JP2007009839A - Exhaust emission device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accelerate storage and reduction of NOx in an exhaust emission device using NOx storage reduction catalyst. <P>SOLUTION: This device is provided with a first reactor 20 discharging in an upstream side of a honeycomb carrier 31 carrying NOx storage reduction catalyst, a second reactor 3 discharging inside of the honeycomb carrier 31, a high voltage power source 50 and ECU 60 controlling the first and the second reactor 20, 38. The ECU 60 makes the first reactor 20 operate at the time of storage by the NOx storage reduction catalyst and makes the second reactor 38 operate at the time of reduction by the NOx storage reduction catalyst. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device, and more particularly to an exhaust gas purification device including a catalyst for purifying nitrogen oxide (NOx) contained in a gas.

As a technique for removing NOx in exhaust gas such as diesel engines and lean burn engines, NOx storage reduction catalysts have been developed and put into practical use. This NOx occlusion reduction catalyst stores NOx as nitrate in the catalyst during lean burn when it is difficult to purify NOx, and performs periodic fuel rich combustion (rich spike) when the NOx occlusion amount increases. As a result, NOx occluded in the catalyst is released to restore the NOx occlusion capability, and NOx is purified to N ₂ .

In addition, in order to suppress sulfur poisoning of the NOx storage reduction catalyst, an apparatus in which a plasma generator is arranged upstream of the NOx storage reduction catalyst has been proposed (Patent Document 1). In this apparatus, the hydrogen H generated by the plasma generator is made to act on the NOx storage reduction catalyst, and the NOx in the exhaust gas is purified by the reducing power of this hydrogen, and the oxidation of SO ₂ is prevented, thereby preventing the oxidation in the exhaust gas. Sulfur poisoning of the NOx occlusion reduction catalyst due to sulfur content is suppressed.
JP 2004-270588 A

By the way, when NOx is reduced in the NOx storage reduction catalyst, it is advantageous if H, OH, HC radicals or the like having high activity obtained from exhaust gas can be used. However, since these radicals have a short lifetime, in a system in which a NOx storage reduction catalyst is disposed behind the plasma generator as in Patent Document 1, even if these radicals are generated by the plasma generator, the NOx storage reduction catalyst It reacts with other components before entering, and the active species (NO ₃ , ammonia, etc.) necessary for reduction cannot be generated on the catalyst due to its activity.

  Accordingly, an object of the present invention is to promote NOx occlusion and reduction in an exhaust gas purification apparatus using a NOx occlusion reduction catalyst.

  An exhaust gas purifying apparatus according to the present invention includes a first discharge device that discharges upstream of a carrier on which a NOx storage reduction catalyst is supported, a second discharge device that discharges inside the carrier, Control means for controlling the second discharge device, wherein the control means operates the first discharge device during storage by the NOx storage reduction catalyst, and the second discharge device during reduction by the NOx storage reduction catalyst. The discharge device is operated.

In the present invention, the first discharge device is operated on the upstream side of the carrier carrying the NOx occlusion reduction catalyst during occlusion by the NOx occlusion reduction catalyst, and the second discharge inside the carrier during reduction by the NOx occlusion reduction catalyst. Operate the device. By the operation of the first discharge device, NO2 is generated from NO in the exhaust gas and supplied to the NOx storage reduction catalyst, and NOx storage is promoted. At the time of reduction, NO ₂ discharged from the catalyst is reduced to N ₂ , and at that time, the reduction reaction is promoted by the highly active H, OH, HC radicals, etc. generated by the operation of the second discharge device. The

  As described above, in the present invention, since the second discharge device is installed inside the carrier on which the NOx storage reduction catalyst is supported, the lifetime of H, OH, HC radicals, etc. generated by the second discharge device is short. The substance can be used for the reduction reaction. In addition, when a substance having a short lifetime such as H, OH, and HC radicals is allowed to act on the NOx occlusion reduction catalyst during occlusion, NOx occluded in the catalyst may be discharged. Since the second discharge device is operated at the time of reduction, such undesirable discharge of NOx can be suppressed.

  In the present invention, the carrier includes a large number of cells through which the exhaust gas passes, the second discharge device includes a discharge electrode and a receiving electrode, and the discharge electrode and the receiving electrode sandwich the cell with the exhaust gas. It is preferable that they are arranged before and after the flow direction. In this case, since the discharge between the discharge electrode and the receiving electrode is performed along the path within the cell, that is, along the surface of a large number of cells or in the vicinity of the surface, the active force generated by the discharge is reduced. The reduction reaction can be favorably promoted by a high substance.

  In the present invention, further comprising a reducing agent supply means for supplying a reducing agent to the carrier, the control means based on a parameter related to the time required for the reducing agent to reach the carrier from its supply point, It is particularly preferable to control the second discharging means. In this case, the stored NOx can be suitably reduced by determining the discharge timing of the second discharge means in consideration of the time until the reducing agent reaches the carrier.

  Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, an exhaust gas purification apparatus 1 according to an embodiment of the present invention is installed in an exhaust path from an engine 70 of a vehicle, and has a substantially cylindrical case 10 and a first case installed in the case 10. A reactor 20 and a catalytic device 30 are included. The engine 70 is a diesel engine using light oil as fuel.

  The case 10 is formed in a substantially cylindrical shape from a heat-resistant conductive material such as metal. The exhaust gas from the engine 70 is introduced into the case 10 in the axial direction, that is, in the direction of arrow A in the figure.

  As shown in FIG. 2, the first reactor 20 is a plasma reactor or a corona reactor, and has a plurality of discharge electrodes 22 and a plurality of receiving electrodes 23 inside a substantially cylindrical insulating frame 21. . The insulating frame 21 is made of an electrically insulating material such as alumina or ceramics, and includes a cylindrical portion 21a and a plurality of flat plate portions 21b. The outer peripheral surface of the insulating frame 21 is held by the case 10 via a flexible alumina mat 27.

  The discharge electrode 22 is fixed to the odd-numbered flat plate portion 21b from the top in FIG. 2 among the plurality of flat plate portions 21b. The discharge electrode 22 is formed by bending a flat plate made of a conductor at two right angles in the same direction, and has a gate-shaped or U-shaped cross-sectional shape in a side view. The upstream end (the left side in FIG. 2) of the discharge electrode 22 is integrally fixed to the collective plate 25 via a pin 24.

  On the other hand, the receiving electrode 23 is fixed to the even-numbered flat plate portion 21b among the plurality of flat plate portions 21b. The receiving electrode 23 is a flat plate made of a conductor, and is fixed by being inserted from a downstream side into a slit provided in the flat plate portion 21 b of the insulating frame 21. An end portion on the downstream side (right side in FIG. 2) of the receiving electrode 23 is integrally fixed to a collective cylinder 26 made of conductors at tongue pieces 23a provided on both side edges thereof. The outer peripheral surface of the collecting cylinder 26 is fixed to the case 10, whereby all the receiving electrodes 23 and the case 10 are electrically connected. Case 10 is electrically grounded.

  As shown in FIG. 3, the discharge electrode 22 has a cross-section perpendicular to the flow direction of the exhaust gas, and the width of the discharge electrode 22 is adjacent to the discharge electrode 22 in the vertical direction (that is, the discharge electrode 22 and the exhaust gas flow). It is smaller than the width of the receiving electrode 23) facing each other across the path, or equal to the width of the receiving electrode 23.

  In FIG. 2 again, the tapered portion 10a formed at the upstream end portion of the case 10 is provided with a substantially truncated cone-shaped concave portion 10b that extends outward, and penetrates the bottom of the concave portion 10b to pass through the power supply plug 40. Is fixed. The power supply plug 40 is used to supply power from the high voltage power supply 50 (see FIG. 1) installed outside the case 10 to the discharge electrode 22. The power supply plug 40 includes an insulator 40a and a plug electrode 40b that penetrates the axis of the insulator 40a. The insulator 40a electrically insulates the power supply path to the discharge electrode 22 and the case 10 from each other. The outer periphery of the insulator 40a is provided with a so-called corrugation-like unevenness, and this unevenness extends the creepage distance and suppresses creeping discharge.

  The tip of the plug electrode 40b (the upper end in FIG. 2) and the collective plate 25 are connected by an L-shaped connecting plate 40c. The plug electrode 40 b, the connecting plate 40 c, the pin 24, and the collective plate 25 constitute a power supply path for supplying power from the high voltage power supply 50 installed outside the case 10 to the discharge electrode 22.

  The catalyst device 30 includes a second reactor 38 including a discharge electrode 32 and receiving electrodes 33a and 33b inside a honeycomb carrier 31 on which a catalyst material is supported. As shown in FIG. 4, the honeycomb carrier 31 includes an upstream portion 31 a and a downstream portion 31 b, and the upstream portion 31 a and the downstream portion 31 b are both divided by a large number of porous partition walls 11. An elongated cell 12, that is, an exhaust gas passage, is provided, and the longitudinal direction of each cell 12 is parallel to the inflow direction of the exhaust gas (A direction in FIG. 2).

The honeycomb carrier 31 is preferably formed of a porous insulator such as alumina Al ₂ O ₃ . In addition, when using another material as the material of the honeycomb carrier 31, it is preferable to apply an alumina coat to the surface of the honeycomb carrier 31. The honeycomb carrier 31 may be of various other structures such as one that alternately plugs exhaust gas passages to filter PM (particulate matter), and one that adsorbs PM by electrostatic force. Can be used.

  The partition walls 11 of the honeycomb carrier 31 are coated with a NOx storage reduction catalyst (NSR) as a catalyst material. The NOx occlusion reduction catalyst is at least selected from alkali metals such as potassium K, sodium Na, lithium Li and cesium Cs, alkaline earths such as barium Ba and calcium Ca, and rare earths such as lanthanum La and yttrium Y. A combination of one and a noble metal such as platinum Pt is preferred.

  The discharge electrode 32 includes a cylindrical outer frame 34 and a flat electrode plate 35 which is fixed to the inner peripheral surface of the outer frame 34 in parallel with each other. The electrode plates 35 are all horizontal. In order to promote discharge, saw-blade irregularities are provided at the upstream and downstream ends of each electrode plate 35. As shown in FIG. 1, a lead wire 46 is connected to the discharge electrode 32, and the lead wire 46 is connected to a high voltage power supply 50 through a cylindrical insulator 45 fixed to the case 10. .

  The receiving electrodes 33a and 33b have cylindrical outer frames 36a and 36b, and flat plate-like electrode plates 37a and 37b fixed in parallel to each other on the inner peripheral surfaces of the outer frames 36a and 36b. The electrode plates 37a and 37b are both vertical. In order to promote discharge, sawtooth-shaped irregularities are provided on the downstream end of the electrode plate 37a and the upstream end of the electrode plate 37b, respectively. The receiving electrodes 33a and 33b are fixed to the case 10 and are thereby electrically grounded.

  The discharge electrode 32 and the receiving electrode 33a, and the discharge electrode 32 and the receiving electrode 33b are installed with the honeycomb carriers 31a and 31b interposed therebetween, respectively. Therefore, as shown in FIG. 5, the discharge electrode 32 and the receiving electrodes 33 a and 33 b of the second reactor 38 are arranged before and after the flow direction of the exhaust gas across the cell 12 that is the working surface of the honeycomb carrier 31. .

  The plug electrode 40 b of the first reactor 20 and the discharge electrode 32 of the second reactor 38 are connected to the high voltage side output terminal of the high voltage power supply 50. The high voltage power source 50 includes an inverter circuit, a transformer, a rectifying diode, a smoothing circuit, and the like, and is configured to boost the direct current from the battery 51 and selectively supply power to the first reactor 20 and the second reactor 38. Has been. The method of feeding from the high voltage power supply 50 can be selected from any waveform and voltage such as direct current, direct current pulse wave, alternating current, alternating current pulse wave, or superposition of direct current and direct current pulse.

  The ECU 60 is configured as a well-known one-chip microprocessor including a CPU, a ROM, a RAM, a storage device, an input / output interface, an A / D converter, and a D / A converter, and is based on detection values and setting values of various sensors. A control signal is output as described later according to a predetermined program.

  The input interface of the ECU 60 includes a crank angle sensor 81 provided in the vicinity of the crankshaft of the engine 70 for detecting the engine speed, a throttle position sensor 82 for detecting the opening of a throttle valve provided in the intake path of the engine 70, and the like. The various sensors are connected. Various actuators such as a high voltage power supply 50 are connected to the output interface of the ECU 60.

  The operation of the present embodiment configured as described above will be described. In operation, a high voltage from the high voltage power supply 50 is selectively applied to the first reactor 20 and the second reactor 38.

When the engine is started, the high voltage power supply 50 is always operated under the control of the ECU 60. While the predetermined lean operation condition is satisfied, electric power is supplied from the high voltage power supply 50 to the first reactor 20 under the control of the ECU 60. When the discharge such as corona discharge between the discharge electrode 22 and receiving electrode 23 occurs, NOx contained in the exhaust gas is changed into NO ₂ by the energy of the plasma, it is supplied to the catalytic converter 30. This NO ₂ is stored in the NOx storage reduction catalyst.

  Predetermined rich spike conditions (for example, the cumulative operation time from the previous rich spike execution exceeds a predetermined value, and the temperature of the catalyst device 30 estimated from the engine water temperature or the like exceeds a predetermined activation temperature) are established. Then, the fuel injection amount and the air-fuel ratio of the engine 70 are controlled by the control of the ECU 60, and the exhaust gas is made rich (over-rich) over a predetermined rich spike time Δt1.

  The ECU 60 also determines the flow rate of the exhaust gas based on parameters related to the time required for the rich exhaust gas to reach the catalyst device 30 from the engine 70 that is the supply point, for example, the engine speed and the throttle valve opening. By dividing the path length, the required time td for the movement of the exhaust gas from the engine 70 to the catalyst device 30 is calculated.

  The ECU 60 controls the high voltage power supply 50 at the timing when the rich exhaust gas reaches the catalyst device 30 (that is, after the time td has elapsed since the rich spike), and the power supply to the first reactor 20 is stopped. In addition, power is supplied to the second reactor 38 in the catalyst device 30 over a predetermined power supply time Δt2 (see FIG. 6). The power supply time Δt2 may be equal to or different from the rich spike time Δt1. The high voltage power supply 50 is controlled by the ECU 60 under the condition that the power supply time Δt2 has elapsed, power supply to the second reactor 38 is stopped, and power supply to the first reactor 20 is resumed.

By this power supply over the power supply time Δt2, a discharge such as a corona discharge occurs between the discharge electrode 32 and the receiving electrodes 33a and 33b of the second reactor 38, and the oxygen O ₂ and hydrocarbons HC in the exhaust gas are converted into H, OH, HC. Radicals etc. are generated. As a result, NO ₂ stored in the NOx storage reduction catalyst supported on the carrier 31 is reduced, converted into N _2, etc. and discharged.

  Here, since the discharge electrode 32 and the receiving electrodes 33a and 33b of the second reactor 38 are arranged before and after the exhaust gas flow direction with the cell 12 serving as the working surface of the honeycomb carrier 31 interposed therebetween, The discharge between the receiving electrodes 33a and 33b is performed using the inside of the cells 12 of the honeycomb carrier 31 as a route, that is, using the surface of a large number of cells 12 or the vicinity of the surface as a route.

As described above, in the present embodiment, the first reactor 20 is supplied with power on the upstream side of the catalyst device 30 during the storage by the NOx storage reduction catalyst, and the second reactor 38 in the catalyst device 30 is supplied during the reduction by the NOx storage reduction catalyst. Power is supplied. By the operation of the first reactor 20, NO ₂ is generated from NO in the exhaust gas and supplied to the catalyst device 30, and NOx occlusion is promoted. At the time of reduction, NO ₂ discharged from the NOx occlusion material of the catalyst device 30 is reduced to N ₂ , and at that time, the highly active H, OH, HC radicals, etc. generated by feeding power to the second reactor 38. , The reduction reaction is promoted.

  Thus, in this embodiment, since the second reactor 38 is installed inside the carrier 31 on which the NOx storage reduction catalyst is supported, the lifetime of H, OH, HC radicals, etc. generated by the second reactor 38 is short. The substance can be used for the reduction reaction. In addition, when a substance having a short lifetime such as H, OH, and HC radicals is allowed to act on the NOx occlusion reduction catalyst during occlusion, NOx occluded in the catalyst may be discharged. Since the two reactors 38 are operated at the time of reduction, such undesirable emission of NOx can be suppressed.

  Further, in the present embodiment, the discharge electrode 32 and the receiving electrodes 33a and 33b of the second reactor 38 are arranged before and after the flow direction of the exhaust gas across the cell 12 which is the working surface of the honeycomb carrier 31. The discharge between the discharge electrode 32 and the receiving electrodes 33a and 33b is performed using the inside of the cells 12 of the honeycomb carrier 31 as a route, that is, using the surface of a large number of cells 12 or the vicinity of the surface as a route. Therefore, in this embodiment, the reduction reaction can be favorably promoted by H, OH, HC radicals and the like having high activity generated by discharge.

  In the present embodiment, traveling fuel is used as the reducing agent, and the ECU 60 is a parameter related to the time required for the rich exhaust gas containing the reducing agent to reach the carrier 31 from the engine 70 as the supply point. Based on the above, the second reactor 38 is controlled, and the discharge timing of the second reactor 38 is determined in consideration of the time td required for the reducing agent to reach the carrier 31. Therefore, the stored NOx is suitably reduced. Can be made.

  Although the present invention has been described with a certain degree of specificity in the above-described embodiments and modifications, various modifications can be made to the present invention without departing from the spirit and scope of the invention described in the claims. It must be understood that changes are possible. That is, the present invention includes modifications and changes that fall within the scope and spirit of the appended claims and their equivalents.

  In particular, various modifications can be made to the structures of the first and second discharge devices. For example, the structure of the discharge electrode and the receiving electrode in the second reactor may be a lattice shape in which flat electrode plates are combined vertically and horizontally, or may be a mesh shape or a mesh shape composed of a large number of rod-shaped conductors. Moreover, in the said embodiment, although the 1st reactor 20 and the catalyst apparatus 30 were accommodated in the single case 10, these may be accommodated in the separate case and mutually connected.

  Moreover, the structure containing the tank which stores a reducing agent other than the structure which uses the fuel for driving | running | working as a reducing agent like the said embodiment may be sufficient. In each of the above embodiments, the first reactor 20 and the second reactor 38 are supplied with power from a single high-voltage power supply 50. However, individual high-voltage power supplies for supplying power to each reactor may be provided. .

  Moreover, in the said embodiment, although this invention was applied to the exhaust gas process of a diesel engine, this invention is applicable also to the exhaust gas process of a gasoline engine or a gaseous fuel engine. In the above embodiment, the present invention is applied to purify exhaust gas from an internal combustion engine of a vehicle. However, the present invention is applied to purify exhaust gas from various internal combustion engines such as ships, aircrafts, and generators in addition to vehicles. These are all possible and belong to the category of the present invention.

It is a side view showing the outline of the exhaust gas purification device concerning the embodiment of the present invention. It is a side view which shows the principal part of the exhaust gas purification apparatus which concerns on embodiment of this invention. It is a front view of a 1st reactor. It is a disassembled perspective view of a 2nd reactor. It is a side view which shows the principal part of a 2nd reactor. It is a time chart which shows each timing of the electric power feeding to a rich spike and a 2nd reactor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification device 10 Case 20 1st reactor 30 Catalytic device 22, 32 Discharge electrode 23, 33a, 33b Receiving electrode 31 Honeycomb carrier 50 High voltage power supply 60 ECU
70 engine

Claims (3)

A first discharge device for discharging on the upstream side of the carrier on which the NOx storage reduction catalyst is supported;
A second discharge device for discharging inside the carrier;
Control means for controlling the first and second discharge devices,
The exhaust gas purifying apparatus, wherein the control means operates the first discharge device during storage by the NOx storage reduction catalyst and operates the second discharge device during reduction by the NOx storage reduction catalyst. The exhaust gas purification device according to claim 1,
The carrier includes a number of cells through which exhaust gas passes,
The second discharge device includes a discharge electrode and a receiving electrode,
The exhaust gas purifying apparatus, wherein the discharge electrode and the receiving electrode are arranged before and after the flow direction of the exhaust gas across the cell. The exhaust gas purifying apparatus according to claim 1 or 2,
A reducing agent supply means for supplying a reducing agent to the carrier;
The control means controls the second discharge device based on a parameter related to a time required for the reducing agent to reach the carrier from a supply point by the reducing agent supply means. Purification equipment.

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