JP2000282853A - Exhaust gas emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of ammonia peaks, while preventing deterioration of emission of NOx by interposing a storage reducing catalyst, a heat exchanger, an ammonia absorption material, and an exhaust gas switching valve in an exhaust system. SOLUTION: A storage reducing catalyst 14 is connected to a first switching valve 13, composed of a noble metal catalyst and a storage material, and provided with a capacity for storage-reducing NOx. A fourth exhaust pipe A1 is connected to an ammonia absorption material 25 for absorbing ammonia via a second pipe connecting member 23. The ammonia absorption material 25 is connected to a third switching valve 27 via a sixth exhaust pipe 26. A rich/lean cycle operation is performed by an engine using a storage reducing catalyst provided with the ammonia absorption material in an exhaust system. At this time, with respect to NOx stored at lean operation, ammonia peaks generated when there is much reducing component quantity at rich operation, can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine and an operation control method. More specifically,
The present invention relates to an exhaust gas purifying apparatus for a lean burn type internal combustion engine having a storage reduction catalyst interposed in an exhaust system, and an improvement in an operation control method thereof.

[0002]

2. Description of the Related Art A lean burn engine is an engine having high efficiency and advantageous in terms of energy saving and emission of carbon dioxide. However, it is difficult to use a conventional three-way catalyst because of its high oxygen concentration in exhaust gas. Can not. Therefore, in recent years, as a NOx reduction catalyst for lean burn engines,
A storage reduction type catalyst has been proposed.

[0003] The storage reduction catalyst stores NOx when the exhaust gas is lean, and releases the stored NOx when the exhaust gas is rich or stoichiometric.
It has the characteristic of reducing released NOx.
Since the amount of occlusion in the lean state is finite, it is necessary to release, reduce and remove occluded NOx before the occluding agent is saturated. For this reason, a technique has been proposed in which the lean burn engine is temporarily operated in a rich or stoichiometric manner, and a rich / lean cycle operation is performed to form a NOx occlusion, release and reduction cycle, thereby reducing NOx.

In the above-described rich (or stoichiometric) state, the stored NOx is reduced by using a three-way catalyst. In the three-way catalyst, NOx is reduced when the oxygen in the exhaust gas is at a very low concentration. However, there is a problem that ammonia is generated when the reduction ability of the catalyst is very strong or rich. . Therefore, even with the storage reduction catalyst,
When the rich amount in the cycle operation is deep or the rich time is long, and the total amount of the reduced amount in the rich exhaust gas is excessive compared with the stored NOx, the released N
There is a problem that the reduction of Ox and NOx in the exhaust gas proceeds excessively, and a peak of ammonia is generated. In order to suppress the generation of the ammonia peak, a method of accurately predicting the NOx concentration that changes depending on the load and the surrounding atmosphere, finely setting the time of the rich / lean cycle and the air-fuel ratio, and performing advanced feedback control, etc. A very precise control method is required to form a more appropriate lean / rich cycle. In particular, when the target NOx emission level is severe, a very high-performance control method is required, and it is difficult to realize the control method.

[0005]

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above-mentioned problems of the prior art, and it has been proposed that an engine using an occlusion reduction catalyst deteriorates NOx emission during lean / rich cycle operation. While trying to prevent
It is an object of the present invention to provide an exhaust gas purifying apparatus and an operation control method for an internal combustion engine capable of preventing the occurrence of an ammonia peak.

[0006]

An internal combustion engine according to the present invention is a lean burn type internal combustion engine which switches between a storage reduction catalyst, a heat exchanger, an ammonia adsorbent, and a flow path of exhaust gas of the internal combustion engine. The valve is interposed in the exhaust system.

Further, the operation control method for an internal combustion engine according to the present invention
In a lean burn type internal combustion engine, the exhaust system of the internal combustion engine is provided with a storage-reduction catalyst, a heat exchanger, and an ammonia adsorbent, and heats exhaust gas passing through the storage-reduction catalyst during lean operation. A lean operation process in which the exchanger passes but the ammonia adsorbent does not pass and the exhaust gas is discharged out of the system, and an exhaust gas that has passed through the storage reduction catalyst during rich operation passes through the heat exchanger and passes through the ammonia adsorbent And a rich operation step of discharging the gas to the outside of the system.

Further, in order to desorb the ammonia adsorbed on the ammonia adsorbent, a predetermined time or a predetermined number of times when the internal combustion engine is subjected to a rich / lean cycle operation,
It is characterized by including a regeneration step in which exhaust gas that does not pass through the heat exchanger during the lean operation is allowed to pass through the ammonia adsorbent. The exhaust gas that has passed through the ammonia adsorbent in the regeneration step is configured to flow in front of the storage reduction catalyst.

The exhaust system of the internal combustion engine is provided with a switching valve for switching a flow path of exhaust gas of the internal combustion engine, and the lean operation step, the rich operation step, and the regeneration step are performed in the same manner. It is preferably performed by switching a switching valve.

In carrying out the operation control method for an internal combustion engine of the present invention, for example, a synthetic zeolite can be used as the ammonia adsorbent.

According to the present invention having the above-described structure, when performing the rich operation, the switching valve is appropriately opened and closed so that the exhaust gas passing through the storage reduction catalyst passes through the exhaust gas heat exchanger. After passing through the ammonia adsorbent. Therefore, when the rich operation is switched, the ammonia generated by the reduction by the excess reducing component is removed by adsorption when passing through the ammonia adsorbent. Therefore, emission of ammonia is suppressed (or prevented).

Here, the adsorbent has a reduced adsorbing capacity under a high temperature environment. In the present invention, when adsorbing ammonia, the adsorbent is passed through the exhaust gas heat exchanger before the adsorbent and the exhaust gas temperature is lowered, so that the ammonia adsorption efficiency is increased. Since the exhaust gas heat exchanger is a component originally used in a stationary cogeneration gas engine or a gas engine heat pump, it does not add a new component.

When the ammonia adsorbent adsorbs more than a predetermined amount of ammonia, it saturates and does not adsorb and remove more ammonia. Therefore, when the engine is operated lean, the exhaust gas is periodically discharged. A part is passed through the adsorbent without passing through the exhaust gas heat exchanger (that is, at a high temperature) to desorb the adsorbed ammonia. At this time, the adsorbent passing gas containing the desorbed ammonia is returned to the position before the storage reduction catalyst. As a result, the desorbed ammonia is oxidized by the storage reduction catalyst and stored as NOx in the storage reduction catalyst, so that the ammonia is not released out of the exhaust system.

[0014] When the NOx emission level is to be made very low with the occlusion reduction catalyst, the time of the rich / lean cycle is shortened, and the NOx occluded during the short lean time is almost completely released and reduced at the time of the rich operation. The goal cannot be achieved. N completely absorbed when rich
Since the release and reduction of Ox must be performed, a peak of ammonia occurs when the NOx concentration changes during lean operation or when the amount of the reducing component increases during the rich operation. Therefore, a technique for predicting the NOx concentration at the time of lean and the amount of the reducing component at the time of rich, and a highly accurate feedback control are required. In addition, when the lean time is shortened, ammonia is generated unless the rich time is shortened in response to the lean time.However, when using gaseous fuel such as a gas engine, the response of the air-fuel ratio adjustment valve is poor and the rich time is reduced. There is a limit to shortening. In the present invention, these problems are solved because ammonia is removed by the adsorbent.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an internal combustion engine and an operation control method according to the present invention will be described below with reference to the drawings.

FIG. 1 shows the structure of an exhaust gas treatment apparatus 2 according to the present invention. A first exhaust pipe 12 that guides exhaust gas Eg from an internal combustion engine (not shown) (for example, a lean burn gas engine) includes:
It is connected to the storage reduction catalyst 14 via a third pipe connecting member 30 described later. The storage reduction catalyst 14 is connected to the first switching valve 13, and the first switching valve 13 is connected to the second switching valve 13.
Are connected to both the exhaust pipe B1 and the fourth exhaust pipe A1. The storage reduction catalyst 14 is composed of, for example, a noble metal catalyst such as platinum or rhodium and a storage material such as alkali or alkaline earth, and has the ability to store and reduce NOx. The second exhaust pipe B1 is connected to a second switching valve 18 via an exhaust gas heat exchanger 16.

The exhaust gas heat exchanger 16 is configured to cool the exhaust gas Eg by heat exchange with cooling water flowing inside.

The second switching valve 18 is connected to a third exhaust pipe D
1 and a fifth exhaust pipe C1, and one third exhaust pipe D1 is connected to a muffler (not shown) via a first pipe coupling member 19.

The fourth exhaust pipe A1 is connected to the second pipe connecting member 2
Ammonia adsorbent 25 that adsorbs ammonia through 3
(For example, synthetic zeolite). The ammonia adsorbent 25 passes through the sixth exhaust pipe 26 to the third
Is connected to the switching valve 27. One of the third switching valves 27 is connected to the third pipe connecting member 19 via a sixth exhaust pipe F1, and the other is connected to the third pipe connecting member 30 via a reflux pipe E1. ing. Reflux tube E1
, A pump or the like (not shown) that presses the recirculated exhaust gas may be attached.

The operation of the above configuration will be described mainly with reference to the flowchart shown in FIG. Engine is operating in normal rich / lean cycle lean operation
(Step S1). The flow of the exhaust gas Eg in this case is
As shown by the bold line in FIG. 2, the NOx enters the storage reduction catalyst 14 from the first exhaust pipe 12 and is stored in the storage reduction catalyst 14. Then, it is determined whether the time of the lean operation has been continued for the predetermined time α (step S2).

If the predetermined time has not been reached, NO is selected and step S2 is repeated. If the lean operation has reached the predetermined time α, the pipe route is switched in step S3. At this time, the first, second, and third switching valves 13, 18, and 27 are switched so that the second, fifth, and sixth exhaust pipes B1, C1, F
1 is opened to allow the exhaust gas Eg to flow as shown in bold in FIG.

In step S4, it is determined whether a predetermined time β has elapsed in the state of step 3. If the predetermined time has not been reached, NO is selected and step S3 is repeated. If the predetermined time β has been reached, step S5 switches the engine to the rich operation. Here, the predetermined time β corresponds to a delay in switching the switching valve, and a value corresponding to the opening / closing speed of the valve is selected.

In step S6, it is determined whether the rich operation has continued for a predetermined time γ, and if NO, S6 is repeated.
If YES, proceed to step S7. In step S7,
It is determined whether or not it is in the playback mode. Here, the regeneration mode is for regenerating the ammonia adsorbent 25. Since the adsorbed ammonia gradually becomes saturated, the ammonia adsorbent 25 periodically flows a high-temperature gas (in the case of this control, a lean exhaust gas that does not pass through an exhaust gas heat exchanger) to remove the adsorbed ammonia. There is a need.
Therefore, although a flowchart is not shown here, when the operation time or the number of times of switching between rich and lean reaches a predetermined value, it is determined that the mode is the regeneration mode.

If NO is determined in step S7, the first, second, and third switching valves 13, 1 are determined in step S8.
8, 27, and the second and third exhaust pipes B1, D1
And exhaust gas Eg flows as shown in FIG. Then, the process returns to step S1, and the lean operation is performed again. At this time, a standby time determined by the opening / closing speed of the valve may be provided as in the case of the lean-to-rich switching.

If it is determined in step S7 that the reproducing mode is set, the process proceeds to step S9, in which the first, second, and third switching valves 13, 18, and 27 are switched, and the fourth, fourth, and fourth switching valves are switched.
The second and third exhaust pipes A1, B1, D1 and the recirculation pipe E1 are opened so that the exhaust gas Eg flows as shown in bold in FIG. Next, in step S10, the engine is operated lean. At this time, a part of the high-temperature lean exhaust gas flows through the ammonia adsorbent 25, so that the adsorbed ammonia is desorbed and flows to the storage reduction catalyst 14. The desorbed ammonia is oxidized by the storage reduction catalyst 14 and stored in the storage reduction catalyst 14 as NOx. When a predetermined amount of gas does not flow through the reflux pipe E1, a device such as a pump for applying pressure is provided in the middle of the reflux pipe E1.

In step S11, it is determined whether a predetermined time α has elapsed in the lean operation. If NO, S10 is repeated. If YES, the process proceeds to step S12, and the regeneration mode is cleared, that is, the above-described ammonia adsorbent 25 is removed. The time since the reproduction or the number of rich / lean cycles is set to zero. Then, the process proceeds to step S3.

Here, it should be noted that the illustrated embodiment is merely an example, and is not intended to limit the technical scope of the present invention.

[0028]

The effects of the present invention are listed below. (1) Since the exhaust system is equipped with an ammonia adsorbent,
When the rich / lean cycle operation is performed by the engine using the storage reduction catalyst, the ammonia peak generated when the amount of the reduced component during the rich operation becomes large with respect to the NOx occluded during the lean operation. Can be suppressed. (2) The regeneration operation can prevent the ammonia adsorbent from being saturated. During the regeneration operation, the desorbed ammonia is stored in the storage reduction catalyst and is not released to the atmosphere. (3) As described above, ammonia is adsorbed by the ammonia adsorbent and the ammonia peak is suppressed, so that it is not necessary to precisely control the ratio of the rich / lean cycle rich operation. (4) Since an exhaust gas heat exchanger is used, ammonia can be adsorbed with high adsorption efficiency. In the regeneration of the ammonia adsorbent, high-temperature exhaust gas passes therethrough, so that the adsorbed ammonia can be efficiently desorbed. (5) Since a conventionally used heat exchanger or the like can be used as it is, there is little factor of cost increase.

[Brief description of the drawings]

FIG. 1 is a block diagram of an exhaust system showing an embodiment of the present invention.

FIG. 2 is a diagram showing a flow of exhaust gas during a lean operation.

FIG. 3 is a diagram showing a flow of exhaust gas during a rich operation.

FIG. 4 is a diagram showing a flow of exhaust gas for regenerating an ammonia adsorbent.

FIG. 5 is a flowchart showing an operation control method according to the present invention.

[Explanation of symbols]

 Eg ··· Exhaust gas B1 ················································································································· 2. Exhaust gas treatment device 12. First exhaust pipe 13. First switching valve 14. NOx storage catalyst device 16. Exhaust gas heat exchanger 18. Second switching valve 19 ... First pipe connecting member 23 Second pipe connecting member 25 Ammonia adsorbent 26 Sixth exhaust pipe 27 Third switching valve 30 Third pipe connecting member

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 41/04 305 F02D 41/04 305Z

Claims (9)

[Claims] In an exhaust gas purifying apparatus for a lean burn internal combustion engine, an exhaust system includes an occlusion reduction catalyst, a heat exchanger, an ammonia adsorbent, and a switching valve for switching a flow path of exhaust gas of the internal combustion engine. An exhaust gas purifying device for an internal combustion engine, wherein the device is interposed. 2. An operation control method for a lean-burn internal combustion engine, wherein an exhaust system of the internal combustion engine is provided with a storage-reduction catalyst, a heat exchanger, and an ammonia adsorbent, and performs rich / lean cycle operation. During the lean operation, the exhaust gas that has passed through the storage reduction catalyst passes through the heat exchanger but does not pass through the ammonia adsorbent and is discharged outside the system, and the exhaust gas that has passed through the storage reduction catalyst during rich operation is A rich operation step of exhausting the system after passing through a heat exchanger and passing through an ammonia adsorbent. 3. The exhaust gas purifying apparatus according to claim 1, wherein
The exhaust system of the internal combustion engine is provided with a storage-reduction catalyst, a heat exchanger, and an ammonia adsorbent, and exchanges heat with the exhaust gas passing through the storage-reduction catalyst during the lean / lean cycle lean operation. The exhaust gas passes through the heat exchanger and passes through the ammonia adsorbent after the exhaust gas passes through the heat exchanger during rich operation. An exhaust gas purifying apparatus for an internal combustion engine, wherein the exhaust gas purifying apparatus is configured to be discharged outside the system. 4. An operation control method for a lean-burn internal combustion engine, wherein the exhaust system of the internal combustion engine is provided with a storage-reduction catalyst, a heat exchanger, and an ammonia adsorbent. A regeneration step in which exhaust gas that does not pass through the heat exchanger is allowed to pass through the ammonia adsorbent when the rich / lean cycle operation of the internal combustion engine has been performed for a predetermined time during the lean operation or a predetermined number of times in order to desorb the ammonia. An operation control method for an internal combustion engine, comprising: 5. The exhaust gas purifying apparatus according to claim 3, wherein
The exhaust system of the internal combustion engine is provided with a storage reduction catalyst, a heat exchanger, and an ammonia adsorbent, and the internal combustion engine is operated for a predetermined time or a predetermined number of times to desorb the ammonia adsorbed on the ammonia adsorbent. An exhaust gas purifying apparatus for an internal combustion engine, wherein exhaust gas not passing through a heat exchanger during lean operation is allowed to pass through an ammonia adsorbent when performing a rich / lean cycle operation. 6. An operation control method for an internal combustion engine using lean combustion, wherein the exhaust gas that has passed through the ammonia adsorbent in the regeneration step is caused to flow in front of the storage reduction catalyst. 7. The exhaust gas purifying apparatus according to claim 5, wherein
An exhaust gas purifying apparatus for an internal combustion engine, wherein the exhaust gas that has passed through the ammonia adsorbent during the regeneration is configured to flow in front of the storage reduction catalyst. 8. An operation control method for an internal combustion engine, wherein the control method according to claim 2, 4, or 7 is used for an internal combustion engine that recovers or cools exhaust gas. 9. An exhaust gas purifying apparatus for an internal combustion engine, wherein the exhaust gas purifying apparatus according to claim 1, 3, 5, or 7 is used for an internal combustion engine that recovers or cools exhaust gas.