JP4114581B2 - Exhaust purification device - Google Patents

Description

  The present invention relates to a purification device for exhaust gas from an internal combustion engine or the like, and more particularly to an exhaust gas purification device for removing hydrocarbon components (hereinafter referred to as “HC”) discharged from an automobile engine.

Exhaust gas from an internal combustion engine such as an automobile engine contains substances such as hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NO _x ). Discharging exhaust gas containing these components as it is causes pollution and environmental degradation, and is restricted by public regulations. Therefore, these components are discharged after being purified by an exhaust purification device that holds the catalyst.

  In recent years, regulations on HC discharged at the start of an internal combustion engine have become particularly strict, and it has been proposed to use HC adsorbents such as zeolite and activated carbon to cope with this.

  For example, in Patent Document 1, in order to solve the problem that this HC adsorbent is weak against heat and the adsorbed HC is released at a temperature exceeding 200 ° C., it has a bypass channel in which the HC adsorbent is arranged. An exhaust purification system is proposed. According to this, exhaust gas is circulated through the HC adsorbent until the warm-up is completed, and HC is desorbed from the HC adsorbent after the warm-up is completed.

  In Patent Document 2, an HC adsorption catalyst is used to provide an exhaust purification device that can effectively purify cold HC and has excellent durability. Here, the HC adsorption catalyst temporarily adsorbs and holds a large amount of HC discharged in a low temperature range at the time of engine start where the three way catalyst is not activated. When activated, HC is gradually released and purified.

JP-A-6-74019 Japanese Patent Laid-Open No. 11-343837

  The problem that a large amount of HC released when the catalyst is low, such as when starting the engine, cannot be completely purified by the catalyst is the same as in the exhaust gas purification devices of Patent Documents 1 and 2, because the HC adsorbent or the HC adsorption catalyst is not used. It is partially solved by using it.

  In particular, Patent Document 1 recognizes that the HC adsorbent releases HC adsorbed at a temperature exceeding 200 ° C. However, before the activity of the downstream exhaust purification catalyst sufficiently increases, the upstream HC adsorbent is still upstream. HC desorbed from the HC adsorbent or HC that has been discharged from the engine may reach the exhaust purification catalyst.

Therefore, the present invention provides a method for using an exhaust purification device that suppresses the release of HC into the atmosphere even when the catalyst activity is not sufficient, such as when the engine is started.

The exhaust purification apparatus used in the method of using the exhaust purification apparatus of the present invention includes an exhaust purification catalyst, a main flow path upstream of the exhaust purification catalyst, a bypass flow path that bypasses the main flow path, and switching that switches between the main flow path and the bypass flow path. valves, and having an optional temperature sensor for measuring the temperature of the exhaust purification catalyst, and the bypass passage, the HC adsorption catalyst and the plasma reactor, that has been especially arranged plasma reactor having a built-in HC adsorption catalyst.

  Here, the “HC adsorption catalyst” may include both an HC adsorbent such as zeolite and a catalytically active component, for example, a noble metal selected from Pt, Pd, and Rh. Even if it is supported, the HC adsorbent and the catalytically active component may be laminated. Therefore, as shown in Patent Document 2, this HC adsorption catalyst adsorbs HC in exhaust gas and oxidizes HC.

According to this exhaust purification device , when the exhaust purification catalyst is less than a predetermined activation temperature and the catalyst has insufficient activity, exhaust gas is circulated through the bypass flow path, HC is adsorbed, and if necessary or always , Catalyst purification of HC can be promoted by plasma. When the exhaust purification catalyst is at a predetermined activation temperature or higher and the catalyst is sufficiently active, exhaust gas can be circulated through the main flow path, and HC contained in the exhaust gas can be purified by the exhaust purification catalyst.

The present invention allows exhaust to flow through the bypass flow path when the exhaust purification catalyst is lower than the first predetermined temperature, and allows exhaust to flow through the main flow path when the exhaust purification catalyst is equal to or higher than the first predetermined temperature. Ru method der use of the exhaust gas purifier. Here, when the exhaust purification catalyst is lower than the first predetermined temperature and the HC adsorption catalyst is higher than the second predetermined temperature or when HC is desorbed from the HC adsorption catalyst, plasma is generated in the plasma reactor.

  In this method of the present invention, the first and second predetermined temperatures can be arbitrarily determined in advance, or these temperatures can be determined dynamically in association with the exhaust flow rate. Further, HC desorption from the HC adsorption catalyst can be detected by an air-fuel ratio sensor disposed on the exhaust downstream side of the HC adsorption catalyst.

  Therefore, in this method, for example, the first predetermined temperature is set to the activation temperature of the exhaust purification catalyst, for example, 300 ° C. or 350 ° C., and the second predetermined temperature is set to the temperature at which HC desorption from the HC adsorption catalyst starts, for example, 150 It can be set to ° C or 200 ° C. In this case, the exhaust purification catalyst is not yet activated sufficiently, but when HC desorption from the HC adsorption catalyst is started, plasma is generated in the plasma reactor and desorption from the HC adsorption catalyst. HC can be purified.

  Also, for example, an air-fuel ratio sensor that directly detects HC desorption from the HC adsorption catalyst is used. When HC desorbs from the HC adsorption catalyst, plasma is generated in the plasma reactor and desorbed from the HC adsorption catalyst. HC can be purified.

  Further, in this method, for example, the first predetermined temperature is set as the activation temperature of the exhaust purification catalyst, and the second predetermined temperature is not yet started to desorb HC from the HC adsorption catalyst. The temperature at which the purified HC can be purified, for example, from room temperature to 150 ° C. can also be used. In this case, when the exhaust purification catalyst is not yet activated sufficiently, the exhaust gas is circulated through the HC adsorption catalyst, and plasma is applied to the HC in the exhaust or the adsorbed HC, thereby reducing the HC lightness / It is possible to promote radicalization to facilitate the reaction and / or to ensure a sufficient processing time.

  In addition, the temperature of the exhaust purification catalyst and the HC adsorption catalyst can be directly measured by the temperature sensor arranged on each catalyst, or the exhaust temperature sensor, cooling water temperature, engine start arranged upstream / downstream of each catalyst. It can be predicted by the period from

  According to the present invention, it is possible to suppress the release of cold HC generated particularly at the time of engine start into the atmosphere.

In the following, the present invention will be specifically described based on the embodiments shown in the drawings. However, these drawings are schematic views of an exhaust purification device used in the method of the present invention. It is not limited to the embodiment.

One embodiment of an exhaust purification device used in the method of the present invention is shown in FIG. In the exhaust gas purification apparatus shown in FIG. 1, exhaust gas from an internal combustion engine such as an automobile engine flows into the exhaust gas purification apparatus 10 in the direction indicated by the arrow 11. The exhaust gas passes through the main flow path 17 or the bypass flow path 18 that bypasses the main flow path 17 and flows into the exhaust purification catalyst 14. Switching between the main flow path 17 and the bypass flow path 18 is performed by the switching valve 16, and the bypass reactor 18 is provided with a plasma reactor 12 containing an HC adsorption catalyst.

  In use of the exhaust gas purification apparatus 10, the switching valve 16 is operated as shown in FIG. 1A to circulate the exhaust gas to the bypass flow path 18, or the switching valve 16 as shown in FIG. 1B. To circulate the exhaust gas through the main flow path 17. That is, when the activity of the exhaust purification catalyst 14 is not sufficiently increased, HC is adsorbed by the HC adsorption catalyst in the plasma reactor 12 so that the HC does not reach the exhaust purification catalyst 14.

  When exhaust gas flows through the bypass flow path 18, plasma is optionally or always generated in the plasma reactor 12 to promote HC catalytic purification. In the plasma reactor 12, for example, plasma can be generated when the HC adsorption catalyst is at a predetermined temperature or higher, or when HC is desorbed from the HC adsorption catalyst. Here, the predetermined temperature of the HC adsorption catalyst is, for example, a value that can be determined based on experiments by a person skilled in the art as a temperature at which HC is desorbed or a temperature at which the catalyst purification of HC can be promoted with the assistance of plasma.

In the following, with reference to the flowchart of FIG. 3, based on the exhaust gas purifying catalyst temperature and HC adsorption catalyst temperature, a description will be given of an exhaust purification apparatus 置使for the process of the present invention.

In use of the exhaust gas purifying apparatus, after the engine is started at step 20, the exhaust gas purifying catalyst temperature T ₁ of with a predetermined temperature T _alpha at step 22, also the exhaust gas purifying catalyst temperature T ₁ is the predetermined temperature T _alpha If it is smaller, the switching valve is operated in step 24 to circulate the exhaust gas to the bypass flow path 18. Here the temperature T _alpha This predetermined is at less than this temperature is set to a temperature which is considered to be insufficient activity of the exhaust purifying catalyst.

After operating the switching valve in step 24 to circulate the exhaust gas through the bypass flow path, in step 26 the HC adsorption catalyst temperature T ₂ is compared with a predetermined temperature T _β, and the HC adsorption catalyst temperature T ₂ is set to the predetermined temperature T. If the temperature is lower than _β , it is determined that HC desorption from the HC adsorption catalyst has not started yet, and the routine returns to step 22. If it is found in step 26 that the HC adsorption catalyst temperature T ₂ is equal to or higher than the predetermined temperature T _β , it is determined that HC desorption from the HC adsorption catalyst has started, and in step 28 the plasma reactor is used. Plasma is generated to promote HC purification by the HC adsorption catalyst, and the process returns to step 22. Here the predetermined temperature T _beta, are set to a temperature that would desorption of HC begins from the HC adsorption catalyst at this or higher.

If it is determined in step 22 that the exhaust purification catalyst temperature T ₁ is _{equal to} or higher than the predetermined temperature T _α , it is considered that the exhaust purification catalyst is sufficiently active to purify HC, and in step 30 the bypass flow path is determined. The plasma reactor is stopped, and the switching valve is operated in step 32 to circulate the exhaust through the main flow path.

Below, each part of the exhaust gas purification apparatus used in the method of the present invention will be described.

  The switching valve used in the present invention may circulate a small amount of exhaust gas in the bypass channel even when exhaust gas is circulated in the main channel. According to this, it is possible to obtain a sufficient residence time for purifying the HC in the small amount of exhaust gas and the HC adsorbed on the HC adsorption catalyst, preferably with the HC adsorption catalyst using plasma, and / or patent literature. As in 1, the HC adsorbed on the HC adsorption catalyst can be gradually desorbed and purified by the exhaust purification catalyst. This switching valve can also be switched in stages according to the exhaust purification catalyst temperature, the exhaust flow rate, and the like.

  The switching valve may be a switching valve 16 that closes one of the flow paths as shown in FIG. 1, but may be a switching valve 16 ′ that simply blocks the main flow path 17 as shown in FIG. Good. In this case, when the valve 16 ′ blocks the main flow path 17, the exhaust flows through the bypass flow path 18. When the valve 16 ′ does not block the main flow path 17, the exhaust flows mainly through the main flow path 17. A relatively small amount of exhaust flows through the bypass channel 18.

The exhaust purification catalyst used in the present invention may be any catalyst that changes CO, HC, NO _x in the exhaust to CO ₂ , H ₂ O and N ₂ , for example, a NO _x storage reduction catalyst or a three-way catalyst. What is called.

_The NO _x storage reduction catalyst (when the exhaust fuel-rich) air-fuel ratio occludes NO _x when the lean state, when a rich spike at given intervals, the occluded NO _x to N ₂ It is a catalyst to reduce. This includes, for example, a porous oxide support such as alumina, a noble metal such as Pt, Rh, Pd, Ir, or Ru, and a NO _x storage material selected from alkali metals, alkaline earth metals, and rare earth elements. It can be used as a supported one.

Three-way catalyst, CO in the exhaust gas is burned in the vicinity of the stoichiometric air-fuel ratio, HC, and NO _x, a catalyst to CO _2, H ₂ O and N _2, for example a mixture of Pt and Rh, or Pt and Pd And a mixture of Rh can be used as those supported on alumina.

  These catalysts can be supported on a powdered or molded support in any suitable amount known in the art by any means such as a washcoat. In addition, for example, this carrier carrying a catalyst is used as a slurry, coated on a substrate formed into a honeycomb shape, dried and fired, and these carriers are formed into a pellet and filled into a cylindrical insulator. It can also be used as a thing.

  The plasma reactor used in the present invention may be any known type of plasma reactor, for example as shown in FIG. Here, (a) and (b) of FIG. 4 are a side view and a sectional view of the plasma reactor, respectively. It should be noted that plasma generally activates chemical species to promote the reaction and decomposes large molecules into relatively small molecules.

  In the plasma reactor shown in FIG. 4, mesh electrodes 44 and 46 are disposed on both ends of an insulating carrier 42 such as a honeycomb structure, and a voltage is applied between these electrodes 44 and 46 by a power supply 48. To generate plasma.

  Here, the mesh electrodes 44 and 46 can be made of any material to which a voltage can be applied. For example, metal materials such as Cu, W, stainless steel, Fe, Pt, and Al, particularly stainless steel can be used.

  An insulating carrier 42 such as a honeycomb structure carries an HC adsorption catalyst, for example, a combination of zeolite and noble metal. The HC adsorption catalyst can be supported on the support in any suitable amount known in the art. For example, a honeycomb carrier carrying an HC adsorbent can be obtained by using a HC adsorption catalyst as a slurry, coating a honeycomb-shaped base material, drying and firing. Here, the HC adsorption catalyst is built in the plasma reactor, but the HC adsorption catalyst and the plasma reactor may be separated and the plasma reactor may be arranged before or after the HC adsorption catalyst.

  The power supply 48 may generate a pulsed or steady DC or AC voltage. As the applied voltage and the pulse period between the mesh electrodes 44 and 46, general values for generating plasma can be used. For example, a pulse voltage of 50 kV to several kV and a pulse period of 2,000 Hz to several tens Hz can be used. These values can be controlled and changed according to the engine state and temperature. A DC voltage, an AC voltage, a periodic waveform voltage, or the like can be applied between both electrodes, and a DC pulse voltage is particularly preferable because corona discharge can be caused satisfactorily. When a DC pulse voltage is used, the applied voltage, pulse width, and pulse period can be arbitrarily selected as long as corona discharge can occur between both electrodes. The voltage of the applied voltage may be subject to certain restrictions from the design of the device and economy, but a high voltage and a short pulse period voltage are desirable from the viewpoint of generating corona discharge satisfactorily. .

It is a schematic diagram which shows one aspect | mode of the exhaust gas purification apparatus used with the method of this invention. It is a figure which shows the deformation | transformation of the switching valve of the exhaust gas purification apparatus used with the method of this invention. It is a flowchart showing the exhaust gas purification apparatus 置使 for the process of the present invention. It is a schematic diagram which shows the plasma reactor which can be used by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Exhaust purification device 11 ... Exhaust flow direction 12 ... Plasma reactor 14 ... Exhaust purification catalyst 16, 16 '... Switching valve 17 ... Main flow path 18 ... Bypass flow path 42 ... Insulating carrier 44, 46 ... Mesh electrode 48 ... Power supply

Claims (2)

Exhaust purification catalyst,
A main flow path upstream of the exhaust purification catalyst,
A bypass channel bypassing the main channel; and
A switching valve for switching between the main flow path and the bypass flow path,
And an exhaust purification device in which an HC adsorption catalyst and a plasma reactor are disposed in the bypass flow path,
When the exhaust purification catalyst is lower than a first predetermined temperature, exhaust gas is circulated through the bypass flow path, and when the exhaust purification catalyst is equal to or higher than a first predetermined temperature, exhaust gas is circulated through the main flow path.
And an exhaust purification apparatus 置使 for the process, wherein the exhaust gas purifying catalyst is less than the first predetermined temperature, and the HC when the adsorption catalyst is equal to or higher than the second predetermined temperature or HC from the HC adsorption catalyst is desorbed Occasionally, the generating a plasma in a plasma reactor, exhaust purification apparatus 置使 method for the. The usage method according to claim 1, further comprising a temperature sensor for measuring a temperature of the exhaust purification catalyst.

Images