JP2007100572A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of improving fuel economy and maintaining catalyst purification capacity by efficiently reducing a sulfur poisoning recovery treatment time or lowering a sulfur poisoning recovery treatable temperature without lowering the burned amount of PM during PM regeneration treatment and excessively increasing the temperature of a particulate filter. <P>SOLUTION: This exhaust emission control device of an internal combustion engine in which the particulate filter carrying an exhaust purifying catalyst is disposed in an exhaust passage comprises a plasma injector having a plasma reforming part. The sulfur poisoning recovery treatment for the exhaust purifying catalyst is performed by adding, to exhaust gases on the upstream side of the exhaust purifying catalyst, active species formed by plasma-reforming a fuel by a plasma injector beforehand so that the sulfur poisoning recovery treatment of the exhaust purifying catalyst is performed when the burning treatment of particulate matters collected by the particulate filter is not performed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly, to a particulate filter that collects soot-like particulate matter (hereinafter referred to as PM) contained in exhaust gas, and to maintain the exhaust gas purification performance. The present invention relates to an exhaust gas purification apparatus for an internal combustion engine having a particulate filter carrying an exhaust gas purification catalyst that requires a poisoning recovery process.

  One of the exhaust purification catalysts for internal combustion engines, which is considered to require sulfur poisoning recovery processing to maintain the exhaust purification performance, is a NOx storage reduction catalyst. From the viewpoint of improving fuel efficiency and exhaust gas regulations, the practical application of lean-burn internal combustion engines in which the majority of the operating range of gasoline internal combustion engines is operated at a lean air-fuel ratio is being promoted, and the application range of diesel internal combustion engines has been expanded. It is being done. In diesel internal combustion engines and lean-burn gasoline internal combustion engines, fuel is burned under a lean air-fuel ratio, that is, excess air, so emissions of incomplete combustion components HC (hydrocarbon) and CO (carbon monoxide) are eliminated. On the other hand, the amount of NOx (nitrogen oxide) and PM emissions increases, and it is necessary to take some measures to prevent the release of harmful NOx and PM discharged into the atmosphere. NOx is produced by a reaction between nitrogen in the air and unburned oxygen. On the other hand, PM is a general term for particulate matter discharged from an internal combustion engine, and is generally generated from the fuel and lubricating oil left around the black smoke (soot) made of carbon and the sulfur content in light oil fuel. It is known that a sulfur compound (sulfate) or the like is adsorbed.

  As a means for reducing the amount of NOx released into the atmosphere, it is known to arrange a NOx storage reduction catalyst in the exhaust system of an internal combustion engine. The NOx occlusion reduction catalyst absorbs NOx in the exhaust by absorbing and adsorbing in the form of nitrate when the inflowing exhaust air-fuel ratio is a lean air-fuel ratio, or both, and when the inflowing exhaust air-fuel ratio is a rich air-fuel ratio. It plays the role of releasing the stored NOx. The released NOx is reduced and purified by reducing components (HC, CO, H2).

  According to the exhaust gas purification apparatus equipped with such a NOx occlusion reduction catalyst, NOx is absorbed well from the exhaust gas of lean combustion with a high oxygen concentration, and is periodically periodic rich-fuel mixture operation (also referred to as rich spike operation). In addition, the oxygen concentration in the exhaust gas can be reduced and reducing components such as HC and CO can be present in the exhaust gas, and the absorbed NOx can be reduced and purified well without being released into the atmosphere.

  However, in such an exhaust purification device equipped with a NOx occlusion reduction catalyst, a decrease in the NOx occlusion capability of the NOx occlusion reduction catalyst due to sulfur components in the fuel, so-called sulfur poisoning, becomes a problem.

Fuels of internal combustion engines, such as fuels such as gasoline and light oil, often contain sulfur components. In this case, SOx (sulfur oxide) such as SO ₂ and SO ₃ is contained in the exhaust gas after combustion. Will be included. It is known that when SOx is present in the exhaust, the NOx occlusion reduction catalyst occludes NOx, while SOx in the exhaust also occludes in the form of sulfate.

  The SOx occluded in the NOx occlusion reduction catalyst is stable and difficult to decompose, and the NOx occlusion reduction catalyst should not desorb from the NOx occlusion reduction catalyst in a temperature range where the NOx occlusion reduction catalyst can occlude NOx in the exhaust and reduce and purify it. Has been revealed.

  For this reason, the NOx occlusion reduction catalyst is used for exhaust gas containing SOx in a temperature range in which NOx in exhaust gas can be occluded and reduced and purified, for example, in a temperature range of 300 ° C. to 450 ° C. While NOx is occluded and reduced and purified, SOx remains in the NOx occlusion reduction catalyst without being decomposed. Therefore, the amount of SOx in the NOx occlusion reduction catalyst increases as time elapses, and thus the amount of NOx that can be occluded by the NOx occlusion reduction catalyst decreases as time elapses, so-called sulfur. The problem of poisoning (or S poisoning) occurs.

  On the other hand, by increasing the NOx occlusion reduction catalyst temperature, for example, by raising the NOx occlusion reduction catalyst temperature to 600 ° C. or higher, SOx occluded in the NOx occlusion reduction catalyst can be thermally decomposed and released. It has been revealed.

  Therefore, in an exhaust purification device equipped with a NOx storage reduction catalyst, as one method of eliminating sulfur poisoning, the NOx storage reduction catalyst temperature is raised while the exhaust air-fuel ratio flowing into the NOx storage reduction catalyst is made to be a rich air-fuel ratio. Sulfur poisoning recovery treatment is applied. By the sulfur poisoning recovery process, SOx stored in the NOx storage reduction catalyst is thermally decomposed, and SOx is released from the NOx storage reduction catalyst while preventing re-storage of the thermally decomposed SOx into the NOx storage reduction catalyst. It becomes possible.

  For example, Japanese Patent Application Laid-Open No. 10-54274 discloses an exhaust purification device for an internal combustion engine that includes a NOx storage reduction catalyst and to which sulfur poisoning recovery processing is applied, and releases SOx from the NOx storage reduction catalyst. It has been shown that the ignition timing is controlled as a method for increasing the NOx storage reduction catalyst temperature in order to achieve this. Specifically, by retarding the ignition timing, the temperature of the exhaust gas flowing into the NOx storage reduction catalyst is increased, and the temperature of the NOx storage reduction catalyst is increased until it reaches a temperature range suitable for the sulfur poisoning recovery process. Is described.

  Further, as one means for reducing the amount of PM released into the atmosphere, a particulate filter is disposed in the exhaust system of the internal combustion engine, and the PM in the exhaust is once collected in the particulate filter. It is known to burn off PM. When a particulate filter is used as a means of reducing the amount of PM released into the atmosphere, exhaust emission becomes difficult as the amount of collected PM increases, and therefore PM regeneration processing, that is, trapping in the particulate filter, becomes difficult. It is necessary to execute the combustion process of the collected PM. However, the PM collected on the particulate filter does not burn unless the temperature is higher than about 600 ° C., whereas the exhaust temperature of a diesel internal combustion engine, for example, is usually much lower than 600 ° C. It is necessary to raise the temperature of the particulate filter in order to combust PM. As a means for raising the temperature of the particulate filter, for example, Japanese Patent No. 3620291 describes that the temperature is raised by arranging a heater in the particulate filter.

Japanese Patent Application Laid-Open No. 10-54274 Japanese Patent No. 3620291

  In order to raise the catalyst temperature in order to perform the SOx poisoning recovery process, heat energy is required, and when additional fuel is supplied to obtain the heat energy, fuel consumption is deteriorated. Moreover, there is a possibility that the performance of the catalyst itself is deteriorated by increasing the catalyst temperature. Therefore, in an exhaust purification device equipped with an exhaust purification catalyst such as a NOx occlusion reduction catalyst that requires sulfur poisoning recovery treatment, sulfur poisoning recovery is performed from both the viewpoints of improving fuel efficiency and maintaining the catalyst purification capability. We believe that shortening the treatment time or lowering the sulfur poisoning recovery treatment temperature is an important issue.

  In response to this problem, for example, in Japanese Patent Application Laid-Open No. 2002-256853, in a purification apparatus for an internal combustion engine in which a plasma generation device is disposed in an exhaust passage upstream of a NOx storage reduction catalyst, a sulfur poisoning recovery process is performed. By selectively operating the plasma generator and plasma-modifying the exhaust itself, that is, reducing the sulfur poisoning recovery processing time by activating the reducing components in the exhaust by plasma reforming and strengthening the reducing power. Shown. However, it is considered that a large amount of energy is required for plasma reforming the exhaust gas having a large capacity, and there is still room for further improvement.

  In addition, in an exhaust purification device having a particulate filter carrying an exhaust purification catalyst that requires a sulfur poisoning recovery process to maintain exhaust purification performance such as a NOx storage reduction catalyst, for example, along with the execution of the sulfur poisoning recovery process The PM regeneration process, that is, the combustion process of the PM collected by the particulate filter is required, but the PM regeneration process is a process in which PM is burned under a lean air-fuel ratio, that is, excess air. During the regeneration process, if active species with high reducing ability are brought into the exhaust to perform the sulfur poisoning recovery process, the oxidizing agent is likely to be consumed, and the PM combustion amount may be reduced. Furthermore, if a highly reducing active species is brought into the exhaust to perform the sulfur poisoning recovery process during the PM regeneration process, the temperature of the particulate filter rises too much, resulting in performance deterioration, and its melting temperature. There is a possibility that the temperature rises above and the particulate filter itself is melted.

  In view of the above problems, the present invention provides a PM combustion during a PM regeneration process in an exhaust purification apparatus including a particulate filter carrying an exhaust purification catalyst that requires a sulfur poisoning recovery process such as a NOx storage reduction catalyst. Without reducing the amount and overheating the particulate filter temperature, the sulfur poisoning recovery processing time can be shortened or the sulfur poisoning recovery processing temperature can be lowered more efficiently. An object of the present invention is to provide an exhaust emission control device capable of improving fuel consumption and maintaining catalyst purification capability.

  According to the first aspect of the present invention, in an exhaust gas purification apparatus for an internal combustion engine in which a particulate filter carrying an exhaust gas purification catalyst is disposed in an exhaust passage, the internal combustion engine has a plasma injector having a plasma reforming portion, and the particulate filter When the collected particulate matter is not combusted, the active species that have been plasma reformed from the fuel by the plasma injector in advance are added to the exhaust upstream of the exhaust purification catalyst. Thus, there is provided an exhaust gas purification apparatus for an internal combustion engine, characterized in that a sulfur poisoning recovery process of the exhaust gas purification catalyst is performed.

  That is, according to the first aspect of the present invention, when the combustion process of the particulate matter collected by the particulate filter is not executed, the exhaust itself is not plasma-modified, but the plasma is preliminarily generated from the fuel by the plasma injector. The highly reactive active species generated by reforming is added to the exhaust upstream of the exhaust purification catalyst, and the sulfur poisoning recovery process of the exhaust purification catalyst is executed.

  According to the first aspect of the present invention, it is possible to promote the combustion reaction, the sulfur poisoning desorption reaction, and the sulfur poisoning recovery process on the exhaust purification catalyst by the highly reactive active species generated by plasma reforming from the fuel. The temperature can be lowered. Thereby, it is possible to shorten the sulfur poisoning recovery processing time and to improve the fuel consumption. In addition, the reduction in the time required for the sulfur poisoning recovery process reduces the time during which the exhaust purification catalyst is exposed to a high temperature, which is caused by the high heat received by the exhaust purification catalyst during the sulfur poisoning recovery process. It is possible to suppress deterioration of the durability performance of the exhaust purification catalyst and to maintain the catalyst purification capability.

  In the first aspect of the invention, when the combustion process of the particulate matter collected by the particulate filter is being performed, the plasma injector is used to perform the plasma reforming from the fuel so as to perform the sulfur poisoning recovery process. The highly reactive active species generated in this way are not added to the exhaust gas, so there is no consumption of oxidant in the exhaust gas by the active species, and the reduction of the combustion amount of the collected particulate matter is prevented. can do. In addition, when the particulate matter collected by the particulate filter is being burned, that is, the particulate filter temperature has already reached the temperature range where the particulate matter can be burned. In addition, it is possible to prevent the particulate filter from being excessively heated by adding the highly reactive active species generated by plasma reforming from the fuel by the plasma injector to the exhaust gas.

  According to the second aspect of the present invention, the activity obtained by plasma reforming from the fuel by the plasma injector in advance so that the temperature of the particulate filter is raised to a temperature at which the particulate matter can be combusted. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the seed is added to exhaust gas upstream of the exhaust gas purification catalyst.

  That is, in the invention of claim 2, when performing the combustion process of the particulate matter collected by the particulate filter, when the temperature of the particulate filter has not reached the combustion processable temperature of the particulate matter, Highly reactive active species generated by plasma reforming from fuel in advance by a plasma injector is added to the exhaust upstream of the exhaust purification catalyst, and promotes the combustion reaction on the NOx occlusion reduction catalyst. The temperature of the filter is raised to a predetermined temperature.

  According to the invention described in each claim, the particulate filter temperature is excessively raised without reducing the PM combustion amount when the combustion process of the particulate matter collected by the particulate filter is being executed. Therefore, it is possible to shorten the sulfur poisoning recovery processing time or to lower the sulfur poisoning recovery processing temperature more efficiently, and to improve the fuel efficiency and maintain the catalyst purification capacity. Has a common effect.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic view showing an embodiment when the exhaust emission control device of the present invention is applied to a diesel internal combustion engine or a lean combustion gasoline internal combustion engine for automobiles.
In FIG. 1, 10 is an internal combustion engine body of a diesel internal combustion engine or a lean internal combustion combustion gasoline internal combustion engine, 11 is an exhaust manifold, 12 is an exhaust pipe, 13 is a NOx storage reduction catalyst, 14 is a particulate carrying a NOx storage reduction catalyst 13. Each filter is shown. In FIG. 1, 20 is a PM regeneration determination means, 21 is a SOx poisoning determination means, 22 is an electronic control unit (ECU), 23 is a plasma injector, 24 is a valve, 25 is a fuel supply unit, and 26 is an active species addition. Port, 27 is a generator, 28 is a battery, and 29 is a power supply device.

  First, each of the internal combustion engine body 10, the exhaust manifold 11, the exhaust pipe 12, the generator 27, and the battery 28, which are the basic configuration of the diesel internal combustion engine or the lean combustion gasoline internal combustion engine shown in FIG.

The internal combustion engine body 10 is a diesel internal combustion engine or an internal combustion engine body of a lean combustion gasoline internal combustion engine that is operated at an air-fuel ratio that is leaner than stoichiometric, and an exhaust passage from the internal combustion engine body 10 An exhaust manifold 11, an exhaust pipe 12, a NOx occlusion reduction catalyst 13, and a particulate filter 14 carrying the NOx occlusion reduction catalyst 13 are arranged in the exhaust system.
The exhaust manifold 11 is connected to the internal combustion engine main body 10 and plays a role of sending exhaust gas from each cylinder disposed in the internal combustion engine main body 10 into one exhaust pipe 12.
The generator 27 is connected to the internal combustion engine body 10 and plays a role of generating electricity in cooperation with the internal combustion engine body 10, and the battery 28 is connected to the generator 27, It plays the role of storing the generated electricity.

Next, each component which the exhaust gas purification apparatus of the internal combustion engine which becomes embodiment shown by FIG. 1 has is demonstrated.
The exhaust gas purification apparatus for an internal combustion engine in the embodiment shown in FIG. 1 generally includes a NOx storage reduction catalyst 13, a particulate filter 14 carrying the NOx storage reduction catalyst 13, a PM regeneration determination unit 20, and an SOx poisoning determination unit 21. An electronic control unit (ECU) 22, a plasma injector 23, a valve 24, a fuel supply unit 25, an active species addition port 26, and a power supply device 29.

  The NOx occlusion reduction catalyst 13 removes NOx from the exhaust gas by absorbing, adsorbing or occluding NOx in the exhaust gas when the oxygen concentration in the exhaust gas flowing into the NOx occlusion reduction catalyst 13 is high, It has a function of releasing the stored NOx when the oxygen concentration in the exhaust gas flowing into the NOx storage-reduction catalyst 13 is low. The released NOx reacts with HC, CO, etc., which are reducing components contained in the exhaust gas, and is reduced and purified.

  Thus, the NOx occlusion reduction catalyst 13 occludes NOx in the exhaust when the oxygen concentration in the exhaust flowing into the NOx occlusion reduction catalyst 13 is high, while SOx in the exhaust flowing into the NOx occlusion reduction catalyst 13 When NO is contained, it is known to store SOx as well as NOx. The fuel supplied to the internal combustion engine body 10 often contains sulfur components, and in this case, the exhaust gas flowing into the NOx storage reduction catalyst 13 contains SOx produced by the combustion of the sulfur content. Therefore, the NOx storage reduction catalyst 13 stores not only NOx but also SOx.

  The SOx occluded in the NOx occlusion reduction catalyst 13 is more stable and difficult to decompose than the NOx occluded in the NOx occlusion reduction catalyst 13, and the NOx occlusion reduction catalyst 13 occludes and reduces NOx in the exhaust gas. As long as the NOx occlusion reduction catalyst 13 is used within a temperature range that can be purified, it is known that the SOx occluded in the NOx occlusion reduction catalyst 13 remains in the NOx occlusion reduction catalyst 13 without being decomposed. Therefore, as long as the NOx occlusion reduction catalyst 13 is used in a temperature range in which the NOx occlusion reduction catalyst 13 can occlude NOx in the exhaust gas and can be reduced and purified, the NOx occlusion reduction catalyst 13 in the NOx occlusion reduction catalyst 13 is gradually increased. The amount of SOx increases, and as a result, the amount of NOx that can be stored in the exhaust gas by the NOx storage reduction catalyst 13 decreases.

However, the temperature of the NOx occlusion reduction catalyst 13 is raised to a predetermined temperature or higher, for example, 600 ° C. or more, and the exhaust air-fuel ratio flowing into the NOx occlusion reduction catalyst 13 is set to a rich air-fuel ratio, so that the sulfur poisoning desorption reaction is performed. It is also known that can be brought about. That is, by raising the temperature of the NOx occlusion reduction catalyst 13 to a predetermined temperature or higher, the SOx occluded in the NOx occlusion reduction catalyst 13 in the form of nitrate is thermally decomposed, desorbed from the NOx occlusion reduction catalyst 13, and NOx. It is known that SOx desorbed from the occlusion reduction catalyst 13 can be reduced and purified by reducing components such as HC, CO, and H ₂ in the exhaust.

  Based on this, the plasma injector 23 promotes a combustion reaction for raising the temperature of the NOx storage reduction catalyst and promotes a sulfur poisoning / desorption reaction by plasma reforming. A highly reactive active species generated from fuel and pre-plasma reformed is added to the exhaust gas upstream of the NOx storage reduction catalyst 13 to efficiently recover the sulfur poisoning of the NOx storage reduction catalyst 13. It will be done.

  The plasma injector 23 has a plasma reforming unit, generates plasma by applying a voltage to the plasma reforming unit in cooperation with the power supply device 29 connected to the battery 28, and has high reactivity from the fuel. Active species can be generated. Highly reactive active species generated by the plasma injector 23 are added to the exhaust gas through an active species addition port 26 disposed on the exhaust pipe 12 upstream of the NOx storage reduction catalyst 13.

  A fuel supply unit 25 is in fluid communication with the plasma injector 23 via a valve 24. The fuel supply unit 25 is a part that serves as a supply source of fuel to be supplied to the plasma injector 23. The valve 24 plays a role of providing an appropriate supply of fuel from the fuel supply unit 25 to the plasma injector 23. The fuel supply unit 25 may also be used as a component that supplies fuel to the internal combustion engine body 10 to operate the internal combustion engine, and as a component that is separate from the component that supplies fuel to the internal combustion engine body 10. It may be formed.

  The SOx poisoning determination means 21 generally has SOx occlusion amount detection means, SOx release amount detection means, and NOx occlusion reduction catalyst temperature detection means, and has a function of estimating the SOx poisoning state of the NOx occlusion reduction catalyst 13. In addition, the SOx poisoning determination means 21 is connected to the electronic control unit 22 (hereinafter referred to as ECU) by the amount of SOx occluded in the NOx occlusion reduction catalyst 13 and the sulfur poisoning recovery process by the plasma injector 23. Each detection information of the amount of SOx released from the exhaust gas and the temperature of the NOx storage reduction catalyst 13 can be transmitted.

  The SOx occlusion amount detection means has a function of estimating the amount of SOx occluded in the NOx occlusion reduction catalyst 13 by the inflowing exhaust gas. For example, the SOx occlusion amount can be estimated from the concentration of the sulfur component in the fuel and the consumed fuel. In this case, the SOx occlusion amount detection means is configured to include components for detecting the concentration of the sulfur component in the fuel and the amount of consumed fuel.

  The SOx emission amount detection means has a function of estimating the amount of SOx released or desorbed from the NOx occlusion reduction catalyst 13 by the sulfur poisoning recovery process by the plasma injector 23. For example, the SOx release amount from the NOx storage reduction catalyst 13 can be estimated from the NOx storage reduction catalyst temperature and the exhaust air-fuel ratio. In this case, the SOx emission amount detection means is configured to include components for detecting the NOx storage reduction catalyst temperature and the exhaust air-fuel ratio. An exhaust air / fuel ratio sensor can be used to detect the exhaust air / fuel ratio.

  The NOx storage reduction catalyst temperature detecting means has a function of estimating the temperature of the NOx storage reduction catalyst 13. The NOx storage reduction catalyst temperature can be estimated based on, for example, temperature information detected by an exhaust temperature sensor disposed in the vicinity of the NOx storage reduction catalyst 13. In this case, the NOx occlusion reduction catalyst detection means is configured to include an exhaust temperature sensor. However, in this case, there is a slight gap between the NOx occlusion reduction catalyst 13 and the exhaust gas temperature sensor. In order to estimate the temperature gradient at this gap, the rotational load, the air-fuel ratio, the heat transfer coefficient, the catalyst reaction rate, etc. Correction is performed using these parameters, and each component for detecting these pieces of information is also a component for estimating the NOx storage reduction catalyst temperature.

  Even if the particulate filter 14 is a particulate filter in which the NOx occlusion reduction catalyst 13 is supported, a filter in which the NOx occlusion reduction type catalyst 13 is supported on a straight flow honeycomb structure is installed upstream of the particulate filter. It may be configured. The particulate filter 14 serves to collect PM discharged from the internal combustion engine body 10, that is, particulate matter, and prevent PM from being released into the atmosphere. As the particulate filter 14, for example, a general filter such as a wall flow type filter having a honeycomb structure formed of a porous material or a fiber type filter type in which ceramic or metal is formed into a fiber is applied. sell.

  When the particulate filter 14 is used as a means for hindering the release of PM in the exhaust to the atmosphere, it is necessary to perform PM regeneration processing, that is, PM is burned and removed. The accumulated amount of PM collected by the particulate filter 14 will increase as time passes. However, if the accumulated amount of PM exceeds a certain allowable amount, clogging occurs. Raises exhaust pressure and hinders operation performance. For this reason, it is necessary to periodically remove accumulated PM to eliminate clogging. As a means for removing the accumulated PM, PM regeneration processing is performed. Specifically, the PM regeneration process is a process of raising the temperature of the particulate filter 14 to a temperature range where PM can directly burn, and oxidizing and burning PM under a lean air-fuel ratio, that is, excess air. This process can avoid an abnormal increase in the exhaust pressure caused by clogging.

  The PM regeneration determination unit 20 generally includes a PM accumulation amount detection unit and a particulate filter temperature detection unit, and has a function of estimating the PM accumulation state and the temperature state of the particulate filter 14. Further, the PM regeneration determination means 20 is configured to be able to transmit the detection information of the PM accumulation amount and temperature of the particulate filter 14 to the ECU 22.

  The PM accumulation amount detection means has a function of estimating the PM accumulation amount accumulated in the particulate filter 14 by the inflowing exhaust gas. For example, the PM accumulation amount can be estimated from the calculated differential pressure and the exhaust flow rate by measuring the pressure in the exhaust passage before and after the particulate filter 14 and calculating the differential pressure between them. In this case, the PM accumulation amount detection means is configured to include a component that detects the exhaust pressure before and after the particulate filter 14 and a component that detects the exhaust flow rate.

  The particulate filter temperature detecting means has a function of estimating the temperature of the particulate filter 14. The particulate filter temperature can be estimated based on, for example, temperature information detected by an exhaust temperature sensor disposed in the vicinity of the particulate filter 14. In this case, the particulate filter temperature detecting means includes an exhaust temperature sensor. However, in this case, there is a slight gap between the particulate filter 14 and the exhaust gas temperature sensor, and parameters such as rotational load, air-fuel ratio, heat transfer coefficient, etc. are used to estimate the temperature gradient at this gap. Correction is performed, and each component for detecting each piece of information is also a component for estimating the particulate filter temperature. Further, in the particulate filter 14 carrying the NOx occlusion reduction catalyst 13 as in this embodiment, the NOx occlusion reduction catalyst temperature and the particulate filter temperature are considered to be substantially the same value, and the particulate filter temperature detection is performed. The means and the NOx occlusion reduction catalyst temperature detecting means may be the same component.

  The ECU 22 performs detection processing of the SOx poisoning determination unit 21 and the PM regeneration determination unit 20 in order to execute the sulfur poisoning recovery process by the plasma injector 23 and to raise the temperature of the particulate filter 14 as necessary. Based on the detection information, the power supply device 29 that applies a voltage to the plasma injector 23 and the operation of the valve 24 are controlled. Further, the ECU 22 is connected to the battery 28 and configured to receive power from the battery 28.

The effects of the exhaust gas purification apparatus for an internal combustion engine of the present embodiment having the above-described components will be described below.
FIG. 2 is a flowchart showing one embodiment of a control routine of sulfur poisoning recovery process control executed in the internal combustion engine shown in FIG. 1 in which the exhaust gas purification apparatus is incorporated.

In the control routine shown in FIG. 2, first, based on the detection information of the SOx poisoning determination means 21, it is determined whether or not there is a need for sulfur poisoning recovery processing. When it is determined that the sulfur poisoning recovery process is not necessary, this control routine ends. However, when it is determined that the sulfur poisoning recovery process is necessary, the PM regeneration determination means 20 then Based on the detection information, the necessity of PM regeneration processing is determined. If it is determined that there is no need for the PM regeneration process, the process proceeds to the sulfur poisoning recovery process step. If it is determined that the PM regeneration process is necessary, the PM regeneration process is first performed. After being executed and confirming that the PM regeneration process has been completed, the process proceeds to the sulfur poisoning recovery process step. Finally, when it is confirmed that the recovery from sulfur poisoning has been completed, a series of sulfur poisoning recovery processes are completed.
Details of each step will be described below.

  First, in step 101, it is determined whether or not there is a need for sulfur poisoning recovery processing for the NOx storage reduction catalyst 13. This determination is made by the ECU 22 based on the detection information of the SOx occlusion amount of the NOx occlusion reduction catalyst 13 from the SOx occlusion amount detection means which is one component of the SOx poisoning judgment means 21. When it is determined that there is no need for the sulfur poisoning recovery process, this control routine is terminated. If it is determined that there is a need for sulfur poisoning recovery processing, the routine proceeds to the subsequent step 102.

  In step 102, it is determined whether or not the PM regeneration process is necessary. This determination is made by the ECU 22 based on the detection information of the PM accumulation amount from the PM accumulation amount detection means which is a component of the PM regeneration determination means 20, and the PM accumulation amount on the particulate filter exceeds a predetermined amount. In this case, it is determined that PM regeneration processing is necessary.

  If it is determined in step 102 that the PM regeneration process is necessary, the process proceeds to step 103, where it is determined whether or not the temperature of the particulate filter 14 is within the PM combustion processable temperature range. This determination is made by the ECU 22 based on the detection information of the particulate filter temperature from the particulate filter temperature detection means which is one component of the PM regeneration determination means 20.

  If it is determined in step 103 that the particulate filter temperature is within the PM combustion processable temperature region, the process proceeds to the subsequent step 105, where the PM regeneration process is executed. However, the particulate filter temperature can be processed by PM combustion. If it is determined that the temperature is not within the temperature range, the process proceeds to step 104 where active reactive species are generated from the fuel by the plasma injector 23 in order to promote the combustion reaction for raising the temperature of the particulate filter. The Specifically, first, the ECU 24 controls the valve 24 and the power supply device 29, the fuel is supplied from the fuel supply unit 25 to the plasma reforming unit of the plasma injector 23, the voltage is applied to the plasma injector 23, and the fuel is supplied. The plasma modification is performed, and active species having high reactivity are generated. Then, the active species generated by the plasma reforming of the fuel are previously stored in the particulate filter 14 carrying the NOx storage reduction catalyst 13 via the active species addition port 26 or the NOx storage reduction installed upstream of the particulate filter. It is added to the exhaust gas upstream of the catalyst 13. As a result, the combustion reaction is promoted on the NOx occlusion reduction catalyst 13, so that the temperature of the particulate filter can be raised. The temperature rise of the particulate filter by the plasma injector 23 is repeatedly executed until it is confirmed that the particulate filter temperature has reached the PM combustion processable temperature region, and the process proceeds to the subsequent step 105.

  In step 105, PM regeneration processing, that is, removal of PM accumulated in the particulate filter 14 by combustion processing is executed. Specifically, when the exhaust air-fuel ratio flowing into the particulate filter 14 is a lean air-fuel ratio, that is, in an oxygen excess state, the temperature of the particulate filter 14 is raised to within the PM fuel processable temperature region, whereby the combustion of PM Processing is executed. The addition of the active species generated by plasma reforming from the fuel in step 104 to the exhaust consumes oxygen in the exhaust and causes a reduction in PM combustion. Therefore, when the temperature of the particulate filter is raised and it is confirmed that the temperature is within the PM combustion processable temperature region, the application of the voltage to the plasma injector 23 is stopped, thereby generating the plasma reforming from the fuel. Addition of active species to exhaust is discontinued. Thereby, consumption of oxygen in the exhaust gas by the active species is avoided, and a decrease in the PM combustion amount can be prevented. In addition, even though the particulate filter temperature has already reached the temperature at which PM can be combusted, highly reactive active species generated by reforming from the fuel are added to the exhaust, It is possible to prevent the particulate filter from overheating.

  In a diesel internal combustion engine or a lean combustion internal combustion engine, the exhaust air / fuel ratio during normal operation is a lean air / fuel ratio, so the particulate filter 14 is within the PM combustion processable temperature region at step 103 without proceeding to step 104. This means that the PM regeneration process is in progress. In addition, the particulate filter temperature is constantly monitored even during the PM regeneration process, and when the particulate filter temperature becomes lower than the PM fuel processable temperature region, in order to temporarily raise the particulate filter temperature, Addition of activated species generated by plasma reforming from fuel to the exhaust may be made.

  In step 106, it is determined whether the PM regeneration process executed in step 105 has ended. This determination is made by the ECU based on the detection information of the PM accumulation amount from the PM accumulation amount detection means that is one component of the PM regeneration determination means 20. If it is determined that the PM regeneration process has not ended, that is, if it is determined that the PM accumulation amount is not less than the predetermined amount, the process returns to step 105 and the PM regeneration is performed until the PM accumulation amount becomes less than the predetermined amount. The process is executed repeatedly.

  If it is determined in step 106 that the PM regeneration process has been completed, then the routine proceeds to step 107 and step 108 where the combustion reaction for increasing the temperature of the NOx storage reduction catalyst is promoted and the NOx storage reduction catalyst 13 is In order to promote the sulfur poisoning desorption reaction in the reactor, active species with high reactivity are generated from the fuel by the plasma injector 23, and the sulfur poisoning recovery process is executed. Specifically, first, the ECU 24 controls the valve 24 and the power supply device 29, the fuel is supplied from the fuel supply unit 25 to the plasma reforming unit of the plasma injector 23, the voltage is applied to the plasma injector 23, and the fuel is supplied. Thus, active species having high reactivity are generated. Then, the active species previously generated by the plasma reforming of the fuel are added to the exhaust gas upstream of the NOx occlusion reduction catalyst 13 via the active species addition port 26, whereby the sulfur poisoning recovery process is executed. The Since the temperature of the NOx occlusion reduction catalyst 13 has already been raised when executing the PM regeneration process from step 103 to step 105, the temperature can be efficiently raised to the sulfur poisoning recovery processable temperature. The temperature state of the NOx occlusion reduction catalyst 13 is determined by the ECU 22 based on the NOx occlusion reduction catalyst temperature information from the NOx occlusion reduction catalyst temperature detection means, which is a constituent element of the SOx poisoning judgment means 21, and the sulfur poisoning recovery process. The ECU 22 appropriately controls the plasma reforming process of the fuel in order to efficiently execute the process.

  In the sulfur poisoning recovery process executed in step 107 and step 108, it should be noted that the fuel that has been plasma-reformed by the plasma injector 23 and vaporized or atomized in advance is raised in the temperature of the NOx storage reduction catalyst. Is added to the exhaust gas upstream of the NOx storage reduction catalyst 13 to bring about a combustion reaction and a sulfur poisoning desorption reaction.

  For example, in a diesel internal combustion engine, as one means for executing a sulfur poisoning recovery process, it is known to spray liquid fuel such as light oil into exhaust gas. Liquid fuel does not react immediately even when sprayed, but starts a combustion reaction after it is vaporized by an exhaust purification catalyst such as a NOx storage reduction catalyst or piping, so there is a time lag between the fuel spray and the start of the oxidation combustion reaction. May occur. In addition, since liquid fuel has low diffusibility compared to vaporized fuel or finely divided fuel, there is a possibility that the reaction promotion region on the exhaust purification catalyst is limited.

  On the other hand, in the present exhaust purification device having a plasma injector, a highly reducible reformed fuel that has been vaporized or finely divided in advance can be added to the exhaust gas, so that the combustion reaction on the exhaust purification catalyst can be prevented. Acceleration, acceleration of sulfur poisoning desorption reaction, and lowering of the sulfur poisoning recovery processable temperature range are enabled, and the time to reach the sulfur poisoning recovery processable temperature and the sulfur poisoning recovery process time are shortened. Is possible.

The active species generated from the plasma reforming of the fuel by the plasma injector 23 may be lower HC, H _2, CO, or the like. FIG. 3 shows a comparison of temperatures required for desorbing the same amount of SOx from the catalyst in the same time when light oil, C ₃ H ₆ , CO and H ₂ are used alone as reducing species. An example of comparison based on reaction analysis is shown. FIG. 4 shows a comparison of the time required for desorbing the same amount of SOx from the catalyst at the same temperature when light oil and H ₂ are used alone as the reducing species. An example of a comparison based on From FIG. 3 and FIG. 4, compared with the case where the light oil which is not plasma-reformed is used as a reducing species, for example, by using H ₂ produced by plasma reforming of fuel as a reducing species, It can be seen that the temperature at which sulfur poisoning recovery treatment can be performed can be lowered, and the time required for the sulfur poisoning recovery treatment can be shortened.

  Further, as one means for performing the sulfur poisoning recovery process, it is known to improve the efficiency of the sulfur poisoning recovery process by plasma reforming the exhaust itself, but in this case, the capacity of the exhaust itself is large. Therefore, it is considered that a large amount of energy needs to be input in order to perform plasma reforming. On the other hand, in the present exhaust purification apparatus, the amount of fuel to be plasma-reformed can be controlled in cooperation with the ECU 22 and the valve 24, and the highly reducible reformed fuel previously vaporized or atomized is exhausted. Since it can be added to the inside, it is possible to efficiently perform the sulfur poisoning recovery process as compared with the case where the large-volume exhaust itself is subjected to plasma reforming.

  In step 109, the combustion reaction on the NOx storage reduction catalyst 13 and the sulfur poisoning desorption reaction are promoted by the plasma reforming of the fuel executed in step 107 and step 108. It is determined whether or not the sulfur poisoning recovery process has been completed. This determination is made by the ECU 22 based on the SOx release amount information from the SOx release amount detection means that is a component of the SOx poisoning determination means 21. If it is determined that the sulfur poisoning recovery process has not ended, the process returns to step 107 again, and the plasma reforming of the fuel by the plasma injector 23 is performed, and the sulfur poisoning recovery process is completed for the plasma reforming of the fuel. It is repeatedly executed until it is determined that it has been done. When it is determined in step 109 that the sulfur poisoning recovery process has been completed, the process proceeds to step 110, in which the application of voltage by the power supply device 29 to the plasma injector 23 is stopped by the ECU 22, and The control routine of poison recovery process control ends.

  In the present exhaust purification apparatus in which the highly reactive active species reformed and generated in advance by plasma is added to the exhaust upstream of the NOx storage reduction catalyst 13, an exhaust purification apparatus that does not use the plasma injector 13 and In comparison, it is possible to shorten the time to reach the sulfur poisoning recovery processable temperature and the sulfur poisoning desorption reaction time, and thus it is possible to shorten the total time spent on the sulfur poisoning recovery process. To do. Thereby, it becomes possible to improve fuel consumption. In addition, the reduction in the time required for the sulfur poisoning recovery process reduces the time during which the exhaust purification catalyst is exposed to a high temperature, which is caused by the high heat received by the exhaust purification catalyst during the sulfur poisoning recovery process. It is possible to suppress deterioration of the durability performance of the exhaust purification catalyst and to maintain the catalyst purification capability. Furthermore, this exhaust purification device can lower the catalyst temperature at which sulfur poisoning recovery treatment is possible, compared with the exhaust purification device that does not use a plasma injector, and the high heat that the catalyst receives during the sulfur poisoning recovery processing. It is possible to suppress the deterioration of the catalyst durability performance due to the catalyst and to maintain the catalyst purification ability.

  In the present embodiment, the NOx occlusion reduction catalyst is shown as an exhaust purification catalyst that requires a sulfur poisoning recovery process to maintain the exhaust purification performance. However, other exhaust purifications that require a sulfur poisoning recovery process are shown. The present exhaust purification device can also be applied to the catalyst.

  In the present embodiment, the plasma injector 23 is used for plasma reforming of the fuel. In addition to the fuel, air is also configured for plasma reforming using the plasma injector 23. Highly reactive active species plasma-modified from fuel and air may be utilized for PM regeneration treatment and sulfur poisoning recovery treatment. The highly reactive active species plasma-modified from air can promote the combustion reaction on the NOx storage reduction catalyst 13 and can help raise the temperature of the NOx storage reduction catalyst temperature and the particulate filter temperature. It is possible to further shorten the regeneration processing time and the sulfur poisoning recovery processing time. In this case, a common plasma injector may be used to plasma reform the fuel and air, and the fuel and air may be plasma reformed using separate respective plasma injectors. May be configured.

  In a diesel internal combustion engine, it is known that fuel is sprayed into the exhaust gas in order to promote the combustion reaction for raising the temperature of the exhaust purification catalyst or the particulate filter because the incomplete combustion component HC is small in the exhaust gas. However, highly reactive active species generated by plasma reforming from air, such as ozone, cause a combustion reaction with HC of the incompletely combusted component in the exhaust gas, and new fuel is introduced into the exhaust gas. It is possible to raise the exhaust purification catalyst temperature or the particulate filter temperature to a predetermined temperature without spraying. The plasma injector can also function as an injector for non-plasmaized fuel when no voltage is applied. Therefore, when separate injectors are provided for air and fuel, the highly reactive active species plasma-modified from air is added to the exhaust gas, while the other plasma injector allows the non-plasma-modified fuel to be added. It can also be added to the exhaust. This is useful, for example, when there is not enough HC component in the exhaust when raising the temperature of the exhaust purification catalyst.

1 is a schematic view showing an embodiment when an exhaust gas purification apparatus of the present invention is applied to a diesel internal combustion engine or a lean combustion gasoline internal combustion engine for automobiles. It is a flowchart figure which shows one Embodiment of the control routine of the sulfur poisoning recovery process control performed with the internal combustion engine shown in FIG. 1 incorporating this exhaust gas purification apparatus. Light oil as the reducing species, in the case of using each of the C ₃ H _6, CO and H ₂ alone, a diagram showing an example of TEMPERATURE COMPARISON required to desorb SOx same amount from the catalyst at the same time is there. It is a figure which shows an example of the comparison of the time required in order to make the same amount of SOx desorb from the catalyst at the same temperature when light oil and H ₂ are used alone as reducing species.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine body 11 Exhaust manifold 12 Exhaust pipe 13 NOx storage reduction catalyst 14 Particulate filter 20 PM regeneration determination means 21 SOx poisoning determination means 22 ECU
23 Plasma Injector 24 Valve 25 Fuel Supply Unit 26 Active Species Addition Port 27 Generator 28 Battery 29 Power Supply Device

Claims (2)

In an exhaust gas purification apparatus for an internal combustion engine in which a particulate filter carrying an exhaust gas purification catalyst is disposed in an exhaust passage,
Having a plasma injector having a plasma reforming section;
When the particulate matter collected by the particulate filter is not burned, the active species that have been previously plasma-reformed from the fuel by the plasma injector are upstream of the exhaust purification catalyst. In addition to the exhaust gas, a sulfur poisoning recovery process of the exhaust purification catalyst is performed,
An exhaust emission control device for an internal combustion engine. In order to raise the temperature of the particulate filter to a temperature at which the particulate matter can be combusted, the active species that have been subjected to plasma reforming from the fuel by the plasma injector in advance than the exhaust purification catalyst. Add to upstream exhaust,
The exhaust emission control device for an internal combustion engine according to claim 1.

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