JPH10176528A - Method for operating internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain the NOx storage and reduction catalyst purifying performance for a long time in an internal combustion engine, which is provided with a NOx storage and reduction catalyst in an exhaust system thereof so as to clean the exhaust gas. SOLUTION: This internal combustion engine is provided with an air-fuel ratio control device (a pipeline 51 and a fuel gas flow control valve 52 or the like) in an intake system thereof so as to alternately changeover the rich operating condition and the lean operating condition on the basis of the signal from an ECU, while at the time of switching from the lean operating condition to the rich operating condition, a part of the exhaust gas is led in through a pipeline 53 and an exhaust gas flow control valve 54 or the like so as to control the generation of knocking and temperature rise of the exhaust gas. This method is especially effective in an internal combustion engine such as a gas engine for cogeneration, of which load operation is conditioned to be operated at 100%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operation method of an internal combustion engine, and more particularly to a purification performance of an NOx storage reduction catalyst in an internal combustion engine provided with a NOx storage reduction catalyst in an exhaust system for purifying exhaust gas. And an operation method of the internal combustion engine that can maintain the pressure for a long period of time.

[0002]

2. Description of the Related Art Nitrogen particles (N) in the exhaust gas of an internal combustion engine
Many methods and apparatuses for removing Ox) have been proposed, one of which includes a so-called NOx storage reduction catalyst in an exhaust system. The NOx storage reduction catalyst includes, for example, alumina as a carrier, and on this carrier, for example, potassium K, sodium Na, lithium Li, an alkali metal such as cesium Cs, barium Ba, an alkaline earth such as calcium Ca, lanthanum La, At least one selected from rare earth elements such as yttrium Y and platinum Pt
If the air ratio of the inflowing exhaust gas is lean, NO
It has a function of absorbing NO and releasing NOx when the oxygen concentration decreases, that is, a function of releasing NOx by storage and reduction.

[0003] The amount of NOx absorbed by the absorbent is limited, and when used in lean exhaust gas for a long time, the absorbent gradually saturates and the NOx absorption efficiency decreases. N for that
When the Ox storage reduction catalyst is used for purifying the exhaust gas of an internal combustion engine, after leaving it in a lean exhaust gas atmosphere for a certain period of time, then an exhaust gas atmosphere having a stoichiometric air-fuel ratio or a rich air-fuel ratio higher than that (that is, an oxygen concentration of The absorbent is exposed to a (reduced atmosphere) to reduce and remove NOx. At the time of reduction and removal, a catalytic action similar to that of the three-way catalyst occurs, and NOx in the exhaust gas is also reduced and removed at the same time. By switching the exhaust gas between the lean state and the rich state, absorption (lean), release, and reduction (rich) are repeated, and high NOx purification performance can be obtained.

As a method of switching the exhaust gas atmosphere between a lean state and a rich state during the operation of the internal combustion engine, an air-fuel ratio control device is provided in an intake system of the internal combustion engine, and an air-fuel ratio control is performed to obtain an operating state (rich or higher) that is equal to or higher than the stoichiometric air-fuel ratio. State) and a lean air-fuel ratio operating state (lean state) alternately, and a switchable two-system exhaust system is provided for the internal combustion engine operated in the lean state. A method has been proposed in which the path is switched and a reducing agent (reducing gas) is supplied from the upstream of the catalyst on the side where NOx is absorbed (see JP-A-8-19728 and JP-A-8-86213). .

[0005]

The exhaust system is divided into two systems, the exhaust path is switched at regular intervals, and a reducing agent (reducing gas) is supplied from the upstream side of the catalyst on the side where NOx is absorbed. Since two systems need to be prepared, there arises a problem of an increase in space and an increase in cost, and a running cost increases because a reducing agent is separately prepared.

On the other hand, the method of continuously operating the air-fuel ratio by switching the air-fuel ratio between a rich state and a lean state by the air-fuel ratio control device involves the following disadvantages. That is, when the combustion state of the internal combustion engine is switched from the lean state to the rich state,
Usually, knocking occurs. In most cases, such as an internal combustion engine for an automobile, which operates with a partial load, knocking can be easily dealt with by, for example, retarding the ignition timing, and even if knocking occurs, partial knocking can be performed. Due to the load operation, there is little damage to the engine. Therefore, in an internal combustion engine for an automobile, a NOx storage reduction catalyst is provided in an exhaust system, and the air-fuel ratio is alternately switched between a rich state and a lean state by an air-fuel ratio control device of the internal combustion engine, thereby purifying exhaust gas over a long period of time. Doing so raises no particular problem.
Also, there is no particular cost increase.

However, in the case of an engine such as a stationary internal combustion engine used for cogeneration which is assumed to be constantly operated at a constant load (100% load) and continuously operated for a long time, knocking occurs during operation. This means that the engine is operated at 100% load, so that the impact given to the engine is large, causing damage to the engine. Further, when the ignition timing is retarded to suppress knocking, the exhaust gas temperature rises, and the high exhaust gas temperature causes damage to the engine. Therefore, in order to secure the durability of the engine, knocking must be minimized in this type of internal combustion engine.

[0008] In other words, in an internal combustion engine such as an internal combustion engine used for cogeneration which is premised on 100% load operation, a NOx storage reduction catalyst is used for purifying exhaust gas, and NOx reduction from the absorbent is performed. It is practically impossible to perform the reduction by switching the air-fuel ratio between the rich state and the lean state by the air-fuel ratio control device. Therefore, the use itself of the NOx storage reduction catalyst has not been put to practical use.

Further, in an internal combustion engine premised on partial load operation, a NOx storage reduction catalyst is used for purifying exhaust gas, and the reduction of NOx from the absorbent is performed by an air-fuel ratio control device using an air-fuel ratio rich state and a lean state. However, even if the operation is performed by switching, the operation at 100% load must be continued for the sake of operation, causing the same problem of engine damage as described above.

[0010] An object of the present invention is to provide an operating method which eliminates the above-mentioned disadvantages in an internal combustion engine in which an exhaust system is provided with a NOx storage reduction catalyst to purify exhaust gas. Has made it possible to purify exhaust gas using a NOx storage reduction catalyst without causing an increase in space around an internal combustion engine or an increase in cost, and without causing damage to the engine during high-load operation. An object of the present invention is to provide a method for operating an internal combustion engine.

[0011]

According to the present invention, there is provided a method of operating an internal combustion engine in which an exhaust system is provided with a NOx storage reduction catalyst to purify exhaust gas. A fuel ratio control device is provided to alternately switch between an operating state above the stoichiometric air-fuel ratio and a lean air-fuel ratio operating state, and at the time of switching from the lean air-fuel ratio operating state to an operating state above the stoichiometric air-fuel ratio, the intake system This is achieved by introducing a part of the exhaust gas (claim 1).

In a preferred embodiment, an internal combustion engine equipped with a supercharger is used, the air-fuel mixture is supplied to the engine through a compressor of the supercharger, and the exhaust gas is discharged through a turbine of the supercharger. The NOx storage reduction catalyst is provided in an exhaust system after the turbine of the supercharger (claim 2). More preferably, in the above operating method, a part of the exhaust gas is taken out of an exhaust system upstream of a turbine of the supercharger, and is introduced into an intake system upstream of a compressor of the supercharger. (Claim 3).

That is, according to the present invention, when other combustion conditions are the same in the combustion of an internal combustion engine, the temperature of the combustion exhaust gas is reduced by introducing the exhaust gas into the air-fuel mixture as shown in FIG. The rate of decrease is proportional to the amount of exhaust gas mixed, and, as shown in FIG. 5, by introducing exhaust gas into the air-fuel mixture, the knocking generation limit output (net average effective pressure; BMEP) And the occurrence of knocking is substantially suppressed.
It is intended to be effectively used in an exhaust gas purification system of an internal combustion engine using an Ox storage reduction catalyst, and an absorbent saturated by absorbing NOx by being exposed to a lean exhaust gas atmosphere is converted to a stoichiometric air-fuel ratio. When reducing and removing NOx by exposure to the above-described rich exhaust gas, the operating state is switched by the air-fuel ratio control device provided in the intake system, and the intake path is switched when the lean state is switched to the rich state. The exhaust gas is introduced into the air-fuel mixture.

[0014] By causing the air-fuel mixture mixed with the exhaust gas to be sucked into the cylinder and burning, the occurrence of knocking is suppressed, and the excessive rise in the exhaust gas temperature is also avoided. Therefore, even when the combustion state is switched by the air-fuel ratio control device not only at the time of the partial load operation but also at the time of the 100 load operation, the occurrence of knocking is suppressed at the time of switching from the lean state to the rich state, and the exhaust gas temperature is also reduced. Do not rise excessively. Therefore, damage to the device due to mechanical irregular vibration and thermal deterioration due to high temperature can be suppressed, and the life of the internal combustion engine is prolonged.

The method for operating an internal combustion engine according to the present invention can be applied to an internal combustion engine which is normally operated under a partial load, such as an internal combustion engine for an automobile, provided that a continuous long-time operation at 100% load is required. It is particularly effective as a method of operating an internal combustion engine for cogeneration, and makes it possible to purify exhaust gas using a NOx storage reduction catalyst, which has not been implemented conventionally, in an internal combustion engine for cogeneration.

[0016]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a first embodiment, in which an operation method of the present invention is applied to a gas engine 20 having a supercharger 10. In this example, gas G and air A, which are fuels, are mixed to a required air ratio by the gas mixer 1, pressurized by the compressor 11 of the supercharger 10, passed through the intake valve 21 and in the cylinder 22 of the gas engine 20. It is sucked in. The intercooler 2 and the throttle 3 are provided on the path from the compressor 11 to the cylinder 22 as usual.
The above-mentioned path constitutes the intake system referred to in the present invention, and this path may be another intake system of a conventionally known internal combustion engine.

The exhaust gas is supplied from the exhaust valve 23 to the supercharger 10.
After driving the Durbin 12 there, it is discharged to the outside air through a catalyst chamber 30 provided in the middle of the exhaust path. The catalyst chamber 30 contains a NOx storage reduction catalyst. At an upstream position of the catalyst chamber 30 in the exhaust path,
Sensors (oxygen sensor, temperature sensor, etc.) 4 for detecting the state of the exhaust gas are provided.
It is sent to the CU (engine control unit). This exhaust system may be a conventionally known one, and is not limited to this. The ECU is also conventionally known.

As shown in the drawing, a pipe line 51 for supplying fuel gas directly into the air-fuel mixture downstream of the gas mixer 1 by bypassing the gas mixer 1 is provided in the intake path. 52 are arranged. Further, a branch pipe 53 is provided in an exhaust path from the exhaust valve 23 to the supercharger 10, and the branch pipe 53 is connected to the intake path at a position upstream of the supercharger 10. A flow regulating valve 54 is disposed in the branch conduit 53. And 54 of both is E
The opening is controlled by a signal from the CU.

The operation method of the gas engine will be described below, taking as an example the case where this gas engine is used as a prime mover for cogeneration. When used as a prime mover for cogeneration, the air-fuel mixture is leaner than the stoichiometric air-fuel ratio by the gas mixer 1 (excess air ratio λ =
1.5 to 2.0), and is continuously operated for 24 hours under a 100% load condition. At the beginning of the operation, the flow control valves 52 and 54 are closed by a signal from the ECU, and the lean exhaust gas is supplied to the turbine 12.
After driving, the catalyst enters the catalyst chamber 30, where NOx is N
It is absorbed by the absorbent of the Ox storage reduction catalyst.

By continuing the operation in that state, the absorbent gradually becomes saturated. The degree of saturation is detected by a sensor (not shown), or the state is switched to a rich operation state in order to reduce NOx in the absorbent based on a relation table between the operation time and the degree of saturation obtained from past experience. This switching is performed by a signal from the ECU in accordance with the pipeline 51.
This is carried out by opening the flow control valve 52 provided in the above to increase the fuel gas amount of the air-fuel mixture. At the same time as (or immediately before) the flow control valve 52 is opened, the ECU issues a command to open the flow control valve 54 provided in the branch conduit 53 from the ECU.

When the flow control valve 52 is opened, a rich operation state is established, and the exhaust gas flows into the catalyst chamber 30 in a low oxygen state (rich state). As a result, the NOx absorbed by the absorbent of the NOx storage reduction catalyst is reduced and removed. at the same time,
NOx in the exhaust gas is also reduced. Although the air-fuel mixture is in a rich state, the occurrence of knocking in the engine is suppressed by introducing exhaust gas there, and
The temperature of the exhaust gas also does not rise excessively.

By continuing the operation in that state, the absorbent is gradually reduced and returns to the original state. The degree of return is detected by a sensor (not shown), or the state is switched from the rich operation state to the lean operation state based on a relation table between the operation time and the saturation degree obtained from past experience. This switching is performed according to a signal from the ECU.
1 is closed, the fuel gas amount of the air-fuel mixture is returned to the normal state, and the flow adjustment valve 54 provided in the branch pipe 53 is also closed. Thereby, the driving normal state is smoothly switched to the lean normal state. Hereinafter, the above-described switching of the operation state is repeatedly performed.

In the above embodiment, the port of the branch pipe 53 for extracting the exhaust gas is provided in the exhaust path from the exhaust valve 23 to the supercharger 10, and the port for introducing the exhaust gas into the air-fuel mixture is supercharged. It is provided immediately upstream of the compressor 11 of the machine 10. When the state is switched from the lean state to the rich state, the amount of excess air decreases, so the amount of air-fuel mixture to be supplied decreases. Usually, a loss occurs because this is dealt with by reducing the air supply by the throttle valve 3. As in this example, by extracting the exhaust gas before the turbine 12, the work of the turbine is reduced and the work of the compressor 11 is reduced, so that the supercharging pressure can be reduced and the loss due to the throttle is reduced. It is possible to do.

An effect similar to that of a so-called wastegate in an internal combustion engine is achieved, and the extra work of the turbine 12 can be reduced. Further, the throttle loss is reduced by the reduction of the supercharging pressure, and there is an advantage that the thermal efficiency of the engine is not reduced.

In the above embodiment, based on various information from the sensors 4 provided in the exhaust path, for example, the opening of the flow control valve 52 provided in the pipe 51 is appropriately controlled,
Naturally, it is also possible to independently perform the air-fuel ratio control in the required operation state. Further, the positions of the exhaust gas extraction port and the introduction port for introducing the extracted exhaust gas to the intake system are not limited to the above-described embodiment, and may be arbitrary provided that the exhaust gas is directed from the high pressure side to the low pressure side. .

FIG. 2 shows another embodiment. In this example, the position of the exhaust gas extraction port is shown in FIG.
However, the position of the introduction port for introducing the extracted exhaust gas to the intake system is provided downstream of the throttle valve 3 of the engine. In this case, an effect that response is improved as compared with the embodiment of FIG. 1 is brought about.

FIG. 3 shows still another embodiment. In this example, the position of the exhaust gas extraction port and the position of the introduction port for introducing the extracted exhaust gas into the intake system are the same as those in FIG. Although the same, the introduction position of the fuel gas supplied when changing the air-fuel ratio from the lean state to the rich state is different from that in FIG. In this example, a separately provided fuel gas pipe 51a is open to the intake port downstream of the throttle 3, and the pipe 51a
The flow control valve 52a provided in the apparatus is opened and closed according to a command from the ECU. In this case, an effect that response and controllability are improved as compared with the embodiment of FIG.

Although not particularly shown, the position of the exhaust gas take-out port is provided in the exhaust path downstream of the compressor 12 of the supercharger 10, and the introduction port of the taken-out exhaust gas to the intake system is provided at the compressor 11 of the supercharger 10. It may be located at a position more upstream than that. The supply of the fuel gas for changing the air-fuel ratio may be directly performed in the cylinder 22. Further, in the above description, a gas engine has been described as an example, but the present invention is similarly applicable to a gasoline engine.

[0029]

By using the operating method according to the present invention, it is possible to purify exhaust gas using the NOx storage reduction catalyst without causing engine damage due to knocking or the like.
The operation can be stably performed over a long period of time simply by alternately switching the operation state of the air-fuel ratio control device equal to or higher than the stoichiometric air-fuel ratio and the lean air-fuel ratio operation state. In particular, the present invention is applied to one such as an internal combustion engine for cogeneration.
It is effective for exhaust gas purification of an internal combustion engine that is operated continuously for a long time on the assumption that the load is 00%.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of a method for operating an internal combustion engine according to the present invention.

FIG. 2 is a diagram illustrating another embodiment of the operating method of the internal combustion engine according to the present invention.

FIG. 3 is a diagram illustrating another embodiment of the method of operating an internal combustion engine according to the present invention.

FIG. 4 is a diagram showing a relationship between a mixing ratio of exhaust gas and an exhaust gas temperature.

FIG. 5 is a diagram showing a relationship between a mixing ratio of exhaust gas and a knocking occurrence limit output (net average effective pressure; BMEP).

[Explanation of symbols]

10 ... absorber, 11 ... compressor, 12 ... turbine,
Reference Signs List 20: internal combustion engine (gas engine), 30: catalyst chamber for accommodating NOx storage reduction catalyst, 52: fuel gas flow control valve constituting a part of air-fuel ratio control device, 54: exhaust gas flow control valve, 1: gas Mixer, 3 ... throttle, A ... air,
G: Gas, ECU: Engine control unit

────────────────────────────────────────────────── ─── front page continued (51) Int.Cl. ⁶ identifications FI F02B 37/00 302 F02M 21/02 311B F02M 21/02 ZAB 25/07 ZAB 311 550R 25/07 ZAB 570P 550 580B 570 B01D 53 / 36 ZAB 580 102H

Claims (5)

[Claims] 1. An operating method for an internal combustion engine in which a NOx storage reduction catalyst is provided in an exhaust system to purify exhaust gas, and an air-fuel ratio control device is provided in an intake system to operate the engine at a stoichiometric air-fuel ratio or higher. And the lean air-fuel ratio operating state is alternately switched, and a part of the exhaust gas is introduced into the intake system when switching from the lean air-fuel ratio operating state to an operating state higher than the stoichiometric air-fuel ratio. Operating method of the internal combustion engine. 2. The method for operating an internal combustion engine according to claim 1, wherein the internal combustion engine is provided with a supercharger, the air-fuel mixture is supplied via a compressor of the supercharger, and the exhaust gas is supplied to the supercharger. A method for operating an internal combustion engine, wherein the exhaust gas is discharged via a turbine of a supercharger, and the NOx storage reduction catalyst is provided in an exhaust system after the turbine of the supercharger. 3. The method for operating an internal combustion engine according to claim 2, wherein a part of the exhaust gas is taken out of an exhaust system upstream of a turbine of the supercharger, and an intake system is upstream of a compressor of the supercharger. A method for operating an internal combustion engine, wherein the method is adapted to be introduced into a vehicle. 4. The method according to claim 1, wherein the internal combustion engine is a power generation internal combustion engine. 5. The method for operating an internal combustion engine according to claim 1, wherein the internal combustion engine is a cogeneration internal combustion engine.