JP2002349254A - Exhaust emission control device for internal combustion engine and its controlling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine and its controlling method which can prolong a life of a catalyst provided in an exhaust pipe of the internal combustion engine such as a lean fuel type gas engine. SOLUTION: A hydrocarbon oxidation catalyst (40B) and an NOx occlusion and reduction catalyst (40B) are arranged in series in an exhaust system (15), and the NOx occlusion and oxidation catalyst (40B) is arranged close to the internal combustion engine (10).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine such as a lean burn type engine. More specifically, the present invention relates to hydrocarbon oxidation catalysts (eg, methane oxidation catalysts) and NO
The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine having an x storage reduction catalyst interposed in an exhaust pipe and a control method thereof.

[0002]

2. Description of the Related Art Exhaust gas emitted from automobiles, aircraft, thermal power plants, various factories, etc. includes nitrogen oxides (NOx) and sulfur oxides (SOx), odorous substances and dust, and unburned (unburned) ) Hydrocarbons (HC). Various measures have been taken for exhaust gases including these, and further research and development have been promoted. Conventionally, gas engines,
In gas turbines, boilers, or heating furnaces, methane, ethane, propane,
Fuel gas containing butane and the like is used, and a lean burn system has been applied in order to increase the combustion efficiency and heat efficiency. These points are the same for a cogeneration system (CGS) capable of simultaneously supplying heat and electricity and a lean burn gas engine in a gas engine heat pump (GHP) used for air conditioning. Exhaust gas of such a lean burn gas engine contains a large amount of oxygen and coexists with lower unburned hydrocarbons including NOx, CO, and methane.

At present, a three-way catalyst is used as a method of purifying exhaust gas in a stoichiometric gas engine. The three-way catalyst can efficiently remove NOx, CO, and unburned hydrocarbons in an extremely narrow air-fuel ratio range (catalyst window) near stoichiometry. However, in the exhaust gas of a lean combustion gas engine, not only the purification performance of NOx is extremely reduced, but also the purification performance of unburned lower hydrocarbons, especially methane, is reduced.

[0004] As a method of removing NOx in the lean combustion exhaust gas, a NOx storage reduction catalyst, ammonia (urea)
A system using a denitration catalyst, an unburned hydrocarbon selective reduction catalyst, or the like has been proposed. Among them, the NOx storage reduction catalyst is obtained by adding a storage agent such as an alkali or alkaline earth to a three-way catalyst. When the exhaust gas is in a lean fuel state, the NOx storage reduction catalyst is NOx storage reduction catalyst.
Is characterized by the fact that the stored NOx is released when the fuel is excessive (rich) or in a stoichiometric state, and the released NOx is reduced.
It is known to have purification performance. However, since alkali and alkaline earth metals are used as occlusion materials,
The purification performance of lower unburned hydrocarbons, particularly methane, in lean burn exhaust gas is very low, and it is impossible to simultaneously remove NOx and lower unburned hydrocarbons.

Lower unburned hydrocarbons in lean burn exhaust gases,
In particular, as a method for removing methane, for example, palladium (Pd) alone or palladium (Pd) is used for palladium (Pd) alone or on a composite carrier of alumina (Al2O3) or zirconia (ZrO2). (Methane oxidation catalyst) to which rhodium (Rh) or the like is added has been proposed. However, because of the high chemical stability of methane, these proposed catalysts have very high noble metal loadings and are costly.

Further, there is a problem that the activity of the methane oxidation catalyst is also reduced at an early stage. The main causes of deterioration are thermal deterioration and sulfur poisoning by SOx contained in exhaust gas. In particular, when the temperature of the exhaust gas is low, sulfur poisoning is remarkable and the activity is remarkably reduced. In the lean burn gas engine used in CGS and GHP, the exhaust gas temperature is 35
Since the temperature is relatively low, that is, 0 to 450 ° C., an early decrease in activity due to sulfur poisoning is a serious problem.

FIG. 16 shows Pt and Pd (10 and 15 respectively).
g / liter) of a methane oxidation catalyst (SV = 30,000 hr-1) supported on alumina in a lean exhaust gas engine at 400 ° C. in lean exhaust gas. Under these conditions, before 100 hours had elapsed, the methane purification rate sharply decreased to about 20% due to sulfur poisoning.

[0008]

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above-mentioned problems of the prior art, and is an internal combustion engine of a type having a relatively low exhaust gas temperature, such as a lean burn gas engine. It is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine capable of extending the life of a methane oxidation catalyst interposed in an exhaust pipe of an internal combustion engine and simultaneously removing NOx, and an operation control method thereof.

[0009]

In connection with the above problems, we have obtained the following findings.

A. By periodically operating the lean-run engine rich, it is possible to suppress a decrease in the activity of the methane oxidation catalyst (lean / rich switching operation). b. Periodic treatment with high-temperature, rich to stoichiometric exhaust gas makes it possible to regenerate the activity of the sulfur-poisoned methane oxidation catalyst (regeneration operation). c. The NOx storage reduction catalyst used as the NOx removal catalyst during lean combustion has the ability to store not only NOx in the exhaust gas but also SOx. When the NOx storage reduction catalyst is used, a lean / rich switching operation is performed, and the NOx stored in the lean state is released when rich.
It is reduced and removed. Further, a high-temperature, rich to stoichiometric regeneration operation may be performed periodically to remove the stored SOx. d. When the methane oxidation catalyst is disposed downstream of the NOx storage reduction catalyst, during lean / rich operation performed by the NOx storage reduction catalyst, SOx is stored in the NOx storage catalyst in addition to the effect of a. The sulfur poisoning of the catalyst is reduced. e. When the methane oxidation catalyst is disposed downstream of the NOx storage reduction catalyst, the regeneration conditions of the NOx storage reduction catalyst are equal to the regeneration conditions of the methane oxidation catalyst. The regeneration of the oxidation catalyst can be performed at the same time.

A characteristic curve (A) in FIG. 17 shows that SO2 is added to a gas simulating a lean exhaust gas composition of a gas engine (lean simulated gas) so as to have a concentration 12 times that of the gas engine exhaust gas. It is the result of measuring the activity change of the methane oxidation catalyst at 400 ° C. The catalyst was the same as in FIG. 16 and measured at SV = 30,000 hr-1. The characteristic curve (B) is a measurement result when the lean simulation gas and the gas simulating the rich exhaust gas composition of the gas engine (rich simulation gas) are alternately flown at the same SO2 concentration. The methane purification rate is a value when a lean simulation gas is flowing during the treatment. As is clear from the results, by switching between lean and rich (lean / rich switching),
It can be seen that the decrease in the activity of the methane oxidation catalyst can be suppressed.
Therefore, it is possible to extend the life of the oxidation catalyst to methane.

FIG. 18 shows a methane oxidation catalyst (similar to FIG. 16) whose activity has been reduced by using an actual lean burn gas engine (constant lean operation) for about 500 hours.
400 after treatment with a rich simulated gas at 0 ° C. for 10 minutes
It shows the methane purification rate at SV = 30,000 hr-1 in a simulated lean gas at ℃. The results show that the activity recovers each time the treatment is performed with the high-temperature rich simulation gas (regeneration treatment). In this test, the regeneration treatment was performed with a rich exhaust gas composition, but it has been found that regeneration is effective even with high-temperature stoichiometric exhaust gas. That is, it is possible to extend the life of the methane oxidation catalyst by performing the regeneration process periodically during the lean operation.

Further, by combining the lean / rich switching and the reproduction processing, the life can be further extended. As shown by a characteristic curve (C) in FIG. 17, as a result of combining the lean / rich switching and the periodic reproduction processing,
It has been found that a decrease in the activity of the methane oxidation catalyst (hydrocarbon oxidation catalyst) can be further suppressed. In this test, the actual concentration of 12
Double SO2 is added, lean / rich switching is performed at 400 ° C., and regeneration processing is performed with a rich simulated gas at 600 ° C. for 10 minutes every 40 minutes.

Here, when the catalyst is treated at a high temperature, there is a concern about thermal deterioration. Therefore, using a real gas engine, a methane oxidation catalyst (similar to that shown in FIG. 16) was used for about 350 hours in a stoichiometric exhaust gas at
As a result of the 000 hr-1 treatment, the decrease in activity was small as shown in FIG. In the case of performing the main reproduction process, as shown by a characteristic curve (C) in FIG. 17, an effect appears in the reproduction process for about 10 minutes. Therefore, when the regular regeneration treatment is performed periodically, the time of exposure to high temperature while the methane oxidation catalyst is used does not become so long. Therefore, from the result of FIG.
It can be seen that the effect of thermal degradation is small.

Next, FIG. 20 shows the result when a methane oxidation catalyst is arranged downstream of the NOx storage reduction catalyst. Here, the methane oxidation catalyst used in FIGS. 17 to 20 was used in which the amount of noble metal was reduced to about １ ／. Comparative Example 1 in FIG. 20 uses only the methane oxidation catalyst, Comparative Example 2 uses only the NOx storage reduction catalyst, and alternately uses the lean simulation gas and the rich simulation gas to which SO2 is added so as to have a concentration 12 times that of the gas engine exhaust gas. The graph shows the respective methane purification rates after flowing at 400 ° C. for 1 hour (aging) and then performing a regeneration treatment with a rich simulation gas at 600 ° C. for 10 minutes (regeneration treatment). The example shows the methane purification rate when the methane oxidation catalyst is arranged downstream of the NOx storage reduction catalyst under the same processing conditions. The NOx storage reduction catalyst is Pt
/ Al2O3 obtained by adding potassium as a NOx occluding material was used. For each catalyst, SV = 30,
The test was performed at 000 hr-1. In Comparative Example 1, the methane purification rate was significantly reduced after aging (1
0.9%). In addition, the methane purification rate (39.1%) after the regeneration treatment is the same as the methane purification rate (4
4.1%). From Comparative Example 2, NO
It can be seen that the x storage reduction catalyst hardly provides methane purification performance. On the other hand, in the embodiment in which the methane oxidation catalyst is arranged downstream of the NOx storage reduction catalyst, the decrease in the activity after aging is small (43.7%), and the activity is almost restored to the initial activity by the regeneration treatment (50.1%). ).

FIG. 21 shows the results obtained when the above test was conducted.
x Indicates the purification rate. In the example, it can be seen that both the purification of NOx by lean / rich switching and the regeneration of sulfur poisoning with respect to the NOx storage capacity of the NOx storage reduction catalyst are sufficiently performed.

As described above, by arranging a small amount of methane oxidation catalyst downstream of the NOx storage reduction catalyst used in the lean burn engine, NOx and methane can be maintained for a long period of time without changing the control method and apparatus. Can be simultaneously removed. As a result, a low-cost simultaneous removal system of NOx and methane is realized by extending the life of the expensive methane oxidation catalyst and reducing the amount of use. At this time, if a sufficiently low NOx is achieved by leaning the engine, the NOx
Since there is no need to remove NOx by the storage reduction catalyst,
At the position of the Ox storage reduction catalyst, an SOx adsorption member (for example, Cu
/ A ₁₂ O ₃ ) to perform lean / rich switching operation and regeneration operation to reduce sulfur poisoning of the methane oxidation catalyst.

Based on such findings, the internal combustion engine of the present invention has a hydrocarbon oxidation catalyst (40B) and a NOx storage reduction catalyst (40A) interposed in series in the exhaust system. The NOx storage reduction catalyst (40A) is disposed on the near side (claim 1). Here, the hydrocarbon oxidation catalyst (40B) is preferably, for example, a methane oxidation catalyst. Further, an SOx adsorbing member may be provided instead of the NOx storage reduction catalyst (40A).

According to the present invention having such a configuration, NO
Since the x storage reduction catalyst is disposed on the internal combustion engine side of the hydrocarbon oxidation catalyst (for example, methane oxidation catalyst), SOx in the exhaust gas is stored by the NOx storage reduction catalyst, and the sulfur poisoning of the hydrocarbon oxidation catalyst is suppressed. Is done.

Further, hydrocarbons such as methane in the exhaust gas are removed by the hydrocarbon oxidation catalyst, and NOx is removed by the NOx storage reduction catalyst.
Ox will be removed at the same time.

If the NOx storage reduction catalyst stores SOx and the NOx storage possible amount decreases, a high-temperature regeneration operation is performed. At that time, the hydrocarbon oxidation catalyst is also regenerated at the same time. Therefore, by performing the regeneration treatment of the NOx storage reduction catalyst, the activity of the hydrocarbon oxidation catalyst can be maintained at a high level, and the life can be prolonged.

An operation control method for an internal combustion engine according to the present invention includes an internal combustion engine having the above-described configuration (10: for example, a lean-burn gas engine; the same applies hereinafter).
In the operation control method, the operation of the internal combustion engine (10) is performed while switching at a predetermined interval between an operation state in which the air-fuel mixture supplied to the internal combustion engine (10) is fuel-rich and an operation state in which the air-fuel mixture is fuel-lean. It is characterized by having a lean / rich switching operation step (Claim 4: FIGS. 1 to 3).

In order to execute the above-described operation control method, the internal combustion engine having the above configuration according to the present invention is provided with an internal combustion engine (1).
0) control means (30) for controlling the air-fuel ratio adjusting mechanism (18, 20) for adjusting the air-fuel ratio of the air-fuel mixture supplied to the air-fuel mixture; And lean / rich switching control means for operating while switching between at predetermined intervals (claim 11: FIGS. 1 to 3). In this case, it is preferable that during the lean / rich switching operation, the lean operation time is longer than the rich operation time so that the average air-fuel ratio in one cycle of the lean / rich cycle switching operation becomes lean.

Here, for example, the intake pipe (12) provided in the internal combustion engine is formed by merging an air supply pipe (12A) and a fuel gas supply pipe (12F), and a mixer ( 14) is provided and a fuel gas supply pipe (12F)
The intake pipe (12) bypasses the mixer (14).
It is preferable that a bypass line (18) that communicates with the branch is branched and a bypass gas flow control valve (20) is interposed. In this case, the “air-fuel ratio adjusting mechanism for adjusting the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine” corresponds to the bypass line (18) and the bypass gas flow control valve (20).

The control means (30) is a control unit for controlling the air-fuel ratio, which comprises an input port for sensor signals, a microcomputer for arithmetic processing, and a bypass gas flow control valve (2).
0) output port for the control signal.

During the lean / rich switching operation, it is desirable to use ignition timing change control or the like in order to suppress fluctuations in the engine generated torque due to changes in the air-fuel ratio.

An operation control method for an internal combustion engine for realizing such knowledge is to perform a regeneration operation for generating high-temperature rich to stoichiometric exhaust gas to perform the NOx storage reduction catalyst (40A) and the methane oxidation catalyst (40A). It is preferable to include a regeneration operation step of periodically performing the regeneration process of Step 40B) (Claim 5: FIG. 1).

In order to carry out the operation control method, the control means (30) controls the air-fuel ratio adjusting mechanisms (18, 20) to supply high-temperature exhaust gas to the internal combustion engine (10). The regeneration operation (high temperature / rich to stoichiometric operation) is performed to generate the NOx storage reduction catalyst (40).
It is preferable to include a regeneration operation control means (34) for periodically performing the regeneration treatment of A) and the hydrocarbon oxidation catalyst (40B) (Claim 12: FIG. 1).

In order to generate exhaust gas having a predetermined temperature, the control means (30) may change the ignition timing according to the load and the number of revolutions of the engine.

Here, the hydrocarbon oxidation catalyst (40B)
Also has the function of a three-way catalyst, so that in a stationary gas engine such as CGS or GHP, in the control method and apparatus according to the present invention, when performing regeneration operation, high-temperature / stoichiometric operation It is preferable to perform a regeneration process of the NOx storage reduction catalyst (40A) and the hydrocarbon oxidation catalyst (40B) with high temperature stoichiometric exhaust gas. At this time, as is conventionally used in the air-fuel ratio control of the three-way catalyst, the main oxygen sensor (5
0) and the signal of the sub-oxygen sensor (51) downstream of the catalyst are processed by the control means (30) to control the air-fuel ratio adjusting mechanism (18, 20) to control the air-fuel ratio to the catalyst window. Is preferred.

Further, the method for controlling an exhaust gas purifying apparatus for an internal combustion engine according to the present invention includes a step of measuring, as a timer value, an operation time immediately after the regeneration operation of the internal combustion engine, and When the operation time exceeds a predetermined time (reference value), it is preferable to execute the regeneration operation step (claim 6: FIGS. 4 and 5).

In order to implement this control method, the operation control device for an internal combustion engine of the present invention uses a timer (6) for measuring the operation time from immediately after the regeneration operation of the internal combustion engine as a timer value.
0), and the control means (30) is configured to cause the internal combustion engine to execute the regeneration operation when the measured timer value exceeds a predetermined time (reference value) (60,
62, 64, 66, 68, and 34) (claim 13: FIGS. 4 and 5).

Here, the operation time immediately after the regeneration indicates the time during which the lean / rich switching operation (in some cases, the lean operation) is continued after the regeneration operation is performed. When this value reaches a predetermined value, the regeneration operation is performed again, so that the periodic regeneration operation is possible.

According to the present invention having such a configuration, by measuring the operation time immediately after the regeneration operation, the SOx
The NOx occlusion reduction catalyst (40A) that occludes methane and the sulfur-poisoned methane oxidation catalyst (40B) can be regenerated at appropriate timing. In other words, whether or not to perform the regeneration operation can be appropriately controlled based on the timer value.

Alternatively, in the operation control method for an internal combustion engine according to the present invention, there is provided a step of detecting a hydrocarbon concentration downstream of the methane oxidation catalyst, and when the detected hydrocarbon concentration exceeds a predetermined value, the regeneration is performed. It is preferable that an operation step is performed (claim 7: FIGS. 6 and 7).

In order to execute the operation control method, a hydrocarbon sensor (72) for detecting the hydrocarbon concentration downstream of the methane oxidation catalyst (40) is provided, and the control means (30) It is preferable (80, 78, 34) to make the internal combustion engine execute the regeneration operation when the determined hydrocarbon concentration exceeds a predetermined value (claim 14: FIGS. 6 and 7).

With this configuration, the degree of performance deterioration due to sulfur poisoning of the hydrocarbon oxidation catalyst (for example, methane oxidation catalyst) is directly determined by the hydrocarbon concentration. You can do it. Therefore, the catalyst can be regenerated at an appropriate timing. In this case, the methane concentration may be directly detected by using a methane sensor as the hydrocarbon sensor. Also,
If the concentration of unburned components (eg, CO) other than hydrocarbons in the exhaust gas is low, oxygen sensors are installed upstream and downstream of the catalyst, and the difference in oxygen concentration between the two oxygen sensors indicates It is also possible to calculate the removal rate of (methane) and start the regeneration operation.

Here, shortly after the start of the internal combustion engine (10), when the exhaust gas temperature is low and the catalyst layer temperature is low, the methane oxidation catalyst (40B) is not activated and unburned Unable to purify hydrocarbons. Therefore, it is preferable to perform the above-described control after detecting the exhaust gas temperature to prevent erroneous detection.

Further, in the operation control method for an internal combustion engine according to the present invention, during the lean / rich switching operation (in some cases,
Measuring the exhaust gas temperature of the internal combustion engine (during the lean operation), adding the operating time immediately after the regeneration operation to the timer value when the exhaust gas temperature is equal to or lower than a predetermined temperature, and A step of not adding the operation time immediately after the regeneration operation to the timer value when the temperature exceeds the predetermined temperature, and preferably performing the regeneration operation step when the timer value exceeds the predetermined time (claim Item 8: FIGS. 8 and 9).

In order to carry out such a control method, it is necessary to perform the lean / rich switching operation (in some cases, the lean operation).
An exhaust temperature sensor (70) for measuring the exhaust gas temperature of the internal combustion engine (10), wherein the control means (30) measures an operation time immediately after the regeneration operation when the exhaust gas temperature is equal to or lower than a predetermined temperature. When the exhaust gas temperature exceeds a predetermined temperature, the operation time immediately after the regeneration operation is not added to the timer value, and when the timer value exceeds the predetermined time, the internal combustion engine (10) It is configured to execute the regeneration operation (74, 80, 62, 60, 66, 64, 6).
8, 34) (claim 15: FIGS. 8, 9).

When the exhaust gas temperature is in a high operating state, the sulfur poisoning is reduced, and the reduction of the hydrocarbon (eg, methane) purification capacity of the methane oxidation catalyst (40B) is small. Therefore, in the present invention described above, if the exhaust gas temperature of the internal combustion engine (10) is high, even if the number of regeneration operations is reduced, the ability of the methane oxidation catalyst (40B) to remove hydrocarbons (for example, methane) is reduced. There is no risk of adverse effects.

In addition, according to the present invention described above,
Thermal damage applied to the methane oxidation catalyst (40B) is reduced. As shown in FIG. 19, the effect of thermal degradation due to the regeneration process is considered to be small, but if the regeneration operation is performed frequently and the time of exposure to a high temperature becomes very long, thermal degradation may occur. Therefore, if the number of times of the reproduction process can be reduced as in the present invention, the risk of thermal degradation can be avoided. Furthermore, since the time of the stoichiometric operation (regeneration operation) in which the heat efficiency of the internal combustion engine (10) is relatively poor is shortened, there is an advantage that the average heat efficiency is improved.

In the operation control method according to the present invention, a step of measuring the post-regeneration operation time of the internal combustion engine, a step of determining a load of the internal combustion engine and determining a correction coefficient based on the load; And correcting the operation time immediately after the regeneration operation based on the measured operation time immediately after the regeneration operation, wherein the regeneration operation is performed when the correction value of the operation time immediately after the regeneration operation exceeds a predetermined value. Preferably, the steps are performed (Claim 9: FIGS. 10 to 1).
2).

In this case, the operation control device for an internal combustion engine according to the present invention includes a timer (60) for measuring an operation time immediately after the regeneration operation of the internal combustion engine (10) and the internal combustion engine (1).
0) load measuring means (52, 54) for measuring the load, the control means (30) determines a correction coefficient based on the load (84), and determines the correction coefficient and the The operation time immediately after the regeneration operation is corrected based on the measured operation time immediately after the regeneration operation (86), and when the correction value of the operation time immediately after the regeneration operation exceeds a predetermined value, the internal combustion engine is corrected. It is preferable that the regenerating operation be performed (84, 86, 88, 90, 34) (claim 16: FIGS. 10 to 12).

Here, the correction coefficient is a coefficient determined from the intake pressure and the engine speed.
In this specification, “time coefficient after reproduction” in relation to FIG.
It is preferable to use what is described.

Further, as the correction value of the operation time immediately after the regeneration operation, it is preferable to use "post-regeneration operation time" defined as the sum of the post-regeneration operation time coefficient multiplied by the timer value.

Since the operating state (air-fuel ratio, fuel gas flow rate, exhaust gas temperature, etc.) of the internal combustion engine (10) can be known from the intake pressure and the engine speed, the load on the internal combustion engine (10) can be calculated. Therefore, the flow rate of the exhaust gas at that time is also known.
Ox storage reduction catalyst (40A) and methane oxidation catalyst (40
The amount of SOx passing through B) can also be converted. Since the post-regeneration operating time coefficient is determined from the intake pressure and the engine speed, the post-regeneration operation time is determined by the amount of S passing through the NOx storage reduction catalyst (40A) and the methane oxidation catalyst (40B).
It changes according to the Ox amount and the exhaust gas temperature. If the passing SOx amount increases, the interval (regeneration interval) from the regeneration operation to the next regeneration operation is shortened, and if the SOx amount decreases, the interval is set to be longer, so that the regeneration operation can be performed at an appropriate timing. Will be possible. In addition, the regeneration interval is set to be short when the exhaust gas temperature is low, and is set to be long when the exhaust gas temperature is high, so that the regeneration operation can be performed at an appropriate timing.

Here, the “operating time after regeneration” is expressed by the following equation. (Driving time after regeneration) = (Saved value of driving time after regeneration) +
{(Regeneration operation time coefficient) * (timer value)} The “regeneration operation time storage value” is the immediately preceding post-regeneration operation time.

In addition, in the operation control method for an internal combustion engine according to the present invention, the stoichiometric operation is performed to regenerate the NOx storage reduction catalyst (40A) and the methane oxidation catalyst (40B) (high-temperature / stoichiometric operation, rich operation, High load operation)
It is preferable to include a step of determining the deterioration of the methane oxidation catalyst (40B) while performing the step, and a step of changing the predetermined value or the predetermined time according to the result of the deterioration determination (Claim 10: 13 to 15).

In order to execute the control method, the control means (30) performs a stoichiometric operation to regenerate the NOx storage reduction catalyst (40A) and the methane oxidation catalyst (40B) (high temperature / stoichiometric operation, rich operation). It is preferable that the deterioration determination of the methane oxidation catalyst (40B) is performed during the operation and the high load operation, and the predetermined value or the predetermined time is changed according to the result of the deterioration determination. (Claim 17: FIGS. 13 to 15).

As described above, the methane oxidation catalyst also has a three-way catalyst function. Therefore, when the regeneration operation is performed at a high exhaust gas temperature in a high-temperature / stoichiometric operation, a rich operation, or a high-load operation, the deterioration determination of the methane oxidation catalyst is performed by using the conventionally proposed deterioration determination method of the three-way catalyst. It can be performed. Here, the deterioration determination method includes, for example, a method of determining the amplitude value of the downstream oxygen sensor (sub-oxygen sensor) (eg, a technique disclosed in Japanese Patent Application Laid-Open No. 5-33632). What is necessary is just to be able to judge the degree. If the degree of deterioration is large, the interval from the regeneration operation to the next regeneration operation is shortened in accordance with the degree to suppress the deterioration of methane emissions.

[0052]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same members are denoted by the same reference numerals. FIG. 1 shows a first embodiment of the present invention. A lean burn type gas engine (internal combustion engine) indicated by reference numeral 10 as a whole includes an intake pipe 12 and an exhaust pipe 15.

The intake pipe 12 is formed by merging an air supply pipe 12A and a fuel gas supply pipe 12F, and a mixer 14 is provided at the junction. Here, the air supplied by the air supply pipe 12A is indicated by an arrow A in FIG. 1, and the fuel gas supplied by the fuel gas supply pipe 12F is indicated by an arrow F. In the intake pipe 12,
A throttle 16 is provided.

A bypass line 18 branches from the fuel gas supply pipe 12F. The bypass line 18 bypasses the mixer 14 and is located upstream of the throttle 16 of the intake pipe 12 (opposite to the gas engine 10). Communicate with
The bypass line 18 is provided with a bypass gas flow control valve 20.

As will be described later, the bypass gas flow control valve 2
In the case of 0, the opening degree is controlled by the control means 30.
The bypass gas flow rate is controlled by controlling the opening of the control valve 20, and the operating state of the gas engine 10 is controlled to a lean state or a rich state. In this case, during the lean / rich switching operation, the lean operation time> the rich operation time is set so that the average air-fuel ratio in one cycle of the lean / rich cycle switching operation is set to be lean.

The exhaust pipe 15 is provided with a NOx storage reduction catalyst 40A and a methane oxidation catalyst 40B in series from the side close to the gas engine 10. Methane oxidation catalyst 40
For example, a type in which a noble metal such as palladium or platinum is supported on alumina or zirconia is used. Note that the NOx storage reduction catalyst 40A and the methane oxidation catalyst 40B may be comprehensively expressed as "catalyst 40".

The control means 30 includes a signal transmission line CL-2.
, A valve opening control signal is started for the bypass gas flow control valve 20. By controlling the valve opening of the bypass gas flow control valve 20 and controlling the bypass gas flow, the air-fuel ratio of the lean burn gas engine 10 can be controlled or changed.

Here, in addition to the intake valve 22 and the exhaust valve 24, a spark plug 26
And a control signal generated from the L / R control means 32 is transmitted to the ignition plug 26 via a signal transmission line CL-2A. A control signal generated from the L / R control means 32 is also transmitted to the throttle 16 via a signal transmission line CL-2B. This is because the ignition timing and the throttle opening are changed to suppress torque fluctuation due to lean / rich switching.

The gas engine 10 is provided with a rotational speed sensor 52, and an intake pressure sensor 54 is provided in a region of the intake pipe 12 between the throttle 16 and the intake valve 22. The rotation speed sensor 52 transmits a detection signal to the rotation speed sensor reading means 56 of the control means 30 via the signal transmission line CL-3. Then, the intake pressure sensor 54 transmits a detection signal to the intake pressure sensor reading means 58 of the control means 30 via the signal transmission line CL-4.

The control means 30 includes a rotational speed sensor reading means 5
The load on the gas engine 10 can be ascertained from both the engine 6 and the intake pressure sensor reading means 58. Gas engine 1
In order to grasp the load of zero and utilize it for lean / rich operation control, both the rotation speed sensor reading means 56 and the intake pressure sensor reading means 58 are connected to the signal transmission line CL-33 through L5.
It is connected to T and RT reading means 93.

The LT / RT reading means 93 is connected to the L / R switching means 96 through the signal transmission line CL-34. The L / R switching means 96 is connected to the signal transmission line CL.
It is connected to the LR timer operating means 94 through -35.

LR is transmitted through the signal transmission line CL-36.
The LR timer 95 operates based on the signal of the timer operating means 94. Then, the value of the LR timer 95 is sent to the L / R switching means 96 through the signal transmission line CL-37, and the operation of lean / rich switching is performed, and the result is subjected to the L / R control through the signal transmission line CL-5. This is sent to the means 32, and the lean / rich switching control is realized.

In the exhaust pipe 15, the methane oxidation catalyst 40
Is provided with a main oxygen sensor 50 upstream and a sub oxygen sensor 51 downstream. The detection signal of the main oxygen sensor 50 is transmitted via a signal transmission line CL-30, and the output signal of the sub oxygen sensor 51 is transmitted via a signal transmission line CL-31.
1, sent to the sub oxygen sensor reading means 92, respectively.

The values of the main oxygen sensor and the sub oxygen sensor are sent to the regeneration operation control means 34 through CL-32. Further, the values of the intake pressure sensor 54 and the rotation speed sensor 52 are sent to the regeneration operation control means 34 through CL-6. Based on the values of these sensors, the stoichiometric air-fuel ratio control is performed according to the operating state of the engine at that time.

From the regeneration operation control means 34, air-fuel ratio control (high temperature / stoichiometric operation, rich operation,
In order to realize air-fuel ratio control corresponding to high-load operation, C
A control signal is sent to the bypass gas flow control valve 20 via L-2. At this time, depending on the magnitude of the load, the exhaust gas temperature may not reach the predetermined temperature during the stoichiometric operation, so a control signal is sent from the regeneration operation control means 34 to the ignition plug 26 via the CL-2A, Change the ignition timing to increase the exhaust gas temperature.

Next, the control of the first embodiment will be described with reference to FIG.

First, the control of the lean / rich switching operation will be described. The rotational speed sensor reading means 56 and the intake pressure sensor reading means 58 read the values of the rotational speed sensor 52 (FIG. 1) and the intake pressure sensor 54 (FIG. 1) (step S0).
1), based on the detection result, LT and RT reading means 93
Then, the lean time LT and the rich time RT corresponding to the operating state are read (step S02). Lean time L
T and the rich time RT are given by a two-dimensional map including the rotation speed and the intake pressure as shown in FIG.

Next, at step S03, L / R switching means 3
In accordance with the instruction of 4, the lean operation is started by the L / R control means 32, and the value of the L / R timer 95 is once cleared by the LR timer operation means 94 and then started.

When the value of the L / R timer 95 reaches the lean time LT in step S04 (step S04
S) In step S05, the L / R control means 32 switches from the lean operation to the rich operation in accordance with the command of the L / R switching means 34, clears the L / R timer 95, and restarts. Next, when the value of the L / R timer 95 reaches the rich time RT in step S06 (step S06
S), and return to step S01.

Here, in performing the regeneration operation periodically, when it is time to perform the regeneration operation, the routine shifts from the lean / rich switching operation control to the regeneration operation control routine. Regeneration operation includes high temperature / stoichiometric operation, rich operation,
Alternatively, the operation is performed for a predetermined time (for example, 10 minutes) in the high load operation. If the exhaust gas temperature does not reach the predetermined temperature, the ignition timing is changed.

The air-fuel ratio control corresponding to the regeneration operation (high temperature
As for the air-fuel ratio control corresponding to the stoichiometric operation, the rich operation, or the high-load operation, the air-fuel ratio control of a three-way catalyst using a conventionally used oxygen sensor may be used. Is omitted. Regarding the ignition timing, the ignition timing may be changed to a preset value in accordance with the intake pressure and the engine speed (in accordance with the engine load). Note that a specific method for starting the regeneration operation control will be described in the second and subsequent embodiments of FIGS.

The second embodiment shown in FIGS. 4 and 5 shows the structure and control in the case where a timer is used for "performing regular regeneration operation" as shown by the characteristic curve (C) in FIG. I have. Here, a difference from the first embodiment, that is, a control newly added to the first embodiment will be described.

The control method during the lean / rich switching operation and the regeneration operation is the same as in the first embodiment. Therefore, in FIG. 4, the lean / rich switching operation control unit includes:
It is assumed that it is included in the L / R switching control means 32.
In addition, the mode of the operation (regeneration operation) at the time of the regeneration process is the same as that of the first embodiment because the high-temperature and stoichiometric operation (or the rich operation or the high-load operation) using the oxygen sensor is performed. Description is omitted.

The control means 30 shown in FIG. 4 is provided with a regeneration operation control means 34. The regeneration operation control means 34 is also configured to control the opening of the bypass gas flow control valve 20 via the signal transmission line CL-2. This is for adjusting the flow rate of the fuel gas flowing through the bypass line 18 to cause the gas engine 10 to perform the regeneration operation (stoichiometric operation). The conditions for performing the regeneration operation and the like will be described later with reference to FIG.

In the configuration shown in FIG. 4, the gas engine 10 is provided with a rotation speed sensor 52, and an intake pressure sensor 54 is provided in a region between the throttle 16 and the intake valve 22 of the intake pipe 12. . The rotation speed sensor 52 transmits a detection signal to the rotation speed sensor reading means 56 of the control means 30 via the signal transmission line CL-3. The intake pressure sensor 54 is connected to the control unit 3 via the signal transmission line CL-4.
A detection signal is transmitted to the zero intake pressure sensor reading means 58.

As will be described later, when performing control relating to the regeneration operation in the second embodiment, information as to whether or not the gas engine 10 is operating is required. Whether or not the gas engine 10 is operating can also be grasped from the information transmitted to the rotation speed sensor reading means 56 and / or the intake pressure sensor reading means 58, so that the rotation is performed via the signal transmission line CL-6. The number sensor reading means 56 and the intake pressure sensor reading means 58
4 is also connected.

Further, in the control according to the second embodiment,
The necessity of the regeneration operation is determined based on the operation time measured by the timer. Therefore, the control means 30 shown in FIG.
Is provided with a timer 60.

The timer 60 is operated by the timer operating means 62 via the line CL-7, and the time (timer value) measured by the timer 60 is read by the timer reading means 64 via the line CL-8.

The read timer value corresponds to line CL-9.
Via the timer value storage means 66. Here, the timer operating means 62 can call the timer value stored in the timer value storing means 66 via the line CL-10.

The timer value read by the timer reading means 64 is transmitted to the reference value comparing means 6 via the line CL-11.
8 and the comparison result in the reference value comparison means 68 is
It is sent to the regeneration operation control means 34 via the line CL-12 and is used as a criterion for judging the start of the regeneration operation.

Next, control of the second embodiment will be described with reference to FIG. First, the rotation speed sensor 52 (FIG. 4)
And / or detecting the start of operation of the gas engine 10 based on the detection result of the intake pressure sensor 54 (FIG. 4) (FIG. 5).
The process proceeds to step S1) and step S2 in the flowchart on the left side, and at the same time, the routine control for determining the start of the regeneration operation (step indicated by reference A2) is started.

In the flowchart on the right side of FIG. 5, the timer value stored at that time is called from the timer value storing means 66 (step S11). For example, if the gas engine 10 is new and has not been operated in the past, the called timer value is zero.

Then, the measurement of the operation time by the timer 60 is started (step S12).

Here, the initial value in the measurement of the operation time is the timer value called from the timer value storage means 66 in step S11. Then, a value obtained by adding the operation time measured in step S12 to the initial value becomes a new timer value.

Next, the new timer value is compared with the reference value by the reference value comparing means 68 (step S1).
3). Then, after waiting until the timer value reaches the reference value (step S13: NO loop), when the timer value becomes larger than the reference value (for example, 8 hours) (step S13: YES), the regeneration operation is performed. (Step S1
4).

Here, the reference value is determined based on the catalyst amounts and performances of the NOx storage reduction catalyst 40A and the methane oxidation catalyst 40B, the methane concentration in the exhaust gas of the gas engine 10, the target methane emission of the gas engine 10, the target life, and the like. ,
Determined on a case-by-case basis. The regeneration operation is performed in the same manner as that described in the first embodiment in FIGS.

After performing the regeneration operation, the timer 60 is stopped, the timer is returned to zero (step S15), and the process returns to step S12.

Here, while the control as shown in the flowchart on the right side of FIG. 5 (steps S11 to S15) is being performed, the flowchart on the left side of FIG.
The control indicated by -S4) is performed.

Referring again to the flowchart on the left side of FIG. 5, it is determined in step S2 whether the engine has stopped. If the engine is not stopped, step S
1 (step S2 is a NO loop). If the engine has stopped (YES in step S2), the timer 60
Is stopped (step S3), and the timer value at that time (same as described in steps S12 and S13) is stored in the timer value storage means 66 (step S4).

As a result of performing the control as shown in FIG. 5, every time the engine operation time reaches the reference value (see step S13),
The regeneration operation of the NOx storage reduction catalyst 40A and the methane oxidation catalyst 40B is performed.

In each of the embodiments shown in FIGS. 4 to 15, the "lean / rich switching operation" in which the lean operation and the rich operation are alternately performed during the operation time other than the regeneration operation. (However, if there is a problem in performing the lean / rich switching operation, only the lean operation may be performed.)

FIGS. 6 and 7 show a third embodiment of the present invention. In the third embodiment, the timing of the regeneration operation is controlled based on the hydrocarbon concentration downstream of the catalyst. Also in the third embodiment shown in FIG. 6, since the lean / rich switching operation control is the same as in the first embodiment, L
/ R control means 32. Also, the operation (regeneration operation) at the time of the regeneration process is the same as that of the first embodiment by performing the high-temperature and stoichiometric operation (or the rich operation and the high-load operation) using the oxygen sensor. Is omitted. Hereinafter, a control method for starting the regeneration operation in the third embodiment will be described. Note that the NOx storage reduction catalyst 40A and the methane oxidation catalyst 40B may be comprehensively expressed as "catalyst 40".

In FIG. 6, an exhaust gas temperature sensor 70 is provided in a region of the exhaust pipe 15 upstream of the catalyst 40. On the other hand, a hydrocarbon sensor (or methane sensor) 72 is provided in a region of the exhaust pipe 15 downstream of the catalyst 40.

Shortly after the gas engine 10 is started, when the exhaust gas temperature is low and the catalyst layer temperature is low, the methane oxidation catalyst 40B is not activated, and the unburned hydrocarbons in the exhaust gas cannot be removed or purified. Therefore, in the state where the exhaust gas temperature is low, the methane oxidation catalyst 4
There is no difference in the concentration of hydrocarbons in the exhaust gas that has passed through 0B, and it is impossible to determine a decrease in the methane purification capacity of the methane oxidation catalyst based on the concentration of hydrocarbons. Therefore, when performing the control relating to the regeneration operation of the third embodiment, information regarding the exhaust gas temperature is required.

The information on the exhaust temperature of the gas engine 10 is sent as a detection signal (exhaust temperature signal) of the exhaust temperature sensor 70 via the signal transmission line CL-20 to the control means 3.
0 is transmitted to the exhaust temperature sensor reading means 74. Then, it is sent to the exhaust gas temperature sensor reference value comparing means 76 via the signal transmission line CL-22, and the exhaust gas temperature reference value (the amount and performance of the methane oxidation catalyst 40, the gas engine 1
0 depending on the concentration of methane in the exhaust gas.
Is determined by the case). The result of the comparison between the exhaust gas temperature and the reference value is sent to the hydrocarbon reference value comparison means 78 via the signal transmission line CL-24.

The information on the hydrocarbon concentration in the exhaust gas passing through the methane oxidation catalyst 40B is obtained from the hydrocarbon sensor 72.
Signal line C as the detection signal (hydrocarbon signal)
It is transmitted to the hydrocarbon sensor reading means 80 via L-26. Then, the signal is transmitted to the hydrocarbon reference value comparison means 78 via the signal transmission line CL-28, and the comparison result is transmitted to the regeneration operation control means 3 via the signal transmission line CL-30.
4

The other components in FIG. 6 are substantially the same as those in FIG. Next, control of the third embodiment will be described with reference to FIG.

First, the value of the exhaust gas temperature sensor 70 is read by the exhaust gas temperature sensor reading means 76, and the exhaust gas temperature on the upstream side of the catalyst 40 is measured (step S2).
1). As described above, in controlling the regeneration operation using the hydrocarbon sensor 72 on the downstream side of the methane oxidation catalyst 40B, the exhaust gas temperature must be higher than a predetermined temperature (reference value). Therefore, it is determined whether or not the exhaust gas temperature measured by the exhaust gas temperature sensor reference value comparing means 76 is higher than the reference value (step S22).

Here, the reference value in step S22,
That is, the exhaust gas temperature that must be reached to control the regeneration operation using the hydrocarbon sensor is:
It is set on a case-by-case basis depending on the nature of the catalyst and the like.

If the exhaust gas temperature has not reached the reference value (NO in step S22), step S21
Return to If the exhaust gas temperature is higher than the reference value (YES in step S22), the condition for controlling the regeneration operation using the measured value of the hydrocarbon sensor is set, and the value of the hydrocarbon sensor 72 is converted to the value of the hydrocarbon sensor 72. The calculation is performed by the hydrogen sensor reading means 80 (step S23).

If the methane purifying ability of the methane oxidizing catalyst 40B is not lowered, the methane oxidizing catalyst 40B purifies the hydrocarbons in the exhaust gas, so that the hydrocarbon concentration in the exhaust gas passing through the methane oxidizing catalyst 40B is low. Numeric value.
On the other hand, if the methane oxidation catalyst is deteriorated and the methane purification ability is reduced, the methane oxidation catalyst 40B cannot sufficiently purify the hydrocarbons in the exhaust gas. The hydrocarbon concentration is a high value. Therefore, it is possible to determine whether or not the methane oxidation catalyst has deteriorated based on the hydrocarbon concentration in the exhaust gas measured by the hydrocarbon sensor 72.

In step S24, the hydrocarbon sensor 72
The hydrocarbon reference value comparing means 78 determines whether or not the hydrocarbon concentration in the exhaust gas measured in step (b) is higher than a predetermined value (reference value). If the hydrocarbon concentration in the exhaust gas passing through the methane oxidation catalyst 40 is lower than the reference value (NO in step S24), it is determined that the methane oxidation catalyst 40B has not deteriorated, and the process returns to step S21. If the exhaust gas concentration is higher than the reference value (Y in step S24)
ES), it is determined that the methane oxidation catalyst 40B has deteriorated and the methane purification ability has been reduced, and the regeneration operation control means 34
To perform a regeneration operation (step S25). Here, the regeneration operation is performed by performing the same control as in the first embodiment and the second embodiment.

In the third embodiment shown in FIGS. 6 and 7, the exhaust temperature sensor 70 and the hydrocarbon sensor 72 are interposed in the exhaust pipe 15 of the gas engine 10. By providing a hydrocarbon sensor and comparing the hydrocarbon concentrations detected by the two, it is possible to determine the degree of deterioration (in other words, determine whether or not the regeneration operation is necessary). That is, if the difference between the hydrocarbon concentrations detected by the hydrocarbon sensors provided upstream and downstream of the catalyst 40 is less than a predetermined value, it is determined that the regeneration operation does not need to be performed. On the other hand, if it is equal to or more than the predetermined value, it is determined that the regeneration operation is necessary, and the regeneration operation is performed, and the methane oxidation catalyst 40
B can be configured to be reproduced. To this end, providing a hydrocarbon sensor upstream and downstream of the catalyst 40, and determining whether or not a regeneration operation is necessary based on a difference in the detected hydrocarbon concentration.
Except for this point, the same configuration and control as in the third embodiment shown in FIGS. 5 and 6 may be performed.

FIGS. 8 and 9 show a fourth embodiment of the present invention. This fourth embodiment is similar to the second embodiment,
The operation time of the gas engine is measured by a timer to control the regeneration operation. However, in the fourth embodiment, control is performed separately for a case where the operation time is measured by a timer and a case where the operation time is not measured, based on the exhaust gas temperature. In that respect, the second
This is different from the embodiment. Here, differences from the second embodiment will be described.

The configuration of the fourth embodiment shown in FIG. 8 is substantially the same as the configuration of the second embodiment of FIG. The control means 30 has a configuration related to the timer 60. However, in FIG. 8, an exhaust temperature sensor 70 for measuring the temperature of the exhaust gas is provided on the upstream side of the catalyst 40, and the detection signal thereof is transmitted through a signal transmission line CL-20 to an exhaust temperature sensor reading means. 74. Then, it is sent to the temperature reference value comparing means 80 via the signal transmission line CL-34.

Here, in the gas engine 10 in the normal operating state where the exhaust gas temperature is high, such as the engine in the high load operating state, for example, the sulfur poisoning of the methane oxidation catalyst 40B becomes difficult to progress, so that the methane purification is performed. The ability does not decrease much. Therefore, the gas engine 1 having a high exhaust gas temperature
At 0, there is no possibility that the methane removal capacity of the methane oxidation catalyst 40B will be adversely affected even if the number of regeneration operations is reduced. In addition to this, as described above, the thermal damage applied to the methane oxidation catalyst 40B is reduced, and the risk of thermal degradation can be avoided. Furthermore, since the time of the stoichiometric operation (regeneration operation) in which the heat efficiency of the gas engine 10 is relatively poor is shortened, there is an advantage that the average heat efficiency is improved.

For this reason, in the fourth embodiment shown in FIGS. 8 and 9, while the exhaust gas temperature is high (for example, 500 ° C. or more), the operation time until the regeneration operation is performed is not counted (the timer is activated). No, do not add to the timer value)
Is performed. In order to perform such control, the temperature reference value comparison means 80 compares the exhaust gas temperature with the reference value, and counts the operating state of the gas engine 10 at that time as the operation time until the regeneration operation is performed. It is determined whether the operation state should be performed or the operation state should not be counted in the operation time.

The judgment result of the temperature reference value comparing means 80 is transmitted to the timer operating means 62 via the signal transmission line CL-36. Accordingly, if the operation state is to be counted in the operation time until the regeneration operation is performed, the timer 60
Operate. On the other hand, if the operation state should not be counted as the operation time, the timer 60 is not operated and is not added to the timer value.

The control of the fourth embodiment will be described with reference to FIG. In the flow chart on the left side of FIG. 5 of the second embodiment, if “YES” is determined in step S1, FIG.
The control of the fourth embodiment is realized by a series of controls starting from A4. In starting the operation of the gas engine 10 (step S1 in the flowchart on the left side of FIG.
S) First, the timer value (timer storage value) stored in the timer value storage means 66 is read (FIG. 9: step S3).
1). Then, the timer reference value (a numerical value obtained by adding the operation time measured by the timer to the timer storage value) and a reference value (corresponding to the operation time until the regeneration operation is performed) are compared by the timer reference value comparison unit 68 ( Step S32). here,
The reference value (a numerical value corresponding to the operation time until the regeneration operation is performed) is determined on a case-by-case basis by the amount of the catalyst and other various conditions.

If the timer value is equal to or less than the reference value (NO in step S32), a control routine for measuring the operation time by the timer 60 in accordance with the exhaust gas temperature is executed.

The exhaust gas temperature is detected by the exhaust temperature sensor 70 upstream of the catalyst 40, and the detection signal is read by the exhaust temperature sensor reading means 74 (step S33). And
The temperature reference value comparison means 80 determines whether the detected exhaust gas temperature is lower than the reference value (step S).
34). Here, the "reference value" is a temperature at which the methane oxidation catalyst 40B is less affected by sulfur poisoning or a decrease in the methane purification capacity of the catalyst is small if the exhaust gas temperature is higher than that temperature. For example, 500 ° C. at which the catalyst capacity is small and the catalyst performance does not decrease is selected as the “reference value” in step S34.

If the exhaust gas temperature is lower than the reference value (YES in step S34), the operation time of the gas engine at that time is added to the operation time until the regeneration operation ("reference value" in step S32). It is the driving time to be done. Therefore, it is determined whether or not the timer 60 is operating (step S35), and if the timer 60 is not operating (step S35 is NO), the timer 60 is operated (step S36). If the timer 60 has been activated (YES in step S35 or after execution of step S36), the process returns to step S32.

If the exhaust gas temperature is higher than the reference value (NO in step S34), the methane oxidation catalyst 40B has a small decrease in methane removal ability due to sulfur poisoning, and should be added to the operation time up to the regeneration operation. is not. Therefore,
It is determined whether or not the timer 60 is operating (Step S)
37) If the timer 60 is operating (step S37)
Is YES), the timer 60 is stopped (step S38), and the measured operation time (timer value) at that time is stored in the timer value storage means 66 (step S3).
9). If the timer 60 is not operating (NO in step S37 or after completing step S39),
Return to 33.

If the timer value exceeds the reference value (the operation time up to the regeneration time) again in step S32 (YES in step S32), the regeneration operation control is performed in the same manner as in the first to third embodiments. The regeneration operation is performed by the means 32 (step S40). When the regeneration operation is completed, the timer 60 is stopped, the operation is returned to zero (step S41), and the process returns to step S33. Here, while the control as shown in the flowchart of FIG. 9 (steps S31 to S41) is being performed, the flowchart on the left side of FIG.
The control shown in S4) is performed.

As described above, according to the fourth embodiment in which the control as shown in FIG. 9 is performed, when the exhaust gas temperature is equal to or higher than the reference value (NO in step S34), the number and time of the regeneration operation are reduced. The thermal deterioration factor for the methane oxidation catalyst 40 is reduced, and the time of the stoichiometric operation (regeneration operation) whose combustion efficiency is relatively low is reduced.

The fifth embodiment of the present invention shown in FIGS. 10 to 12 has a configuration similar to the second embodiment shown in FIGS. However, in the fifth embodiment, as shown in FIG. 10, the post-regeneration operation time coefficient reading means 84, the post-reproduction operation time value calculation means 86, the post-regeneration operation time value comparison means 88, and the post-regeneration operation time value storage means 90 are used. The method for determining the start of the regeneration operation is different from that of the second embodiment shown in FIGS.
Here, differences from the second embodiment will be described.

Here, the phrase “driving time after regeneration” is as follows:
This is a numerical value related to the operation time during which the lean / rich switching operation is being performed, and means a numerical value obtained by correcting the post-regeneration operation time from the end of the immediately preceding regeneration operation to that point in a manner described later. And in the control of the fifth embodiment,
Whether or not the regeneration operation is performed is determined based on whether or not the post-regeneration operation time exceeds a predetermined time (reference value).

In FIG. 10, the detection result of the intake pressure sensor 54 and the detection result of the rotation speed sensor 52 are transmitted to the post-regeneration operating time coefficient reading means 84 via the signal transmission line CL-40. Operating time coefficient reading means 84 after regeneration
Stores a table or map as shown in FIG. 12, and determines a post-regeneration operating time coefficient from the intake pressure and the engine speed. As described above, since the operating state of the engine (air-fuel ratio, fuel gas flow rate, exhaust gas temperature, exhaust gas flow rate, etc.) can be known from the intake pressure and the engine speed, the load at that time can be calculated. Further, since the amount of SOx passing through the methane oxidation catalyst can be converted, the regeneration operation can be performed at an appropriate timing according to the amount of SOx passed and the exhaust gas temperature.

The post-regeneration operation time coefficient determined by the post-reproduction operation time coefficient reading means 84 is the signal transmission line CL-42.
Is transmitted to the post-regeneration operating time value calculating means 86 via the.
In the post-regeneration operating time value calculating means 86, the signal transmission line C
The timer value is transmitted from the timer reading means 64 via L-44, and the post-regeneration operation time is calculated in a manner described later with reference to FIG.

The post-regeneration operation time calculated by the post-reproduction operation time value calculation means 86 is sent to the post-regeneration operation time value comparison means 88 via the signal transmission line CL-46, and the comparison result is sent to the signal transmission line CL. It is sent to the regeneration operation control means 34 via -52, and the regeneration operation is performed. The post-regeneration operation time is transmitted from the post-regeneration operation time value comparison means 88 to the post-regeneration operation time value storage means 90 via the signal transmission line CL-48. The post-regeneration operation time stored in the post-regeneration operation time value storage means 90 is sent to the post-regeneration operation time value calculation means 86 via the signal transmission line CL-50 and used for calculating the post-regeneration operation time. Can be

Next, the control of the fifth embodiment will be described with reference to FIG. In FIG. 11, first, the symbol “A
6 ”is executed. That is, it is determined whether or not the lean-burn gas engine 10 (FIG. 10) is in a start-up operation (step S51). Gas engine 10
If the start operation is performed (YES in step S51), the process proceeds to step S67, and executes a control routine (routine of steps S52 to S66) starting with reference numeral "A5".

In the control routine starting with reference numeral “A5”, first, the post-regeneration operation time storage means 90 reads the post-regeneration operation time stored therein (post-regeneration operation time storage value).
Is read (step S52). Here, immediately after the end of the regeneration operation or when the engine 10 is new, the post-regeneration operation time value is zero.

Next, the detection result of the rotation speed sensor 52 and the detection result of the intake pressure sensor 54 are read (step S5).
3), and transmit to the post-regeneration operating time coefficient reading means 84. The detection result of the rotation speed sensor 52 and the intake pressure sensor 5
From the detection result of No. 4, the post-regeneration operation time coefficient is determined by a map as shown in FIG. 12 stored in the post-regeneration operation time coefficient reading means 84 (step S54).

The post-regeneration operating time coefficient of the map shown in FIG. 12 is set to be large when the load is high (the exhaust gas flow rate is large) because the amount of SOx passing through the methane oxidation catalyst increases. . Further, when the temperature of the exhaust gas is low, the influence of sulfur poisoning increases, so that the value is set to increase. Each post-regeneration operating time coefficient is determined on a case-by-case basis by the characteristics of the engine, the capacity of the methane oxidation catalyst, and the like.

When the post-regeneration operation time coefficient is determined (step S54 is completed), the operation of the timer 60 is started (step S55), and the measured value (timer value) is read (step S56). The post-regeneration operation time is calculated by the value calculation means 86 (step S57).

In calculating the post-regeneration operation time, a value obtained by multiplying the post-regeneration operation time storage value read in step S52 by the post-regeneration operation time coefficient read in step S54 by the timer value read in step S56 is used. to add. That is, the post-regeneration operation time is calculated by the following equation. (Driving time after regeneration) = (Saved value of driving time after regeneration) +
{(Post-regeneration operation time coefficient) * (Timer value)} The post-reproduction operation time calculated in this way is compared with a reference value by the post-reproduction operation time value comparison means 88 (step S58).

Here, the reference value is determined so that the regeneration operation should be performed when the post-regeneration operation time exceeds the numerical value. -Pre-determined on a case-by-case basis.

If the post-regeneration operation time does not exceed the reference value (NO in step S58), it is determined that it is not necessary to perform the regeneration operation. In that case, the rotation speed sensor 5
2 and the detection result of the intake pressure sensor 54 (step S59), and the post-regeneration operation time coefficient reading means 84 determines whether or not the post-regeneration operation time coefficient needs to be changed (step S59). S60) If it is determined that the rotation speed and the intake pressure have not changed and it is not necessary to change the post-regeneration operating time coefficient (step S6).
(0 is NO), the process returns to step S56.

On the other hand, when the rotational speed and the intake pressure change and the post-regeneration operation time coefficient needs to be changed (YES in step S60), the post-regeneration operation time coefficient is changed (step S61), and the regeneration is performed. The post-reproduction storage time at that point may be stored by the post-operation time storage means 90 (step S62), the timer 60 may be stopped, returned to zero, and restarted (step S63). When step S63 is completed, the process returns to step S56 to read the timer value.

In step S58, step S57
If the post-regeneration operation time calculated in step S1 exceeds the reference value (YES in step S58), it is determined that the stage in which regeneration operation is required has been reached. At that time, the regeneration operation is performed by the regeneration operation control means 34, so that the catalyst 40 is regenerated (step S64). Then, the timer 60 is stopped and returned to zero (step S65), and the regeneration operation time value is cleared (step S66). Upon completion of the step S66, the process returns to the step S53.

While the control routine of steps S52 to S66 is being executed, steps S67 and subsequent steps of the control routine starting with reference numeral S51 are always executed. That is, it is determined whether or not the stop processing of the gas engine 10 has been performed (step S67). If the stop processing of the gas engine 10 has been performed (step S67 is YES), the timer 6 is stopped.
0 is returned to zero (Step S68), and the post-regeneration operating time storage means 90 stores (saves) the post-regeneration operation time at that time (Step S69). And
It returns to step S51. By the above control, an appropriate regeneration operation is performed according to the load, that is, according to the SOx amount of the exhaust gas that has passed through the NOx storage reduction catalyst and the methane oxidation catalyst and the temperature of the exhaust gas.

FIGS. 13 to 15 show a sixth embodiment of the present invention. In the sixth embodiment, a reference value used as a reference for starting the regeneration operation used in the second, fourth, and fifth embodiments is changed according to the degree of deterioration of the methane oxidation catalyst 40B. In the control in each of the second, fourth and fifth embodiments, the reference value as the threshold level for determining whether or not to perform the regeneration operation is used as a constant. In the sixth embodiment,
Control is performed to change various reference values themselves. for that reason,
The sixth embodiment is used as control of another routine in the control of the second, fourth, and fifth embodiments.

Next, the control of the sixth embodiment will be described with reference to FIG. Here, only the control of changing the reference value newly added in the sixth embodiment will be described. FIG.
In, the output signal of the sub oxygen sensor 51 is sent to the sub oxygen sensor reading means 92 of the control means 30 via the signal transmission line CL-31.

Then, based on the output signal value of the sub oxygen sensor 51 sent from the sub oxygen sensor reading means 92 via the signal transmission line CL-90, the average amplitude value calculating means 100 outputs the output of the sub oxygen sensor 51. Is obtained. The value is sent to the reference value reading means 102 via the signal transmission line CL-92, and the map (for example, FIG.
) To select the optimum reference level.

Next, via the signal transmission line CL-94,
The reference value is changed to an optimum reference value by the reference value changing means 104, and the value of the reference value is reflected on the regeneration operation control performed by the regeneration operation control means 34 via the signal transmission line CL-96.

When the methane oxidation catalyst 40B is deteriorated, the methane oxidation catalyst 40 cannot sufficiently oxidize and remove methane unless the interval between regeneration operations (regeneration interval) is shortened. Therefore, the degree of deterioration of the methane oxidation catalyst 40 is determined based on a known catalyst deterioration determination method, and the reference value is changed to set a regeneration interval corresponding to the degree of deterioration.

As described above, since the methane oxidation catalyst also has the function of a three-way catalyst, the deterioration of the methane oxidation catalyst 40B is determined during the regeneration operation by using the three-way catalyst deterioration determination method. In the sixth embodiment, as a deterioration determination method, for example, a determination method is made based on the magnitude of the amplitude value of the oxygen sensor on the downstream side (the side separated from the engine 10) of the catalyst 40 (for example, Japanese Unexamined Patent Publication No.
No. 33632).

In FIG. 14, first, the methane oxidation catalyst 4
Whether OB is being regenerated (regeneration operation is in progress)
It is determined whether or not it is (step S71). During the regeneration operation, that is, when the methane oxidation catalyst 40B is operating in the same manner as the three-way catalyst (YES in step S71), the amplitude average value calculation means 100 reads the sub oxygen read by the sub oxygen sensor reading means 92. The average value of the amplitude of the signal of the sensor 51 is calculated (step S72). Next, the reference value reading means 102 reads a reference value according to the average amplitude value of the signal of the sub oxygen sensor 51 using the map (FIG. 15) (step S73). Then, the reference value changing means 104
In, the reference value is changed (step S74).

As described above, when the oxygen sensor is provided on the downstream side of the catalyst 40, the methane oxidation is determined by the amplitude value of the output signal of the sub-oxygen sensor 51, as is apparent from the known technique relating to the three-way catalyst. The degree of deterioration of the catalyst 40B is determined. That is, the amplitude of the oxygen sensor output signal downstream of the catalyst is smaller for a newer catalyst that has not deteriorated, and the amplitude is larger for a deteriorated catalyst. Therefore, for example, FIG.
By creating a table or a map as shown in the above, a reference value corresponding to the degree of catalyst deterioration can be obtained.

In FIG. 15, the “reference value” is a control other than the control using the hydrocarbon concentration shown in FIGS. 6 and 7 (the control using the operation time, the exhaust gas temperature or the engine load combined with the operation time). The reference value used in the control
It is comprehensively represented by reference numerals a, b, c, d, and e.

In FIG. 16, the amplitude value increases as the value on the right increases. That is, the more the state on the right side of FIG. 16, the more the methane oxidation catalyst 40 is deteriorated. Therefore, in FIG. 16, the reference value on the right side is set smaller, so that the reproduction interval on the left side is shortened.

The illustrated embodiment is merely an example.
It is not intended to limit the technical scope of the present invention. For example, in the sixth embodiment of FIGS. 13 to 15, the catalyst deterioration determination is not limited to the determination based on the amplitude of the oxygen sensor output signal on the downstream side of the catalyst. Any conventionally known three-way catalyst deterioration degree determination technology can be applied.
In the illustrated embodiment, a case is described in which a NOx storage reduction catalyst and a methane oxidation catalyst are interposed. However, the present invention is also applicable to a case where another NOx storage reduction catalyst and a methane oxidation catalyst are interposed. Include.

[0143]

The effects of the present invention are listed below. (1) Since SOx in the exhaust gas can be stored by the NOx storage reduction catalyst, deterioration of the hydrocarbon oxidation catalyst (for example, methane oxidation catalyst) due to sulfur poisoning is reduced. (2) By performing the regeneration operation of the NOx storage reduction catalyst, the regeneration treatment of the hydrocarbon oxidation catalyst (for example, methane oxidation catalyst) can be performed at the same time, and the life can be extended. (3) By performing the regeneration operation at appropriate intervals, thermal damage to the methane oxidation catalyst can be suppressed, and a decrease in the average thermal efficiency of the engine can be suppressed. (4) By extending the life of an expensive methane oxidation catalyst supporting a large amount of noble metal, cost can be reduced by reducing the amount of the catalyst. (5) By extending the life of an expensive methane oxidation catalyst supporting a large amount of noble metal, the catalyst replacement interval can be lengthened and maintenance costs can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a control flowchart of the first embodiment.

FIG. 3 is a table showing a relationship between an engine speed, an intake pressure, a lean time LT, and a rich time RT used in the first embodiment.

FIG. 4 is a block diagram showing a second embodiment of the present invention.

FIG. 5 is a diagram illustrating a control flowchart according to a second embodiment.

FIG. 6 is a block diagram showing a third embodiment of the present invention.

FIG. 7 is a diagram illustrating a control flowchart according to a third embodiment.

FIG. 8 is a block diagram showing a fourth embodiment of the present invention.

FIG. 9 is a diagram illustrating a control flowchart according to a fourth embodiment.

FIG. 10 is a block diagram showing a fifth embodiment of the present invention.

FIG. 11 is a diagram illustrating a control flowchart according to a fifth embodiment.

FIG. 12 is a table showing a relationship between an engine speed, an intake pressure, and a post-regeneration operating time coefficient used in the fifth embodiment.

FIG. 13 is a block diagram showing a sixth embodiment of the present invention.

FIG. 14 is a diagram illustrating a control flowchart according to a sixth embodiment of the present invention.

FIG. 15 is a table showing a relationship between a sub oxygen sensor output signal amplitude average value and a reference value used in the sixth embodiment.

FIG. 16 is a diagram showing a change over time in a purification rate of a conventional methane oxidation catalyst.

FIG. 17 is a view showing a result of comparing a change in a purification rate of a methane oxidation catalyst in a conventional (lean only), lean / rich switching, lean / rich switching + regeneration processing.

FIG. 18 is a diagram showing a methane purification rate when a regeneration treatment is performed on a methane oxidation catalyst.

FIG. 19 is a diagram showing a change in the purification rate of a methane oxidation catalyst when a process is performed using actual exhaust gas at a high temperature and stoichiometry.

FIG. 20 is a table showing the methane purification rates of one example of the present invention as a table.

FIG. 21 is a table showing a NOx removal rate in one example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Lean combustion type gas engine (internal combustion engine) 12 ... Intake pipe 12A ... Air supply pipe 12F ... Fuel gas supply pipe 14 ... Mixer 15 ... Exhaust pipe A ... Air F: fuel gas 16: throttle 18: bypass line 20: bypass gas flow control valve 22: intake valve 24: exhaust valve 26: spark plug 30: control means 32 ... lean / rich control means (L / R control means) 34 ... regeneration operation control means 40 ... methane oxidation catalyst 50 ... sensor 52 ... rotation speed sensor 54 ... intake pressure sensor 60 timer 70 exhaust gas temperature sensor 72 hydrocarbon sensor

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) F02D 41/04 301 F02D 41/04 305A 305 330M 330 B01D 53/36 103B (72) Inventor Masaki Motomichi Tokyo Gas Co., Ltd., 1-5-20 Kaigan, Minato-ku, Tokyo (72) Inventor Toru Matsui Tokyo Gas Co., Ltd., 1-5-20 Kaigan, Minato-ku, Tokyo (72) Hiromichi Yamamoto Tokyo, Inventor Tokyo Gas Co., Ltd., 1-5-20 Kaigan, Minato-ku, Tokyo (72) Inventor Kota Yokoyama 4-1-2, Hirano-cho, Chuo-ku, Osaka City, Osaka Prefecture Osaka Gas Co., Ltd. (72) Hiroshi Sasaki (1-2) Within Osaka Gas Co., Ltd. (72) Inventor Keiji Taniguchi 19-18 Sakuradacho, Atsuta-ku, Nagoya-shi, Aichi F-term within Gas Co., Ltd. (reference) 3G091 AA12 AA19 AB02 AB06 BA11 BA14 BA27 BA32 BA33 CA18 DA03 DC01 EA01 EA06 EA17 FB09 HA09 3G301 HA15 HA22 JA21 JA25 MA01 ND01 NE02 PA07Z PD01Z PD02Z PD11Z PE01Z 4D048 AA02 AB05 CC32 CC47 DA01 DA02 DA08 DA20 EA04

Claims (17)

[Claims] 1. An exhaust system for an internal combustion engine, wherein a hydrocarbon oxidation catalyst and a NOx storage reduction catalyst are interposed in series in an exhaust system, and the NOx storage reduction catalyst is arranged on a side close to the internal combustion engine. Gas purification device. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein said hydrocarbon oxidation catalyst is a methane oxidation catalyst. 3. An SOx instead of the NOx storage reduction catalyst
2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein an adsorbent is used. 4. The operation control method for an exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the operating state is such that the air-fuel mixture supplied to the internal combustion engine is rich in fuel, and the fuel is lean. An operation control method for an exhaust gas purifying apparatus for an internal combustion engine, wherein the internal combustion engine is operated by a lean / rich switching operation in which the operation is performed while switching the operation state at predetermined intervals. 5. The exhaust gas purification of an internal combustion engine according to claim 4, further comprising a regeneration operation step of performing a regeneration operation for generating a high-temperature exhaust gas to periodically perform a regeneration process of the NOx storage reduction catalyst and the hydrocarbon oxidation catalyst. Operation control method of the device. 6. A step of measuring an operation time immediately after the regeneration operation of the internal combustion engine as a timer value, wherein the regeneration operation step is executed when the measured timer value exceeds a predetermined time. Item 6. An operation control method for an exhaust gas purification device for an internal combustion engine according to Item 5. 7. The method according to claim 5, further comprising a step of detecting a hydrocarbon concentration downstream of the hydrocarbon oxidation catalyst, wherein the regeneration operation step is performed when the detected hydrocarbon concentration exceeds a predetermined value. An operation control method for an exhaust gas purification device for an internal combustion engine. 8. A step of measuring an exhaust gas temperature of the internal combustion engine, a step of adding an operation time immediately after the regeneration operation to a timer value when the exhaust gas temperature is equal to or lower than a predetermined temperature, and A step of not adding an operation time immediately after the regeneration operation to the timer value when the time exceeds the regeneration operation, and executing the regeneration operation step when the timer value exceeds a predetermined time. An operation control method for a gas purification device. 9. A step of measuring an operation time immediately after the regeneration operation of the internal combustion engine, a step of obtaining a load of the internal combustion engine and determining a correction coefficient based on the load, and a step of determining the correction coefficient and the measured Correcting the operating time immediately after the regeneration operation based on the operation time immediately after the regeneration operation, and executing the regeneration operation step when the correction value of the operation time immediately after the regeneration operation exceeds a predetermined value. An operation control method for an exhaust gas purifying apparatus for an internal combustion engine according to claim 5, wherein 10. A step of judging deterioration of the hydrocarbon oxidation catalyst during the regeneration treatment of the NOx storage reduction catalyst and the hydrocarbon oxidation catalyst, and the predetermined value or the predetermined time corresponding to a result of the deterioration judgment. The method for controlling operation of an exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 5 to 9, further comprising the step of: 11. A control means for controlling an air-fuel ratio adjusting mechanism for adjusting an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine,
4. The control device according to claim 1, further comprising: a lean / rich control unit configured to switch between an operation state in which the air-fuel mixture is fuel-rich and an operation state in which the air-fuel mixture is fuel-lean at predetermined intervals to continue operation. An exhaust gas purifying apparatus for an internal combustion engine according to any one of the preceding claims. 12. The control means controls the air-fuel ratio adjusting mechanism to cause the internal combustion engine to perform a regeneration operation for generating high-temperature exhaust gas to perform a regeneration process of the NOx storage reduction catalyst and the hydrocarbon oxidation catalyst. The exhaust gas purifying apparatus for an internal combustion engine according to claim 11, further comprising a regeneration operation control means for performing the regeneration operation. 13. A timer for measuring an operation time immediately after the regeneration operation of the internal combustion engine as a timer value, wherein the control means causes the internal combustion engine to perform the regeneration when the measured timer value exceeds a predetermined time. 13. The exhaust gas purifying apparatus for an internal combustion engine according to claim 12, wherein the apparatus is configured to perform an operation. 14. A hydrocarbon sensor for detecting a hydrocarbon concentration downstream of the hydrocarbon oxidation catalyst, wherein the control means controls the internal combustion engine to perform the regeneration operation when the detected hydrocarbon concentration exceeds a predetermined value. 13. The exhaust gas purifying apparatus for an internal combustion engine according to claim 12, wherein the exhaust gas purifying apparatus is configured to execute the following. 15. An exhaust temperature sensor for measuring an exhaust gas temperature of an internal combustion engine, wherein the control means adds an operation time immediately after the regeneration operation to a timer value when the exhaust gas temperature is equal to or lower than a predetermined temperature, When the exhaust gas temperature exceeds a predetermined temperature, the operation time immediately after the regeneration operation is not added to the timer value, and when the timer value exceeds the predetermined time, the internal combustion engine is configured to execute the regeneration operation. Claim 12
Exhaust gas purification device for internal combustion engines. 16. A control apparatus comprising: a timer for measuring an operation time immediately after the regeneration operation of the internal combustion engine; and load measuring means for measuring a load of the internal combustion engine, wherein the control means is configured to perform a control based on the load. The correction coefficient is determined, the operation time immediately after the regeneration operation is corrected by the correction coefficient and the measured operation time immediately after the regeneration operation, and the correction value of the operation time immediately after the regeneration operation exceeds a predetermined value. 13. The exhaust gas purifying apparatus for an internal combustion engine according to claim 12, wherein the exhaust gas purifying apparatus is configured to cause the internal combustion engine to execute the regeneration operation in the case. 17. The control means determines a deterioration of the hydrocarbon oxidation catalyst during a regeneration process of the NOx storage reduction catalyst and the hydrocarbon oxidation catalyst, and performs the predetermined determination in accordance with a result of the deterioration determination. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 12 to 16, wherein a value or a predetermined time is changed.