JP2001317332A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device improving the durability of a particulate filter and capable of avoiding clogging in a short period. SOLUTION: The particulate filter 11 is provided in the middle of an exhaust pipe 9 in which exhaust gas 7 flows, and a first oxidation catalyst 12 and a second oxidation catalyst 13 are provided on the upstream side and the downstream side across the particulate filter 11 respectively so that the exhaust gas 7 passing through the first oxidation catalyst 12 can be guided to the second oxidation catalyst 13 by properly detouring the particulate filter 11 through a by-path passage 14. The particulate filter 11 is used only under the condition that the particulates trapped by the particulate filter 11 can be regenerated by self-combustion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust emission control device applied to an internal combustion engine such as a diesel engine.

[0002]

2. Description of the Related Art Particulate matter (particulate matter) emitted from a diesel engine is:
Soot composed of carbonaceous material and SO composed of high-boiling hydrocarbon component
F (Soluble Organic Fraction: Soluble Organic Component) and a small amount of sulfate (mist-like sulfuric acid component) as a main component. Conventionally, a particulate filter is provided in the exhaust pipe through which gas flows.

[0003] This type of particulate filter has a porous honeycomb structure made of a ceramic such as cordierite, and the inlets of each of the flow paths partitioned in a lattice are alternately plugged, and the inlets are plugged. For outlets that are not done, their outlets are plugged,
Only the exhaust gas that has passed through the porous thin wall that defines each flow path is discharged downstream.

Since the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging. Although it is necessary to regenerate the curated filter, in the normal operating state of the diesel engine, there are few opportunities to obtain a high exhaust temperature enough for the particulates to self-combust,
In general, it has been considered that active heating is performed by attaching an electric heater or the like.

[0005]

However, in such a conventional means, the heat load during regeneration of the particulate filter is large, which tends to cause erosion or cracking, thereby reducing the durability of the particulate filter. On the other hand, when active heating by an electric heater or the like is not performed, there is a problem that the particulate filter is clogged in a short period of time.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an exhaust gas purifying apparatus capable of improving the durability of a particulate filter and avoiding clogging in a short period of time. And

[0007]

According to the present invention, a particulate filter is provided in the middle of an exhaust pipe through which exhaust gas flows, and first oxidation is performed on the upstream and downstream sides of the particulate filter. An exhaust system comprising a catalyst and a second oxidation catalyst, respectively, wherein the exhaust gas passing through the first oxidation catalyst can be guided to the second oxidation catalyst by appropriately bypassing the particulate filter. Purifying device.

[0008] Therefore, according to the present invention, if the regeneration conditions under which the particulate matter collected by the particulate filter can be removed by self-combustion without applying active heating by an electric heater or the like are established, When the exhaust gas that has passed through one oxidation catalyst is led to the second oxidation catalyst through a particulate filter, and the particulates in the exhaust gas are collected by the particulate filter, a relatively high temperature upstream of the particulate filter can be obtained. By passing high exhaust gas through the first oxidation catalyst,
The oxidation reaction of NO, HC and CO in the exhaust gas is promoted,
NO ₂ is generated by the oxidation of NO, and active oxygen is generated in the course of the oxidation reaction of HC and CO, and these strong oxidizing NO ₂ and active oxygen are led to the particulate filter.

Then, the soot and SOF in the particulate matter trapped in the particulate filter are ignited at a lower level than in the case where the conventional particulate filter is arranged alone, with the aid of oxidation by the NO ₂ and active oxygen. It starts burning at the temperature and is efficiently burned off.

[0010] Incidentally, the first oxidation catalyst is not limited to not exhibiting a direct effect of reducing particulates.
The SOF content of the particulates in the exhaust gas that has passed through the first oxidation catalyst is mainly because the SOF content of the particulates is also combusted and removed.
It will be reduced to some extent before reaching the particulate filter.

On the other hand, when the regeneration conditions for the particulates to self-burn on the particulate filter are not established, the exhaust gas passing through the first oxidation catalyst is led to the second oxidation catalyst by bypassing the particulate filter. This prevents the particulate filter from trapping particulates that are difficult to remove by combustion, so that the particulates in the exhaust gas that bypasses the particulate filter move on the surface of the second oxidation catalyst. At this time, the soot and the SOF in the particulates are supported by the oxidation by the NO ₂ and the active oxygen, and start burning at a relatively low ignition temperature to be efficiently burned and removed.

That is, the case where the regeneration conditions under which the particulates are self-burning on the particulate filter is not satisfied mainly refers to the case where the exhaust gas temperature is low while the load of the internal combustion engine is low, and In such a case, the particulates contained in the exhaust gas have a composition with a higher SOF content than the soot, so that the first and second oxidation catalysts, which have a high effect of reducing the SOF content, are sufficiently substituted. Is effective, and in particular, the oxidation support of NO ₂ and active oxygen generated by the first oxidation catalyst works effectively in the second oxidation catalyst, and the particulates can be removed without using a particulate filter. This is a major factor that can be removed by burning.

Further, in the present invention, it is preferable that the surface of the particulate filter is also coated with an oxidation catalyst. In this case, NO ₂ and active oxygen are also generated on the surface of the particulate filter immediately after being generated. Since it reacts with the collected particulates, the burning of the particulates is further supported.

Further, HC and CO in the exhaust gas are oxidized by the first oxidation catalyst upstream of the particulate filter, so that HC and CO in the exhaust gas reaching the particulate filter are removed. The amount is reduced, the selectivity of the oxidation reaction to NO or the like is increased in the oxidation catalyst on the surface of the particulate filter, and the generation of NO ₂ or active oxygen in the oxidation catalyst on the surface of the particulate filter is further promoted.

Further, in the present invention, it is preferable that the first oxidation catalyst is disposed near the outlet of the exhaust manifold and is spaced apart from the particulate filter at a required interval. In the relatively high temperature region near the outlet of the exhaust manifold, NO ₂ and active oxygen are generated from the exhaust gas with good reactivity, and the reaction time required for the generation is sufficiently secured and guided to the particulate filter. It becomes possible.

In the present invention, when the exhaust gas passing through the first oxidation catalyst is guided to the second oxidation catalyst by appropriately bypassing the particulate filter, the exhaust gas passing through the first oxidation catalyst is subjected to particulate matter. It suffices to provide a bypass flow path that bypasses the filter and leads to the second oxidation catalyst, and flow path switching means provided at a branch point of the bypass flow path with respect to the exhaust pipe.

According to this configuration, the flow of the exhaust gas is switched to the bypass flow path by the flow path switching means, so that the exhaust gas passing through the first oxidation catalyst can be easily bypassed through the particulate filter. .

Further, specific means for switching the flow of the exhaust gas to the bypass flow path by the flow path switching means include a temperature sensor for detecting the temperature of the exhaust gas near the inlet of the particulate filter; And a load sensor for detecting the load of the internal combustion engine, and illuminates the operating state of the internal combustion engine and the current exhaust gas temperature based on detection signals from the temperature sensor, the rotation sensor, and the load sensor. In addition, when it is determined that the regeneration conditions for the particulates to self-burn on the particulate filter are not satisfied, a control device for outputting a bypass command for switching the flow of the exhaust gas to the bypass channel side to the channel switching means May be configured.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an engine (internal combustion engine) which is a diesel engine. In the engine 1 shown here, a turbocharger 2 is provided. The air 4 guided from the air cleaner 3 is sent to the compressor 2a of the turbocharger 2 through the intake pipe 5, and the compressor 2a
The pressurized air 4 is further sent to an intercooler 6 for cooling, and the air 4 is guided from the intercooler 6 to an intake manifold (not shown) and introduced into each cylinder of the engine 1.

Exhaust gas 7 discharged from each cylinder of the engine 1 is sent to a turbine 2b of the turbocharger 2 through an exhaust manifold 8,
Exhaust gas 7 driving the turbine 2b is discharged to the outside of the vehicle via an exhaust pipe 9.

A particulate filter 11 held by a casing 10 is provided in the exhaust pipe 9 through which the exhaust gas 7 flows, and the particulate filter 11 is a flow-through filter made of cordierite ceramics. In this embodiment, the surface of the particulate filter 11 is coated with an oxidation catalyst such as platinum / alumina.

The turbine 2b of the turbocharger 2
Immediately after (in the vicinity of the outlet of the exhaust manifold 8), a first oxidation catalyst 12, which is formed by supporting platinum / alumina on a stainless steel metal carrier, is provided at a required distance from the particulate filter 11 in the exhaust pipe 9. The first oxidation catalyst 12 is spaced apart and formed as a relatively small-capacity flow-through type honeycomb structure having a diameter substantially equal to the diameter of the exhaust pipe 9.

Further, a second oxidation catalyst 13 in which a platinum / alumina oxidation catalyst is supported on a stainless steel metal carrier is provided downstream of the particulate filter 11 in the casing 10. The second oxidation catalyst 13 is formed as a flow-through type honeycomb structure having a larger capacity than the first oxidation catalyst 12 described above.

The casing 10 in the exhaust pipe 9
And a boundary position between the particulate filter 11 and the second oxidation catalyst 13 of the casing 10 is connected by a bypass flow path 14, and the first oxidation catalyst 1
The exhaust gas 7 that has passed through 2 can be led to the second oxidation catalyst 13 by bypassing the particulate filter 11 via the bypass flow path 14.

Here, switching valves 15 and 16 are provided at the branch point of the bypass passage 14 with respect to the exhaust pipe 9 so that the flow of the exhaust gas 7 can be appropriately switched to the bypass passage 14 side.
(Flow path switching means) are provided.

The engine 1 is provided with a rotation sensor 17 for detecting the engine rotation speed, and is provided with a rotation speed signal 17a from the rotation sensor 17 and a fuel pump (not shown). The load signal 18a from the load sensor 18 (a sensor for detecting the fuel injection amount) is used as the control device 1
9 is input.

The exhaust pipe 9 near the inlet of the particulate filter 11 is provided with a temperature sensor 20 for detecting the temperature of the exhaust gas 7 flowing through the exhaust pipe 9. A signal 20a is input to the control device 19.

On the other hand, in the control device 19, the temperature of the exhaust gas 7 determined from the temperature signal 20a is compared with the operation state determined from the rotation speed signal 17a and the load signal 18a.
It is determined whether or not the particulates are in an operation state in which the particulates can self-burn. When it is determined on the particulate filter 11 that the regeneration conditions for the particulates to self-burn are not satisfied, the exhaust gas is exhausted. Bypass command 1 for switching the flow of gas 7 to bypass flow path 14
5a and 16a are output to the switching valves 15 and 16, respectively.

That is, in the control device 19, a control map created by data such as a preliminary experiment as shown in FIG. 2 is set, and as shown in the control map as an operation area A, the engine 1 Since the operating region A in which the particulates can self-combust on the particulate filter 11 is generally grasped from the relationship between the load and the rotation speed, the rotation speed signal 17a of the rotation sensor 17 and the load sensor 1
By judging whether or not the current operating state is in the operating region A based on the load signal 18a of No. 8, it is possible to substantially determine whether or not the regeneration condition of the particulate filter 11 is satisfied. However, when it is determined that the exhaust gas 7 is in the operating region A, the temperature range of the exhaust gas 7 assumed in the operating region A and the temperature of the exhaust gas 7 measured based on the temperature signal 20a from the temperature sensor 20 are determined. Compare with
The bypass commands 15a and 16a are canceled only when the measured temperature falls within the temperature range.

When it is determined that the load is lower than the operation region A and the operation region B is lower in temperature of the exhaust gas 7,
The bypass commands 15a and 16a are output, and the switching valve 1
5 and 16 switch the flow of the exhaust gas 7 to the bypass 14 side.

If the regeneration conditions are such that the particulates collected by the particulate filter 11 can be removed by self-combustion without the need for active heating by an electric heater, etc. The temperature signal 20a from the sensor 20 and the rotation speed signal 17a of the rotation sensor 17
Based on the load signal 18a of the load sensor 18, the operating state of the engine 1 and the current exhaust gas 7
And it is determined that regeneration conditions for the particulates to self-burn on the particulate filter 11 are satisfied.
The switching valves 15 are closed and the switching valve 16 is opened, and the flow of the exhaust gas 7 is guided to the particulate filter 11.

As described above, the exhaust gas 7 that has passed through the first oxidation catalyst 12 is guided to the second oxidation catalyst 13 through the particulate filter 11, and the particulates in the exhaust gas 7 are collected by the particulate filter 11. Then, the relatively high-temperature exhaust gas 7 on the upstream side of the particulate filter 11 passes through the first oxidation catalyst 12, whereby the oxidation reaction of NO, HC, and CO in the exhaust gas 7 is promoted, and the NO NO ₂ is generated by the oxidation, and active oxygen is generated in the course of the oxidation reaction of HC and CO. These strong oxidizing NO ₂ and active oxygen are led to the particulate filter 11.

Then, the soot and SOF in the particulate matter collected in the particulate filter 11 are supported by the oxidation by the NO ₂ and active oxygen, so that the soot and the SOF content are smaller than in the case where the conventional particulate filter 11 is arranged alone. The fuel starts burning at a low ignition temperature and is efficiently burned and removed.

It should be noted that the first oxidation catalyst 12 does not necessarily exert a direct effect of reducing particulates, but also has an action of burning and removing the SOF content in the particulates. The amount of particulate SOF in the exhaust gas 7 having passed through 12 is reduced to some extent before reaching the particulate filter 11.

On the other hand, if the regeneration condition for the particulates to self-burn on the particulate filter 11 is not established, the temperature signal 20a from the temperature sensor 20 and
The rotation speed signal 17a of the rotation sensor 17 and the load sensor 18
The operating condition of the engine 1 is compared with the current temperature of the exhaust gas 7 by the control device 19 on the basis of the load signal 18a, and the regeneration conditions for the particulate filter to self-burn on the particulate filter 11 are not established. Thus, the bypass commands 15a and 16a are output, the switching valve 15 is opened and the switching valve 16 is closed, and the flow of the exhaust gas 7 is switched to the bypass flow path 14 side.

As described above, the exhaust gas 7 that has passed through the first oxidation catalyst 12 is guided to the second oxidation catalyst 13 by bypassing the particulate filter 11, and thereby the particulate filter 11, which is difficult to burn and remove, is formed. When the trapping is avoided, when particulates in the exhaust gas 7 bypassing the particulate filter 11 move on the surface of the second oxidation catalyst 13, soot and SOF content in the particulates are reduced. Are oxidized by the NO ₂ and active oxygen, start burning at a relatively low ignition temperature, and are efficiently burned and removed.

That is, on the particulate filter 11
Regeneration conditions for the particulates to self-burn are not established
Is mainly when the load of the internal combustion engine is low.
This indicates the case where the exhaust gas 7 temperature is low.
In the exhaust gas 7 in the case of
Has a composition with more SOF than soot,
A first oxidation catalyst 12 having a high effect of reducing the OF content and
The second oxidation catalyst 13 is sufficiently effective for substitution.
In particular, NO generated by the first oxidation catalyst 12 _TwoAnd live
Support for oxidation of reactive oxygen is effectively produced by the second oxidation catalyst 13.
Use the particulate filter 11
Is a major factor in removing particulates without burning.
Because

Therefore, according to the above embodiment, the particulate filter 11 is used only under the condition that the particulate matter collected by the particulate filter 11 can be regenerated by self-combustion. The collected particulates can be efficiently burned and removed with the aid of oxidation by NO ₂ and active oxygen. In addition, when the regeneration conditions of the particulate filter 11 are not established, the particulate filter 11 is bypassed. Since the second oxidation catalyst 13 is mainly used, and particulates containing a large amount of SOF can be efficiently burned and removed with the aid of oxidation by NO ₂ and active oxygen, the heat load on the particulate filter 11 is significantly reduced as compared with the conventional case. To greatly increase the durability of the particulate filter 11. The particulate matter can be improved and clogging of the particulate matter in a short period can be avoided.

Further, in this embodiment, in particular, since the oxidation catalyst is also coated on the surface of the particulate filter 11, NO ₂ and active oxygen are also generated on the surface of the particulate filter 11 and collected immediately. It reacts with the particulates, so that the burning of the particulates can be further supported.

Further, since HC and CO in the exhaust gas 7 are oxidized by the first oxidation catalyst 12 upstream of the particulate filter 11, the HC and CO in the exhaust gas 7 reaching the particulate filter 11 are And the selectivity of the oxidation reaction to NO or the like by the oxidation catalyst on the surface of the particulate filter 11 increases,
It can be expected that the generation of NO ₂ and active oxygen in the oxidation catalyst on the surface of the particulate filter 11 is further promoted.

Further, since the first oxidation catalyst 12 is disposed near the outlet of the exhaust manifold 8 and is spaced apart from the particulate filter 11 at a required interval, the first oxidation catalyst 12 has a relatively high temperature near the outlet of the exhaust manifold 8. From the exhaust gas 7 with high reactivity
O generates _two or active oxygen, moreover, the particulate filter 11 with sufficient reaction time required for the generation
It is possible to lead to.

In fact, according to the results of experiments conducted by the present inventors, as shown in FIG. 3, the diesel engine was continuously operated under medium speed and medium load conditions, and the inlet pressure of the particulate filter 11 was reduced. Observation of the transition shows that when the exhaust gas purifying device of the embodiment specifically illustrated in FIG.
Even if continuous operation time is about 100 hours, about 600mm
While maintaining the pressure at about Aq, the inlet pressure of the particulate filter 11 fluctuates in a substantially flat state, whereas a conventional apparatus equipped with only a single particulate filter in a single stage is employed to actively employ an electric heater or the like. If the heating was not carried out, the particulate filter gradually became clogged with the passage of time and the inlet pressure increased, and the pressure increased to about 850 mmAq after about 100 hours of continuous operation. And the remarkable effectiveness of the exhaust gas purification apparatus according to the embodiment of FIG. 1 has already been confirmed.

It should be noted that the exhaust gas purifying apparatus of the present invention is not limited to the above-described embodiment, and it is needless to say that various changes can be made without departing from the gist of the present invention.

[0045]

According to the exhaust gas purifying apparatus of the present invention described above, the following various excellent effects can be obtained.

(I) Collected by a particulate filter
That can be regenerated by self-combustion of waste particulates
Use a particulate filter only under
Particulates collected by the particulate filter
NO_TwoEfficient combustion with oxygen and active oxygen assisted oxidation
It can be removed by burning, and the particulate matter
If the conditions for regenerating ruta are not
Bypass the heat filter and mainly use the second oxidation catalyst.
And use NOx for particulates with a lot of SOF _TwoAnd live
Efficient combustion removal by supporting oxidation by reactive oxygen
The thermal load of the particulate filter.
Can be significantly reduced,
The durability can be greatly improved and the particulate
Short-term clogging of the board can be avoided.

(II) If the surface of the particulate filter is coated with an oxidation catalyst, NO ₂ and active oxygen are also generated on the surface of the particulate filter, and immediately react with the collected particulates. Therefore, it is possible to further support the combustion of the particulates, and to further oxidize HC and CO in the exhaust gas upstream of the particulate filter by the first oxidation catalyst. Can be formed, so that H in the exhaust gas reaching the particulate filter
C, and the small amount of CO can increase the selectivity of the oxidation reaction to such NO in the oxidation catalyst of the particulate filter surface, more the production of NO ₂ and active oxygen in the oxidation catalyst of the particulate filter surface It can be further promoted.

(III) When the first oxidation catalyst is disposed near the outlet of the exhaust manifold and is spaced apart from the particulate filter at a required interval, a relatively high temperature region near the outlet of the exhaust manifold is provided. Thus, NO ₂ and active oxygen can be generated from the exhaust gas with good reactivity, and the reaction time required for the generation can be sufficiently ensured and guided to the particulate filter.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an embodiment for implementing the present invention.

FIG. 2 is a graph showing an example of a control map set in the control device of FIG.

FIG. 3 is a graph comparing the progress of clogging of a particulate filter with a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine (internal combustion engine) 7 Exhaust gas 8 Exhaust manifold 9 Exhaust pipe 11 Particulate filter 12 First oxidation catalyst 13 Second oxidation catalyst 14 Bypass flow path 15 Switching valve (flow path switching means) 15a Bypass command 16 Switching valve (Flow path switching means) 16a Bypass command 17 Rotation sensor 17a Rotation speed signal (detection signal) 18 Load sensor 18a Load signal (detection signal) 19 Controller 20 Temperature sensor 20a Temperature signal (detection signal)

Claims (5)

[Claims] 1. A particulate filter is provided in an exhaust pipe through which exhaust gas flows, and a first oxidation catalyst and a second oxidation catalyst are provided upstream and downstream of the particulate filter. And an exhaust gas purifying apparatus, wherein exhaust gas passing through the first oxidation catalyst can be guided to the second oxidation catalyst by appropriately bypassing the particulate filter. 2. The exhaust gas purifying apparatus according to claim 1, wherein an oxidation catalyst is coated on the surface of the particulate filter. 3. The exhaust gas purification system according to claim 1, wherein the first oxidation catalyst is arranged near an outlet of the exhaust manifold and is spaced apart from the particulate filter at a required interval. apparatus. 4. A bypass flow path for guiding exhaust gas passing through the first oxidation catalyst to a second oxidation catalyst by bypassing a particulate filter, and a flow path provided at a branch point of the bypass flow path with respect to an exhaust pipe. 4. The exhaust gas purifying apparatus according to claim 1, further comprising a switching unit. 5. A temperature sensor for detecting an exhaust gas temperature near an inlet of a particulate filter, a rotation sensor for detecting a rotation speed of an internal combustion engine, and a load sensor for detecting a load of the internal combustion engine. Based on the detection signals from the rotation sensor and the load sensor, the operating condition of the internal combustion engine is compared with the current exhaust gas temperature, and it is determined that the regeneration conditions for the particulates to self-burn on the particulate filter are not satisfied. 5. An exhaust gas purifying apparatus comprising: a control device configured to output a bypass command for switching a flow of exhaust gas to a bypass flow path side toward the flow path switching means.