JPH1113457A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control nitrogen oxides in the gaseous emission in time of engine transient driving so favorable enough. SOLUTION: A carrier 20 of a catalyst 15 set up in an engine exhaust passage is provided with a separation wall 21 equipped with permeability, extending in the direction of an exhaust passage axis J-J and separating the exhaust passage into an open passage 22 and a close passage 23. An exhaust control catalyst for purifying nitrogen oxides is set up only on top of an inner wall surface of the open passage 22. When a temperature of exhaust flowing into the catalyzer 15 went up, a high temperature area, where a reducing agent is completely oxidizable, is formed in a spot around an exhaust upstream end of the exhaust emission control catalyst, but the reducing agent taken into the close passage 23 flows in this passage 23 without being completely oxidized, and then it passes through the separation wall 21, arriving at a relatively low temperature section, and it reduces the nitrogen oxides in the exhaust emission control catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine.

[0002]

Exhaust purification device for a diesel engine which is adapted to reduce NO _X is known by the reducing agent BACKGROUND ART In an engine exhaust passage an exhaust gas purifying catalyst by supplying a reducing agent to arranged exhaust gas purifying catalyst in the ( See JP-A-6-26328).

[0003]

The exhaust gas purifying catalyst is usually carried on a carrier having a so-called honeycomb shape. The honeycomb-shaped carrier has a plurality of open passages having both an exhaust upstream end and an exhaust downstream end open. , The exhaust gas sequentially flows in each open passage from the exhaust upstream end to the exhaust downstream end. In this case, when the temperature of the exhaust gas flowing into the exhaust purification catalyst rises, first, a high-temperature portion is formed around the exhaust upstream end of the exhaust purification catalyst, and this high-temperature portion is sequentially formed from the exhaust upstream end of the exhaust purification catalyst toward the exhaust downstream end. It will expand. However, the reducing agent when the temperature of the hot section is quite high now actively reacts with oxygen than NO _X, most of the results are supplied to the exhaust purifying catalyst reducing agent is completely oxidized in the high temperature portion, Therefore, the reducing agent hardly reaches the exhaust gas downstream side portion of the exhaust gas purification catalyst where the NO _X reducing action can be performed, and thus the N 2
The O _X there is a problem that can not be satisfactorily reduced.

[0004]

[MEANS FOR SOLVING THE PROBLEMS]
According to the first invention, the engine is disposed in the engine exhaust passage.
Supplying a reducing agent to the exhaust purification catalyst
NO by this reducing agent _XInternal combustion engine designed to reduce
The separation wall extending substantially in the axial direction of the exhaust passage.
Divides the exhaust passage into a pair of passages, and
Close the exhaust downstream end of one of the passages
To form a closed passage and open by the other passage
Forming a passage and forming the separating wall from a breathable material
After the exhaust gas that has flowed into the closed passage passes through the separation wall
Coming with exhaust flowing into the open passage and flowing through the open passage
So that the exhaust purification catalyst is placed on the inner wall surface of the open passage.
Only placed in. That is, in the first invention,
The reducing agent that has flowed into the passage closes without being completely oxidized.
It flows through the chain passage and then flows into the open passage. That
As a result, the NO_XPart where reduction action can be performed
Can be supplied with a reducing agent, and
Even when the temperature of the exhaust gas flowing into the catalyst increases
NO_XIs well purified.

According to a second aspect, in the first aspect, a plurality of the closed passages and the open passages are provided, and the closed passages and the open passages are alternately arranged. That is, in the second invention, since it is located a large amount of the exhaust purification catalyst in a closed path a large amount of the NO _X is reduced simultaneously. According to a third aspect, in the first aspect, the flow path resistance of the separation wall increases as approaching the exhaust downstream end. If the flow path resistance of the separation wall is formed uniformly in the axial direction of the exhaust passage, most of the exhaust flowing into the closed passage passes through the separation wall around the downstream end of the exhaust and flows into the open passage. Most of the reducing agent flowing into the exhaust gas is supplied to the exhaust gas purification catalyst around the downstream end of the exhaust gas, which is not preferable. Therefore, in the third invention, the flow resistance of the separation wall is increased as approaching the downstream end of the exhaust gas, so that the exhaust gas flowing into the closed passage uniformly passes through the separation wall in the axial direction of the exhaust passage. ing.

[0006]

FIG. 1 shows a case where the present invention is applied to a diesel engine. Referring to FIG. 1, 1 is an engine body, 2 is a piston, 3 is a combustion chamber, 4 is an intake port,
Reference numeral 5 denotes an intake valve, 6 denotes an exhaust port, 7 denotes an exhaust valve, and 8 denotes a fuel injection valve for directly injecting fuel into the combustion chamber 3.
The intake port 4 of each cylinder is connected to a common surge tank 10 via a corresponding intake branch pipe 9, and the surge tank 10 is connected to an air cleaner 12 via an intake duct 11. An intake throttle valve 13 interlocked with an accelerator pedal 40 is arranged in the intake duct 11. On the other hand, the exhaust port 6 of each cylinder is connected to a common exhaust manifold 14,
The exhaust manifold 14 is connected to a catalytic converter 16 containing a catalyst 15, and the catalytic converter 16 is connected to the exhaust pipe 1.
7 is connected. Further, the fuel injection valve 8 of each cylinder is connected to a fuel pump 19 via a common fuel pressure accumulating chamber 18. In this manner, fuel injection can be performed a plurality of times in one combustion cycle of each cylinder. Each fuel injection valve 8 is controlled based on an output signal from the electronic control unit 30.

An electronic control unit (ECU) 30 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 32, R
An AM (random access memory) 33, a CPU (microprocessor) 34, an input port 35, and an output port 36 are provided. A temperature sensor 37 u for generating an output voltage proportional to the temperature of exhaust gas flowing into the catalyst 15 is attached to the exhaust manifold 14, and the catalyst 15
A temperature sensor 37d for generating an output voltage proportional to the temperature of the exhaust gas flowing out of the apparatus is attached. The output voltages of these temperature sensors 37u and 37d are input to the input port 35 via the corresponding AD converters 38, respectively. The temperature of the exhaust gas flowing into the catalyst 15, that is, the inlet temperature Tu represents the temperature of the exhaust upstream end of the catalyst 15, and the temperature of the exhaust gas flowing out of the catalyst 15, that is, the outlet temperature Td represents the temperature of the exhaust downstream end of the catalyst 15. Represents. Also, the input port 35
Is connected to a crank angle sensor 39 that generates an output pulse every time the crankshaft rotates, for example, 30 degrees.
The CPU 34 determines the engine speed N based on the output pulse.
Is calculated. Further, the output voltage of the depression amount sensor 41 that generates an output voltage proportional to the depression amount DEP of the accelerator pedal 40 is input to the input port 35 via the corresponding AD converter 38. On the other hand, the output port 36 is connected to each fuel injection valve 8 via the drive circuit 42.

FIG. 2 is an enlarged sectional view of the catalyst 15. The catalyst 15 includes a carrier 20 having a cylindrical shape as a whole, and the carrier 20 is formed of a porous material such as zeolite, alumina, cordierite, SiC, or a porous metal plate. As zeolite, for example, Z
High silica content zeolites such as SM-5 type, ferrierite, mordenite and the like can be used. The carrier 20 includes a plurality of separation walls 21 extending substantially in the exhaust passage axis JJ direction.
These separation walls 21 divide the exhaust passage into a plurality of passages and a plurality of open passages 22 alternately and repeatedly arranged.
And a plurality of closed passages 23 are formed. The open passage 22 has both an exhaust upstream end 22u and an exhaust downstream end 22d open, so that the exhaust flowing into the open passage 22 from the exhaust upstream end 22u as shown by an arrow in FIG. After flowing through the inside, it flows out from the exhaust downstream end 22d. On the other hand, the exhaust passage upstream end 23u of the closed passage 23 is open but the exhaust downstream end 23d is closed. Therefore, the closed passage 23 flows into the closed passage 23 from the exhaust upstream end 23u as shown by an arrow in FIG. The exhaust gas passes through the separation wall 21 and is adjacent to the open passage 2.
2 and merges with the exhaust gas flowing through the open passage 22, and then flows out from the exhaust downstream end 22 d of the open passage 22.

The flow resistance of the separation wall 21 is designed to increase as it approaches the exhaust downstream end. As a result, the exhaust gas flowing into the closed passage 23 uniformly passes through the separation wall 21 in the exhaust passage axis JJ direction.
As shown in FIG. 3, the exhaust purification catalyst 24 is supported on the inner wall surface 22a of the open passage 22, but is not supported on the inner wall surface 23a of the closed passage 23. Although the exhaust purification catalyst 24 may be configured in any manner, in the diesel engine 1 of FIG. 1, the exhaust purification catalyst 24 is composed of a noble metal such as platinum Pt and palladium Pd. The exhaust purification catalyst 24 selectively reacts NO _X in exhaust gas flowing in an oxygen atmosphere containing a reducing agent such as hydrocarbon (HC) and carbon monoxide (CO) with these HC, CO, and the like.
Thereby, NO _X can be reduced to nitrogen N ₂ . That is, the exhaust purification catalyst 24 is the exhaust gas flowing is as containing a reducing agent, even if an oxygen atmosphere to reduce the NO _X in the inflowing exhaust gas.

[0010] There is also not clear portion for the mechanism of the NO _X reduction effect of this case. However, the NO _X reduction action is considered to be performed by the following mechanism. That is, the case where the exhaust purification catalyst 24 is formed of platinum Pt will be described. When NO in the exhaust reaches the surface of platinum Pt, it is oxidized while adhering to the surface of platinum Pt (2NO + O ₂ → 2NO ₂ ), and becomes active. Is done. On the other hand, when HC in the exhaust reaches platinum Pt, it is partially oxidized or CO is generated, and then the partially oxidized HC and CO reach active NO ₂ , and thus NO _X is reduced. . It should be noted that the same mechanism is used when another noble metal is used for the exhaust purification catalyst 24.

The NO _X reduction action of the exhaust gas purifying catalyst 24 is performed when the exhaust gas purifying catalyst 24 is in an active state, that is, when the temperature of the exhaust gas purifying catalyst 24 is lower than the lower limit threshold L
It is most efficient when it is between T and the upper threshold UT. This is because if the temperature of the exhaust purification catalyst 24 is lower than the lower threshold LT of the activation temperature, the oxidation reaction of NO or HC is less likely to occur or NO ₂ is not activated, while the temperature of the exhaust purification catalyst 24 is lower. There is thought to be due to a higher than upper threshold UT HC comes to actively react with oxygen than NO _X. When the exhaust purification catalyst 24 is formed of platinum Pt, the lower threshold LT is about 200 ° C. and the upper threshold UT is about 300 ° C.

In the diesel engine shown in FIG. 1, the air-fuel ratio of the air-fuel mixture burned in the combustion chamber 3 is kept leaner than the stoichiometric air-fuel ratio in order to reduce smoke and particulates discharged from the engine. For this reason, the exhaust purification catalyst 24 is maintained in an oxygen atmosphere. Therefore, if the reducing agent is present in the exhaust purification catalyst 24, the NO _X in the inflowing exhaust gas is satisfactorily reduced in the exhaust purification catalyst 24. In this case, unburned HC and CO discharged from the engine can act as a reducing agent, but NO _X to be purified compared to unburned HC discharged from the diesel engine, etc.
The amount is overwhelmingly large, i.e. reducing agents for favorably purify NO _X becomes insufficient. Therefore, the fuel (hydrocarbons) as a reducing agent secondarily fed to the exhaust purification catalyst 24 by performing the sub-fuel injection from the fuel injection valve 8, thereby as the reducing agent does not run out to NO _X I have.

That is, in addition to the normal fuel injection, for example, around the compression top dead center, ie, the main fuel injection, the fuel injection valve 8 performs the second fuel injection, ie, the auxiliary fuel injection, during the expansion stroke or the exhaust stroke. Thus, the fuel is secondarily supplied into the exhaust gas. It should be noted that the fuel from the auxiliary fuel injection hardly contributes to the engine output. In the present embodiment, as described above, the flow path resistance of the separation wall 21 is configured to increase as approaching the exhaust downstream end,
Therefore, the exhaust gas flowing into the closed passage 23 is
Through the exhaust passage axis JJ direction. As a result, it becomes possible reducing agent is uniformly supplied to the exhaust purifying catalyst 24, thus it is possible to more satisfactorily purify NO _X.

Referring again to FIG. 3, an auxiliary catalyst 25 is carried on the inner wall surface 23a of the closed passage 23. The auxiliary catalyst 25 has a lower oxidizing power than the exhaust purification catalyst 24 supported on zeolite, for example, copper Cu, iron F
e and other transition metals. The auxiliary catalyst 25 partially oxidizes the reducing agent flowing into the closed passage 23, but does not completely oxidize it. The zeolite adsorbs HC when the temperature is low, and adsorbs H when the temperature is high.
It has an HC absorbing / releasing action of releasing C. Therefore, the auxiliary catalyst 25 adsorbs excess HC when the temperature is low, releases the HC which is adsorbed at higher temperatures, the HC then reducing the NO _X and led to the exhaust purification catalyst 24. Accordingly, the insufficient HC in order of the NO _X reduction action is further prevented.

Next, the exhaust gas purifying method according to the present invention will be described in detail with reference to FIGS. 4 and 5, x represents an exhaust passage axis J from the exhaust upstream end of the catalyst 15.
-X indicates the position, and Tx indicates the temperature of the exhaust gas purification catalyst 24 at the position x. FIG. 4 shows a case where the temperature of the exhaust gas flowing into the catalyst 15 decreases, for example, during the engine deceleration operation. When the temperature of the exhaust gas flowing into the catalyst 15 decreases, the temperature around the exhaust upstream end of the catalyst 15 first decreases, but the temperature around the exhaust downstream end is maintained at a high temperature. As a result, an inactive region AI is formed on the exhaust gas upstream side of the exhaust purification catalyst 24, and an active region AA is formed on the exhaust gas downstream side. In this case, the HC that has flowed into the open passage 22 flows into the active area AA after flowing through the inactive area AI, and thus the HC reaches the active area AA without being completely oxidized. As a result, the partially oxidized HC (H
C ^* ) and CO are produced. On the other hand, a part of HC flowing into the closed passage 23 is partially oxidized HC ^* and CO is produced by the auxiliary catalyst 25, these HC ^* and CO then flow into the active region AA through the separation wall 21 I do. At this time, in the active area AA, the active state NO
₂ (NO ₂ ^* ) adheres to the surface of the platinum Pt, so that NO ₂ ^* is reduced by these HC ^* and CO.

Incidentally, the flow resistance of the closed passage 23 is larger than that of the open passage 22 and, therefore, the exhaust flow velocity in the closed passage 23 is lower than that in the open passage 22. Lower than. That is, for a while after the temperature of the exhaust gas flowing into the catalyst 15 decreases, the temperature in the closed passage 23 at the same position x is higher than that in the open passage 22 at the same position x. As a result, even if the low temperature inactive region AI of the exhaust purification catalyst 24 expands, HC ^* and CO can be generated in the auxiliary catalyst 25 adjacent to the inactive region AI. These HC ^* and CO are then converted into the active region AA
In Italy, it is possible to more satisfactorily reduce NO _X and thus.

FIG. 5 shows a case where the temperature of the exhaust gas flowing into the catalyst 15 rises, for example, during an engine acceleration operation. When the temperature of the exhaust gas flowing into the catalyst 15 rises, first, the temperature around the exhaust upstream end of the catalyst 15 rises, however, the temperature around the exhaust downstream end is kept low. As a result, the active region AA is formed on the exhaust gas upstream side of the exhaust purification catalyst 24, and the inactive region AI is formed on the exhaust gas downstream side. In this case, HC that has flowed into the open passage 22 is first deactivated in the inactive region A.
I, and flows into the hot inert region AI.
Most are completely oxidized. That is, the open passage 2
Most of the HC that has flowed into 2 cannot reach the active area AA. However, HC flowing into the closed passage 23,
Alternatively, HC released from the auxiliary catalyst 25 flows through the closed passage 23 without being completely oxidized, and HC ^* and C
In the form of O, it reaches a closed passage 23 adjacent to the active area AA.
These HC ^* and CO then flow through the separation wall 21 into the active area AA, thus reducing NO ₂ ^* .

That is, since the region where the reducing agent is not completely oxidized is formed to a position adjacent to the active region AA bypassing the high temperature inactive region AI of the exhaust purification catalyst 24, the exhaust gas flowing into the exhaust purification catalyst 24 is formed. also it is possible to supply the reducing agent to the active region AA of the exhaust purification catalyst 24 when the temperature increases, thus it is possible to ensure good NO _X reduction action.

For a while after the temperature of the exhaust gas flowing into the catalyst 15 rises for the above-mentioned reason, the same position x
, The temperature in the closed passage 23 is lower than that in the open passage 22. As a result, even if the high-temperature inactive region AI of the exhaust gas purification catalyst 24 expands, this inactive region AI
HC ^* and CO may be generated in the auxiliary catalyst 25 adjacent to the fuel cell. These HC ^* and CO are then led to the active region AA, it is possible to more satisfactorily reduce NO _X and thus.

As described above, in the present embodiment, NO _X can be satisfactorily purified regardless of whether the temperature of the exhaust gas flowing into the catalyst 15 decreases or rises. can also be satisfactorily purify NO _X. By the way, when the entire exhaust purification catalyst 24 is not in the active state, the auxiliary fuel injection is performed to
Reducing agent The reducing agent be supplied would be discharged from the exhaust purifying catalyst 24 without being or oxidized without reducing the NO _X in. On the other hand, when the inlet temperature Tu is higher than the upper threshold UT and the outlet temperature Td is higher than the upper threshold UT, it can be determined that the temperature of the entire exhaust purification catalyst 24 is higher than the upper threshold UT. When the inlet temperature Tu is lower than the lower threshold LT and the outlet temperature Td is lower than the lower threshold LT, the exhaust purification catalyst 24
It can be determined that the overall temperature is lower than the lower threshold LT. Therefore, in this embodiment, Tu> UT and T
When d> UT, or when Tu <LT and Td <LT, the auxiliary fuel injection is stopped. Therefore, it is possible to effectively utilize the reducing agent for of the NO _X reduction.

FIG. 6 shows a routine for controlling the auxiliary fuel injection. This routine is executed, for example, in a main routine. With reference to FIG.
Then, it is determined whether the inlet temperature Tu is higher than the upper limit threshold value UT of the activation temperature of the exhaust gas purification catalyst 24 and the outlet temperature Td is higher than the upper limit threshold value UT. When Tu> UT and Td> UT, it is determined that the temperature of the entire exhaust purification catalyst 24 is higher than the limit threshold UT, and step 51 is performed.
To stop the auxiliary fuel injection. When Tu ≦ UT or Td ≦ UT, the process then proceeds to step 52,
The inlet temperature Tu is lower than the lower threshold LT of the activation temperature of the exhaust gas purification catalyst 24, and the outlet temperature Td is lower than the lower threshold L.
It is determined whether it is lower than T or not. Tu <LT and Td
When <LT, it is determined that the temperature of the entire exhaust purification catalyst 24 is lower than the lower threshold LT, and the routine proceeds to step 51, where the sub fuel injection is stopped. When Tu ≧ LT or Td ≧ LT, the routine proceeds to step 53, where the sub fuel injection is executed.

In the above-described embodiment, in order to supply the reducing agent to the catalyst 15, the auxiliary fuel is injected from the fuel injection valve 8 during the engine expansion stroke or the exhaust stroke. However, for example, a reducing agent injection valve is installed in the exhaust manifold 14, and from this reducing agent injection valve, for example, hydrocarbons such as gasoline, isooctane, hexane, heptane, light oil, and kerosene, or butane and propane which can be stored in a liquid state. , Or a secondary supply of hydrogen or carbon monoxide.

Further, the present invention can be applied to a spark ignition type engine. In this case, the reducing agent can be supplied to the catalyst 15 by temporarily making the air-fuel ratio of the air-fuel mixture burned in the combustion chamber 3 rich.

[0024]

The NO _X in the exhaust gas can be satisfactorily purified during engine transient operation, according to the present invention.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is an enlarged sectional view of a catalyst.

FIG. 3 is a partially enlarged view of the sectional view of FIG. 2;

FIG. 4 is a diagram illustrating an exhaust gas purifying operation when the temperature of exhaust gas flowing into an exhaust gas purifying catalyst is reduced.

FIG. 5 is a diagram illustrating an exhaust gas purifying operation when the temperature of exhaust gas flowing into an exhaust gas purifying catalyst is increased.

FIG. 6 is a flowchart for executing sub fuel injection control.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 3 ... Combustion chamber 8 ... Fuel injection valve 14 ... Exhaust manifold 15 ... Catalyst 20 ... Carrier 21 ... Separation wall 22 ... Open passage 23 ... Closed passage 24 ... Exhaust purification catalyst 25 ... Auxiliary catalyst J ... Exhaust passage axis

Claims (3)

[Claims] 1. A engine internal combustion engine so as to reduce the NO _X by the reducing agent in the exhaust gas control catalyst by supplying a reducing agent to exhaust an exhaust gas purification catalyst disposed in the passageway,
The exhaust passage is divided into a pair of passages by a partition wall extending substantially in the axial direction of the exhaust passage, and the exhaust downstream end of one of the pair of passages is closed to form a closed passage by the one passage and the other end. By forming an open passage by the passage, and forming the separation wall from a permeable material, the exhaust gas flowing into the closed passage flows into the open passage after passing through the separation wall and merges with the exhaust flowing through the open passage. An exhaust gas purifying apparatus, wherein the exhaust gas purifying catalyst is arranged only on the inner wall surface of the open passage. 2. The exhaust gas purifying apparatus according to claim 1, comprising a plurality of the closed passages and the open passages, wherein the closed passages and the open passages are alternately and repeatedly arranged. 3. The exhaust gas purification apparatus according to claim 1, wherein the flow path resistance of the separation wall increases as approaching the exhaust downstream end.