JP2006161768A - Exhaust purification device - Google Patents

Abstract

An exhaust emission control device capable of always obtaining a high NOx reduction rate regardless of operating conditions is provided.
An exhaust gas purification apparatus configured to reduce and purify NOx by providing a NOx occlusion reduction catalyst 5 in the middle of exhaust flow paths 2 and 4, wherein the NOx occlusion reduction catalyst 5 in the exhaust flow paths 2 and 4 is provided. Is provided with a fuel reforming catalyst structure 7 or plasma fuel reforming means for decomposing the fuel into H ₂ and CO.
[Selection] Figure 1

Description

  The present invention relates to an exhaust emission control device.

Conventionally, exhaust purification is performed with an exhaust purification catalyst installed in the middle of the exhaust pipe. This type of exhaust purification catalyst oxidizes NOx in exhaust gas when the exhaust fuel ratio is lean. Thus, a NOx occlusion reduction catalyst having the property of temporarily storing in the form of nitrate and decomposing and releasing NOx through the intervention of unburned HC, CO, etc. when the O ₂ concentration in the exhaust gas decreases is reduced and purified. Are known.

  As this type of NOx occlusion reduction catalyst, platinum / barium / alumina catalyst, platinum / potassium / alumina catalyst, and the like have already been known.

In the NOx occlusion reduction catalyst, when the occlusion amount of NOx increases and reaches the saturation amount, no more NOx can be occluded, and therefore, O _{2 of} the exhaust gas flowing into the NOx occlusion reduction catalyst periodically. It is necessary to decompose and release NOx by reducing the concentration.

For example, when used in a gasoline engine, by reducing the operating air-fuel ratio of the engine (operating the engine when the air-fuel ratio is rich in fuel), the O ₂ concentration in the exhaust gas is reduced and the exhaust gas in the exhaust gas Although it is possible to promote the decomposition and release of NOx by increasing the reducing components such as unburned HC and CO, when the NOx storage reduction catalyst is used as an exhaust gas purification device for a diesel engine, the air-fuel ratio is high when the fuel is rich. Is difficult to drive.

For this reason, by adding fuel (HC) to the exhaust gas upstream of the NOx storage reduction catalyst, the added fuel is used as a reducing agent to react with O ₂ on the NOx storage reduction catalyst. ₂ It is necessary to reduce the concentration (see, for example, Patent Document 1).
JP 2000-356127 A

However, in the method of adding fuel upstream of the NOx storage reduction catalyst in this way, a part of HC generated by evaporation of the added fuel reacts with O ₂ in the exhaust gas on the surface of the NOx storage reduction catalyst. (Combustion), and NOx decomposition and release is started after the O ₂ concentration in the atmosphere around the NOx storage reduction catalyst becomes almost zero, so that HC is O ₂ on the surface of the NOx storage reduction catalyst. NOx is efficiently removed from the NOx occlusion reduction catalyst under operating conditions where the combustion temperature (about 220-250 ° C) required for reaction (combustion) with NOx cannot be obtained (for example, slow driving in cities with heavy traffic). There was a problem that the NOx occlusion reduction catalyst could not be decomposed and released, and the regeneration of the NOx occlusion reduction catalyst did not proceed efficiently, so that the recovery rate of the NOx occlusion site in the catalyst volume was reduced and the occlusion capacity was lowered.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an exhaust emission control device that can always obtain a high NOx reduction rate regardless of operating conditions.

The present invention is an exhaust emission control device configured to reduce and purify NOx by installing a NOx storage reduction catalyst in the middle of an exhaust flow path, wherein fuel is supplied to the upstream side of the NOx storage reduction catalyst in the exhaust flow path. The present invention relates to an exhaust emission control device provided with a fuel reforming catalyst structure or plasma fuel reforming means that decomposes into H ₂ and CO.

In the present invention, a plasma generating means for oxidizing NO into NO ₂ may be disposed upstream of the fuel reforming catalyst structure or the plasma fuel reforming means in the exhaust passage.

In the present invention, the plasma generating means may be controlled to oxidize NO to NO ₂ when the exhaust fuel ratio is lean to promote NOx occlusion by the NOx occlusion reduction catalyst.

In the present invention, the fuel reforming catalyst structure or the plasma fuel reforming means may be controlled to reduce the NOx of the NOx occlusion reduction catalyst by decomposing the fuel into H ₂ and CO when the air-fuel ratio is rich in fuel.

  In the present invention, the fuel reforming catalyst structure or the plasma fuel reforming means may be controlled such that when the exhaust temperature is sufficiently high, the fuel is supplied without being decomposed and the fuel is instantly concentrated.

Thus, according to the present invention, since it can be decomposed into H ₂ and CO by the fuel reforming catalyst structure or the plasma fuel reforming means, NO x on the surface of the NO x storage reduction catalyst is converted by H ₂ and CO. efficiently reducing treatment in N _2, as a result, it is possible to obtain a very high NOx reduction ratio irrespective of the various operating conditions. Further, fuel, by the fuel reforming catalyst structure or a plasma fuel reformer unit is decomposed into H ₂ and CO, it is possible to obtain a high NOx reduction rate from a relatively low temperature region by highly reactive H ₂ and CO Therefore, NOx contained in the exhaust gas exhausted outside the vehicle can be maintained even under operating conditions in which low-exhaust and low-exhaust temperature operating conditions are likely to continue, such as slow driving in cities with heavy traffic. This can be reduced more effectively than before.

According to the present invention, when a plasma generating means for oxidizing NO into NO ₂ is disposed upstream of the fuel reforming catalyst structure or the plasma fuel reforming means in the exhaust passage, the plasma generating means converts NO to NO ₂ regardless of the temperature. Therefore, NOx occlusion by the NOx occlusion reduction catalyst can be facilitated.

In the present invention, a plasma generating means, the exhaust fuel ratio is controlled so as to promote the NOx occlusion by oxidation to NOx storage reduction catalyst of NO to NO ₂ in the lean, the NOx storage by the NOx storage reduction catalyst more readily can do.

In the present invention, the fuel reforming catalyst structure or a plasma fuel reformer unit, the air-fuel ratio is controlled so that the fuel is decomposed into H ₂ and CO reducing NOx of the NOx storage reduction catalyst during the fuel-rich, H ₂ Further, NOx on the surface of the NOx storage reduction catalyst can be more efficiently reduced to N ₂ by CO and CO.

In the present invention, when the fuel reforming catalyst structure or the plasma fuel reforming means is controlled so that the fuel is supplied without being decomposed and the fuel is instantly concentrated when the exhaust temperature is sufficiently high, the NOx occlusion reduction catalyst NOx on the surface can be reduced to N ₂ appropriately.

According to the above-described exhaust purification apparatus of the present invention, NO can be oxidized to NO ₂ or the fuel can be decomposed into H ₂ and CO regardless of the temperature, so that a high NOx reduction rate can always be obtained. An excellent effect can be achieved.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 to 4 show an example of an embodiment in which the present invention is implemented using a NOx occlusion reduction catalyst. In the middle of an exhaust pipe 4 through which exhaust gas 3 discharged from a diesel engine 1 through an exhaust manifold 2 flows. The NOx occlusion reduction catalyst 5 having a flow-through type honeycomb structure is mounted on the casing 6.

  A fuel reforming catalyst structure 7 or plasma fuel reforming means 8 is provided upstream of the casing 6 in the exhaust pipe 4.

  Here, a preferred example of the fuel reforming catalyst structure 7 is shown. As shown in FIGS. 1 and 3, the fuel reforming catalyst structure 7 includes an introduction pipe 9 and an exhaust pipe 10 that communicate with the exhaust pipe 4 and has an internal structure. A fuel reformer 12 that forms the space 11, a fuel reforming catalyst 13 installed in the fuel reformer 12, and a fuel addition nozzle 14 that adds fuel from the upstream side to the internal space 11 of the fuel reformer 12. And an introduction valve 15 for opening and closing the introduction pipe 9 and a discharge valve 16 for opening and closing the discharge pipe 10.

  On the other hand, as a preferred example of the plasma fuel reforming means 8, as shown in FIGS. 2 and 4, the plasma fuel reforming means 8 includes a plasma fuel reformer 17 communicating with the exhaust pipe 4, and a plasma fuel reforming. The plasma fuel reformer 17 forms an internal space 19 that leads to the exhaust pipe 4 and serves as a ground electrode, and an internal portion of the exhaust unit 20. An introduction portion 22 that forms a mixed gas flow path 21 so as to guide a fuel mixed gas of fuel such as light oil and air to the space 19, an insulator portion 23 disposed between the discharge portion 20 and the introduction portion 22, and an introduction portion 22 and a high voltage electrode 24 supported by 22. In the figure, reference numeral 25 denotes a cooling water flow path for cooling the discharge part 20, and 26 denotes a fixing bolt for fixing the discharge part 20 and the introduction part 22. Further, the discharge portion 20 may be an insulator without using the end portion 20a on the high voltage electrode 24 side as a ground electrode.

  On the upstream side of the fuel reforming catalyst structure 7 or the plasma fuel reforming means 8 in the exhaust pipe 4, as shown in FIGS. 1 and 2, a plasma generator comprising a pair of flat plate electrodes arranged opposite to each other in the exhaust pipe 4. 27 and a plasma generating means 29 including a high voltage power source 28 for applying a voltage to the plasma generator 27 is provided.

  The diesel engine 1 is equipped with a rotation sensor 30 that detects the engine speed, and from a rotation speed signal 30a from the rotation sensor 30 and an accelerator sensor 31 (a sensor that detects the depression angle of the accelerator pedal). Load signal 31 a and a temperature signal 32 a from a temperature sensor 32 installed in the exhaust pipe 4 are input to the control device 33.

  On the other hand, in the control device 33, the amount of NOx generated and the like are estimated based on the current operating state determined from the rotation speed signal 30a from the rotation sensor 30 and the load signal 31a from the accelerator sensor 31. The fuel reforming catalyst structure 7 or the plasma fuel reforming means 8 and the plasma generating means 29 are controlled from the estimated NOx generation amount, the temperature signal 32a from the temperature sensor 32, and the like. Here, the control device 33 may control the fuel reforming catalyst structure 7 or the plasma fuel reforming means 8 and the plasma generating means 29 in response to a signal from another sensor.

  In FIGS. 1 and 2, reference numeral 34 denotes a turbocharger, 35 denotes an intake pipe, and 36 denotes an intercooler.

  The operation of the embodiment of the present invention will be described below.

  In various operating states, when the amount of NOx generated from the rotation sensor 30 and the accelerator sensor 31 is estimated and the temperature sensor 32 detects the temperature, the control device (control means) 33 controls the plasma generation means 29 appropriately. 28a is sent to control the plasma generating means 29, and in the case of the fuel reforming catalyst structure 7, the control device (control means) 33 sends control signals 9a and 10a to the fuel reforming catalyst structure 7 to send the fuel addition nozzle 14 In the case of the plasma fuel reforming means 8, the control device (control means) 33 sends a control signal 18a to the plasma fuel reforming means 8 in the case of the plasma fuel reforming means 8. The amount of fuel added and the supply of the high voltage power source 18 are controlled.

Next, in the plasma generating means 29, a high voltage is applied to the flat plate plasma generator 27 by the high voltage power source 28 to generate plasma in the exhaust pipe 4, and the NO in the exhaust gas 3 is not affected by the temperature. Is oxidized to NO ₂ .

The fuel reforming catalyst structure 7 controls the amount of fuel added to the fuel reformer 12 and the temperature, and controls the generation of H ₂ and CO generated by the fuel reforming catalyst 13 to control the exhaust gas 3. Supply inside. On the other hand, the plasma fuel reforming means 8 generates a plasma in the internal space 19 by barrier discharge by applying a high voltage to the high voltage electrode 24 from the high voltage power source 18 and is not affected by the temperature in the internal space 19. The fuel is reformed into H ₂ and CO, and a reformed gas (hydrogen mixed gas) is supplied into the exhaust gas 3.

Here, at the time of the exhaust fuel ratio lean, activates the plasma generating means 29 by the control signal 28a from the controller 33, and to promote NOx storage by the NOx storage reduction catalyst 5 oxidizes NO to NO _2, The When the air-fuel ratio when reducing NOx is rich in fuel, the fuel reforming catalyst structure 7 or the plasma fuel reforming means 8 is operated by the control signals 9a, 10a, and 18a from the control device 33, and the fuel is H ₂ and CO 2. The NOx occluded by the NOx occlusion reduction catalyst 5 is efficiently reduced by being decomposed into the exhaust gas 3 and supplied into the exhaust gas 3.

  Further, when the exhaust temperature is sufficiently high (350 ° C. or higher), the control device 33 does not process the fuel reforming catalyst 13 of the fuel reforming catalyst structure 7 or the high voltage electrode of the plasma fuel reforming means 8. Without applying a high voltage to 24, the fuel may flow down and supplied without decomposition, and the fuel may be enriched instantaneously as a rich spike, and NOx occluded in the NOx occlusion reduction catalyst 5 may be reduced.

And Thus, according to the embodiment of the present invention, the fuel reforming since it can decompose into H ₂ and CO by the catalyst structure 7 or plasma fuel reformer unit 8, the surface of the NOx storage reduction catalyst 5 by H ₂ and CO The above NOx is efficiently reduced to N _2, and as a result, it is possible to always obtain a high NOx reduction rate regardless of various operating conditions.

Furthermore, the fuel at the fuel reforming catalyst structure 7 or plasma fuel reformer unit 8 is decomposed into H ₂ and CO, obtain a high NOx reduction rate from a relatively low temperature region by highly reactive H ₂ and CO Therefore, it is included in the exhaust gas that is discharged outside the vehicle even under operating conditions where low-exhaust and low-exhaust temperature driving conditions are likely to continue, such as slow driving in cities with heavy traffic. NOx can be reduced more effectively than before.

In the embodiment of the present invention, when the plasma generating means 29 for oxidizing NO into NO ₂ is arranged upstream of the fuel reforming catalyst structure 7 or the plasma fuel reforming means 8 in the exhaust passage, the plasma generating means 29 Since NO can be oxidized to NO ₂ regardless of the temperature, NOx occlusion by the NOx occlusion reduction catalyst 5 can be facilitated.

In the embodiment of the present invention, when the plasma generation means 29 is controlled by the control device 33 to oxidize NO to NO ₂ when the exhaust fuel ratio is lean and promote NOx occlusion by the NOx occlusion reduction catalyst 5, The NOx occlusion by the NOx occlusion reduction catalyst 5 can be further facilitated.

In the embodiment of the present invention, the fuel reforming catalyst structure 7 or the plasma fuel reforming means 8 causes the control device 33 to decompose the fuel into H ₂ and CO when the air-fuel ratio is rich in the fuel and to reduce the NOx storage reduction catalyst 5. When controlled to reduce NOx, it is possible to reduction treatment of NOx on more efficiently N ₂ surface of the NOx storage reduction catalyst 5 by H ₂ and CO.

In the embodiment of the present invention, the fuel reforming catalyst structure 7 or the plasma fuel reforming means 8 supplies the fuel non-decomposingly when the exhaust temperature is sufficiently high (350 ° C. or higher) by the control device 33. manner when it is controlled to rich fuel, can be properly reduction to N ₂ to NOx on the surface of the NOx storage reduction catalyst 5.

  Note that the exhaust emission control device of the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

It is the schematic which shows the case where it is an example of embodiment which implements this invention, and a fuel reforming catalyst structure is used. It is the schematic which shows the case where it is an embodiment which implements this invention, and a plasma fuel reforming means is used. It is the schematic which shows the fuel reforming catalyst structure of this invention. It is the schematic which shows the plasma fuel reforming means of this invention.

Explanation of symbols

2 Exhaust manifold (exhaust flow path)
4 Exhaust pipe (exhaust flow path)
5 NOx occlusion reduction catalyst 7 Fuel reforming catalyst structure 8 Plasma fuel reforming means 29 Plasma generating means

Claims (5)

In the middle of the exhaust passage equipped with a NOx storage reduction catalyst an exhaust purification apparatus that is configured to reduce and purify NOx, the upstream side of the NOx storage reduction catalyst in the exhaust passage, the fuel H ₂ and CO An exhaust gas purification apparatus provided with a fuel reforming catalyst structure or plasma fuel reforming means that decomposes into a gas. The exhaust emission control device according to claim 1, wherein a plasma generating means for oxidizing NO into NO ₂ is disposed upstream of the fuel reforming catalyst structure or the plasma fuel reforming means in the exhaust passage. The exhaust emission control device according to claim 2, wherein the plasma generating means is controlled to oxidize NO to NO ₂ when the exhaust fuel ratio is lean to promote NOx occlusion by the NOx occlusion reduction catalyst. _2. The exhaust gas purification according to claim 1, wherein the fuel reforming catalyst structure or the plasma fuel reforming means is controlled to reduce the NOx of the NOx occlusion reduction catalyst by decomposing the fuel into H ₂ and CO when the air-fuel ratio is rich. apparatus.   2. The exhaust emission control device according to claim 1, wherein the fuel reforming catalyst structure or the plasma fuel reforming means is controlled so that the fuel is supplied in an undecomposed manner and the fuel is instantly concentrated when the exhaust temperature is sufficiently high.

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