JP2002221025A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of stabilizing electric discharge and improving efficiency of purifying exhaust gas with low electric power and from low temperature condition. SOLUTION: A plasma generating device 2 and a DPF 32 with catalyst is arranged separately in an upstream side and a downstream side in a exhaust gas passage 6. Particulate pollutant (PM) and gaseous pollutant (NOx and the like) are efficiently purified by combination of purifying actions of the DPF 32 with catalyst and plasma generated from the plasma generating device 2. The plasma generating device 2 is controlled to be turned on in a low temperature condition to compensate deterioration of purifying performance of the DPF 32 with catalyst in the low temperature condition.

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 which promotes a purification reaction of exhaust gas by utilizing electric discharge, and more particularly to a method of decomposing particulate and gaseous pollutants contained in exhaust gas of a diesel engine or the like. The present invention relates to an exhaust purification device to be removed.

[0002]

2. Description of the Related Art In exhaust gas from diesel engines and the like,
Particulate pollutants mainly composed of carbon (hereinafter referred to as PM:
Harmful substances such as gaseous pollutants such as Particulate Matter) and nitrogen oxides (hereinafter referred to as NOx). Exhaust gas purifying technology for removing harmful substances (PM, NOx, etc.) in the exhaust gas at an emission source has been studied. As disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 9-329015 (see FIG. 10), this technique uses a dielectric between a pair of electrodes 101 and 102 including a discharge electrode 101 and a dielectric electrode 102 connected to an AC high-voltage power supply 100. Dust collection part (porous filter layer) 103
Is arranged. Discharge spaces 104 and 105 are provided between the electrodes 101 and 102 and the dust collecting unit 103, respectively.

A gas 106 to be processed flows into one discharge space 104, passes through a dust collecting section 103, and then a processing end gas 107 is discharged through the other discharge space 105. When the processing target gas 106 passes through the dust collecting part 103, PM is trapped inside the dust collecting part 103, and then reacts with plasma generated by discharge to be converted into carbon dioxide and removed from the dust collecting part 103. In addition, gaseous pollutants such as NOx are purified while increasing the probability of collision with plasma generated by discharge while passing through the dust collecting portion 103.

[0004]

However, Japanese Patent Publication No. 9-3
The exhaust purification device disclosed in Japanese Patent No. 29015 discloses a dust collecting portion 103 between a pair of electrodes 101 and 102, and a discharge space 1
04, 105, the electrodes 101, 1
02 increases. When the distance between the electrodes 101 and 102 is increased, the required applied voltage (the voltage at which discharge can be generated) increases, which causes a problem that the discharge becomes difficult.

Further, depending on the discharge plasma generated by constantly energizing between the electrodes 101 and 102, particulate pollutants (PM), which are harmful substances, and gaseous pollutants (NOx, etc.) in exhaust gas are removed. In the case where power is supplied for obtaining discharge plasma from an in-vehicle battery whose power supply is limited, the electrodes 101, 1
The amount of power that can be supplied during 02 is limited. Therefore, when the emission amount of harmful substances is large, the size of the power generation unit is increased and the load on the internal combustion engine due to the power generation is increased.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine, which can stabilize discharge and increase the efficiency of purifying exhaust gas with low power.

[0007]

In order to solve the above-mentioned problems, according to the exhaust gas purifying apparatus for an internal combustion engine according to the first aspect of the present invention, the discharge unit and the dust collection unit are connected to each other in the flow path through which the exhaust gas flows. It was configured to be arranged separately on the upstream side and the downstream side. In other words, since the dust collecting part is not scissored between the electrodes of the discharge part,
The distance between the electrodes does not increase, and the arrangement of the dust collection unit does not affect the discharge unit, so that the discharge in the discharge unit is stabilized.

The dust collecting portion disposed downstream of the flow path through which the exhaust gas flows has an opening at a first end and an inlet chamber sealed at a second end, and an opening at a second end. An outlet chamber with one end sealed was provided, and the inlet chamber and the outlet chamber were alternately arranged while being partitioned by a partition wall of a porous filter layer carrying a catalyst.

Accordingly, in the case of particulate contaminants (PM), both the collision with the plasma in the discharge part and the dust collection part (the catalyst part carried on the partition walls of the porous filter layer). Is purified. On the other hand, gaseous pollutants (NOx
Etc.), the catalyst is purified by the action of the catalyst when passing through the inside of the partition wall of the porous filter layer.

According to the second aspect of the present invention, the porous filter layer is made of a ceramic material. The ceramic material is a material that easily forms many fine holes and has excellent heat resistance, and can stably maintain a fine hole shape even under high-temperature exhaust gas.

According to the third aspect of the present invention, the dust collecting portion seals one end of each of the passages constituting the honeycomb body alternately,
The end face of the honeycomb body was formed in a checkered pattern, and was formed of porous ceramic in which a partition wall of each passage supported a catalyst.

The dust collecting portion of the honeycomb structure has a wide contact area with the exhaust while reducing the exhaust resistance, and can be a high-strength dust collecting portion as a structure.

According to a fourth aspect of the present invention, the catalyst supported on the partition walls of the porous ceramic material is a NOx storage catalyst. Then, the combustion in the engine is controlled so as to intermix lean air-fuel ratio combustion (during lean combustion), stoichiometric air-fuel ratio combustion, and dense air-fuel ratio combustion (rich combustion), and particulate contaminants (PM) and gas Pollutants (NOx, etc.)
Is to purify.

By combining the purifying action of the above-mentioned dust collecting section carrying the NOx storage catalyst with the purifying action of radicals or active gas generated from the discharge section, particulate contaminants (PM) and gas It is possible to efficiently purify state pollutants (such as NOx).

According to a fifth aspect of the present invention, when the temperature of the dust collecting section is high, the power supply to the discharge section is stopped. In other words, when the temperature of the dust collecting part is low, the particulate matter (P) is reacted with radicals, active gas, and the like generated by energizing the discharge part.
M) as well as gaseous pollutants (such as NOx). Then, when the temperature of the dust collecting section becomes high, the gaseous pollutants (NOx, etc.) react with the activated catalyst under high temperature conditions and are purified, and the particulate pollutants (PM) are removed under high temperature conditions. Because it promotes combustion and is purified,
Stop supplying power to the discharge unit. As described above, it is possible to suppress the power consumption in the discharge unit and to purify the particulate pollutant (PM) and the gaseous pollutant (NOx or the like) with high efficiency.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an exhaust gas purifying apparatus for an internal combustion engine according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that, as shown in FIGS.
Is a plasma generator 2 arranged in the middle of an exhaust pipe 31 of an engine 30, which is an internal combustion engine, and a DPF (D
iesel Particulate Filter)
32, and a high-voltage power generation unit 4 for applying a high-frequency AC high voltage to the electrodes 3 arranged in the plasma generator 2. Further, the plasma generator 2 and a DPF with a catalyst are used.
32 are arranged separately on the upstream side and the downstream side of the flow path through which the exhaust gas flows. That is, the plasma generator 2 is arranged on the upstream side of the flow path through which the exhaust gas flows, and the DPF with the catalyst is provided.
32 is disposed at a position on the downstream side of the exhaust gas of the plasma generator 2.

First, the configuration of the plasma generator 2 is shown in FIG.
This will be described with reference to FIG. FIG. 2 is a schematic configuration diagram of the plasma generator 2 according to one embodiment of the present invention. FIG. 3 shows FIG.
FIG. 3 is a detailed view showing an insulating substrate 5 in the inside. In the plasma generator 2, a plurality of insulating substrates 5 are arranged in parallel at predetermined intervals, and a flat flow path 6 through which exhaust gas passes is formed between the insulating substrates 5. Each of the insulating substrates 5 is formed of a dielectric heat-resistant insulator (for example, ceramic such as alumina, glass, or the like) in which electric discharge easily occurs.

In each insulating substrate 5, a discharge electrode 3 formed by a printed conductor or a conductive plate is embedded. A connection terminal portion 3a (see FIG. 3) formed on one side of each of the electrodes 3 is connected to a high-voltage power generator 4 for generating a high-frequency high-voltage AC voltage, and the other is connected to a ground (earth potential) side. ing. As described above, the electrodes 3 are arranged to face each other with the flow path 6 through which the exhaust gas flows, and a high-frequency AC high voltage from the high-voltage power generation unit 4 is applied to the plurality of electrodes 3 to generate plasma. Item 1 constitutes the discharge section.

Next, the structure of the DPF 32 with a catalyst disposed at a position downstream of the exhaust gas of the plasma generator 2 will be described with reference to FIGS. 4, 5 and 6. FIG. FIG. 4 is a perspective view of the DPF 32 with a catalyst shown in FIG. FIG. 5 is a schematic configuration diagram showing a cross-sectional structure of a DPF with a catalyst. FIG.
It is explanatory drawing which shows the effect | action in the partition A part in FIG.

The DPF 32 with a catalyst has an entrance chamber 12 having a first end 10 opened and a second end 11 sealed by a sealing member 15, a second end 11 opened and a first end 10 opened. The outlet chamber 13 is sealed by the sealing member 15. In this embodiment, as shown in FIG. 4, a honeycomb structure is adopted, and both end faces 1 of the first end 10 and the second end 11 are formed.
0 and 11 are checkerboard patterns. The inlet side chamber 12 and the outlet side chamber 13 are alternately arranged while being partitioned by a partition wall 14 made of a porous ceramic material carrying a catalyst, thereby constituting a dust collecting section according to claim 1.

A NOx storage catalyst is carried on a partition wall 14 which is in contact with the inlet chamber 12 and the outlet chamber 13. This NO
The x storage catalyst contains Pt (platinum) and Ba (barium) as main components, and is also called a NOx storage reduction three-way catalyst.
An electronic control unit (hereinafter simply referred to as ECU) that controls the combustion in the engine so as to intermix lean air-fuel ratio combustion (at the time of lean combustion), stoichiometric air-fuel ratio combustion, and dense air-fuel ratio combustion (rich combustion). ) To purify particulate pollutants (PM) and gaseous pollutants (NOx and the like) using the above-described DPF 32 with catalyst under such combustion control conditions.

The above system combines the purifying action of the DPF 32 with the catalyst carrying the NOx storage catalyst and the purifying action by the plasma generated from the plasma generator 2 to provide highly efficient particulate contaminants ( PM),
In addition, the exhaust gas purifying apparatus 1 is configured to purify gaseous pollutants (NOx and the like). In addition, as shown in FIG.
The exhaust gas introduced into the inlet chamber 12 is discharged from the outlet chamber 1.
3 is made of a porous ceramic material having a gap-like space so as to pass through and be discharged. B in FIG. 6 indicates PM captured in the gap-like space.

Plasma generator 2 and DPF 32 with catalyst
Means that the plasma generator 2 is arranged separately on the upstream side and the downstream side of the flow path through which the exhaust gas flows, and the plasma generator 2 is not influenced by the DPF 32 with a catalyst. That is, the plasma generator 2
Since the DPF 32 with a catalyst, which is a dust collecting portion, is not sandwiched between the electrodes 3, the distance L between the electrodes 3 (shown in FIG. 2) does not increase. Here, as the distance between the electrodes 3 increases, the required applied voltage (voltage at which discharge can be generated) increases, making discharge difficult.
Since 32 is arranged separately from the plasma generator 2, the distance L between the electrodes 3 can be set arbitrarily. Therefore, the distance between the electrodes 3 at which the discharge in the discharge section is stable can be set, and the plasma generator 2 with stable discharge can be realized.

In the exhaust gas purifying apparatus 1 having the above-described structure, after the engine 30 is started, the high-voltage power generator 4 does not always supply a high-frequency high-voltage AC voltage to the plasma generator 2 but includes a catalyst. A temperature detection unit (not shown) is provided at a peripheral position where the temperature of the DPF 32 can be detected,
A control unit (not shown) for controlling the power supply to the plasma generator 2 according to the temperature state detected by the temperature detector is provided in the high-voltage power supply 4 or the ECU. Then, for example, when detecting that the DPF 32 with a catalyst is in a high temperature state, the control unit controls to stop the power supply to the plasma generator 2.

When the temperature detecting section detects that the catalyst is in a low temperature state in which the catalyst is not active or insufficient in activity, radicals and active gas generated by energizing the plasma generator 2 are removed. After reacting, particulate pollutants (PM) and gaseous pollutants (NOx, etc.)
To purify. When the temperature detecting unit detects that the exhaust gas can be purified only by the catalyst in a high temperature state, the power supply to the plasma generator 2 is stopped. The details of these purification reactions will be described later.

The operation of the exhaust gas purifying apparatus 1 configured as described above will be described below. When the engine 30 is started, exhaust gas containing harmful components such as gaseous pollutants such as NOx and particulate contaminants (PM) is led to the plasma generator 2, and the temperature detector is in a low temperature state. Is detected from the high-voltage power generator 4
A high-frequency high-voltage AC voltage is applied to the plurality of electrodes 3 opposed to each other with the.

When this high-frequency high-voltage AC voltage is applied to the electrodes 3 and a discharge is generated between the electrodes 3, oxygen molecules in the exhaust gas react with accelerated electrons e due to the discharge, and O radicals (O *) are generated. Generated. Then, the O radical (O *) and nitrogen monoxide (NO) in the exhaust gas are combined,
Nitrogen dioxide (NO ₂ ) is produced.

Here, the particulate pollutants (PM) in the exhaust gas, which are harmful components, are purified by soot (SOOT) containing carbon (C) as a main component and unreacted component containing hydrocarbon (HC) as a main component. Combustion bodies (SOF) are roughly classified. The carbon (C) and the hydrocarbon (HC) react with nitrogen dioxide (NO ₂ ) generated by the discharge as shown in the following equation. In the case of soot (SOOT), C + NO ₂ → CO ₂ + N
O, and in the case of an unburned body (SOF), HC +
It reacts like NO ₂ → CO ₂ + H ₂ O + NO.

The particulate contaminants (PM) react with nitrogen dioxide (NO ₂ ) generated by the discharge even in a low-temperature environment. The PM purification reaction is captured by the partition wall 14 made of a porous ceramic material having a gap-like space, increases the chance of contact with radicals or active gas from the upstream side, is converted into carbon dioxide, and is converted into carbon dioxide. Removed from the gap-shaped space.

Next, in the purification of nitrogen oxides (NOx) of gaseous pollutants which are harmful components, gaseous pollutants (N
Ox) and O radicals (O *) generated by the discharge undergo a reduction reaction as shown in the following equation while passing through both the plasma generator 2 and the DPF 32 with a catalyst, and produce harmless gases (CO ₂ , N _2). ), And discharged as water.

Nitrogen oxide (NOx) is converted to nitrogen dioxide (N
O ₂ ) and nitric oxide (NO), and oxidizes nitric oxide (NO) to nitrogen dioxide (NO ₂ ) by discharge to promote purification of exhaust gas. Further, hydrocarbon (HC) as a reducing agent is contained in exhaust gas as an unburned component. Therefore, in the case of nitrogen dioxide (NO ₂ ),
NO ₂ + HC → N ₂ + CO ₂ + H ₂ O and is purified.
In particular, nitrogen dioxide (NO ₂ ) has a property of being easily reduced. Particulate pollutants (PM) are burned by the oxidizing action of the catalyst.

A catalyst-equipped DP carrying a NOx storage catalyst
In F32, nitrogen oxides (NOx
Etc.) and the oxidation of particulate pollutants (PM), and emit as harmless gas and water.

For power saving, when the temperature detector for detecting the temperature around the DPF 32 with the catalyst detects that the temperature around the DPF 32 with the catalyst is in a high temperature state after starting the engine, that is, the temperature of the catalyst carried on the DPF 32 with the catalyst rises, When activated, the power supply to the plasma generator 2 is stopped. At this time, gaseous pollutants (such as NOx) and particulate pollutants (P
M) reacts with the activated catalyst under high temperature conditions to purify.

FIG. 7 shows the relationship between NO ₂ generated by the plasma generator of the present invention and the ambient temperature. When the power supply to the plasma generator 2 is stopped, the temperature becomes lower as indicated by the broken line (b). Since the catalyst-added DPF 32 is not active in the range, the lower the temperature becomes, the more the amount of NO ₂ generated becomes insufficient. However, it reacts with the plasma generated by energizing the plasma generator 2 to generate nitrogen dioxide (NO ₂ ) even in a low temperature range as shown by the solid line (a), and the particulate matter in the exhaust gas Promotes purification of pollutants (PM) and NOx.

FIG. 8 shows the relationship between the NOx occluded by the DPF 32 with catalyst and its surrounding temperature. When the plasma generator 2 is energized, NO is oxidized to NO ₂ , NOx located downstream of exhaust gas
Since the occlusion by the occlusion catalyst is facilitated, the amount of NOx occluded by the NOx occlusion catalyst is indicated by a solid line (c) as compared with the case where the power supply to the plasma generator 2 is stopped (broken line (d)). In the low temperature range.

FIG. 9 shows the relationship between the PM burning in the plasma generator and the DPF 32 with a catalyst and the surrounding temperature. The state where the combustion of the PM is not promoted when the DPF 32 with the catalyst is in a low temperature state (dashed line (f)) In contrast, due to the discharge itself for energizing the plasma generator 2 and the promotion of oxidation by NO ₂ , PM combustion is promoted even in a low temperature range (solid line (e)).

As described above, the DP with a catalyst particularly at a low temperature is used.
The reduction in the purification performance of particulate contaminants (PM) and gaseous pollutants (NOx and the like) by F32 is compensated for by energizing the plasma generator 2. Also, at high temperature, even if the power supply to the plasma generator 2 is stopped, the DPF with catalyst
32 is activated to purify particulate pollutants (PM) and gaseous pollutants (such as NOx). Therefore, the power consumption of the plasma generation device 2 of the exhaust gas purification device 1 combining the plasma generation device 2 and the DPF 32 with a catalyst is suppressed,
Further, it is possible to provide an exhaust gas purifying apparatus for an internal combustion engine, which is capable of purifying particulate pollutants (PM) and gaseous pollutants (NOx and the like) with high efficiency.

In the practice of the present invention, a catalyst-equipped D
The catalyst supported on the PF32 was a NOx storage catalyst, but instead of the NOx storage catalyst, a selective reduction catalyst, a three-way catalyst,
Any one of the catalyst and the oxidation catalyst may be selected, or a plurality of catalysts may be used in combination. According to this, when the supported catalyst is an oxidation catalyst, it promotes the oxidation of particulate contaminants (PM), and the harmless gas (C
O ₂ , NO) and water. In addition, regardless of whether the supported catalyst is a selective reduction catalyst, a three-way catalyst, or an oxidation catalyst, there is an effect of promoting the action of purifying nitrogen oxides (such as NOx) of gaseous pollutants.

In implementing the present invention, the temperature of the catalyst-provided DPF 32 can be estimated by detecting the temperature of the catalyst-provided DPF 32 regardless of whether the temperature detector is disposed in the exhaust gas passage or in any vicinity including the plasma generator 2. As a possible temperature signal, a signal that can control the energization of the plasma generator 2 can be used.

Further, in the embodiment of the present invention, the place where the temperature control unit is disposed is provided inside the high-voltage power supply generator 4, but it may be provided inside the ECU.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an entire exhaust gas purification apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a plasma generator of one embodiment of the present invention.

3A and 3B show details of the insulating substrate in FIG. 2, wherein FIG. 3A is a plan view and FIG. 3B is a side view of FIG.

FIG. 4 is a perspective view of the DPF with a catalyst shown in FIG. 1;

FIG. 5 is a schematic configuration diagram showing a cross-sectional structure of a DPF with a catalyst.

FIG. 6 is an explanatory diagram showing an operation at a partition A portion in FIG.

FIG. 7 shows NO ₂ generated by the plasma generator of the present invention.
FIG. 4 is a characteristic diagram showing a relationship between the temperature and the ambient temperature.

FIG. 8 is a characteristic diagram showing a relationship between NOx stored in a DPF with a catalyst and an ambient temperature thereof.

FIG. 9 is a characteristic diagram showing a relationship between PM burning in a plasma generating device and a DPF with a catalyst and its surrounding temperature.

FIG. 10 is a schematic configuration diagram of a conventional plasma generator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Exhaust purification device 2 Plasma generator 3 Electrode (discharge part) 5 Insulating substrate 6 Flow path 32 DPF with catalyst (dust collection part)

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F01N 3/02 301 F01N 3/02 301C 321A 321 3/28 301C 3/28 301 9/00 Z 9/00 B01D 53 / 36 103B F term (reference) 3G090 AA03 AA06 DA11 DA13 DB01 DB02 DB03 3G091 AA02 AA18 AA28 AB02 AB03 AB05 AB06 AB13 AB14 BA00 BA03 BA14 BA15 BA19 DB10 EA15 EA18 FA02 FA04 FB02 FB10 FB11 FB12 FC07 GA06 GB10 GB24 GB07 GB17 GB24 HA38 4D019 AA01 BA05 BB07 BC07 CA01 4D048 AA06 AA14 AB01 BA15X BA30X BB02 CD05 EA03

Claims (5)

[Claims] A discharge unit disposed upstream of a flow path through which exhaust gas of an internal combustion engine flows to generate plasma; and a particulate contaminant in the exhaust gas disposed in the flow path downstream of the discharge unit. A dust collecting portion for capturing the dust, wherein the dust collecting portion has an opening at a first end and a sealed second end, and an opening at the second end, and the first end is open. An exhaust purification device for an internal combustion engine, comprising: a sealed outlet chamber; wherein the inlet chamber and the outlet chamber are alternately arranged while being partitioned by a partition wall of a porous filter layer supporting a catalyst. . 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the porous filter layer is formed using a ceramic material. 3. The dust collecting section alternately seals one end of each passage constituting the honeycomb body, the end face of the honeycomb body has a checkerboard pattern, and the partition wall of each passage has a catalyst. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purifying apparatus is made of a porous ceramic that carries thereon. 4. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein said catalyst is a NOx storage catalyst. 5. The method according to claim 1, wherein when the temperature of the dust collecting section is high, the current supply to the discharging section is stopped.
An exhaust gas purification apparatus for an internal combustion engine according to any one of claims 4 to 4.