JP2013124608A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device that has proper purification performance by preventing wasteful exhaust of reducing gas such as ammonia produced from an urea aqueous solution and achieving acceleration of ammonia decomposition reaction and reductive reaction in an SCR catalyst.SOLUTION: An exhaust emission control device of an internal combustion engine (10), which has an NOx selective-reduction catalyst (36) provided in an exhaust passage (18), includes: an exhaust air reflux passage (44) which communicates between an upstream-side reflux gas exhaust port (46) and a reflux gas introduction port (42) provided on a downstream side of the NOx selective-reduction catalyst; a reflux control valve (48) for opening and closing the exhaust air reflux passage; and straightening means (40, 50 and 52) for straightening reflux gas in the exhaust air reflux passage.

Description

The present invention, _the NO _X selective reducing catalyst provided in an exhaust passage of an internal combustion engine, to decompose the reducing agent solution supplied to the upstream side of the _the NO _X selective reducing catalyst to generate NH _3, and wherein _the NO _X selective reducing catalyst The present invention relates to a technical field of an exhaust gas purification device for an internal combustion engine that makes NO _X contained in exhaust gas react with the generated NH ₃ under the catalytic action of the above to make it harmless.

  As a diesel engine exhaust gas purification method, an SCR (Selective Catalytic Reduction) system using an aqueous urea solution has been put into practical use. The SCR system injects a urea aqueous solution as a reducing agent into exhaust gas, and decomposes urea in the urea aqueous solution into ammonia using heat retained in the exhaust gas.

This decomposition process into ammonia consists of the following three-stage reaction formula. As the temperature required for the reaction in each step, the retained heat of the exhaust is used.
First step: CO (NH ₂ ) ₂ aq (urea aqueous solution) → CO (NH ₂ ) ₂ (solid urea)
<Production of solid urea by evaporation of water; reaction required temperature of 100 ° C. or higher>
Second step: CO (NH ₂ ) ₂ (solid urea) → HNCO (isocyanic acid) + NH 3
<Thermal decomposition of solid urea; reaction required temperature 130-200 ° C.>
Third step: HNCO + H ₂ O → NH 3 + CO ₂
<Hydrolysis of isocyanic acid; reaction required temperature of 200 ° C. or higher>

In the SCR system, an SCR catalyst is disposed on the downstream side of the urea aqueous solution injection section, and NO _X contained in the exhaust gas is adsorbed on the SCR catalyst, and is subjected to a reduction reaction with ammonia and decomposed into nitrogen and water. (see the following reaction formula) you are reducing the exhaust concentration of NO _{X.
NO X + NH3 = NO 2 +} H 2 O

  By the way, a diesel engine mounted vehicle may be provided with a DPF (Diesel Particulate Filter) device that removes particulate matter in exhaust gas. When the SCR system is provided in the exhaust passage of the vehicle, it is generally arranged on the downstream side of the DPF device and on the lower floor of the vehicle in consideration of the heat resistance of the SCR catalyst and the arrangement space. In this case, the exhaust temperature reaching the SCR catalyst is low, but on the other hand, as described above, the decomposition reaction into ammonia requires a certain temperature or higher (preferably 200 ° C. or higher). Also, a catalytic activation temperature is required when a reduction reaction is performed with the SCR catalyst using the produced ammonia. For this reason, under a situation where the exhaust temperature is low, such as at the time of start-up or low speed / low load driving, the decomposition reaction of the urea aqueous solution into ammonia and the reduction reaction in the SCR catalyst are difficult to proceed. As a result, the injected urea aqueous solution and the generated ammonia are directly discharged to the downstream side of the catalyst, and the consumption amount and purification efficiency of the urea aqueous solution may be reduced.

  In order to raise the exhaust gas temperature, it is also known to perform an early temperature raising operation such as post-injection, which causes deterioration of fuel consumption and exhaust properties. As described above, the disposition position of the SCR catalyst is far from the engine, and the exhaust temperature greatly decreases. Therefore, it is not easy to raise the exhaust temperature upstream of the SCR catalyst.

Patent Document 1 discloses an example of an exhaust purification device using this type of SCR catalyst (selective reduction catalyst). In Patent Document 1, in particular, an oxidation catalyst is provided in front of the SCR catalyst, and a bypass passage is provided so that exhaust gas diverted from the upstream side of the oxidation catalyst is introduced downstream of the oxidation catalyst. Yes. Then, by controlling the flow rate in the bypass passage, excessive NO ₂ generation in the oxidation catalyst is suppressed so that the NO / NO ₂ ratio in the exhaust gas is in an optimal range of 1 to 1.5, and NO _X purification performance is improved.

Japanese Patent No. 4267538

It has improved the NO _X purification performance by optimizing the above-mentioned Patent Document 1, NO / NO ₂ ratio. However, as described above, the arrangement position of the SCR catalyst is far from the engine, and the exhaust temperature is greatly reduced. Therefore, there is a problem that the decomposition reaction of the urea aqueous solution into ammonia and the promotion of the reduction reaction in the SCR catalyst are not sufficient. In particular, if ammonia generated by the decomposition reaction of the urea aqueous solution is discharged without being reacted, the discharged ammonia is wasted, and the consumption amount of the urea aqueous solution is increased correspondingly, resulting in poor efficiency.

  The present invention has been made in view of the above problems, and prevents the reduction gas such as ammonia generated from the aqueous urea solution from being wasted, and promotes the decomposition reaction of ammonia and the reduction reaction in the SCR catalyst. An object of the present invention is to provide an exhaust purification device having good purification performance.

For exhaust gas purification apparatus for an internal combustion engine according to the present invention is to solve the above problems, _the NO _X selective reducing catalyst provided in an exhaust passage of an internal combustion engine, the reducing agent solution supplied to the upstream side of the _the NO _X selective reducing catalyst decomposed to generate NH _3, in an exhaust gas purification apparatus for an internal combustion engine to harmless is reacted with NH ₃ produced the the NO _X contained in the exhaust gas under the catalytic action of the _the NO _X selective reducing catalyst, exhaust from the NO _X recirculated gas inlet port provided on the downstream side of the selective reduction catalyst, said bypassing _the NO _X selective reducing catalyst, leading to the _the NO _X selective recirculation gas discharge port provided on the upstream side of the reduction catalyst A recirculation passage, a recirculation control valve that opens and closes between the downstream side of the NO _X selective reduction catalyst and the exhaust recirculation passage, and exhaust gas introduced from the recirculation gas inlet in the exhaust recirculation passage At the exit And rectifying means for rectifying so as to flow in the direction.

According to the present invention, by utilizing the pressure difference between the upstream side and the downstream side of the NO _X selective reducing catalyst, the NH ₃ discharged downstream from _the NO _X selective reducing catalyst, _the NO _X selective through the exhaust gas recirculation passage Reflux to the upstream side of the reduction catalyst. Thereby, NH ₃ contained in the exhaust gas is not discharged to the outside and is not wasted. By thus effectively reused NH _3, and it is possible to improve the NO _X purification efficiency in _the NO _X selective reducing catalyst, it is possible to reduce the consumption of the reducing agent solution.

Preferably, the rectifying means may include a check valve for preventing a backflow of the reflux gas flowing through the exhaust gas recirculation passage. The pressure difference between the upstream side and the downstream side of the NO _X selective reduction catalyst varies depending on the pulsation effect of the exhaust passage. Therefore, depending on the conditions, the pressure on the upstream side of the NO _X selective reduction catalyst may be higher than that on the downstream side, and the reflux gas flowing through the exhaust gas recirculation passage may flow backward from the recirculation gas discharge port toward the recirculation gas introduction port. There can be. In this aspect, by providing a check valve in the exhaust gas recirculation passage, such a back flow can be prevented and the recirculation gas can be reliably introduced from the recirculation gas inlet to the recirculation gas outlet.

The rectifying means is provided downstream of the recirculation gas inlet, and controls the exhaust gas pressure downstream of the NO _X selective reduction catalyst by adjusting the flow rate of the exhaust gas in the exhaust passage. A control valve may be provided. In this aspect, the pressure on the downstream side of the NO _X selective reduction catalyst can be controlled by controlling the opening degree of the pressure control valve. Thereby, the magnitude of the pressure difference between the upstream side and the downstream side of the NO _X selective reduction catalyst can be adjusted, and the amount of the reflux gas introduced into the exhaust gas recirculation passage can be controlled.

  The rectifying means may include a pressure pump that pumps exhaust gas introduced from the recirculation gas introduction port toward the recirculation gas discharge port in the exhaust recirculation passage. In this aspect, since the recirculation gas flowing through the exhaust gas recirculation passage can be directly pumped by the pressure pump, the amount of recirculation gas introduced into the exhaust gas recirculation passage can be adjusted more reliably.

  The reflux gas discharge port may be provided on the downstream side of the reducing agent supply port. According to this aspect, the recirculation gas supplied from the recirculation gas discharge port can be well dispersed with respect to the reductant solution sprayed from the reductant supply port carried by the flow of the exhaust gas.

Further, the recirculation gas supplied from the recirculation gas discharge port may be supplied in a direction opposite to a traveling direction of the exhaust gas flowing through the upstream side exhaust passage of the NO _X selective reduction catalyst. According to this aspect, the recirculation gas supplied from the recirculation gas discharge port can be well agitated with the exhaust gas flowing through the exhaust passage.

Further, it is preferable to further include a first heating means for heating the reflux gas introduced into the exhaust gas recirculation passage. According to this embodiment, by heating the recirculation gas to increase the exhaust gas temperature to be supplied to the NO _X selective reducing catalyst, it is possible to promote the reduction reaction in _the NO _X selective reducing catalyst.

Also, it may further comprise a second heating means for heating the _the NO _X selective reducing catalyst. Deposits formed by the urea aqueous solution adhering to the upstream inlet portion of the NO _X selective reduction catalyst and the exhaust passage in the vicinity thereof tend to accumulate. According to this aspect, the deposit fixed by the second heating means can be heated and sublimated to remove the deposit and to generate NH ₃ . Then, the generated NH ₃ is supplied again to the upstream side of the NO _X selective reduction catalyst via the exhaust gas recirculation passage, whereby the purification efficiency can be improved efficiently.

According to the present invention, by utilizing the pressure difference between the upstream side and the downstream side of the NO _X selective reducing catalyst, the NH ₃ discharged downstream from _the NO _X selective reducing catalyst, _the NO _X selective through the exhaust gas recirculation passage Reflux to the upstream side of the reduction catalyst. Thereby, NH ₃ contained in the exhaust gas is not discharged to the outside and is not wasted. By thus effectively reused NH _3, and it is possible to improve the NO _X purification efficiency in _the NO _X selective reducing catalyst, it is possible to reduce the consumption of the reducing agent solution.

It is a mimetic diagram showing the whole exhaust-air-purification device composition concerning a 1st embodiment. It is an enlarged view which shows the modification of the structure of the recirculation | reflux gas discharge port vicinity. It is a schematic diagram which shows the whole structure of the exhaust gas purification apparatus which concerns on 2nd Embodiment. It is a schematic diagram which shows the whole structure of the exhaust gas purification apparatus which concerns on 3rd Embodiment.

  Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this embodiment are not intended to limit the scope of the present invention to that unless otherwise specified.

(First embodiment)
An embodiment in which the device of the present invention according to the first embodiment is applied to an in-vehicle diesel engine 10 will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic diagram showing an overall configuration of an exhaust emission control device according to the first embodiment. In FIG. 1, a cylinder head 14 is provided on an upper part of a cylinder block 12 of an in-vehicle diesel engine 10, and an intake pipe 16 and an exhaust pipe 18 are connected to the cylinder head 14. The exhaust pipe 18 is connected to the exhaust turbine 20 a of the supercharger 20. An oxygen concentration sensor 22 is provided on the downstream side of the exhaust turbine 20a. An oxidation catalyst 24 is provided downstream of the oxygen concentration sensor 22, and a DPF device 26 is provided further downstream of the oxidation catalyst 24.

Of the exhaust pipe 18 on the downstream side of the exhaust turbine 20a, a portion where the DPF device 26 is provided is arranged in the vertical direction (this portion is referred to as a vertical portion 18a). On the downstream side of the vertical portion 18a, the exhaust pipe 18 is provided with a horizontal portion 18b arranged in a substantially horizontal direction via a bent portion 18c. The horizontal portion 18b includes, in order from the upstream side, a NO _X sensor 30 that detects the NO _X concentration in the exhaust, a urea water supply device 32 that supplies a urea aqueous solution that is a reducing agent solution to the exhaust pipe 18, and a catalytic converter 34. Is provided. An SCR catalyst 36 is built in the catalytic converter 34. The urea water supply device 32 sprays urea aqueous solution into the exhaust gas upstream of the catalytic converter 34. When the exhaust gas temperature reaches the ammonia generation temperature or higher, the sprayed urea aqueous solution is based on the above reaction formula. Decomposed into ammonia. The generated ammonia reacts with the NO _X adsorbed in the SCR catalyst 36 located downstream, are used in the NO _X purification of exhaust gases.

A downstream exhaust pipe 18 of the catalytic converter 34, NO _X sensor 38 for detecting the NO _X concentration in the exhaust gas catalytic converter 34 after passing through is provided on the downstream side of the NO _X sensor 38, a catalytic converter A pressure control valve 40 for controlling the pressure of exhaust gas (exhaust pressure) on the downstream side of 34 is provided. The pressure control valve 40 can adjust the exhaust pressure downstream of the catalytic converter 34 by adjusting the opening degree. The detected values of the NO _X concentration sensors 30 and 38 indicate the NO _X concentration of the exhaust gas before and after the NO _X purification device, and the NO _X purification rate of the exhaust gas is detected based on these detected values. It has become.

  In this configuration, the exhaust e is discharged from the cylinder head 14 by the operation of the on-board diesel engine 10, and the exhaust e exhausted to the exhaust pipe 18 is downstream of the exhaust pipe 18 by the exhaust turbine 20 a of the supercharger 20. Sent.

  Here, a recirculation gas inlet 42 is provided downstream of the catalytic converter 34 in the exhaust passage 18, and a part of the exhaust gas is introduced into the exhaust recirculation passage 44 from the recirculation gas introduction port 42. The exhaust gas recirculation passage 44 bypasses the catalytic converter 34 and communicates with a recirculation gas discharge port 46 provided on the upstream side of the catalytic converter 34. The exhaust gas recirculation passage 44 in the vicinity of the recirculation gas introduction port 42 is provided with a recirculation control valve 48 that opens and closes between the downstream exhaust passage 18 and the exhaust gas recirculation passage 44 of the catalytic converter 34. Note that the reflux control valve 48 may be one that turns on and off the open / close state, or may be configured to arbitrarily adjust the reflux amount.

  The exhaust gas introduced from the exhaust pipe 18 is recirculated to the exhaust gas recirculation passage 44 in accordance with the pressure difference between the recirculation gas introduction port 42 and the recirculation gas discharge port 46. The exhaust gas recirculation passage 44 is provided with a rectifying means for rectifying the exhaust gas introduced from the recirculation gas introduction port 42 so as to flow toward the recirculation gas discharge port 46, and the flow of the recirculation gas is controlled. . In this embodiment, in particular, a check valve 50, a pressure control valve 40, and a pressure feed pump 52 described below are provided as the rectifying means.

  The check valve 50 is provided in the vicinity of the recirculation gas discharge port 46 of the exhaust recirculation passage 44 and prevents the recirculation gas introduced from the recirculation gas introduction port 42 from flowing back to the recirculation gas introduction port 42 side. Yes. The pressure difference between the recirculation gas introduction port 42 and the recirculation gas discharge port 46 varies from time to time due to the pulsation effect of the exhaust pipe 18. Therefore, depending on the operating state of the diesel engine 10, the pressure on the upstream side of the catalytic converter 34 may be higher than that on the downstream side, and the reflux gas flowing through the exhaust gas recirculation passage 44 flows from the recirculation gas discharge port 46 to the recirculation gas introduction port 44. It is possible that it will flow backward. In this embodiment, such a backflow can be prevented by providing a check valve 50 as a rectifying means.

  The pressure control valve 40 is provided downstream of the recirculation gas inlet 42 of the exhaust pipe 18 and controls the exhaust gas pressure by adjusting the flow rate of the exhaust gas in the exhaust passage 19. The opening degree of the pressure control valve 40 is adjusted by a controller such as an ECU, thereby changing the pressure difference between the recirculation gas introduction port 42 and the recirculation gas discharge port 46 to return to the exhaust gas recirculation passage 44. The amount of gas introduced can be controlled.

  The pressure pump 52 is provided in the vicinity of the middle stream of the exhaust gas recirculation passage 44, and pumps the exhaust gas introduced from the recirculation gas introduction port 42 toward the recirculation gas discharge port 46. As a result, the recirculation gas flowing through the exhaust gas recirculation passage 44 can be directly pumped by the pressure pump 52, so that the introduction amount of the recirculation gas can be controlled more reliably and accurately.

In this embodiment, by providing the exhaust gas recirculation passage 44 having such a rectifying means, NH ₃ discharged downstream from the catalytic converter 34 is recirculated to the upstream side of the catalytic converter 34 through the exhaust gas recirculation passage 44. Let Thereby, NH ₃ contained in the exhaust gas can be reused by the catalytic converter 34 without being discharged and wasted, so that the purification efficiency can be improved and the consumption of the reducing agent solution can be reduced. .

  Further, the exhaust gas recirculation passage 44 is connected in the vicinity of the recirculation gas discharge port 46 so as to be orthogonal to the exhaust pipe 18. As a result, the recirculation gas supplied from the recirculation gas outlet 46 is well agitated with the exhaust gas flowing through the exhaust pipe 18, so that the NOx reduction reaction can be promoted efficiently.

  Here, FIG. 2 is an enlarged view showing a modification of the structure in the vicinity of the reflux gas discharge port 46. In this modification, the exhaust gas recirculation passage 44 is supplied so that the recirculation gas supplied from the recirculation gas discharge port 46 is supplied in the direction opposite to the traveling direction of the exhaust gas flowing through the exhaust pipe 18. It is attached so that it may have an oblique angle with respect to. With this configuration, the agitation between the recirculation gas supplied from the exhaust gas recirculation passage 44 and the exhaust gas flowing through the exhaust pipe 18 can be improved, and better purification performance can be expected.

  In FIG. 2, the reflux gas discharge port 46 is provided on the downstream side from the installation location of the urea water supply device 32. Thereby, the recirculation gas supplied from the recirculation gas discharge port 46 is well dispersed by the exhaust gas flowing through the exhaust pipe 18, and the reduction reaction in the catalytic converter 34 can be promoted efficiently.

(Second Embodiment)
FIG. 3 is a schematic diagram showing the overall configuration of the exhaust emission control device according to the second embodiment. Note that the exhaust emission control device according to this example is basically similar to the first embodiment described above, and common portions are denoted by common reference numerals, and redundant descriptions are omitted as appropriate.

  In the second embodiment, an electric heater 54 for heating the reflux gas is provided in the exhaust gas reflux passage 44 for introducing and supplying the reflux gas. Particularly in the present embodiment, the coil portion 62 that is spirally wound along the outer periphery of the exhaust gas recirculation passage 44 is obtained by energizing the resistor 60 with DC power charged in the battery 58 mounted on the vehicle. Although it is configured so that the reflux gas can be heated to raise the temperature, it goes without saying that the present invention is not limited to this form. In this way, the temperature of the relatively low-temperature recirculated gas introduced from the downstream side of the catalytic converter 34 is raised by the electric heater 54, thereby improving the reduction reactivity when re-supplied to the catalytic converter 34 after recirculation. be able to. The resistor 60 is a variable resistor, and the amount of heating can be controlled by adjusting the resistance value.

(Third embodiment)
FIG. 4 is a schematic diagram illustrating the overall configuration of the exhaust emission control apparatus according to the third embodiment. Note that the exhaust purification apparatus according to the present embodiment is basically similar to the first and second embodiments described above, and common portions are denoted by common reference numerals, and duplicate descriptions are omitted as appropriate. And

In the third embodiment, the catalytic converter 34 is surrounded by the electric heater 64. Deposits generated due to a reaction failure or the like easily adhere to the vicinity of the upstream inlet of the SCR catalyst 36 built in the catalytic converter 34 and the vicinity of the inlet of the exhaust pipe 18 connected to the SCR catalyst 36. The electric heater 64 generates NH ₃ by heating and sublimating the fixed deposit in this way, and regenerates the generated NH ₃ to the catalytic converter 34 via the exhaust gas recirculation passage 44 for purification. Can be used. Thereby, the purification efficiency in the catalytic converter 34 can be further improved, and the consumption of the reducing agent solution supplied to the upstream side exhaust passage of the NO _X selective reduction catalyst can be effectively reduced.

  As with the electric heater 54, the electric heater 64 is configured to operate by energizing the resistor 60 with DC power charged in a battery 58 mounted on the vehicle. The resistor 60 is a variable resistor, and the amount of heating can be controlled by adjusting the resistance value. Although the electric heater 64 is basically provided over the entire catalytic converter 34, it is provided so as to extend to the vicinity of the inlet of the exhaust pipe 18 connected to the SCR catalyst 36 in which the deposit is particularly easily fixed. It has been.

  In addition, the detection value of each said sensor is input into the control apparatus which is controllers, such as ECU. Based on these detected values, the control device controls and controls each part of the vehicle including the rectifying means and the electric heaters 54 and 64 described above. In FIG. 1, FIG. 2 and FIG. 4, the control device is omitted so as not to complicate the illustration, but detection values are obtained from these various sensors, and control signals are transmitted to and received from each part.

As described above, according to the exhaust gas purification apparatus according to the present embodiment, NH ₃ discharged downstream from the catalytic converter 34 is exhausted using the pressure difference between the upstream side and the downstream side of the catalytic converter 34. The refrigerant is recirculated to the upstream side of the catalytic converter 34 through the recirculation passage 44. Thereby, NH ₃ contained in the exhaust gas is not discharged to the outside and is not wasted. Thus, by effectively reusing NH ₃ , the NO _X purification efficiency in the catalytic converter 34 can be improved and the consumption of the urea aqueous solution can be reduced.

In the present invention, an NO _X selective reduction catalyst is provided in the exhaust passage of the internal combustion engine, and the reducing agent solution supplied to the upstream exhaust passage of the NO _X selective reduction catalyst is decomposed to generate NH ₃ , and the NO _X selection is performed. The present invention is applicable to an exhaust gas purification apparatus for an internal combustion engine that makes NO _X in exhaust gas react with NH ₃ under the catalytic action of a reduction catalyst to render it harmless.

DESCRIPTION OF SYMBOLS 10 In-vehicle diesel engine 12 Cylinder block 14 Cylinder head 16 Intake pipe 18 Exhaust pipe 20 Supercharger 20a Exhaust turbine 22 Oxygen concentration sensor 24 Oxidation catalyst 26 DPF device 30, 38 NO _X sensor 32 Urea water supply device 34 Catalytic converter 36 SCR Catalyst 40 Pressure control valve 42 Recirculation gas introduction port 44 Exhaust gas recirculation passage 46 Recirculation gas discharge port 48 Recirculation control valve 50 Check valve 52 Pressure feed pump 54, 64 Electric heater

Claims (8)

An NO _X selective reduction catalyst is provided in the exhaust passage of the internal combustion engine, and the reducing agent solution supplied to the upstream side of the NO _X selective reduction catalyst is decomposed to generate NH _3, and the catalytic action of the NO _X selective reduction catalyst the NO _X contained in the exhaust gas under the exhaust purification system of an internal combustion engine to harmless is reacted with NH ₃ produced the,
Exhaust from the NO _X recirculated gas inlet port provided on the downstream side of the selective reduction catalyst, said bypassing _the NO _X selective reducing catalyst, leading to the _the NO _X selective recirculation gas discharge port provided on the upstream side of the reduction catalyst A reflux path;
A recirculation control valve that opens and closes between the downstream side of the NO _X selective reduction catalyst and the exhaust gas recirculation passage;
An exhaust gas purification apparatus for an internal combustion engine, comprising: rectification means for rectifying the exhaust gas introduced from the recirculation gas introduction port in the exhaust recirculation passage so as to flow toward the recirculation gas discharge port.   2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the rectifying means includes a check valve for preventing a backflow of the recirculation gas flowing through the exhaust gas recirculation passage. The rectifying means is provided on the downstream side of the recirculation gas introduction port, and a pressure control valve for controlling the exhaust gas pressure on the downstream side of the NO _X selective catalyst by adjusting the flow rate of the exhaust gas in the exhaust passage. The exhaust emission control device for an internal combustion engine according to claim 1 or 2, further comprising:   The said rectification | straightening means is equipped with the pressure feed pump which pumps the exhaust gas introduce | transduced from the said recirculation | gas recirculation gas inlet into the said recirculation | reflux gas discharge port in the said exhaust gas recirculation passage. An exhaust emission control device for an internal combustion engine according to claim 1.   The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the recirculation gas discharge port is provided downstream of the reducing agent supply port. The recirculation gas supplied from the recirculation gas discharge port is supplied in a direction opposite to a traveling direction of the exhaust gas flowing upstream of the NO _X selective reduction catalyst. An exhaust emission control device for an internal combustion engine according to any one of the preceding claims.   The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 6, further comprising first heating means for heating the recirculation gas introduced into the exhaust recirculation passage. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 7, further comprising a second heating means for heating the NO _X selective reduction catalyst.

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