2

Thus, the NOx purification rate can be further improved. Further, the flow rate of the exhaust gas diverted to each branch pipe may be controlled by a single flow rate control valve disposed at the branch portion of the exhaust pipe.

[0020] Further, as the reducing agent, various fuels such as light oil, gasoline, alcohols and the like mainly containing hydrocarbons may be used according to the reduction reaction in the NOx reduction catalyst. In this case, as a control of the flow control valve, the ratio force between NO and NO in the exhaust gas introduced into the NOx reduction catalyst approaches a predetermined ratio suitable for the NOx reduction reaction by the NOx reduction catalyst.

2

What should I do?

Claims

The scope of the claims

[1] a reduction catalyst disposed in the engine exhaust pipe for reducing and purifying nitrogen oxides;

A plurality of oxidation catalysts disposed in each branch pipe branched into a plurality of exhaust pipes located upstream of the reduction catalyst and having different oxidation capacities for oxidizing nitric oxide into nitrogen dioxide;

A flow rate control valve capable of controlling the flow rate of the exhaust gas divided into each branch pipe independently and in multiple stages, an exhaust flow rate sensor for detecting the volume flow rate of the exhaust gas,

A temperature sensor for detecting a catalyst temperature of the oxidation catalyst;

Based on the volume flow rate detected by the exhaust flow sensor and the catalyst temperature detected by the temperature sensor, the ratio of nitrogen monoxide and nitrogen dioxide in the exhaust gas introduced into the reduction catalyst becomes a predetermined ratio. A control unit that controls the flow control valve so as to approach,

An exhaust emission control device comprising:

2. The control unit according to claim 1, wherein the control unit controls the flow rate control valve with reference to a map in which control values corresponding to a volume flow rate of exhaust gas and a catalyst temperature of the oxidation catalyst are set. Exhaust purification equipment.

3. The exhaust emission control device according to claim 1, wherein the exhaust flow rate sensor indirectly detects a volume flow rate of the exhaust gas from an intake mass flow rate and an engine fuel consumption rate.

4. The exhaust gas purification apparatus according to claim 1, wherein the temperature sensor indirectly detects a catalyst temperature of the oxidation catalyst from an exhaust gas temperature upstream of the oxidation catalyst.

5. The exhaust emission control device according to claim 1, wherein the predetermined ratio is a ratio suitable for a reduction reaction of nitrogen oxides by the reduction catalyst.

[6] A reduction catalyst disposed in the engine exhaust pipe for reducing and purifying nitrogen oxides;

An oxidation catalyst that is disposed on one of the two branch pipes branched from the exhaust pipe located upstream of the reduction catalyst to oxidize nitrogen monoxide to nitrogen dioxide;

A flow rate control valve capable of controlling the exhaust flow rate divided into each branch pipe independently and in multiple stages; An exhaust flow sensor for detecting the volume flow of the exhaust;

An exhaust emission control device comprising:

7. The control unit according to claim 6, wherein the control unit controls the flow control valve with reference to a map in which control values corresponding to a volume flow rate of exhaust gas and a catalyst temperature of the oxidation catalyst are set. Exhaust purification equipment.

8. The exhaust emission control device according to claim 6, wherein the exhaust flow rate sensor indirectly detects a volume flow rate of exhaust gas from an intake mass flow rate and an engine fuel consumption rate.

9. The exhaust gas purification apparatus according to claim 6, wherein the temperature sensor indirectly detects the catalyst temperature of the oxidation catalyst from the exhaust gas temperature upstream of the oxidation catalyst.

10. The exhaust emission control device according to claim 6, wherein the predetermined ratio is a ratio suitable for a reduction reaction of nitrogen oxides by the reduction catalyst.

[11] A reduction catalyst disposed in the engine exhaust pipe for reducing and purifying nitrogen oxides;

Of the branch pipes branched into a plurality of exhaust pipes located upstream of the reduction catalyst, at least one of the branch pipes is disposed, and the monoacid-nitrogen is converted to diacid-nitrogen. A plurality of oxidation catalysts having different oxidation capacities, and

Based on the volume flow rate detected by the exhaust flow sensor and the catalyst temperature detected by the temperature sensor, the ratio of nitrogen monoxide and nitrogen dioxide in the exhaust gas introduced into the reduction catalyst becomes a predetermined ratio. A control unit that controls the flow control valve so as to approach, An exhaust emission control device comprising:

12. The control unit according to claim 11, wherein the control unit controls the flow control valve with reference to a map in which control values corresponding to a volume flow rate of exhaust gas and a catalyst temperature of the oxidation catalyst are set. Exhaust purification equipment.

13. The exhaust emission control device according to claim 11, wherein the exhaust flow rate sensor indirectly detects a volume flow rate of exhaust gas from a mass flow rate of intake air and a fuel consumption rate of the engine.

14. The exhaust gas purification apparatus according to claim 11, wherein the temperature sensor indirectly detects the catalyst temperature of the oxidation catalyst from the exhaust gas temperature upstream of the oxidation catalyst.

15. The exhaust emission control device according to claim 11, wherein the predetermined ratio is a ratio suitable for a reduction reaction of nitrogen oxides by the reduction catalyst.