JP2010270663A - Exhaust emission purifying apparatus for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission purifying apparatus for internal combustion engine, capable of using a fuel in order to reduce NOx occluded in a NOx occlusion catalyst, and preventing S poisoning of the NOx occlusion catalyst in a simple manner and at a low cost. <P>SOLUTION: An exhaust emission purifying apparatus 10 for internal combustion engine includes an exhaust gas pipe 17 for discharging an exhaust gas from an internal combustion engine 11, the NOx occlusion catalyst 22 for occluding NOx contained in the exhaust gas, an S component trap catalyst 23 provided on the upstream side of the NOx occlusion catalyst 22, for trapping the S component contained in the exhaust gas, a fuel supply pipe 24 for reduction for connecting a fuel tank 12 for supplying a fuel for reduction for reducing NOx occluded in the NOx occlusion catalyst 22 and the exhaust gas pipe 17 at the downstream side of the S component trap catalyst 23, and an S component absorbent agent 25 provided on the upstream side of a fuel injection engine 26 for reduction in the fuel supply pipe 24 for reduction, for adsorbing the S component contained in fuel. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to an exhaust gas purification apparatus for an internal combustion engine provided with an NOx storage catalyst for storing nitrogen oxides (hereinafter referred to as NOx) contained in exhaust gas in an exhaust pipe.

  During combustion of an internal combustion engine, the generation of NOx due to a sudden rise in temperature and pressure in the piston is inevitable, and particularly in a diesel engine that takes in a large amount of air, the amount of NOx produced also increases. Further, since sulfur compounds (hereinafter referred to as S component) are included in the fuel and the lubricating oil, sulfur oxides (hereinafter referred to as SOx) are also included in the exhaust gas. In the exhaust pipe, a NOx storage catalyst is provided to capture NOx in the exhaust, and SOx is also captured by the NOx storage catalyst together with NOx. However, the amount of SOx stored in the NOx storage catalyst gradually increases. As the amount of NOx that can be stored gradually decreases, it is necessary to regenerate the NOx storage catalyst.

  Since the regeneration treatment of the NOx storage catalyst is performed by performing a high temperature treatment in a reducing atmosphere, there has been a problem that the noble metal catalyst in the NOx storage catalyst is thermally deteriorated. Therefore, Patent Document 1 discloses an exhaust gas purification apparatus for an internal combustion engine in which a SOx trap catalyst is provided on the upstream side of the NOx storage catalyst in order to prevent SOx from being sent to the NOx storage catalyst.

  Specifically, the exhaust emission control device of Patent Document 1 is included in the exhaust and air-fuel ratio control means that keeps the air-fuel ratio of the exhaust flowing into the SOx trap catalyst lean without causing the air-fuel ratio to flow into the SOx trap catalyst during operation. Estimation means for estimating a SOx trap rate indicating a ratio of SOx trapped in the SOx trap catalyst in SOx. When releasing the trapped NOx from the NOx storage catalyst, the reducing agent is supplied from the reducing agent supply valve into the exhaust passage so that the air-fuel ratio of the exhaust gas flowing into the NOx storage catalyst is temporarily made rich. Yes.

  Further, as other technologies related to exhaust purification, technologies for removing S component in fuel are disclosed in Patent Documents 2 and 3. Patent Document 2 discloses a sulfur-containing compound removing device installed between a fuel tank and an injector of an engine, a tank of a gas station or a tank lorry, and the amount of SOx in exhaust gas discharged from the engine. It is described that the durability of the NOx storage catalyst can be improved.

  Patent Document 3 provides a highly efficient and compact sulfur compound removal device that can be mounted on a vehicle by using a sulfur compound removal method in which a fuel is brought into a supercritical or subcritical state and brought into contact with a sulfur compound adsorbent. It is described that poisoning (S poisoning) due to the S component of the catalyst can be prevented and the exhaust gas can be cleaned.

JP 2005-133610 A JP 2002-161285 A JP 2005-042051 A

  However, in the apparatus of Patent Document 1, for example, when fuel is used as the reducing agent, the NOx storage catalyst is poisoned with S by the S component contained in the fuel. In addition, when a reducing agent other than fuel is used, a separate reducing agent charging tank is installed, and the user is forced to replenish the dedicated reducing agent. From the viewpoint of cost reduction and convenience improvement, etc. There is room for improvement.

  On the other hand, in the apparatuses of Patent Documents 2 and 3, the S component derived from the lubricating oil is not considered at all. The S component contained in the exhaust is assumed to have a fuel-derived component and a lubricant-derived component having the same degree, and in the devices of Patent Documents 2 and 3, the S component derived from the lubricant is contained in the exhaust. Therefore, like the apparatus of Patent Document 1, the NOx storage catalyst is poisoned with S. As described above, according to the prior art, S poisoning of the NOx storage catalyst cannot be completely avoided by a low-cost and simple method.

  It is an object of the present invention to use an exhaust purification device for an internal combustion engine that can use fuel to reduce NOx stored in a NOx storage catalyst and can reliably prevent S poisoning of the NOx storage catalyst. Is to provide.

  An exhaust gas purification apparatus for an internal combustion engine according to the present invention is provided in a fuel tank filled with fuel to be supplied to the internal combustion engine, an exhaust pipe for exhausting exhaust gas from the internal combustion engine, and included in the exhaust pipe. Opening and closing the NOx storage catalyst for storing NOx, the reduction fuel supply pipe for supplying the reduction fuel for reducing NOx stored in the NOx storage catalyst from the fuel tank to the exhaust pipe, and the reduction fuel supply pipe An exhaust purification device for an internal combustion engine, comprising: a fuel injection valve that injects fuel; an S component trap catalyst that is provided upstream of a NOx storage catalyst in an exhaust pipe and traps an S component contained in the exhaust; And an S component adsorbent provided on the upstream side of the fuel injection valve in the fuel tank or the reducing fuel supply pipe and adsorbing the S component contained in the fuel.

  According to the above configuration, since the S component trap catalyst and the S component adsorbent can completely prevent the S component from being fed into the NOx storage catalyst, the NOx storage catalyst is not poisoned by S. Therefore, the NOx storage catalyst does not need to be regenerated at high temperature, eliminates thermal degradation and fuel consumption loss of the NOx storage catalyst due to regeneration, and does not need to increase the capacity of the NOx storage catalyst and the amount of noble metal catalyst in consideration of thermal degradation. Thus, the NOx storage catalyst can be made compact and low in cost.

  The reducing fuel supply pipe is preferably connected between the S component trap catalyst and the NOx storage catalyst in the exhaust pipe.

  According to the above configuration, the amount of fuel used as the reducing agent can be reduced compared with the case where the reducing fuel supply pipe is connected to the upstream side of the S component trap catalyst, and the reduction efficiency of the NOx storage catalyst can be reduced. Can be improved. Further, since the S component trap catalyst is not exposed to the reducing atmosphere, there is no possibility that the S component is detached from the S component trap catalyst and the NOx storage catalyst is poisoned by S.

  Further, it is preferable that the S component adsorbent is further provided in a fuel supply pipe connecting the fuel tank and the internal combustion engine.

  According to the above configuration, the load of the S component trap catalyst can be halved. That is, since the S component from the fuel can be removed by the S component adsorbent, the amount of the S component introduced into the S component trap catalyst can be greatly reduced (halved). The capacity can be greatly reduced.

  According to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, fuel can be used to reduce NOx stored in the NOx storage catalyst, and S poisoning of the NOx storage catalyst can be reliably prevented. It becomes possible.

It is a mimetic diagram showing a schematic structure of an exhaust emission control device of an internal-combustion engine in an embodiment concerning the present invention.

  Embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an exhaust purification device 10 for an internal combustion engine.

  As shown in FIG. 1, an exhaust gas purification device 10 for an internal combustion engine (hereinafter referred to as an exhaust gas purification device 10) is a vehicle equipped with an internal combustion engine 11 and a fuel tank 12 filled with fuel to be supplied to the internal combustion engine 11. This is a device for purifying exhaust gas by trapping NOx and SOx contained in the exhaust gas of the internal combustion engine 11.

  The internal combustion engine 11 includes a plurality of cylinders 13 serving as combustion chambers, an injector 14 including an electronically controlled fuel injection valve that injects fuel into each cylinder 13, an intake manifold (not shown) that supplies air to each cylinder 13, and each An exhaust manifold 15 that exhausts exhaust from the cylinder 13 is provided. The exhaust manifold 15 is connected to an exhaust turbocharger 16, and an exhaust pipe 17 extends from the exhaust turbocharger 16.

  The fuel tank 12 is a container filled with fuel such as gasoline or light oil supplied to the internal combustion engine 11. A fuel supply pipe 18 extends from the fuel tank 12, and the fuel supply pipe 18 is connected to each injector 14 of each cylinder 13 via a common rail 19. The common rail 19 is a device that uniformly supplies the fuel pressurized by the electronically controlled high-pressure pump 20 to each injector 14, and realizes fine control of fuel injection pressure, injection timing, and injection amount by electronic control. To do. A return pipe 21 is provided from the common rail 19 to return excess fuel to the fuel tank 12.

  The vehicle is equipped with an electronic control unit (not shown) that controls each element of the internal combustion engine 11. The electronic control unit is composed of a computer and controls fuel discharge, intake air, and the like based on information from sensors (not shown). The electronic control unit also has a function of controlling the opening / closing state of a reduction fuel injection valve 26, which will be described later, to adjust the injection amount of the reduction fuel.

  As described above, the exhaust purification device 10 is a device that traps NOx and SOx contained in the exhaust gas of the internal combustion engine 11 to purify the exhaust, and also has a function of reducing the trapped NOx and detoxifying it. Have. As shown in FIG. 1, the exhaust purification device 10 includes an exhaust pipe 17, a NOx storage catalyst 22 provided in the exhaust pipe 17, and an S component trap catalyst 23 provided upstream of the NOx storage catalyst 22 in the exhaust pipe 17. And as a main component. Further, the exhaust purification device 10 includes a reducing fuel supply pipe 24 and an S component adsorbent 25 that traps an S component in the fuel as main components.

  The NOx storage catalyst 22 has a function of trapping NOx in the exhaust, and is provided to prevent NOx from being discharged into the atmosphere. Further, as will be described in detail later, it also has a function of detoxifying and releasing trapped NOx. The NOx storage catalyst 22 having such a function is provided in the exhaust pipe 17 as described above, and is composed of a catalyst substance, a NOx adsorbent, and a catalyst carrier that carries these.

  Examples of the catalyst carrier include a three-dimensional network monolith carrier, a pellet carrier, and a honeycomb particulate filter. The particulate filter has a plurality of exhaust flow passages extending in parallel, and is made of a porous material such as cordierite, for example. A layer of a NOx storage agent is formed on the surface of a catalyst carrier such as a particulate filter, and a noble metal catalyst is dispersed and supported as a catalyst material to constitute the NOx storage catalyst 22.

  As the noble metal catalyst, for example, platinum (Pt) is used, and as the component constituting the NOx storage agent, for example, alkali metal such as potassium (K), sodium (Na), cesium (Cs), barium (Ba) ), Alkaline earth metals such as calcium (Ca), and rare earth metals such as lanthanum (La) and yttrium (Y) are used.

According to the NOx storage catalyst 22, for example, has been become NO ₂ oxidation NO contained in the exhaust gas on the platinum (Pt), components of the NOx storage agent (e.g., barium oxide BaO) combined with nitrate ions It is absorbed by the NOx storage agent in the form of (NO ₃ ⁻ ). When the oxygen concentration in the exhaust gas is high, that is, under normal exhaust conditions, NO ₂ is generated on the surface of platinum (Pt), and NOx in the exhaust gas is nitrate ions unless the NOx absorption capacity of the NOx storage agent is saturated. It is absorbed by the NOx storage agent in the form of (NO ₃ ⁻ ).

On the other hand, when the NOx occlusion catalyst 22 is made into a reducing atmosphere with a reducing fuel described later, the oxygen concentration in the exhaust gas decreases, so that the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ). Then, nitrate ions NO ₃ ⁻ in the NOx storage agent are released from the NOx storage agent in the form of NO ₂ , and the released NOx is reduced by unburned HC and CO contained in the exhaust gas, and N ₂ (H ₂ O, CO ₂ ) and released into the atmosphere.

  The S component trap catalyst 23 provided on the upstream side of the NOx storage catalyst 22 has a function of trapping S components in the exhaust gas, particularly SOx. By providing the S component trap catalyst 23 on the upstream side of the NOx storage catalyst 22, it is possible to prevent the SOx discharged from the internal combustion engine 11 from being sent to the NOx storage catalyst 22.

The S component trap catalyst 23 can be composed of a catalyst material, an SOx adsorbent, and a catalyst carrier that supports them, and each component such as the catalyst material should be of the same type as the NOx storage catalyst 22. Can do. By the S component trap catalyst 23, SOx contained in the exhaust gas diffuses in the catalyst carrier, is oxidized by platinum (Pt) present on the surface thereof, and is then absorbed by the SOx adsorbent. That is, SO ₂ oxidized by platinum is trapped by diffusing into the SOx adsorbent coat layer formed on the catalyst support in the form of sulfate ions (SO ₄ ²⁻ ) to form sulfates.

  The S component trap catalyst 23 can be replaced when the trapping ability of the S component is reduced, or the trapped S component can be released. From the viewpoint, it is preferable that an S component having a capacity that does not need to be replaced and the lap catalyst 23 are mounted in advance in consideration of the travel distance of the vehicle. In particular, when the S component adsorbent 25 described later is also provided on the fuel supply side of the internal combustion engine 11, the amount of S component trapped by the S component trap catalyst 23 is halved. Even if it is made compact, it can be made unnecessary to replace.

  As described above, when the NOx storage catalyst 22 is in a reducing atmosphere, the oxygen concentration in the exhaust gas decreases, so that the adsorbed NOx can be rendered harmless and released. The exhaust purification device 10 includes a reducing fuel supply pipe 24 that uses fuel as a reducing agent for reducing the NOx storage catalyst 22 and supplies the reducing fuel to the NOx storage catalyst 22.

  The reducing fuel supply pipe 24 is a pipe for supplying the reducing fuel for the NOx storage catalyst 22 as described above, and connects the fuel tank 12 to the exhaust pipe 17. The reducing fuel supply pipe 24 is provided with a reducing fuel injection valve 26 in the vicinity of the connection between the high-pressure pump 20 and the exhaust pipe 17, and the reduced reducing fuel is supplied to the reducing fuel injection valve 26. By opening and closing, it is injected into the exhaust pipe 17. The reducing fuel injection valve 26 is opened under the control of the electronic control unit when attempting to detoxify and release NOx trapped from the NOx storage catalyst 22.

  An S component adsorbent 25 is provided in the reducing fuel supply pipe 24 to remove the S component contained in the fuel. Therefore, the reducing fuel supply pipe 24 may be connected to the upstream side of the S component trap catalyst 23 in the exhaust pipe 17, but is preferably connected to the downstream side as shown in FIG. When the reducing fuel is injected into the exhaust pipe 17, it is mixed with the exhaust gas, and the NOx storage catalyst 22 provided on the downstream side is brought into a reducing atmosphere. Note that the reducing fuel supply pipe 24 may be connected to the exhaust pipe 17 in a portion where the NOx storage catalyst 22 is filled.

  With the configuration shown in FIG. 1, the amount of fuel used as a reducing agent can be reduced compared to the case where the reducing fuel supply pipe 24 is connected to the upstream side of the S component trap catalyst, and the NOx storage catalyst. The reduction efficiency of 22 can be improved. Further, when the S component trap catalyst 23 is placed in a reducing atmosphere, the trapped S component may be released. However, with the configuration shown in FIG. 3, the S component trap catalyst 23 is not exposed to the reducing atmosphere. Therefore, there is an effect that there is no possibility that the S component is detached from the S component trap catalyst 23 and the NOx storage catalyst 22 is poisoned with S.

  As described above, the S component adsorbent 25 has a function of adsorbing the S component contained in the fuel, and is provided upstream of the reducing fuel injection valve 26 in the reducing fuel supply pipe 24. Further, the S component adsorbent 25 can also be provided in the fuel supply pipe 18 that connects the fuel tank 12 and the internal combustion engine 11. With such a configuration, the load on the S component trap catalyst 23 is halved. be able to. That is, since the S component derived from the fuel can be removed by the S component adsorbent 25, the amount of the S component introduced into the S component trap catalyst 23 can be greatly halved.

  The exhaust purification device 10 can be provided with two high-pressure pumps 20 for supplying fuel to the internal combustion engine 11 and for supplying fuel for reduction to the NOx storage catalyst 22, but as shown in FIG. One S component adsorbent 25 can also be provided in a connecting pipe between the fuel tank 12 and the high-pressure pump 20 (also used as the fuel supply pipe 18 and the reducing fuel supply pipe 24) by using the pump 20. Further, the S component adsorbent 25 can be brought into contact with the fuel by immersing it in the fuel in the fuel tank 12, and in this case, the natural flow of the fuel may be used, or forced circulation is used. May be.

The S component adsorbent 25 is not particularly limited as long as it is a material that can adsorb and remove the S component in the fuel. Examples of the S component adsorbent 25 include porous materials such as mesoporous silica (FSM), zeolite, acidic clay, and activated carbon, activated alumina, titanium oxide (TiO ₂ ), nickel oxide (NiO), manganese dioxide ( Metal oxides such as MnO ₂ ), potassium permanganate (KMnO ₄ ), manganese sulfate (MnSO ₄ ), vanadium oxide (V ₂ O ₅ ), and molybdenum oxide (MoO ₃ ); metal catalysts such as platinum and nickel Can be used. As the S component adsorbent 25, a catalyst similar to the S component trap catalyst 23 can be used.

  As described above, the exhaust purification device 10 is provided in the exhaust pipe 17 at the upstream side of the NOx storage catalyst 22 that stores NOx contained in the exhaust, and the S component contained in the exhaust. The S component trap catalyst 23 to be trapped, the reduction fuel supply pipe 24 connected between the S component trap catalyst 23 and the NOx storage catalyst 22 from the fuel tank 12, and the reduction fuel injection valve in the reduction fuel supply pipe 24 Since the S component adsorbent 25 is provided upstream of the S 26, it is possible to completely prevent the S component from being fed into the NOx storage catalyst 22.

  Therefore, the high temperature regeneration process of the NOx storage catalyst 22 is not required, the thermal deterioration and fuel efficiency loss of the NOx storage catalyst 22 due to the regeneration process are eliminated, and the capacity of the NOx storage catalyst 22 and the amount of the noble metal catalyst in consideration of the thermal deterioration are reduced. Increment is not required, and the NOx storage catalyst 22 can be made compact and low in cost. In addition, the amount of fuel used as the reducing agent can be reduced, and the reduction efficiency of the NOx storage catalyst can be improved. Further, since the reducing fuel supply pipe 24 is connected between the S component trap catalyst 23 and the NOx storage catalyst 22, the S component trap catalyst 23 is not exposed to the reducing atmosphere. There is no possibility that the S component is detached and the NOx storage catalyst 22 is poisoned with S. That is, fuel can be used to reduce the NOx stored in the NOx storage catalyst 22, and S poisoning of the NOx storage catalyst 22 can be reliably prevented.

  DESCRIPTION OF SYMBOLS 10 Exhaust gas purification device of internal combustion engine, 11 Internal combustion engine, 12 Fuel tank, 13 cylinders, 14 injector, 15 Exhaust manifold, 16 Exhaust turbocharger, 17 Exhaust pipe, 18 Fuel supply pipe, 19 Common rail, 20 High pressure pump, 21 Return pipe , 22 NOx storage catalyst, 23 S component trap catalyst, 24 fuel supply pipe for reduction, 25 S component adsorbent, 26 fuel injection valve for reduction.

Claims (3)

An exhaust pipe for exhausting the exhaust from the internal combustion engine;
A NOx storage catalyst that is provided in the exhaust pipe and stores NOx contained in the exhaust;
A reducing fuel supply pipe for supplying a reducing fuel for reducing NOx stored in the NOx storage catalyst from the fuel tank to the exhaust pipe;
A fuel injection valve for reduction for injecting the fuel for reduction by opening and closing the fuel supply pipe for reduction;
An exhaust gas purification apparatus for an internal combustion engine comprising:
An S component trap catalyst that is provided upstream of the NOx storage catalyst in the exhaust pipe and traps the S component contained in the exhaust;
An S component adsorbent that is provided upstream of the fuel injection valve in the fuel tank or the fuel supply pipe for reduction, and adsorbs the S component contained in the fuel;
An exhaust emission control device for an internal combustion engine, comprising: The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
The fuel supply pipe for reduction is
An exhaust purification device for an internal combustion engine, which is connected between an S component trap catalyst and a NOx storage catalyst. The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2,
S component adsorbent is
Further, the exhaust gas purification apparatus for an internal combustion engine is provided in a fuel supply pipe connecting the fuel tank and the internal combustion engine.

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