JP2007113497A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

Hydrogen sulfide discharged during sulfur poisoning regeneration of an exhaust purification means such as a NOx catalyst is suitably oxidized and removed.
An exhaust gas purification apparatus for an internal combustion engine according to the present invention is provided in an exhaust passage 15 of the internal combustion engine 10 and includes an exhaust gas purification means 20 for purifying exhaust gas discharged from a combustion chamber 13 and an exhaust gas purification means 20. Are provided with oxidizing gas supply means 40 and 41 capable of supplying an oxidizing gas to the exhaust passage 15 at the downstream position. Since the oxidizing gas is supplied to a position downstream of the exhaust purification means 20, the oxidizing gas can oxidize and remove the hydrogen sulfide discharged during the sulfur poisoning regeneration of the exhaust purification means 20, The SOx produced after the decomposition of hydrogen sulfide is not re-adsorbed to the exhaust gas purification means 20, and the sulfate removal efficiency at the time of sulfur poisoning regeneration can be increased.
[Selection] Figure 1

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly to an exhaust gas purification device for an internal combustion engine provided with exhaust gas purification means such as a catalyst for purifying exhaust gas.

In recent years, NOx catalysts have been put into practical use to purify nitrogen oxides (NOx) contained in the exhaust gas of lean combustion internal combustion engines. For example, in the case of a NOx storage reduction catalyst, the NOx catalyst is a catalyst in which an alkaline earth such as barium (Ba) and a noble metal such as platinum (Pt) are supported on alumina as a carrier, and NOx in exhaust gas is supported. Is stored in the NOx catalyst in the form of nitrate (Ba (NO ₃ ) ₂ ). The NOx catalyst occludes NOx in the exhaust gas when the internal combustion engine is operating at a lean air-fuel ratio, while it operates when the exhaust air-fuel ratio of the internal combustion engine is operated at a rich air-fuel ratio less than the stoichiometric air-fuel ratio. It has the function of releasing and reducing the stored NOx.

However, since sulfur (S) is contained in the fuel and engine lubricating oil, sulfur is also contained in the exhaust gas. For this reason, the NOx catalyst has the property of storing the sulfur component in the exhaust gas as a sulfate such as BaSO ₄ and being poisoned (S poison) by the sulfur component. Since sulfate stored in the NOx catalyst is more stable than nitrate, it is not easily released from the NOx catalyst even if the exhaust air-fuel ratio is rich in fuel, and is gradually accumulated in the NOx catalyst. When the amount of sulfate in the NOx catalyst increases, the amount of NOx that can be absorbed by the NOx catalyst gradually decreases, causing a problem that the NOx storage capacity of the NOx catalyst decreases.

Therefore, by increasing the temperature of the sulfur-poisoned NOx catalyst and placing the NOx catalyst in a reducing atmosphere, the stored sulfate is decomposed into sulfur oxide (SOx) and separated from the NOx catalyst, and the NOx is stored. It is known to restore or regenerate ability. However, when regenerating the NOx catalyst poisoned with S, for example, SOx desorbed by the following chemical reaction formula reacts with hydrogen (H ₂ ) in the exhaust gas to generate hydrogen sulfide (H ₂ S). .
BaSO ₄ + CO → BaCO ₃ + SO ₂
SO ₂ + H ₂ → H ₂ S + O ₂

  Such hydrogen sulfide has a property of generating a strong odor, and if released into the atmosphere, for example, an unpleasant odor is emitted around a vehicle equipped with an internal combustion engine, which is not preferable.

  Therefore, various measures for preventing such a strange odor caused by hydrogen sulfide have been proposed. For example, Patent Document 1 discloses a catalyst to which a specific component that suppresses the generation of hydrogen sulfide is added. Patent Document 2 discloses the generation of hydrogen sulfide during the S-poisoning regeneration of the NOx storage reduction catalyst. An apparatus for executing control for suppressing the above is disclosed.

  However, the catalyst disclosed in Patent Document 1 itself suppresses the generation of hydrogen sulfide, and the hydrogen sulfide discharged from the NOx catalyst at the time of S poisoning regeneration when a normal NOx catalyst is used. No measures are taken. Further, in the apparatus disclosed in Patent Document 2, hydrogen sulfide is discharged in a relatively small amount during S poisoning regeneration of the NOx catalyst, and no measures are taken against this hydrogen sulfide.

  On the other hand, Patent Document 3 discloses that fine particles in exhaust gas collected by a particulate filter are oxidized by an active oxygen release agent carried on the particulate filter. In this process, when the particulate filter recovers from S poisoning, the temperature of the particulate filter is raised, and hydrogen sulfide generated thereby is oxidized and decomposed into SOx by active oxygen generated from the active oxygen release agent.

Japanese Patent Publication No. 6-511117 JP 2004-108176 A JP 2002-97926 A

  According to the apparatus described in Patent Document 3, hydrogen sulfide generated when S particulate poisoning of a particulate filter is recovered can be oxidatively decomposed by the active oxygen released from the active oxygen releasing agent of the filter itself. Is considered to be able to prevent or suppress the release of hydrogen sulfide into the atmosphere.

  However, since this apparatus oxidizes and decomposes hydrogen sulfide released from the particulate filter into SOx by the active oxygen release agent of the filter itself, there is no doubt that the decomposed SOx will adhere to the filter again. Therefore, there remains a problem in the efficiency of removing sulfates at the time of S poison recovery.

  Therefore, the present invention was created in view of the above circumstances, and its purpose is to purify exhaust gas from an internal combustion engine that can suitably oxidize and remove hydrogen sulfide discharged during sulfur poisoning regeneration of exhaust gas purification means such as a NOx catalyst. To provide an apparatus.

  In order to achieve the above object, an aspect of an exhaust gas purification apparatus for an internal combustion engine according to the present invention is provided in an exhaust passage of the internal combustion engine, and purifies exhaust gas discharged from a combustion chamber, and the exhaust gas purification device. And an oxidizing gas supply means capable of supplying an oxidizing gas to the exhaust passage at a position downstream of the means.

  According to this aspect of the present invention, the oxidizing gas can be supplied to the exhaust passage at a position downstream of the exhaust purification unit, and therefore, the exhaust gas is discharged by the oxidizing gas during the sulfur poisoning regeneration of the exhaust purification unit. The oxidized hydrogen sulfide can be removed by oxidation. In particular, since oxidizing gas is supplied at a position downstream of the exhaust purification means, SOx produced after hydrogen sulfide decomposition, which causes a problem in the apparatus described in Patent Document 3, is re-adsorbed to the exhaust purification means. Thus, it is possible to increase the efficiency of removing sulfate during sulfur poisoning regeneration.

Preferably, the exhaust passage is provided in at least one of the exhaust passage at a position upstream of the exhaust purification means and the exhaust passage at a position between the exhaust purification means and the oxidizing gas supply position. Exhaust air-fuel ratio detection means for detecting the air-fuel ratio of the gas;
Provided in at least one of the exhaust passage at a position upstream of the exhaust purification means and the exhaust passage at a position between the exhaust purification means and the oxidizing gas supply position, and detects the temperature of the exhaust gas Exhaust temperature detection means is further provided.

  Hydrogen sulfide is discharged from the exhaust purification means during the sulfur poisoning regeneration of the exhaust purification means. Whether or not the sulfur poisoning regeneration is performed depends on whether the exhaust purification means is in a reducing atmosphere and the ambient temperature is predetermined. Depends on whether it is above temperature. According to this preferred embodiment, since the air-fuel ratio and temperature of the exhaust gas can be detected, whether or not sulfur poisoning regeneration is being performed can be determined based on these values, and the oxidizing gas It is possible to set the supply start timing appropriately.

  Preferably, at least two of the exhaust air / fuel ratio detection means are configured to have the exhaust passage at a position upstream of the exhaust purification means and a position between the exhaust purification means and the oxidizing gas supply position. It is provided in both of the passages.

  If the exhaust air-fuel ratio detection means is provided only in the exhaust passage at a position between the exhaust purification means and the oxidizing gas supply position (that is, only at a position downstream of the exhaust purification means), the following problem occurs. Arise. At the time of sulfur poisoning regeneration, the supplied reducing agent is consumed by the exhaust purification means, and if there is a surplus, it is discharged downstream of the exhaust purification means. In this case, the rich air-fuel ratio is provided on the downstream side of the exhaust purification means, and the supply of the oxidizing gas can be started by detecting this with the exhaust air-fuel ratio detection means on the downstream side. However, if there is no surplus and the amount of reducing agent supplied is exactly the same as the amount of reducing agent consumed in the exhaust purification means, typically it is a rich air-fuel ratio upstream of the exhaust purification means but downstream of the exhaust purification means. It becomes a stoichiometric air-fuel ratio. At this time, the air-fuel ratio on the downstream side of the exhaust purification means is not rich. Therefore, only the exhaust air-fuel ratio detection means on the downstream side does not know whether or not sulfur poisoning regeneration is in progress. As a result, the supply start timing of the oxidizing gas is determined. I can't figure it out. Eventually, even though hydrogen sulfide is discharged during sulfur poisoning regeneration, oxidizing gas may not be supplied and hydrogen sulfide may be discharged to the atmosphere.

  According to the preferred embodiment, the exhaust air-fuel ratio detection means upstream of the exhaust purification means can detect the rich air-fuel ratio and reliably start the supply of the oxidizing gas. Further, the exhaust air / fuel ratio detection means downstream of the exhaust purification means can grasp the amount of oxidizing gas required for the reaction with the reducing agent discharged from the exhaust purification means so that the amount of oxidizing gas can be suitably controlled. become.

  Further, when the air-fuel ratio detected by the exhaust air-fuel ratio detection means is the stoichiometric air-fuel ratio or richer side, and the exhaust temperature detected by the exhaust temperature detection means is a predetermined value or more, The apparatus further includes an oxidizing gas supply control means for executing the supply of the oxidizing gas by the oxidizing gas supply means.

  It is preferable to supply the oxidizing gas only at the time of sulfur poisoning regeneration in which hydrogen sulfide is discharged from the exhaust purification means. This is because generation of oxidizing gas requires energy such as electric power. According to this preferred form, the supply of oxidizing gas is executed only when the sulfur poisoning regeneration condition is met such that the air-fuel ratio is the stoichiometric air-fuel ratio or richer side and the exhaust temperature is equal to or higher than a predetermined value. This makes it possible to prevent wasteful consumption of oxidizing gas generation energy.

  The apparatus further comprises a sulfate amount estimating means for estimating the amount of sulfate adsorbed on the exhaust gas purification means, and the oxidizing gas supply control means estimates the sulfate amount estimating means at the time of supplying the oxidizing gas. It is preferable to control the amount of oxidizing gas supplied from the oxidizing gas supply means based on the amount of sulfate and the air / fuel ratio detected by the exhaust air / fuel ratio detecting means.

  According to this preferred embodiment, it is possible to appropriately control the amount of oxidizing gas in consideration of the amount of hydrogen sulfide discharged from the exhaust purification unit and the excessive amount of reducing agent discharged from the exhaust purification unit. Become. In particular, since the excess reducing agent is oxidized by the oxidizing gas, hydrogen sulfide is once decomposed into SOx by the oxidizing gas, and then the SOx is reduced again to hydrogen sulfide due to the presence of the excess reducing agent. Is prevented.

  In addition, it is preferable that the supply position of the oxidizing gas is separated from the exhaust purification unit by a distance at least so that the supplied oxidizing gas is not substantially thermally decomposed by the high temperature of the exhaust purification unit. As a result, the oxidizing gas can be used efficiently.

  Further, the exhaust purification means may be composed of at least one of a NOx catalyst, a three-way catalyst, an HC adsorbent, a NOx adsorbent, and a particulate matter oxidation catalyst. The exhaust gas purification means may be anything as long as it is sulfur poisoning, that is, the exhaust gas purification performance is deteriorated due to adhesion of sulfur.

  The oxidizing gas is preferably composed of either active oxygen or ozone. In particular, the oxidizing gas is preferably made of ozone which has a stronger oxidizing power than the active oxygen, has a long life, and is more practical.

  According to the present invention, an excellent effect is exhibited that hydrogen sulfide discharged at the time of sulfur poisoning regeneration of an exhaust purification means such as a NOx catalyst can be suitably oxidized and removed.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a system diagram schematically showing an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention. In the figure, reference numeral 10 denotes an internal combustion engine, that is, an engine. The engine of the present embodiment is a spark ignition internal combustion engine, more specifically, a direct injection gasoline engine. However, the engine in the present invention is not limited to a direct injection gasoline engine, and may be, for example, a compression ignition internal combustion engine, that is, a diesel engine. In short, the engine type and type are not limited as long as the exhaust gas contains a sulfur component. 11 is an intake manifold communicated with the intake port, 12 is an exhaust manifold communicated with the exhaust port, and 13 is a combustion chamber. In the present embodiment, fuel supplied from a fuel tank (not shown) to the high pressure pump 17 is pumped to the delivery pipe 18 by the high pressure pump 17 and accumulated in a high pressure state, and the high pressure fuel in the delivery pipe 18 is fuel injection valve 14 is directly injected into the combustion chamber 13. Exhaust gas from the engine 10 passes from the exhaust manifold 12 through the turbocharger 19 and then flows into the exhaust passage 15 downstream thereof. After being purified as described later, the exhaust gas is discharged to the atmosphere.

  The exhaust passage 15 is provided with a NOx catalyst 20 for purifying NOx in the exhaust gas as an exhaust purification means for purifying the exhaust gas discharged from the combustion chamber 13. However, the exhaust purification means is not limited to the NOx catalyst 20, and any exhaustion purification means may be used as long as it is poisoned by the sulfur component contained in the exhaust gas and loses the inherent exhaust purification performance. Other examples of such exhaust purification means include three-way catalysts, HC adsorbents, NOx adsorbents and particulate matter oxidation catalysts. Further, the exhaust gas purification means may comprise a combination of two or more of these.

The NOx catalyst 20 of this embodiment is an NOx storage reduction catalyst (NSR: NOx Strage Reduction). In this case, the NOx catalyst 20 is configured such that a noble metal such as platinum Pt as a catalyst component and a NOx absorbing component are supported on the surface of a base material made of an oxide such as alumina Al ₂ O ₃ . The NOx absorption component was selected from, for example, alkali metals such as potassium K, sodium Na, lithium Li and cesium Cs, alkaline earth metals such as barium Ba and calcium Ca, and rare earth elements such as lanthanum La and yttrium Y. Consists of at least one. The NOx storage reduction catalyst 20 absorbs NOx when the air-fuel ratio of the exhaust gas flowing into it is leaner than a predetermined value (typically the theoretical air-fuel ratio), and the oxygen concentration in the exhaust gas flowing into the NOx catalyst 20 When NO is reduced, the absorbed NOx is released, that is, the absorbed NOx is released. In this embodiment, a direct-injection gasoline engine is used, and lean burn operation can be performed. Therefore, during the lean burn operation, the exhaust air-fuel ratio is lean, and the NOx catalyst 20 absorbs NOx in the exhaust. . Further, when the reducing agent is supplied on the upstream side of the NOx catalyst 20 and the air-fuel ratio of the inflowing exhaust gas becomes rich, the NOx catalyst 20 releases the absorbed NOx. The released NOx reacts with the reducing agent and is reduced and purified.

  Any reducing agent may be used as long as it generates a reducing component such as hydrocarbon HC or carbon monoxide CO in the exhaust gas. Gas such as hydrogen or carbon monoxide, liquid such as propane, propylene, or butane or carbonization of gas. Liquid fuels such as hydrogen, gasoline, light oil and kerosene can be used. In this embodiment, gasoline, which is a fuel, is used as a reducing agent in order to avoid complications during storage and replenishment. As a method for supplying the reducing agent, for example, fuel is injected from an injection valve (not shown) separately provided in the exhaust passage 15 upstream of the NOx catalyst 20, or a larger amount of fuel than normal is injected. A method of performing so-called post-injection in which fuel is injected from the fuel injection valve 14 or fuel is injected from the fuel injection valve 14 in the later stage of the expansion stroke or the exhaust stroke is possible. Thus, the supply of the reducing agent for the purpose of releasing and reducing NOx in the NOx catalyst 20 is referred to as a rich spike.

By the way, the NOx catalyst 20 may be a selective reduction type NOx catalyst (SCR: Selective Catalitic Reduction). This selective reduction type NOx catalyst has a base material such as zeolite or alumina that supports a noble metal such as Pt, a base metal surface that supports a transition metal such as Cu by ion exchange, and the base material. Examples include those having a titania / vanadium catalyst (V ₂ O ₅ / WO ₃ / TiO ₂ ) supported on the surface. In this selective reduction type NOx catalyst, under the condition that the air-fuel ratio of the inflowing exhaust gas is lean, HC and NO in the exhaust gas are reacted steadily and simultaneously so that N ₂ , O ₂ , H ₂ O, etc. Purified. However, the presence of HC is essential for NOx purification. Even if the air-fuel ratio is lean, unburned HC is always contained in the exhaust gas, and this can be used to reduce and purify NOx. Further, the reducing agent may be supplied by performing rich spike like the NOx storage reduction catalyst. In this case, ammonia or urea can be used as the reducing agent in addition to those exemplified above.

Explaining other exhaust purification means, the three-way catalyst is formed by supporting a noble metal such as Pt, Pd and Rh on a porous oxide such as alumina and ceria, and in an atmosphere near the stoichiometric air-fuel ratio (stoichiometric). HC, CO and NOx in the exhaust gas can be purified at the same time. As the HC adsorbent, for example, a porous adsorbent mainly composed of silica (for example, SiO ₂ supported between layered crystals of SiO ₄ ), a porous material such as zeolite, and the like are used in a number of thin axial flows. HC formed in a cylindrical shape having a channel (cell), adsorbing HC components in the exhaust flowing in when the adsorbent temperature is low, into the porous pores and adsorbing when the adsorbent temperature is high Performs absorption and release of HC that releases components. This is particularly effective for reducing the so-called cold HC at the cold start of the engine. The NOx adsorbent is made of porous zeolite or the like, and holds NO or NO ₂ in the exhaust gas as it is, not in the form of nitrate. The particulate matter oxidation catalyst is supported on the surface of a particulate filter that mainly collects particulate matter (PM) emitted from diesel engines, and the collected particulate matter is kept at a relatively low temperature. Oxidation (combustion) removal, for example, noble metals such as platinum Pt, palladium Pd, rhodium Rh, alkali metals such as potassium K, sodium Na, lithium Li, cesium Cs, barium Ba, calcium Ca, strontium Sr And at least one selected from alkaline earth metals such as lanthanum La, yttrium Y, rare earth elements such as cerium Ce, and transition metals such as iron Fe.

Returning to FIG. 1, in the present embodiment, an oxidizing gas supply means capable of supplying an oxidizing gas to the exhaust passage 15 at a position downstream of the NOx catalyst 20 is provided. In the present embodiment, the oxidizing gas is ozone (O ₃ ) having a relatively high oxidizing power. However, this oxidizing gas may be another oxidizing gas, such as active oxygen. The ozone supply means as the oxidizing gas supply means includes an ozone supply member 40 as an oxidizing gas supply member inserted into the exhaust passage 15 and an oxidizing gas connected to the ozone supply member 40 via the ozone supply passage 42. It is comprised from the ozone generator 41 as a gas generation means. The ozone generated by the ozone generator 41 reaches the ozone supply member 40 through the ozone supply passage 42 and is injected and supplied into the exhaust passage 15 from the supply port 43 provided in the ozone supply member 40 toward the downstream side. The supply port 43 is plural (two) in this embodiment, but may be one. The ozone supply member 40 extends in the diameter direction of the exhaust passage 15, and the supply ports 43 are arranged at predetermined intervals in the longitudinal direction of the ozone supply member 40 so that ozone is evenly distributed in the exhaust passage 15.

  As the ozone generator 41, a form in which ozone is generated while flowing air or oxygen as a raw material in a discharge tube to which a high voltage can be applied, or any other type can be used. Here, the air or oxygen as the raw material is a gas taken from outside the exhaust passage 15, for example, a gas contained in the outside air, and is not a gas contained in the exhaust gas in the exhaust passage 15. Note that air or oxygen used as a raw material is not limited to dry air or oxygen. In the ozone generator 41, ozone generation efficiency is higher when a low temperature source gas is used than when a high temperature source gas is used. Therefore, by generating ozone using the gas outside the exhaust passage 15 in this way, it is possible to improve the ozone generation efficiency.

  The ozone generator 41 is connected to an electronic control unit (hereinafter referred to as an ECU (Electrical Control Unit)) 100 as control means, and generates ozone when the ECU 100 is turned on, and generates ozone when the ECU 100 is turned off. Stop generating. The generated ozone is supplied into the exhaust passage 15 from the supply port 43 of the ozone supply member 40 as described above, whereby ozone supply is executed. In the present embodiment, ozone generated by turning on the ozone generator 41 is supplied immediately when ozone is supplied. However, ozone may be generated and stored in advance, and ozone may be supplied by switching valves. Good. It is also possible to supply ozone by pressurizing it with a pump or a compressor.

  The exhaust passage 15 is provided with two air-fuel ratio sensors 54A and 54B as exhaust air-fuel ratio detection means, and these air-fuel ratio sensors 54A and 54B are connected to the ECU 100. One air-fuel ratio sensor 54A is provided in the exhaust passage 15 at a position upstream of the NOx catalyst 20, and the other air-fuel ratio sensor 54A is provided in the exhaust passage 15 at a position between the NOx catalyst 20 and the ozone supply member 40. ing. These air-fuel ratio sensors 54A and 54B are referred to as an upstream air-fuel ratio sensor and a downstream air-fuel ratio sensor, respectively. During normal operation of the engine, the ECU 100 calculates the exhaust air / fuel ratio of the engine based on the output signal of the upstream air / fuel ratio sensor 54A. The air-fuel ratio sensors 54A and 54B are global air-fuel ratio sensors capable of detecting a relatively wide range of air-fuel ratios, and linearly output voltage signals as output signals in accordance with the detected air-fuel ratios. The ECU 100 feedback-controls the fuel injection amount of the engine 10 so that the exhaust air-fuel ratio detected by the upstream air-fuel ratio sensor 54A approaches a predetermined target air-fuel ratio. At this time, the target air-fuel ratio is set to a value leaner than the stoichiometric air-fuel ratio (for example, A / F = 18) during lean burn operation, and the target air-fuel ratio is stoichiometric (for example, A / F = 14. 7).

  The exhaust passage 15 is provided with a temperature sensor 53 as exhaust temperature detection means, and the temperature sensor 53 is connected to the ECU 100. ECU 100 calculates the exhaust gas temperature based on the output signal of temperature sensor 53. The temperature sensor 53 is made of, for example, a thermocouple, and the tip as a temperature measuring unit is positioned at the center of the exhaust passage 15. Similarly, the temperature sensor 53 linearly outputs a voltage signal as an output signal in accordance with the detected exhaust gas temperature. The temperature sensor 53 is provided in the exhaust passage 15 at a position upstream of the NOx catalyst 20, but may be provided in the exhaust passage 15 at a position between the NOx catalyst 20 and the ozone supply member 40.

  ECU 100 executes rich spike control according to a predetermined program stored in advance. That is, when a predetermined rich spike execution condition is satisfied, the ECU 100 simultaneously injects fuel from a separately provided rich spike injection valve or injects a larger amount of fuel from the fuel injection valve 14 than usual. The rich spike is executed by performing post injection from the fuel injection valve 14. As a result, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 20 becomes richer than the stoichiometric air-fuel ratio, the NOx stored in the NOx catalyst 20 is released, and the unburned components (CO, HC) in the exhaust gas are released. It reacts and is reduced and purified. Thus, the rich spike control means is constituted by the ECU 100.

  In the exhaust gas purification apparatus according to this embodiment, sulfur components in the exhaust gas are absorbed or adsorbed on the NOx catalyst 20 in the form of sulfate during engine operation, and the NOx catalyst 20 is sulfur poisoned (S poisoned). The Specifically, the sulfur component in the exhaust gas is absorbed by the NOx absorption component such as barium of the NOx catalyst 20 in the form of sulfate. As the sulfate gradually accumulates in the NOx catalyst 20, the NOx storage capacity of the NOx catalyst 20 decreases.

  Therefore, in order to recover the NOx storage ability of the NOx catalyst 20, sulfur poisoning regeneration in which sulfate is desorbed or released from the NOx catalyst 20 is performed. This sulfur poisoning regeneration is performed by setting the atmosphere of the NOx catalyst 20 as a reducing atmosphere and setting the atmosphere temperature to a relatively high temperature (for example, 400 ° C.) or higher. More specifically, when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 20 is stoichiometric or richer than that and the inflowing exhaust gas temperature is equal to or higher than the predetermined temperature, sulfur poisoning regeneration is performed. . At this time, the sulfate absorbed in the NOx catalyst 20 is decomposed into sulfur oxides (SOx) and desorbed from the NOx catalyst 20.

  The exhaust temperature at which the sulfate can be desorbed, for example, 400 ° C. or higher is a temperature that can be reached relatively easily in the case of a gasoline engine as in this embodiment, but in the case of a diesel engine that originally has a low exhaust temperature. Then, it is a temperature that is relatively difficult to reach. On the other hand, the temperature at which the stored NOx can be released and reduced in the NOx catalyst is lower than the temperature at which sulfate can be desorbed. For example, NOx can be released and reduced at about 200 to 300 ° C. Thus, sulfate is more stable than nitrate, and cannot be removed unless the ambient temperature is higher than that of nitrate. The exhaust temperature at which the sulfate can be desorbed varies depending on the material and structure of the exhaust purification means, and may be, for example, 500 ° C. or higher.

  Such sulfur poisoning regeneration is first performed simultaneously with the purification of the stored NOx released in the NOx catalyst. That is, the purification of the stored NOx release is realized by the above-described rich spike control, and at this time, the exhaust air-fuel ratio is rich. Therefore, at this time, if the exhaust temperature is a temperature at which sulfate can be desorbed, the sulfate is naturally desorbed from the NOx catalyst and decomposed into SOx. In the case of the gasoline engine as in this embodiment, such a high exhaust temperature is relatively frequent. Therefore, if rich spike control for NOx emission reduction is performed, in many cases, sulfur poisoning is simultaneously performed. Playback is executed.

  Second, when the engine is for a vehicle, the air-fuel ratio is made rich at every predetermined timing in consideration of the travel distance, fuel consumption, fuel type (regular or high-octane), sulfur concentration in the fuel, etc. In this method, the exhaust gas temperature is raised to a predetermined temperature or higher to perform sulfur poisoning regeneration. This is a control dedicated to sulfur poisoning regeneration. For example, at every predetermined travel distance, the air-fuel ratio is temporarily made rich and the exhaust temperature is raised to a predetermined temperature or higher by increasing the engine speed, etc. Playback can be performed. In addition, like these first and second methods, sulfur poisoning regeneration that is intentionally performed by performing predetermined control is referred to as forced regeneration.

  Third, even if it is not during forced regeneration, sulfur poisoning regeneration is automatically performed if the engine is in an operating state that satisfies the sulfur poisoning regeneration condition. Specifically, for example, when the engine is operating at a high load when the vehicle is traveling uphill, the air-fuel ratio feedback control is stopped, the exhaust air-fuel ratio becomes richer than stoichiometric, and the exhaust temperature can be desorbed with sulfate. When the temperature is reached, the sulfate is naturally desorbed from the NOx catalyst and decomposed into SOx. Such sulfur poisoning regeneration performed without special control is called natural regeneration.

By the way, as described above, during the sulfur poisoning regeneration, the produced SOx reacts with hydrogen (H ₂ ) in the exhaust gas to produce hydrogen sulfide (H ₂ S). If this hydrogen sulfide is released from the exhaust passage into the atmosphere, it will cause an unpleasant odor, which is not preferable.

Therefore, in the exhaust purification apparatus of the present embodiment, hydrogen sulfide discharged from the NOx catalyst 20 at the time of sulfur poisoning regeneration is oxidized to SOx by ozone as an oxidizing gas before being released into the atmosphere. This prevents the release of hydrogen sulfide into the atmosphere and the generation of off-flavors associated therewith. Specifically, ozone generated by the ozone generator 41 is supplied from the ozone supply member 40 into the exhaust passage 15 at a position downstream of the NOx catalyst 20. Thereby, hydrogen sulfide discharged from the NOx catalyst 20 can be oxidized into SOx by ozone after the discharge, and discharge of hydrogen sulfide into the atmosphere can be prevented in advance. The reaction between hydrogen sulfide H ₂ S and ozone O ₃ is represented by the following formula.
H ₂ S + O ₃ → H ₂ O + SO ₂
As can be seen, the reaction between hydrogen sulfide H ₂ S and ozone O ₃ is an equimolar reaction.

  In particular, the ozone supply position (that is, the position of the supply port 43) in the exhaust passage 15 is a position on the downstream side of the NOx catalyst 20, more specifically, a position separated from the NOx catalyst 20 by a predetermined distance downstream. By doing so, SOx produced after the decomposition of hydrogen sulfide, which becomes a problem in the apparatus described in Patent Document 3, is not re-adsorbed to the NOx catalyst, and the sulfate removal efficiency during sulfur poisoning regeneration is eliminated. Can be increased.

  Here, the NOx catalyst 20 is at a high temperature during the sulfur poisoning regeneration, and if ozone is supplied immediately after the vicinity of the NOx catalyst 20, the ozone is thermally decomposed, and the oxidizing ability of hydrogen sulfide is reduced accordingly. End up. In general, ozone is thermally decomposed at a temperature of about 250 ° C. Therefore, the distance L from the NOx catalyst 20 (especially its downstream end) to the ozone supply position is preferably set to a distance that does not substantially cause such ozone thermal decomposition, and is ideally as long as possible. It is preferable to do this.

  If ozone is supplied upstream of the NOx catalyst 20, ozone reacts with NOx and SOx in the exhaust gas and is consumed, so this should be avoided.

  By the way, it is preferable to supply ozone only at the time of sulfur poisoning regeneration in which hydrogen sulfide is discharged from the NOx catalyst 20. This is because, in order to generate ozone with the ozone generator 41, electric power is required. Therefore, useless consumption of ozone leads to useless consumption of electric power, which leads to deterioration of fuel consumption. For example, even if the ozone generator 41 is always turned on and ozone supply is always performed, the discharge of hydrogen sulfide can be prevented, but this should be avoided.

  Therefore, in the present embodiment, it is determined whether or not sulfur poisoning regeneration is being executed based on the exhaust air / fuel ratio detected by the upstream air / fuel ratio sensor 54A and the exhaust gas temperature detected by the temperature sensor 53. Only when it is being executed, the ozone generator 41 is turned on and ozone supply is executed. Specifically, the ECU 100 performs sulfur poisoning regeneration when the detected exhaust air-fuel ratio is a stoichiometric value or a richer value and the detected exhaust temperature is equal to or higher than the predetermined temperature (for example, 400 ° C.). It is determined that it is being executed, and the ozone generator 41 is turned on. According to this, regardless of whether it is forced regeneration or natural regeneration, ozone is supplied only under a situation where hydrogen sulfide is discharged, and wasteful consumption of ozone and ozone-generated power can be prevented. In other words, the exhaust air-fuel ratio and the exhaust temperature are conditions that determine the ozone supply start timing.

  As shown in FIG. 1, in this embodiment, the upstream air-fuel ratio sensor 54A is provided on the upstream side of the temperature sensor 53, but this arrangement may be reversed.

  By the way, in view of the efficient use of ozone as described above, it is preferable to supply the minimum amount of ozone commensurate with the amount of discharged hydrogen sulfide. Therefore, in the present embodiment, the following control is executed in order to realize the supply of such an optimal amount of ozone.

  First, the ECU 100 estimates the amount of sulfate adsorbed on the NOx catalyst 20 during normal operation other than during sulfur poisoning regeneration. For example, the amount of adsorbed sulfate is estimated according to a predetermined map based on the amount of fuel consumed and the fuel properties (including the amount of sulfur contained, regular premium, etc.) consumed since the previous sulfur poisoning regeneration.

Next, when the ECU 100 determines that it is during sulfur poisoning regeneration based on the outputs of the upstream air-fuel ratio sensor 54A and the temperature sensor 53, the downstream air-fuel ratio sensor 54B causes the exhaust air on the downstream side of the NOx catalyst 20 to be exhausted. Detect the fuel ratio. During the sulfur poisoning regeneration, a reducing agent (fuel) is supplied to the NOx catalyst 20, and fuel-rich exhaust gas is supplied to the NOx catalyst 20. Therefore, from the NOx catalyst 20, in addition to the sulfur oxide SOx and hydrogen sulfide H ₂ S produced by the decomposition of the sulfate, in many cases, an excessive reducing agent component (used for the decomposition of the nitrate and sulfate) ( HC, CO, _{H 2,} etc.) are discharged. In this way, the supplied reducing agent is consumed by the NOx catalyst 20, and the excess is discharged from the NOx catalyst 20. Therefore, the exhaust air-fuel ratio differs between the upstream side and the downstream side of the NOx catalyst 20, and it is preferable to provide air-fuel ratio sensors on the upstream side and the downstream side of the NOx catalyst 20, respectively, as in this embodiment.

  On the other hand, the amount of ozone supplied at this time needs to be at least such that all of the discharged hydrogen sulfide is oxidatively decomposed. For this reason, at least equimolar ozone with the discharged hydrogen sulfide is supplied. Since the amount of sulfate adsorbed on the NOx catalyst 20 is estimated, for example, the relationship between the estimated value of this adsorbed sulfate amount and the amount of discharged hydrogen sulfide is mapped in advance, and the amount of discharged hydrogen sulfide is in accordance Supply the amount of ozone.

However, there is a problem that the excess reducing agent discharged from the NOx catalyst 20 reacts with ozone and consumes ozone. For example the reducing agent is the case of CH _2, the reaction can be expressed by the following equation.
CH ₂ + O ₃ → H ₂ O + CO ₂

  If this happens, ozone will not be able to decompose hydrogen sulfide by the amount consumed. Accordingly, the amount of ozone to be supplied is a value obtained by adding the amount consumed by the reaction with the discharged surplus reducing agent to the amount necessary for the decomposition of the discharged hydrogen sulfide. An air-fuel ratio sensor 54B is provided downstream of the NOx catalyst 20 in order to determine the amount of reaction with the excess reducing agent. It should be noted that a reducing agent such as unburned HC is easier to react with ozone than hydrogen sulfide.

  A map showing the relationship between the air-fuel ratio downstream of the NOx catalyst and the corresponding ozone amount is input to the ECU 100 as shown in FIG. This map is created based on experiments and the like. The amount of ozone here is the amount of ozone consumed by the reaction with the excess reducing agent, and the air-fuel ratio is a value corresponding to that excess reducing agent. As the air-fuel ratio increases (that is, on the lean side), the surplus reducing agent decreases, so the amount of ozone decreases. The ECU 100 refers to the map of FIG. 2 based on the downstream air-fuel ratio detected by the downstream air-fuel ratio sensor 54B and refers to the amount of ozone consumed by the reaction with the excess reducing agent (hereinafter referred to as the reducing agent ozone amount). To decide.

Next, the ECU 100 determines an ozone amount (hereinafter referred to as an H ₂ S ozone amount) necessary for decomposing hydrogen sulfide generated from the adsorbed sulfate based on the estimated adsorbed sulfate amount. That is, as indicated by J in FIG. 3, it is assumed that the total amount of adsorbed sulfate is instantaneously decomposed into hydrogen sulfide (between 0 and t1) simultaneously with the start of sulfur poisoning regeneration, and the discharge of hydrogen sulfide is instantaneous. The H ₂ S ozone to H ₂ S must be instantaneously supplied in equimolar amounts corresponding to the total amount of discharged hydrogen sulfide. On the other hand, as indicated by K in FIG. 3, the total amount of adsorbed sulfate is decomposed over a relatively long time (0 to t2), and thus hydrogen sulfide may be discharged little by little. In this case, it is necessary to supply the H ₂ S ozone to the amount corresponding to the amount of discharged hydrogen sulfide little by little over a relatively long time.

Since it is unpredictable how hydrogen sulfide is actually discharged, in the present embodiment, the maximum H ₂ S ozone amount (for example, O3max shown in the figure) that is appropriate when it is assumed that the hydrogen sulfide is instantaneously discharged. ) For the expected maximum time (eg t2 shown). As a result, ozone may be partly wasted (corresponding to the blank area in the broken line), but the entire amount of hydrogen sulfide can be reliably oxidatively decomposed with ozone, and it is necessary to be realistically appropriate. Hydrogen sulfide can be oxidatively decomposed with a minimum amount of ozone.

Furthermore, since excess reducing agent is oxidized by ozone, hydrogen sulfide H ₂ S is prevented from being decomposed into SOx by ozone, and then the SOx is prevented from being reduced again to H ₂ S due to the presence of the reducing agent. . This point will be described later.

Here, since the ozone supply control is digital processing, the ozone supply amount is determined every predetermined time (for example, several tens of milliseconds). That is, the ozone supply amount is determined by adding the reductant ozone amount and the H ₂ S ozone amount every predetermined time. Then, electric power corresponding to the determined ozone supply amount is output from the ECU 100 to the ozone generator 41, and the ozone supply amount is controlled. This control is performed until a predetermined time elapses from the start of sulfur poisoning regeneration (from t = 0 to t = 2 in FIG. 3).

  Incidentally, the air-fuel ratio sensor may be only the downstream air-fuel ratio sensor 54B, and the upstream air-fuel ratio sensor 54A may be omitted. However, in this case, the following problems occur. That is, as described above, at the time of sulfur poisoning regeneration, the supplied reducing agent is consumed by the NOx catalyst 20, and if there is a surplus, it is discharged downstream of the NOx catalyst 20. In this case, the air-fuel ratio is rich on the downstream side of the NOx catalyst 20, and this fact is detected by the downstream-side air-fuel ratio sensor 54B, thereby determining that sulfur poisoning is being regenerated and starting the ozone supply control as described above. be able to.

  However, there may be a case where there is no surplus and the amount of supplied reducing agent is just the same as the amount of reducing agent consumed in the NOx catalyst 20. For example, the rich air-fuel ratio is upstream of the NOx catalyst 20, but the stoichiometric air-fuel ratio is downstream of the NOx catalyst 20. Depending on the composition of the exhaust purification means, hydrogen sulfide may be discharged to the downstream side even if the upstream side is at the stoichiometric air-fuel ratio. In these cases, the air-fuel ratio on the downstream side of the NOx catalyst is not rich. Therefore, it is impossible to determine whether or not sulfur poisoning regeneration is in progress only by the downstream air-fuel ratio sensor 54B, and as a result, ozone supply cannot be started. In this case as well, actually, the sulfate absorbed in the NOx catalyst 20 is discharged as hydrogen sulfide by the supply of the reducing agent, but the ozone supply cannot be executed or started. Will be discharged into the atmosphere. In view of such circumstances, it is preferable that the air-fuel ratio sensor is provided with both the upstream air-fuel ratio sensor 54A and the downstream air-fuel ratio sensor 54B.

Next, the result of the experiment using the simulation gas (model gas) performed in connection with the present embodiment is shown below.
[Experiment 1]
(1) Experimental apparatus FIG. 4 shows the whole experimental apparatus, and FIG. 5 shows the details of the V part of FIG. 61 is a plurality of gas cylinders, and each gas cylinder is filled with a raw material gas for making a simulated gas imitating the exhaust gas composition of a gasoline engine. The source gas here is a gas such as N ₂ , O ₂ , and CO. A simulation gas generator 62 includes a mass flow controller, and generates a simulation gas MG by mixing each raw material gas by a predetermined amount. As shown in detail in FIG. 5, the simulation gas MG passes through a three-way elbow 72 after passing through a NOx catalyst (occlusion reduction type) 64 disposed in the quartz tube 63, and then passes through an exhaust duct (not shown) to the outside. Discharged.

As shown in FIG. 4, the gaseous oxygen O ₂ supplied from the oxygen cylinder 67 is branched into two, and the flow rate is controlled by the flow rate control unit 68 on one side and then supplied to the ozone generator 69. In the ozone generator 69, oxygen is selectively and partially converted into ozone O _3, and these oxygen and ozone (or only oxygen) reach the ozone analyzer 70. On the other side of the branch, the flow rate of oxygen is controlled by another flow rate control unit 71, and then mixed with the gas supplied from the ozone generator 69 to reach the ozone analyzer 70. The ozone analyzer 70 measures the ozone concentration of the gas that has flowed into it, that is, the supply gas, and then the flow rate of the supply gas is controlled by the flow rate control unit 71. Excess supply gas is discharged to the outside through an exhaust duct (not shown), and the supply gas whose flow rate is controlled is connected to the simulation gas MG at a three-way elbow 72 positioned downstream of the NOx catalyst 64 as shown in FIG. Mixed. The mixed gas is processed by an exhaust gas analyzer 77 for measuring SOx, SO ₂ , and H ₂ S concentrations and an ozone analyzer 78 for measuring ozone concentrations, and then discharged to the outside from an exhaust duct (not shown). .

  An electric heater 73 is provided on the outer peripheral portion of the quartz tube 63 so that the temperature of the NOx catalyst 64 is controlled. Further, a temperature sensor 75 for measuring the temperature at the position immediately upstream of the NOx catalyst 64 is provided.

The NOx storage reduction catalyst 64 used here has a diameter of 30 mm, a length of 25 mm, a cell wall thickness of 4 mil (milli inch length, 1/1000 inch) (about 0.1 mm), and a cell count of 400 cpsi (cells per square inch) ( A cordierite honeycomb structure of about 62 pieces / cm ² ) coated with γ-Al ₂ O ₃ was used. The coating amount is 120 g / L (however, the denominator L (liter) means per 1 L of catalyst). To this, barium acetate was supported by water absorption and calcined at 500 ° C. for 2 hours. The supported amount of barium acetate is 0.1 mol / L. This catalyst was immersed in a solution containing ammonium hydrogen carbonate and dried at 250 ° C. Furthermore, Pt was supported using an aqueous solution containing dinitrodiammine platinum, dried, and then fired at 450 ° C. for 1 hour. The supported amount of Pt is 2 g / L.

Next, this NOx catalyst 64 was installed in a laboratory flow reactor, and a simulated gas having the following composition was passed at 400 ° C. for 4 hours to poison the sulfur. The flow rate of the simulation gas is 10 L / min.
Simulated gas composition: SO ₂ 200 ppm, O ₂ 10%, H ₂ O 3%, balance N ₂

(2) Experimental conditions The sulfur-poisoned NOx catalyst 64 is placed in the quartz tube 63 of FIG. 5, and the electric heater 73 is controlled so that the temperature detected by the temperature sensor 75 is constant (600 ° C.). Then, N ₂ is allowed to flow as a simulation gas until the temperature becomes constant. When the temperature is stabilized at a constant level, a simulation gas having the following composition is circulated, and at the same time, downstream of the NOx catalyst 64. Supply gas from the ozone generator 69 is supplied. Here, when ozone supply is performed, the ozone generator 69 is turned on. As a result, the supply gas supplied to the downstream side of the NOx catalyst 64 becomes a mixed gas of ozone and oxygen. Conversely, when ozone supply is not performed, the ozone generator 69 is turned off. Thereby, the supply gas supplied to the downstream side of the NOx catalyst 64 is only oxygen. The composition of the simulation gas is, _{H 2} is 5000ppm by volume concentrations respectively, _{H 2} O is 3%, the remainder being _{N 2.} The flow rate of the simulation gas is 10 L (liter) / min. The composition of the supply gas containing ozone is 50000 ppm of ozone O ₃ and the balance is O ₂ . The flow rate of the supply gas is 2 L (liter) / min.

The H ₂ S amount and SOx amount after supplying the supply gas are measured by the exhaust gas analyzer 77, and the composition ratio (mol ratio) of H ₂ S and SOx for 10 minutes after the supply gas supply starts (experiment start). It was calculated from the time integration of each concentration.

(3) Examples and Comparative Examples / Examples Experiments were performed with the ozone generator 69 turned on.
Comparative Example The experiment was performed with the ozone generator 69 turned off.

(4) Experimental Results FIG. 6 shows a comparison of the composition ratio (mol ratio) of H ₂ S and SOx. As can be seen, in the example, since ozone was supplied, there was no discharge of hydrogen sulfide H ₂ S, and all sulfur desorbed from the NOx catalyst 64 was decomposed into SOx, whereas ozone was supplied in the comparative example. As a result, most of the hydrogen sulfide is H ₂ S. From this result, it can be confirmed that hydrogen sulfide is effectively oxidized and decomposed into SOx by supplying ozone.

[Experiment 2]
In this experiment, the temperature at which the sulfur component adsorbed on the catalyst was desorbed as hydrogen sulfide H ₂ S was determined by the following method.

First, the catalyst used was a carrier obtained by adsorbing barium acetate on a carrier in which γ-Al ₂ O ₃ and TiO ₂ were mixed at a weight ratio of 1: 1 and calcined at 500 ° C. for 2 hours. The supported amount of barium acetate is 0.2 mol per 120 g of support. This catalyst was immersed in a solution containing ammonium hydrogen carbonate and dried at 250 ° C. Furthermore, Pt was supported using an aqueous solution containing dinitrodiammine platinum, dried, and then fired at 450 ° C. for 1 hour. The amount of Pt supported is 2 g per 120 g carrier. This catalyst was formed into pellets having a diameter of 2 to 3 mm and used in experiments.

  Next, 2 g of the pellet catalyst thus adjusted was placed in a laboratory flow reactor, and a simulated gas having the following composition was allowed to flow for 4 hours while repeating a cycle of a lean composition of 55 seconds and a rich composition of 5 seconds. , Sulfur poisoned. The flow rate of the simulated gas is 10 L / min for both the lean composition and the rich composition.

Lean composition simulation gas: CO 700 ppm, C ₃ H ₆ 800 ppm, CO ₂ 10.5%, NO 800 ppm, O ₂ 4.1%, H ₂ O 3%, SO ₂ 200 ppm
Rich composition simulation gas: CO 5900 ppm, C ₃ H ₆ 2230 ppm, CO ₂ 10.5%, NO 100 ppm, O ₂ 0.42%, H ₂ O 3%, SO ₂ 200 ppm
This sulfur-poisoned catalyst was installed in a laboratory flow reactor and heated at a rate of 10 ° C. per minute while flowing a He gas containing 1% of H ₂ to reduce the amount of desorbed H ₂ S. Asked.

The desorption profile of H ₂ S obtained by this experiment is shown in FIG. From this result, it is understood that the ozone used in this experiment should be supplied under the condition of this temperature or higher because H ₂ S desorption occurs at 400 ° C. or higher.

[Experiment 3]
In this experiment, it was confirmed that the oxidation of hydrogen sulfide by ozone was inhibited by the reducing agent present in the exhaust gas.

This experiment was performed using the same experimental apparatus as in Experiment 1. Then, a simulated gas having the following composition was circulated under a temperature condition of 200 ° C., a supply gas containing ozone was mixed with the simulated gas downstream of the catalyst, and the amounts of H ₂ S and SOx were measured with an analyzer.
Simulated gas composition: H ₂ 10000 ppm or 0 ppm, H ₂ S 200 ppm, balance N ₂

The flow rate of the simulation gas is 10 L / min. Further, the composition of the supply gas is 50,000 ppm for ozone O ₃ and the remaining is O ₂ . The flow rate of the supply gas is 1 L (liter) / min.

Regarding the experimental results, when the simulated gas contained 10,000 ppm of H _2, the proportion of H ₂ S contained in the simulated gas that was oxidized to SOx was 2%. In contrast, if the simulated gas does not contain _{H 2} 100% of the _{H 2} S contained in the simulated gas is oxidized to SOx. From this result, it can be seen that when the reducing component coexists with the exhaust gas, the oxidation of H ₂ S by ozone is inhibited. According to the embodiment, in addition to the oxidized H ₂ S discharged from the catalyst (NOx catalyst), the oxidized ozone of the reducing component (HC and the like) is also supplied, so the entire amount of discharged H ₂ S is reduced. It can be reliably oxidized.

  As mentioned above, although embodiment of this invention has been described, this invention can also take other embodiment.

1 is a system diagram schematically showing an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention. It is a map which shows the relationship between the air fuel ratio downstream of a NOx catalyst, and the ozone amount corresponding to this. It is a graph showing the relationship between the logarithmic H _{2 S} amount of ozone supplied and time. It is a figure which shows the whole experimental apparatus of the experiment conducted in relation to this embodiment. It is the detail of the V section of FIG. The composition ratio of H ₂ S and SOx is a graph showing a comparison of (mol ratio). It is a graph showing the elimination profile of H 2 _S.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 13 Combustion chamber 15 Exhaust passage 20, 64 NOx catalyst 40 Ozone supply member 41 Ozone generator 53 Temperature sensor 54A, 54B Air-fuel ratio sensor 100 Electronic control unit (ECU)

Claims (8)

An exhaust purification means provided in an exhaust passage of the internal combustion engine for purifying exhaust gas discharged from the combustion chamber;
An exhaust gas purification apparatus for an internal combustion engine, comprising: an oxidizing gas supply means capable of supplying an oxidizing gas to the exhaust passage at a position downstream of the exhaust purification means. Provided in at least one of the exhaust passage at a position upstream of the exhaust purification means and the exhaust passage at a position between the exhaust purification means and the oxidizing gas supply position, and detects the air-fuel ratio of the exhaust gas Exhaust air-fuel ratio detection means for
Provided in at least one of the exhaust passage at a position upstream of the exhaust purification means and the exhaust passage at a position between the exhaust purification means and the oxidizing gas supply position, and detects the temperature of the exhaust gas The exhaust gas purification device for an internal combustion engine according to claim 1, further comprising exhaust gas temperature detection means.   At least two exhaust air-fuel ratio detection means are provided in both the exhaust passage at a position upstream of the exhaust purification means and the exhaust passage at a position between the exhaust purification means and the oxidizing gas supply position. The exhaust emission control device for an internal combustion engine according to claim 2, wherein the exhaust gas purification device is provided respectively.   When the air-fuel ratio detected by the exhaust air-fuel ratio detection means is the stoichiometric air-fuel ratio or richer than that and the exhaust temperature detected by the exhaust temperature detection means is a predetermined value or more, the oxidizing property 4. The exhaust gas purification apparatus for an internal combustion engine according to claim 2, further comprising an oxidizing gas supply control means for executing supply of oxidizing gas by the gas supplying means. A sulfate amount estimating means for estimating the amount of sulfate adsorbed on the exhaust purification means;
The oxidizing gas supply control means, based on the sulfate amount estimated by the sulfate amount estimating means and the air-fuel ratio detected by the exhaust air-fuel ratio detecting means when the oxidizing gas is supplied, The exhaust gas purification apparatus for an internal combustion engine according to claim 4, wherein the amount of oxidizing gas supplied from the oxidizing gas supply means is controlled.   The supply position of the oxidizing gas is separated from the exhaust purification unit by a distance at least so that the supplied oxidizing gas is not substantially thermally decomposed by the high temperature of the exhaust purification unit. Item 6. An exhaust emission control device for an internal combustion engine according to any one of Items 1 to 5.   The internal combustion engine according to any one of claims 1 to 6, wherein the exhaust purification means includes at least one of a NOx catalyst, a three-way catalyst, an HC adsorbent, a NOx adsorbent, and a particulate matter oxidation catalyst. Exhaust purification device. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 7, wherein the oxidizing gas comprises any of active oxygen and ozone.

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