JP2005155359A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of suppressing poisoning of NOx retention material by CO<SB>2</SB>. <P>SOLUTION: The exhaust emission control device is provided with an exhaust emission control means 8 arranged in an exhaust gas passage 5 of the internal combustion engine 1 and including NOx retention material 13 capable of retaining NOx and a CO<SB>2</SB>reduction means 7 arranged to reduce CO<SB>2</SB>in exhaust gas flowing in the NOx retention material. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine that purifies exhaust gas using a holding material capable of holding NOx, such as an NOx storage reduction catalyst.

An internal combustion engine exhaust gas purification apparatus is known in which an NOx absorbent that absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean and releases NOx absorbed when the oxygen concentration in the inflowing exhaust gas decreases is disposed in the engine exhaust passage. (See Patent Document 1). In addition, Patent Documents 2 to 4 and Non-Patent Document 1 exist as prior art documents related to the present invention.
Japanese Patent No. 2658757 JP 11-262632 A JP-A-6-346768 JP-A-6-336914 Toshiba Review Vol. 56, no. 8 (2001) p. 11-14

NOx holding materials such as NOx absorbents and NOx storage reduction catalysts adsorb CO ₂ in the exhaust as well as NOx. The adsorbed CO ₂ forms carbonate in the NOx holding material. This carbonate poisons the NOx holding material and inhibits the adsorption of NOx, thereby reducing the NOx holding performance.

Accordingly, an object of the present invention is to provide an exhaust purification device for an internal combustion engine capable of suppressing poisoning of a NOx holding material by CO ₂ .

The exhaust gas purification apparatus for an internal combustion engine of the present invention reduces exhaust gas purification means having a NOx holding material that is disposed in an exhaust passage of the internal combustion engine and can hold NOx, and CO ₂ in the exhaust gas flowing into the NOx holding material. The above-described problem is solved by providing the CO ₂ reduction means arranged in this way (Claim 1).

According to the exhaust purification system of the present invention, it is possible to reduce CO ₂ in the exhaust gas flowing into the NOx retention member by CO ₂ reduction unit. Therefore, poisoning of the NOx holding material by CO ₂ can be suppressed.

The exhaust emission control device of the present invention may be provided with a CO ₂ absorption / release material that absorbs CO ₂ in the first state and releases CO ₂ in the second state as the CO ₂ absorbing means (claim). Item 2). It is possible to absorb CO ₂ in the exhaust to a first state of the CO ₂ absorbing material, it is possible to reduce the CO ₂ in the exhaust gas flowing into the NOx retention member.

In the exhaust emission control device of the present invention, the CO ₂ absorption / release material may be disposed so as to reduce CO ₂ in the exhaust gas flowing into the exhaust gas purification means into the exhaust passage. By arranging the CO ₂ absorption / release material and the exhaust gas purification means in the exhaust passage in this way, a large number of CO ₂ absorption / release materials can be arranged.

In the exhaust purification apparatus of the present invention, the CO ₂ absorption / release material may be carried integrally with the NOx holding material on the exhaust purification means (claim 4). Thus, the exhaust purification device can be made compact by carrying the CO ₂ absorption / release material and the NOx holding material integrally with the exhaust purification means. Thereby, the mountability of the exhaust emission control device can be improved.

The exhaust purification apparatus of the present invention is provided with an NOx storage material as an NOx holding material, in which the air-fuel ratio of the inflowing exhaust gas is set to stoichiometric or rich, and the function is restored when heated to a predetermined temperature or higher. The function of the NOx catalyst may be regenerated at the time of CO ₂ release of the CO ₂ absorption / release material (Claim 5). In the functional regeneration, since such NOx and sulfur that was stored (S) is released from the NOx storage reduction catalyst, CO ₂ is not adsorbed to the NOx catalyst. Therefore, by reproducing the function of the NOx catalyst at the time of CO ₂ emission of CO ₂ absorbing material, to suppress the poisoning of the NOx catalyst by the CO ₂ released from without CO ₂ absorbing material providing the additional equipment it can.

When CO ₂ is released from the CO ₂ absorption / release material (when CO _{2 is} released), the exhaust temperature rises depending on the intentional release of CO ₂ and the operating state of the internal combustion engine. This includes both the case where CO ₂ has been released without being released.

In the exhaust emission control device of the present invention, an NOx storage reduction catalyst is provided as the NOx holding material, in which the air-fuel ratio of the inflowing exhaust gas is set to stoichiometric or rich and is heated to a predetermined temperature or more to regenerate the function. The first state and the second state are associated with different temperature ranges, and at the time of function regeneration of the NOx catalyst, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is set to stoichiometric or rich. Then, the NOx catalyst may be heated to the predetermined temperature or higher (Claim 6). When the air-fuel ratio of the exhaust is set to stoichiometric or rich after heating the NOx catalyst to a predetermined temperature or higher, the temperature of the CO ₂ absorption / release material becomes the second temperature range due to the heating effect of the NOx catalyst, and the NOx catalyst There is a possibility that CO ₂ released from the CO ₂ absorption / release material before flowing into the function regeneration state flows into the NOx catalyst. Therefore, first set the air fuel ratio of the exhaust gas to stoichiometric or rich, then to heat the NOx catalyst than a predetermined temperature, it is possible to reproduce the function of the NOx catalyst at the time of CO ₂ emission of CO ₂ absorbing material. Therefore, poisoning of the NOx catalyst by CO ₂ can be suppressed.

The exhaust gas purification apparatus of the present invention is disposed downstream of the CO ₂ absorption / release material, bypassing the exhaust gas purification means to guide the exhaust gas downstream, and the flow of exhaust gas to the exhaust gas purification means and the bypass passage The bypass valve may switch the flow of exhaust gas to the bypass passage when CO _{2 is} released from the CO ₂ absorption / release material. In this case, CO ₂ since absorbing materials of CO ₂ bypass valve upon release leads to exhaust to bypass the exhaust gas purification unit downstream, preventing the flow of the CO ₂ absorbing materials CO ₂ in the NOx retention material released from can do. Therefore, poisoning of the NOx holding material by CO ₂ can be suppressed.

Exhaust purification system of the present invention, the CO ₂ absorbing material, a first exhaust stream flowing through the exhaust in the order of the NOx retention material, the NOx retention material, the CO ₂ absorbing material sequentially to the exhaust flows second of And at least one switching valve capable of selectively switching between the exhaust flow and the switching valve even when the exhaust flow is switched to the second exhaust flow when CO _{2 is} released from the CO ₂ absorption / release material. Good (claim 8). In this case, CO ₂ is switched to flow of exhaust when CO ₂ emission-absorbing material to a second exhaust stream, may be CO ₂ absorbing material is prevented from flowing into the NOx retention material of CO ₂ released. Further, since both the first exhaust flow and the second exhaust flow pass through the NOx holding material, it is possible to prevent the exhaust from being discharged to the outside as it is.

According to the present invention, since CO ₂ in the exhaust gas flowing into the NOx holding material can be reduced, poisoning of the NOx holding material by CO ₂ can be suppressed. Therefore, the NOx holding performance of the NOx holding material can be improved.

FIG. 1 shows an internal combustion engine to which an exhaust emission control device according to an embodiment of the present invention is applied. The internal combustion engine 1 of FIG. 1 is configured as a diesel engine including a plurality (four in FIG. 1) of cylinders 2. Each cylinder 2 is provided with an injector 3. An intake passage 4 and an exhaust passage 5 are connected to the internal combustion engine 1, and an exhaust purification device 6 is provided in the exhaust passage 5. The exhaust purification device 6 includes a CO ₂ absorption / release material 7 as CO ₂ reduction means and an exhaust purification catalyst 8 as exhaust purification means having an NOx storage reduction NOx catalyst 13 as NOx holding material. The NOx catalyst 13 sets the air-fuel ratio of the inflowing exhaust gas to a stoichiometric or rich state, and is heated to a predetermined regeneration temperature (for example, 600 ° C. to 650 ° C.) or higher to remove the adsorbed sulfur (S) and the like. Release and regenerate function. The exhaust passage 5 is connected to the intake passage 4 by an EGR passage 9 in order to return a part of the exhaust gas to the intake passage 4. The EGR passage 9 is provided with an EGR valve 10 for adjusting the EGR amount.

  The operating state of the internal combustion engine 1 is controlled by an engine control unit (ECU) 11. The ECU 11 is configured as a computer in which a microprocessor and peripheral devices such as ROM and RAM necessary for its operation are combined. For example, the ECU 11 controls the operation of the injector 3 so that fuel is supplied into the cylinder 2 at a predetermined timing. Further, when the internal combustion engine 1 is operated in an idling or low load state, the opening of the EGR valve 10 is increased to increase the flow rate of the exhaust gas supplied to the intake passage 4, and the combustion temperature of the internal combustion engine 1 is increased. Perform low-temperature combustion to reduce.

The CO ₂ absorption / release material 7 is mainly composed of a composite oxide of lithium such as lithium zirconate (Li ₂ ZrO ₃ ), for example, and absorbs CO ₂ in the first temperature range (for example, 400 degrees to 580 degrees). , A known one having the characteristic of releasing CO ₂ in the second temperature range (for example, 630 to 700 degrees).

ECU11 has exceeded a predetermined amount of CO ₂ absorbing material 7 CO ₂ amount absorbed by the (CO ₂ absorption amount) to determine when to release the CO ₂ absorbing material 7 of the CO ₂ (the emission turn a predetermined amount) case, by heating the CO ₂ absorbing material 7 to a second temperature range to release the CO ₂ from the CO ₂ absorbing material 7. FIG. 2 is a flowchart showing a CO ₂ release control routine executed by the ECU 11 to release CO ₂ from the CO ₂ absorption / release material 7. The control routine of FIG. 2 is repeatedly executed at a predetermined cycle during the operation of the internal combustion engine 1.

In the control routine of FIG. 2, the ECU 11 first calculates the total CO ₂ absorption amount (C _CO2 ) in step S11. The total CO ₂ absorption amount (C _CO2 ) is calculated by the following method, for example.
First, the exhaust gas flow rate and the CO ₂ amount in the exhaust gas are calculated from the fuel amount supplied to the internal combustion engine 1 and the intake air amount. Then, CO ₂ absorbing material and temperature of 7, an exhaust flow rate and the CO ₂ partial pressure in the calculated exhaust gas from the amount of CO ₂ in the exhaust, CO ₂ calculated in the control routine of FIG. 2 that the last run Based on the total amount of absorption, the absorption rate or release rate of CO ₂ of the CO ₂ absorption / release material 7 is specified. Thereafter, the current total CO ₂ absorption amount (C _CO2 ) is calculated based on the specified absorption rate or release rate and the total CO ₂ absorption amount calculated in the previous control routine.

Next, in step S12, the ECU 11 determines whether or not the total CO ₂ absorption amount (C _CO2 ) has exceeded a predetermined release start amount (C ₁ ). If it is determined that the discharge start predetermined amount (C ₁ ) has not been exceeded, the current control routine is terminated.

On the other hand, if it is determined that the release start predetermined amount (C ₁ ) has been exceeded, the process proceeds to step S13, where the ECU 11 makes the air-fuel ratio of the exhaust stoichiometric or rich and the NOx catalyst 13 is heated to a predetermined regeneration temperature. Thus, the exhaust gas temperature is raised to regenerate the function of the NOx catalyst 13. When the NOx catalyst 13 is poisoned by S contained in the exhaust gas, the NOx retention performance of the NOx catalyst 13 poisoned by S deteriorates. Therefore, when the NOx catalyst 13 is poisoned by a predetermined amount of S, the NOx catalyst 13 is heated to a predetermined regeneration temperature and the air-fuel ratio of the exhaust is stoichiometric or rich so that the S adsorbed on the NOx catalyst 13 is absorbed. And the function of the NOx catalyst 13 is regenerated (S regeneration). When the function of the NOx catalyst 13 is regenerated, the ECU 11 first causes the internal combustion engine 1 to perform low-temperature combustion to make the air-fuel ratio of the exhaust stoichiometric or rich, and then the main injection of fuel into the cylinder 2 by the injector 3 Thereafter, so-called post-injection in which fuel is additionally injected from the injector 3 into the cylinder 2 is performed to raise the exhaust gas temperature to a predetermined regeneration temperature.

In the next step S14 ECU 11 is a CO ₂ absorbing material 7 is raised to a second temperature range, to release CO ₂ from the CO ₂ absorbing material 7. Thereafter, the current control routine is terminated.

Thus CO ₂ absorbing material during CO ₂ release of 7 by regenerating the function of the NOx catalyst 13, it is possible to suppress the poisoning of the NOx catalyst 13 by the CO _2. Further, the amount of fuel consumed for heating can be reduced by simultaneously performing the CO ₂ release from the CO ₂ absorption / release material 7 and the functional regeneration of the NOx catalyst 13.

  The method for regenerating the function of the NOx catalyst 13 is not limited to the combination of low temperature combustion and post injection. For example, after causing the internal combustion engine 1 to perform low temperature combustion, the function of the NOx catalyst 13 is performed by performing so-called VIGOM injection in which fuel is injected from the injector 3 into the cylinder 2 from the exhaust top dead center of the piston to the initial stage of the intake stroke. May be played back. In this case, post-injection may be further added, and the function of the NOx catalyst 13 may be regenerated by combining low-temperature combustion, VIGOM injection, and post-injection. Further, an addition injector for adding fuel to the exhaust gas may be provided in the exhaust passage 5, and the function of the NOx catalyst 13 may be regenerated by combining fuel addition by the addition injector and low-temperature combustion. Also in this case, the internal combustion engine 1 is first subjected to low temperature combustion, and then fuel is added to the exhaust. Further, when the internal combustion engine 1 has a low load, the air-fuel ratio of the exhaust gas can be made rich by causing the internal combustion engine 1 to perform low temperature combustion, and the exhaust gas temperature can be raised. Therefore, in this case, the function of the NOx catalyst 13 can be regenerated only by low temperature combustion.

The arrangement method of the CO ₂ absorption / release material 7 is not limited to the method shown in FIG. For example, as shown in FIGS. 3 and 4, the CO ₂ storage / release material 7 and the NOx storage reduction catalyst 13 may be integrally supported on the carrier 12 of the exhaust purification catalyst 8.

When the flow of exhaust gas in the exhaust purification catalyst 8 is a straight flow (flow in the direction of arrow A in FIGS. 3A and 3B), the NOx catalyst 13 is supported on the carrier 12 as shown in FIG. The CO ₂ absorption / release material 7 is supported on the NOx catalyst 13. By disposing the NOx catalyst 13 and the CO ₂ absorption / release material 7 in this manner, the exhaust gas with reduced CO ₂ can flow into the NOx catalyst 13. Further, as shown in FIG. 3 (b), the NOx catalyst 13 having a CO ₂ absorbing material 7 is supported on the carrier 12 may be on to further carry the CO ₂ absorbing material 7 thereof.

When the flow of exhaust gas in the exhaust purification catalyst 8 is a wall flow (flow in the direction of arrow B in FIG. 4), the CO ₂ adsorbing / releasing material 7 is placed on one side of the carrier 12 as shown in FIG. The NOx storage reduction catalyst 13 is supported. By thus carrying CO ₂ absorbing material 7, it is possible to reduce the CO ₂ in the exhaust gas flowing into the NOx catalyst 13.

In this way, the exhaust purification device 6 can be made compact by carrying the NOx catalyst 13 and the CO ₂ absorption / release material 7 integrally on the carrier 12 of the exhaust purification catalyst 8.

The inflow of CO ₂ released from the CO ₂ absorption / release material 7 into the exhaust purification catalyst 8 can also be prevented by changing the exhaust flow in the exhaust passage 5. For example, as shown in FIG. 5, the exhaust gas purification catalyst 8 is disposed between the bypass passage 14 that bypasses the exhaust gas purification catalyst 8 and leads the exhaust gas downstream, and the CO ₂ absorption / release material 7 and the exhaust gas purification catalyst 8. And a bypass valve 15 that switches the flow of exhaust gas to the bypass passage 14 may be provided in the exhaust passage 5, and the flow of exhaust gas may be switched to the bypass passage 14 when CO _{2 is} released from the CO ₂ absorption / release material 7.

Further, as shown in FIG. 6, the first exhaust flow (the exhaust gas flows between the internal combustion engine 1 and the CO ₂ absorption / release material 7 in the order of the CO ₂ absorption / release material 7 and the exhaust purification catalyst 8 ( Exhaust flow in the direction of arrow C in FIG. 6A) and second exhaust flow in which exhaust flows in the order of the exhaust purification catalyst 8 and the CO ₂ absorption / release material 7 (exhaust flow in the direction of arrow D in FIG. 6B). A switching valve 16 that can selectively switch between and may be provided.

The operation of the switching valve 16 in FIG. 6 is controlled by the ECU 11. FIG. 7 is a flowchart showing a CO ₂ release control routine executed by the ECU 11 of FIG. 6 to release CO ₂ from the CO ₂ absorption / release material 7. The control routine of FIG. 7 is repeatedly executed at a predetermined cycle during the operation of the internal combustion engine 1. In FIG. 7, the same processes as those in FIG. 2 are denoted by the same reference numerals, and the description thereof is omitted.

In the control routine of FIG. 7, ECU 11 first calculates the CO ₂ absorbing materials for CO ₂ absorption amount _{(C CO2)} at step S11. In step S12, the next ECU 11 determines whether or not the CO ₂ absorption total amount (C _CO2 ) is larger than the predetermined amount (C ₁ ) for starting the release. When it is determined that the total CO ₂ absorption amount is equal to or less than the predetermined amount at the start of release, the process proceeds to step S21, and the ECU 11 operates to the switching valve 16 so that the exhaust flow becomes the first exhaust flow shown in FIG. Instruct. Thereafter, the current control routine is terminated.

On the other hand, when it is determined that the total CO ₂ absorption amount is larger than the predetermined amount at the start of release, the process proceeds to step S22, where the ECU 11 switches the switching valve 16 so that the exhaust flow becomes the second exhaust flow shown in FIG. Instruct the operation. In subsequent step S13, the ECU 11 regenerates the function of the NOx catalyst 13. In the next step S14, ECU 11 is a CO ₂ absorbing material 7 is raised to a second temperature range, to release CO ₂ from the CO ₂ absorbing material 7. Thereafter, the current control routine is terminated.

Thus, CO ₂ upon release of the CO ₂ absorbing material 7, an exhaust gas purification by passing an exhaust in the order of the catalyst 8, CO ₂ absorbing material 7, CO ₂ absorbing material 7 of the CO ₂ released from the exhaust Inflow to the purification catalyst 8 can be prevented. Further, it is possible to prevent the exhaust from the internal combustion engine 1 from being discharged to the outside as it is. In FIG. 6, the exhaust flow is switched by one switching valve 16, but the first exhaust flow and the second exhaust flow may be switched by combining two or more valves.

  The present invention is not limited to the above-described embodiments, and may be implemented in various forms. For example, the internal combustion engine 1 is not limited to a diesel engine, and the present invention can also be applied to a gasoline engine. The exhaust purification catalyst is not limited to the one in which the NOx storage reduction catalyst is supported on the carrier, and various exhaust purification catalysts can be applied. For example, a filter substrate for collecting particulates may be used in which an NOx storage reduction catalyst material is supported. The NOx occlusion in the NOx catalyst is not limited as long as it can hold NOx.

The figure which shows the internal combustion engine to which the exhaust emission control device which concerns on one Embodiment of this invention was applied. Flowchart illustrating the CO ₂ release control routine by the ECU in FIG. 1 executes. Figure the NOx catalyst and CO ₂ absorbing material shows an embodiment of an exhaust gas purification catalyst supported integrally. Figure the NOx catalyst and CO ₂ absorbing material is shown another embodiment of an exhaust gas purification catalyst supported integrally. The figure which shows 2nd embodiment of the exhaust gas purification apparatus of this invention. The figure which shows 3rd embodiment of the exhaust gas purification apparatus of this invention. Flowchart illustrating the CO ₂ release control routine executed by the ECU of FIG.

Explanation of symbols

1 engine 5 exhaust passage 6 exhaust gas purifier 7 CO ₂ absorbing material (CO ₂ reduction means)
8 Exhaust gas purification catalyst (exhaust gas purification means)
13 NOx storage reduction catalyst (NOx retention material)
14 Bypass passage 15 Bypass valve 16 Switching valve

Claims (8)

Exhaust purification means having a NOx holding material arranged in the exhaust passage of the internal combustion engine and capable of holding NOx; CO ₂ reduction means arranged to reduce CO ₂ in the exhaust flowing into the NOx holding material; An exhaust emission control device for an internal combustion engine, comprising: _2. The internal combustion engine according to claim 1, wherein a CO ₂ absorbing / releasing material that absorbs CO _{2 in a} first state and releases CO _{2 in a} second state is provided as the CO ₂ reducing means. Engine exhaust purification system. _3. The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the CO ₂ absorption / release material is disposed so as to reduce CO ₂ in the exhaust gas flowing into the exhaust gas purification means in the exhaust passage. . The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the CO ₂ absorption / release material is carried integrally with the NOx holding material on the exhaust gas purification means. An NOx storage reduction catalyst that regenerates the function by setting the air-fuel ratio of the inflowing exhaust to stoichiometric or rich and being heated to a predetermined temperature or higher is provided as the NOx holding material,
5. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the function of the NOx catalyst is regenerated when CO _{2 is} released from the CO ₂ absorption / release material. An NOx storage reduction catalyst that regenerates the function by setting the air-fuel ratio of the inflowing exhaust to stoichiometric or rich and being heated to a predetermined temperature or higher is provided as the NOx holding material,
The first state and the second state are associated with different temperature ranges,
4. The function regeneration of the NOx catalyst, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is set to stoichiometric or rich, and then the NOx catalyst is heated to the predetermined temperature or higher. 5. An exhaust emission control device for an internal combustion engine according to 4. A bypass passage that bypasses the exhaust purification means and guides the exhaust downstream; a bypass valve that is disposed downstream of the CO ₂ absorption / release material and can switch the flow of exhaust gas to the exhaust purification means and the bypass passage; With
The bypass valve, the exhaust purification system of an internal combustion engine according to the flow of exhaust when CO ₂ emission of the CO ₂ absorbing material in claim 3, characterized in that switching to the bypass passage. The CO ₂ absorbing material, a first exhaust stream flowing through the exhaust in the order of the NOx retention material, the NOx retention material, the CO ₂ absorbing and releasing a second exhaust stream flowing through the exhaust in the order of design, selectively the Comprising at least one switching valve that can be switched;
4. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the switching valve switches an exhaust flow to the second exhaust flow when CO _{2 is} released from the CO ₂ absorption / release material.

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