JP2008163886A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of improving NOx conversion performance. <P>SOLUTION: This exhaust emission control device is provided in an exhaust gas passage of the internal combustion engine, and is provided with an NOx retainer, an ozone formation means forming ozone, an ozone storage means storing ozone formed by the ozone formation means, and an ozone introduction means introducing ozone stored in the ozone storage means into am upstream of the NOx retainer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine.

  Conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-89246, an exhaust gas purifying apparatus having a NOx occlusion reduction type catalyst (hereinafter referred to as “NSR catalyst”) is known. More specifically, the NSR catalyst has a catalytic function for purifying nitrogen oxide (NOx), hydrocarbon (HC), etc. contained in the combustion gas discharged from the internal combustion engine, and stores NOx in the catalyst. And a catalyst having a function. During lean operation where the reducing agent is insufficient, NOx that is not purified by the catalyst may be released to the atmosphere. According to the NSR catalyst, NOx can be occluded inside the catalyst, and during the rich or stoichiometric operation after the catalyst activation, the occluded NOx can be reacted with a reducing agent such as HC for purification.

  Further, at the time of cold start of the internal combustion engine that does not exhibit catalytic activity, the NOx oxidation reaction is not activated, and the above-described occlusion reaction is not performed efficiently. Therefore, according to the conventional system, ozone is added to the exhaust gas at the cold start. Ozone can oxidize NOx in the gas phase. For this reason, even before the catalytic activity is expressed, NOx can be effectively oxidized, and the storage amount of NOx can be increased.

JP 2002-89246 A JP-A-5-192535 JP 2005-538295 A Japanese Patent Laid-Open No. 9-235103 JP 2001-19407 A

  By the way, the amount of NOx discharged from the internal combustion engine varies depending on the operating state of the internal combustion engine. For this reason, in the above-described conventional system in which ozone is added at the time of cold start of the internal combustion engine, ozone must be generated in an amount corresponding to the amount of NOx to be discharged. It is also conceivable that the ozone generated will be insufficient. In order to avoid such a situation, it may be possible to use a large ozone generator with high ozone generation capability, but the weight and physique of the system will increase, so it is not suitable for mounting on a moving body such as a vehicle. It is. Therefore, in the conventional system, the exhausted NOx cannot be effectively stored, and the NOx purification performance may be deteriorated.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can improve NOx purification performance.

In order to achieve the above object, a first invention is an exhaust gas purification apparatus provided in an exhaust passage of an internal combustion engine,
NOx retention material;
Ozone generating means for generating ozone;
Ozone storage means for storing ozone generated by the ozone generation means;
Ozone introduction means for introducing ozone stored by the ozone storage means upstream of the NOx holding material;
It is characterized by providing.

The second invention is the first invention, wherein
The NOx holding material is a NOx occlusion reduction type catalyst integrated with a three-way catalyst.

The third invention is the first invention, wherein
The NOx holding material is arranged upstream of the three-way catalyst.

The fourth invention is the invention according to any one of the first to third inventions,
The ozone storage means includes a pressure vessel, and the ozone is compressed and stored in the pressure vessel.

The fifth invention is the invention according to any one of the first to fourth inventions,
The ozone storage means includes an ozone adsorbent that adsorbs ozone, and the ozone is adsorbed and stored in the ozone adsorbent.

The sixth invention is the fifth invention, wherein
The ozone adsorbent contains silica gel as a component.

The seventh invention is the invention according to any one of the first to sixth inventions,
The ozone generating means generates ozone during operation of the internal combustion engine.

Further, an eighth invention is the invention according to any one of the first to seventh inventions,
The ozone introducing means introduces ozone immediately after the internal combustion engine is started.

  According to 1st invention, the ozone produced | generated by the ozone production | generation means can be stored by an ozone storage means. For this reason, according to the present invention, by effectively using the stored ozone, ozone shortage due to ozone generation delay is avoided, and the retention performance of the NOx retention material that occludes or adsorbs NOx is effectively reduced. Can be suppressed. Further, since the generated ozone can be stored, it is not necessary to generate a large amount of ozone at a time. For this reason, a small ozone generator with low ozone generation capability can be used, and the system efficiency can be improved.

  According to the second invention, the NOx occlusion reduction catalyst in which the NOx holding material and the three-way catalyst are integrated is used, so that the desorbed NOx can be efficiently reacted on the catalyst. Moreover, since the number of parts is reduced by integrating, manufacturing cost can be suppressed.

  Further, the occlusion element supported on the NOx holding material is considered to be a catalyst poison for the noble metal of the catalyst. According to the third invention, since the NOx holding material and the three-way catalyst are separately arranged in the exhaust passage of the internal combustion engine, the activity of the three-way catalyst can be further increased. In addition, since the three-way catalyst is arranged downstream of the NOx holding material, after the activity of the three-way catalyst is developed to some extent, the NOx that has not been occluded in the NOx holding material can be purified in the three-way catalyst. , NOx purification performance can be improved.

  According to the fourth invention, since the pressure vessel is provided as the ozone storage means, the ozone can be stored easily by compressing the ozone.

  According to the fifth invention, since the ozone adsorbing material is provided as the ozone storage means, ozone can be easily stored by adsorbing ozone onto the ozone adsorbing material.

  According to the sixth invention, silica gel having a function of adsorbing ozone can be used as the ozone adsorbent.

  According to the seventh aspect, since ozone is generated during operation of the internal combustion engine, ozone can be generated using the energy of the internal combustion engine.

  According to the eighth invention, the ozone stored in the ozone storage means immediately after the start of the internal combustion engine is introduced upstream of the NOx holding material. For this reason, according to the present invention, ozone can be effectively introduced into the NOx holding material before the catalytic activity is expressed, and the NOx occlusion performance can be improved.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted. The present invention is not limited to the following embodiments.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining the configuration of the first embodiment of the present invention. As shown in FIG. 1, the exhaust gas purifying apparatus 10 of the present embodiment is an internal combustion engine (hereinafter also simply referred to as “engine”).
12 is attached.

An exhaust pipe 14 is connected to the exhaust side of the engine 12. An exhaust purification catalyst 20 is disposed in the middle of the exhaust pipe 14. Further, a NOx occlusion reduction type catalyst 22 (hereinafter referred to as “NSR catalyst 22”) is disposed inside the exhaust purification catalyst 20. Inside the NSR catalyst 22, platinum (Pt) and barium carbonate (BaCO ₃ ), which are noble metals, are supported on a ceramic carrier. Pt functions as an active site that activates an oxidation reaction of CO, HC, etc., or a reduction reaction of NOx. BaCO ₃ functions as a NOx storage agent that stores NOx as nitrate. Hereinafter, the carrier carrying Pt is referred to as “catalyst”, and the carrier carrying BaCO ₃ is referred to as “NOx holding material”.

The exhaust gas purification device 10 of the present embodiment includes an ozone supply device 30. More specifically, the ozone supply device 30 includes an ozone generator 36 that generates ozone (O ₃ ) using oxygen introduced from the air port 32. A piping 38 is connected to the ozone generator 36, and an ozone injection port 34 is provided at the tip thereof. The ozone injection port 34 is disposed in the exhaust purification catalyst 20 so as to inject ozone toward the NSR catalyst 22.

  Further, an ozone storage device 40 for storing the generated ozone is arranged in the pipe 38. The ozone storage device 40 is composed of a pressure vessel, and the inside thereof is filled with silica gel that adsorbs ozone. The configuration, function, and the like of the ozone storage device 40 are not the main part of the present invention and are well-known techniques, and thus detailed description thereof is omitted.

  A pump 42 is disposed upstream of the ozone storage device 40 in the pipe 38. The pump 42 functions as power for circulating the gas inside the pipe. Further, a valve 44 for controlling the open / closed state of the pipe 38 is disposed downstream of the ozone storage device 40.

  The system according to the present embodiment includes an ECU (Electronic Control Unit) 50 as shown in FIG. The ozone supply device 30 described above is connected to the output unit of the ECU 50. Various sensors for detecting the operating condition and operating state of the engine 12 are connected to the input unit of the ECU 50. The ECU 50 calculates the ozone injection timing and the injection amount based on various types of input information, and drives various devices of the ozone supply device 30.

[Operation of Embodiment 1]
(NOx occlusion reduction operation using ozone)
Next, the operation of this embodiment will be described with reference to FIGS. On the catalyst of the NSR catalyst 22 disposed inside the exhaust purification catalyst 20, NOx reacts with HC or CO and is decomposed into N ₂ , H ₂ O, CO _{2 and the} like. Thereby, NOx contained in the exhaust gas is effectively purified. However, at the time of cold start of the internal combustion engine 12 where the NSR catalyst 22 has not reached the activation temperature, the three-way activity is low and NOx contained in the exhaust gas cannot be purified.

  Therefore, in the present embodiment, NOx that cannot be purified is occluded and the situation where it is released to the atmosphere is suppressed. As means for storing NOx, ozone is introduced into the exhaust gas. More specifically, when the engine 12 is cold started, ozone generated by the ozone supply device 30 is injected from the ozone injection port 34 toward the NSR catalyst 22.

FIG. 2 is a schematic diagram for explaining the NOx occlusion reaction, and is an enlarged view showing the inside of the NSR catalyst 22. As shown in this figure, before the exhaust purification catalyst 20 is activated at a low temperature, NOx reacts with ozone in the gas phase and is oxidized. More specifically, the following reaction occurs.
NO + O ₃ → NO ₂ + O ₂ (1)
NO ₂ + O ₃ → NO ₃ + O ₂ (2)
NO ₂ + NO ₃ → N ₂ O ₅ (3)
(NO ₂ + NO ₃ ← N ₂ O ₅ )

NOx oxidized to NO ₂ , NO ₃ , or N ₂ O ₅ is occluded as a nitrate such as Ba (NO ₃ ) _{2 in} the NOx holding material. Thereby, NOx can be occluded effectively, and the situation where NOx is released into the atmosphere before the three-way activity of the exhaust purification catalyst 20 can be effectively suppressed.

The stored NOx reacts with a reducing agent such as HC contained in the exhaust gas and is purified after the NSR catalyst 22 is activated. FIG. 3 is a schematic diagram for explaining the reduction reaction of NOx, and is an enlarged view showing the inside of the NSR catalyst 22. As shown in this figure, after the catalyst activity, the adsorbed NOx is reduced by a reducing agent such as HC contained in the exhaust gas, and decomposed into N ₂ , H ₂ O, CO _{2 and the} like. Thus, by efficiently performing NOx occlusion and reduction reaction, it is possible to effectively purify NOx occluded before the catalytic activity is expressed.

  Further, according to the gas phase reaction of ozone shown in the above formulas (1) and (2), NOx can be oxidized without being on the catalyst. It is also possible to separate and carry a noble metal. Thereby, the NOx storage agent which becomes a catalyst poison for the noble metal can be separated, and the purification efficiency in the catalyst can be improved.

In the above NOx occlusion reaction, NO ₂ , NO ₃ , N ₂ O ₅ , or HNO ₃ produced by reacting these nitrogen oxides with water can be occluded, the NOx occlusion amount by the form NO ₂ is limited. Therefore, by the above reaction formula (2) is actively performed, if it is possible to much NO ₂ in the form of NO _3, it is possible to dramatically increase a NOx storage amount.

However, since the activation energy required for the reaction of the above equation (2) is higher than the energy required for the reaction of the above equation (1), the reaction of the above equation (1) takes precedence over the reaction of the above equation (2). Get up. Therefore, when the molar amount of ozone contained in the exhaust gas is less than the molar amount of NO are not occur only to the above reaction formula (1), NO is only so that the not oxidized to NO _2.

Therefore, the ozone introduction amount is controlled so that the molar amount of ozone introduced into the exhaust gas is larger than the molar amount of NO contained in the exhaust gas. Accordingly, the NO ₂ by the reaction of the equation (2) can be oxidized to NO _3, it is possible to increase the NOx storage amount.

Preferably, if the amount of ozone introduced is controlled so that the molar amount of ozone introduced into the exhaust gas is at least twice the molar amount of NO contained in the exhaust gas, NO can be oxidized to NO ₃ , and the NOx occlusion amount can be dramatically increased.

(Ozone storage operation in ozone storage device)
As described above, in the present embodiment, ozone is injected toward the NSR catalyst 22 when the engine 12 is cold started. Thus, NOx discharged from the engine 12 is effectively occluded before the three-way activity of the NSR catalyst 22 is expressed, and the release to the atmosphere is suppressed.

  However, the amount of NOx discharged from the engine 12 varies depending on the operating state of the engine 12 and the like. For this reason, when a large amount of NOx is discharged, the necessary ozone amount may exceed the ozone generation amount of the ozone generator 36. In such a case, NOx that could not be stored in the NSR catalyst 22 would be released to the atmosphere.

  Therefore, in the present embodiment, the ozone storage device 40 is used. The ozone storage device 40 is a device that can store the ozone generated in the ozone generator 36 inside. More specifically, in the operation of storing ozone in the ozone storage device 40, first, ozone is generated by the ozone generator 36 during operation of the engine 12. Next, the pump 42 is driven with the valve 44 closed, and ozone is stored inside the ozone storage device 40.

  The ozone stored in the ozone storage device 40 is injected from the ozone injection port 34 toward the NSR catalyst 22 during an ozone introduction period such as when the engine 12 is cold started. More specifically, the pump 42 is driven with the valve 44 opened. Thereby, since a desired amount of ozone corresponding to the amount of NOx discharged can be effectively introduced into the NSR catalyst 22, even when a large amount of NOx is discharged, NOx is efficiently stored. Can do.

  In addition, according to the exhaust gas purification apparatus 10 of the present embodiment, ozone can be generated and stored while ozone is not added, so the ozone generator 36 can be downsized. System efficiency can be improved.

  By the way, in the first embodiment described above, the NSR catalyst 22 in which Pt, which is a noble metal, and BaCO3, which functions as a NOx storage agent, is disposed on the ceramic support inside the exhaust purification catalyst 20, The catalyst configuration to be arranged is not limited to this. That is, according to the gas phase reaction of ozone shown in the above formulas (1) and (2), NOx can be oxidized without being on the catalyst. It is also possible to separate and carry a noble metal. More specifically, for example, the NOx storage agent and the noble metal may be separated and supported on the upstream side and the downstream side of the carrier.

  FIG. 4 is a view showing an internal configuration of an exhaust purification catalyst 60 applicable as a modification of the exhaust purification catalyst 20. As shown in this figure, a NOx holding material 62 is disposed inside the exhaust purification catalyst 60. Further, a three-way catalyst 64 is disposed further downstream of the NOx holding material 62. Further, an ozone injection port 34 that injects ozone toward the NOx holding material 62 is disposed on the upstream side of the NOx holding material 62.

  According to such a configuration, the three-way catalyst 64 on which the noble metal is supported and the NOx holding material 62 on which the NOx occlusion agent that is a catalyst poison for the noble metal are separately arranged, so that the purification efficiency of the catalyst is improved. Can be improved. Further, since the three-way catalyst 64 is arranged downstream of the NOx holding material 62, after the activity of the three-way catalyst 64 is expressed to some extent, the NOx that could not be stored in the NOx holding material 62 is stored in the three-way catalyst 64. The purification treatment can be performed, and the NOx purification performance can be improved.

  Further, the internal structure of the NSR catalyst 22 is not only a structure for supporting the NOx storage agent and the noble metal separately on the upstream side and the downstream side of the carrier, but also separately supporting the upper layer side and the lower layer side of the carrier. It is good also as a structure to do. In the case where the layers are separated and supported, it is preferable to arrange the noble metal in the upper layer of the NOx storage agent and reduce the NOx released from the NOx storage agent with the noble metal.

  Further, in the first embodiment described above, the ozone injection port 34 is arranged in the exhaust purification catalyst 20, but the arrangement of the ozone injection port 34 is not limited to this. That is, as long as ozone can be added to the exhaust gas introduced into the exhaust purification catalyst 20, the exhaust pipe 14 may be disposed upstream of the exhaust purification catalyst 20.

In Embodiment 1 described above, BaCO ₃ is used as the NOx storage agent, but the material is not limited to this. That is, alkali metals such as Na, K, Cs, and Rb, alkaline earth metals such as Ba, Ca, and Sr, and rare earth elements such as Y, Ce, La, and Pr may be used as necessary. Further, the material of the catalyst used for the NSR catalyst 22 is not limited to Pt, and Rh, Pd, etc., which are noble metal materials, may be used as necessary.

  Moreover, in Embodiment 1 mentioned above, although the pressure | voltage resistant container with which the silica gel which functions as an ozone adsorbent was filled inside is used as the ozone storage device 40, the structure of the ozone storage device 40 is restricted to this. Absent. That is, as long as ozone can be stored, the structure may be only a pressure vessel, and the container filled with silica gel does not need to be a pressure vessel. Further, the ozone adsorbent is not limited to silica gel, and another material that functions as an ozone adsorbent may be used as necessary.

  In the first embodiment described above, the ozone supply device 30 is the “ozone introducing means” in the first invention, the ozone generator 36 is the “ozone generating means” in the first invention, and the ozone storage device. Reference numeral 40 corresponds to the “ozone storage means” in the first invention.

It is a figure for demonstrating the structure of Embodiment 1 of this invention. It is a schematic diagram for demonstrating the occlusion reaction of NOx using ozone. It is a schematic diagram for demonstrating the reduction reaction of NOx. FIG. 6 is a view for explaining the configuration of an exhaust purification catalyst 60 as a modification of the configuration of the exhaust purification catalyst 20.

Explanation of symbols

10 Exhaust Gas Purifier 12 Internal Combustion Engine (Engine)
14 Exhaust pipe 20 Exhaust purification catalyst 22 NOx storage reduction catalyst (NSR catalyst)
30 Ozone supply device 32 Air port 34 Ozone injection port 36 Ozone generator 38 Piping 40 Ozone storage device 42 Pump 44 Valve 50 ECU (Electronic Control Unit)
60 Exhaust purification catalyst 62 NOx holding material 64 Three way catalyst

Claims (8)

An exhaust gas purification device provided in an exhaust passage of an internal combustion engine,
NOx retention material;
Ozone generating means for generating ozone;
Ozone storage means for storing ozone generated by the ozone generation means;
Ozone introduction means for introducing ozone stored by the ozone storage means upstream of the NOx holding material;
An exhaust gas purifying device for an internal combustion engine, comprising:   The exhaust gas purifying device for an internal combustion engine according to claim 1, wherein the NOx holding material is a NOx occlusion reduction type catalyst integrated with a three-way catalyst.   The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the NOx holding material is disposed upstream of the three-way catalyst.   The exhaust gas purifying device for an internal combustion engine according to any one of claims 1 to 3, wherein the ozone storage means includes a pressure vessel, and the ozone is compressed and stored in the pressure vessel.   The exhaust gas purification of an internal combustion engine according to any one of claims 1 to 4, wherein the ozone storage means includes an ozone adsorbent that adsorbs ozone, and the ozone is adsorbed and stored in the ozone adsorbent. apparatus.   6. The exhaust gas purifying device for an internal combustion engine according to claim 5, wherein the ozone adsorbent contains silica gel as a component.   The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein the ozone generating means generates ozone during operation of the internal combustion engine.   The exhaust gas purifying device for an internal combustion engine according to any one of claims 1 to 7, wherein the ozone introduction means introduces ozone immediately after the internal combustion engine is started.

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