JPH08281069A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

PURPOSE: To surely and efficiently purify harmful oxides such as nitrogen oxides, etc., in exhaust gas, even though an internal-combustion engine is on either operation state in a cold state or a warming-up state, in an exhaust gas purification device of the internal-combustion engine inserting provided with a reduction catalyst in an exhaust path from the internal-combustion engine. CONSTITUTION: Plural reduction catalysts 20, 22, 24 are arranged in series in the exhaust path 4 from the internal-combustion engine, and plural reducing substance feed nozzles 30, 32, 34 for feeding reduction substance toward each of these reduction catalysts are disposed in the upperstream side of each reduction catalyst. The reducing substance feed nozzles are controlled in accordance with an operation state of the internal-combustion engine, thus supply of the reducing substance from each reducing substance feed nozzle is appropriately performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly to a device for reducing and removing harmful oxides in exhaust gas.

[0002]

2. Description of the Related Art Exhaust gas from an internal combustion engine such as an automobile engine may contain oxides such as nitrogen oxides (NOx) depending on the operating condition of the internal combustion engine. This NOx has an adverse effect on the environment, and it is not preferable to discharge it to the atmosphere. Therefore, a reduction catalyst that accelerates the reduction process of NOx is provided in the exhaust passage extending from the internal combustion engine, whereby NOx is converted into nitrogen (H ₂ ) or carbon dioxide (CO ₂ ) by unburned hydrocarbon (HC) or the like.
_It is decomposed into ₂ ) to prevent the release of NOx into the atmosphere.

However, the purification efficiency of the reduction catalyst depends on the temperature, and if the temperature of the exhaust gas or the reduction catalyst is low,
The purification efficiency is also low. Therefore, in this case, NOx is not sufficiently reduced and is discharged into the atmosphere.
In order to solve such a problem, the number of reducing catalysts is increased, or a reducing substance (for example, HC) is forcibly supplied to the vicinity of the reducing catalyst to create a reducing atmosphere, thereby reducing NOx. Devices to facilitate are known.

[0004]

In recent years, a device having an increased number of the above reduction catalysts and a reducing substance (for example,
It has been considered to combine both of the devices for supplying (HC) to promote the reduction of NOx better. That is, an apparatus has been proposed that supplies a reducing substance (HC) to the most upstream reduction catalyst of a plurality of reduction catalysts.

In such a device, when the internal combustion engine is in a cold state where it has not yet warmed up, such as immediately after starting the internal combustion engine, the exhaust gas temperature is low, so the reducing substance (HC) is immediately activated. That is, it is not activated, that is, it is gradually activated while flowing in the plurality of reduction catalysts. Therefore, the reducing substance (HC) is
It will be used primarily by the reduction catalyst located downstream to reduce NOx.

On the other hand, when the internal combustion engine is sufficiently warmed up, the exhaust gas temperature is high and the reducing substance (HC) is easily activated, so that the reducing substance (HC) is substantially in the most upstream reduction catalyst. It becomes a completely activated state, and eventually, only the most upstream reduction catalyst is used to reduce NOx. Normally, most of the internal combustion engine is warmed up when it is operated. Therefore, in such a device, the frequency of use of the reduction catalyst located downstream is very low,
Only the most upstream reduction catalyst is overused and deteriorates rapidly, which is not efficient.

The present invention has been made based on the above-mentioned circumstances, and its purpose is to provide nitrogen in exhaust gas regardless of whether the internal combustion engine is in a cold state or a warm-up state. An object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can reliably and efficiently purify harmful oxides such as oxides (NOx).

[0008]

In order to achieve the above-mentioned object, the invention of claim 1 has a plurality of reduction catalysts provided in series in an exhaust passage from an internal combustion engine and the exhaust passage, and each of the reducing catalysts has an individual exhaust catalyst. A plurality of reducing substance supply nozzles, which are provided upstream of the reducing catalyst and supply the reducing substance toward the reducing catalyst, and the reducing substance supply nozzles according to the operating state of the internal combustion engine. And a control means for controlling the supply.

Further, in the invention of claim 2, the control means supplies the reducing substance from all of the reducing substance supply nozzles when the exhaust temperature from the internal combustion engine is high, and the exhaust temperature is controlled to be high. In a low operating state, the reducing substance is supplied only from the most upstream reducing substance supply nozzle. In the invention of claim 3,
A plurality of reducing catalysts provided in series in an exhaust passage from the internal combustion engine, and a plurality of reducing catalysts provided in the exhaust passage, each upstream of the respective reducing catalysts, and supplying a reducing substance toward the reducing catalysts. A reducing substance supply nozzle, temperature detecting means for detecting exhaust gas temperature or the temperature of the reducing catalyst, and control means for controlling the supply of the reducing substance by the reducing substance supply nozzle according to the output from the temperature detecting means. It is characterized by including.

Further, in the invention of claim 4, the controller controls the reducing substance supply nozzle when the exhaust gas temperature or the temperature of the reducing catalyst is equal to or higher than the catalyst activation temperature that maximizes the purification rate of the reducing catalyst. It is characterized in that the reducing substance is supplied from all of them, and when the temperature is not higher than the catalyst activation temperature, the reducing substance is supplied only from the most upstream reducing substance supply nozzle.

According to a fifth aspect of the invention, the internal combustion engine is a diesel engine. Further, the invention of claim 6 is characterized in that the internal combustion engine is a lean burn engine.

[0012]

According to the exhaust gas purification device for an internal combustion engine of claim 1,
A plurality of reducing substance supply nozzles provided respectively upstream of the plurality of reducing catalysts arranged in series in the exhaust passage from the internal combustion engine are controlled by the control means according to the operating state of the internal combustion engine. As a result, an appropriate amount of reducing substance according to each situation is supplied from each reducing substance supply nozzle toward the reduction catalyst, and the harmful oxides in the exhaust gas are satisfactorily reduced and removed. At the same time, the reducing substance also combines with the residual oxygen that adheres to the reducing catalyst and reduces the reducing function, and the purification performance of the reducing catalyst is maintained.

Further, according to the exhaust gas purifying apparatus for an internal combustion engine of claim 2, when the exhaust gas temperature from the internal combustion engine is high, the reducing substance is supplied from all of the reducing substance supply nozzles while the exhaust gas temperature is high. In the low operating state, the reducing substance is supplied only from the most upstream reducing substance supply nozzle, and the reducing substance is used appropriately without waste,
In addition, the reduction catalyst is used efficiently, and the harmful oxides in the exhaust gas are satisfactorily reduced and removed.

Further, according to the exhaust gas purifying apparatus for an internal combustion engine of claim 3, a plurality of reducing substances are provided respectively upstream of a plurality of reducing catalysts arranged in series in an exhaust passage from the internal combustion engine. The supply nozzle is controlled by the control means in accordance with the exhaust temperature or the temperature of the reducing catalyst, whereby an appropriate amount of reducing substance is supplied from each reducing substance supply nozzle toward the reducing catalyst and discharged. The harmful oxides in the gas are reduced and removed well. At the same time, the reducing substance also combines with the residual oxygen that adheres to the reducing catalyst and reduces the reducing function, and the purification performance of the reducing catalyst is maintained. Further, according to the exhaust gas purification apparatus for an internal combustion engine of claim 4, when the exhaust gas temperature or the temperature of the reduction catalyst is equal to or higher than the catalyst activation temperature which maximizes the purification rate of the reduction catalyst, the reduction substance is supplied from all of the reducing substance supply nozzles. While being supplied
When the exhaust temperature or the temperature of the reducing catalyst is equal to or lower than the catalyst activation temperature, the reducing substance is supplied only from the reducing substance supply nozzle on the most upstream side, the reducing substance is preferably used without waste, and the reducing catalyst is used. It is used efficiently and the harmful oxides in the exhaust gas are well reduced and removed.

Further, according to the exhaust gas purifying apparatus for an internal combustion engine of claim 5, the reducing substance is contained in the exhaust gas from the diesel engine in a particularly large amount and is excellently combined with the residual oxygen adhering to the reducing catalyst. Therefore, the harmful oxides in the exhaust gas are reduced and removed, and the reduction of the purification performance of the reduction catalyst due to the adhesion of residual oxygen is suitably prevented. Further, according to the exhaust gas purification apparatus for an internal combustion engine of claim 6, a harmful oxide particularly contained in a large amount in the exhaust gas from the lean burn engine is satisfactorily reduced, and the residual substance attached to the reducing substance and the reducing catalyst remains. Due to the combination with oxygen, the reduction of the purification performance of the reduction catalyst due to the adhesion of residual oxygen can be preferably prevented.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration diagram of an exhaust emission control device. As shown in the figure, an exhaust pipe (exhaust passage) 4 extends from an exhaust port 2 of a vehicle engine (for example, a diesel engine) 1. A reduction catalyst unit (for example, a NOx catalyst unit) 10 is interposed in the exhaust pipe 4, and a muffler (not shown) is attached to the rear end portion.

FIG. 2 is a plan sectional view showing the structure of the NOx catalyst unit 10. As shown in the figure, NO
The housing 12 of the x catalyst unit 10 is arranged so as to be continuous with the exhaust pipe 4. Housing 12
There is a predetermined interval inside the NO
The x catalyst 20, the NOx catalyst 22, and the NOx catalyst 24 are provided so that their outer peripheral surfaces are in contact with the inner wall surface of the housing 12.

These NOx catalysts 20, 22, 24 are
For example, the engine 1 is composed of a zeolite carrier or the like.
Nitrogen oxides (NOx) in the exhaust gas discharged from the exhaust gas are once adsorbed to generate nitrogen (N ₂ ) and carbon dioxide (CO ₂ ) in the presence of a reducing agent such as hydrocarbon (HC). It has the function of reducing to. NOx catalyst 20, 22, 24
Of the fuel injection nozzle 30, the fuel injection nozzle 32, and the fuel injection nozzle 3 in this order from the upstream side such that the housing 12 penetrates the housing 12 at the respective upstream ends of the housing 12 so that the front ends thereof face the inside of the housing 12.
A plurality of reducing substance supply nozzles 4 are provided respectively. These fuel injection nozzles 30, 32, 34 are injectors for injecting fuel (for example, light oil) in a mist state, and a fuel pipe 36 is branched and connected to each rear end portion. The fuel pipe 36 is connected to a fuel tank (not shown). As a result, NOx
Fuel (light oil) can be supplied to the inside of the catalyst unit 10.

Further, these fuel injection nozzles 30, 32,
34 includes an electric fuel injection valve whose opening changes according to an electric signal, and an electronic control unit (ECU) 4
It is electrically connected to 0. A temperature sensor (temperature detecting means) 42 for detecting the exhaust temperature TEXH is attached to the exhaust pipe 4 at a position slightly upstream of the NOx catalyst unit 10. The temperature sensor 42 is also electrically connected to the ECU 40.

The above-mentioned temperature sensor 42 is connected to the input side of the electronic control unit (ECU) functioning as the control means, and the fuel injection nozzles 30, 32 and 34 are connected to the output side. When a detection signal is supplied from the temperature sensor 42, the ECU 40 supplies an operation signal to each of the fuel injection nozzles 30, 32 and 34 in response to this signal.

The operation of the exhaust gas purification device thus constructed will be described below. When the engine 1 is started,
The temperature sensor 42 starts to detect the exhaust gas temperature TEXH. Then, a detection signal is supplied from the temperature sensor 42 to the ECU 40, and the ECU 40 causes the exhaust temperature TEXH based on the detection signal to be detected.
Determines whether the temperature has reached a predetermined temperature TS. As the predetermined temperature TS, for example, a temperature at which the engine 1 can be considered to have changed from the cold state to the warm operating state is used.

FIG. 3 shows the catalyst temperature TC and the NOx catalyst 20.
The graph showing the relationship with the purification efficiency η of is shown. In the figure, the catalyst temperature TC changes approximately equal to the exhaust temperature TEXH, and the purification efficiency η shows the NOx catalyst 20.
Shows the reducing ability of. As shown in the figure, the purification efficiency η increases with an increase in the catalyst temperature TC, that is, the exhaust gas temperature TEXH, becomes maximum at a predetermined temperature (catalyst activation temperature) T1, and then decreases.

Here, the predetermined temperature T1 is the temperature of the engine 1
It has been found that the temperature of the exhaust gas is considered to have changed from the cold state to the warm operating state, and therefore, it is usually necessary to determine whether or not the exhaust gas temperature TEXH has reached the predetermined temperature TS. Predetermined temperature T S
1 is used. The predetermined temperature T1 has a unique value that varies depending on the type (material, etc.) of the NOx catalyst, so that the predetermined temperature TS changes depending on the type of NOx catalyst.

When it is determined that the exhaust gas temperature TEXH has not reached the predetermined temperature Ts, the ECU 40 supplies the operation signal only to the fuel injection nozzle 30 located on the most upstream side, and only the fuel injection nozzle 30 receives the operation signal. Inject a fixed amount of fuel. As a result, the fuel is atomized together with the exhaust gas and N
It will sequentially flow into the Ox catalysts 20, 22, and 23.
Then, a large amount of hydrocarbon (HC) contained in the fuel acts as a reducing agent, and NOx is reduced in the NOx catalysts 20, 22, 23.

When the exhaust gas temperature TEXH is low, the HC does not activate immediately, and the NOx catalyst 20 and the NOx are not activated.
The catalyst is gradually activated while passing through the x catalyst 22. Therefore, in this case, most of the HC is mainly mainly NOx catalyst 24.
It will function as a reducing agent inside. Normally, when the exhaust temperature TEXH is low, the amount of NOx generated is small, so that NOx is substantially completely reduced even by injecting fuel from the fuel injection nozzle 30 and does not adversely affect the environment. Further, by not injecting the fuel from the fuel injection nozzles 32 and 34 on the downstream side in this way, the fuel is not discharged into the atmosphere in a raw gas state, so There is no adverse effect on the environment by supplying

On the other hand, the exhaust temperature TEXH is determined by the ECU 40.
When it is determined that the temperature has reached the predetermined temperature TS, the ECU
40 supplies an operation signal to all of the fuel injection nozzles 30, 32, 34, and these fuel injection nozzles 30, 32, 34
A predetermined amount of fuel is injected from each (state shown in FIG. 2). As a result, the fuel injected from the fuel injection nozzle 30 is injected into the NOx catalyst 20, the fuel injected from the fuel injection nozzle 32 into the NOx catalyst 22, and the fuel injected from the fuel injection nozzle 34 into the NOx catalyst 24. It will be atomized together with the exhaust gas.

When the exhaust gas temperature TEXH is high as described above, the HC in the fuel is immediately activated and reformed, so that the HC in the fuel injected from the fuel injection nozzle 30 is NOx.
In the catalyst 20, HC in the fuel from the fuel injection nozzle 32 is absorbed in the NOx catalyst 22 and also in the fuel injection nozzle 3
HC in the fuel from No. 4 is well used as a reducing agent in the NOx catalyst 24 and is completely used up.

Normally, when the exhaust temperature TEXH is high, N
A large amount of Ox is generated, but in this way the NOx catalyst 2
If all the catalytic functions of 0, 22, and 24 are effectively used, NOx will be reduced almost completely without being emitted into the atmosphere, and will not adversely affect the environment. Further, when the exhaust gas temperature TEXH is at an intermediate temperature, that is, near the predetermined temperature Ts, it is possible to perform control so that the ECU 40 supplies an operation signal only to the two fuel injection nozzles upstream of the fuel injection nozzles 30 and 32. . In this case, the NOx catalyst 2 in which the exhaust gas is located second
Even if there is HC that is not activated when passing through 2, the unactivated HC is in a sufficiently activated state by the time it reaches the NOx catalyst 24, and is in the state of raw gas. NOx without being discharged into the atmosphere as it is
It will be used well and completely in catalyst 24 to fully reduce NOx.

If the engine 1 is a diesel engine, the exhaust gas may contain a large amount of residual oxygen (O ₂ ), and this O ₂ tends to adhere to the NOx catalyst. As described above, if O ₂ adheres to the NOx catalyst, the NOx purification efficiency decreases, but as described above, fuel is injected from the fuel injection nozzle and HC is discharged.
When O is supplied, this O ₂ also reacts with HC and CO ₂ and H ₂
Since it is decomposed into O, the purification efficiency of the NOx catalyst is always maintained excellent.

As described above in detail, in the exhaust emission control device of the present invention, the NOx catalyst is replaced by the NOx catalysts 20, 22,
The fuel injection nozzles 30, 32, and 34 are arranged at the upstream positions of the NOx catalysts 20, 22, and 24 so as to be divided and provided in series as shown in FIG. 24, and the emission changes according to the operating state of the engine 1. Since the fuel injection nozzle for injecting fuel is selected based on the gas temperature and a proper amount of fuel is injected, the reducing agent HC in the fuel is prevented from being discharged into the atmosphere and is effective without waste. Further, it is possible to use all of the NOx catalysts 20, 22, and 24 efficiently to reduce NOx in the exhaust gas satisfactorily and surely, and to appropriately diffuse NOx into the atmosphere. It can be prevented.

In the above embodiment, the fuel injection nozzle 3
The fuel injected from 0, 32, and 34 is light oil, for example, but other fuels containing a reducing agent such as HC as a main component may be used. Further, in the above-described embodiment, the engine 1 is, for example, a diesel engine, but may be a gasoline engine, and particularly NOx emission amount and residual O 2
It has a great effect on a lean-burn engine with a large emission of ₂ . However, in this case, it is preferable to inject gasoline from the fuel injection nozzle, the exhaust passage from the gasoline engine is provided with an oxidation catalyst (three-way catalyst, etc.) together with a reduction catalyst (NOx catalyst), and carbon monoxide CO It is preferable to purify harmful components such as.

In the above embodiment, the exhaust temperature TEXH of the engine 1 is detected, but the invention is not limited to this.
Catalyst temperature TC of any of the NOx catalysts 20, 22, 24
May be detected. In this case, a more accurate control can be performed because the cold state and the warm-up state of the engine 1 are directly determined by whether or not the catalyst temperature TC has reached the predetermined temperature T1. it can.

[0033]

As described above, according to the exhaust gas purifying apparatus for an internal combustion engine of claim 1, a plurality of reducing catalysts provided in series in an exhaust passage from the internal combustion engine and an individual reducing catalyst in the exhaust passage, respectively. A plurality of reducing substance supply nozzles provided upstream of the catalyst for supplying the reducing substance toward the reducing catalyst, and control means for controlling the supply of the reducing substance by the reducing substance supply nozzles according to the operating state of the internal combustion engine. Since it is equipped with, the appropriate amount of reducing substance according to each situation is supplied from each reducing substance supply nozzle toward the reduction catalyst, and the harmful oxides in the exhaust gas are satisfactorily reduced. Can be removed. At the same time, the residual oxygen adhering to the reduction catalyst can be removed, and the purification performance of the reduction catalyst can always be kept good.

According to another aspect of the exhaust gas purifying apparatus for an internal combustion engine, the control means supplies the reducing substance from all of the reducing substance supply nozzles when the exhaust gas temperature from the internal combustion engine is high and the exhaust gas is exhausted. When the temperature is low, the reducing substance is supplied only from the most upstream reducing substance supply nozzle, so the reducing substance is always used properly without waste,
In addition, the reduction catalyst can be efficiently used to satisfactorily reduce and remove harmful oxides in the exhaust gas.

Further, according to the exhaust gas purifying apparatus for an internal combustion engine of claim 3, a plurality of reducing catalysts are provided in series in an exhaust passage from the internal combustion engine, and the reducing catalyst is positioned in the exhaust passage upstream of each reducing catalyst. A plurality of reducing substance supply nozzles for supplying a reducing substance toward the reducing catalyst, a temperature detecting means for detecting the exhaust gas temperature or the temperature of the reducing catalyst, and a reducing substance supply according to the output from the temperature detecting means. Since it is provided with a control means for controlling the supply of the reducing substance by the nozzle, it is possible to supply an appropriate amount of the reducing substance from each reducing substance supply nozzle to the reduction catalyst according to each situation, and to discharge the reducing catalyst. The harmful oxides in the gas can be satisfactorily reduced and removed. At the same time, the residual oxygen adhering to the reduction catalyst can be removed, and the purification performance of the reduction catalyst can always be kept good.

Further, according to the exhaust gas purifying apparatus for an internal combustion engine of claim 4, the control means supplies the reducing substance when the exhaust gas temperature or the temperature of the reducing catalyst is equal to or higher than the catalyst activation temperature which maximizes the purifying rate of the reducing catalyst. Supplying reducing substances from all of the nozzles,
When the temperature is lower than the catalyst activation temperature, the reducing substance is supplied only from the most upstream reducing substance supply nozzle. Therefore, the reducing substance can be used properly without waste, and the reducing catalyst can be used efficiently, thereby reducing the exhaust gas. The harmful oxides therein can be satisfactorily reduced and removed.

According to the exhaust gas purifying apparatus for an internal combustion engine of claim 5, since the internal combustion engine is a diesel engine,
In addition to reducing and removing harmful oxides in exhaust gas,
It is possible to satisfactorily remove the residual oxygen that is particularly contained in the exhaust gas from the diesel engine and adheres to the reduction catalyst, and it is possible to always maintain the purification performance of the reduction catalyst in a suitable manner. Further, according to the exhaust gas purifying apparatus for an internal combustion engine of claim 6, since the internal combustion engine is a lean burn engine, it is possible to satisfactorily reduce and remove harmful oxides contained in exhaust gas from the lean burn engine. It is possible to satisfactorily remove the residual oxygen contained in the exhaust gas and adhering to the reduction catalyst, and it is possible to always maintain the purification performance of the reduction catalyst in a suitable manner.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an exhaust emission control device.

FIG. 2 is a plan sectional view of a reduction catalyst unit including a plurality of reduction catalysts.

FIG. 3 is a graph showing the relationship between the catalyst temperature TC of the reduction catalyst and the purification efficiency η.

[Explanation of symbols]

 Reference Signs List 1 engine 4 exhaust pipe (exhaust passage) 10 NOx catalyst unit 20 NOx catalyst (reduction catalyst) 22 NOx catalyst (reduction catalyst) 24 NOx catalyst (reduction catalyst) 30 fuel injection nozzle (reducing substance supply nozzle) 32 fuel injection nozzle (reduction) Substance supply nozzle) 34 Fuel injection nozzle (reducing substance supply nozzle) 36 Fuel pipe 40 Electronic control unit (ECU) 42 Temperature sensor (temperature detection means)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeru Haruto 5-3-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation

Claims (6)

[Claims] 1. A plurality of reduction catalysts provided in series in an exhaust passage from an internal combustion engine, and a plurality of reduction catalysts provided in the exhaust passage, respectively, located upstream of the respective reduction catalysts, and reduced toward the reduction catalyst. An internal combustion engine, comprising: a plurality of reducing substance supply nozzles for supplying a substance; and a control means for controlling the supply of the reducing substance by the reducing substance supply nozzle according to an operating state of the internal combustion engine. Exhaust purification device. 2. The control means supplies the reducing substance from all of the reducing substance supply nozzles in an operating state where the exhaust gas temperature from the internal combustion engine is high. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the reducing substance is supplied only from the upstream side of the reducing substance supply nozzle. 3. A plurality of reduction catalysts provided in series in an exhaust passage from an internal combustion engine, and a plurality of reduction catalysts provided in the exhaust passage, respectively, located upstream of the respective reduction catalysts, and reduced toward the reduction catalyst. A plurality of reducing substance supply nozzles for supplying a substance, a temperature detecting means for detecting an exhaust temperature or a temperature of the reducing catalyst, and a supplying of the reducing substance by the reducing substance supply nozzle according to an output from the temperature detecting means. An exhaust emission control device for an internal combustion engine, comprising: a control unit for controlling. 4. The control means supplies the reducing substance from all of the reducing substance supply nozzles when the exhaust gas temperature or the temperature of the reducing catalyst is equal to or higher than a catalyst activation temperature that maximizes the purification rate of the reducing catalyst. 4. The exhaust emission control device for an internal combustion engine according to claim 3, wherein when the catalyst activation temperature is lower than or equal to the catalyst activation temperature, the reducing substance is supplied only from the most upstream side reducing substance supply nozzle. 5. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the internal combustion engine is a diesel engine. 6. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the internal combustion engine is a lean burn engine.