JP2008274850A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve mountability on a vehicle, by compactly arranging a particulate filter and a selective reduction type catalyst, while securing sufficient reaction time for generating ammonia from urea water. <P>SOLUTION: This exhaust emission control device has the particulate filter 5 in the middle of an exhaust pipe 4, and has the selective reduction type catalyst 6 selectively reacting NOx with the ammonia even in coexistence of oxygen on its downstream side, and is constituted so that the urea water is added as a reducing agent between the selective reduction type catalyst 6 and the particulate filter 5. The particulate filter 5 and the selective reduction type catalyst 5 are arranged in series by opposing mutual respective outlet side end parts. A connecting flow passage 9 is arranged for introducing exhaust gas 3 exhausted from the outlet side end part of the particulate filter 5 to an inlet side end part of the selective reduction type catalyst 6 by bypassing the selective reduction type catalyst 6. A urea water adding injector 11 is provided in the middle of the connecting flow passage 9. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device.

  Conventionally, a diesel engine is equipped with a selective reduction catalyst having a property of selectively reacting NOx with a reducing agent even in the presence of oxygen in the middle of an exhaust pipe through which exhaust gas flows, and the selective reduction catalyst A required amount of a reducing agent is added to the upstream side of the catalyst so that the reducing agent undergoes a reduction reaction with NOx (nitrogen oxide) in the exhaust gas on the selective catalytic reduction catalyst, thereby reducing the NOx emission concentration. There is what I did.

On the other hand, in the field of industrial flue gas denitration treatment in plants and the like, the effectiveness of a method for reducing and purifying NOx using ammonia (NH ₃ ) as a reducing agent is already widely known. Since it is difficult to ensure safety with respect to traveling with ammonia itself, in recent years, the use of non-toxic urea water as a reducing agent has been studied.

That is, if urea water is added to the exhaust gas upstream of the selective catalytic reduction catalyst, the urea water in the exhaust gas is thermally decomposed into ammonia and carbon dioxide gas by the following formula, and the exhaust gas is exhausted on the selective catalytic reduction catalyst. NOx is reduced and purified well by ammonia.
[Chemical 1]
(NH ₂ ) ₂ CO + H ₂ O → 2NH ₃ + CO ₂

  On the other hand, when purifying exhaust gas from a diesel engine, it is not enough to remove NOx in the exhaust gas, and particulates contained in the exhaust gas are also collected through the particulate filter. However, when this type of particulate filter is employed, it is necessary to regenerate the particulate filter by appropriately burning and removing the particulate before the exhaust resistance increases due to clogging.

  For this reason, a flow-through type oxidation catalyst is attached to the inlet side of the particulate filter, and fuel is added to the exhaust gas upstream from the oxidation catalyst when the amount of particulate accumulation increases. It is considered to forcibly regenerate the filter.

  In other words, if fuel is added to the exhaust gas upstream of the oxidation catalyst, the added fuel (HC) undergoes an oxidation reaction while passing through the preceding oxidation catalyst. The catalyst bed temperature of the outgoing particulate filter is raised, the particulates are burned out, and the particulate filter is regenerated.

In general, as a specific means for performing the fuel addition as described above, the post-injection is executed at the timing of non-ignition later than the compression top dead center following the main injection of fuel performed near the compression top dead center. It is considered to add fuel to the exhaust gas, but in order to efficiently use the added fuel for forced regeneration and to oxidize the added fuel before the exhaust gas temperature drops as much as possible, It is considered that it is preferable to dispose the curate filter upstream of the selective reduction catalyst (for example, see Patent Document 1 below).
JP 2005-42687 A

  However, when the particulate filter is arranged upstream of the selective catalytic reduction catalyst, urea water is added to the selective catalytic reduction catalyst between the particulate filter and the selective catalytic reduction catalyst. Therefore, if an attempt is made to secure a sufficient reaction time until the urea water added to the exhaust gas is thermally decomposed into ammonia and carbon dioxide, the distance from the urea water addition position to the selective catalytic reduction catalyst is increased. As a result, there is a problem that the particulate filter and the selective catalytic reduction catalyst have to be spaced apart from each other by a sufficient distance, so that the mountability on the vehicle is significantly impaired.

  The present invention has been made in view of the above circumstances, and realizes a compact arrangement of the particulate filter and the selective catalytic reduction catalyst while ensuring a sufficient reaction time to generate ammonia from the urea water. The purpose is to improve the mountability to the vehicle.

  The present invention includes a particulate filter that collects particulates in exhaust gas in the middle of an exhaust pipe, and selective reduction that can selectively react NOx with ammonia even in the presence of oxygen on the downstream side of the particulate filter. An exhaust gas purification apparatus configured to add urea water as a reducing agent between the selective reduction catalyst and the particulate filter, each of the particulate filter and the selective reduction catalyst. The outlet side ends of the particulate filter are arranged in series so that the exhaust gas discharged from the outlet side end of the particulate filter bypasses the selective catalytic reduction catalyst and is guided to the inlet side end of the selective catalytic reduction catalyst. A communication flow path is provided, and urea water addition means for adding urea water in the middle of the communication flow path is provided.

  Thus, in this way, the exhaust gas discharged from the outlet end portion of the particulate filter is introduced into the inlet end portion of the selective catalytic reduction catalyst via the connecting flow path. As a result, the particulate filter and the selective catalytic reduction catalyst are arranged close to each other in series, but a long distance from the urea water addition position in the middle of the connecting flow path to the selective catalytic reduction catalyst is ensured to keep the urea water and the exhaust gas. It is possible to promote mixing with the water, and a reaction time sufficient to generate ammonia from the urea water is ensured.

  Further, in the present invention, the particulate filter and the selective catalytic reduction catalyst are arranged in series with their inlet ends facing each other, and the exhaust gas discharged from the outlet end of the particulate filter is particulated. A communication flow path that bypasses the filter and leads to the inlet side end of the particulate filter may be provided, and urea water addition means for adding urea water may be provided in the middle of the communication flow path.

  Furthermore, when carrying out the present invention more specifically, the communication flow path that communicates between the outlet side end portion of the particulate filter and the inlet side end portion of the selective catalytic reduction catalyst has an outlet side end portion of the particulate filter. An exhaust gas collected in the gas collecting chamber, and a gas collecting chamber that collects exhaust gas immediately after exiting from the outlet end portion by colliding with a wall surface and changing the direction in a substantially perpendicular direction. Mixing pipe extracted toward the inlet side end of the selective catalytic reduction catalyst, and exhaust gas introduced by the mixing pipe collide with the wall surface and disperse it while changing the direction in a substantially right angle, and the dispersed exhaust gas Is preferably constituted by a gas dispersion chamber surrounding the inlet side end so that can be introduced into the inlet side end of the selective catalytic reduction catalyst.

  Further, in the present invention, an oxidation catalyst for oxidizing the unburned fuel content in the exhaust gas is provided on the inlet side of the particulate filter, and the fuel addition means for adding fuel to the exhaust gas upstream of the oxidation catalyst In this case, the fuel added by the fuel addition means is oxidized on the oxidation catalyst, and as a result, the exhaust gas that has been heated by the reaction heat flows into the outlet side. The catalyst bed temperature of the curate filter is raised, the particulates are burned out, and the particulate filter is regenerated.

  When doing so, a fuel injection device that injects fuel into each cylinder of the engine is adopted as a fuel addition means, and fuel injection into the cylinder is controlled to leave a large amount of unburned fuel in the exhaust gas. In this case, it is preferable that the fuel is added.

  In the present invention, it is preferable that an ammonia reduction catalyst for oxidizing excess ammonia is provided on the exit side of the selective catalytic reduction catalyst. In this way, the selective catalytic reduction catalyst can be used for the reduction reaction. The excess ammonia is oxidized by the ammonia reduction catalyst on the exit side.

  According to the exhaust emission control device of the present invention described above, various excellent effects as described below can be obtained.

  (I) According to the first, second, and third aspects of the present invention, the particulate filter and the selective reduction catalyst are compact while ensuring a sufficient reaction time for ammonia to be produced from the urea water. Therefore, it is possible to significantly improve the mounting property on the vehicle as compared with the conventional case.

  (II) According to the inventions described in claims 4 and 5 of the present invention, the fuel added by the fuel addition means is oxidized on the oxidation catalyst, and the exhaust gas heated by the reaction heat flows into the outlet side. It is possible to burn up the particulates by raising the catalyst bed temperature of the particulate filter, and to actively regenerate the particulate filter.

  (III) According to the invention described in claim 6 of the present invention, surplus ammonia that has passed through the selective reduction catalyst in an unreacted state can be oxidized and rendered harmless, and finally the atmosphere The possibility that ammonia may remain in the exhaust gas discharged into the exhaust gas can be avoided.

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

  FIG. 1 shows an example of an embodiment for carrying out the present invention. In the exhaust purification apparatus of this embodiment, the exhaust pipe 4 through which the exhaust gas 3 discharged from the diesel engine 1 through the exhaust manifold 2 flows is shown. In addition, a particulate filter 5 that collects particulates in the exhaust gas 3 and a selective reduction type catalyst that has the property of selectively reacting NOx with ammonia even in the presence of oxygen on the downstream side of the particulate filter 5. 6 are respectively held in series by casings 7 and 8 and are arranged in series with their respective outlet ends facing each other, and the outlet end of the particulate filter 5 and the selective catalytic reduction catalyst 6 are inserted. The exhaust gas 3 discharged from the outlet side end of the particulate filter 5 bypasses the selective catalytic reduction catalyst 6 and is connected to the side end by the communication channel 9. It is made to introduce into the entrance side end of.

  2 and 3, the communication channel 9 surrounds the outlet end of the particulate filter 5 and wall the exhaust gas 3 immediately after exiting from the outlet end. A gas collecting chamber 9A that is caused to collide with the gas and collect in an approximately perpendicular direction, and the exhaust gas 3 collected in the gas collecting chamber 9A is extracted toward the inlet side end of the selective catalytic reduction catalyst 6 and A mixing pipe 9B provided with a urea water addition injector 11 (urea water addition means) in the middle and the exhaust gas 3 guided by the mixing pipe 9B collide with the wall surface and are dispersed while being changed in a direction substantially at right angles. In addition, a U-shaped structure is formed by the gas dispersion chamber 9 </ b> C surrounding the inlet side end so that the dispersed exhaust gas 3 can be introduced into the inlet side end of the selective catalytic reduction catalyst 6.

  However, although the case where the urea water addition injector 11 is provided in the middle of the mixing pipe 9B is illustrated here, it is also possible to provide the urea water addition injector 11 in the gas collecting chamber 9A.

  Further, particularly in the present embodiment, an oxidation catalyst 14 that oxidizes unburned fuel in the exhaust gas 3 is provided on the entry side in the casing 7 in which the particulate filter 5 is held, An ammonia reduction catalyst 15 for oxidizing excess ammonia is provided on the exit side of the casing 8 in which the selective catalytic reduction catalyst 6 is held, and a tail pipe is provided at the exit end of the casing 8. An exhaust chamber 16 equipped to the side is formed.

  Further, as shown in FIG. 1, an accelerator sensor 17 (load sensor) for detecting the accelerator opening as a load of the diesel engine 1 is provided in the accelerator of the driver's seat, and at an appropriate position of the diesel engine 1. A rotation sensor 18 for detecting the rotation speed is provided, and the accelerator opening signal 17a and the rotation speed signal 18a from the accelerator sensor 17 and the rotation sensor 18 constitute an engine control computer (ECU: Electronic Control Unit). It is input to the device 19.

  On the other hand, in the control device 19, the fuel injection timing and the injection toward the fuel injection device 20 for injecting the fuel into each cylinder according to the current operation state determined from the accelerator opening signal 17a and the rotation speed signal 18a. A fuel injection signal 20a for commanding the amount is output.

  Here, the fuel injection device 20 is constituted by a plurality of injectors (not shown) provided for each cylinder, and the electromagnetic valves of these injectors are appropriately opened by a fuel injection signal 20 a from the control device 19. Thus, the fuel injection timing and the injection amount (valve opening time) are appropriately controlled.

  However, in the present embodiment, the control device 19 determines the fuel injection signal 20a in the normal mode based on the accelerator opening signal 17a and the rotation speed signal 18a, while the particulate filter 5 is forcedly regenerated. When it is necessary to perform this, the normal mode is switched to the regeneration mode, and the non-ignition timing (start timing) later than the compression top dead center following the main injection of fuel performed near the compression top dead center (crank angle 0 °) The fuel injection signal 20a is determined so as to perform post injection at a crank angle of 90 ° to 130 °.

  That is, in the example shown here, the fuel injection device 20 is employed as the fuel addition means, and the post injection is performed at the non-ignition timing later than the compression top dead center following the main injection as described above. As a result of this post-injection, unburned fuel (mainly HC: hydrocarbon) is added to the exhaust gas 3, and the unburned fuel passes through the oxidation catalyst 14 at the front stage of the particulate filter 5. The catalyst bed temperature of the particulate filter 5 on the outlet side is raised by the inflow of the exhaust gas 3 heated by the reaction heat, and the particulates are burned and removed.

  Further, the control device 19 extracts the fuel injection amount determined from the rotational speed of the diesel engine 1 and the output value of the fuel injection signal 20a, and the diesel generation from the particulate generation map based on the rotational speed and the injection amount. The basic generation amount of particulates based on the current operation state of the engine 1 is estimated, and the basic generation amount is multiplied by a correction coefficient considering various conditions relating to the generation of particulates, and the current operation state The final generation amount is obtained by subtracting the particulate processing amount at, and the final generation amount is momentarily accumulated to estimate the particulate deposition amount. The deposition amount has reached a predetermined target value. When it is estimated, the fuel injection control is switched from the normal mode to the regeneration mode, and the exhaust gas 3 in the upstream side of the particulate filter 5 Fuel is adapted to be added.

  There are various ways of estimating the amount of particulate deposition, and it is of course possible to estimate the amount of particulate deposition using a method other than the estimation method exemplified here. It is also possible to estimate the accumulated amount of particulates based on the differential pressure before and after the curate filter, or to estimate the accumulated amount of particulates based on the operation time and travel distance.

  Further, the control device 19 estimates the amount of NOx generated based on the rotational speed of the diesel engine 1 and the amount of fuel injected, and the addition of a necessary amount of urea water corresponding to the amount of NOx generated is added to the urea water addition. It is instructed to the injector 11 as a valve opening command signal 11a.

  Thus, if the exhaust gas purification apparatus is configured in this way, the particulate filter 5 collects the particulates in the exhaust gas 3 and also the urea water addition injector 11 in the middle of the mixing pipe 9B on the downstream side thereof. As a result, urea water is added to the exhaust gas 3 and thermally decomposed into ammonia and carbon dioxide, and the NOx in the exhaust gas 3 is reduced and purified well by ammonia on the selective catalytic reduction catalyst 6. Simultaneous reduction of particulates and NOx is achieved.

  At this time, the exhaust gas 3 discharged from the outlet end portion of the particulate filter 5 is introduced into the inlet end portion of the selective catalytic reduction catalyst 6 via the connecting flow path 9. While the curative filter 5 and the selective catalytic reduction catalyst 6 are arranged close to each other in series, a long distance from the urea water addition position in the middle of the connecting flow path 9 to the selective catalytic reduction catalyst 6 is secured to Mixing with the exhaust gas 3 can be promoted, and a sufficient reaction time is secured for the generation of ammonia from the urea water.

  In particular, in the present embodiment, the exhaust gas 3 immediately after coming out from the outlet end of the particulate filter 5 collides with the wall surface of the gas collecting chamber 9A and is gathered while changing its direction in a substantially perpendicular direction. Therefore, the exhaust gas 3 is effectively introduced into the mixing pipe 9B in a turbulent state, and the urea water added in the middle of the mixing pipe 9B is promoted very well.

  Further, the exhaust gas 3 guided by the mixing pipe 9B collides with the wall surface of the gas dispersion chamber 9C and is dispersed while being changed in a direction substantially perpendicular, so that the inlet side end portion of the selective catalytic reduction catalyst 6 can be dispersed. In contrast, the exhaust gas 3 is introduced in a dispersed manner without causing a bias.

  In this embodiment, when it becomes necessary to perform forced regeneration of the particulate filter 5, the fuel injection control in the control device 19 is switched from the normal mode to the regeneration mode, and is added on the diesel engine 1 side by post injection. The oxidized fuel is oxidized by the oxidation catalyst 14 in the previous stage, and the catalyst bed temperature of the particulate filter 5 on the outlet side rises due to the inflow of the exhaust gas 3 heated by the reaction heat, and the particulates are burned out. Of course, the filter 5 can be actively regenerated.

  Therefore, according to the above embodiment, it is possible to realize a compact arrangement of the particulate filter 5 and the selective catalytic reduction catalyst 6 while ensuring a sufficient reaction time for ammonia to be generated from urea water. As a result, the mountability on the vehicle can be greatly improved.

  Further, the fuel added by the post injection by the fuel injection device 20 is oxidized on the oxidation catalyst 14, and the catalyst bed temperature of the particulate filter 5 on the outlet side is raised by the inflow of the exhaust gas 3 heated by the reaction heat. Since the particulates can be burned out, the particulate filter 5 can be actively regenerated.

  Moreover, since the excess ammonia that has passed through the selective reduction catalyst 6 in an unreacted state can be oxidized by the ammonia reduction catalyst 15 to be rendered harmless, the exhaust gas 3 that is finally discharged into the atmosphere It is also possible to avoid the possibility of ammonia remaining therein.

  4 and 5 show another embodiment of the present invention, and in the example shown here, the output side end portions are opposed to each other in the embodiment shown in FIGS. 1 to 3 and arranged in series. The layout of the particulate filter 5 and the selective catalytic reduction catalyst 6 was changed to a reverse layout in which the inlet end portions of the particulate filter 5 and the selective reduction type catalyst 6 are arranged in series, and the particulate filter 5 The side end portion and the inlet side end portion of the selective catalytic reduction catalyst 6 are connected by the same communication flow path 9 as described above, and the exhaust gas 3 discharged from the outlet side end portion of the particulate filter 5 is the particulate filter. 5 is introduced to the inlet side end of the selective catalytic reduction catalyst 6.

  Thus, even when the exhaust gas purification device is configured in this way, the exhaust gas 3 discharged from the outlet side end portion of the particulate filter 5 passes through the communication flow path 9 to form the selective reduction catalyst 6. It is the same that it is introduced into the inlet side end, and the particulate filter 5 and the selective catalytic reduction catalyst 6 are arranged in close proximity in series, but selected from the urea water addition position in the middle of the connecting flow path 9 It becomes possible to promote the mixing of urea water and the exhaust gas 3 by ensuring a long distance to the reduction catalyst 6.

  As a result, the particulate filter 5 and the selective catalytic reduction catalyst 6 are compact while securing a reaction time sufficient for ammonia to be generated from the urea water, as in the case of the above-described embodiments of FIGS. Arrangement can be realized, and mounting on a vehicle can be greatly improved as compared with the conventional arrangement.

  The exhaust emission control device of the present invention is not limited to the above-described embodiment. In the above embodiment, the fuel injection device is employed as the fuel addition means, and the fuel is performed near the compression top dead center. Fuel is added to the exhaust gas by performing post-injection at a timing of non-ignition later than the compression top dead center following the main injection of the engine, but the timing of main injection into the cylinder is delayed from normal The fuel may be added to the exhaust gas, and only the means for adding fuel by controlling the fuel injection into the cylinder and leaving a large amount of unburned fuel in the exhaust gas. In addition, an injector may be provided as a fuel addition means at an appropriate position of the exhaust pipe (or an exhaust manifold), and fuel may be directly injected into the exhaust gas by this injector, It is of course that various changes and modifications may be made without departing from the scope and spirit of the present invention.

It is the schematic which shows an example of the form which implements this invention. FIG. 2 is an enlarged detailed view showing a main part of FIG. 1. FIG. 3 is a perspective view of the exhaust purification device of FIG. 2. It is detail drawing which shows another form example of this invention. It is a perspective view of the exhaust emission control device of FIG.

Explanation of symbols

1 Diesel engine (engine)
DESCRIPTION OF SYMBOLS 3 Exhaust gas 4 Exhaust pipe 5 Particulate filter 6 Selective reduction type catalyst 9 Connection flow path 9A Gas collection chamber 9B Mixing pipe 9C Gas dispersion chamber 11 Urea water addition injector (urea water addition means)
14 Oxidation catalyst 15 Ammonia reduction catalyst 20 Fuel injection device (fuel addition means)

Claims (6)

  A particulate filter for collecting particulates in the exhaust gas is provided in the middle of the exhaust pipe, and a selective reduction catalyst capable of selectively reacting NOx with ammonia even in the presence of oxygen on the downstream side of the particulate filter. An exhaust emission control device configured to be able to add urea water as a reducing agent between the selective reduction catalyst and the particulate filter, wherein the particulate filter and the selective reduction catalyst are respectively connected to the outlet ends. A connecting flow path that leads the exhaust gas exhausted from the outlet end portion of the particulate filter to the inlet end portion of the selective catalytic reduction catalyst by bypassing the selective catalytic reduction catalyst. An exhaust gas purification apparatus provided with urea water addition means for adding urea water in the middle of the communication channel.   A particulate filter for collecting particulates in the exhaust gas is provided in the middle of the exhaust pipe, and a selective reduction catalyst capable of selectively reacting NOx with ammonia even in the presence of oxygen is provided downstream of the particulate filter. An exhaust gas purification apparatus configured to be able to add urea water as a reducing agent between the selective reduction catalyst and the particulate filter, wherein the particulate filter and the selective reduction catalyst are respectively connected to the respective inlet ends. The parts are arranged in series so that the exhaust gas discharged from the outlet end of the particulate filter bypasses the particulate filter and is connected to the inlet end of the particulate filter to provide a communication channel, An exhaust gas purification apparatus comprising urea water addition means for adding urea water in the middle of the communication channel.   Immediately after the communication flow path communicating between the exit end of the particulate filter and the entrance end of the selective catalytic reduction catalyst surrounds the exit end of the particulate filter and exits from the exit end Gas collecting chamber that collides the exhaust gas with the wall surface and changes the direction in a substantially perpendicular direction, and the exhaust gas collected in the gas collecting chamber is extracted toward the inlet end of the selective catalytic reduction catalyst The pipe and the exhaust gas guided by the mixing pipe collide with the wall surface and can be dispersed while changing the direction in a substantially perpendicular direction, and the dispersed exhaust gas can be introduced into the inlet side end portion of the selective catalytic reduction catalyst. The exhaust gas purification apparatus according to claim 1 or 2, wherein the exhaust gas purification chamber is constituted by a gas dispersion chamber surrounding the inlet side end portion.   An oxidation catalyst for oxidizing unburned fuel in the exhaust gas is provided on the inlet side of the particulate filter, and a fuel addition means for adding fuel to the exhaust gas on the upstream side of the oxidation catalyst is provided. The exhaust emission control device according to claim 1, 2, or 3.   Fuel injection device that injects fuel into each cylinder of the engine is adopted as fuel addition means, and fuel addition is executed by controlling fuel injection into the cylinder and leaving a large amount of unburned fuel in the exhaust gas The exhaust emission control device according to claim 4, wherein the exhaust purification device is configured.   6. The exhaust emission control device according to claim 1, wherein an ammonia reduction catalyst that oxidizes surplus ammonia is provided on the exit side of the selective catalytic reduction catalyst.

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