JP4352842B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to an exhaust gas purification apparatus for an internal combustion engine provided with an exhaust gas purification catalyst carrying a NOx catalyst in an exhaust passage.

As this type of exhaust purification device, for example, an exhaust purification device provided with an NOx storage reduction catalyst (hereinafter referred to as NOx catalyst) in an exhaust passage is known.
In this type of exhaust purification device, a reducing agent is added to the exhaust gas in order to eliminate sulfur poisoning of the NOx catalyst (hereinafter referred to as SOx poisoning) caused by sulfur components contained in the engine fuel. A reducing agent addition device is provided in the exhaust system. Then, by supplying the reducing agent by the reducing agent addition device, SOx poisoning of the exhaust purification catalyst is eliminated, and the exhaust purification capability is recovered.

More specifically, the temperature of the NOx catalyst is raised to a temperature higher than the SOx separation temperature (for example, 650 ° C.), and the reducing agent is intermittently added to the exhaust gas flowing into the NOx catalyst. SOx poisoning recovery control is known in which a lean air-fuel ratio or a rich air-fuel ratio is set in the vicinity of the air-fuel ratio (for example, Patent Document 1). Further, SOx poisoning recovery control (for example, Patent Document 3) is known in which the target air-fuel ratio is gradually shifted to the rich air-fuel ratio side in accordance with the NOx catalyst poisoning amount to suppress the SOx emission concentration to a low level. Yes. In addition, as the NOx catalyst poisoning amount increases, SOx poisoning recovery control (for example, Patent Document 4) that makes the rich period longer than the lean period, and as a pre-stage of SOx poisoning recovery control, a reducing agent is contained in the exhaust gas. A temperature raising technique (for example, Patent Document 2) that raises the temperature of the NOx catalyst by adding NO is known.
JP 2001-82137 A Japanese Patent Laid-Open No. 11-107827 JP 2000-161107 A JP 2000-274232 A

By the way, according to the intensive studies of the present inventors, various points to be improved have been found in the conventional SOx poisoning recovery control.
First, it should be noted that when the SOx poisoning recovery control is performed, a reducing agent is added to the exhaust gas flowing into the NOx catalyst. It may be discharged from the exhaust passage without being provided. In addition, in some cases, the reducing agent was condensed at the end portion (tail end) of the exhaust passage having a low ambient temperature and discharged as white smoke from the exhaust passage.

  Moreover, since generation | occurrence | production of white smoke originates in the reducing agent which was not used for reaction, the generation | occurrence | production can be suppressed by reducing the supply amount of the reducing agent which should be supplied to a NOx catalyst. However, when the supply amount of the reducing agent is small, the reaction between the NOx catalyst and the reducing agent becomes slow, the time required for recovery becomes longer, and the reliability of the SOx poisoning recovery control may be lowered.

  In particular, in an internal combustion engine in which the flow rate and flow rate of exhaust gas change every moment according to the running state, such as an internal combustion engine used for running a vehicle, a certain degree of control is required in order to obtain certainty of SOx poisoning recovery control. It is necessary to set the amount of addition of the reducing agent (control value) with a margin of excess, and in an internal combustion engine operated in such a use environment, the reliability of SOx poisoning recovery control is suppressed while suppressing the generation of white smoke. It was virtually difficult to maintain.

  Further, as a further point of interest, in order to perform SOx poisoning recovery control in a short time and with a small amount of addition, a larger amount of addition is required than the amount of addition per unit time in which generation of white smoke is a concern. However, as long as generation of white smoke is a concern, it is difficult to add the reducing agent at this preferred addition amount, and an appropriate value for the addition amount has to be obtained within this constraint. That is, conventionally, since there is a concern about the generation of white smoke, the SOx poisoning recovery control cannot be performed efficiently.

  The present invention has been made in consideration of the above-described technical background, and provides an exhaust purification technology capable of efficiently performing SOx poisoning recovery control while suppressing the generation of white smoke accompanying SOx poisoning recovery control. Let it be an issue.

In order to solve the above technical problem, the present invention has the following configuration.
That is, the present invention has an exhaust purification catalyst carrying an NOx storage reduction catalyst in the exhaust passage and supplies a reducing agent into the exhaust gas flowing into the exhaust purification catalyst, so that the ambient atmosphere of the exhaust purification catalyst An exhaust gas purification apparatus for an internal combustion engine comprising poisoning recovery means for performing poisoning recovery control for eliminating sulfur poisoning of the exhaust gas purification catalyst by alternately changing between an oxidizing atmosphere and a reducing atmosphere,
Wherein the downstream of the exhaust purifying catalyst, so as to include a low-boiling component can avoid condensation of the reducing agent component which has not been subjected to the reaction of the poisoning recovery control, by contacting catalysts to change the composition of the reducing agent component There is provided a catalytic catalyst comprising a catalytic substance for changing the composition of the reducing agent component to a composition containing a low boiling point component having a boiling point or less that can avoid condensation at least at the end opening of the exhaust passage. It is characterized by.

  According to the exhaust gas purification apparatus of the present invention configured as described above, the composition of the reducing agent component that has not been subjected to the poisoning recovery control downstream of the exhaust gas purification catalyst carrying the NOx storage reduction catalyst is reduced to the low boiling point. A contact catalyst that suppresses the generation of white smoke by changing to a composition containing components is provided. For this reason, when the reducing agent is supplied, the reducing agent component that has not been subjected to the poisoning recovery control reaction is lowered in boiling point with the passage of the contact catalyst disposed downstream of the exhaust purification catalyst, and thus the reducing agent The generation of white smoke accompanying the condensation of components is suppressed.

  Here, the NOx storage reduction catalyst stores NOx in the exhaust gas when the ambient atmosphere is in a high oxygen concentration state, and when the ambient atmosphere is in a low oxygen concentration state and a reducing agent component is present, It has a function of reducing the stored NOx. Further, examples of the exhaust purification catalyst carrying the NOx storage reduction catalyst include an exhaust purification catalyst composed of the NOx storage reduction catalyst itself, a particulate filter comprising an NOx storage reduction catalyst supported on a filter substrate, and the like. Can be illustrated.

  Further, the contact catalyst has a decomposition / reforming ability for decomposing a reducing agent component that has not been subjected to the poisoning recovery control reaction and reforming the composition of the reducing agent component to a composition containing the low boiling point component. The structure containing the catalyst substance which has may be sufficient. According to this configuration, the composition of the reducing agent component is modified to a composition containing a low boiling point component by decomposition of the reducing agent component.

Further, the contact catalyst may be a cracking catalyst that thermally decomposes a reducing agent component that has not been subjected to the poisoning recovery control reaction to change it to a low boiling point component. Further, the contact catalyst may be a reforming catalyst that modifies a reducing agent component that has not been subjected to the poisoning recovery control reaction and changes it to a low boiling point component. Further, the contact catalyst may be configured to support at least one of alumina, silica, zirconia, titania, and zeolite.

The contact catalyst may be provided immediately downstream of the exhaust purification catalyst.
According to this configuration, the thermal energy generated by the reaction of the reducing agent can be used for the activation of the contact catalyst. Note that the term “directly downstream” is preferably set within a distance from the exhaust purification catalyst that can keep the temperature of the contact catalyst at the activation temperature or higher when the poisoning recovery control is executed.

Further, a casing for accommodating the exhaust purification catalyst is provided in the exhaust passage,
The contact catalyst may be provided downstream of the exhaust purification catalyst and inside the casing.

  According to this configuration, since the contact catalyst is accommodated in the casing that accommodates the exhaust purification catalyst, the thermal energy generated by the reaction between the reducing agent and the exhaust purification catalyst can be efficiently transmitted to the contact catalyst.

Thus, in the present invention, a low boiling point component that can avoid condensation of a reducing agent component that has not been used to eliminate sulfur poisoning of the exhaust purification catalyst downstream of the exhaust purification catalyst that supports the NOx storage reduction catalyst. Therefore, the generation of white smoke is suppressed by changing the composition of the reducing agent component.
Therefore, when supplying the reducing agent to the exhaust purification catalyst, it is possible to supply an appropriate amount of reducing agent suitable for efficiently eliminating sulfur poisoning of the exhaust purification catalyst while suppressing the generation of white smoke. . The various contents described above can be combined as much as possible without departing from the problems and technical ideas of the present invention.

  As described above, according to the present invention, there is provided an exhaust purification technology capable of efficiently performing SOx poisoning recovery control while suppressing generation of white smoke accompanying SOx poisoning recovery control that eliminates sulfur poisoning of the exhaust purification catalyst. can do.

Hereinafter, preferred embodiments of an exhaust emission control device for an internal combustion engine 1 according to the present invention will be described.
In the present embodiment, an example in which the exhaust gas purification apparatus of the present invention is applied to a diesel engine for driving a vehicle will be described. FIG. 1 is a diagram showing a schematic configuration of an exhaust gas purification apparatus including an internal combustion engine 1 according to the present invention and an exhaust system and a control system thereof.

<Schematic configuration of the internal combustion engine 1 and its exhaust system and control system>
The internal combustion engine 1 is a diesel engine for driving a vehicle. Further, in the middle of the exhaust passage 11 of the internal combustion engine 1, an NOx storage reduction catalyst (hereinafter referred to as NOx catalyst) 12 and a particulate filter 13 carrying a NOx catalyst on a filter base material are accommodated. A casing 14 (catalytic converter) is provided. The particulate filter is disposed in the casing 14 downstream of the NOx catalyst 12.

An exhaust gas temperature sensor 21 that outputs an electrical signal corresponding to the temperature of the exhaust gas is provided upstream and downstream of the particulate filter 13 in the casing 14. Further, an exhaust A / F sensor 22 that outputs an electrical signal corresponding to the air-fuel ratio of the exhaust gas flowing out through the casing 14 is provided downstream of the casing 14. Further, the exhaust port (not shown) of the engine main body 1a is provided with a reducing agent supply valve 5 for supplying engine fuel as a reducing agent in the exhaust gas flowing into the casing 14, for example.

Further, the internal combustion engine 1 shown in the present embodiment includes an electronic control unit (ECU: Electronic Control Unit) 30 that executes various programs for controlling the internal combustion engine 1. The ECU 30 is a control device that controls the operating state of the internal combustion engine 1 in accordance with, for example, the operating conditions of the internal combustion engine 1 or the driver's request. Further, the ECU 30 reads the outputs of various sensors such as the exhaust A / F sensor 22 and the exhaust temperature sensor 21 and estimates the air-fuel ratio of the exhaust gas flowing into the casing 14 from the output value of the exhaust A / F sensor 22. Further, the ECU 30 estimates the floor temperature of the particulate filter 13 provided in the casing 14 from the output value of the exhaust temperature sensor 21.
Here, the air-fuel ratio of the exhaust gas is a value obtained by equivalently converting the mass of the reducing agent into the mass of the fuel when the reducing agent is other than fuel.

  Further, the ECU 30 supplies the reducing agent supply valve 5 to the reducing agent supply valve 5 at an appropriate timing in order to supply the reducing agent with the supply amount determined in consideration of the operating state, the air-fuel ratio of the exhaust gas, the temperature of the particulate filter 13 and the like. A valve opening signal is output. Examples of the situation where the reducing agent should be supplied include a situation where SOx poisoning due to the sulfur component occluded in the NOx catalyst 12 or the particulate filter 13 should be eliminated.

  In a situation where SOx poisoning is to be eliminated, the NOx catalyst 12 and the particulate filter 13 are heated to 650 ° C. or higher, and then are exhausted into the exhaust gas flowing into the casing 14 housing the NOx catalyst 12 and the particulate filter 13. The ECU 30 executes so-called “SOx poisoning recovery control” in which the reducing agent is intermittently added and the ambient atmosphere is alternately changed to a lean air-fuel ratio and a rich air-fuel ratio in the vicinity of the theoretical air-fuel ratio.

  Further, by executing this SOx poisoning recovery control, thermal decomposition of the sulfur component (specifically, barium sulfate BaSO4) is promoted, and the thermally decomposed sulfur component is combined with the exhaust gas flowing into the casing 14 and the NOx catalyst 12. And emitted from the particulate filter 13.

  As described above, in the internal combustion engine 1 shown in the present embodiment, the reducing agent is supplied into the exhaust gas flowing into the NOx catalyst 12 and the particulate filter 13, so that the ambient atmosphere of the NOx catalyst 12 and the particulate filter 13 is oxidized. The SOx poisoning recovery control is performed at an appropriate timing to alternately change between the (rich air fuel ratio) and the reducing atmosphere (lean air fuel ratio) to eliminate sulfur poisoning.

By the way, when the SOx poisoning recovery control is executed, the reducing agent is supplied to the exhaust gas. Depending on the situation, a part of the reducing agent is not used for the reaction of the SOx poisoning recovery control. It may flow downstream. Further, the reducing agent may condense at the terminal opening of the exhaust passage 11 to generate white smoke.
For this reason, in the present embodiment, a casing 16 containing a contact catalyst 15 composed of an HC cracking catalyst or a reforming catalyst is separately assembled downstream of the casing 14 containing the NOx catalyst 12 and the particulate filter 13, and white smoke is produced. Generation is suppressed.

The casing 16 containing the contact catalyst 15 is provided immediately downstream of the casing 14 containing the NOx catalyst 12 and the particulate filter 13.
Preferably, the casing 16 is disposed at a close distance of the casing 14 that can maintain the bed temperature of the contact catalyst 15 at an activation temperature or higher (for example, 400 ° C. or higher) during execution of SOx poisoning recovery control. ing.

  Further, the contact catalyst 15 is a catalyst configured to include at least one catalyst component such as alumina, silica, zirconia, titania, zeolite, etc., and the reducing agent component that has not been subjected to the SOx poisoning recovery control reaction is, for example, As shown in FIG. 2, in the process of passing through the contact catalyst 15, it is changed to a low boiling point component that can avoid condensation in the exhaust passage 11.

  FIG. 2 is a spectrum graph of the reducing agent component collected upstream of the contact catalyst 15. FIG. 3 is a spectrum graph of the reducing agent component collected downstream of the contact catalyst 15.

  As shown in FIG. 2, the reducing agent component in the exhaust gas is a high boiling point component having 10 or more carbon atoms (cf C10; boiling point of n-decane = 174 ° C.) that tends to be white smoke. And is reformed to, for example, pentane having 5 carbon atoms, so that its boiling point is lowered to about 37 ° C., which is difficult to condense even at the end opening of the exhaust passage 11. Therefore, in the downstream of the contact catalyst 15, the condensation of the reducing agent component is suppressed as the boiling point of the reducing agent component that has not been subjected to the SOx poisoning recovery control reaction is reduced, and thus the generation of white smoke is also suppressed. It will be.

  As described above, in the exhaust gas purification apparatus for the internal combustion engine 1 shown in the present embodiment, the reducing agent component that has not been used to eliminate SOx poisoning downstream of the casing 14 that houses the NOx catalyst 12, the particulate filter 13, and the like. Generation | occurence | production of white smoke is suppressed by changing the composition of a reducing agent component so that the low boiling point component which can avoid condensation is included.

  For this reason, like the internal combustion engine 1 shown in the present embodiment, there is a concern that white smoke may be generated even in a usage environment in which the flow rate and flow rate of the exhaust gas change every moment due to changes in the running state of the vehicle. Instead, an appropriate amount of reducing agent required for control can be supplied into the exhaust gas. Therefore, the certainty of SOx poisoning recovery control can be improved.

  In addition, in the NOx catalyst 12 or the particulate filter 13 having a NOx catalyst supported on the filter base material, white smoke may be generated when performing SOx poisoning recovery control in a short time with a small amount of reducing agent. However, according to the present invention, the NOx catalyst 12 and the particulate filter 13 are supplied with the necessary amount of reducing agent without concern about the generation of white smoke. Therefore, SOx poisoning can be eliminated in a short time with a small amount of reducing agent. Therefore, in the internal combustion engine 1 as shown in the present embodiment using engine fuel as the reducing agent, reduction in fuel consumption can be expected.

  Note that the above-described embodiment is merely an embodiment of the present invention, and details thereof can be appropriately changed according to various specifications.

  First, in the above-described embodiment, for example, a separate casing 16 is assembled downstream of the casing 14 housing the NOx catalyst 12 and the particulate filter 13 and the contact catalyst 15 is disposed in the exhaust passage 11. A configuration in which the NOx catalyst 12 and the casing 14 housing the particulate filter 13 are integrated and the contact catalyst 15 is disposed immediately downstream of the particulate filter 13 is also conceivable.

  In this example, since the NOx catalyst 12, the particulate filter 13, and the contact catalyst 15 use a single casing, the thermal energy generated by the reaction of the reducing agent can be efficiently used for the activation of the contact catalyst. it can.

Further, in the above-described embodiment, as the contact catalyst 15, for example, a catalyst including at least one catalyst component such as alumina, silica, zirconia, titania, zeolite or the like is adopted, but it is not always necessary. If it is a catalytic substance having decomposition and reforming ability to decompose the reducing agent component that has not been subjected to the SOx poisoning recovery control reaction and reform the composition of the reducing agent component to a composition containing a low boiling point component, Various selections are possible.
Thus, the exhaust emission control device for the internal combustion engine 1 according to the present invention can be variously modified in its detailed configuration.

1 is a schematic configuration diagram of an exhaust emission control device including an internal combustion engine and an exhaust system and a control system thereof according to an embodiment of the present invention. The spectrum graph of the reducing agent component extract | collected upstream of the contact catalyst. The spectrum graph of the reducing agent component extract | collected downstream of the contact catalyst.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 1a Engine main body 5 Reducing agent supply valve 11 Exhaust passage 12 Occlusion reduction type NOx catalyst 13 Particulate filter 14 Casing 15 Contact catalyst 16 Casing 21 Exhaust temperature sensor 22 Exhaust A / F sensor 30 ECU

Claims (7)

An exhaust purification catalyst carrying an NOx storage reduction catalyst is provided in the exhaust passage, and a reducing agent is supplied into the exhaust gas flowing into the exhaust purification catalyst, whereby the ambient atmosphere of the exhaust purification catalyst is changed to an oxidizing atmosphere and a reducing atmosphere. And an exhaust gas purification apparatus for an internal combustion engine comprising poisoning recovery means for executing poisoning recovery control for eliminating sulfur poisoning of the exhaust gas purification catalyst by alternately changing
Wherein the downstream of the exhaust purifying catalyst, so as to include a low-boiling component can avoid condensation of the reducing agent component which has not been subjected to the reaction of the poisoning recovery control, by contacting catalysts to change the composition of the reducing agent component There is provided a catalytic catalyst comprising a catalytic substance for changing the composition of the reducing agent component to a composition containing a low boiling point component having a boiling point or less that can avoid condensation at least at the end opening of the exhaust passage. An exhaust emission control device for an internal combustion engine.   The catalyst having a decomposition and reforming ability for decomposing a reducing agent component that has not been subjected to the poisoning recovery control reaction and reforming the composition of the reducing agent component to a composition containing the low boiling point component. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the exhaust gas purification device is configured to contain a substance. 3. The internal combustion engine according to claim 1, wherein the contact catalyst is a cracking catalyst that thermally decomposes a reducing agent component that has not been subjected to the poisoning recovery control reaction to change it to a low boiling point component. 4. Engine exhaust purification system. Said contact catalyst, wherein the reducing agent component which has not been subjected to the reaction of the poisoning recovery control by reforming, according to claim 1 or 2, characterized in that a reforming catalyst to change the low-boiling components An exhaust purification device for an internal combustion engine. The exhaust purification device for an internal combustion engine according to any one of claims 1 to 4, wherein the contact catalyst carries at least one of alumina, silica, zirconia, titania, and zeolite. The exhaust purification device for an internal combustion engine according to any one of claims 1 to 5, wherein the contact catalyst is provided immediately downstream of the exhaust purification catalyst. A casing that houses the exhaust purification catalyst is provided in the exhaust passage,
The exhaust purification device for an internal combustion engine according to any one of claims 1 to 6, wherein the contact catalyst is provided downstream of the exhaust purification catalyst and inside the casing.

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