WO2020262589A1

WO2020262589A1 - Stirring device

Info

Publication number: WO2020262589A1
Application number: PCT/JP2020/025154
Authority: WO
Inventors: 慶子柴田
Original assignee: いすゞ自動車株式会社
Priority date: 2019-06-28
Filing date: 2020-06-26
Publication date: 2020-12-30
Also published as: JP2021008821A

Abstract

A stirring device 10 according to the present invention is provided with a stirring unit 11 that is arranged between a urea water injection valve 2, which is arranged midway along an exhaust passage 1 where an exhaust gas G1 passes, and a selective reduction catalyst device 3. With respect to this stirring device 10, the stirring unit 11 comprises a porous body 15, which is capable of adsorbing the urea water, on a surface that faces the urea water injection valve 2.

Description

Stirrer

The present disclosure relates to a stirrer, and more particularly to a stirrer that suppresses the precipitation of white products caused by urea water.

As a stirrer, a mixer that promotes the diffusion of urea water injected from a urea water injection valve has been proposed (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2008-144644

By the way, if the amount of urea water injected from the urea water injection valve is large, the flow rate of the exhaust gas flowing through the exhaust passage is small, or the temperature of the exhaust gas is low, the urea water stirred by the mixer does not diffuse. It adheres to the exhaust passage and the selective reduction catalyst device in the form of liquid or droplets. From the adhered urea water, a white product in which urea, melamine, cyanuric acid, biuret and the like are solidified is precipitated.

When the white product is precipitated, the urea water is not hydrolyzed by that amount, and the amount of ammonia produced is reduced. Further, when the temperature of the exhaust gas rises and the precipitated white product is thermally decomposed, ammonia is produced. That is, the precipitation of this white product causes the amount of ammonia supplied to the selective reduction catalyst device to be too small or too large. As a result, there are problems that the reduction rate of nitrogen oxides in the selective reduction catalyst device decreases and the amount of ammonia passing through the selective reduction catalyst device increases.

An object of the present disclosure is to provide a stirring device that suppresses the precipitation of white products caused by urea water.

The stirrer of one aspect of the present disclosure that achieves the above object is the urea water injection valve arranged at the middle position of the exhaust passage through which the exhaust gas passes and the urea water injection valve arranged downstream of the flow of the exhaust gas. In a stirrer having a stirrer arranged between the selective reduction catalyst device and the stirrer, the stirrer has a porous body capable of adsorbing urea water on the surface facing the urea water injection valve. It is characterized by.

According to one aspect of the present disclosure, it is possible to adsorb liquid or droplet urea water that could not be hydrolyzed because the stirring portion has a porous body. This is advantageous in preventing the urea water from directly adhering to the exhaust passage and the selective reduction catalyst device, and the white product due to the urea water is deposited on the exhaust passage and the selective reduction catalyst device. It can be suppressed.

FIG. 1 is a block diagram illustrating the stirring device of the embodiment. FIG. 2 is a perspective view of the stirring portion of FIG. FIG. 3 is a cross-sectional view shown by arrow III in FIG. FIG. 4 is a cross-sectional view shown by an arrow IV in FIG. FIG. 5 is a flow chart illustrating a heating method in the stirring device of the embodiment.

The embodiment of the stirring device in the present disclosure will be described below. In the figure, the white arrow indicates the exhaust gas G1, the X direction is the direction from the upstream side to the downstream side with respect to the flow of the exhaust gas G1, and the Y direction is the direction opposite to the X direction. The alternate long and short dash line in the figure indicates a signal line.

As illustrated in FIGS. 1 and 2, the stirring device 10 of the present embodiment is arranged at an intermediate position of the exhaust passage 1 of an internal combustion engine mounted on a vehicle (not shown), and includes a stirring unit 11 and a dielectric heating unit 12. It is composed of.

The exhaust passage 1 is composed of a cylindrical pipe, and is a passage through which exhaust gas G1 discharged from a plurality of cylinders of an internal combustion engine (not shown) passes, and extends from a diverse exhaust pipe communicating with the plurality of cylinders to an outlet to the outside of the vehicle. It is a passage. A urea water injection valve 2 and a selective reduction catalyst device 3 are arranged in order in the X direction at an intermediate position of the exhaust passage 1. The urea water injection valve 2 is a device that injects urea water toward the inside of the exhaust passage 1. The selective reduction catalyst device 3 is configured by supporting a catalyst such as zeolite on a porous ceramic carrier, and contains ammonia generated by hydrolyzing the injected urea water by the heat of the exhaust gas G1 as a reducing agent in the exhaust gas G1. It is a device that selectively reduces and purifies the nitrogen oxides produced.

The position where the urea water injection valve 2 is arranged in the exhaust passage 1 is not limited to the downstream side with respect to the flow of the exhaust gas G1 with respect to the turbocharger (not shown), and may be the upstream side with respect to the exhaust gas pipe or the turbine of the turbocharger. The urea water injection valve 2 may be arranged on the upstream side of the charger, and the selective reduction catalyst device 3 may be arranged on the downstream side of the turbocharger. Further, examples of the devices arranged on the upstream side of the urea water injection valve 2 and the downstream side of the selective reduction catalyst device 3 with respect to the flow of the exhaust gas G1 include an oxidation catalyst device, a filter device, and an ammonia adsorption catalyst device 4 (not shown). However, it is not particularly limited. In addition, the urea water injection valve 2 may be inserted into the exhaust passage 1 and may be arranged in a space formed by recessing a part of the inner wall of the exhaust passage 1.

The stirring unit 11 is arranged inside the exhaust passage 1 between the urea water injection valve 2 and the selective reduction catalyst device 3, and the urea water injected from the urea water injection valve 2 collides with each other to stir the collided urea water. It is a device to do. The stirring unit 11 is preferably arranged in the vicinity of the urea water injection valve 2, and more preferably arranged at a position where the urea water droplets injected from the urea water injection valve 2 can collide.

In the urea water injection valve 2 of the present embodiment, the injection portion where the urea water is injected is opened toward the lower right side in the drawing, and the urea water is injected in the direction from the upper left to the lower right in the drawing. Urea. The jetted urea water has droplets of various particle sizes, and the droplets of urea water having a small particle size have a small inertial force and flow along the flow of the exhaust gas G1, so that they are easily diffused into the exhaust gas G1 and ammonia. Is easily hydrolyzed. On the other hand, since the droplets of urea water having a large particle size have a large inertial force, they are difficult to diffuse into the exhaust gas G1, and after being injected from the urea water injection valve 2, they go straight in a predetermined traveling direction. In the present embodiment, the position where the urea water droplets collide is on the path of the urea water droplets having a large particle size injected from the urea water injection valve 2.

An axial fan motor is exemplified as the stirring unit 11, but the configuration is not limited to the axial fan motor as long as it can stir the urea water flowing through the exhaust passage 1. For example, the stirring unit 11 may be a fixed straightening vane in which a large number of holes through which the exhaust gas can pass are formed in a plate facing the flow of the exhaust gas. However, the stirring unit 11 can improve the diffusivity of urea water by rotating like an axial fan motor, and can uniformly mix the volatilized urea.

The stirring unit 11 of the present embodiment has a propeller fan 13 composed of a plurality of blades 14 and a porous body 15. The propeller fan 13 may have a plurality of blades 14 arranged at intervals in the pipe circumferential direction of the exhaust passage 1 so as to rotate in the pipe circumferential direction, and the hub or casing having a built-in drive motor may be used. The description will be omitted. The propeller fan 13 is preferably configured so that the exhaust gas G1 can be blown in the direction in which the exhaust gas G1 flows.

The porous body 15 is arranged on each of the surfaces of the plurality of blades 14 facing the urea water injection valve 2. The surface of the blade 14 facing the urea water injection valve 2 is a surface facing the upstream side with respect to the flow of the exhaust gas G1 and a surface facing the Y direction. The porous body 15 is not limited to the blade 14, and may be arranged on a surface of the hub or casing facing the Y direction. The porous body 15 may be arranged on a part of a plurality of blades 14 of the propeller fan 13, but it is preferable that the porous body 15 is arranged on all of the plurality of blades 14.

The porous body 15 is a member capable of adsorbing urea water, and it is desirable that the porous body 15 is a metal porous body capable of physically adsorbing urea water. The physical adsorption is a phenomenon in which droplets of urea water are adsorbed on the pores of the porous body 15 by van der Waals force, which is a phenomenon different from chemisorption. The porous body 15 may be made of a material that can withstand the temperature reached by the exhaust gas G1 passing through the stirring unit 11. The porous body 15 is preferably made of a metal having excellent heat resistance. In addition, as the metal porous body, those having a large number (innumerable) pores on the surface and inside due to sintering of metal powder, compression or lamination of metal cloth, or dissolution of gas in molten metal. Illustrated.

The porous body 15 of the present embodiment is composed of a metal cloth 17 formed by entwining metal fibers 16. The porous body 15 may be composed of one metal cloth 17, but it is desirable that the porous body 15 is formed by laminating a plurality of metal cloths 17 in the direction in which the exhaust gas G1 flows. By forming the porous body 15 with a plurality of metal cloths 17, the porous body 15 can have pores of various sizes.

Stainless steel is exemplified as the metal fiber 16. Examples of the metal cloth 17 are woven fabrics, knitted fabrics, and non-woven fabrics in which metal fibers 16 are entangled, but it is desirable that the metal cloth 17 is made of a non-woven fabric having non-uniform and complicated pores.

As illustrated in FIG. 3, it is desirable that the size of the pores of the porous body 15 becomes smaller in the X direction, and the porous body 15 formed by laminating the metal cloth 17 is a metal arranged on the downstream side. It is desirable that the size of the pores in the cloth 17 is smaller than the size of the pores in the metal cloth 17 arranged on the upstream side. In the present disclosure, the size of the pores of the porous body 15 is an average value of the sizes of a large number of pores existing in each of the layers. The minimum size of the pores of the porous body 15 is preferably set to about the particle size of droplets of urea water that are easily diffused into the exhaust gas G1 and easily hydrolyzed to ammonia, and the maximum size is It is preferable to set the particle size of the urea water droplets injected from the urea water injection valve 2 to about the maximum value.

The size of the pores in the metal cloth 17 becomes smaller as the constituent metal fibers 16 become denser. Therefore, in the porous body 15 made of the metal cloth 17, it is desirable that the metal fibers 16 become denser in the X direction, and it is more desirable that the metal fibers 16 become denser in order in the X direction.

The number of laminated metal cloths 17 in the porous body 15 is not particularly limited. The metal cloth 17 is preferably made of a non-woven fabric having non-uniform pores and complicated pores, but when a plurality of metal cloths 17 are laminated, not all the metal cloths 17 need to be made of the non-woven fabric, and the knitted fabric And a non-woven fabric may be used in combination.

When urea water is injected from the urea water injection valve 2 when the temperature of the exhaust gas G1 is low, the urea water having a small particle size diffuses and is hydrolyzed in the exhaust gas G1. On the other hand, urea water having a large particle size travels straight in the injection direction due to inertial force and collides with the stirring unit 11. The urea water that collides with the stirring unit 11 is adsorbed on the porous body 15. At this time, droplets of urea water having a large particle size are adsorbed on the metal cloth 17 having relatively large pores, and urea water having a small particle size passing through the metal cloth 17 is adsorbed on the metal cloth 17 having small pores. Will be done.

When the particle size of the urea water droplets is smaller than the pores of the porous body 15, the urea water droplets are separated from the porous body 15 and diffused into the exhaust gas G1 to be hydrolyzed. That is, the droplets of urea water having a particle size larger than the pores are not separated from the porous body 15 and the adsorption is maintained.

In this way, since the stirring unit 11 has the porous body 15, it is possible to adsorb liquid or droplet-shaped urea water that is difficult to hydrolyze. This is advantageous in preventing the urea water from directly adhering to the exhaust passage 1 and the selective reduction catalyst device 3, and white products caused by the urea water are formed in the exhaust passage 1 and the selective reduction catalyst device 3. Precipitation can be suppressed.

As illustrated in FIGS. 1 and 4, the dielectric heating unit 12 is a radio wave absorber 18 arranged inside the exhaust passage 1 between the urea water injection valve 2 and the selective reduction catalyst device 3, and the exhaust passage 1. It is a device that has a radio wave oscillator 19 arranged outside and heats the stirring unit 11 by dielectric heating. The heating target of the dielectric heating unit 12 may be a part of the stirring unit 11, and the heating target of the dielectric heating unit 12 of the present embodiment is the porous body 15 of the stirring unit 11.

The radio wave absorber 18 is arranged at the outer edge of the stirring unit 11 when viewed in the X direction. In the present disclosure, the outer edge portion of the stirring portion 11 is the outer edge portion of the portion for stirring urea water, and is not the casing but the tip end portion of the blade 14 of the propeller fan 13 in the present embodiment.

It is desirable that the radio wave absorber 18 is arranged at each of the tip portions of the plurality of blades 14 of the propeller fan 13 so as to be able to transfer heat to the outer edge portion of the porous body 15 when viewed in the X direction. The radio wave absorber 18 does not have to be installed on the blade 14 in which the porous body 15 is not installed among the plurality of blades 14.

Examples of the radio wave absorber 18 include a resistance absorbing material, a dielectric absorbing material, and a magnetic absorbing material. The radio wave absorber 18 is preferably one that can withstand the temperature reached by the exhaust gas G1, and more preferably a resistant absorbing material or a magnetic absorbing material made of a metal material.

Since the radio wave absorber 18 is arranged at the tip of the blade 14, the porous body 15 of the present embodiment has a portion of the entire surface of the blade 14 facing the urea water injection valve 2 excluding the tip. It shall cover.

The radio wave oscillator 19 is a device that is arranged outside the exhaust passage 1 and oscillates radio waves toward the radio wave absorber 18 arranged inside the exhaust passage 1, and examples thereof include a magnetron, a klystron, and a traveling wave tube. To. It is desirable that a plurality of radio wave oscillators 19 are arranged outside the exhaust passage 1 at intervals when viewed in the X direction.

It is desirable that the radio wave oscillated by the radio wave oscillator 19 is a microwave, and the dielectric heating unit 12 is preferably configured to heat at least a part of the stirring unit 11 by microwave heating.

The radio wave oscillator 19 is electrically connected to a control device 21 electrically connected to the temperature acquisition device 20, and the control device 21 controls the oscillation of radio waves based on the temperature Tx acquired by the temperature acquisition device 20. ..

The temperature acquisition device 20 is a temperature sensor that acquires the temperature Tx of the exhaust gas G1 passing through the selective reduction catalyst device 3. It is desirable that the temperature acquisition device 20 is arranged on the upstream side of the selective reduction catalyst device 3 with respect to the flow of the exhaust gas G1, and it is more desirable that the temperature acquisition device 20 is arranged in the vicinity of the urea water injection valve 2.

The control device 21 is hardware composed of a central processing unit (CPU) that performs various information processing, an internal storage device that can read and write programs and information processing results used for performing various information processing, and various interfaces. Is. The control device 21 may be composed of a dosing control unit that controls the injection of urea water from the urea water injection valve 2.

The control device 21 has a heating determination unit 22 and a heating control unit 23 as functional elements. Each functional element is stored as a program in the internal storage device, and is executed by the central processing unit in a timely manner. In addition to the program, each functional element may be composed of a programmable controller (PLC) or an electric circuit in which each functions independently.

The heating determination unit 22 inputs the temperature Tx of the exhaust gas G1 acquired by the temperature acquisition device 20 and determines whether or not the temperature Tx falls within the range of the preset lower limit value Ta or more and the upper limit value Tb or less. It is a functional element that outputs the determined result to the heating control unit 23.

The heating control unit 23 is a functional element that controls the radio wave oscillator 19 to oscillate radio waves when the determination result of the heating determination unit 22 is input and the temperature Tx falls within a preset range.

The range of the lower limit value Ta or more and the upper limit value Tb or less is a temperature range set in advance by experiments and tests, and is on the low temperature side of the temperature range in which urea water injection is permitted from the urea water injection valve 2. Set to range. The temperature range in which the injection of urea water is permitted from the urea water injection valve 2 here means that the urea water can be hydrolyzed to ammonia, and the selective reduction catalyst device 3 uses ammonia as a reducing agent to use nitrogen oxides. It is a reducibly activated temperature range. Further, the range on the low temperature side of the temperature range is a range in which the reaction rate of hydrolysis from urea water to ammonia is slower than the range on the high temperature side of the temperature range.

As illustrated in FIG. 5, the heating method of the stirring device 10 is a method that is repeatedly performed at predetermined cycles during the operation of an internal combustion engine (not shown). In the present disclosure, the predetermined cycle is a cycle in which the temperature acquisition device 20 acquires the temperature Tx. The passage of one cycle in the flow chart is indicated by "return".

When the operation of the internal combustion engine is started, the temperature acquisition device 20 acquires the temperature Tx (S110). Then, the heating determination unit 22 determines whether or not the acquired temperature Tx is equal to or higher than the lower limit value Ta (S120). When the lower limit value Ta is set to the temperature at which the injection of urea water is started from the urea water injection valve 2, this step is not a comparison between the temperature Tx and the lower limit value Ta, but a step of determining the presence or absence of injection of urea water. May be.

Then, when it is determined that the temperature Tx is equal to or higher than the lower limit value Ta (S120: YES), the heating determination unit 22 determines whether or not the acquired temperature Tx is equal to or lower than the upper limit value Tb (S130). On the other hand, when it is determined that the temperature Tx is lower than the lower limit value Ta (S120: NO), the process returns to the start.

Then, when it is determined that the temperature Tx is equal to or less than the upper limit value Tb (S130: YES), the heating control unit 23 issues a command to the radio wave oscillator 19, oscillates the radio wave (S140), and returns to the start. On the other hand, when it is determined that the temperature Tx exceeds the upper limit value Tb (S130: NO), the heating control unit 23 stops the oscillation of the radio wave of the radio wave oscillator 19 (S150) and returns to the start.

When the radio wave oscillator 19 oscillates a radio wave, the radio wave absorber 18 absorbs the oscillated radio wave and generates heat. Then, the heat generated in the radio wave absorber 18 is transferred to the porous body 15 to heat the urea water adsorbed on the porous body 15. The heated urea water droplets volatilize, desorb from the porous body 15, diffuse into the exhaust gas G1, and are hydrolyzed.

In this way, by dielectrically heating the stirring unit 11 by the dielectric heating unit 12, it is possible to volatilize the urea water that could not be volatilized at the temperature Tx of the exhaust gas G1. This is advantageous in preventing the urea water from directly adhering to the exhaust passage 1 and the selective reduction catalyst device 3, and white products caused by the urea water are formed in the exhaust passage 1 and the selective reduction catalyst device 3. Precipitation can be suppressed.

The dielectric heating unit 12 heats the stirring unit 11 by dielectric heating. Dielectric heating is superior to induction heating in terms of uniform heating, rapid heating, and selective heating. That is, the dielectric heating unit 12 is advantageous in avoiding the heating delay by rapidly heating the temperature Tx of the exhaust gas G1 which changes from moment to moment. Further, the dielectric heating unit 12 is advantageous for heating only the stirring unit 11 by selective heating.

In the above-described embodiment, the stirring device 10 includes both the stirring unit 11 having the porous body 15 and the dielectric heating unit 12, but the stirring device 10 does not have the dielectric heating unit 12 and has the porous body 15. The stirring unit 11 may be composed of only the stirring unit 11, and the stirring device 10 may be composed of the stirring unit 11 and the dielectric heating unit 12 which do not have the porous body 15.

As described above, since the stirring unit 11 has the porous body 15, the stirring device 10 can adsorb liquid or droplet urea water that could not be hydrolyzed. Further, the stirring device 10 can volatilize urea water that could not be volatilized at the temperature Tx of the exhaust gas G1 by dielectrically heating the stirring unit 11 by the dielectric heating unit 12.

On the other hand, the stirring device 10 including both the stirring unit 11 having the porous body 15 and the dielectric heating unit 12 adsorbs the liquid or droplet-shaped urea water that could not be hydrolyzed by the porous body 15. Then, when the stirring device 10 cannot volatilize the adsorbed urea water at the temperature Tx of the exhaust gas G1, the adsorbed urea water can be volatilized by dielectrically heating the stirring unit 11 by the dielectric heating unit 12.

As described above, according to the stirring device 10 including both the stirring unit 11 having the porous body 15 and the dielectric heating unit 12, the urea water is selectively used in the exhaust passage and as compared with the stirring device not provided with either one. It is advantageous to prevent direct adhesion to the reduction catalyst device, and it is possible to suppress precipitation of white products due to urea water in the exhaust passage and the selective reduction catalyst device.

The amount of urea water that can be adsorbed by the porous body 15 of the stirrer 10 is set in advance by experiments and tests, and when urea water cannot be volatilized at the temperature Tx of the exhaust gas G1, urea is injected from the urea water injection valve 2. The amount of water jetted may be such that urea water does not scatter from the porous body 15.

Further, the porous body 15 may be installed at the bottom of the exhaust passage 1 on the upstream side of the selective reduction catalyst device 3 on the downstream side of the stirring unit 11 with respect to the flow of the exhaust gas G1. The bottom portion of the exhaust passage 1 here is a place where liquid or droplet urea water easily adheres. The place where the porous body 15 is installed in the exhaust passage 1 is preferably in the vicinity of the stirring unit 11. Further, it is desirable that the size of the pores of the porous body 15 installed in the exhaust passage 1 decreases from the center of the pipe toward the outside in the pipe radial direction.

A radio wave absorber 18 that abuts on the porous body 15 installed in the exhaust passage 1 may be provided, and a radio wave oscillator 19 that oscillates a radio wave toward the radio wave absorber 18 may be provided.

In the above-described embodiment, the radio wave absorber 18 is arranged at the tip of the blade 14, and the porous body 15 is removed from the entire surface of the blade 14 facing the urea water injection valve 2. Although the configuration in which the portion is arranged so as to cover the portion is illustrated, the porous body 15 may be arranged on the surface of the radio wave absorber 18 facing the urea water injection valve 2.

This application is based on a Japanese patent application (Japanese Patent Application No. 2019-121555) filed on June 28, 2019, the contents of which are incorporated herein by reference.

The stirring device according to the present disclosure is useful in that it can suppress the precipitation of white products caused by urea water in the exhaust passage and the selective reduction catalyst device.

1 Exhaust passage 2 Urea water injection valve 3 Selective reduction catalyst device 10 Stirrer 11 Stirrer 15 Porous body

Claims

A stirring unit arranged between the urea water injection valve arranged in the middle of the exhaust passage through which the exhaust gas passes and the selective reduction catalyst device arranged on the downstream side with respect to the flow of the exhaust gas from the urea water injection valve. A stirring device provided, wherein the stirring unit has a porous body capable of adsorbing urea water on a surface facing the urea water injection valve.
The stirring device according to claim 1, wherein the porous body is made of a metal cloth in which metal fibers are entangled.
The stirring device according to claim 2, wherein the porous body is formed by laminating a plurality of the metal cloths in a direction in which exhaust gas flows.
The stirring device according to any one of claims 1 to 3, wherein the size of the pores of the porous body decreases from the upstream side to the downstream side with respect to the flow of exhaust gas.
The porous body is provided with a dielectric heating unit having a radio wave absorber abutting on an outer edge portion of the porous body and a radio wave oscillator arranged outside the exhaust passage when viewed in the direction of flow of exhaust gas, and the porous body is the radio wave oscillator. The stirring device according to any one of claims 1 to 4, which is heated by heat transfer from the radio wave absorber that has absorbed radio waves output from.