JPH11343842A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the sulfate contamination of atmosphere caused by exhaust gas from an internal combustion engine. SOLUTION: Upstream and downstream catalyst converters 3 and 4 are provided in an exhaust passage. These catalyst converters 3 and 4 are prepared by carrying oxygen catalysts on carriers, a non-carrying part 33 carrying no oxygen catalysts is provided in the vicinity of the axial center of the upstream catalyst converter 3, and a closing part 44 for preventing the distribution of exhaust gas is provided in the vicinity of the axial center of the downstream catalyst converter 4. Reducing agents are added from an injection nozzle 6 into an exhaust pipe 2 in the upstream side of the upstream catalyst converter 3.

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 capable of reducing sulfate emissions.

[0002]

2. Description of the Related Art In an internal combustion engine such as a diesel engine,
In order to purify hydrocarbons (HC), carbon monoxide (CO), and the like in exhaust gas discharged from an engine, a catalyst having an oxidizing ability (for example, an oxidation catalyst) may be disposed in an exhaust passage. On the other hand, the exhaust gas of an internal combustion engine such as a diesel engine, sulfur contained in the fuel are included sulfur dioxide generated by the combustion (SO _2), SO ₂ in the exhaust gas high temperature region Is oxidized by the catalyst to produce SO ₃ . This SO ₃ has a strong reactivity and turns into sulfate, and further reacts with moisture to form sulfate particles such as sulfuric acid mist, which may be a source of environmental pollution.

It has been found that the amount of SO ₃ generated rapidly increases when the temperature of the catalyst exceeds a certain temperature (for example, 450 ° C.), and increases as the amount of excess oxygen increases in the catalyst. Since the exhaust gas containing excess oxygen in an internal combustion engine combustion is performed at a lean air-fuel ratio as a diesel engine is exhausted, it can be said to be in easy atmosphere generates SO _3.

As a measure for preventing environmental pollution due to sulfate in exhaust gas, Japanese Patent Application Laid-Open No. 53-100314 is disclosed.
There is a technique disclosed in Japanese Unexamined Patent Publication (Kokai) No. H11-26095. This technology supplies the reducing agent into the exhaust gas in an exhaust passage upstream of the catalyst, and reacts the reducing agent with free oxygen in the exhaust gas to reduce the excess oxygen concentration in the exhaust gas. The amount of SO ₃ generated on the catalyst is reduced, and the generated SO ₃ is reduced by a reducing agent to form SO ₂
By doing so, the amount of sulfate particles in the exhaust gas is reduced. This publication also describes that SO ₃ is less likely to be generated as the concentration of the reducing agent in the exhaust gas is higher.

[0005] From the above, when the following three conditions are satisfied, the amount of SO ₃ generation sharply increases. In order to reduce the amount of SO ₃ generation, it is only necessary that these conditions are not satisfied. I understand. Increase the catalyst temperature (exhaust gas temperature) Increase the oxygen concentration in the exhaust gas Decrease the reducing agent concentration in the exhaust gas

[0006]

By the way, in a portion of the exhaust passage where the catalyst is arranged (hereinafter referred to as a catalyst zone), a portion near the center of the axis along the exhaust gas flow direction has an amount of heat generated by the exhaust gas in the exhaust pipe. Since it is not released to the outside, the temperature in the portion near the axial center in the catalyst zone becomes higher than that in the surrounding portion. Since the temperature is high, the reducing agent is consumed more in the vicinity of the axial center in the catalyst zone than in the surrounding portions. Therefore, if the amount of the reducing agent supplied to the exhaust passage is set to be just right in the peripheral portion of the catalyst zone, the reducing agent is consumed on the front end side near the axial center of the catalytic zone, and the axial center is reduced. Since the reducing agent is not supplied to the rear end side in the vicinity and the temperature is high, a large amount of SO ₃ is generated in an internal combustion engine, such as a diesel engine, which burns at a significantly lean air-fuel ratio. Was a problem.

On the other hand, if the amount of the reducing agent to be supplied upstream of the catalyst zone is set so that the reducing agent is also supplied to the rear end side in the vicinity of the shaft center, the reducing agent supply in the portion around the vicinity of the shaft center This is also problematic as the amount becomes excessive and the excess unreacted reductant passes through the catalyst zone and is released to the atmosphere.

[0008] The present invention has been made in view of such problems of the prior art, and the problem to be solved by the present invention is to reduce the presence of a reducing agent up to the downstream end of a catalyst having oxidizing ability. By doing so, the object is to reduce the SO ₃ generation amount and prevent air pollution by sulfate particles.

[0009]

The present invention has the following features to attain the object mentioned above. The present invention provides a catalyst zone containing an oxidizing catalyst in an exhaust passage through which an exhaust gas containing an excess amount of oxygen discharged from an internal combustion engine flows, and adding a reducing agent upstream of the catalyst zone. In the exhaust gas purifying apparatus for an internal combustion engine provided with the means, the catalyst zone is provided with a closing portion at a portion near an axial center along an exhaust gas flow direction in an exhaust passage, for preventing exhaust gas flow near the axial center. It is characterized by having been done.

In the catalyst zone, exhaust gas and reducing agent are
It is blocked by the blocking part from passing near the center,
Exhaust gas and reducing agent will flow outside the blockage.
You. As exhaust gas and reducing agent pass outside the blockage,
The CO in the gas and HC and the reducing agent of the unburned fuel are the catalyst acids.
It reacts with the oxygen in the exhaust gas and is oxidized by the
_TwoAnd H_TwoIt becomes O and flows out of the catalyst zone.

Further, since the outside of the closed portion in the catalyst zone is separated from the center of the shaft, the temperature is not as high as that of the closed portion. Further, since the temperature outside the closed portion is not as high as that of the closed portion, the consumption of the reducing agent is reduced. As a result, the concentration of the reducing agent at the rear end of the catalyst zone can be equal to or higher than the predetermined concentration. Therefore, in this catalyst zone, SO ₂ in the exhaust gas does not change to SO ₃ .

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, a reducing agent addition position and a catalyst zone (hereinafter referred to as a catalyst zone) in which a reducing agent is added into the exhaust passage by the reducing agent adding means. This catalyst zone is referred to as a downstream catalyst zone).
(Hereinafter, for convenience of explanation, this catalyst zone is referred to as an upstream catalyst zone). In the upstream catalyst zone, the catalyst is not carried in the vicinity of the axial center of the exhaust passage in the exhaust gas flow direction. A non-supporting part is provided.

[0013] The exhaust gas and the reducing agent flow into the downstream catalyst zone through the unsupported portion of the upstream catalyst zone and the outside thereof. Since the catalyst having oxidizing ability is not supported on the non-supporting portion, the exhaust gas and the reducing agent flowing through the non-supporting portion flow into the downstream catalyst zone without being oxidized. Therefore, the required amount of the reducing agent in the downstream catalyst zone can be secured. When the exhaust gas passes outside the unsupported portion of the upstream catalyst zone, HC and CO in the exhaust gas are oxidized and the exhaust gas is purified. Further, since the temperature outside the non-supporting portion is not as high as that of the non-supporting portion, SO ₂ in the exhaust gas does not change to SO ₃ outside the non-supporting portion.

In the present invention, the oxidizing catalyst may be an oxidation catalyst, a storage reduction type NOx catalyst or a selective reduction type NOx.
A catalyst and the like can be exemplified. Here, the storage reduction type N
The Ox catalyst refers to a catalyst that absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases.For example, alumina is used as a carrier, and on this carrier, For example, at least one selected from the group consisting of alkali metals such as potassium K, sodium Na, lithium Li and cesium Cs, alkaline earths such as barium Ba and calcium Ca, lanthanum La and rare earths such as yttrium Y, and platinum Pt. Such a noble metal is supported. In addition, selective reduction type NO
x catalyst refers to N2 in the presence of hydrocarbons in an oxygen-rich atmosphere.
A catalyst that reduces or decomposes Ox.
The catalyst includes a catalyst in which a transition metal such as u is supported by ion exchange, a catalyst in which a noble metal is supported on zeolite or alumina, and the like.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described below with reference to FIGS. Note that this embodiment is an embodiment in which the present invention is applied to a diesel engine as an internal combustion engine.

FIG. 1 is a diagram showing a schematic configuration of an exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment. Light oil as fuel is burned in the vehicle diesel engine 1 at a lean air-fuel ratio, and exhaust gas exhausted from the engine 1 is supplied to an exhaust pipe (exhaust passage) 2, an upstream catalytic converter (second catalytic zone) 3, and a downstream side. The air is exhausted to the atmosphere through a catalytic converter (catalyst zone) 4 and an exhaust pipe (exhaust passage) 5. The upstream catalytic converter 3 and the downstream catalytic converter 4 will be described later in detail.

The exhaust pipe 2 is provided with an injection nozzle 6 for injecting light oil, which is the fuel of the engine 1, into the exhaust gas as a reducing agent. The injection nozzle 6 is connected via a reducing agent supply pipe 7 to a reducing agent supply device 8 composed of a pump or the like. EC
The operation is controlled by 9).

More specifically, a preliminary experiment is performed on the engine 1 in advance, and an optimum amount of the reducing agent for purifying the exhaust gas at that time is determined according to the operating state of the engine 1. The relationship with the amount of the reducing agent added is mapped and stored in the ROM of the ECU 9. The ECU 9 reads out the necessary amount of the reducing agent to be added with reference to the map according to the operating state of the engine 1 and controls the operation of the reducing agent supply device 8 so that the amount of the added reducing agent is injected from the injection nozzle 6. I do.

In this embodiment, the injection nozzle 6,
The reducing agent supply pipe 7 and the reducing agent supply device 8 constitute a reducing agent adding unit. Note that the reducing agent adding means may perform so-called expansion stroke injection in which fuel (light oil) is injected into a cylinder during the expansion stroke of the engine 1 instead of injecting light oil from the injection nozzle 6 into the exhaust pipe 2. It is possible.

The ECU 9 is composed of a digital computer and includes a ROM (Read Only Memory), a RAM (Random Access Memory), a CPU (Central Processor Unit), an input port, and an output port interconnected by a bidirectional bus. In addition to performing the basic control such as the fuel injection amount control of No. 1, in this embodiment, the control of the amount of reducing agent added to the exhaust pipe 2 is performed.

For these controls, an input signal from a rotation speed sensor 10 and an input signal from an accelerator opening sensor 11 are input to input ports of the ECU 9. The rotation speed sensor 10 outputs an output signal corresponding to the rotation speed of the engine 1 as an EC.
U9, and the ECU 9 calculates the engine speed from this output signal. The accelerator opening sensor 11 outputs an output signal corresponding to the accelerator opening to the ECU 9, and the ECU 9 calculates an engine load from the output signal. The engine operation state is determined by the engine speed and the engine load.

The upstream-side catalytic converter 3 has a large number of cells 31 as shown in the sectional view of FIG.
Carrier made by coating alumina on a metallic monolith
No. 2 is constituted by supporting a noble metal having high oxidation activity such as platinum (Pt), palladium (Pd), rhodium (Rh) as an oxidation catalyst. However, in the upstream catalytic converter 3, the central portion including the axial center along the flow direction of the exhaust gas is a non-supporting portion 33 over the entire length of the upstream catalytic converter 3. Only the oxidation catalyst is not supported at all. That is, the upstream-side catalytic converter 3 has a structure in which the periphery of the non-support portion 33 on which the oxidation catalyst is not supported is surrounded by the support portion 34 on which the oxidation catalyst is supported.

On the other hand, the downstream-side catalytic converter 4 has a large number of cells 41 as shown in the sectional view of FIG.
A carrier 42 made by coating an aluminum-based metal monolith with alumina, and carrying a noble metal having high oxidation activity such as platinum (Pt), palladium (Pd), and rhodium (Rh) as an oxidation catalyst; . However, at the upstream end of the downstream catalytic converter 4, a closing plate 43 for closing the cell 41 at the center is fixed to a center portion including the axial center along the flow direction of the exhaust gas. The central portion of the catalytic converter 4 is the downstream catalytic converter 4
Is formed as a closed portion 44 over the entire length of the cover. This closing part 4
4 has its upstream end closed by the closing plate 43, so that exhaust gas does not flow. That is, the downstream side catalytic converter 4 is connected to the closing portion 44 through which the exhaust gas cannot flow.
Is surrounded by a flow portion 45 through which exhaust gas can flow.

Next, the operation of the exhaust gas purifying apparatus will be described. Exhaust gas emitted by burning fuel (light oil) in the engine 1 includes CO, HC that is an unburned fuel component,
It contains SO ₂ generated by burning the sulfur content in the fuel. Further, since the fuel is burned in the engine 1 at a lean air-fuel ratio, the exhaust gas of the engine 1 contains an excessive amount of oxygen.

This exhaust gas flows through the exhaust pipe 2 and flows into the upstream catalytic converter 3 along with the reducing agent (HC) injected from the injection nozzle 6 on the way. Part of the exhaust gas and the reducing agent (HC) flows through the non-supporting portion 33 of the upstream catalytic converter 3, and the rest flows through the supporting portion 34 to the downstream catalytic converter 4. The passage of the exhaust gas and the reducing agent (HC) through the non-supporting portion 33 is caused by the downstream catalytic converter 4.
This is to secure the reducing agent (HC) to be supplied to the fuel cell. That is, CO in the exhaust gas flowing through the non-supporting portion 33 of the upstream side catalytic converter 3, HC in the unburned fuel, and the reducing agent (HC)
Since the oxidation catalyst is not supported on the non-supporting portion 33, the oxygen flows through the non-supporting portion 33 into the downstream catalytic converter 4 without being oxidized.

The exhaust gas flowing through the non-supporting section 33 has a high oxygen concentration, and the non-supporting section 33 has a higher temperature than the supporting section 34. Since (HC) is not consumed, the concentration of the reducing agent is high. Accordingly, SO ₂ in the exhaust gas is reduced to S
It does not change to O ₃ .

On the other hand, the carrier 3 of the upstream catalytic converter 3
Most of the CO and unburned fuel HC and the reducing agent (HC) in the exhaust gas flowing through the exhaust gas 4 react with the oxygen in the exhaust gas by the action of the oxidation catalyst carried on the carrier 34 and are oxidized. , C
O ₂ and H ₂ O flow into the downstream catalytic converter 4. In addition, surplus reducing agent (HC) not consumed in the support portion 34 also flows into the downstream catalytic converter 4.

In the carrier section 34, the non-carrier section 33
And a large amount of oxygen in the exhaust gas is consumed as a result, so that the oxygen concentration becomes extremely low in the entire region from the front end to the rear end of the support portion 34, and
Since the concentration of the reducing agent (HC) is equal to or higher than the predetermined concentration in the entire region of the support portion 34, SO ₂ in the exhaust gas is reduced to SO ₃
Does not change.

Therefore, in the upstream catalytic converter 3, SO ₂ in the exhaust gas does not change to SO ₃ in both the non-supporting portion 33 and the supporting portion 34.

The exhaust gas and the reducing agent (HC) that have passed through the upstream catalytic converter 3 flow into the downstream catalytic converter 4 as described above. Since the exhaust gas cannot flow through the section 44, the exhaust gas and the reducing agent (HC)
Will flow through the distribution section 45. And
When the exhaust gas and the reducing agent (HC) flow through the circulation part 45, the CO and the unburned fuel HC in the exhaust gas and the reducing agent (H
C) is oxidized by reacting with oxygen in the exhaust gas by the action of the oxidation catalyst carried in the flow part 45, and flows out to the exhaust pipe 5 as CO ₂ or H ₂ O.

In the circulation section 45, the oxygen in the exhaust gas is consumed, and as a result, the oxygen concentration in the entire area from the front end to the rear end of the circulation section 45 becomes extremely low. Further, since the flow portion 45 is separated from the shaft center in the downstream-side catalytic converter 4, the temperature does not become as high as that of the closing portion 44. Further, since the temperature of the circulation part 45 is not high, the consumption of the reducing agent (HC) is reduced, and as a result, the concentration of the reducing agent (HC) also becomes higher than the predetermined concentration at the rear end of the circulation part 45. Therefore, the SO 4 in the exhaust gas is
₂ does not change to SO ₃ .

In other words, the injection nozzle 6 is set so that the concentration of the reducing agent at the rear end of the flow part 45 is equal to or higher than the predetermined concentration.
From the preliminary experiment to determine the amount of reducing agent to be injected from
It controls the reducing agent supply device 8.

As described above, according to the exhaust gas purifying apparatus of this embodiment, the exhaust gas can be purified by oxidizing HC and CO in the exhaust gas, and the SO ₃ can be purified.
Can be extremely reduced, and air pollution by sulfate particles can be prevented.

In the above-described embodiment, light oil (HC) is used as the reducing agent added to the exhaust gas. However, the reducing agent is not limited to HC, and urea, ammonia, or the like can be used. is there.

Although the above-described embodiment is an embodiment in which the present invention is applied to a diesel engine as an internal combustion engine, the present invention is also applicable to a gasoline engine capable of burning under excess oxygen. .

[0036]

According to the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the flow of exhaust gas in the vicinity of the axial center of the catalyst zone provided in the exhaust passage of the internal combustion engine is prevented. By providing the closing portion, the exhaust gas and the reducing agent do not flow to the high temperature portion of the catalyst zone, and as a result, the amount of SO ₃ generated can be extremely reduced.
As a result, an excellent effect of preventing sulfate contamination of the atmosphere can be obtained.

In the case where a second catalyst zone is provided between the reducing agent addition position and the catalyst zone, and a non-supporting portion which does not support the catalyst is provided near the axial center of the second catalyst zone. Can supply a required amount of a reducing agent to a catalyst zone located downstream of the second catalyst zone, thereby reducing the amount of SO ₃ generated in the downstream catalyst zone. Therefore, it is possible to prevent sulfate contamination of the atmosphere.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an exhaust gas purification device for an internal combustion engine according to the present invention.

FIG. 2 is a longitudinal sectional view of an upstream side catalytic converter in the exhaust gas purifying apparatus for an internal combustion engine of the embodiment.

FIG. 3 is a longitudinal sectional view of a downstream catalytic converter in the exhaust gas purifying apparatus for an internal combustion engine of the embodiment.

[Explanation of symbols]

 Reference Signs List 1 diesel engine (internal combustion engine) 2 exhaust pipe (exhaust passage) 3 upstream catalytic converter (second catalyst zone) 4 downstream catalytic converter (catalyst zone) 5 exhaust pipe (exhaust passage) 6 injection nozzle (reducing agent adding means) 7) Reducing agent supply pipe (reducing agent adding means) 8 Reducing agent supplying device (reducing agent adding means) 33 Non-supporting part 34 Supporting part 44 Closing part 45 Flowing part

Claims (2)

[Claims] 1. A reducing agent for providing a catalyst zone containing an oxidizing catalyst in an exhaust passage through which exhaust gas containing excess oxygen discharged from an internal combustion engine flows, and adding a reducing agent upstream of the catalyst zone. In the exhaust gas purifying apparatus for an internal combustion engine provided with the addition means, the catalyst zone has a blockage near a shaft center in an exhaust passage along a flow direction of the exhaust gas, the blockage blocking an exhaust gas flow in a portion near the shaft center. An exhaust gas purification device for an internal combustion engine, which is provided. 2. A second catalyst zone containing a catalyst having an oxidizing ability is provided between the catalyst zone and a reducing agent addition position where a reducing agent is added into the exhaust passage by the reducing agent adding means. The second catalyst zone includes a portion near the axial center along the exhaust gas flow direction in the exhaust passage.
The exhaust purification device for an internal combustion engine according to claim 1, wherein a non-supporting portion that does not support a catalyst is provided.