JP2004308549A - Emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an emission control device promoting atomization or vaporization of an added fuel, while suppressing influence of exhaust gas on an air-fuel ratio. <P>SOLUTION: The emission control device 20 for an internal combustion engine, comprises: an exhaust gas emission control means 12 disposed in an exhaust gas passage 6; a fuel addition means 24 adding the fuel to the exhaust gas passage 6 at an upstream side of the exhaust gas emission control means 12 and pressurized exhaust gas supply means 15, 16, 18, 21, 22, 24 for taking out a part of the exhaust gas from the exhaust gas passage 6 and pressurizing the exhaust gas to generate pressurized exhaust gas, and for supplying the pressurized exhaust gas to an upstream side of the exhaust gas emission control means 12 of the exhaust gas passage 6, together with the fuel added by the fuel addition means 24. Since an amount of oxygen in the exhaust gas is lesser than that in the air, the atomization of the added fuel can be promoted, while suppressing the influence of the exhaust gas flowing through the exhaust gas emission control means 12 on the air-fuel ratio. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust purification device that purifies exhaust gas of an internal combustion engine.
[0002]
[Prior art]
2. Description of the Related Art Generally, in a direct injection type internal combustion engine mounted on an automobile or the like, for example, a diesel engine, it is required to remove nitrogen oxides (NOx) contained in exhaust gas. In response to such demands, there has been proposed an exhaust gas purifying apparatus in which a NOx occluding agent is disposed in an exhaust gas passage of an internal combustion engine.
[0003]
The NOx storage agent used in such an exhaust gas purification device stores NOx when the air-fuel ratio of the exhaust gas is lean, reduces the air-fuel ratio in the exhaust gas, and reduces the reducing agent such as HC or CO in the exhaust gas. Has the effect of releasing stored NOx and purifying it by reduction (storage and desorption of NOx and reduction purifying action). By utilizing this effect, when the air-fuel ratio of the exhaust gas is lean, NOx in the exhaust gas is stored in the NOx storage agent, and when the storage efficiency of the NOx storage agent has been reduced for a certain period of time or before the storage efficiency has decreased. By performing control to temporarily make the air-fuel ratio of the exhaust gas flowing into the NOx storage agent rich (hereinafter, this control is referred to as rich spike control), the NOx stored in the NOx storage agent is released and reduced and purified. ing.
[0004]
In this specification, the term "occlusion" is used to include both "absorption" and "adsorption". Therefore, the “NOx storage agent” includes both the “NOx absorber” and the “NOx adsorbent”, the former accumulating NOx in the form of nitrate or the like, and the latter storing NOx.₂Adsorb in the form of Further, the term “release” from the NOx storage agent is used to include the meaning of “release” corresponding to “adsorption” in addition to “release” corresponding to “absorption”.
[0005]
By the way, the fuel of the internal combustion engine sometimes contains a sulfur (S) component, and in this case, sulfur oxides (SOx) are contained in the exhaust gas. If SOx is present in the exhaust gas, the NOx storage agent stores SOx in the exhaust gas by exactly the same mechanism as that of storing NOx.
[0006]
However, SOx stored in the NOx storage agent is relatively stable, and generally tends to be easily stored in the NOx storage agent. When the SOx storage amount of the NOx storage agent increases, the NOx storage capacity of the NOx storage agent decreases, and it becomes impossible to sufficiently remove NOx in the exhaust gas. (S poisoning) problem occurs. In particular, this problem of sulfur poisoning is likely to occur in diesel engines that use light oil containing relatively large amounts of sulfur components as fuel.
[0007]
On the other hand, it is known that SOx stored in the NOx storage agent can be released by the same mechanism as NOx. Therefore, the rich spike control described above is also performed in this case. However, since SOx is stored in the NOx storage agent in a relatively stable form, even if rich spike control is performed at a temperature at which normal NOx desorption and reduction purification is performed (for example, about 250 ° C. or higher), the NOx storage agent can be stored in the NOx storage agent. It is difficult to release the stored SOx. Therefore, in order to eliminate sulfur poisoning (that is, perform sulfur poisoning regeneration), the NOx occluding agent is heated to a higher temperature than during normal NOx desorption and reduction purification, that is, a sulfur release temperature (for example, 600 ° C. or higher). ) To perform rich spike control.
[0008]
As described above, in the exhaust emission control device using the NOx storage agent as described above, in the control for purifying the NOx storage agent (release and reduction of NOx, regeneration of sulfur poisoning, etc.), rich spike control or NOx storage In some cases, rich spike control by raising the temperature of the agent (hereinafter, collectively referred to simply as "rich spike control") is performed. As a method of performing the rich spike control, a method of adding a fuel (light oil) into an exhaust gas passage on the upstream side of the NOx storage agent is known.
[0009]
However, this method has a problem that light oil as a fuel to be added is difficult to atomize and vaporize, and a large amount of NOx occluding agent adheres to an upstream portion. That is, fuel (light oil) is not supplied to the entire NOx storage agent, and as a result, purification (reduction and reduction of NOx, regeneration of sulfur poisoning, etc.) may be insufficient. On the other hand, if the fuel is to be supplied to the downstream side of the NOx storage agent, the added amount of the fuel increases and the fuel efficiency deteriorates, and the added fuel may be discharged to the outside to generate white smoke. is there.
[0010]
With respect to such a problem, Patent Literature 1 discloses a method of promoting atomization of fuel by spraying a fuel (light oil) using a part of supercharged air. There is also known a method of providing an air compressor and spraying fuel using compressed air supplied by the compressor to promote atomization of the fuel.
[0011]
[Patent Document 1]
JP-A-8-2000047
[Patent Document 2]
JP-A-2002-70600
[Patent Document 3]
JP-A-6-28218
[Patent Document 4]
JP-A-6-93842
[Patent Document 5]
JP-A-2000-110552
[0012]
[Problems to be solved by the invention]
However, in the atomization accelerating method using these air, although the atomization accelerating effect is obtained, the air-fuel ratio of the exhaust gas is greatly affected by the air supplied together with the fuel, and the air-fuel ratio of the exhaust gas is enriched. (Performing rich spike control) becomes more difficult. This is because the amount of air required for achieving the target rich air-fuel ratio increases because the amount of air in the exhaust gas increases due to the air supplied together with the fuel to promote atomization. Therefore, if the rich spike control is performed while promoting the atomization using the air, the fuel efficiency is deteriorated.
[0013]
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an exhaust gas purification apparatus that may add fuel into an exhaust gas passage on an upstream side of exhaust gas purification means such as a NOx storage agent. It is another object of the present invention to provide an exhaust gas purifying apparatus capable of promoting atomization or vaporization of added fuel while suppressing the influence of exhaust gas on the air-fuel ratio.
[0014]
[Means for Solving the Problems]
The present invention provides an exhaust emission control device described in each claim as means for solving the above problems.
According to a first aspect of the present invention, there is provided an exhaust gas purifying means disposed in an exhaust gas passage, a fuel adding means for adding fuel to the exhaust gas passage upstream of the exhaust gas purifying means, and A part is taken out and pressurized to generate pressurized exhaust gas, and the pressurized exhaust gas is supplied to the exhaust gas passage upstream of the exhaust gas purifying means together with the fuel added by the fuel adding means. An exhaust gas purification device for an internal combustion engine, comprising: exhaust gas supply means.
[0015]
When fuel is added into the exhaust gas passage on the upstream side of the exhaust gas purifying means, if the added fuel is difficult to atomize and vaporize, the added fuel adheres to the upstream portion of the exhaust gas purifying means and the exhaust gas is exhausted. In some cases, it is not supplied to the entire purification means and the intended purpose cannot be sufficiently achieved. In such a case, if air is supplied together with the added fuel to promote atomization of the fuel, the amount of fuel required to achieve the target exhaust gas air-fuel ratio increases, and the fuel efficiency deteriorates. .
[0016]
On the other hand, according to the first aspect, the pressurized exhaust gas is supplied together with the fuel added by the fuel adding means. Since the amount of oxygen in the exhaust gas is smaller than that in the air, according to the first invention, atomization of the added fuel while suppressing the effect of the exhaust gas flowing through the exhaust gas purifying means on the air-fuel ratio is suppressed. Can be promoted. Further, if the temperature of the supplied compressed exhaust gas is high, there is also an effect of promoting the vaporization of the added fuel. Thus, rich spike control can be performed by, for example, promoting the atomization or vaporization of the added fuel while suppressing the deterioration of fuel efficiency. In this case, the fuel is supplied to the entire exhaust gas purifying means or a wider range of the exhaust gas purifying means due to the promotion of atomization or vaporization. As a result, the purpose of the rich spike control (for example, And purifying the exhaust gas purifying means (performing NOx emission reduction, sulfur poisoning regeneration, etc.) and the like can be sufficiently achieved.
[0017]
In a second aspect based on the first aspect, the pressurized exhaust gas supply means suctions and pressurizes exhaust gas through an exhaust gas outlet provided in the exhaust gas passage, and pressurizes the exhaust gas. Pressurized exhaust gas storage means for storing the pressurized exhaust gas, and pressurized exhaust gas supply for controlling a method of supplying the pressurized exhaust gas stored in the pressurized exhaust gas storage means to the exhaust gas passage Method control means.
According to the second aspect, the same functions and effects as those of the first aspect can be obtained with a relatively simple configuration. In particular, since the pressurized exhaust gas is stored, the pressurized exhaust gas can be supplied with good responsiveness.
[0018]
In a third aspect based on the second aspect, the exhaust gas outlet is provided downstream of the exhaust gas purifying means.
According to the third aspect, a part of the exhaust gas purified by the exhaust gas purifying means is supplied again to the upstream side of the exhaust gas purifying means, so that emission can be improved. Further, since the exhaust gas introduced into the pressurized exhaust gas supply means is purified by the exhaust gas purification means, the occurrence of clogging or the like in each component constituting the pressurized exhaust gas supply means is reduced. There is also the effect of doing.
[0019]
According to a fourth aspect of the present invention, in the second or third aspect, when the fuel addition by the fuel adding means is performed by intermittently injecting the fuel a plurality of times, the supply of the pressurized exhaust gas is changed to the first fuel. The control is performed by the pressurized exhaust gas supply method control means so as to continue from the time when the injection is started to the time when the last fuel injection is completed.
According to the fourth invention, the atomization or vaporization of the added fuel can be surely promoted by the simplified control while suppressing the influence of the exhaust gas on the air-fuel ratio.
[0020]
In a fifth aspect based on the second or third aspect, the pressurized exhaust gas supply method control means controls a supply timing of the pressurized exhaust gas, and the supply timing is controlled by the fuel addition means for adding fuel. Is synchronized with the timing of the fuel injection.
According to the fifth aspect, the pressurized exhaust gas can be used without waste, and the atomization or vaporization of the added fuel can be promoted while suppressing the effect of the exhaust gas on the air-fuel ratio.
[0021]
According to a sixth aspect of the present invention, in any one of the first to fifth aspects of the present invention, there is further provided a flow control means for controlling a flow rate of the exhaust gas flowing through the exhaust gas purifying means, and When fuel is added to the passage, the flow rate control means reduces the flow rate of the exhaust gas flowing through the exhaust gas purifying means, and the pressurized exhaust gas is mixed with the fuel added by the fuel adding means together with the exhaust gas. The gas is supplied to the passage upstream of the exhaust gas purifying means.
[0022]
If the flow rate of the exhaust gas flowing through the exhaust gas purifying means can be controlled, the amount of fuel required to achieve the target exhaust gas air-fuel ratio is reduced by reducing the flow rate of the exhaust gas and adding fuel. Therefore, deterioration of fuel efficiency can be suppressed. However, in this case, it is considered that it becomes more difficult to sufficiently atomize the added fuel because the flow rate of the exhaust gas decreases. As a result, it is considered that it becomes difficult to supply the additional fuel to the entire exhaust gas purifying means.
[0023]
According to the sixth aspect of the present invention, when the fuel is added by reducing the flow rate of the exhaust gas flowing through the exhaust gas purifying means, the pressurized exhaust gas and the fuel may be exhausted from the exhaust gas passage through the exhaust gas passage. It is supplied upstream of the gas purification means. By doing so, the pressurized exhaust gas promotes atomization or vaporization of the fuel, and the dispersibility of the fuel can be improved. As a result, the added fuel can be supplied to the entire exhaust gas purifying means or a wider range of the exhaust gas purifying means.
[0024]
In a seventh aspect based on any one of the first to sixth aspects, the exhaust gas purifying means includes a NOx storage agent, and when the NOx or SOx stored in the NOx storage agent is released, the exhaust gas purifying means includes: Is supplied to the exhaust gas passage upstream of the exhaust gas purifying means together with the fuel added by the fuel adding means.
[0025]
According to the seventh aspect, rich spike control can be performed by promoting atomization or vaporization of the added fuel while suppressing deterioration of fuel efficiency. In this case, the fuel is supplied to the entire exhaust gas purifying means including the NOx occluding agent or to a wider range of the exhaust gas purifying means due to the promotion of atomization or vaporization. The NOx release reduction or sulfur poisoning regeneration of the occluding agent can be sufficiently performed.
[0026]
In an eighth aspect based on any of the first to seventh aspects, the pressurized exhaust gas supply means has an oxygen concentration reducing means for reducing the oxygen concentration of the exhaust gas taken out from the exhaust gas passage. .
According to the eighth aspect, since the pressurized exhaust gas having a reduced oxygen concentration is generated, the influence of the exhaust gas flowing through the exhaust gas purifying means on the air-fuel ratio can be further suppressed and the mist of the added fuel can be reduced. Gasification or vaporization can be promoted. Thus, for example, rich spike control can be performed by further promoting atomization or vaporization of the added fuel while further suppressing deterioration in fuel efficiency.
[0027]
In a ninth aspect based on the eighth aspect, in the eighth aspect, the oxygen concentration reducing means includes an oxidation catalyst arranged in a passage through which the exhaust gas taken out from the exhaust gas passage passes, and adding the fuel upstream of the oxidation catalyst. And a fuel adding means different from the fuel adding means.
The fuel in the exhaust gas extracted from the exhaust gas passage is consumed by adding fuel from the fuel adding device different from the fuel adding device and reacting in the oxidation catalyst, and the exhaust gas extracted from the exhaust gas passage is used. Oxygen concentration can be reduced. That is, according to the ninth aspect, the above-mentioned oxygen concentration reducing means can be constituted relatively easily, and the same operation and effect as the eighth aspect can be obtained.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention can be carried out using either a NOx absorbent or a NOx adsorbent, which is a NOx storage agent. Hereinafter, a case using a NOx absorbent will be described. In each drawing, the same or similar components are denoted by common reference numerals.
[0029]
FIG. 1 shows a case where the present invention is applied to a diesel engine. The present invention can be applied to other types of internal combustion engines such as gasoline engines.
In FIG. 1, reference numeral 2 denotes an engine body, 4 denotes an intake passage, and 6 denotes an exhaust gas passage. The exhaust gas passage 6 is provided with the exhaust gas purification device 10 of the present invention. The exhaust gas purification device 10 installed in this portion will be described in detail later with the exhaust gas purification devices 20, 30, and 40 having three different configurations. I do.
[0030]
The electronic control unit (ECU) 8 is a known type of digital computer in which a CPU (central processing unit), a RAM (random access memory), a ROM (read only memory), and an input / output port are connected by a bidirectional bus. In addition to performing basic control of the engine such as fuel injection amount control by exchanging signals with the main body 2, in each embodiment of the present invention, as will be described below, exchanging signals with each component of the exhaust gas purifying apparatus, and Control is also performed.
[0031]
FIG. 2 is a diagram showing an exhaust gas purification device 20 that is installed in a portion of the exhaust gas purification device 10 shown in FIG. 1 and forms a part of the exhaust gas passage 6. As shown in FIG. 2, the exhaust gas purification device 20 includes a filter 14 disposed in the exhaust gas passage 6, and the filter 14 has a function of removing exhaust particulates in the exhaust gas. The NOx absorbent 12 is carried on the filter 14 as described later, and constitutes an exhaust gas purifying means.
[0032]
A nozzle 24 for adding fuel (light oil) to the exhaust gas passage 6 at the time of purification control of the NOx absorbent 12 and the like is provided upstream of the filter 14 carrying the NOx absorbent 12. . The nozzle 24 is configured to be able to supply a pressurized exhaust gas described later together with the added fuel in order to promote atomization or vaporization of the added fuel. The nozzle 24 may have a configuration such as a known two-fluid nozzle or an air assist nozzle, for example. The fuel addition method, that is, the amount of added fuel, the addition timing (injection timing), and the like are adjusted by controlling the operation of the nozzle 24 by the ECU 8.
[0033]
An exhaust gas outlet 15 for extracting a part of the exhaust gas from the exhaust gas passage 6 is provided downstream of the filter 14 carrying the NOx absorbent 12, and a pump or a pump connected to the outlet 15 is provided. Exhaust gas is sucked through the outlet 15 and pressurized by a compressor (hereinafter simply referred to as “pump”) 16. The pump 16 is controlled by the ECU 8.
[0034]
Exhaust gas sucked and pressurized by the pump 16 is sent to the tank 21 and stored as pressurized exhaust gas. In the embodiment shown in FIG. 1, a check valve 18 for preventing a backflow from the tank 21 is provided in a pressurized exhaust gas passage between the pump 16 and the tank 21.
The pressurized exhaust gas stored in the tank 21 is sent to the above-described nozzle 24 and supplied to the exhaust gas passage 6 together with the added fuel. The amount and supply timing are adjusted by controlling the operation of the control valve 22 provided between the tank 21 and the nozzle 24 by the ECU 8. Note that control means corresponding to the control valve 22 may be incorporated in the nozzle 24, and the ECU 8 may control the nozzle 24 to control both the fuel addition method and the pressurized exhaust gas supply method.
[0035]
FIG. 3 shows an enlarged sectional view of the filter 14. Referring to FIG. 3, the filter 14 is made of a porous ceramic, and the exhaust gas flows from left to right in the figure as indicated by arrows. In the filter 14, first passages 38 having the plugs 34 provided on the upstream side and second passages 44 having the plugs 42 provided on the downstream side are alternately arranged to form a honeycomb shape. When the exhaust gas flows from left to right in the figure, the exhaust gas flows through the porous ceramic partition from the second passage 44, flows into the first passage 38, and flows downstream. At this time, the exhaust particulates (particulates) in the exhaust gas are collected by the porous ceramic and removed from the exhaust gas, thereby preventing the exhaust particulates from being released into the atmosphere.
[0036]
The NOx absorbent 12 is carried on the surfaces of the partition walls of the first passage 38 and the second passage 44 and in the pores inside. The NOx absorbent 12 is at least selected from alkali metals such as potassium K, sodium Na, lithium Li, cesium Cs, alkaline earths such as barium Ba and calcium Ca, lanthanum La, and rare earths such as yttrium Y. One consists of a noble metal such as platinum Pt. The NOx absorbent 12 absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and releases the absorbed NOx if the air-fuel ratio of the NOx absorbent inflowing exhaust gas decreases and the reducing agent is present, thereby reducing the NOx. It has a purifying action (NOx absorption / release and reduction purifying action).
[0037]
Since a diesel engine is used in the configuration shown in FIG. 1, the exhaust gas air-fuel ratio in the normal state is lean, and the NOx absorbent 12 absorbs NOx in the exhaust gas in the normal state. Then, when the NOx absorption efficiency of the NOx absorbent 12 decreases for a certain period of time, it becomes necessary to release and reduce NOx from the NOx absorbent 12. In the exhaust gas purifying apparatus 20, when it is necessary to release NOx from the NOx absorbent 12 and reduce and purify the exhaust gas, the exhaust gas passage on the upstream side of the NOx absorbent 12 (filter 14) from the nozzle 24 is required. 6, rich spike control is performed by supplying fuel (light oil) to the NOx absorbent 12, so that the NOx absorbed by the NOx absorbent 12 is released and the released NOx is reduced and purified.
[0038]
Although the detailed mechanism of the absorption / release and reduction / purification is not clear, it is considered that the absorption / release and reduction / purification are performed by the mechanism shown in FIG. Next, this mechanism will be described by taking as an example a case where platinum Pt and barium Ba are supported, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths, and rare earths.
[0039]
That is, when the air-fuel ratio of the exhaust gas flowing into the NOx absorbent becomes considerably lean, the oxygen concentration in the exhaust gas flowing into the NOx absorbent greatly increases, and as shown in FIG.₂Is O₂ ⁻Or O^2-On the surface of platinum Pt. On the other hand, NO in the exhaust gas flowing into the NOx absorbent becomes O 2 on the surface of the platinum Pt.₂ ⁻Or O^2-Reacts with NO₂(2NO + O₂→ 2NO₂). NO generated next₂Is absorbed in the NOx absorbent 12 while being further oxidized on the platinum Pt and combined with the barium oxide BaO, and as shown in FIG.₃ ⁻And diffuses into the NOx absorbent 12 in the form of In this way, NOx is absorbed in the NOx absorbent 12.
[0040]
As long as the oxygen concentration in the exhaust gas flowing into the NOx absorbent is high, NO₂Is generated and the NOx absorption capacity of the NOx absorbent 12 is not₂Is absorbed in the NOx absorbent 12 and nitrate ions NO₃ ⁻Is generated. On the other hand, the oxygen concentration in the exhaust gas flowing into the NOx absorbent decreases and the NOx₂The reaction proceeds in the reverse direction (NO₃ ⁻→ NO₂) And thus the nitrate ion NO in the NOx absorbent 12₃ ⁻Is NO₂From the NOx absorbent 12 in the form of That is, when the oxygen concentration in the exhaust gas flowing into the NOx absorbent decreases, NOx is released from the NOx absorbent 12. If the degree of leanness of the exhaust gas flowing into the NOx absorbent decreases, the oxygen concentration in the exhaust gas flowing into the NOx absorbent decreases. Therefore, if the degree of leanness of the exhaust gas flowing into the NOx absorbent decreases, NOx is reduced from the NOx absorbent 12. Will be released.
[0041]
On the other hand, at this time, if the air-fuel ratio of the exhaust gas flowing into the NOx absorbent is reduced, HC and CO become oxygen O on the platinum Pt.₂ ⁻Or O^2-And oxidize. Further, when the air-fuel ratio of the exhaust gas flowing into the NOx absorbent is reduced, the oxygen concentration in the exhaust gas flowing into the NOx absorbent is extremely reduced.₂Is released and this NO₂Is reduced and purified by reacting with unburned HC and CO as shown in FIG. 4 (B). Thus, NO on the surface of platinum Pt₂Is no longer present, NO from the NOx absorbent 12 goes one after another.₂Is released. Therefore, when the air-fuel ratio of the exhaust gas flowing into the NOx absorbent is reduced, NOx is released from the NOx absorbent 12 in a short period of time and reduced and purified.
[0042]
Here, the air-fuel ratio of the exhaust gas refers to the ratio of the air and the fuel supplied to the exhaust gas passage 6 on the upstream side of the NOx absorbent 12 and the engine combustion chamber or the intake passage 4. Therefore, when no air or fuel is supplied to the exhaust gas passage 6, the air-fuel ratio of the exhaust gas becomes equal to the operating air-fuel ratio of the engine (combustion air-fuel ratio in the engine combustion chamber).
[0043]
Next, the mechanism of sulfur poisoning of the NOx absorbent 12 will be described. When the SOx component is contained in the exhaust gas, the NOx absorbent 12 absorbs the SOx in the exhaust gas by the same mechanism as the above-described NOx absorption. That is, when the air-fuel ratio of the exhaust gas is lean, SOx in the exhaust gas (eg, SOx₂) Is oxidized on platinum Pt to form SO₃ ⁻, SO₄ ⁻And combines with barium oxide BaO to form BaSO₄To form BaSO₄Is relatively stable, and the crystal is liable to be coarsened, so that once formed, it is difficult to be decomposed and released. For this reason, BaSO in the NOx absorbent 12₄When the generation amount of NOx increases, the amount of BaO that can participate in NOx absorption decreases, and the NOx absorption capacity decreases.
[0044]
In order to eliminate this sulfur poisoning, BaSO generated in the NOx absorbent 12 is used.₄Is decomposed at high temperature, and the SO₃ ⁻, SO₄ ⁻Is reduced under a substantially stoichiometric air-fuel ratio or a rich atmosphere (hereinafter, simply referred to as a rich atmosphere) containing light lean gaseous SO2.₂To be released from the NOx absorbent 12. That is, in order to eliminate sulfur poisoning, the NOx absorbent 12 needs to be in a high temperature and rich atmosphere state.
[0045]
In the present exhaust gas purification apparatus 20, when it is necessary to eliminate such sulfur poisoning, fuel (light oil) is supplied from the nozzle 24 to the exhaust gas passage 6 upstream of the NOx absorbent 12 (filter 14). The NOx absorbent 12 is supplied and the reaction raises the temperature of the NOx absorbent 12 and creates a rich atmosphere, thereby releasing sulfur from the NOx absorbent 12. That is, rich spike control is performed by adding fuel (light oil) from the nozzle 24 to the exhaust gas passage, thereby releasing sulfur.
[0046]
As described above, in the present exhaust gas purification apparatus 20, when it becomes necessary to purify the NOx absorbent 12 (such as the above-described NOx release reduction and sulfur poisoning regeneration), rich spike control is performed. Therefore, fuel (light oil) is added into the exhaust gas passage 6 from the nozzle 24 on the upstream side of the NOx absorbent 12 (filter 14). More specifically, fuel addition is started when a predetermined rich spike control start condition is satisfied, and thereafter, fuel addition is ended when a predetermined rich spike control end condition is satisfied. The rich spike control start condition here indicates that the NOx absorbent needs to be purified as described above. For example, the previous NOx absorbent purification (NOx release reduction or sulfur poisoning regeneration , Etc.), the condition may be satisfied when the vehicle travel distance from the time when the vehicle travels to a predetermined value. The rich spike control end condition here indicates that the purification of the NOx absorbent 12 has been completed. For example, this condition is satisfied when the duration of the current rich spike control has reached a predetermined value. Things.
[0047]
When fuel is added to perform such rich spike control, the exhaust gas purifying apparatus 20 uses pressurized exhaust gas that has been suctioned and pressurized by the pump 16 and stored in the tank 20 in advance. (Light oil) together with the NOx absorbent 12 (filter 14). This promotes the atomization or vaporization of the added fuel (light oil) while suppressing the influence of the exhaust gas flowing through the NOx absorbent 12 on the air-fuel ratio, and consequently suppresses the deterioration of the fuel consumption as a result of the NOx absorption as described above. It is intended to purify the agent 12 effectively.
[0048]
That is, when the fuel (light oil) is added into the exhaust gas passage 6 on the upstream side of the NOx absorbent 12 for the purpose of purifying the NOx absorbent 12, the light oil to be added is generally atomized and vaporized. Therefore, the added fuel adheres to the upstream portion of the NOx absorbent 12 (the filter 14) and is not supplied to the entire NOx absorbent, so that it is difficult to sufficiently purify the NOx absorbent 12. In such a case, if air is supplied together with the added fuel to promote atomization of the fuel, the amount of fuel required to achieve the target exhaust gas air-fuel ratio (or rich atmosphere) increases, and the fuel efficiency is reduced. It gets worse. That is, since the amount of air in the exhaust gas increases due to the air supplied to promote the atomization, the amount of fuel required to achieve the target exhaust gas air-fuel ratio (or rich atmosphere) increases. It will be lost.
[0049]
On the other hand, in the present exhaust gas purification apparatus 20, pressurized exhaust gas is supplied together with the added fuel. Since the amount of oxygen in the exhaust gas is smaller than that in the air, this makes it possible to suppress the effect of the exhaust gas flowing through the NOx absorbent 12 (the filter 14) on the air-fuel ratio and to atomize the added fuel. Can be promoted. In addition, the temperature of the exhaust gas is high to some extent, and the temperature rises when pressurized. However, if the temperature of the pressurized exhaust gas at the time of supply is kept high, the effect of promoting the vaporization of the added fuel is also obtained. can get. Thus, rich spike control can be performed by promoting the atomization or vaporization of the added fuel while suppressing the deterioration of fuel efficiency. Then, the fuel is supplied to the entire NOx absorbent 12 (filter 14) or a wider range thereof due to the promotion of atomization or vaporization. As a result, NOx which is the object of rich spike control while suppressing fuel consumption deterioration is suppressed. Purification (reduction of NOx, regeneration of sulfur poisoning, etc.) of the absorbent 12 can be performed sufficiently and effectively.
[0050]
In addition, the relationship between the fuel addition timing (injection timing) and the supply timing of the pressurized exhaust gas can be appropriately determined from the viewpoint of promoting the atomization or vaporization of the added fuel. Alternatively, from the viewpoint of promoting vaporization, it is preferable that the pressurized exhaust gas is supplied while the fuel addition (injection) is actually performed. That is, for example, in the case where fuel addition for rich spike control is performed intermittently by multiple fuel injections, as shown in FIG. The fuel injection is continued from the start of the injection to the end of the last fuel injection. In this case, atomization or vaporization of the added fuel can be reliably promoted by the simplified pressurized exhaust gas supply control while suppressing the effect of the exhaust gas on the air-fuel ratio. Alternatively, as shown in FIG. 5B, the supply timing of the pressurized exhaust gas and the timing of the fuel injection may be synchronized. In this case, it is possible to use the pressurized exhaust gas without waste and promote the atomization or vaporization of the added fuel while suppressing the effect of the exhaust gas on the air-fuel ratio.
[0051]
The relationship between the fuel addition timing (injection timing) and the supply timing of the pressurized exhaust gas is adjusted by controlling the operation of the control valve 22 and the nozzle 24 by the ECU 8 as is clear from the above description. You. In the present exhaust gas purifying apparatus 20, since the pressurized exhaust gas is generated in advance and stored in the tank 21, it is possible to supply the pressurized exhaust gas only by controlling the control valve 22. As compared with the case of generating pressurized exhaust gas, pressurized exhaust gas can be supplied with high responsiveness. Also, the pressurized exhaust gas stored in the tank 21 can be applied to applications that normally use compressed air, such as driving a valve actuator for exhaust braking and driving other accessories. .
[0052]
Further, in the present exhaust gas purification apparatus 20, the exhaust gas outlet 15 is provided downstream of the filter 14 carrying the NOx absorbent 12. Therefore, a part of the exhaust gas purified by the NOx absorbent 12 and the filter 14 is purified again by these, so that the emission can be improved. In addition, since the exhaust gas passing through the pump 16, the check valve 18, the tank 21, the control valve 22, and the like is purified by the NOx absorbent 12 and the filter 14, the occurrence of clogging or sticking in these devices may occur. This also has the effect of reducing
[0053]
Next, an exhaust gas purification device 30 having another configuration will be described with reference to FIG. In addition, here, description of the configuration, operation and effect common to the above-described exhaust gas purification device 20 is omitted in principle.
The exhaust gas purification device 30 shown in FIG. 6 is installed in the exhaust gas purification device 10 shown in FIG. 1 and is a part of the exhaust gas passage 6 like the above-described exhaust gas purification device 20 (see FIG. 2). Is composed. Comparing the configuration of the exhaust purification device 30 with the configuration of the exhaust purification device 20 described above, in the exhaust purification device 30, a bypass passage 6B that bypasses the NOx absorbent 12 (the filter 14) is provided, and a main passage 6A is provided. The difference lies in that a flow control valve 26 is provided at a portion where the NOx absorbent 12 (filter 14) joins with the bypass passage 6B on the downstream side. The operation of the flow control valve 26 is controlled by the ECU 8, and the flow rate of the exhaust gas flowing through the NOx absorbent 12 (filter 14) is controlled by controlling the ratio of the flow rate of the exhaust gas flowing through the two passages 6A and 6B as necessary. Can be adjusted.
[0054]
In the present exhaust gas purifying device 30, the flow control valve 26 is in a position shown by a solid line in FIG. 6 in a normal state, and almost all exhaust gas passes through the NOx absorbent 12 (filter 14). However, when the rich spike control is performed by adding the fuel as described above, the position is adjusted, and the flow rate of the exhaust gas flowing through the NOx absorbent 12 (the filter 14) is reduced. This is intended to reduce the amount of fuel required to achieve a target exhaust gas air-fuel ratio by reducing the flow rate of exhaust gas and adding fuel. Usually, when the flow rate of the exhaust gas is reduced in this manner, it becomes more difficult to sufficiently atomize the added fuel, and the necessity of promoting the atomization or vaporization of the fuel increases.
[0055]
In the present exhaust gas purifying apparatus 30, when fuel is added by reducing the flow rate of the exhaust gas flowing through the NOx absorbent 12 (the filter 14), the pressurized exhaust gas stored in the tank 21 As in the case of the exhaust gas purification device 20, the fuel is supplied to the upstream side of the NOx absorbent 12 in the main passage 6A together with the added fuel. In this way, the pressurized exhaust gas enhances the atomization or vaporization of the fuel and improves the dispersibility of the fuel in situations where there is a greater need to promote the atomization or vaporization of the fuel. As a result, it is possible to supply the added fuel to the entire NOx absorbent 12 (filter 14) or a wider range thereof, and to purify the NOx absorbent 12 (the purpose of the rich spike control while suppressing the deterioration of fuel economy). NOx release reduction, sulfur poisoning regeneration, etc.) can be performed sufficiently and effectively.
[0056]
Next, with reference to FIG. 7, a description will be given of an exhaust gas purification apparatus 40 having still another configuration. In addition, here, description of the configuration, operation and effect common to the above-described exhaust gas purification device 20 is omitted in principle.
The exhaust purification device 40 shown in FIG. 7 is similar to the exhaust purification device 20 (see FIG. 2) and the exhaust purification device 30 (see FIG. 6) described above, and is similar to the exhaust purification device 10 shown in FIG. It is installed and forms a part of the exhaust gas passage 6. Although the basic configuration of the exhaust gas purification device 40 is substantially the same as the configuration of the above-described exhaust gas purification device 20, the exhaust gas purification device 40 includes an oxidation catalyst 27 between the pump 16 and the check valve 18, and the oxidation catalyst 27. The difference is that a fuel addition nozzle 29 for adding fuel is provided upstream of the catalyst 27.
[0057]
The operation of the fuel addition nozzle 29 is controlled by the ECU 8 so that fuel is added upstream of the oxidation catalyst 27 as needed, that is, when the pump 16 is operated to generate pressurized exhaust gas. Controlled. By doing so, the fuel added from the fuel addition nozzle 29 reacts with the oxidation catalyst 27 to consume oxygen in the exhaust gas, so that a pressurized exhaust gas with a reduced oxygen concentration can be obtained. .
[0058]
The pressurized exhaust gas having the reduced oxygen concentration is stored in the tank 21 and, together with the added fuel in the fuel addition for the rich spike control, as in the case of the other exhaust gas purification devices 20 and 30 described above. The fuel is supplied to the exhaust gas passage and used to promote atomization or vaporization of the added fuel. By using the pressurized exhaust gas having the reduced oxygen concentration as described above, it is possible to further suppress the influence of the exhaust gas flowing through the NOx absorbent 12 on the air-fuel ratio and promote the atomization or vaporization of the added fuel. Can be. That is, thereby, rich spike control can be performed while further suppressing deterioration in fuel efficiency.
[0059]
In the configuration of the exhaust gas purification device 40 shown in FIG. 7, the oxidation catalyst 27 and the fuel addition nozzle 29 are provided between the pump 16 and the check valve 18, but the oxidation catalyst 27 and the fuel addition nozzle 29 If the fuel addition nozzle 29 is located on the upstream side of the oxidation catalyst 27, the fuel addition nozzle 29 may be provided anywhere between the exhaust gas outlet 15 and the tank 21, for example, provided between the exhaust gas outlet 15 and the pump 16. Is also good. Regarding the oxidation catalyst 27, in order to quickly raise the temperature of the oxidation catalyst 27 and activate it, no matter where the oxidation catalyst 27 is provided between the exhaust gas outlet 15 and the tank 21, the exhaust gas passage 6 can be formed by devising the piping shape. (I.e., close to the exhaust pipe).
[0060]
In each of the above-mentioned exhaust gas purifying apparatuses, the filter 14 carrying the NOx absorbent 12 is used as the exhaust gas purifying means. However, the present invention is not limited to this. Only the agent, only the NOx storage agent, or only the filter, or any combination thereof may be used.
When the temperature of the exhaust gas purifying means is to be increased by adding fuel, fuel is supplied to the entire exhaust gas purifying means or a wider range of the exhaust gas purifying means by promoting atomization or vaporization of the added fuel by pressurized exhaust gas. By doing so, it is possible to raise the temperature while suppressing the temperature difference between each part of the exhaust gas purifying means. Therefore, for example, even when only the filter is used, the fuel is supplied to the entire filter or a wider range of the filter according to the description of each exhaust gas purification device described above, and the entire filter or the wider filter is provided. It becomes possible to raise the temperature while suppressing the occurrence of a temperature difference in the range. This makes it possible to efficiently oxidize and remove the exhaust particulates trapped in the filter over the entire filter or over a wider range thereof. In addition, when the temperature of the supplied compressed exhaust gas is high, the vaporization of the added fuel is promoted and the temperature can be raised quickly.
[0061]
【The invention's effect】
According to the invention described in each claim, in an exhaust gas purifying apparatus that may add fuel to an exhaust gas passage on the upstream side of an exhaust gas purifying means such as a NOx storage agent, the influence of the exhaust gas on the air-fuel ratio is reduced. It is possible to promote the atomization or vaporization of the added fuel while suppressing it.
[Brief description of the drawings]
FIG. 1 is a diagram showing a case where an exhaust emission control device of the present invention is applied to a diesel engine.
FIG. 2 is an explanatory diagram showing an exhaust gas purification device of the present invention.
FIG. 3 is an enlarged cross-sectional view of a filter carrying a NOx absorbent.
FIG. 4 is a diagram for explaining the NOx absorption / release and reduction / purification actions.
FIG. 5 is a diagram for explaining a relationship between fuel addition timing (injection timing) and pressurized exhaust gas supply timing.
FIG. 6 is an explanatory diagram showing another exhaust gas purification device of the present invention.
FIG. 7 is an explanatory view showing still another exhaust gas purification apparatus of the present invention.
[Explanation of symbols]
10, 20, 30, 40 ... Exhaust gas purification device
2. The body of the engine
4: Intake passage
6. Exhaust gas passage
8 Electronic control unit (ECU)
12 ... NOx absorbent
14 ... Filter
15 ... Exhaust gas outlet
16. Pump or compressor
18. Check valve
21 ... Tank
24 ... Nozzle

Claims (9)

Exhaust gas purifying means arranged in the exhaust gas passage;
Fuel addition means for adding fuel to the exhaust gas passage upstream of the exhaust gas purification means;
A part of the exhaust gas is taken out from the exhaust gas passage and pressurized to generate a pressurized exhaust gas, and the pressurized exhaust gas and the fuel added by the fuel adding device are mixed with the exhaust gas purifying means of the exhaust gas passage. And a pressurized exhaust gas supply means for supplying the exhaust gas to an upstream side of the exhaust gas. The pressurized exhaust gas supply means,
Exhaust gas suction pressurizing means for suctioning and pressurizing exhaust gas through an exhaust gas outlet provided in the exhaust gas passage;
Pressurized exhaust gas storage means for storing the pressurized exhaust gas,
2. The exhaust gas purification system according to claim 1, further comprising: a pressurized exhaust gas supply method control unit that controls a method of supplying the pressurized exhaust gas stored in the pressurized exhaust gas storage unit to the exhaust gas passage. apparatus. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the exhaust gas outlet is provided downstream of the exhaust gas purifying means. In a case where the fuel addition by the fuel addition means is performed by intermittent multiple fuel injections, the supply of the pressurized exhaust gas is terminated from the time when the first fuel injection is started to the time when the last fuel injection is completed. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2 or 3, wherein the apparatus is controlled by the pressurized exhaust gas supply method control means so as to be continued until the exhaust gas is supplied. 3. The pressurized exhaust gas supply method control means controls a supply timing of the pressurized exhaust gas, and the supply timing is synchronized with a fuel injection timing for fuel addition by the fuel addition means. 4. The exhaust gas purification device for an internal combustion engine according to 3. A flow control means for controlling a flow rate of the exhaust gas flowing through the exhaust gas purifying means; and when the fuel adding means adds fuel to the exhaust gas passage, the flow control means controls the exhaust gas purifying means. The flow rate of exhaust gas flowing through the exhaust gas passage is reduced, and the pressurized exhaust gas is supplied to the exhaust gas passage upstream of the exhaust gas purification means together with the fuel added by the fuel addition means. 6. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 5. The exhaust gas purifying means includes a NOx occluding agent, and when the NOx or SOx stored in the NOx occluding agent is released, the pressurized exhaust gas and the fuel added by the fuel adding means are combined with the fuel in the exhaust gas passage. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 6, which is supplied to an upstream side of the exhaust gas purification means. The internal combustion engine according to any one of claims 1 to 7, wherein the pressurized exhaust gas supply unit includes an oxygen concentration reduction unit configured to reduce an oxygen concentration of the exhaust gas extracted from the exhaust gas passage. Exhaust gas purification device. The oxygen concentration reducing means includes an oxidation catalyst disposed in a passage through which the exhaust gas taken out from the exhaust gas passage passes, and a fuel addition means different from the fuel addition means for adding fuel upstream of the oxidation catalyst. The exhaust gas purification device for an internal combustion engine according to claim 8, further comprising:

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