JP2017025710A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress or reduce the occurrence of while smoke in an exhaust system for an internal combustion engine in which a plurality of catalyst devices are arranged in series with each other.SOLUTION: An exhaust emission control system for an internal combustion engine includes: an upstream side catalyst device provided in an exhaust passage of the internal combustion engine, and including an upstream side oxidation catalyst having such characteristics that sulfur compounds in exhaust gas are adsorbed/desorbed thereto/therefrom; and a downstream side catalyst device located in the exhaust passage downstream of the upstream side catalyst device, and including a downstream side catalyst having such characteristics that the sulfur compounds in the exhaust gas are adsorbed/desorbed thereto/therefrom. During upstream side temperature rise processing for temperature rise of a predetermined element as part of the upstream side catalyst device, exhaust gas temperature drop processing is performed for temperature drop of exhaust gas so that the temperature of exhaust gas exhausted from the upstream side catalyst device is lower than a downstream side desorption temperature at which the sulfur compounds adsorbed to the downstream side catalyst can be desorbed therefrom before the exhaust gas reaches the downstream side catalyst device.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine.

  In an exhaust system of an internal combustion engine, a filter is provided in the exhaust passage in order to suppress discharge of particulate matter (hereinafter referred to as “PM”) in the exhaust to the outside. Since the PM in the exhaust gas is collected and gradually accumulated in the filter with the operation of the internal combustion engine, a filter regeneration process is performed to prevent clogging. For example, in a diesel engine, since the air-fuel ratio of exhaust gas is generally the lean air-fuel ratio, unburnt fuel is supplied into the exhaust gas and oxidized by an oxidation catalyst or the like provided upstream of the filter. The temperature is raised, so that the deposited PM is removed by oxidation.

  On the other hand, fuels and lubricating oils used in diesel engines and the like generally contain sulfur. When sulfur compounds (SOx) generated from such sulfur are adsorbed to the oxidation catalyst as the fuel burns, oxidation occurs. The catalyst function as a catalyst will fall. In particular, when the catalyst or the like contains alumina, the sulfur compound is easily adsorbed thereon, so that the influence of the sulfur compound is increased. Thus, for example, Patent Document 1 discloses a technique for removing sulfur compounds adsorbed on an exhaust purification device of an internal combustion engine. In this technique, the temperature of the exhaust purification device is set to the amount of sulfur adsorbed when sulfur compounds are removed. The temperature is raised to a temperature range in which the compound can be released and generation of white smoke (sulfate white smoke) is suppressed.

JP 2013-29038 A JP 2014-206076 A International Publication No. 2011-125205 JP 2000-303826 A

  In order to increase the degree of purification of exhaust discharged from the internal combustion engine, a plurality of catalysts having a predetermined exhaust purification ability may be installed in series in the exhaust passage. In such an exhaust system configuration, a temperature gradient is likely to occur between the catalyst located on the upstream side and the catalyst located on the downstream side, and it is not easy to finely control the temperature of each catalyst. On the other hand, the sulfur compounds contained in the exhaust can be adsorbed on the catalyst, or the adsorbed sulfur compounds can be desorbed, but this adsorption and desorption phenomenon also tends to be greatly influenced by the temperature of the catalyst. . For this reason, when a plurality of catalysts are included in series in the exhaust system of the internal combustion engine, it is difficult to appropriately control the temperature of each catalyst, so that it is difficult to control the amount of sulfur compounds in the exhaust, and white smoke may be generated. is there.

  In particular, when a component such as a catalyst on the upstream side of the exhaust system is heated according to a predetermined purpose, the sulfur compound adsorbed there may be desorbed and flow into the downstream catalyst together with the high-temperature exhaust gas. There is. Then, if the high-temperature exhaust gas flows into the downstream catalyst, if the sulfur compound is separated from the downstream catalyst and further sulfur compound is added to the exhaust gas, the possibility of generating white smoke increases. Become.

The present invention has been made in view of the above-described problems, and an object thereof is to provide a technique for suppressing or reducing the generation of white smoke in an exhaust system of an internal combustion engine in which a plurality of catalysts are arranged in series. And

  In the present invention, in order to solve the above problem, when a predetermined temperature raising process is performed on the upstream side of the exhaust system, the exhaust temperature flowing into the catalyst located further downstream is adsorbed by the downstream catalyst. A configuration is adopted in which the sulfur compound is controlled to be below the temperature at which it can be desorbed. With such a configuration, it is possible to suppress the possibility that white smoke is generated by the sulfur compound being desorbed from the upstream and downstream catalysts and the concentration of the sulfur compound in the exhaust gas being increased.

  Specifically, the present invention relates to an exhaust gas purification system for an internal combustion engine, which is provided in an exhaust passage of the internal combustion engine and includes an upstream catalyst having a characteristic of adsorbing and desorbing sulfur compounds in the exhaust gas. A downstream catalyst device including a downstream catalyst having a characteristic of adsorbing and desorbing sulfur compounds in the exhaust gas, located downstream of the upstream catalyst device in the exhaust passage, and the upstream catalyst device In the upstream temperature raising process for raising the temperature of a predetermined element constituting a part, the temperature of the upstream catalyst is higher than the upstream desorption temperature at which the sulfur compound adsorbed on the upstream catalyst can be desorbed. An upstream temperature raising unit that performs the upstream temperature raising process at a high temperature, and an exhaust gas that is discharged from the upstream catalyst device when the upstream temperature raising process is performed by the upstream temperature raising part The temperature of the exhaust gas is the downstream side catalytic device An exhaust temperature controller that performs an exhaust gas temperature lowering process for lowering the exhaust gas temperature so that the sulfur compound adsorbed on the downstream catalyst by the time it reaches is lower than the downstream desorption temperature at which it can be desorbed; Is provided.

  The exhaust gas purification system for an internal combustion engine according to the present invention includes an upstream side catalyst device and a downstream side catalyst device, and each catalyst device is disposed at a position along the exhaust flow direction in the exhaust passage of the internal combustion engine, and In particular, the catalyst device disposed on the upstream side is identified as the upstream catalyst device, and the catalyst device disposed on the downstream side is identified as the downstream catalyst device. In other words, the upstream side catalyst device and the downstream side catalyst device are formed by separating the upstream side and the downstream side of the exhaust gas purification structure such as a plurality of exhaust gas purification catalysts provided in the exhaust passage so as not to overlap. Is.

  Here, the upstream temperature raising unit executes an upstream temperature raising process for raising the temperature of a predetermined element constituting at least a part of the upstream catalyst device. The upstream temperature raising process is a process for raising the temperature of a predetermined element in accordance with a predetermined purpose. In the process or as a result of the process, the temperature of the upstream catalyst is higher than the upstream desorption temperature. It becomes temperature. Therefore, when the upstream temperature raising process is performed, the sulfur compound adsorbed on the upstream catalyst is desorbed, and the high temperature exhaust discharged from the upstream catalyst device is located downstream. Flow into.

  At this time, if the exhaust gas temperature flowing into the downstream side catalyst device is relatively high, the sulfur compound adsorbed on the downstream side catalyst of the downstream side catalyst device may start to desorb. Here, when the sulfur compound adsorbed on the downstream catalyst is desorbed during the upstream temperature raising process, the sulfur compound desorbed from the upstream catalyst is desorbed from the downstream catalyst. When sulfur compounds are added and the amount of sulfur compounds in the exhaust gas is increased, white smoke is likely to be generated. In particular, in the upstream temperature raising process, the temperature rise of a predetermined element in the upstream catalyst device is controlled, but in the conventional technology, the exhaust temperature flowing into the downstream catalyst device is not sufficiently controlled. Therefore, the desorption state of the sulfur compound in the downstream side catalyst device is not sufficiently controlled, so that the amount of the sulfur compound in the exhaust gas may increase and white smoke may be generated.

In the present invention, the upstream temperature raising process is not limited to a specific process as long as it is a process for raising the temperature of a predetermined element included in the upstream catalyst device. Further, the predetermined element may be a component other than the upstream catalyst, or the upstream catalyst. For example, when the upstream catalyst device includes an upstream catalyst having oxidation ability and a filter that collects particulate matter in the exhaust gas disposed on the downstream side, An example is a process of supplying a fuel component to the upstream catalyst and oxidizing and removing the particulate matter collected by the filter using the oxidation heat generated there. In this case, the filter is a predetermined element. As another method, a temperature increasing process for desorbing a sulfur compound adhering to the upstream catalyst can be exemplified as one of the upstream temperature increasing processes. In this case, the upstream catalyst itself is a predetermined element.

  Therefore, the exhaust gas temperature control unit detects that the temperature of the exhaust gas discharged from the upstream catalyst device is removed from the downstream side until the exhaust gas reaches the downstream catalyst device when the upstream temperature raising process is being performed. Exhaust temperature lowering processing is performed so that the temperature is lower than the separation temperature. The downstream desorption temperature is a temperature at which the sulfur compound adsorbed on the downstream catalyst included in the downstream catalyst device can be desorbed. In this way, the exhaust temperature control unit performs the exhaust temperature lowering process, so that the upstream temperature rising process is performed on the upstream side catalyst device, and the desorbed sulfur compound flows into the downstream side catalyst device. Even so, since further desorption of the sulfur compound from the downstream side catalyst device is suppressed, the generation of white smoke in the exhaust can be suppressed or reduced.

  Here, in the exhaust gas purification system for an internal combustion engine, the exhaust gas discharged from the upstream side catalyst device when the upstream side temperature raising process is performed by the upstream side temperature raising unit is reduced in the exhaust temperature drop. An exhaust gas temperature estimation unit that estimates an exhaust gas temperature when it is assumed that the downstream catalyst device has been reached without processing may be further provided. In this case, when the exhaust temperature estimated by the exhaust temperature estimation unit is equal to or higher than the downstream desorption temperature, the exhaust temperature control unit executes the exhaust temperature lowering process. When the exhaust temperature estimated by the exhaust temperature estimation unit is equal to or higher than the downstream side desorption temperature, that is, when the exhaust gas temperature reduction process is not performed, sulfur compounds can be desorbed from the downstream side catalyst and white smoke can be generated. Only when the exhaust gas temperature reduction process is performed, the exhaust gas whose temperature has been lowered flows into the downstream side catalyst device, and the exhaust gas purification configuration such as the downstream side catalyst contained therein is excessively cooled. Can be avoided. In general, it is preferable that a component such as an exhaust purification catalyst belongs to an appropriate temperature range in order to effectively exhibit its exhaust purification ability. Therefore, it is possible to suitably maintain the exhaust purification ability of the downstream catalyst by performing the exhaust temperature lowering process as necessary as in the present invention.

  Here, the exhaust gas purification system for an internal combustion engine described above is for removing sulfur compounds adsorbed on the downstream side catalyst device before the upstream side temperature raising process is performed by the upstream side temperature raising unit. A first sulfur removal unit that raises the temperature of the downstream catalyst to a temperature equal to or higher than the downstream desorption temperature may be further provided. Before the upstream temperature raising process is performed, the first sulfur removal unit can increase the temperature of the downstream catalyst device to the downstream desorption temperature, thereby reducing the amount of sulfur compounds adsorbed on the downstream catalyst. it can. Preferably, the first sulfur removing unit maintains the catalyst temperature until the amount of sulfur compound adsorbed on the downstream catalyst is substantially zero.

  By reducing the amount of adsorbed sulfur compound in this way, an adsorption margin for the sulfur compound in the downstream catalyst is created. Therefore, when the sulfur compound is desorbed from the upstream catalyst in the upstream temperature raising process, the exhaust temperature lowering process suppresses the desorption of the sulfur compound from the downstream catalyst, and further desorbs from the upstream catalyst device. This makes it easier to store the sulfur compound in the downstream catalyst, and thus the generation of white smoke can be effectively suppressed or reduced.

In the exhaust gas purification system for an internal combustion engine up to the above, the upstream side catalyst device includes the upstream side catalyst and a filter that is disposed on the downstream side of the upstream side catalyst and collects particulate matter in the exhaust gas. You may have. The upstream temperature raising unit supplies the fuel of the internal combustion engine to the upstream catalyst in the upstream temperature raising process, so that the particulate matter collected in the filter can be removed by oxidation. The filter is heated to a certain temperature. At this time, although the sulfur compound adsorbed on the upstream side catalyst can be desorbed, the exhaust gas temperature flowing into the downstream side catalyst device can be lowered by the exhaust temperature lowering process, and the generation of white smoke is preferably suppressed or It becomes possible to reduce.

  Further, in the exhaust gas purification system for an internal combustion engine having the upstream catalyst and the filter, the upstream catalyst device selectively reduces NOx in the exhaust gas using ammonia as a reducing agent downstream of the filter. Further, the downstream side catalyst device may include the downstream side catalyst having oxidation ability, which is disposed on the downstream side of the selective reduction type NOx catalyst. In this case, the downstream desorption temperature is set to a catalyst temperature at which the sulfur compound adsorbed on the downstream catalyst having oxidation ability can be desorbed. Also in the exhaust gas purification apparatus for an internal combustion engine configured in this way, the generation of white smoke due to the desorption of sulfur compounds adsorbed on the downstream catalyst can be effectively suppressed or reduced.

  Here, in the exhaust gas purification system for an internal combustion engine up to the above, the temperature of the downstream catalyst is raised within a range in which white smoke is not generated in the exhaust gas flowing out from the downstream catalyst device after the upstream temperature raising process is completed. You may further provide the 2nd sulfur removal part which makes it warm and removes the sulfur compound which has adsorb | sucked to this downstream catalyst. With such a configuration, after the upstream temperature raising process is completed, sulfur compounds adsorbed on the downstream catalyst can be desorbed while suppressing white smoke, and the exhaust gas purification ability of the downstream catalyst can be recovered. It becomes possible. In particular, when sulfur compounds are desorbed from the upstream catalyst due to the upstream temperature rise process and are adsorbed and stored in the downstream catalyst, white smoke is generated after the upstream temperature rise process is started. Can be effectively suppressed or reduced.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the technique which suppresses or reduces generation | occurrence | production of white smoke in the exhaust system of the internal combustion engine in which the some catalyst is arrange | positioned in series.

1 is a diagram showing a schematic configuration of an exhaust gas purification system for an internal combustion engine according to the present invention. It is a figure which shows schematic structure of the upstream catalyst apparatus and downstream catalyst apparatus which are formed in the exhaust gas purification system shown in FIG. 2 is a flowchart of first filter regeneration control for performing filter regeneration processing, which is executed in the exhaust purification system shown in FIG. 1. FIG. 2 is a diagram comparing the release of sulfur compounds and the transition of catalyst temperature in an ASC catalyst included in the exhaust purification system shown in FIG. 1. 6 is a flowchart of second filter regeneration control for performing filter regeneration processing, which is executed in the exhaust purification system shown in FIG. 1.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

  An embodiment of an exhaust gas purification system for an internal combustion engine according to the present invention will be described with reference to the drawings attached to the present specification. FIG. 1 is a diagram showing a schematic configuration of an exhaust gas purification system for an internal combustion engine according to the present embodiment. The internal combustion engine 1 is a diesel engine for driving a vehicle.

An exhaust passage 2 is connected to the internal combustion engine 1. A filter 4 and a selective reduction type NOx catalyst (SCR catalyst) 5 are provided in the exhaust passage 2 in the exhaust passage 2. The filter 4 is a wall flow type filter that collects PM in the exhaust, and the SCR catalyst 5 is disposed on the downstream side of the filter 4. A supply valve 7 for supplying urea water for generating ammonia that acts as a reducing agent in the SCR catalyst 5 is disposed between the filter 4 and the SCR catalyst 5. The supply valve 7 is connected to a tank 8 in which urea water that is a precursor of ammonia is stored. Therefore, when the urea water stored in the tank 8 is supplied into the exhaust gas from the supply valve 7, the urea water is hydrolyzed by the heat of the exhaust gas, and ammonia is generated. Then, the ammonia reaches the SCR catalyst 5 and is adsorbed. In the SCR catalyst 5, a reduction reaction between ammonia and NOx in the exhaust occurs, and NOx is purified. In the present embodiment, urea water is supplied from the supply valve 7 as described above, but ammonia or ammonia water may be directly supplied to the exhaust gas instead.

  An oxidation catalyst (hereinafter referred to as “ASC catalyst”) 6 for oxidizing ammonia slipping from the SCR catalyst 5 is provided on the downstream side of the SCR catalyst 5. A fuel supply valve 62 capable of supplying the fuel of the internal combustion engine 1 to the ASC catalyst 6 through the exhaust gas flowing into the ASC catalyst 6 is disposed on the exhaust passage 2 between the ASC catalyst 6 and the SCR catalyst 5. . The fuel supplied to the exhaust gas from the fuel supply valve 62 is oxidized by the ASC catalyst 6, and the temperature of the ASC catalyst 6 can be raised.

The ASC catalyst 6 may be a catalyst configured by combining an oxidation catalyst and an SCR catalyst that reduces ammonia in exhaust gas using ammonia as a reducing agent. In this case, for example, an oxidation catalyst is formed by supporting a noble metal such as platinum (Pt) on a carrier made of aluminum oxide (Al ₂ O ₃ ), zeolite, or the like, and copper (Cu SCR catalyst may be formed by supporting a base metal such as iron or iron (Fe). By using the ASC catalyst 6 as a catalyst having such a configuration, HC, CO, and ammonia in the exhaust can be oxidized, and further, NOx is generated and generated by oxidizing a part of ammonia. NOx can also be reduced with excess ammonia.

  Further, an oxidation catalyst 3 having an oxidation function is provided on the upstream side of the filter 4. A fuel supply valve 61 that can supply the fuel of the internal combustion engine 1 to the oxidation catalyst 3 via the exhaust gas flowing into the oxidation catalyst 3 is disposed on the upstream side of the oxidation catalyst 3. The fuel supplied to the exhaust gas from the fuel supply valve 61 is oxidized by the oxidation catalyst 3, and the temperature of the exhaust gas flowing into the filter 4 located downstream can be raised.

  Here, on the upstream side of the SCR catalyst 5, a NOx sensor 10 for detecting the NOx concentration in the exhaust gas flowing into the SCR catalyst 5 is provided, and on the downstream side of the ASC catalyst 6, the NOx in the exhaust gas flowing out from the ASC catalyst 6. A NOx sensor 11 for detecting the concentration is provided. Further, a temperature sensor 13 for detecting the exhaust temperature flowing out of the oxidation catalyst 3 is provided downstream of the oxidation catalyst 3 and upstream of the filter 4, and downstream of the filter 4 and upstream of the SCR catalyst 5. Is provided with a temperature sensor 14 for detecting the exhaust gas temperature flowing out from the filter 4. Further, a temperature sensor 15 that detects an exhaust gas temperature flowing out from the SCR catalyst 5 is provided downstream of the SCR catalyst 5 and upstream of the ASC catalyst 6. Although not shown, a differential pressure sensor for detecting the differential pressure between the exhaust pressure upstream of the filter 4 and the exhaust pressure downstream is also provided in the exhaust passage 2.

The internal combustion engine 1 is also provided with an electronic control unit (ECU) 20 that controls the operating state of the internal combustion engine 1, an exhaust purification system, and the like. The ECU 20 includes the above-described NOx sensors 10 and 11, a differential pressure sensor (not shown), temperature sensors 13, 14 and 15, a crank position sensor 21 and an accelerator opening sensor 22, and an intake passage 25 of the internal combustion engine 1. The installed air flow meter 26 and the like are electrically connected, and the detection value of each sensor is passed to the ECU 20. Therefore, the ECU 20 determines the intake air amount based on the detection value of the air flow meter 26, the exhaust flow rate calculated based on the intake air amount, the engine speed based on the detection of the crank position sensor 21, and the engine based on the detection of the accelerator opening sensor 22. It is possible to grasp parameters relating to the operating state of the internal combustion engine 1 such as a load.

  In this embodiment, the NOx concentration in the exhaust gas flowing into the SCR catalyst 5 can be detected by the NOx sensor 10, but the exhaust gas discharged from the internal combustion engine 1 (the exhaust gas before being purified by the SCR catalyst 5) That is, the NOx concentration of the exhaust gas flowing into the SCR catalyst 5 is related to the operating state of the internal combustion engine, and can be estimated based on the operating state of the internal combustion engine 1.

  Here, in a partial section (hereinafter referred to as “predetermined section”) of the exhaust passage 2 between the SCR catalyst 5 and the ASC catalyst 6, a sub exhaust passage 2a is provided in parallel to the predetermined section. A switching valve 33 for switching the flow of exhaust gas is provided at the upstream merging portion of the merging portion between the sub exhaust passage 2 a and the exhaust passage 2. Therefore, the switching valve 33 switches whether the exhaust gas flowing out from the SCR catalyst 5 flows into a predetermined section of the exhaust passage 2 or into the sub exhaust passage 2a. The passage diameter of the sub-exhaust passage 2a is set to be approximately the same as the passage diameter of the exhaust passage 2 in the predetermined section. On the other hand, the sub-exhaust passage 2a is promoted so as to promote exhaust heat radiation. A sub muffler 9 is installed in the passage 2a. Therefore, when the exhaust gas flowing out from the SCR catalyst 5 reaches the ASC catalyst 6 via the sub-muffler 9, it reaches the ASC catalyst 6 via the predetermined section of the exhaust passage 2 without passing through the sub-muffler 9. Compared with that, the temperature is greatly reduced. The process of lowering the exhaust temperature by flowing the exhaust through the sub muffler 9 in this way is referred to as a temperature reduction process.

In the exhaust gas purification system 1 of the internal combustion engine 1 configured as described above, the ECU 20 issues an instruction to the supply valve 7 according to the NOx concentration in the exhaust gas detected and estimated as described above, and is necessary for the reduction and purification of NOx. An amount of urea water is supplied into the exhaust. For example, the actual NOx purification rate (hereinafter referred to as “actual NOx purification rate”) determined by the SCR catalyst 5 and the ASC catalyst 6 determined by the following formula 1 is within a predetermined range preferable from the viewpoint of exhaust purification. The urea water supply from the supply valve 7 may be controlled. Alternatively, the urea water supply amount from the supply valve 7 is determined based on the estimated ammonia amount adsorbed on the SCR catalyst 5. Also good.
NOx purification rate = 1- (detected value of NOx sensor 11) / (detected value of NOx sensor 10) (1)

  Further, in the exhaust purification system, PM in the exhaust is collected by the filter 4. By collecting PM by the filter 4, the amount of PM released to the outside can be suppressed. However, if the amount of accumulated PM in the filter 4 increases, the operating state of the internal combustion engine 1 is affected. Therefore, in order to oxidize and remove the accumulated PM, fuel is supplied from the fuel supply valve 61 to the exhaust gas, and the supplied fuel is oxidized by the oxidation ability of the oxidation catalyst 3 to increase the exhaust gas temperature flowing into the filter 4. A filter regeneration process (corresponding to the upstream temperature increase process of the present invention) is performed. Generally, it is necessary to raise the temperature of the filter 4 to about 500 ° C. in order to oxidize and remove PM accumulated by the filter regeneration process.

Here, the exhaust gas purification system of the internal combustion engine 1 is provided with an oxidation catalyst 3 and an ASC catalyst 6 as catalysts having oxidation ability. The functions of these oxidizing catalysts are as described above, but each catalyst contains alumina in order to exhibit the oxidizing ability. Alumina has a characteristic of adsorbing sulfur compounds (SOx) in exhaust gas. Specifically, in general, the lower the temperature, the more easily the sulfur compounds are adsorbed, and the sulfur compounds adsorbed when reaching a certain high temperature state. Is desorbed, and the higher the temperature, the greater the degree of desorption. In particular, the ASC catalyst 6 arranged on the downstream side is exposed to the sulfur compound generated by the oxidation ability of the upstream oxidation catalyst 3 or the sulfur compound desorbed from the oxidation catalyst 3. Therefore, it is easy to adsorb sulfur compounds. Therefore, if the ASC catalyst 6 is suddenly exposed to high-temperature exhaust gas, the sulfur compound adsorbed on the ASC catalyst 6 is desorbed, and the desorbed sulfur compound is combined with moisture in the exhaust gas. Smoke may be generated. In particular, when a plurality of components such as an exhaust purification catalyst and a filter are arranged in series in the exhaust passage 2 as in the above exhaust purification system, temperature control of each catalyst or the like is not easy, and thus there is a risk of white smoke generation. Is likely to occur.

  Therefore, in the exhaust gas purification system of the internal combustion engine 1, when the ASC catalyst 6 is exposed to high-temperature exhaust gas, the exhaust temperature is controlled so that the temperature of the ASC catalyst 6 becomes a temperature at which white smoke can be suppressed. In order to explain the exhaust temperature control, the exhaust purification catalyst, the filter, and the like provided in series in the exhaust passage 2 are classified as shown in FIG. Specifically, the oxidation catalyst 3, the filter 4, and the SCR catalyst 5 located on the upstream side in the exhaust passage 2 are referred to as an upstream catalyst device 41, and the ASC catalyst 6 located on the downstream side thereof is referred to as a downstream catalyst device 42. As described above, the exhaust purification catalyst and the like are classified into the exhaust purification catalyst provided in the exhaust passage 2 and the downstream exhaust purification catalyst (in this embodiment, the ASC catalyst 6) where white smoke is a concern. The exhaust purification catalyst or the like (in this embodiment, the oxidation catalyst 3, the filter 4 and the SCR catalyst 5) arranged upstream of the above is performed. The fuel supply valve 61 is arranged on the upstream side of the upstream side catalyst device 41 (that is, upstream of the oxidation catalyst 3 located on the most upstream side of the upstream side catalyst device 41), and is upstream of the upstream side catalyst device 41. A fuel supply valve 62 is disposed between the side catalyst device 41 and the downstream catalyst device 42 (that is, upstream of the ASC catalyst 6).

  Here, the white smoke related to the ASC catalyst 6 described above is likely to be generated when the ASC catalyst 6 is exposed to a relatively high temperature exhaust gas. Therefore, in this embodiment, it is considered that the ASC catalyst 6 is exposed to a relatively high temperature exhaust when the filter regeneration process is performed on the filter 4 constituting the upstream side catalyst device 41, and white smoke at the time of the filter regeneration process is considered. The control shown in the flowchart of FIG. 3 is illustrated as exhaust temperature control for suppression. The control is executed by a control program stored in the ECU 20.

  First, in S101, it is determined whether or not there is a request for executing filter regeneration processing (regeneration request). In the present embodiment, PM accumulation in the filter 4 is determined based on a detection value by a differential pressure sensor (not shown), that is, an exhaust pressure difference between the upstream side and the downstream side of the filter 4 and a detection value by the air flow meter 26. When the amount is estimated and the estimated amount of PM deposition exceeds a predetermined amount of accumulation, the regeneration request is issued. The PM accumulation amount in the filter 4 is calculated based on the history of the PM amount contained in the exhaust gas that is estimated based on the operation state of the internal combustion engine 1 without using the exhaust pressure difference or the like by the differential pressure sensor. May be. If an affirmative determination is made in S101, the process proceeds to S102, and if a negative determination is made, this control is terminated.

  Next, in S102, the switching valve 33 is controlled so that the exhaust flow is conducted to the exhaust passage 2 side. Specifically, when the exhaust gas is already flowing through the exhaust passage 2, the switching operation by the switching valve 33 is not performed, and when the exhaust gas is flowing through the sub-muffler 9 side for some purpose, the switching by the switching valve 33 is performed. The operation is performed, and the exhaust gas is guided to the exhaust passage 2 side. When the process of S102 ends, the process proceeds to S103.

In S103, filter regeneration processing is started. Specifically, the fuel component is supplied from the fuel supply valve 61 into the exhaust gas. The supply of the fuel component from the fuel supply valve 61 is the exhaust temperature detected by the temperature sensor 14, that is, the exhaust temperature flowing out from the filter 4, and the exhaust temperature reflecting the oxidation reaction heat of the deposited PM is accumulated. It is controlled so as to have a predetermined target temperature necessary for the oxidation removal of PM. After S103, the filter regeneration process is continued until an affirmative determination is made in S109 described later. The temperature of the oxidation catalyst 3 when the filter regeneration process is being performed is higher than the desorption temperature at which the sulfur compound adsorbed on the oxidation catalyst 3 is desorbed. Therefore, when the sulfur compound is adsorbed on the oxidation catalyst 3, the adsorbed sulfur compound is desorbed during the filter regeneration process, and the sulfur in the exhaust gas flowing downstream from the oxidation catalyst 3. The concentration of the compound may increase. The details of the desorption temperature of the sulfur compound in the catalyst will be described later with reference to FIG. When the process of S103 ends, the process proceeds to S104.

  In S <b> 104, the exhaust temperature that flows out from the upstream side catalyst device 41, that is, the outflow temperature T <b> 1 that is the exhaust temperature that flows out from the SCR catalyst 5, is acquired based on the detected value by the temperature sensor 15. Next, in S105, the exhaust temperature immediately after flowing out from the upstream side catalyst device 41 is assumed to have flowed straight into the downstream side catalyst device 42 without passing through the sub-muffler 9, that is, from the upstream side catalyst device 41. The inflow temperature T2, which is the exhaust temperature that flows into the ASC catalyst 6 when the outflowed exhaust reaches the ASC catalyst 6 without being subjected to the temperature lowering process by the sub muffler 9, is based on the outflow temperature T1 acquired in S104. Is estimated. The inflow temperature T2 is estimated in this way in order to suppress the generation of white smoke caused by the ASC catalyst 6 in consideration of how high the ASC catalyst 6 is placed during the filter regeneration process. Because.

  For the estimation of the inflow temperature T2, the amount of heat released from the exhaust in the exhaust passage 2 from the SCR catalyst 5 to the ASC catalyst 6 is taken into consideration. A part of the thermal energy of the exhaust moves from the exhaust flowing through the exhaust passage 2 to the outside through the exhaust passage, so that the exhaust temperature decreases. Therefore, physical parameters related to the movement of the thermal energy, for example, the temperature difference between the exhaust temperature (exhaust temperature detected by the temperature sensor 15) and the external temperature, the exhaust flow rate, the heat radiation section (from the SCR catalyst 5 to the ASC catalyst 6). The inflow temperature T2 can be calculated on the basis of the length of the predetermined section of the exhaust passage 2 and the shape of the exhaust passage forming the section. When the process of S105 ends, the process proceeds to S106.

  In S106, it is determined whether or not the inflow temperature T2 estimated in S105 is equal to or higher than the reference inflow temperature T0. The reference inflow determination temperature T0 is an exhaust temperature related to the catalyst temperature at which the sulfur compound adsorbed on the ASC catalyst 6 is assumed to be desorbed. Here, the desorption of the sulfur compound in the ASC catalyst 6 will be described with reference to FIG. The upper part (a) of FIG. 4 shows the transition of the amount of sulfur compound desorbed from the ASC catalyst 6 when the temperature is raised, and the lower part (b) shows the transition of the temperature of the ASC catalyst 6 corresponding to the transition. In the ASC catalyst 6, a plurality of types of sulfur compounds are adsorbed to the contained alumina, and the desorption temperatures of the respective sulfur compounds are different. Therefore, as shown in FIG. 4 (b), the temperature of the ASC catalyst 6 is increased stepwise according to the desorption temperature, so that the sulfur compounds corresponding to each temperature are desorbed from the ASC catalyst 6. Will be separated. The reference inflow temperature T0 is set according to the desorption temperature of the sulfur compound having the lowest desorption temperature among the sulfur compounds having different desorption temperatures as shown in FIG. As another method, in the case where the type of sulfur compound having the largest adsorption amount among the sulfur compounds adsorbed on the ASC catalyst 6 can be grasped in advance, the reference inflow is determined according to the desorption temperature of the sulfur compound. The temperature T0 may be set. The concept regarding the desorption temperature of the sulfur compound in the ASC catalyst 6 can be similarly applied to the desorption temperature of the sulfur compound in the oxidation catalyst 3. If a positive determination is made in S106, the process proceeds to S107, and if a negative determination is made, the process proceeds to S108.

Here, when an affirmative determination is made in S106 and the process proceeds to S107, if the exhaust temperature that has flowed out of the upstream side catalyst device 41 reaches the downstream side catalyst device 42 straight without passing through the sub-muffler 9, the ASC catalyst 6 It means that the temperature is equal to or higher than the temperature at which the sulfur compound adsorbed thereon can be desorbed. This means that the sulfur compound is desorbed from the ASC catalyst 6 and the concentration of the sulfur compound in the exhaust increases when the ASC catalyst 6 is exposed to the high-temperature exhaust gas while the filter regeneration process is being performed. . In the filter regeneration process, the oxidation catalyst 3 included in the upstream side catalyst device 41 is also at a relatively high temperature, so that the concentration of sulfur compounds in the exhaust gas flowing out from the upstream side catalyst device 41 tends to be higher. For this reason, it can be said that during the filter regeneration process, if a sulfur compound is further desorbed from the ASC catalyst 6, white smoke is likely to be generated. Therefore, even if the exhaust from the upstream side catalyst device 41 does not contain sulfur compounds to the extent that white smoke is generated, generation of white smoke is caused by addition of the desorbed sulfur compounds from the ASC catalyst 6 to the exhaust. Even if the exhaust from the upstream side catalyst device 41 is suspected to contain some sulfur compounds that generate some white smoke, white smoke is generated by the desorbed sulfur compounds from the ASC catalyst 6 being added to the exhaust. There is concern that this will become prominent.

  Therefore, if an affirmative determination is made in S106, the flow of exhaust gas is guided to the sub muffler 9 side by the switching valve 33. As a result, the sub-muffler 9 performs the exhaust temperature lowering process. That is, the exhaust gas flowing out from the upstream side catalyst device 41 flows through the sub-muffler 9, so that the temperature is lowered as compared with the case where the exhaust gas flows through the exhaust passage 2 before reaching the downstream side catalyst device 42. This suppresses or reduces the desorption of sulfur compounds from the ASC catalyst 6 included in the downstream side catalyst device 42 during the period during which the filter regeneration process is being performed, so that white smoke is generated as much as possible. Can be suppressed.

  Further, when the negative determination is made in S106 and the process proceeds to S108, even if the exhaust gas temperature flowing out from the upstream side catalyst device 41 reaches the downstream side catalyst device 42 straight without passing through the sub-muffler 9, the ASC catalyst 6 It means that the temperature does not reach a temperature at which the sulfur compound adsorbed thereon can be desorbed. This means that even if the ASC catalyst 6 is exposed to the exhaust gas during the filter regeneration process, the sulfur compound is not desorbed from the ASC catalyst 6 and the concentration of the sulfur compound in the exhaust gas does not increase. Here, the ASC catalyst 6 itself is provided in order to oxidize so that ammonia slipping the SCR catalyst 5 does not leak to the outside as it is. Therefore, it is preferable to keep the temperature of the ASC catalyst 6 high in order to keep the oxidation ability as high as possible. Therefore, when a negative determination is made in S106, the flow of exhaust gas is guided to the exhaust passage 2 side by the switching valve 33. Thereby, the exhaust temperature lowering process by the sub muffler 9 is avoided.

  When the process of S107 or S108 ends, the process proceeds to S109. In S109, it is determined whether or not the filter regeneration process should be terminated. For example, when the fuel supply to the exhaust gas is started to increase the temperature of the filter 4 and the temperature reaches a predetermined target temperature, the filter regeneration process ends when a predetermined time required for the oxidation removal of PM has elapsed. Can be determined. If an affirmative determination is made in S109, the process proceeds to S110, and if a negative determination is made, the processes in and after S104 are repeated. In S110, the fuel supply to the exhaust gas that is being performed to raise the temperature of the filter 4 is stopped, and the flow of the exhaust gas is guided to the exhaust passage 2 side by the switching valve 33, and this control is completed. .

  According to the above control, when it is estimated that when the filter regeneration process of the filter 4 is performed, the ASC catalyst 6 rises to a temperature at which the sulfur compound adsorbed thereon can be desorbed, the sub-muffler 9 is entered. The exhaust gas temperature is lowered by introducing the exhaust gas. Thereby, generation | occurrence | production of white smoke during a filter reproduction | regeneration process can be suppressed, or reduction of white smoke can be aimed at. Further, since the exhaust temperature lowering process is executed when an affirmative determination is made in S106, it is possible to avoid an undesirably lower exhaust temperature and to maintain the temperature of the ASC catalyst 6 as much as possible. .

  In the present embodiment, the ECU 20 executes the filter regeneration process, so that the ECU 20 functions as an upstream temperature raising unit according to the present invention. Further, when the ECU 20 executes the process of S105, the ECU 20 functions as an exhaust temperature estimating unit according to the present invention. Further, when the ECU 20 executes the process of S107, the ECU 20 functions as an exhaust temperature control unit according to the present invention.

<Modification>
FIG. 3 shows the control for suppressing the generation of white smoke when the filter regeneration process of the filter 4 is performed, but the control is included in the upstream side catalyst device 41 instead of the filter regeneration process. The above-described control for suppressing the generation of white smoke may also be applied during other processing for increasing the temperature of the constituent elements. For example, when the temperature of the oxidation catalyst 3 is raised and the sulfur compound adsorbed on the oxidation catalyst 3 is desorbed to restore the oxidation ability of the oxidation catalyst 3, the same control is applied to the ASC catalyst 6 It is possible to suppress or reduce the generation of white smoke due to the above.

  Further, in the control shown in FIG. 3, the sub-muffler 9 is used for the exhaust temperature lowering process when an affirmative determination is made in S106. Instead of this mode, the sub-muffler 9 is used between the SCR catalyst 5 and the ASC catalyst 6. An exhaust cooler that exchanges heat with the exhaust flowing through the exhaust passage 2 is installed, and when the affirmative determination is made in S106, the exhaust cooler is operated, and when the negative determination is made, the exhaust cooler is stopped. If the exhaust cooler is used in this way, the exhaust temperature can be controlled to a lower temperature more appropriately, and thus it is possible to more reliably suppress the generation of white smoke due to the ASC catalyst 6.

  When the filter regeneration process is executed in the exhaust gas purification system of the internal combustion engine 1, a second embodiment of the control for suppressing or reducing white smoke generated by the desorption of sulfur compounds from the ASC catalyst 6 will be described. This will be described with reference to FIG. The control shown in FIG. 5 is performed by executing a control program stored in the ECU 20, as in the control shown in FIG. Of the processes included in the control shown in FIG. 5, the processes substantially the same as those included in the control shown in FIG. 3 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the control shown in FIG. 5, the amount of the sulfur compound adsorbed on the ASC catalyst 6 is used as will be described later. The amount of the sulfur compound is calculated at any time by a predetermined calculation process executed in the ECU 20 in parallel with the control shown in FIG. Specifically, in the calculation process of the amount of sulfur compound, the assumed value of the sulfur concentration contained in the fuel used in the internal combustion engine 1 and the driving history of the internal combustion engine 1 (combustion conditions such as engine load and engine speed, The concentration transition of the sulfur compound in the exhaust gas flowing through the exhaust passage 2 is calculated based on the driving period and the like. Then, considering the adsorption / adhesion to the exhaust purification catalyst, the filter, the wall surface of the exhaust passage 2, etc. through which the exhaust containing the sulfur compound reaches the ASC catalyst 6, In this way, it is estimated and calculated how the sulfur compound is adsorbed.

  In the ASC catalyst 6, sulfur compounds are adsorbed or desorbed from the catalyst depending on the catalyst temperature. Therefore, in the calculation process of the amount of adsorbed sulfur compound, it is preferable to consider the entry / exit (adsorption, desorption) of the sulfur compound in the ASC catalyst 6 based on the temperature of the ASC catalyst 6. Note that the temperature of the ASC catalyst 6 can be obtained by using a detection value of a temperature sensor (not shown in FIG. 1) disposed on the downstream side of the ASC catalyst 6.

Here, the control shown in FIG. 5 will be described. In this control, when the process of S102 ends, the process proceeds to S201. Note that the process of S201 is performed before the process of S103. That is, the process of S201 is executed before the filter regeneration process of the filter 4 is performed. In S201, the amount of sulfur compound adsorbed on the ASC catalyst 6 calculated by the above calculation process is read, and the sulfur compound adsorbed on the ASC catalyst 6 is removed according to the amount of sulfur compound. In the removal treatment, preferably all sulfur compounds adsorbed on the ASC catalyst 6 are removed. Specifically, fuel is supplied from the fuel supply valve 62 into the exhaust gas, and the sulfur is adsorbed on the ASC catalyst 6 by the ASC catalyst 6 being oxidized by the oxidation ability of the ASC catalyst 6. The temperature is raised to a threshold temperature at which separation is possible. The relationship between the desorption of sulfur compounds and the catalyst temperature in the ASC catalyst 6 is as shown in FIG. Therefore, in the sulfur compound removal process in S201, after the temperature of the ASC catalyst 6 is raised to around T0, the catalyst temperature is gradually raised to remove the sulfur compound as shown in FIG. 4B. . By performing the process of S201 in this way, the adsorption amount of the sulfur compound in the ASC catalyst 6 is reduced as much as possible before the filter regeneration process is started in S103. When the sulfur compound adsorbed on the ASC catalyst 6 is removed by the process of S201, the removal amount is reflected in the calculation process.

  Here, when the temperature rise rate becomes too high when the temperature of the ASC catalyst 6 is raised, the amount of sulfur compounds released into the exhaust per unit time increases, so that white smoke is likely to be generated. Further, the amount of sulfur compound released per unit time increases as the amount of sulfur compound adsorbed on the ASC catalyst 6 increases. Therefore, in the sulfur compound removal process in S201, the temperature rise rate of the ASC catalyst 6, that is, the exhaust from the fuel supply valve 62 is prevented so as not to generate white smoke based on the amount of sulfur compound adsorbed on the ASC catalyst 6. The fuel supply speed is controlled. Specifically, the correlation between the temperature of the ASC catalyst 6, the amount of sulfur compound adsorbed on the ASC catalyst 6, and a suitable fuel supply speed in a range where no white smoke is generated is measured by a prior experiment or the like. It is stored in the ECU 20 in the form of a control map. Then, the fuel supply speed by the fuel supply valve 62 is acquired by accessing the control map based on the adsorption amount of the sulfur compound calculated in the calculation process and the temperature of the ASC catalyst 6. When the process of S201 ends, the process proceeds to S103.

  In this control, the amount of sulfur compound adsorbed on the ASC catalyst 6 is updated by the above calculation processing before the processing of S107 or S108 ends and the determination of S109 is performed. In this update, the temperature environment in which the ASC catalyst is exposed by the processing of S107 or S108 while the filter regeneration processing is performed, that is, the catalyst temperature of the ASC catalyst 6 is taken into consideration. Furthermore, at this time, the filter regeneration process is being performed, so that the oxidation catalyst 3 is also placed in a high temperature environment. Therefore, the sulfur compound adsorbed on the oxidation catalyst 3 is desorbed into the exhaust gas and can reach the ASC catalyst 6. Therefore, in the above calculation process, the amount of sulfur compounds adsorbed on the ASC catalyst 6 is also taken into account by taking into account the amount of sulfur compounds that can desorb from the upstream catalyst device 41 including the oxidation catalyst 3 and reach the ASC catalyst 6. Is calculated.

  Further, in this control, when the processing of S110 ends, the process proceeds to S202. In S202, after the completion of the filter regeneration process, as in S201, the amount of sulfur compound adsorbed on the ASC catalyst 6 calculated by the calculation process is read, and white smoke is not generated according to the amount of sulfur compound. In this manner, the sulfur compound adsorbed on the ASC catalyst 6 is removed. If the sulfur compound adsorbed on the ASC catalyst 6 is removed by the process of S202, the removal amount is reflected in the calculation process. After the process of S202, this control ends.

  In this way, in the control shown in FIG. 5, the sulfur compound adsorbed on the ASC catalyst 6 is removed before the filter regeneration process is performed. Therefore, after that, when the filter regeneration process is performed, the sulfur compound released from the internal combustion engine 1 and the sulfur compound released from the upstream side catalyst device 41 are adsorbed and released to the outside of the exhaust purification system. Can be suppressed. In particular, in the filter regeneration process, the catalyst temperature of the ASC catalyst 6 is controlled to a temperature at which the sulfur compound is not released by the processes of S106 to S108. Adsorption can be suitably performed. Therefore, the generation of white smoke during the filter regeneration process can be suppressed or reduced as much as possible. Even if the adsorption of the sulfur compound progresses and there is no room for the adsorption capacity of the ASC catalyst 6, the generation of white smoke is suppressed as much as possible by controlling the catalyst temperature of the ASC catalyst 6 in the processing of S106 to S108. Or it can be mitigated.

In addition, since the removal of the sulfur compound adsorbed on the ASC catalyst 6 is performed again after the filter regeneration process is completed so as not to generate white smoke, the generation of white smoke is suppressed before and after the filter regeneration process is performed. Mitigation is preferably achieved.

  In the present embodiment, as in the first embodiment, when the ECU 20 executes the filter regeneration process, the ECU 20 functions as an upstream temperature raising unit according to the present invention, and the ECU 20 executes the process of S105. Thus, the ECU 20 functions as an exhaust gas temperature estimation unit according to the present invention, and the ECU 20 executes the process of S107, so that the ECU 20 functions as an exhaust gas temperature control unit according to the present invention. Furthermore, when the ECU 20 executes the process of S201, the ECU 20 functions as the first sulfur removal unit according to the present invention, and when the ECU 20 executes the process of S202, the ECU 20 performs the process according to the present invention. 2 Functions as a sulfur removal unit.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Exhaust passage 3 ... Oxidation catalyst 4 ... Filter 5 ... SCR catalyst 6 ... ASC catalyst 7 ... Supply valve 8 ... Tank 9 ... Sub muffler 13, 14, 15 ... temperature sensor 20 ... ECU
21 ... Crank position sensor 22 ... Accelerator opening sensor 41 ... Upstream side catalyst device 42 ... Downstream side catalyst devices 61, 62 ... Fuel supply valve

Claims (6)

An upstream side catalyst device including an upstream side catalyst provided in an exhaust passage of the internal combustion engine and having a characteristic of adsorbing and desorbing sulfur compounds in the exhaust;
A downstream side catalyst device including a downstream side catalyst located on the downstream side of the upstream side catalyst device in the exhaust passage and having a characteristic of adsorbing and desorbing sulfur compounds in the exhaust; and
In the upstream temperature raising process for raising the temperature of a predetermined element constituting at least a part of the upstream catalyst device, the temperature of the upstream catalyst makes it possible to desorb the sulfur compound adsorbed on the upstream catalyst. An upstream temperature raising unit that performs the upstream temperature raising process that is higher than the upstream desorption temperature;
When the upstream temperature raising process is performed by the upstream temperature raising unit, the temperature of the exhaust discharged from the upstream catalyst device is reduced to the downstream until the exhaust reaches the downstream catalyst device. An exhaust temperature control unit that performs an exhaust temperature lowering process for lowering the exhaust temperature so that the sulfur compound adsorbed on the side catalyst is lower than the downstream side desorption temperature at which the sulfur compound can be desorbed;
An exhaust purification system for an internal combustion engine, comprising: Exhaust gas discharged from the upstream catalyst device when the upstream temperature raising process is being performed by the upstream temperature raising unit is transferred to the downstream catalyst device in a state where the exhaust temperature lowering process is not performed. An exhaust temperature estimation unit for estimating the exhaust temperature when it is assumed that the exhaust gas has reached,
When the exhaust temperature estimated by the exhaust temperature estimation unit is equal to or higher than the downstream desorption temperature, the exhaust temperature control unit performs the exhaust temperature lowering process;
The exhaust gas purification system for an internal combustion engine according to claim 1. In order to remove sulfur compounds adsorbed on the downstream side catalyst device before the upstream side temperature raising process is performed by the upstream side temperature raising unit, the temperature of the downstream side catalyst is set to the downstream side desorption temperature. A first sulfur removal unit that raises the temperature to the above temperature;
The exhaust gas purification system for an internal combustion engine according to claim 1 or 2. The upstream side catalyst device includes the upstream side catalyst having oxidation ability, and a filter that is disposed on the downstream side of the upstream side catalyst and collects particulate matter in exhaust gas,
The upstream temperature raising section is a temperature at which particulate matter collected by the filter can be oxidized and removed by supplying fuel of the internal combustion engine to the upstream catalyst in the upstream temperature raising process. Heating the filter to a temperature,
The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 3. The upstream side catalyst device further includes a selective reduction type NOx catalyst that selectively reduces NOx in the exhaust gas using ammonia as a reducing agent on the downstream side of the filter,
The downstream side catalyst device includes the downstream side catalyst having an oxidizing ability, which is disposed on the downstream side of the selective reduction type NOx catalyst,
The downstream desorption temperature is a catalyst temperature at which the sulfur compound adsorbed on the downstream catalyst having oxidation ability can be desorbed.
The exhaust gas purification system according to claim 4. After the upstream temperature raising process is completed, the temperature of the downstream catalyst is raised within a range where white smoke is not generated in the exhaust gas flowing out of the downstream catalyst device, and sulfur adsorbed on the downstream catalyst A second sulfur removal unit for removing the compound,
The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 5.

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