JP2009264308A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine can reduce emission of NOx, by introducing EGR just after starting an engine regardless of an operation state, by realizing rich operation for reducing the NOx included in exhaust gas from the engine, by introducing the EGR by reducing the attachment and deposition of a deposit in an EGR passage. <P>SOLUTION: This exhaust emission control device is provided with a fuel reformer 50 separately from an exhaust passage 4 of the internal combustion engine 1. and is provided with a first introducing passage 57 for introducing reducing gas manufactured by the fuel reformer 50 into the exhaust passage 4 from the upstream side of an NOx control catalyst 32 among the exhaust passage 4, and a second introducing passage 58 for introducing a part of the exhaust gas into a recirculating passage 6 recirculating in an intake passage 2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine. Specifically, the present invention relates to an exhaust gas purification apparatus for an internal combustion engine that includes a NOx purification catalyst that adsorbs or occludes NOx in exhaust gas and reduces the adsorbed or occluded NOx.

  In the present invention, the term “rich” indicates that the air / fuel ratio of the fuel in question (hereinafter referred to as “air-fuel ratio”) is smaller than the stoichiometric air-fuel ratio, and is referred to as “lean”. The term indicates that the air / fuel ratio of the fuel in question is greater than the stoichiometric air / fuel ratio described above. In the following description, the mass ratio of air to fuel in the air-fuel mixture flowing into the internal combustion engine (hereinafter also referred to as engine) is referred to as the engine air-fuel ratio, and the mass ratio of air to combustible gas in the exhaust passage is defined as the exhaust gas. It is called air-fuel ratio.

Conventionally, a technique for purifying nitrogen oxide (hereinafter referred to as “NOx”) contained in exhaust gas is known.
For example, in Patent Documents 1 and 2 and Non-Patent Document 1, a NOx occlusion reduction catalyst (hereinafter referred to as “LNT”) is provided in the exhaust passage, and the exhaust gas is passed through the oxidation catalyst during the lean operation in which the exhaust gas has excessive oxygen. There is shown an exhaust purification device that stores NOx by reacting with alkali metal or alkaline earth metal and stores it, and reduces the stored NOx during a rich operation in which the oxygen concentration of the exhaust gas becomes low. In this exhaust purification apparatus, NOx occlusion and NOx reduction can be performed periodically by repeating the lean operation and the rich operation.

  Further, for example, in Non-Patent Document 2, NOx is adsorbed on the catalyst during a lean operation in which the exhaust gas has excess oxygen, and then a lean operation is performed to periodically form a state where the oxygen concentration in the exhaust gas is low. A method is shown in which NOx adsorbed during lean operation is periodically reduced by periodically synthesizing and supplying carbon oxide.

More specifically, in the method shown in Non-Patent Document 2, first, during the lean operation in which the exhaust gas is excessive in oxygen, the following formulas (1) to (3) indicate that nitrogen monoxide present in the exhaust gas and Nitrogen dioxide is adsorbed on the catalyst.
NO → NO (adsorption) (1)
2NO + O ₂ → 2NO ₂ (2)
NO ₂ → NO ₂ (Adsorption) (3)
Next, rich operation is performed and carbon monoxide is synthesized. The carbon monoxide synthesized here produces hydrogen by an aqueous gas shift reaction represented by the following formula (4) in an environment where the oxygen partial pressure is low.
CO + H ₂ O → H ₂ + CO ₂ (4)
Further, this hydrogen reacts with nitric oxide in a reducing atmosphere to generate ammonia, and this ammonia is adsorbed on the catalyst by the following formula (5).
5H ₂ + 2NO → 2NH ₃ (adsorption) + 2H ₂ O (5)
As described above, NOx in the exhaust gas or NOx adsorbed on the catalyst is reduced by the following formulas (6) to (8) using ammonia generated from carbon monoxide as a final reducing agent.
4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O (6)
2NH ₃ + NO ₂ + NO → 2N ₂ + 3H ₂ O (7)
8NH ₃ + 6NO ₂ → 7N ₂ + 12H ₂ O (8)

  In addition, for example, Patent Documents 3 and 4 provide a fuel reformer in which an LNT is provided in the exhaust passage, and further, a hydrocarbon gas is reformed upstream of the LNT to produce a reducing gas containing hydrogen and carbon monoxide. An exhaust purification system provided with a vacuum vessel is shown. In particular, this exhaust purification system uses a fuel reformer that produces a reducing gas such that hydrogen is larger than carbon monoxide by volume ratio. According to this system, it is possible to selectively reduce NOx in the exhaust gas by adding a reducing gas containing hydrogen from the upstream side of the LNT into the exhaust gas.

Here, as a method for producing a reducing gas from a hydrocarbon fuel, for example, a partial oxidation reaction using oxygen as an oxidant is known as shown in the following formula (9).
_{C n H m + 1 / 2nO} 2 → nCO + 1 / 2mH 2 (9)
This partial oxidation reaction is an exothermic reaction using fuel and oxygen, and the reaction proceeds spontaneously. For this reason, once reaction starts, it can continue producing hydrogen, without supplying heat from the outside. Further, in such a partial oxidation reaction, when a fuel and oxygen coexist at a high temperature, a combustion reaction as shown in the following formula (10) also proceeds.
_{C n H m + (n +} 1 / 4m) O 2 → nCO 2 + 1 / 2mH 2 O (10)
Further, a steam reforming reaction represented by the following formula (11) using steam as an oxidant is known.
_{C n H m + nH 2 O} → nCO + (n + 1 / 2m) H 2 (11)
This steam reforming reaction is an endothermic reaction using fuel and steam, and is not a reaction that proceeds spontaneously. For this reason, the steam reforming reaction is easily controlled with respect to the partial oxidation reaction described above.

Further, for example, Patent Documents 5 and 6 show a technique (hereinafter also referred to as EGR) of returning a part of the exhaust gas to the intake passage again as a technique for reducing NOx contained in the exhaust gas from the engine. Yes. In this technology, when exhaust gas containing a large amount of hydrocarbons or soot flows into a passage for recirculating a part of the exhaust gas to the intake passage (hereinafter referred to as EGR passage), The soot may condense and the EGR passage may be blocked. For this reason, a contrivance has been made such that a catalyst (hereinafter referred to as an EGR catalyst) is installed in front of the EGR passage, the exhaust gas is purified by the action of the EGR catalyst, and then the exhaust gas is introduced into the EGR passage.
Japanese Patent No. 2,586,738 Japanese Patent No. 2600492 Japanese Patent No. 3642273 JP 2002-89240 A JP 2000-38962 A JP 2003-254170 A “Development of NOx occlusion reduction type three-way catalyst system” Proceedings of Automobile Engineering Society Vol. 26, no. 4, October 1995 "A NOx Reduction System Using Ammonia Storage- Selective Catalytic Reduction in Rich and Lean Poorations", 15 Achener Koloquanchuen Mohrent 259-270

However, for example, when the engine lean operation and rich operation are repeated as in the techniques disclosed in Patent Documents 1 and 2 and Non-Patent Documents 1 and 2 described above, there are the following problems.
That is, when the exhaust air-fuel ratio is made rich by performing rich operation, NOx stored in the LNT is desorbed, but if the NOx stored in the LNT is large, the NOx is not reduced and flows out downstream of the LNT. As a result, the NOx purification performance may be reduced.
Therefore, it is conceivable to increase the frequency of rich operation and reduce NOx frequently so that the NOx storage amount in the LNT does not increase. However, the region where the rich operation can be performed is limited depending on the operation state of the engine such as the rotation speed and the torque. For this reason, it is difficult to reduce NOx frequently regardless of the operating state of the engine.

In addition, the exhaust gas purification systems of Patent Documents 3 and 4 are different from the techniques shown in Patent Documents 1 and 2 described above, basically, hydrogen is not contained in exhaust gas with excess oxygen, regardless of lean operation and rich operation. This is a technique of adding carbon monoxide and hydrocarbons.
However, in the case where LNT is purified by adding a reducing agent such as hydrogen or carbon monoxide into the exhaust gas containing excess oxygen, NOx can be purified only at about 200 ° C. For example, when the temperature of LNT is 200 ° C. or higher, the added hydrogen and carbon monoxide are combusted. For this reason, under such a temperature, the amount of reducing agent added is insufficient, and the progress of the NOx reduction reaction is not sufficient.

Further, in the case where a fuel reformer is provided in an exhaust passage in which the exhaust amount constantly varies, as in the exhaust purification systems of Patent Documents 3 and 4, in order to produce hydrogen effectively with the fuel reformer. Therefore, it is necessary to increase the time during which the reforming catalyst of the fuel reformer and the exhaust gas are in contact with each other. Thus, in order to increase the reaction time, it is necessary to enlarge the reforming catalyst, which leads to an increase in cost.
Further, in order to operate the fuel reformer in a stable state, it is necessary to keep the reaction temperature in the reforming catalyst of the fuel reformer constant. However, when the fuel reformer is provided in the exhaust passage in which the oxygen amount, the water vapor amount, and the temperature constantly change as in the above-described exhaust purification systems of Patent Documents 3 and 4, the fuel reformer is stabilized. It is difficult to drive in a state.

In the techniques of Patent Documents 5 and 6, in order to introduce more EGR gas into the intake passage, there is a cooling device (hereinafter referred to as an EGR cooler) for cooling the exhaust gas passing through the EGR passage. It is customary to be provided.
By the way, as described above, when rich combustion is performed in order to make the exhaust air-fuel ratio flowing into the LNT rich, the exhaust contains hydrocarbons in addition to carbon monoxide and the like. In addition, when post-combustion is performed, unburned fuel is included in addition to this. For this reason, if EGR is introduced for the purpose of reducing NOx in the exhaust during the rich operation, the exhaust mixed with hydrocarbons and unburned fuel passes through the EGR passage. For this reason, when the exhaust gas is cooled by the EGR cooler, hydrocarbons and end-burning fuel are deposited as deposits in the EGR passage and accumulate as a result. As a result, the EGR passage becomes narrower, and in the worst case, the EGR passage is blocked. Introduction becomes impossible.

  In addition, since the exhaust gas is at a low temperature immediately after the engine is started, hydrocarbons and unburned fuel are likely to adhere to the EGR passage even during lean operation. In order to suppress this, a device such as an oxidation catalyst is installed upstream of the EGR passage. However, since the oxidation catalyst is not activated immediately after the engine is started, sufficient EGR purification performance cannot be obtained. For this reason, EGR cannot be introduced immediately after startup, leading to an increase in NOx emission.

  The present invention has been made in view of the problems as described above, and its purpose is to reduce the NOx contained in the exhaust from the engine by introducing EGR while reducing the adhesion and accumulation of deposits in the EGR passage. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that realizes rich operation and can introduce EGR immediately after engine start regardless of the operation state, thereby reducing NOx emission.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, a fuel reformer is provided separately from the exhaust passage of the internal combustion engine, and reducing gas produced by the fuel reformer is introduced into the exhaust passage from the upstream side of the NOx purification catalyst in the exhaust passage. It is found that the above-mentioned problems can be solved by providing the first introduction passage and the second introduction passage for introducing a part of the exhaust gas into the recirculation passage that recirculates the exhaust gas into the intake passage. It came to. More specifically, the present invention provides the following.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 1 is provided in an exhaust passage of the internal combustion engine in which periodic lean and rich control is performed, and an exhaust air / fuel ratio of the exhaust gas flowing through the exhaust passage is used as the exhaust air / fuel ratio. NOx purification means having at least a NOx purification catalyst that adsorbs or occludes NOx in the exhaust when the air-fuel ratio is made lean and reduces the adsorbed or occluded NOx when the exhaust air-fuel ratio is made rich. In the exhaust purification apparatus, the NOx purification means includes a first purification catalyst and a second purification catalyst that is the NOx purification catalyst provided downstream of the first purification catalyst, and the exhaust gas of the internal combustion engine The purifying device is provided in the recirculation passage, the enrichment means for enriching the exhaust air-fuel ratio, the recirculation passage for recirculating part of the exhaust gas into the intake passage of the internal combustion engine, and the recirculation passage A recirculation catalyst having a gasification performance; a fuel reformer that is provided separately from the exhaust passage and reforms the fuel to produce a reducing gas; and the reducing gas produced by the fuel reformer, A first introduction passage for introducing the exhaust passage from the upstream side of the first purification catalyst into the exhaust passage, and a reducing gas produced by the fuel reformer, the recirculation of the recirculation passage. And a second introduction passage for introducing the catalyst into the reflux passage from the upstream side of the catalyst.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 2 is the exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the first introduction passage uses a reducing gas produced by the fuel reformer as the exhaust passage. Of these, the exhaust gas is introduced into the exhaust passage from the upstream side of the first purification catalyst.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 3 is the exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the recirculation catalyst activity estimating means for measuring or estimating the active state of the recirculation catalyst, and the first introduction. An introduction passage switching means for switching between a passage and the second introduction passage, and the introduction passage switching means, when it is estimated by the reflux catalyst activity estimation means that the reflux catalyst is active, Switching to the first introduction passage is performed, and when it is estimated that the passage is inactive, switching to the second introduction passage is performed.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 4 is the exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the reducing gas produced by the fuel reformer is passed through the first introduction passage. When introduced into the recirculation passage, at least one of the amount of air and the amount of fuel supplied to the fuel reformer is prevented so that the air-fuel ratio of the intake air sucked into the combustion chamber of the internal combustion engine does not become rich. It further comprises fuel reformer control means for controlling the amount of the reducing gas introduced by adjusting.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 5 is the exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the NOx emission amount is calculated based on the rotational speed of the internal combustion engine and the generated torque of the internal combustion engine. NOx emission amount estimating means for estimating, NOx emission amount estimated by the NOx emission amount estimating means, intake air amount of the internal combustion engine, fuel consumption amount of the internal combustion engine, operating time of the internal combustion engine, and exhaust gas An adsorption NOx amount estimating means for estimating an adsorption NOx amount of the second purification catalyst based on at least one of the oxygen concentrations, wherein the enrichment means is estimated by the adsorption NOx amount estimation means. The exhaust air-fuel ratio is enriched when the adsorbed NOx amount is equal to or greater than a predetermined adsorbed NOx amount determination value.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 6 is the exhaust gas purification apparatus for an internal combustion engine according to claim 5, wherein the temperature of at least one of the first purification catalyst and the second purification catalyst is estimated or detected. And an adsorption NOx amount determination value determining unit that determines the predetermined adsorption NOx amount determination value based on the catalyst temperature estimated by the catalyst temperature estimation unit.

  The exhaust purification device for an internal combustion engine according to claim 7 is the exhaust purification device for an internal combustion engine according to claim 6, wherein the enrichment means is a first rich by introduction of a reducing gas produced by the fuel reformer. And the second enrichment control means by post combustion or rich combustion, and the exhaust air / fuel ratio is enriched by the first enrichment control means in accordance with the operating state of the internal combustion engine. Or whether to enrich by the second enrichment control means.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 8 is the exhaust gas purification apparatus for an internal combustion engine according to claim 7, wherein the enrichment means is the temperature of the first purification catalyst estimated by the catalyst temperature estimation means, At least one of the temperature of the second purification catalyst estimated by the catalyst temperature estimation means, the adsorption NOx amount estimated by the adsorption NOx amount estimation means, the rotational speed of the internal combustion engine, and the generated torque of the internal combustion engine. Accordingly, it is selected whether the exhaust air-fuel ratio is enriched by the first enrichment control means or enriched by the second enrichment control means.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 9 is the exhaust gas purification apparatus for an internal combustion engine according to any one of claims 6 to 8, wherein the enrichment means has an exhaust air / fuel ratio when enriching the exhaust air / fuel ratio. The main injection amount of the internal combustion engine, the sub injection amount of the internal combustion engine, the intake air amount of the internal combustion engine, and the introduction amount of reducing gas produced by the fuel reformer so as to coincide with a predetermined target value And adjusting at least one of them.

  An exhaust purification device for an internal combustion engine according to claim 10 is the exhaust purification device for an internal combustion engine according to claim 9, wherein the predetermined target value of the exhaust air-fuel ratio is estimated by the catalyst temperature estimation means. , The temperature of the second purification catalyst estimated by the catalyst temperature estimation means, the adsorption NOx amount estimated by the adsorption NOx amount estimation means, the duration of the enrichment control by the enrichment means, the rotation of the internal combustion engine The exhaust air / fuel ratio target value determining means for determining the number based on at least one of the number and the torque generated by the internal combustion engine is further provided.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 11 is the exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 10, wherein the reducing gas produced by the fuel reformer is carbon monoxide, hydrogen, Among these, carbon monoxide has the largest volume fraction, and hydrocarbon has the smallest volume fraction.

  13. The exhaust gas purification apparatus for an internal combustion engine according to claim 12, wherein the internal combustion engine is a compression ignition type internal combustion engine, and the fuel used is light oil. It is characterized by being.

According to the first aspect of the present invention, the reducing gas produced by the fuel reformer can be introduced into the exhaust passage from the upstream side of the second purification catalyst (NOx catalyst) through the first introduction passage. 2 It can be introduced into the reflux passage (hereinafter referred to as EGR passage) from the upstream side of the reflux catalyst (hereinafter referred to as EGR catalyst) through the introduction passage. Since the EGR catalyst disposed in the EGR passage has low activity under low temperature conditions, the high temperature reducing gas produced by the fuel reformer can be introduced, so that the temperature of the EGR catalyst can be increased. Since the reducing gas contains carbon monoxide and hydrogen that are excellent in low-temperature oxidizability, the oxidation reaction (exothermic reaction) of carbon monoxide and hydrogen proceeds from a lower temperature region. It is possible to increase the amount of the active substance quickly, and early activation is possible. For this reason, deposit adhesion and accumulation can be reduced, and blockage of the EGR passage can be avoided. Accordingly, it is possible to realize a rich operation in which NOx contained in the exhaust from the engine is reduced, and it is possible to introduce EGR immediately after the engine is started, for example, immediately after the engine is started, and to reduce NOx emission.
Further, since the EGR gas in the low temperature region is clean, the EGR gas can be introduced immediately after the engine is started. As a result, the combustion temperature in the combustion chamber can be lowered, and the NOx emission from the engine can be reduced. . Furthermore, the EGR effect gas such as carbon dioxide and water vapor generated when carbon monoxide and hydrogen are oxidized on the EGR catalyst can suppress an increase in combustion temperature, and can contribute to a reduction in NOx emissions.
Further, by introducing the reducing gas into the exhaust passage, the engine air-fuel ratio control is made lean and the combustion of the internal combustion engine is maintained in an optimal state, while the exhaust air flowing into the second purification catalyst (NOx catalyst) is exhausted. The fuel ratio can be made rich. Therefore, the NOx purification performance can be improved regardless of the operating state of the internal combustion engine. Since the engine air-fuel ratio can be kept lean, oil dilution does not occur unlike when the exhaust air-fuel ratio is changed by supplying fuel by post injection or the like.
In addition, by providing a fuel reformer that produces reducing gas separately from the exhaust passage, the reducing gas is always supplied with optimum efficiency regardless of the operating state of the internal combustion engine, the oxygen concentration and the water vapor concentration of the exhaust gas, etc. While being able to be manufactured, this reducing gas can be introduced into the EGR passage or the exhaust passage. When the fuel reformer is provided in the exhaust passage, it is necessary to enlarge the fuel reformer so that the fuel reformer can be operated without affecting the exhaust component, temperature, and flow velocity. According to the invention, by providing the fuel reformer separately from the exhaust passage, it is not necessary to increase the size of the apparatus, and stable operation is possible. Furthermore, by providing the fuel reformer separately from the exhaust passage, it is possible to control the system separately from the control of the internal combustion engine, and to activate the reforming catalyst provided in the fuel reformer at an early stage.
Moreover, the reduction reaction rate in the second purification catalyst (NOx catalyst) can be improved by introducing a reducing gas containing hydrogen. Thereby, when the exhaust air-fuel ratio is made rich, it is possible to prevent NOx adsorbed or stored in the second purification catalyst (NOx catalyst) from being desorbed without being reduced.

  According to the second aspect of the present invention, the reducing gas produced by the fuel reformer can be introduced into the exhaust passage from the upstream side of the first purification catalyst through the first introduction passage. Therefore, before the NOx is reduced by the second purification catalyst (NOx catalyst), the reducing gas can flow into the first purification catalyst, and the NOx concentration flowing into the second purification catalyst can be reduced. it can. Therefore, the amount of NOx slip when NOx is reduced by the second purification catalyst can be reduced, and the NOx purification rate can be improved.

  According to the third aspect of the present invention, the first introduction passage and the second introduction passage can be switched according to the active state of the EGR catalyst. That is, it is possible to select whether the reducing gas produced by the fuel reformer is introduced into the EGR passage or the exhaust passage according to the active state of the EGR catalyst. Specifically, when it is estimated that the EGR catalyst is not activated, the temperature of the EGR catalyst is increased by switching to the second introduction passage and introducing reducing gas into the EGR passage. As a result of enabling early activation of the EGR catalyst, NOx contained in the exhaust gas can be more effectively reduced.

  According to the fourth aspect of the present invention, when the reducing gas produced by the fuel reformer is introduced into the EGR passage through the first introduction passage, the intake air sucked into the combustion chamber of the internal combustion engine is emptied. The amount of reducing gas introduced is controlled by adjusting at least one of the amount of air and the amount of fuel supplied to the fuel reformer so that the fuel ratio does not become rich. For this reason, even when reducing gas is introduced into the EGR passage, the air-fuel ratio of the intake air sucked into the combustion chamber can be avoided from being rich, and stable operation is possible.

  According to the fifth aspect of the invention, first, the NOx emission amount is estimated based on the rotational speed and the generated torque of the internal combustion engine, the estimated NOx emission amount, the intake air amount of the internal combustion engine, and the fuel consumption amount of the internal combustion engine. The amount of adsorbed NOx of the second purification catalyst (NOx catalyst) is estimated based on at least one of the operation time of the internal combustion engine and the oxygen concentration in the exhaust gas. Next, when the estimated amount of adsorbed NOx is greater than or equal to a predetermined adsorbed NOx amount determination value, the exhaust air / fuel ratio is enriched. As a result, the amount of NOx adsorbed or occluded by the NOx catalyst increases excessively, and the amount of NOx that flows out without being reduced when enriched can be reduced. In addition, it is possible to avoid a significant deterioration in fuel consumption due to an increase in the frequency of enrichment more than necessary.

  According to the sixth aspect of the present invention, the predetermined adsorption NOx amount determination value is determined based on the catalyst temperature of at least one of the first purification catalyst and the second purification catalyst. Can be For this reason, the supply amount of a reducing agent can always be adjusted appropriately.

According to the seventh aspect of the present invention, the exhaust air / fuel ratio is enriched by introducing reducing gas produced by the fuel reformer or exhaust air is exhausted by post-combustion or rich combustion according to the operating state of the internal combustion engine. Whether to enrich the fuel ratio is selected.
According to the invention described in claim 8, at least one of the temperature of the first purification catalyst, the temperature of the second purification catalyst (NOx catalyst), the amount of adsorbed NOx, the rotational speed of the internal combustion engine, and the generated torque of the internal combustion engine. Accordingly, it is selected whether to enrich the exhaust air-fuel ratio by introducing reducing gas produced by the fuel reformer, or to enrich the exhaust air-fuel ratio by post-combustion or rich combustion.
That is, the richness due to the introduction of the reducing gas depends on the operating conditions such as the temperature of the first purification catalyst, the temperature of the second purification catalyst (NOx catalyst), the amount of adsorbed NOx, the rotational speed of the internal combustion engine, and the generated torque of the internal combustion engine. Or enrichment by post-combustion or rich combustion is selected, so that the amount of NOx that flows out without being reduced can be more effectively reduced, and the temperatures of the first purification catalyst and the second purification catalyst are increased. Therefore, it is possible to avoid the thermal deterioration being promoted.

  According to the ninth aspect of the invention, the main injection amount of the internal combustion engine, the sub injection amount of the internal combustion engine, and the internal combustion engine of the internal combustion engine are set such that the exhaust air / fuel ratio when enriching the exhaust air / fuel ratio matches a predetermined target value. At least one of the intake air amount and the introduction amount of the reducing gas produced by the fuel reformer is adjusted. Thus, since the exhaust air-fuel ratio at the time of enrichment can be set to a desired value, highly efficient NOx purification can be achieved by always realizing an optimal air-fuel ratio for reducing NOx.

  According to the tenth aspect of the present invention, the predetermined target value of the exhaust air-fuel ratio is set such that the temperature of the first purification catalyst, the temperature of the second purification catalyst (NOx catalyst), the amount of adsorbed NOx, and the enrichment control by the enrichment means. It is determined based on at least one of the duration, the rotational speed of the internal combustion engine, and the generated torque of the internal combustion engine. As a result, the exhaust gas having the optimum exhaust air / fuel ratio can always flow into the first purification catalyst and the second purification catalyst (NOx catalyst).

According to the invention described in claim 11, the reducing gas produced by the fuel reformer contains carbon monoxide, hydrogen, and hydrocarbons. Of these, carbon monoxide has the highest volume fraction, and hydrocarbon has the lowest volume fraction.
In a fuel reformer that reforms hydrocarbon fuel, a reducing gas containing carbon monoxide, hydrogen, and light hydrocarbons is produced only by a partial oxidation reaction using only hydrocarbon fuel and air as raw materials. In the exhaust gas purification apparatus according to the present invention, a reducing gas containing more carbon monoxide than hydrogen is preferably used. For this reason, in the present invention, a catalyst or system for concentrating hydrogen such as a shift reaction is unnecessary, and since the partial oxidation reaction is an exothermic reaction, it is not necessary to supply energy from the outside once the reaction starts. Therefore, a small and simple fuel reformer can be obtained. Since the fuel reformer can be downsized, the light-off time of the fuel reformer can be shortened, and the reducing gas can be quickly introduced into the exhaust passage and the reflux passage as necessary.
In addition, light hydrocarbon components that are generated as a secondary component can also contribute to the reduction of NOx by being introduced into the first purification catalyst or the second purification catalyst (NOx catalyst).

  According to the invention described in claim 12, the applied internal combustion engine is a compression ignition type internal combustion engine, and the fuel to be used is light oil. In a compression ignition type internal combustion engine such as diesel, since operation is normally performed in a lean state, purification of NOx has been a problem in the past. However, by applying the exhaust purification device according to the present invention, it is efficient. NOx purification is possible.

  Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of an engine and an exhaust purification device thereof according to a first embodiment of the present invention. The engine 1 is a diesel engine that directly injects fuel into the combustion chamber of each cylinder 7, and each cylinder 7 is provided with a fuel injection valve (not shown). These fuel injection valves are electrically connected by an electronic control unit (hereinafter referred to as ECU) 40, and the valve opening time and valve closing time of the fuel injection valve are controlled by the ECU 40.

  The engine 1 includes an intake passage 2 through which intake air flows, an exhaust passage 4 through which exhaust flows, an EGR passage 6 that recirculates part of the exhaust gas in the exhaust passage 4 to the intake passage 2, and intake air into the intake passage 2. A supercharger 8 for pumping is provided.

  The intake passage 2 is connected to an intake port of each cylinder 7 of the engine 1 through a plurality of branch portions of an intake manifold 3 (also serving as a part of the intake passage 2). The exhaust passage 4 is connected to the exhaust port of each cylinder 7 of the engine 1 through a plurality of branch portions of the exhaust manifold 5. The EGR passage 6 branches from the exhaust manifold 5 and reaches the intake manifold 3.

  The supercharger 8 includes a turbine (not shown) provided in the exhaust passage 4 and a compressor (not shown) provided in the intake passage 2. The turbine is driven by the kinetic energy of the exhaust flowing through the exhaust passage 4. The compressor is rotationally driven by the turbine, pressurizes the intake air, and pumps it into the intake passage 2. The turbine includes a plurality of variable vanes (not shown), and is configured to change the turbine rotation speed (rotational speed) by changing the opening of the variable vanes. The vane opening degree of the turbine is electromagnetically controlled by the ECU 40.

  A throttle valve 9 for controlling the intake air amount of the engine 1 is provided on the upstream side of the supercharger 8 in the intake passage 2. The throttle valve 9 is connected to the ECU 40 via an actuator, and the opening degree is electromagnetically controlled by the ECU 40. An intercooler 15 for cooling the intake air pressurized by the supercharger 8 is provided on the downstream side of the supercharger 8 in the intake passage 2.

  The EGR passage 6 connects the exhaust manifold 5 and the intake manifold 3 and recirculates a part of the exhaust discharged from the engine 1. The EGR passage 6 includes an EGR cooler 12 that cools the recirculated exhaust gas, an EGR valve 13 that controls the flow rate of the recirculated exhaust gas, an EGR catalyst 11 having oxidation performance upstream of the EGR cooler 12, and an EGR gas temperature sensor. 14 are provided. The EGR valve 13 is connected to the ECU 40 via an actuator (not shown), and the valve opening degree is electromagnetically controlled by the ECU 40. The EGR gas temperature sensor 14 is connected to the ECU 40, and the detection signal of the EGR gas temperature sensor 14 is supplied to the ECU 40.

The EGR catalyst 11 is not particularly limited as long as it has oxidation performance, and a conventionally known oxidation catalyst, three-way catalyst, or the like can be used. Hereinafter, an example of a method for preparing the EGR catalyst will be shown. For example, a material containing each of these components together with an aqueous medium so as to have a blending composition of Pt = 2.4 g / L, Pd = 6.0 g / L, Al ₂ O ₃ = 150 g / L, and binder = 10 g / L. A slurry is obtained by putting into a ball mill and stirring and mixing. An EGR catalyst can be prepared by coating the obtained slurry on a support made of Fe—Cr—Al alloy and drying and firing at 600 ° C. for 2 hours.

In the EGR passage 6, on the upstream side of the EGR catalyst 11, a fuel that reforms the fuel gas to produce a reducing gas containing carbon monoxide (CO), hydrogen (H ₂ ), and hydrocarbon (HC). The reformer 50 is connected via the second introduction passage 58. The reducing gas produced by the fuel reformer 50 is introduced into the EGR passage 6 from the upstream side of the EGR catalyst 11 and flows into the NOx purification catalyst 32.

A three-way catalyst (first purification catalyst) 31 and a NOx purification catalyst (second purification catalyst) 32 are provided on the downstream side of the exhaust passage 4. The three-way catalyst (hereinafter referred to as TWC) 31 and the NOx purification catalyst 32 are provided with a catalyst temperature sensor (not shown).
The TWC 31 as the first purification catalyst can be prepared, for example, by the following preparation method. Pt = 2.4 g / L, Rh = 1.2 g / L, Pd = 6.0 g / L, CeO ₂ = 50 g / L, Al ₂ O ₃ = 150 g / L, binder = 10 g / L As described above, a material containing these components is put into a ball mill together with an aqueous medium, and a slurry is obtained by stirring and mixing. TWC31 can be prepared by coating the obtained slurry on a support made of Fe—Cr—Al alloy, and drying and firing at 600 ° C. for 2 hours.

The NOx purification catalyst 32 as the second purification catalyst preferably contains rhodium (Rh) in order to enhance the NOx reduction ability. In addition, even in a sudden change in oxygen concentration, it is necessary to enhance the oxygen storage capacity in order to exhibit stable catalytic action, and it is preferable that cerium (Ce) is contained as an element.
More specifically, the NOx purification catalyst 32 is a catalyst supported on a support of alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), and a composite oxide of cerium and rare earth (hereinafter referred to as ceria composite oxide). Has the function of holding platinum (Pt) and rhodium (Rh) that act as ceria, ceria or ceria-based composite oxide having NOx adsorption ability, and the generated ammonia (NH ₃ ) as ammonium ions (NH ₄ ⁺ ) It is preferable to provide zeolite.

As the NOx purification catalyst 32, a NOx purification catalyst having a two-layer structure is more preferably used. Hereinafter, an example of a method for preparing a two-layer NOx purification catalyst will be described. For example, as a lower layer, Pt = 4.5 g / L, Rh = 1.0 g / L, CeO ₂ = 60 g / L, Al ₂ O ₃ = 30 g / L, Ce—Pr—La—Ox = 60 g / L, Nd A material containing these components is put into a ball mill together with an aqueous medium so as to obtain a blending composition of -Zr-Ox = 20 g / L, and a slurry is obtained by stirring and mixing. The resulting slurry is formed by coating a cordierite carrier.
In addition, as an upper layer, a material containing these components is ball milled together with an aqueous medium so as to have a composition of Fe · Ce ion exchange β zeolite = 75 g / L, Al ₂ O ₃ = 7 g / L, and binder = 8 g / L. The slurry is obtained by stirring and mixing. The obtained lower layer is coated on the above-mentioned lower layer, dried at 600 ° C. for 2 hours, and calcined, whereby the NOx purification catalyst 32 can be prepared.

When the amount of adsorbed ammonia in the NOx purification catalyst 32 decreases, the NOx purification capacity decreases, so that a reducing agent is supplied to the NOx purification catalyst 32 (hereinafter referred to as reduction) in order to reduce NOx as appropriate. In this reduction, for example, the air-fuel ratio (engine air-fuel ratio) of the air-fuel mixture in the combustion chamber of the engine 1 is stoichiometrically determined by increasing the amount of fuel injected from the fuel injection valve and decreasing the amount of intake air by the throttle valve 9. By making the ratio richer than the ratio, the reducing agent is supplied to the NOx purification catalyst 32.
Specifically, by reducing the air-fuel ratio (exhaust air-fuel ratio) of the exhaust discharged from the engine 1 by post combustion or rich combustion, the concentration of the reducing agent in the exhaust flowing into the NOx purification catalyst 32 becomes the oxygen concentration. It becomes higher and reduction is performed. Further, as will be described later, by introducing reducing gas produced by the fuel reformer into the exhaust passage 4 or the EGR passage, the exhaust air-fuel ratio is enriched and reduction is performed.

Hereinafter, NOx purification in the NOx purification catalyst 32 will be described.
First, when the engine air-fuel ratio is set leaner than the stoichiometric ratio and so-called lean burn operation is performed, the concentration of the reducing agent in the exhaust gas flowing into the NOx purification catalyst 32 becomes lower than the oxygen concentration. As a result, nitric oxide (NO) and oxygen (O ₂ ) in the exhaust gas react with each other by the action of the catalyst, and are adsorbed as NO ₂ on the ceria or ceria-based composite oxide.

Next, so-called rich operation is performed in which the engine air-fuel ratio is set to be richer than the stoichiometric ratio, and the exhaust air-fuel ratio is enriched. That is, when reduction is performed to make the reducing agent concentration in the exhaust gas higher than the oxygen concentration, carbon monoxide (CO) in the exhaust gas reacts with water (H ₂ O), and carbon dioxide (CO ₂ ) and hydrogen ( H ₂ ) is generated, and the hydrocarbon (HC) in the exhaust gas reacts with water to generate hydrogen (H ₂ ) together with carbon monoxide (CO) and carbon dioxide (CO ₂ ). Furthermore, NOx contained in the exhaust gas, NOx (NO, NO ₂ ) adsorbed on ceria or ceria-based complex oxide (and platinum), and generated hydrogen (H ₂ ) act as a catalyst. To produce ammonia (NH ₃ ) and water (H ₂ O). The ammonia (NH ₃ ) produced here is adsorbed on the zeolite in the form of ammonium ions (NH ₄ ⁺ ).

Next, when lean burn operation is performed in which the engine air-fuel ratio is set leaner than the stoichiometric ratio, and the reducing agent concentration in the exhaust gas flowing into the NOx purification catalyst 32 is set lower than the oxygen concentration, ceria or ceria NOx is adsorbed on the system complex oxide. Further, in the state where ammonium ions (NH ₄ ⁺ ) are adsorbed on the zeolite, NOx and oxygen (O ₂ ) in the exhaust gas react with ammonia (NH ₃ ) to react with nitrogen (N ₂ ) and water (H ₂ O). ) Is generated.

Thus, according to the NOx purification catalyst 32, ammonia (NH ₃ ) generated during the supply of the reducing agent is adsorbed on the zeolite, and ammonia (NH ₃ ) adsorbed during the lean burn operation reacts with NOx. It is possible to efficiently purify NOx.

Further, in the exhaust passage 4, upstream of the NOx purification catalyst 32 and downstream of the TWC 31, the fuel gas is reformed and carbon monoxide (CO), hydrogen (H ₂ ), and hydrocarbon ( A fuel reformer 50 for producing a reducing gas containing HC) is connected via a first introduction passage 57. The reducing gas produced by the fuel reformer 50 is introduced into the exhaust passage 4 from between the TWC 31 and the NOx purification catalyst 32 and flows into the NOx purification catalyst 32.

  The fuel reformer 50 includes an introduction passage branched from an introduction passage switching valve 56 into a first introduction passage 57 connected at one end to the exhaust passage 4 and a second introduction passage 58 connected at one end to the EGR passage 6. A fuel gas supply device 52 that supplies fuel gas, a fuel gas adjustment valve 51 that adjusts the amount of fuel gas supplied by the fuel gas supply device 52, a compressor 54, and an amount of air supplied by the compressor An air regulating valve 53 and a reforming catalyst 55 provided in the introduction passage are included. The introduction passage switching valve 56 is connected to the ECU 40.

  The fuel gas supply device 52 gasifies the fuel stored in the fuel tank and supplies the fuel gas to the reforming catalyst 55 while adjusting the flow rate by the fuel adjustment valve 51. Further, the air supplied from the compressor is adjusted in its flow rate by the air adjusting valve 53, and then is uniformly mixed with the fuel gas and supplied to the reforming catalyst 55. The fuel reformer 50 is connected to the ECU 40, and the fuel gas supply amount and the air supply amount are controlled by the ECU 40. Further, the amount of reducing gas introduced into the exhaust passage 4 can be controlled by controlling the amount of fuel gas and air supplied.

  The reforming catalyst 55 contains rhodium and ceria. The reforming catalyst 55 reforms the fuel gas supplied from the fuel gas supply device 52 to produce a reducing gas containing hydrogen, carbon monoxide, and hydrocarbons. More specifically, the reforming catalyst 55 has a pressure higher than atmospheric pressure due to a partial oxidation reaction between the hydrocarbon fuel in the fuel gas and air, and has a volume fraction of carbon monoxide higher than that of hydrogen. A reducing gas containing a large amount of is produced. Further, as described above, the partial oxidation reaction is an exothermic reaction. Thereby, the fuel reformer 50 can introduce a reducing gas having a temperature higher than that of the EGR gas flowing in the upstream side of the EGR catalyst 11 in the EGR passage 6 into the EGR passage 6. In addition, reducing gas having a temperature higher than that of the exhaust gas flowing upstream of the NOx purification catalyst 32 in the exhaust passage 4 can be introduced into the exhaust passage 4.

Hereinafter, an example of a method for preparing the reforming catalyst 55 will be described. For example, in order to obtain a blending composition of Pt = 0.8 g / L, Rh = 0.8 g / L, CeO ₂ = 150 g / L, and binder = 10 g / L, the materials containing these components are ball milled together with an aqueous medium. The slurry is obtained by adding, stirring and mixing. The reforming catalyst 55 can be prepared by coating the obtained slurry on a Fe—Cr—Al alloy carrier, and drying and firing at 600 ° C. for 2 hours.

  The reforming catalyst 55 is connected to a heater (not shown) that includes a glow plug, a spark plug, and the like, and the reforming catalyst 55 can be heated when the fuel reformer 50 is started. It is possible. The fuel reformer 50 is provided separately from the exhaust passage 4. That is, the fuel gas supply device 52 and the reforming catalyst 55 of the fuel reformer 50 are not provided in the exhaust passage 4.

The ECU 40 includes a crank angle position sensor (not shown) that detects the rotation angle of the crankshaft of the engine 1, an accelerator sensor (not shown) that detects the amount of depression of an accelerator pedal of a vehicle driven by the engine 1, and an engine 1, an air flow meter 21 that detects the amount of intake air (the amount of air that is newly sucked into the engine 1 per unit time), an exhaust temperature sensor 34 that detects the temperature of the exhaust gas flowing into the NOx purification catalyst 32, TWC 31, and A UEGO sensor 33 is connected to detect the oxygen concentration of the exhaust gas flowing into the NOx purification catalyst 32, that is, the exhaust air-fuel ratio, and detection signals from these sensors are supplied to the ECU 40.
Here, the rotational speed of the engine 1 is calculated by the ECU 40 based on the output of the crank angle position sensor. Further, the generated torque of the engine 1 is calculated by the ECU 40 based on the fuel injection amount of the fuel injection valve determined according to the depression amount of an accelerator pedal (not shown).

  The ECU 40 shapes an input signal waveform from various sensors, corrects a voltage level to a predetermined level, converts an analog signal value into a digital signal value, and a central processing unit (hereinafter, referred to as a central processing unit). CPU). In addition, the ECU 40 includes a storage circuit that stores various calculation programs executed by the CPU, calculation results, and the like, a fuel reformer 50, an introduction passage switching valve 56, a throttle valve 9, an EGR valve 13, a supercharger 8, And an output circuit for outputting a control signal to the fuel injection valve of the engine 1.

  The engine 1 is normally operated with the engine air-fuel ratio set to a lean side with respect to the stoichiometric ratio, and rich control for setting the engine air-fuel ratio to the rich side with respect to the stoichiometric ratio is periodically performed.

FIG. 3 is a flowchart showing a procedure of engine control in the first embodiment. First, in step S1, the active state of the EGR catalyst 11 is measured or estimated, and it is estimated whether the EGR catalyst 11 is in an active state or an inactive state. If the EGR catalyst 11 is estimated to be YES in the active state, the process proceeds to step S2, and if NO is estimated in the inactive state, the process proceeds to step S3.
Here, the active state of the EGR catalyst 11 is estimated based on the EGR gas temperature measured by the EGR gas temperature sensor 14 disposed downstream of the EGR catalyst 11. More specifically, when the EGR gas temperature is equal to or lower than a certain value, the EGR catalyst 11 is determined to be in an inactive state, and the reducing gas is guided to the upstream portion of the EGR catalyst 11. When the EGR gas temperature downstream of the EGR catalyst 11 is equal to or higher than a certain value, it is determined that the EGR catalyst 11 is activated, and the reducing gas introduction passage is connected to the exhaust passage 4 side through the first introduction passage. Switch to 57.

In step S2, the introduction passage switching valve 56 switches to the first introduction passage 57, and the addition of H ₂ gas (reducing gas) into the EGR passage 6 is stopped. In step S3, the introduction passage switching valve 56 switches to the second introduction passage 58, and the H ₂ gas (reducing gas) is added into the EGR passage 6. In step S3, the air amount supplied to the fuel reformer 50 is adjusted by the air amount adjusting valve 53 so that the air-fuel ratio of the intake air sucked into the combustion chamber of the engine 1 does not become rich, and the fuel reforming is performed. The amount of reducing gas introduced is controlled by adjusting the amount of fuel supplied to the vessel 50 by the fuel amount adjusting valve 51.

  Next, the process proceeds to step S4, where enrichment control by the enrichment means is performed.

FIG. 4 is a flowchart showing a procedure of the enrichment control performed in step S4. First, in step S21, the adsorption NOx amount of the NOx purification catalyst is estimated, and it is determined whether or not the estimated adsorption NOx amount is equal to or greater than a predetermined adsorption NOx amount determination value. If this determination is YES, the process proceeds to step S22, and if NO, the enrichment control is terminated.
Here, the adsorption NOx amount of the NOx purification catalyst is estimated by estimating the NOx emission amount based on the rotation speed and generated torque of the engine 1, the estimated NOx emission amount, and the intake air amount of the engine 1 measured by the air flow meter 21. It is estimated based on at least one of the fuel consumption of the engine 1, the operating time of the engine 1, and the oxygen concentration in the exhaust gas measured by the UEGO sensor.
The adsorbed NOx amount determination value is determined based on the estimated catalyst temperature by estimating or detecting at least one of the temperature of the TWC 31 and the temperature of the NOx purification catalyst 32. The estimation or detection of the catalyst temperature is estimated or detected by a catalyst temperature sensor provided in each of the TWC 31 and the NOx purification catalyst 32.

In step S22, it is determined whether or not the temperature of the NOx purification catalyst (LNC) 32 is equal to or lower than a certain value. If the determination is YES, the process proceeds to step S27, and if the determination is NO, the process proceeds to step S23.
Here, the temperature of the NOx purification catalyst 32 is estimated or detected by a catalyst temperature sensor. Further, in addition to the temperature of the NOx purification catalyst 32, it may be determined whether at least one of the temperature of the TWC 31, the amount of adsorbed NOx, the rotational speed of the engine 1, and the generated torque is equal to or less than a certain value. Note that the temperature of the TWC 31 is estimated or detected by a catalyst temperature sensor provided in the TWC 31, and the amount of adsorbed NOx is estimated by the same procedure as in step S4.

  In step S23, an exhaust air-fuel ratio target value for normal rich control (second rich control) is determined. This exhaust air-fuel ratio target value is determined based on at least one of the temperature of the TWC 31, the temperature of the NOx purification catalyst 32, the amount of adsorption NOx, the duration of the enrichment control, the rotational speed of the engine 1, and the generated torque.

In step S24, normal enrichment control (second enrichment control) is performed. Here, as the normal enrichment control, post combustion or rich combustion is performed.
Further, the exhaust air-fuel ratio during the normal enrichment control is monitored by the UEGO sensor, and the normal enrichment control is performed so as to coincide with the target value of the exhaust air-fuel ratio determined in step S23. More specifically, the enrichment control is performed by adjusting at least one of the main injection amount, the sub injection amount, and the intake air amount of the engine 1.

  In step S25, it is determined whether or not the normal rich timer is zero. If this determination is YES, the process proceeds to step S26, and after starting the normal rich timer, the process proceeds to step S33, and in the case of NO, the process proceeds to step S33.

Returning to step S22, when the temperature of the NOx purification catalyst (LNC) 32 is equal to or lower than a predetermined value, the process proceeds to step S27, and in step S27, the exhaust air-fuel ratio target for H ₂ enrichment control (first enrichment control). Determine the value. This exhaust air-fuel ratio target value is determined by the same procedure as in the normal enrichment control.

In step S28, H ₂ enrichment control (first enrichment control) is performed. Here, the H ₂ enrichment control is performed by introducing the reducing gas produced by the fuel reformer 50 into the exhaust passage 4. Specifically, by reducing the intake throttle 9, the intake air amount of the engine 1 is reduced, and the addition of reducing gas from the fuel reformer 50 into the exhaust passage 4 is started.
Further, the exhaust air / fuel ratio during the H ₂ enrichment control is monitored by the UEGO sensor, and the amount of reducing gas introduced is adjusted so as to match the target value of the exhaust air / fuel ratio determined in step S27 to enrich the H ₂ . Implement control.

In step S29, the H ₂ enrichment control timer and the normal rich timer are started, and the process proceeds to step S30. In step S30, it is determined whether or not the temperature of the NOx purification catalyst (LNC) 32 is equal to or higher than a certain value.
If this determination is YES, the process proceeds to step S32, the H ₂ enrichment control is stopped, the H ₂ enrichment control timer is set, and the process proceeds to step S33.
If the determination is NO, the process moves to step S31, and it is determined whether or not the H ₂ enrichment control timer has passed a certain time. If this determination is YES, the process proceeds to step S32, the H ₂ enrichment control is stopped, the H ₂ enrichment control timer is set, and the process proceeds to step S33. If the determination is NO, the process proceeds to step S33.

  In step S33, it is determined whether or not the normal rich timer has passed a predetermined time. If this determination is YES, the process proceeds to step S34, the enrichment control is stopped, the normal rich timer is set, and the enrichment control is terminated. When the determination is NO, the enrichment control is continued and the enrichment control is terminated.

As described above in detail, according to the present embodiment, the reducing gas produced by the fuel reformer 50 is exhausted from the upstream side of the second purification catalyst (NOx catalyst) 32 through the first introduction passage 57. 4 can be introduced into the reflux passage (hereinafter referred to as EGR passage) 6 from the upstream side of the reflux catalyst (hereinafter referred to as EGR catalyst) 11 through the second introduction passage 57. When the EGR catalyst 11 disposed in the EGR passage 6 has low activity under low temperature conditions, the high temperature reducing gas produced by the fuel reformer 50 can be introduced, so that the temperature of the EGR catalyst 11 can be increased. it can. Since the reducing gas contains carbon monoxide and hydrogen that are excellent in low-temperature oxidation properties, the oxidation reaction (exothermic reaction) of carbon monoxide and hydrogen proceeds from a lower temperature region. As a result, the temperature of the EGR catalyst 11 is increased. It can be raised early, and early activation is possible. For this reason, deposit adhesion and accumulation can be reduced, and blockage of the EGR passage 6 can be avoided. Accordingly, it is possible to realize a rich operation in which NOx contained in the exhaust from the engine 1 is reduced, and it is possible to introduce EGR even immediately after the engine is started, for example, immediately after the engine is started, and to reduce NOx emission.
In addition, since the EGR gas in the low temperature region is clean, the EGR gas can be introduced immediately after the engine is started. As a result, the combustion temperature in the combustion chamber can be lowered, and the NOx emission from the engine 1 can be reduced. it can. Furthermore, the EGR effect gas such as carbon dioxide and water vapor generated when carbon monoxide and hydrogen are oxidized on the EGR catalyst 11 can suppress an increase in combustion temperature, and can contribute to a reduction in NOx emissions. .
Further, by introducing the reducing gas into the exhaust passage 4, the engine air-fuel ratio is made lean, and the exhaust gas flowing into the second purification catalyst (NOx catalyst) 32 is maintained while maintaining the combustion in the engine 1 in an optimum state. The air-fuel ratio can be enriched. Therefore, the NOx purification performance can be improved regardless of the operating state of the engine 1. Since the engine air-fuel ratio can be kept lean, oil dilution does not occur unlike when the exhaust air-fuel ratio is changed by supplying fuel by post injection or the like.
Further, by providing the fuel reformer 50 for producing reducing gas separately from the exhaust passage 4, the reducing performance is always reduced with optimum efficiency regardless of the operating state of the engine 1 and the oxygen concentration and water vapor concentration of the exhaust gas. Gas can be produced, and this reducing gas can be introduced into the EGR passage 6 or the exhaust passage 4. When the fuel reformer 50 is provided in the exhaust passage 4, it is necessary to enlarge the fuel reformer 50 so that the fuel reformer 50 can be operated without affecting the exhaust components, temperature, and flow velocity. According to the embodiment, by providing the fuel reformer 50 separately from the exhaust passage 4, it is not necessary to increase the size of the apparatus, and stable operation is possible. Furthermore, by providing the fuel reformer 50 separately from the exhaust passage 4, it is possible to control the system different from the control of the engine 1, and to activate the reforming catalyst provided in the fuel reformer 50 at an early stage.
Moreover, the reduction reaction rate in the second purification catalyst (NOx catalyst) 32 can be improved by introducing a reducing gas containing hydrogen. Thereby, when the exhaust air-fuel ratio is made rich, NOx adsorbed or stored in the second purification catalyst (NOx catalyst) 32 can be prevented from being desorbed without being reduced.

  Further, according to the present embodiment, the first introduction passage 57 and the second introduction passage 58 can be switched according to the active state of the EGR catalyst 11. That is, depending on the active state of the EGR catalyst 11, it can be selected whether the reducing gas produced by the fuel reformer 50 is introduced into the EGR passage 6 or the exhaust passage 4. Specifically, when the EGR catalyst 11 is not activated, the temperature of the EGR catalyst 11 can be increased by introducing a reducing gas into the EGR passage 6 so that the EGR catalyst 11 can be activated early. As a result, NOx contained in the exhaust gas can be more effectively reduced.

  Further, according to the present embodiment, when the reducing gas produced by the fuel reformer 50 is introduced into the EGR passage 6 through the first introduction passage 57, the intake air sucked into the combustion chamber of the engine 1. The amount of reducing gas introduced is controlled by adjusting at least one of the amount of air and the amount of fuel supplied to the fuel reformer 50 so that the air-fuel ratio of the fuel does not become rich. For this reason, even when reducing gas is introduced into the EGR passage 6, the air-fuel ratio of the intake air sucked into the combustion chamber can be avoided from being rich, and stable operation is possible.

  Further, according to the present embodiment, first, the NOx emission amount is estimated based on the rotational speed and generated torque of the engine 1, the estimated NOx emission amount, the intake air amount of the engine 1, the fuel consumption amount of the engine 1, The adsorbed NOx amount of the second purification catalyst (NOx catalyst) 32 is estimated based on at least one of the operation time of the engine 1 and the oxygen concentration in the exhaust gas. Next, when the estimated amount of adsorbed NOx is greater than or equal to a predetermined adsorbed NOx amount determination value, the exhaust air / fuel ratio is enriched. As a result, the amount of NOx adsorbed or occluded in the NOx catalyst 32 increases too much, and the amount of NOx that flows out without being reduced when enriched can be reduced, and at the same time, the fuel consumption associated with excessive enrichment Can be avoided.

Further, according to the present embodiment, the predetermined adsorption NOx amount determination value is determined based on the catalyst temperature of at least one of the first purification catalyst 31 and the second purification catalyst 32. Can be For this reason, the supply amount of a reducing agent can always be adjusted appropriately.
Further, according to the present embodiment, the exhaust air / fuel ratio is enriched by introducing reducing gas produced by the fuel reformer 50 according to the operating state of the engine 1, or the exhaust air is exhausted by post combustion or rich combustion. Whether to enrich the fuel ratio is selected.
Further, according to the present embodiment, at least one of the temperature of the first purification catalyst 31, the temperature of the second purification catalyst (NOx catalyst) 32, the amount of adsorbed NOx, the rotational speed of the engine 1, and the generated torque of the engine 1. Accordingly, it is selected whether to enrich the exhaust air-fuel ratio by introducing the reducing gas produced by the fuel reformer 50, or to enrich the exhaust air-fuel ratio by post-combustion or rich combustion.
That is, the introduction of the reducing gas according to the operating conditions such as the temperature of the first purification catalyst 31, the temperature of the second purification catalyst (NOx catalyst) 32, the amount of adsorbed NOx, the rotational speed of the engine 1, and the generated torque of the engine 1. Is selected, or enrichment by post-combustion or rich combustion is selected, so that the amount of NOx that flows out without being reduced can be reduced more effectively, and the first purification catalyst and the second purification catalyst are heated to a high temperature. Therefore, it is possible to avoid the thermal deterioration being promoted.

Further, according to the present embodiment, the engine 1 main injection amount, the engine 1 sub-injection amount, and the engine 1 intake are adjusted so that the exhaust air-fuel ratio when enriching the exhaust air-fuel ratio matches a predetermined target value. At least one of the amount of air and the amount of reducing gas introduced by the fuel reformer 50 is adjusted. Thus, since the exhaust air-fuel ratio at the time of enrichment can be set to a desired value, highly efficient NOx purification can be achieved by always realizing an optimal air-fuel ratio for reducing NOx.
Further, according to the present embodiment, the predetermined target value of the exhaust air-fuel ratio is set to the temperature of the first purification catalyst 31, the temperature of the second purification catalyst (NOx catalyst) 32, the amount of adsorbed NOx, and the enrichment control by the enrichment means. Is determined based on at least one of the duration of the engine, the number of revolutions of the engine 1, and the torque generated by the engine 1. As a result, the exhaust gas having the optimum exhaust air / fuel ratio can always flow into the first purification catalyst 31 and the second purification catalyst (NOx catalyst) 32.

Further, according to the present embodiment, the reducing gas produced by the fuel reformer 50 includes carbon monoxide, hydrogen, and hydrocarbons. Of these, carbon monoxide has the highest volume fraction, and hydrocarbon has the lowest volume fraction.
In the fuel reformer 50 for reforming hydrocarbon fuel, a reducing gas containing carbon monoxide, hydrogen, and light hydrocarbons is produced only by a partial oxidation reaction using only hydrocarbon fuel and air as raw materials. However, in the present embodiment, a reducing gas containing more carbon monoxide than hydrogen is preferably used. For this reason, in this embodiment, a catalyst or system for concentrating hydrogen such as a shift reaction is unnecessary, and since the partial oxidation reaction is an exothermic reaction, it is necessary to supply energy from the outside once the reaction starts. Therefore, the fuel reformer 50 can be made small and simple. Since the fuel reformer 50 can be downsized, the light-off time of the fuel reformer 50 can be shortened, and the reducing gas can be quickly introduced into the exhaust passage 4 and the reflux passage 6 as necessary.
In addition, light hydrocarbon components that are generated as a secondary component can also contribute to the reduction of NOx by being introduced into the first purification catalyst 31 and the second purification catalyst (NOx catalyst) 32.
Moreover, according to this embodiment, the applied engine 1 is a compression ignition type internal combustion engine, and the fuel to be used is light oil. In a compression ignition type internal combustion engine such as diesel, since operation is normally performed in a lean state, it has been conventionally considered to purify NOx. However, by applying the exhaust purification device according to this embodiment, it is efficient. NOx purification is possible.

  In the present embodiment, the ECU 40 performs enrichment means, part of the reflux catalyst activity estimation means, part of the introduction passage switching means, part of the fuel reformer control means, part of the NOx emission amount estimation means, catalyst temperature estimation. A part of the means, a part of the adsorption NOx amount determination value determining means, a first enrichment control means, a second enrichment control means, and a part of the exhaust air / fuel ratio target value determination means are configured. Specifically, step S1 in FIG. 3 corresponds to the reflux catalyst activity estimation means, steps S2 to 3 correspond to the introduction passage switching means, step S4 corresponds to the enrichment means, and step S21 in FIG. 4 corresponds to NOx. Step S22 corresponds to the catalyst temperature estimation means, steps 23 to 26 correspond to the second enrichment control means, and steps S27 to 32 correspond to the first rich. Steps S23 and S27 correspond to the exhaust air / fuel ratio target value determining means.

  Next, a second embodiment of the present invention will be described with reference to the drawings, but the description of the same configuration as the first embodiment will be omitted. In addition, since the engine control procedure in the present embodiment is the same as that in the first embodiment, the flowchart and the description thereof are also omitted.

  FIG. 2 is a diagram showing a configuration of an engine and an exhaust purification device thereof according to the second embodiment of the present invention. As shown in FIG. 2, the basic configuration of the exhaust emission control device according to this embodiment is the same as that of the first embodiment, and the only difference is that the first introduction passage 57 is connected to the upstream side of the TWC 31. It is.

  According to the present embodiment, the same effects as those of the first embodiment can be obtained, and the reducing gas produced by the fuel reformer 50 can be supplied from the TWC (first purification catalyst) 31 through the first introduction passage 57. Can also be introduced into the exhaust passage 4 from the upstream side. Therefore, before the NOx is reduced by the NOx catalyst (second purification catalyst) 32, the reducing gas can flow into the TWC (first purification catalyst) 31 and the NOx catalyst (second purification catalyst) 32. The NOx concentration flowing into the gas can be reduced. Therefore, the NOx slip amount when NOx is reduced by the NOx catalyst (second purification catalyst) 32 can be reduced, and the NOx purification rate can be further improved.

It is a figure which shows the structure of the engine which concerns on 1st embodiment, and its exhaust gas purification apparatus. It is a figure which shows the structure of the engine which concerns on 2nd embodiment, and its exhaust gas purification apparatus. It is a flowchart which shows the procedure of the engine control which concerns on 1st embodiment. It is a flowchart which shows the procedure of the engine control which concerns on 1st embodiment.

Explanation of symbols

1 Engine 4 Exhaust passage 6 EGR passage 11 EGR catalyst 14 EGR gas temperature sensor 21 Air flow meter 31 TWC
32 NOx purification catalyst 33 UEGO sensor 34 Exhaust gas temperature sensor 40 ECU
50 Fuel reformer 56 Introduction passage switching valve 57 First introduction passage 58 Second introduction passage

Claims (12)

NOx in the exhaust gas when the exhaust air-fuel ratio is made lean by setting the air-fuel ratio of the exhaust gas that is provided in the exhaust passage of the internal combustion engine where periodic lean and rich control are performed and the exhaust air flowing through the exhaust passage as the exhaust air-fuel ratio. An internal combustion engine exhaust purification device comprising NOx purification means having at least a NOx purification catalyst that reduces the adsorbed or occluded NOx when the exhaust air-fuel ratio is made rich.
The NOx purification means includes a first purification catalyst and a second purification catalyst that is the NOx purification catalyst provided on the downstream side of the first purification catalyst,
The exhaust gas purification device for the internal combustion engine includes:
Enriching means for enriching the exhaust air-fuel ratio;
A recirculation passage for recirculating part of the exhaust gas into the intake passage of the internal combustion engine;
A reflux catalyst having oxidation performance provided in the reflux passage;
A fuel reformer that is provided separately from the exhaust passage and reforms the fuel to produce a reducing gas;
A first introduction passage for introducing the reducing gas produced by the fuel reformer into the exhaust passage from the upstream side of the second purification catalyst in the exhaust passage;
And a second introduction passage for introducing the reducing gas produced by the fuel reformer into the recirculation passage from the upstream side of the recirculation catalyst in the recirculation passage. Engine exhaust purification system.   The first introduction passage introduces reducing gas produced by the fuel reformer into the exhaust passage from the upstream side of the first purification catalyst in the exhaust passage. The exhaust gas purification apparatus for an internal combustion engine according to claim 1. A reflux catalyst activity estimating means for measuring or estimating an activity state of the reflux catalyst;
An introduction passage switching means for switching between the first introduction passage and the second introduction passage,
The introduction passage switching means switches to the first introduction passage when the reflux catalyst activity estimation means estimates that the reflux catalyst is active, and when it is estimated that the reflux catalyst activity is inactive. 3. The exhaust gas purification device for an internal combustion engine according to claim 1, wherein the second introduction passage is switched.   When the reducing gas produced by the fuel reformer is introduced into the recirculation passage through the first introduction passage, the air-fuel ratio of the intake air sucked into the combustion chamber of the internal combustion engine does not become rich. In addition, the fuel reformer control means may further comprise a fuel reformer control means for controlling an introduction amount of the reducing gas by adjusting at least one of an air amount and a fuel amount supplied to the fuel reformer. Item 4. The exhaust gas purification apparatus for an internal combustion engine according to any one of Items 1 to 3. NOx emission amount estimation means for estimating the NOx emission amount based on the rotational speed of the internal combustion engine and the generated torque of the internal combustion engine;
Based on at least one of the NOx emission amount estimated by the NOx emission amount estimating means, the intake air amount of the internal combustion engine, the fuel consumption amount of the internal combustion engine, the operating time of the internal combustion engine, and the oxygen concentration in the exhaust gas. And an adsorption NOx amount estimating means for estimating the adsorption NOx amount of the second purification catalyst,
2. The enrichment unit enriches the exhaust air-fuel ratio when the adsorption NOx amount estimated by the adsorption NOx amount estimation unit is equal to or greater than a predetermined adsorption NOx amount determination value. 4. An exhaust emission control device for an internal combustion engine according to any one of 4). Catalyst temperature estimating means for estimating or detecting the temperature of at least one of the first purification catalyst and the second purification catalyst;
The internal combustion engine according to claim 5, further comprising an adsorption NOx amount determination value determining unit that determines the predetermined adsorption NOx amount determination value based on the catalyst temperature estimated by the catalyst temperature estimation unit. Exhaust purification device.   The enrichment means includes first enrichment control means by introduction of reducing gas produced by the fuel reformer, and second enrichment control means by post-combustion or rich combustion, and 7. The method of selecting whether the exhaust air-fuel ratio is enriched by the first enrichment control means or enriched by the second enrichment control means according to an operating state of the internal combustion engine. An exhaust gas purification apparatus for an internal combustion engine as described.   The enrichment means is estimated by the temperature of the first purification catalyst estimated by the catalyst temperature estimation means, the temperature of the second purification catalyst estimated by the catalyst temperature estimation means, and the adsorption NOx amount estimation means. The exhaust air / fuel ratio is enriched by the first enrichment control means according to at least one of the adsorbed NOx amount, the rotational speed of the internal combustion engine, and the generated torque of the internal combustion engine, or the second enrichment is performed. 8. The exhaust gas purification apparatus for an internal combustion engine according to claim 7, wherein the control means selects whether or not to enrich.   The enrichment means is configured so that the exhaust air-fuel ratio when enriching the exhaust air-fuel ratio matches a predetermined target value, the main injection amount of the internal combustion engine, the sub-injection amount of the internal combustion engine, The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 6 to 8, wherein at least one of an intake air amount and an introduction amount of reducing gas produced by the fuel reformer is adjusted.   The predetermined target value of the exhaust air-fuel ratio is determined by the temperature of the first purification catalyst estimated by the catalyst temperature estimation means, the temperature of the second purification catalyst estimated by the catalyst temperature estimation means, and the adsorption NOx amount estimation means. Exhaust air / fuel ratio target value determining means for determining based on at least one of the estimated amount of adsorbed NOx, the duration of enrichment control by the enrichment means, the rotational speed of the internal combustion engine, and the torque generated by the internal combustion engine The exhaust emission control device for an internal combustion engine according to claim 9, further comprising:   The reducing gas produced by the fuel reformer contains carbon monoxide, hydrogen, and hydrocarbons. Of these, carbon monoxide has the highest volume fraction and has the lowest volume fraction. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 10, wherein is an hydrocarbon.   The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 11, wherein the internal combustion engine is a compression ignition type internal combustion engine and the fuel to be used is light oil.

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