JP2005273546A - Exhaust emission control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control system by which NOx in exhaust gas can be promptly subjected to a reduction decomposition treatment without greatly reducing fuel economy in rich-mixture operation at the time of restart of start-up or restart of driving. <P>SOLUTION: In the exhaust emission control system 10, a NO<SB>x</SB>-storage reduction catalyst 12, in which an activator is carried on a honeycomb-type carrier made of cordierite, is provided upstream of the exhaust gas-flow in the casing 11, and a slip purifying catalyst 13, in which an activator is carried on a honeycomb-type carrier made of cordierite, is provided down stream of the exhaust-gas flow. A PM-removing filter 14, in which materials (SiC, Si<SB>3</SB>N<SB>4</SB>, etc.) having higher heat capacity per unit volume than that of the carrier materials of the catalysts 12, 13 is provided between the catalysts 12, 13. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purification apparatus that removes harmful substances in exhaust gas.

  For example, FIG. 2 shows an example of a conventional exhaust gas purification device that removes nitrogen oxides (NOx) and particulate matter (PM) in exhaust gas of a diesel engine vehicle.

  As shown in FIG. 2, an exhaust gas purification device 110 is provided in the middle of the exhaust pipe 106 connected to the exhaust manifold of the diesel engine. On the upstream side in the exhaust gas flow direction inside the casing 111 of the exhaust gas purification apparatus 110, a flow-through type nitrogen oxide storage reduction catalyst 112 in which an active material is supported on a honeycomb type carrier made of cordierite is disposed. Yes. A flow-through type slip purification catalyst 113 such as a three-way catalyst in which an active substance is supported on a honeycomb type carrier made of cordierite is disposed on the downstream side in the exhaust gas flow direction inside the casing 111. . A PM removal filter (DPF) 114 made of cordierite is disposed between the catalysts 112 and 113 inside the casing 111.

  In such an exhaust gas purifying apparatus 110, when the diesel engine is operated (lean operation) at an air-fuel ratio larger than the stoichiometric air-fuel ratio, that is, when the amount of oxygen in the exhaust gas is large, nitrogen oxides in the exhaust gas After the NOx storage reduction catalyst 112 stores, the DPF 114 collects PM in the exhaust gas, and the slip purification catalyst 113 decomposes slips such as carbon monoxide (CO) and hydrocarbon (HC) in the exhaust gas. By removing the harmful substances in the exhaust gas, the diesel engine is operated at an air-fuel ratio below the stoichiometric air-fuel ratio (rich operation), that is, when the amount of oxygen in the exhaust gas is small, the nitrogen oxidation After the catalyst 112 reduces and decomposes the nitrogen oxides stored in the object storage type reduction catalyst 112 and the nitrogen oxides in the exhaust gas, the PM in the exhaust gas is converted into DPF. 14 collected by the slip purification catalyst 113 slip such as CO and HC in the exhaust gas is decomposed, so as to remove harmful substances in exhaust gas.

  By the way, if the nitrogen oxide storage reduction catalyst 112 is not heated to at least 200 ° C. or higher during the rich operation, the efficiency of the nitrogen oxide reductive decomposition treatment is greatly reduced. Only the nitrogen oxide adsorbed and held by the oxide storage reduction catalyst 112 is released, and the removal efficiency of harmful substances in the exhaust gas is greatly reduced.

  For this reason, in a diesel engine vehicle equipped with the exhaust gas purifying device 110, for example, if the stop state or idling state after traveling operation continues for a predetermined time or more, it is maintained at 200 ° C. or higher by the thermal energy of exhaust gas during traveling operation. The nitrogen oxide occlusion-type reduction catalyst 112 that has been released gradually dissipates heat to 200 ° C. or less, and it becomes impossible to perform reductive decomposition treatment of nitrogen oxides in the exhaust gas at the time of restart operation or rich operation at the time of resumption of travel. Therefore, for example, the exhaust gas temperature raising means for instantly heating the nitrogen oxide storage reduction catalyst 112 to 200 ° C. or higher by using excessive fuel to raise the exhaust gas temperature from the diesel engine higher than usual. Is prepared.

JP-A-11-223123 JP 2002-295243 A Shoji Shoji and four others, “Application of Simultaneous NOx and PM Purification System to Diesel Engines for Commercial Vehicles”, Academic Lecture Preprints, Automobile Engineering Association of Japan, September 17, 2003, No.88- 03, p.23-28 (No.20035567)

  However, if the nitrogen oxide storage reduction catalyst 112 of the exhaust gas purification device 110 is frequently heated by the exhaust gas temperature raising means as described above, there is a problem that the fuel consumption of the diesel engine vehicle is greatly reduced. .

  Therefore, the present invention provides an exhaust gas purifying apparatus capable of immediately reducing and decomposing nitrogen oxides in exhaust gas at the time of resuming start-up or at the time of rich operation at the time of resuming running without significantly reducing fuel consumption. The purpose is to provide.

  An exhaust gas purifying apparatus according to a first aspect of the present invention for solving the above-described problem includes a casing provided in an exhaust pipe, and nitrogen oxidation that is disposed inside the casing and processes nitrogen oxides in the exhaust gas. And a particulate matter removal filter that is disposed inside the casing and collects particulate matter in the exhaust gas, and the heat capacity per unit volume of the particulate matter removal filter is the nitrogen oxidation It is characterized by being larger than the heat capacity per unit volume of the material storage type reduction catalyst.

  An exhaust gas purifying apparatus according to a second aspect of the present invention is the exhaust gas purification apparatus according to the first aspect, wherein the particulate matter removal filter is 1.5 times or more per unit volume than a heat capacity of the support material of the nitrogen oxide storage reduction catalyst. It is made of a material having a heat capacity.

  According to a third aspect of the present invention, there is provided the exhaust gas purifying apparatus according to the second aspect, wherein the support of the nitrogen oxide storage reduction catalyst is made of cordierite, and the particulate matter removing filter is made of silicon carbide or silicon nitride. Features.

  An exhaust gas purification apparatus according to a fourth aspect of the present invention includes the slip purification catalyst according to any one of the first to third aspects of the invention, which is disposed inside the casing and decomposes unpurified components in the exhaust gas. In addition, the heat capacity per unit volume of the particulate matter removal filter is larger than the heat capacity per unit volume of the slip purification catalyst.

  The exhaust gas purifying apparatus according to a fifth invention is the exhaust gas purifying apparatus according to the fourth invention, wherein the particulate matter removal filter has a heat capacity of 1.5 times or more per unit volume than the heat capacity of the carrier material of the slip purification catalyst. It is characterized by comprising.

  According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the carrier for the slip purification catalyst is made of cordierite, and the particulate matter removing filter is made of silicon carbide or silicon nitride.

  The exhaust gas purifying apparatus according to a seventh aspect of the present invention is the exhaust gas purifying apparatus according to any one of the fourth to sixth aspects, wherein the nitrogen oxide storage reduction catalyst is disposed upstream of the exhaust gas flow direction in the casing, The slip purification catalyst is disposed on the downstream side in the exhaust gas flow direction in the casing, and the particulate matter removal filter is disposed between the nitrogen oxide storage reduction catalyst and the slip purification catalyst in the casing. It is characterized by being.

  According to the exhaust gas purification apparatus according to the first aspect of the present invention, the heat capacity per unit volume of the particulate matter removal filter is larger than the heat capacity per unit volume of the nitrogen oxide storage type reduction catalyst. Since the particulate matter removal filter can accumulate more heat energy than the reduction catalyst, even if the amount of heating by the exhaust gas is significantly reduced, the particulate matter removal filter releases the accumulated heat energy and nitrogen oxidation. The object storage-type reduction catalyst can be maintained at a temperature higher than the minimum function expression temperature for a longer period than before.

  For this reason, in a vehicle equipped with this exhaust gas purifying device, nitrogen oxides in exhaust gas during rich operation can be immediately reduced and decomposed, from the stop state or idling state of the vehicle to when restarting or when restarting traveling. Since the time can be extended significantly compared to the conventional case, for example, the frequency of use of the exhaust gas temperature raising means that makes it possible to immediately perform reductive decomposition treatment by using excessive fuel to raise the exhaust gas temperature higher than usual. It can be greatly reduced. Therefore, the nitrogen oxides in the exhaust gas can be immediately reduced and decomposed at the time of resuming start-up or at the time of rich operation at the time of resuming running without significantly reducing fuel consumption.

  According to the exhaust gas purification apparatus of the second invention, the particulate matter removal filter is made of a material having a heat capacity of 1.5 times or more per unit volume than the heat capacity of the support material of the nitrogen oxide storage reduction catalyst. The effect of the first invention can be remarkably exhibited.

  According to the exhaust gas purification apparatus of the third aspect of the invention, since the support of the nitrogen oxide storage reduction catalyst is made of cordierite, and the particulate matter removal filter is made of silicon carbide or silicon nitride, in addition to the effects described above Sufficient strength can be expressed.

  According to the exhaust gas purification apparatus of the fourth invention, since the heat capacity per unit volume of the particulate matter removal filter is larger than the heat capacity per unit volume of the slip purification catalyst, more heat energy than the slip purification catalyst. The particulate matter removal filter can accumulate, so even if the amount of heating by the exhaust gas is significantly reduced, the thermal energy accumulated by the particulate matter removal filter is released, and the slip purification catalyst is raised above the minimum function expression temperature. It can be held for a longer period than before.

  According to the exhaust gas purification apparatus of the fifth invention, the particulate matter removal filter is made of a material having a heat capacity of 1.5 times or more per unit volume than the heat capacity of the carrier material of the slip purification catalyst. The effect of the second invention can be remarkably exhibited.

  According to the exhaust gas purification apparatus of the sixth aspect of the invention, since the carrier of the slip purification catalyst is made of cordierite and the particulate matter removal filter is made of silicon carbide or silicon nitride, in addition to the effects described above, sufficient strength is achieved. Can be expressed.

  According to the exhaust gas purification apparatus pertaining to the seventh aspect of the invention, the nitrogen oxide storage reduction catalyst is disposed upstream of the exhaust gas flow direction in the casing, and the slip purification catalyst is disposed downstream of the exhaust gas flow direction in the casing. Since the particulate matter removing filter is disposed between the nitrogen oxide storage reduction catalyst and the slip purification catalyst in the casing, the heating of both the catalysts by the heat radiation of the particulate matter removing filter is efficiently performed. While performing, it is possible to reliably remove harmful substances in the exhaust gas.

  An embodiment of an exhaust gas purification apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of an exhaust gas purification apparatus.

  As shown in FIG. 1, a proximal end of an intake pipe 102 is connected to an intake manifold 101 provided at an intake port of the diesel engine 100. A throttle valve 103 is provided on the proximal end side of the intake pipe 102. An air cleaner 104 is provided on the distal end side of the intake pipe 102.

  The exhaust manifold 105 provided at the exhaust port of the diesel engine 100 is connected to the proximal end of the exhaust pipe 106 and the proximal end of the exhaust recirculation pipe 107. The distal end of the exhaust gas recirculation pipe 107 is connected to the proximal end side of the intake pipe 102 with respect to the throttle valve 103. A flow control valve 108 is provided in the middle of the exhaust gas recirculation pipe 107.

In the middle of the exhaust pipe 106, the exhaust gas purification apparatus 10 according to the present embodiment is provided. On the upstream side in the exhaust gas flow direction inside the casing 11 of the exhaust gas purification apparatus 10, a flow-through type nitrogen oxide storage reduction catalyst 12 in which an active material is supported on a honeycomb type carrier made of cordierite is disposed. Yes. A flow-through type slip purification catalyst 13 such as a three-way catalyst in which an active substance is supported on a honeycomb type carrier made of cordierite is disposed on the downstream side in the exhaust gas flow direction inside the casing 11. Between the catalysts 12 and 13 inside the casing 11, a material (for example, carbonized) having a larger heat capacity (preferably 1.5 times or more) per unit volume than the support material (cordierite) of the catalysts 12 and 13. A PM removal filter (DPF) 14 using silicon (SiC), silicon nitride (Si ₃ N ₄ ), or the like is provided.

  In this embodiment, when the diesel engine 100 is started and air is supplied from the intake pipe 102 to the intake manifold 101 via the air cleaner 104 and the throttle valve 103, the air is supplied from the intake port of the diesel engine 100. The gas is supplied into each cylinder, burned together with the fuel, and discharged from the exhaust port to the exhaust manifold 105.

  A part of the exhaust gas discharged from the diesel engine 100 to the exhaust manifold 105 is recirculated to the intake manifold 101 via the exhaust recirculation pipe 107 and the flow rate control valve 108, and the intake air of the diesel engine 100 is taken together with newly taken air. It is supplied from the port into each cylinder and burned again.

  On the other hand, the remaining exhaust gas that has not recirculated flows into the casing 11 of the exhaust gas purification device 10 from the exhaust pipe 106 and is purified by flowing through the nitrogen oxide storage reduction catalyst 12, the DPF 14, and the slip purification catalyst 13. Processed and discharged to the outside.

  Specifically, the exhaust gas purification apparatus 10 is operated (lean operation) with the diesel engine 100 at an air / fuel ratio larger than the stoichiometric air / fuel ratio, that is, when the amount of oxygen in the exhaust gas is large, After the nitrogen oxide storage type reduction catalyst 12 stores the nitrogen oxide, the DPF 14 collects PM in the exhaust gas, and the slip purification catalyst 13 oxidizes and decomposes slips that are unpurified components such as CO and HC in the exhaust gas. By processing, harmful substances in the exhaust gas are removed, and the diesel engine 100 is operated (rich operation) at an air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio, that is, in exhaust gas such as during low-speed driving or acceleration driving. When the amount of oxygen is small, after the catalyst 12 has reduced and decomposed the nitrogen oxides stored in the nitrogen oxide storage reduction catalyst 12 and the nitrogen oxides in the exhaust gas. The PM in the exhaust gas collected is DPF 14, by slipping purification catalyst 13 slip is unpurified components of CO and HC and the like in the exhaust gas is oxidative decomposition treatment is to remove harmful substances in exhaust gas.

  Thus, when the exhaust gas purification device 10 purifies the exhaust gas from the diesel engine 100, the inside of the casing 11 of the exhaust gas purification device 10 removes harmful substances in the exhaust gas by the thermal energy of the exhaust gas from the diesel engine 100. It is kept at a temperature (200 ° C. or higher) that can be decomposed.

  At this time, since the DPF 14 is made of a material having a larger heat capacity per unit volume than the support material of the catalysts 12 and 13 (1.5 times or more), it accumulates more heat energy than the catalysts 12 and 13. It becomes like this.

  For this reason, in a diesel engine vehicle equipped with the exhaust gas purification device 10, for example, the vehicle enters a stopped state or an idling state after traveling operation, and the amount of heating inside the exhaust gas purification device 10 due to the exhaust gas from the diesel engine 100 becomes extremely small. However, since the heat energy accumulated in the DPF 14 is released, the catalysts 12 and 13 are held at a function-expressing minimum temperature (for example, 200 ° C.) or higher for a longer period than before.

  Thereby, the exhaust gas purifying device 10 can immediately reduce and decompose nitrogen oxides in the exhaust gas at the time of rich operation, and the time from the stop state or idling state of the diesel engine vehicle to the start restart or the travel restart time, For example, use of an exhaust gas temperature raising means that makes it possible to immediately reduce and decompose the exhaust gas from the diesel engine 10 by using excessive fuel so that the exhaust gas temperature from the diesel engine 10 becomes higher than usual. The frequency can be greatly reduced.

  Therefore, according to the exhaust gas purification apparatus 10 according to the present embodiment, the nitrogen oxides in the exhaust gas can be immediately subjected to reductive decomposition treatment at the time of start-up restart or rich operation at the time of restart of travel without significantly reducing the fuel consumption. it can.

  Further, since the DPF 14 is disposed between the nitrogen oxide storage reduction catalyst 12 and the slip purification catalyst 13 in the casing 11, the heat storage energy of the DPF 14 is transferred to the nitrogen oxide storage reduction catalyst 12 and the slip catalyst. It can be efficiently applied to both of the purification catalyst 13 and not only enables the immediate reduction and decomposition treatment of nitrogen oxides by the nitrogen oxide storage reduction catalyst 12, but also allows the slip purification catalyst 13 to remove CO and HC, etc. Immediate oxidative decomposition treatment of slip, which is a purification component, can also be made possible.

In this embodiment, the DPF 14 made of SiC or Si ₃ N ₄ is applied. However, the present invention is not limited to this, and the heat capacity per unit volume is higher than the support material of the nitrogen oxide storage reduction catalyst or the slip purification catalyst. If the DPF is made of a large material, the same effect as in the case of the present embodiment can be obtained, and in particular, the heat capacity per unit volume is 1 than the support material of the nitrogen oxide storage reduction catalyst or the slip purification catalyst. It is preferable that the DPF is made of more than 5 times the material because the effect is remarkably increased. Further, the nitrogen oxide storage reduction catalyst 12 and the slip purification catalyst such as SiC and Si ₃ N _{4 of} the present embodiment are preferable. It is a DPF 14 made of a sintered ceramic material having a heat capacity per unit volume of 1.5 times or more (about 1.66 times) than 13 carrier materials (cordierite). When, it is possible to obtain a favorable result in strength, it is very suitable.

  Further, in the present embodiment, the case of the exhaust gas purification device 10 in which the casing 11 includes the nitrogen oxide storage reduction catalyst 12, the slip purification catalyst 13, and the DPF 14 has been described. However, the present invention is not limited to this, and the slip purification catalyst. Even in the case of an exhaust gas purification apparatus in which only the nitrogen oxide storage reduction catalyst and the DPF are housed in the casing, the same effect as in the case of the present embodiment can be obtained. At this time, it is also possible to arrange the DPF inside the casing on the upstream side in the exhaust gas circulation direction and arrange the nitrogen oxide storage reduction catalyst on the downstream side in the exhaust gas circulation direction.

  For example, when the exhaust gas purifying apparatus according to the present invention is mounted on a diesel engine vehicle, it can remove harmful substances in the exhaust gas while suppressing a significant decrease in fuel consumption. it can.

It is a schematic block diagram of embodiment of the exhaust gas purification apparatus which concerns on this invention. It is a schematic block diagram of an example of the conventional exhaust gas purification apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Exhaust gas purification device 11 Casing 12 Nitrogen oxide occlusion type reduction catalyst 13 Slip purification catalyst 14 PM removal filter (DPF)
100 Diesel Engine 101 Intake Manifold 102 Intake Pipe 103 Throttle Valve 104 Air Cleaner 105 Exhaust Manifold 106 Exhaust Pipe 107 Exhaust Recirculation Pipe 108 Flow Control Valve

Claims (7)

A casing provided in the exhaust pipe;
A nitrogen oxide storage reduction catalyst disposed inside the casing for treating nitrogen oxides in exhaust gas;
A particulate matter removal filter that is disposed inside the casing and collects particulate matter in the exhaust gas, and
The exhaust gas purification apparatus, wherein a heat capacity per unit volume of the particulate matter removal filter is larger than a heat capacity per unit volume of the nitrogen oxide storage reduction catalyst. In claim 1,
The exhaust gas purification apparatus, wherein the particulate matter removal filter is made of a material having a heat capacity of 1.5 times or more per unit volume than a heat capacity of a support material of the nitrogen oxide storage reduction catalyst. In claim 2,
The support for the nitrogen oxide storage reduction catalyst is made of cordierite,
The exhaust gas purification apparatus, wherein the particulate matter removal filter is made of silicon carbide or silicon nitride. In any one of Claims 1-3,
With a slip purification catalyst that is disposed inside the casing and decomposes unpurified components in the exhaust gas,
The exhaust gas purification apparatus, wherein a heat capacity per unit volume of the particulate matter removal filter is larger than a heat capacity per unit volume of the slip purification catalyst. In claim 4,
The exhaust gas purifying apparatus, wherein the particulate matter removal filter is made of a material having a heat capacity of 1.5 times or more per unit volume than a heat capacity of a carrier material of the slip purification catalyst. In claim 5,
The carrier of the slip purification catalyst is made of cordierite,
The exhaust gas purification apparatus, wherein the particulate matter removal filter is made of silicon carbide or silicon nitride. In any one of Claims 4-6,
The nitrogen oxide storage reduction catalyst is disposed upstream of the exhaust gas flow direction in the casing,
The slip purification catalyst is disposed on the downstream side in the exhaust gas flow direction in the casing;
The exhaust gas purification apparatus, wherein the particulate matter removal filter is disposed between the nitrogen oxide storage reduction catalyst and the slip purification catalyst in the casing.

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