JP2007100578A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a sulfur poisoning recovery processing time or a sulfur poisoning recovery processing possible temperature in an exhaust purification device equipped with an exhaust purification catalyst such as a NOx occlusion reduction catalyst which requires sulfur poisoning recovery processing. To provide an exhaust emission control device capable of more efficiently reducing the temperature, improving fuel efficiency and maintaining catalyst purification capability.
An exhaust gas purification apparatus for an internal combustion engine is an exhaust gas purification apparatus for an internal combustion engine in which an exhaust gas purification catalyst is disposed in an exhaust passage. The internal combustion engine exhaust gas purification apparatus includes a plasma injector having a plasma reforming unit, and fuel is previously generated by the plasma injector. The active species obtained by plasma reforming from at least one of air and air are added to the exhaust upstream of the exhaust purification catalyst, and the sulfur poisoning recovery process of the exhaust purification catalyst is performed.
[Selection] Figure 1

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to an exhaust gas purification apparatus for an internal combustion engine equipped with an exhaust gas purification catalyst that requires a sulfur poisoning recovery process to maintain exhaust gas purification performance.

  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 lean-burn gasoline internal combustion engines and diesel 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) generated by the reaction between nitrogen in the air and unburned oxygen increases.

  In order to reduce the amount of harmful NOx produced in a relatively large amount into the atmosphere in this way, it is known to arrange a NOx storage reduction catalyst in the exhaust system of the 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.

Japanese Patent Application Laid-Open No. 10-54274

  However, in order to raise the catalyst temperature, thermal energy is required, and when additional fuel is supplied to obtain the thermal energy, fuel consumption is deteriorated. Further, there is a possibility that the performance of the catalyst itself is deteriorated due to the high 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 view of the above problems, the present invention requires a sulfur poisoning recovery process. In an exhaust gas purification apparatus equipped with a catalyst such as a NOx occlusion reduction catalyst, the sulfur poisoning recovery process is shortened or sulfur poisoning is performed. It is an object of the present invention to provide an exhaust emission control device that can lower the recovery processable temperature more efficiently, improve fuel efficiency, and maintain catalyst purification capability.

  According to the first aspect of the present invention, an exhaust gas purification apparatus for an internal combustion engine in which an exhaust gas purification catalyst is disposed in an exhaust passage has a plasma injector having a plasma reforming portion, and at least one of fuel and air is previously produced by the plasma injector. The exhaust gas of the internal combustion engine, wherein the activated species that have been subjected to plasma reforming is added to the exhaust upstream of the exhaust purification catalyst, and the sulfur purification recovery process of the exhaust purification catalyst is performed A purification device is provided.

  That is, in the first aspect of the invention, the exhaust itself is not plasma-modified in order to bring highly reactive active species to the exhaust, but is generated by plasma reforming from at least one of air and fuel by a plasma injector in advance. The activated reactive species having high reactivity are added to the exhaust upstream of the exhaust purification catalyst, and the sulfur poisoning recovery process is executed. Highly reactive active species generated by plasma reforming from at least one of air and fuel can improve the efficiency of the sulfur poisoning recovery process.

Specifically, the combustion reaction on the exhaust purification catalyst can be promoted by highly reactive active species generated by plasma reforming from air. As a result, the time required to reach the sulfur poisonable temperature can be shortened, and the fuel consumption can be improved. 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. Further, for example, 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 because the incomplete combustion component HC is small in the exhaust gas. However, according to the present invention, the highly reactive active species generated by plasma reforming from air, for example, ozone (O ₃ ), enables efficient combustion with HC, which is a small incomplete combustion component in the exhaust gas. A reaction is brought about, and the exhaust purification catalyst temperature can be raised to a predetermined temperature without spraying new fuel into the exhaust.

  In addition, highly reactive active species generated by plasma reforming from fuel promotes combustion reaction on the exhaust purification catalyst, promotes sulfur poisoning desorption reaction, and lowers the sulfur poisoning recovery treatment temperature. Can be planned. Thereby, the sulfur poisoning recovery processing time can be shortened, and it becomes possible to improve the fuel consumption and maintain the catalyst purification ability as in the case of the plasma reforming from the air described above.

  According to the invention of claim 2, the sulfur poisoning recovery treatment of the exhaust purification catalyst is effected by plasma reforming from active species and air produced by plasma reforming from fuel by the plasma injector. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein both the active species and the active species are utilized.

  That is, in the invention of claim 2, both the active species brought about by plasma reforming from the fuel and the active species brought about by plasma reforming from the air in the sulfur poisoning recovery treatment of the exhaust purification catalyst. Is utilized. As a result, more efficient sulfur is obtained by appropriately utilizing the useful effects of the active species brought about by plasma reforming from fuel and the active species brought about by plasma reforming from air. It is possible to realize poisoning recovery processing.

  According to the invention of claim 3, the active species brought about by plasma reforming from the fuel by the plasma injector contains hydrogen gas, and the activated species brought about by plasma reforming from the air The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein ozone is contained.

  That is, in the invention of claim 3, hydrogen gas is included in the active species brought about by plasma reforming from the fuel, and ozone is contained in the active species brought about by plasma reforming from the air. limit.

  According to a fourth aspect of the present invention, the exhaust of the internal combustion engine according to any one of the first to third aspects, further comprising dew condensation detection means for sensing a dew condensation state of the plasma injector. A purification device is provided.

  That is, in the invention of claim 4, the exhaust gas purification apparatus has dew condensation detection means and can detect the dew condensation state of the plasma injector, thereby causing moisture dew condensation in the exhaust gas inside the plasma injector. It is possible to avoid a plasma injector failure or an increase in power consumption due to electric leakage.

  According to the invention described in each claim, the sulfur poisoning recovery processing time can be shortened or the sulfur poisoning recovery processing temperature can be lowered more efficiently, and fuel efficiency can be improved and catalyst purification ability can be improved. There is a common effect that can be maintained.

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 combustion gasoline internal combustion engine, 11 is an exhaust manifold, 12 is an exhaust pipe, and 13 is a NOx occlusion reduction catalyst. In FIG. 1, 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 / air supply unit, 26 is an active species addition port, and 27 is power generation. , 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 In the exhaust system, an exhaust manifold 11, an exhaust pipe 12, and an NOx storage reduction catalyst 13 are arranged.
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, an SOx poisoning determination means 21, an electronic control unit (ECU) 22, a plasma injector 23, a valve 24, fuel / air. It has the supply part 25, the active species addition port 26, the electric power supply apparatus 29, and the dew condensation detection means 30.

  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 plasma-reacts highly reactive active species in order to promote a combustion reaction for increasing the temperature of the NOx storage reduction catalyst and / or promote a sulfur poisoning desorption reaction. A highly reactive active species generated from at least one of fuel and air depending on the quality and plasma-modified in advance is added to the exhaust gas upstream of the NOx storage reduction catalyst 13 to reduce sulfur poisoning of the NOx storage reduction catalyst 13. It plays the role of recovering efficiently.

  The plasma injector 23 has a plasma reforming unit, generates plasma by applying a voltage to the plasma reforming unit in cooperation with a power supply device 29 connected to the battery 28, and at least one of fuel and air Highly reactive active species can be produced. 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 / air supply unit 25 is in fluid communication with the plasma injector 23 via a valve 24. The fuel / air supply unit 25 is a part that serves as a supply source of fuel and air supplied to the plasma injector 23. The valve 24 plays a role of providing appropriate supply of either fuel or air from the fuel / air supply unit 25 to the plasma injector 23. The fuel / air supply unit 25 may also be used as each component that supplies fuel and air to the internal combustion engine body 10 to operate the internal combustion engine, and each of the fuel and air is supplied to the internal combustion engine body 10. Each component to be supplied may be formed as a separate component.

  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. Further, the SOx poisoning determination means 21 is released from the NOx occlusion reduction catalyst 13 by the electronic control device 22 (hereinafter referred to as ECU), the amount of SOx occluded in the NOx occlusion reduction catalyst 13 and the sulfur poisoning recovery process. Each detection information of the amount of SOx and the temperature of the NOx occlusion 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 release amount detection means has a function of estimating the amount of SOx released or desorbed from the NOx storage reduction catalyst 13 by the sulfur poisoning recovery process. 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 temperature detecting means includes 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.

  The dew condensation detection means 30 may cause a leakage due to the condensation of the plasma injector 23 in order to avoid a failure of the plasma injector 23 due to a leakage due to a condensation of moisture in the exhaust gas inside the plasma injector 23 or an increase in power consumption. It has a function of determining presence or absence, and is configured to be able to transmit this determination information to the ECU 22. Specifically, the determination of the possibility of leakage due to condensation is performed by monitoring the amount of current by installing an ammeter, or by specifying a humidity condition that does not cause a leak and installing a hygrometer However, it may be performed by monitoring the humidity, but may be determined by any other appropriate method. When the plasma injector 23 is used in performing the sulfur poisoning recovery process, if voltage is applied to generate plasma in the state where condensation is present in the plasma reforming portion of the plasma injector 23, electricity is generated due to condensation. Electric leakage may occur. In particular, in the low temperature region, there is a high possibility that electric leakage will occur due to condensation of moisture in the exhaust gas, and it is useful to provide the dew condensation detection means 30 as a component of the exhaust gas purification apparatus in order to avoid this electric leakage. However, the dew condensation detection means 30 is not indispensable, and may not be provided as a component of the exhaust purification apparatus, and is appropriately provided according to the use environment condition and the design condition.

  The ECU 22 applies a voltage to the plasma injector 23 based on the detection information of the SOx poisoning determination means 21 and the detection information of the dew condensation detection means 30 in order to execute the sulfur poisoning recovery process by the plasma injector 23. It plays a role of controlling the operation of the valve 24. 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 an embodiment of a control routine of sulfur poisoning recovery process control executed in the internal combustion engine shown in FIG. 1 to which the present exhaust purification apparatus is applied.

In the control routine shown in FIG. 2, when it is determined that there is a need for sulfur poisoning recovery processing based on the detection information of the SOx poisoning determination unit 21, first, the dew condensation detection unit 30 may cause a leakage due to condensation. The presence or absence is determined. When it is determined that there is a possibility of electric leakage, purge of the plasma reforming unit, that is, condensation removal from the plasma reforming unit is executed. When it is determined that there is no possibility of electric leakage, active species are generated from the air by the plasma injector 23, and the combustion reaction for increasing the temperature of the NOx storage reduction catalyst 13 is promoted. When it is confirmed that the temperature of the NOx storage reduction catalyst 13 has been raised to a predetermined temperature, next, active species are generated from the fuel by the plasma injector, and the release of SOx from the NOx storage reduction catalyst 13 is performed. Therefore, the sulfur poisoning elimination reaction is promoted. 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, a determination is made as to whether or not the power supply device 29 is allowed to apply a voltage to the plasma injector 23 in order to operate the plasma injector 23. Specifically, this determination is made by the ECU 22 based on detection information from the dew condensation detection means 30 that determines whether or not there is a possibility of electric leakage due to dew condensation on the plasma injector 23.

  If it is determined in step 102 that there is a possibility of electric leakage due to condensation in the plasma injector 23, the process proceeds to step 103, where the plasma reforming portion of the plasma injector 23 is purged, that is, condensation is removed. The process is repeated until it is determined that there is no possibility of leakage due to condensation of the plasma injector 23. By executing the purge of the plasma reforming section, the water vapor in the exhaust gas is condensed inside the plasma injector 23, and the water is transmitted to leak electricity, thereby avoiding a problem that causes the plasma injector 23 to malfunction. In addition, an increase in power consumption due to electric leakage can be prevented, and plasma can be generated efficiently.

  As for the purge method of the plasma injector 23, for example, air can be circulated to the plasma reforming section, or water removal by a heater can be considered, but other suitable methods can also be used. Good. When moisture is removed by circulating air through the plasma reforming section, the ECU 24 controls the valve 24 to supply air to the plasma injector 23. If the dew condensation detection means 30 is not provided as a component of the exhaust gas purification device, the process proceeds to step 104 without executing steps 102 and 103.

  If it is determined in step 102 that there is no possibility of electric leakage due to condensation of the plasma injector 23, the process proceeds to step 104, and the plasma injector 23 is promoted to accelerate the combustion reaction for raising the NOx storage reduction catalyst temperature. The generation of highly reactive active species from the air. Specifically, first, the ECU 24 controls the valve 24 and the power supply device 29, air is supplied from the fuel / air supply unit 25 to the plasma reforming unit of the plasma injector 23, and a voltage is applied to the plasma injector 23. Plasma reforming to air is performed, and highly reactive active species are generated. Then, the active species previously generated by the plasma reforming of the air are added into the exhaust gas upstream of the NOx storage reduction catalyst 13 through the active species addition port 26.

One of the active species generated in step 102 is ozone (O ₃ ) generated by plasma reforming to oxygen. The generated ozone is added to the exhaust gas upstream of the NOx storage reduction catalyst 13 so that the oxidizing power of oxygen can be improved, and the combustion reaction on the NOx storage reduction catalyst is promoted even in a low temperature region. It is possible to reduce the time required to reach the sulfur poisoning recovery processable temperature. As a result, the time required to reach the sulfur poisonable temperature can be shortened, and the fuel consumption can be improved. 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 step 105, it is determined whether or not the temperature of the NOx occlusion reduction catalyst 13 has reached a predetermined temperature due to the temperature rise of the NOx occlusion reduction catalyst 13 by the plasma reforming of air by the plasma injector 23 executed in step 104. Is made. This determination is made by the ECU 22 based on the NOx occlusion reduction catalyst temperature information from the NOx occlusion reduction catalyst temperature detection means, which is one component of the SOx poisoning judgment means 21. When it is determined that the NOx occlusion reduction catalyst temperature has not reached the predetermined temperature, the process returns to Step 104 again, and the plasma reforming of the air by the plasma injector 23 is performed, and the plasma reforming is performed at the NOx occlusion reduction catalyst temperature. Is repeatedly performed until it is determined that the predetermined temperature has been reached.

  If it is determined in step 105 that the NOx occlusion reduction catalyst temperature has reached a predetermined temperature, then the routine proceeds to step 106 where a plasma injector is used to promote the sulfur poisoning desorption reaction on the NOx occlusion reduction catalyst 13. The highly reactive active species is produced from the fuel by the fuel. Specifically, first, the fuel / air supply unit 25, the valve 24, and the power supply device 29 are controlled by the ECU 22, fuel is supplied from the fuel / air supply unit 25 to the plasma reforming unit of the plasma injector 23, and the plasma injector 23 is supplied. A voltage is applied to the gas, plasma reforming to fuel is performed, and highly reactive active species are generated. The active species generated in advance by the plasma reforming of the fuel are added to the exhaust gas upstream of the NOx storage reduction catalyst 13 through the active species addition port 26.

  In step 106, it should be noted that the fuel that has been plasma-reformed by the plasma injector 23 and vaporized or atomized in advance to the exhaust upstream of the NOx storage reduction catalyst 13 in order to promote the sulfur poisoning desorption reaction. Is to be added.

  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. Further, since liquid fuel has low diffusibility compared to vaporized fuel or finely divided fuel, there is a possibility that the reaction region on the exhaust purification catalyst is limited.

  In contrast, in the present exhaust purification apparatus having a plasma injector, sulfur-poisoning on the exhaust purification catalyst can be performed because highly reformed reformed fuel previously vaporized or finely divided can be added to the exhaust. It is possible to accelerate the desorption reaction and lower the temperature range in which sulfur poisoning recovery processing is possible, and to shorten the sulfur poisoning recovery processing time. In addition, by adding a highly reducible reformed fuel that has been vaporized or atomized in advance to the exhaust gas, the combustion reaction on the NOx occlusion reduction catalyst 13 can be promoted, and the sulfur poisoning recovery processable temperature is reached. It is also possible to reduce the arrival time.

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 sulfur poisoning recovery processing temperature can be lowered and the sulfur poisoning recovery processing time 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 this exhaust purification apparatus, the amount of fuel or air to be plasma-reformed can be controlled in cooperation with the ECU 22 and the valve 24, and reformed with high reducibility that has been vaporized or atomized in advance. Since the fuel can be added to the exhaust, it is possible to efficiently perform the sulfur poisoning recovery process as compared with the case where the large capacity exhaust itself is subjected to plasma reforming.

  In step 107, whether or not the sulfur poisoning recovery process of the NOx occlusion reduction catalyst 13 has been completed by the promotion of the sulfur poisoning desorption reaction by the plasma reforming of fuel by the plasma injector 23 performed in step 106. Judgment is made. 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 106 again, and the plasma reforming of the fuel by the plasma injector 23 is executed, and the sulfur poisoning recovery process is completed for the plasma reforming of the fuel. It is repeatedly executed until it is determined. When it is determined in step 107 that the sulfur poisoning recovery process has been completed, the process proceeds to step 108, where the ECU 22 stops the application of voltage to the plasma injector 23 by the power supply device 29, and the sulfur poisoning recovery process is completed. The control routine of poison recovery process control ends.

  FIG. 5 is a diagram showing an example of a temperature transition of the NOx storage reduction catalyst 13 throughout the control routine of the sulfur poisoning recovery process control shown in FIG. In FIG. 5, T1 indicates the time required to reach the sulfur poisoning recovery process possible temperature, T2 indicates the sulfur poisoning desorption reaction time, and T3 indicates the total time spent for the sulfur poisoning recovery process. Further, in FIG. 5, the NOx occlusion reduction catalyst 13 when the plasma injector 23 is used in order to show a comparison of T1, T2 and T3 in the sulfur poisoning recovery process when the plasma injector 13 is used and when it is not used. The temperature transition of the NOx occlusion reduction catalyst 13 when the plasma injector 23 is not used is indicated by a broken line.

  In the control routine of the sulfur poisoning recovery process control shown in FIG. 2, the time T1 to reach the sulfur poisoning recovery processable temperature is mainly related to step 104, and the sulfur poisoning desorption reaction time T2 is mainly related to step 106. is connected with. In the present exhaust purification apparatus capable of adding highly reactive active species generated by reforming air or fuel in advance with plasma to the exhaust upstream of the NOx storage reduction catalyst 13, exhaust purification without using the plasma injector 13. Compared with the apparatus, the time T1 to reach the sulfur poisoning recovery processable temperature and the sulfur poisoning desorption reaction time T2 can be shortened, and thus the total time T3 spent on the sulfur poisoning recovery process can be shortened. It is possible 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, in executing the sulfur poisoning recovery process, the plasma injector 13 causes the highly reactive active species plasma-modified from the air and the highly reactive activity plasma-modified from the fuel. It is configured so that both species can be utilized, but highly reactive active species brought about by reforming from air or highly reactive species brought about by reforming from fuel Alternatively, only one of the active species may be used.

  Furthermore, in the present embodiment, each of air and fuel is configured to be plasma-reformed using one plasma injector 13, but each of air and fuel is plasma-reformed with separate injectors. May be configured. Assuming that the plasma injector 23 can also function as an injector for non-plasmaized fuel when no voltage is applied, air and fuel are separated from each other by, for example, plasma from air. While the modified reactive species having high reactivity are added to the exhaust gas, the other plasma injector can add the non-plasma modified fuel into the exhaust gas.

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. It is a figure which shows an example of the temperature transition of the NOx storage reduction catalyst 13 throughout the control routine of sulfur poisoning recovery process control shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine main body 11 Exhaust manifold 12 Exhaust pipe 13 NOx storage reduction catalyst 21 SOx poisoning determination means 22 ECU
DESCRIPTION OF SYMBOLS 23 Plasma injector 24 Valve 25 Fuel / air supply part 26 Active species addition port 27 Generator 28 Battery 29 Power supply apparatus 30 Condensation detection means

Claims (4)

In an exhaust gas purification apparatus for an internal combustion engine in which an exhaust gas purification catalyst is disposed in an exhaust passage,
Having a plasma injector having a plasma reforming section;
The activated species previously plasma-modified from at least one of fuel and air by the plasma injector is added to the exhaust upstream of the exhaust purification catalyst, and the sulfur poisoning recovery process of the exhaust purification catalyst is performed. Do,
An exhaust emission control device for an internal combustion engine.   In the sulfur poisoning recovery treatment of the exhaust purification catalyst, both the active species brought about by plasma reforming from the fuel and the active species brought about by plasma reforming from the air are utilized by the plasma injector. The exhaust emission control device for an internal combustion engine according to claim 1, wherein   The active species brought about by plasma reforming from the fuel by the plasma injector contains hydrogen gas, and the activated species made by plasma reforming from the air contain ozone. An exhaust emission control device for an internal combustion engine according to claim 1 or 2.   The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3, further comprising condensation detection means for sensing a condensation state of the plasma injector.

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