JP2001193442A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable efficient exhaust emission control by using electric discharge. SOLUTION: Insulating substrate 16, 17 are arranged in parallel with a prescribed space, a flow path 15 for exhaust gas is formed between each insulating substrate 16, 17, also coating of a catalyst is applied to a surface of each insulating substrate 16, 17. Each flow path 15 is provided with by mixing a part (discharge part A generating discharge) counter posing discharge electrodes 18, 19 embedded in the insulating substrates 16, 17 and a nondischarge part B generating no discharge. Since a purifying window of the discharge part A exists in a region of temperature which is lower than that of a purifying window of the nondischarge part B (catalyst), exhaust gas is purified mainly in the discharge part A in a spot of temperature lower than the purifying window of the nondischarge part B, on the contrary, exhaust gas is purified mainly in the nondischarge part B in a spot of temperature higher than the purifying window of the discharge part A. In this way, in whatever way the distribution of temperature may change in this exhaust gas purifier device 11, the exhaust gas can be purified in either one of the discharge part A or the nondischarge part B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine which uses an electric discharge to promote an exhaust gas purifying reaction.

[0002]

2. Description of the Related Art In recent years, a new exhaust gas purifying technology for purifying exhaust gas using discharge energy has been studied. For example, as shown in U.S. Pat. No. 5,746,051, a plurality of flat electrodes are arranged in parallel at predetermined intervals in a discharge type exhaust gas purification apparatus, and an AC high voltage is applied between the discharge electrodes to achieve uniform discharge. There is one in which exhaust gas is purified by flowing exhaust gas into a flow path between discharge electrodes while forming a field.

[0003]

In such a discharge-type exhaust gas purifying apparatus, there is a temperature range called a purifying window in which the purifying rate is increased by the temperature, similarly to a catalytic converter such as a three-way catalyst. Although a high purification rate can be obtained within the purification window, there is a characteristic that the purification rate sharply drops when the purification window is removed. In particular,
When the temperature is higher than the purification window, nitrogen (N ₂ ) in the exhaust gas is oxidized by high heat and discharge energy to generate nitrogen oxides (NOx), and there is a possibility that the NOx emission increases.

Therefore, the discharge type exhaust gas purifying apparatus alone cannot sufficiently purify the exhaust gas when the temperature falls outside the purification window. Therefore, Japanese Patent Application Laid-Open No. 6-106
As disclosed in Japanese Patent Publication No. 52, a discharge-type exhaust gas purification device is combined with a catalytic converter, and when the exhaust gas temperature is equal to or lower than a set temperature, the discharge-type exhaust gas purification device is operated.
It has been proposed to purify exhaust gas by discharging and, when the temperature of the exhaust gas is higher than a set temperature, turn off the discharge and purify the exhaust gas with a catalytic converter.

However, the temperature of the exhaust gas purifying device does not change uniformly as a whole, but the temperature of the upstream portion close to the engine tends to be higher than that of the downstream portion. The temperature difference between the parts tends to increase.
Therefore, even if the temperature of the upstream part exceeds the set temperature, the temperature of the downstream part may be lower than the set temperature. In such a case,
When the discharge of the entire apparatus is turned off, the exhaust gas purification rate may be rather lowered. On the other hand, if the set temperature of the discharge on / off is set to a high temperature and the off time of the discharge is delayed, there is a possibility that the temperature of the upstream portion becomes too high and NOx is generated. May increase. In short, the temperature distribution in the exhaust gas purification device changes variously depending on the exhaust gas temperature and the exhaust gas flow rate that change according to the engine operating state, and the temperature difference in the exhaust gas purification device tends to increase. It is difficult to turn on and off properly.
In addition, a temperature sensor for detecting the temperature in the exhaust gas purification device is required, and a control system needs to be configured to turn on / off the discharge based on the output of the temperature sensor.
On the whole, there is a disadvantage that the cost is high.

[0006] The present invention has been made in view of such circumstances, and an object of the present invention is to achieve a high purification rate without being affected by the temperature distribution in the exhaust gas purification apparatus. To provide an exhaust gas purifying apparatus for an internal combustion engine that can satisfy the demand for cost reduction by simplifying the above.

[0007]

In order to achieve the above object, a first aspect of the present invention relates to a portion in which discharge occurs in a flow path in an exhaust gas purifying apparatus (hereinafter referred to as a "discharge portion") and no discharge. The discharge electrode is configured so as to mix a portion (hereinafter, referred to as a “non-discharge portion”), and a catalyst is provided at least in the non-discharge portion. In this way, the exhaust gas flowing through the flow path in the exhaust gas purification device passes through the discharge part and the non-discharge part, and in the process of passing through the discharge part, the purification reaction is promoted by the discharge (the catalyst exists in the discharge part. In this case, the purification reaction is promoted by both the discharge and the catalyst), and the purification reaction is promoted by the catalyst in the process of passing through the non-discharge portion.

In general, as shown in FIG. 6, the purifying window of the discharge section is located in a lower temperature range than the purifying window of the non-discharging section. Exhaust gas is purified in the discharge part, and conversely, in places where the temperature is higher than the purification window of the discharge part, the exhaust gas is mainly purified in the non-discharge part. Therefore, if the discharge section and the non-discharge section are mixed, the exhaust gas can be purified by any of the discharge section and the non-discharge section, no matter how the temperature distribution in the exhaust gas purification device changes,
A high purification rate can always be obtained without being greatly affected by the temperature distribution in the exhaust gas purification device. Moreover, since there is no need to turn on / off the discharge in accordance with the temperature, a temperature sensor is not required, the configuration is simple, and the demand for cost reduction can be satisfied.

In this case, the catalyst may be filled in the form of pellets in the flow channel. Alternatively, the catalyst may be coated on the inner wall surface of the flow channel. By doing so, the exhaust resistance (pressure loss) in the flow path can be reduced, and the engine output does not need to be reduced.

Further, the ratio between the discharge part and the non-discharge part may be changed according to the temperature distribution in the exhaust gas purifying apparatus. For example, in a place where the temperature in the exhaust gas purification device tends to be higher, the ratio of the non-discharge portion where the temperature of the purification window is higher than the discharge portion is increased, and conversely,
In a place where the temperature tends to be low, it is preferable to increase the ratio of the discharge part whose temperature of the purification window is lower than that of the non-discharge part.
With this configuration, the exhaust gas can be purified by efficiently using the discharge portion and the non-discharge portion according to the temperature distribution in the exhaust gas purification device, and the exhaust gas purification rate can be increased.

[0011] In this case, as in the fourth aspect, the upstream portion in the exhaust gas purifying apparatus may be configured such that the discharge portion is smaller than the downstream portion. In other words, the exhaust gas purifying device does not uniformly change the temperature as a whole, but the temperature of the upstream portion closer to the internal combustion engine tends to be higher than that of the downstream portion. If the discharge section is configured to be reduced, the ratio of the discharge section to the non-discharge section can correspond to the temperature distribution in the exhaust gas flow direction.

In general, the flow rate of exhaust gas in an exhaust gas purifying apparatus is not uniform, but is large at a central portion and decreases at peripheral portions. The temperature of a central portion having a high exhaust gas flow rate is higher than that of a peripheral portion having a low exhaust gas flow rate. Tend.

In view of this point, the exhaust gas purifying apparatus may be configured such that the central portion in the exhaust gas purifying apparatus has fewer discharge portions than the peripheral portion. With this configuration, the ratio between the discharge part and the non-discharge part can be made to correspond to the temperature distribution generated by the exhaust gas flow distribution.

It is preferable that the discharge section and the non-discharge section are arranged so that all the exhaust gas flowing in the flow path passes through the discharge section at least once. In this way, all the exhaust gas flowing in the flow path can be reliably exposed to the discharge field, and the exhaust gas purification effect by the discharge can be enhanced.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment (1)] An embodiment (1) of the present invention will be described below with reference to FIGS.
As shown in FIG. 5, the exhaust gas purifying device 11 is provided in the middle of an exhaust pipe 13 of an engine 12, which is an internal combustion engine. The purification housing 14 of the exhaust gas purification device 11
In order to form many flow paths 15, it is formed thicker than the exhaust pipe 13.

As shown in FIG. 1, two types of insulating substrates 16 and 17 are alternately arranged in parallel at a predetermined interval in a purification housing 14, and a flat gas through which exhaust gas passes between the insulating substrates 16 and 17 is provided. A channel 15 is formed. Each insulating substrate 1
Reference numerals 6 and 17 are made of a dielectric heat-resistant insulator (for example, ceramics such as alumina, glass, or the like) which easily generates electric discharge, and the surfaces of the insulating substrates 16 and 17 (the inner wall surface of the flow path 16) A catalyst (not shown) for promoting a purification reaction of the exhaust gas is coated.

As shown in FIGS. 2 and 3, a plurality of discharge electrodes 18 and 19 are formed by printed conductors or conductive plates inside the insulating substrates 16 and 17, respectively. As shown in FIG. 2, the insulating substrate 16 on the upper surface or the lower surface of each flow path 15 is formed such that a plurality of strip-shaped discharge electrodes 18 extend at right angles to the exhaust gas flow direction. Is connected to a connection terminal 20 formed at the left end of the.
As shown in FIG. 3, the insulating substrate 17 facing the insulating substrate 16 is formed such that a plurality of strip-shaped discharge electrodes 19 extend in parallel with the exhaust gas flow direction, and one end of each discharge electrode 19 is integrally formed with the discharge electrode 19. The connection conductor 21 is connected by the formed connection conductor 21, and the connection conductor 21 is connected to the connection terminal 22 formed on the right end of the insulating substrate 17.

As shown in FIG. 1, the connection terminal 20 of the insulating substrate 16 on one side of each flow path 15 is connected to the ground side, and the connection terminal 22 of the insulating substrate 17 facing the insulating substrate 16 is For example, it is connected to an output terminal of a high voltage generator 23 that generates a high frequency AC high voltage. As a result, when the high-voltage generator 23 operates, a high-frequency AC high voltage is applied between the plurality of strip-shaped discharge electrodes 18 and 19 facing each other across the flow path 15, and a discharge is generated in each flow path 15. I do.

In this case, since the upper and lower discharge electrodes 18 and 19 opposed to each other across the flow path 15 are arranged so as to be orthogonal to each other when viewed from above, the portion where the upper and lower discharge electrodes 18 and 19 are opposed to each other (upper part). The discharge occurs only in the overlapping portions as viewed from above, and no discharge occurs in other portions. As a result, in each flow path 15, a discharge portion A where discharge occurs and a non-discharge portion B where discharge does not occur are mixed. In the present embodiment (1), as shown in FIG. 4, a large number of discharge portions A are arranged in the channel 15 at predetermined intervals in the vertical and horizontal directions, and the non-discharge portions B are formed so as to surround the periphery of each discharge portion A. Have been.

In the embodiment (1) described above, the discharge section A and the non-discharge section B
Exhaust gas flowing through each flow path 15
In the process of passing through the discharge portion A and the non-discharge portion B and passing through the discharge portion A, the purification reaction is promoted by both the discharge and the catalyst on the inner wall of the flow path 15. Purification reaction is promoted.

In general, as shown in FIG. 6, since the purification window of the discharge section A exists in a lower temperature range than the purification window of the non-discharge section B, the temperature of the purification window is lower than the purification window of the non-discharge section B. Then, the exhaust gas is mainly purified in the discharge section A, and conversely, in places where the temperature is higher than the purification window of the discharge section A, the exhaust gas is mainly purified in the non-discharge section B. Therefore, the discharge part A and the non-discharge part B
Is mixed, exhaust gas can be purified in either the discharge part A or the non-discharge part B, regardless of how the temperature distribution in the exhaust gas purification device 11 changes. A high purification rate can always be obtained without being greatly affected by the temperature distribution. Moreover, since there is no need to turn on / off the discharge in accordance with the temperature, a temperature sensor is not required, the configuration is simple, and the demand for cost reduction can be satisfied.

[Embodiment (2)] In the embodiment (1), as shown in FIG. 4, the non-discharge portion B extends to both ends of the flow path 15 along the exhaust gas flow direction. There is a possibility that part of the exhaust gas flowing into the exhaust gas 11 may flow out of the exhaust gas purification device 11 through only the non-discharge portion B.

In the embodiment (2) of the present invention, a plurality of the insulating substrates 16 of FIG. 2 are arranged in parallel at a predetermined interval, and the upper and lower discharge electrodes 18 of each flow path 15 are opposed to each other. As shown in the figure, a plurality of strip-shaped discharge portions A are formed in the flow channel 15 so as to extend at a predetermined interval at right angles to the exhaust gas flow direction,
A non-discharge portion B is formed between each discharge portion A.

In this configuration, since the discharge part A and the non-discharge part B extend at right and left ends across the flow path 15 at right angles, all exhaust gas flowing in the flow path 15 is discharged from the discharge part A and the non-discharge part. B and B are always passed, and a higher purification rate can be obtained.

[Embodiment (3)] In the embodiment (3) of the present invention shown in FIG. 8 and FIG.
2 are formed in a staggered manner, a plurality of the insulating substrates 31 are arranged in parallel at a predetermined interval, and the upper and lower discharge electrodes 32 of each flow path 15 are opposed to each other, as shown in FIG. Road 1
5, a discharge portion A and a non-discharge portion B are formed in a staggered manner.
Also in the embodiment (3), as in the embodiment (2),
All the exhaust gas flowing in the flow path 15 always passes through both the discharge part A and the non-discharge part B, so that a higher purification rate can be obtained.

[Embodiment (4)] In the exhaust gas purifying apparatus, the temperature does not change uniformly as a whole, but the temperature in the upstream portion closer to the engine tends to be higher than that in the downstream portion. Therefore, in the embodiment (4) of the present invention, as shown in FIG. 10, a plurality of strip-shaped discharge portions A and non-discharge portions B are formed in the flow path 15 so as to extend alternately at right angles to the exhaust gas flow direction. At the same time, by forming the width of the discharge portion A such that the upstream portion is narrower than the downstream portion, the discharge portion A is configured to be smaller in the upstream portion than in the downstream portion. With this configuration, the exhaust gas can be purified by efficiently using the discharge portion A and the non-discharge portion B according to the temperature distribution in the exhaust gas purification device, and the exhaust gas purification rate can be increased.

[Embodiment (5)] The flow rate of the exhaust gas in the exhaust gas purifying apparatus is not uniform, but is large at the central portion and reduced at the peripheral portion. Also tend to be hot.

Considering this point, in the embodiment (5) of the present invention, as shown in FIG. 11, a plurality of strip-shaped discharge portions A and non-discharge portions B are alternately formed in the flow path 15 in the exhaust gas flow direction. And the width of the discharge portion A is formed to be narrower at the central portion than at the peripheral portion, so that the central portion has a smaller discharge portion A than the peripheral portion. It is composed. In this way, the ratio between the discharge part A and the non-discharge part B can be made to correspond to the temperature distribution generated by the exhaust gas flow distribution, and the discharge part A and the non-discharge part B can be used efficiently to reduce the exhaust gas. Can be purified.

In the present embodiment (5), similarly to the above embodiment (4), the width of each discharge portion A is formed so that the width of the upstream portion is smaller than that of the downstream portion. You may comprise so that the discharge part A may become fewer in a downstream part than a downstream part.

In addition, the present invention is not limited to the above embodiments, and the shape and arrangement pattern of the discharge electrode and the discharge portion A (non-discharge portion B) may be appropriately changed, and the exhaust gas flow path may be formed in a honeycomb shape. You may.

In each of the above embodiments, both the discharge portion A and the non-discharge portion B are coated with the catalyst. However, the catalyst may be coated only on the non-discharge portion B. Also,
The pellets of the catalyst may be filled in the channel.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional front view of an exhaust gas purifying apparatus according to an embodiment (1).

FIG. 2 is a cross-sectional view of an insulating substrate.

FIG. 3 is a cross-sectional view of another insulating substrate facing the insulating substrate of FIG. 2;

FIG. 4 is a plan view showing an arrangement pattern of a discharge part A and a non-discharge part B according to the embodiment (1).

FIG. 5 is a schematic configuration diagram of the entire exhaust gas purification system.

FIG. 6 is a purification characteristic diagram for explaining a relationship between a purification window of a discharge part A and a purification window of a non-discharge part B;

FIG. 7 is a plan view showing an arrangement pattern of a discharge portion A and a non-discharge portion B according to the embodiment (2).

FIG. 8 is a cross-sectional view of the insulating substrate of the embodiment (3).

FIG. 9 is a plan view showing an arrangement pattern of a discharge part A and a non-discharge part B according to the embodiment (3).

FIG. 10 is a plan view showing an arrangement pattern of a discharge part A and a non-discharge part B according to the embodiment (4).

FIG. 11 is a plan view showing an arrangement pattern of a discharge part A and a non-discharge part B according to the embodiment (5).

[Explanation of symbols]

11 ... exhaust gas purification device, 12 ... engine (internal combustion engine),
13 ... exhaust pipe, 14 ... purification housing, 15 ... flow path, 1
6, 17: insulating substrate, 18, 19: discharge electrode, 23: high voltage generator, A: discharge part, B: non-discharge part.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/28 301 B01D 53/36 101A

Claims (6)

[Claims] 1. An exhaust gas purifying apparatus for an internal combustion engine for purifying exhaust gas by causing a plurality of discharge electrodes to face each other across a flow path through which exhaust gas of the internal combustion engine flows and generating discharge in the flow path. Part where discharge occurs in the road (hereinafter referred to as “discharge part”)
An exhaust gas purifying apparatus for an internal combustion engine, wherein the discharge electrode is configured so as to mix a discharge-free portion (hereinafter referred to as a “non-discharge portion”) and a catalyst is provided at least in the non-discharge portion. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the catalyst is coated on an inner wall surface of the flow channel. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a ratio between the discharge section and the non-discharge section is changed according to a temperature distribution in the exhaust gas purifying apparatus. 4. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the discharge portion is configured to be smaller in an upstream portion of the exhaust gas purifying device than in a downstream portion. apparatus. 5. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the central portion of the exhaust gas purifying apparatus is configured such that the number of the discharge portions is smaller in a central portion than in a peripheral portion. apparatus. 6. The discharge section and the non-discharge section are arranged so that all exhaust gas flowing in the flow path passes through the discharge section at least once.
An exhaust gas purifying apparatus for an internal combustion engine according to any one of the above.