JP2005291062A - Filter device, and exhaust emission control device provided with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter device, in which exhaust emission can be controlled while preventing overheating or deterioration of fuel economy, and an exhaust gas emission control device provided with it. <P>SOLUTION: This filter device 220, provided on an exhaust passage R in an internal combustion engine 2, comprises filter base material 22 carrying catalyst 221 having an oxidation function on its surface. On the surface of the catalyst 221, heat-resistant oxide 22 that does not contribute to combustion of particulate PM in exhaust gas is coated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a filter device for purifying exhaust gas discharged from a diesel engine, and an exhaust gas purification device including the same.

  A particulate filter (hereinafter referred to as “DPF”) is used on the exhaust gas passage of a diesel engine, which is an internal combustion engine, in order to collect particulates with carbon fine particles or the like mixed in the exhaust gas as the core without releasing them into the atmosphere. Is written). When the amount of particulates collected by the DPF increases, clogging and exhaust pressure increase. Therefore, it is necessary to periodically burn the filter and incinerate the particulates to regenerate the DPF.

In general, particulates can be oxidized with oxygen at a high temperature of about 600 ° C. Therefore, for DPF regeneration, forced regeneration in which exhaust temperature or filter temperature is increased to about 600 ° C. and forced combustion is performed, and oxidation is performed upstream of the DPF. There is a continuous regeneration in which a catalyst is disposed and the particulates collected and accumulated in the DPF by NO ₂ generated by the oxidation catalyst are continuously burned. At the time of forced regeneration, an additive containing HC such as fuel is mixed in the exhaust gas and burned on the oxidation catalyst, and the DPF is heated by heating DPF using the heat and oxygen at that time to burn the particulates. Forced regeneration is performed.

Here, the reaction during continuous regeneration and forced regeneration will be described using the following equations (1) to (4).
Reaction of continuous regeneration Oxidation catalyst 2NO + O ₂ → 2NO ₂ (1)
DPF PM + NO ₂ → CO + NO (2)
Reaction during forced regeneration Oxidation catalyst Fuel (HC) + O ₂ → CO ₂ + H ₂ O + heat (3)
DPF PM + O ₂ → COX (4)
As the DPF, a CSF (Catalyzed Soot Filter) carrying a catalyst having an oxidation function or a filter carrying a NOx catalyst may be used. When CSF is used, NO ₂ is generated by the function of the supported oxidation catalyst, so that the continuous regeneration performance is improved with respect to a filter not supporting the catalyst. In the case of a filter carrying a NOx catalyst, the purification device is smaller than when the NOx catalyst and the filter are separately provided.
In urban travel where there is a lot of traffic such as traffic jams, the exhaust gas temperature does not become so high that continuous regeneration is established. Therefore, forced regeneration is necessary to remove particulates collected by the filter.
Patent Document 1 describes a catalyst in which a refractory inorganic oxide layer is laminated on an HC adsorbent layer supported on a catalyst support.

JP 2003-135970 A

  Particulates in the exhaust gas are collected in the DPF, but if forced regeneration is performed with a large amount of collected gas, the particulates will self-ignite and it is difficult to control the temperature of the filter. May be warm. When the temperature rises excessively, the filter temperature may rise to a temperature exceeding the heat resistance limit of the fill base material, leading to damage to the filter. The limit value of the amount of particulates that is not overheated is called the “deposition amount limit value”.

In the case of a DPF in which an oxidation catalyst, NOx catalyst or the like is supported on a filter base material, the burning rate of the particulates increases, and in this case, the particulates are easily ignited, and the limit value of the accumulation amount is greatly reduced. .
For this reason, when a filter member carrying various catalysts as described above is used as a DPF, forced regeneration must be frequently performed, which causes a reduction in fuel consumption. Even when the filter member carrying the catalyst is used as the DPF to clear the problem of fuel consumption, the excessive temperature rise cannot be denied unless the accumulated amount of particulates can be detected accurately.

Patent Document 1 describes a catalyst in which a refractory inorganic oxide layer is laminated on an HC adsorbent layer supported on a catalyst carrier. The function of the refractory inorganic oxide layer here is the HC adsorbent. This is to suppress the separation rate and amount of hydrocarbon (HC) retained in the layer, and does not prevent excessive temperature rise or fuel consumption deterioration, or suppress particulate combustion time.
An object of the present invention is to provide a filter device capable of purifying exhaust gas while preventing excessive temperature rise and fuel consumption deterioration, and an exhaust gas purification device including the same.

  In order to achieve the above object, a filter device according to the present invention is capable of burning particulates in exhaust gas on the surface of a catalyst having an oxidation function carried on the surface of a filter base provided in an exhaust passage of an internal combustion engine. It is characterized by coding a heat-resistant oxide that does not contribute.

  According to the present invention, a filter device that is provided in an exhaust passage of an internal combustion engine and collects particulates in exhaust gas flowing through the exhaust passage, and an additive containing hydrocarbons in an exhaust passage upstream of the filter device The exhaust gas purifying device having a supply device for supplying a heat-resistant oxide that does not contribute to combustion of particulates in the exhaust gas on the surface of the catalyst having an oxidation function carried on the surface of the filter base material as a filter device It is characterized by using a catalytic device that is coded.

  These catalysts having an oxidation function include NOx storage catalyst that stores NOx during lean operation of the internal combustion engine and exhausts and reduces NOx during rich operation, and selective reduction that reduces NOx using urea or ammonia as a reducing agent. It may be a type (SRC) catalyst. As the filter device, an oxidation catalyst may be disposed on the upstream side of the filter base material.

According to the present invention, the heat-resistant oxide that does not contribute to the combustion of the particulates in the exhaust gas is coded on the surface of the catalyst having the oxidation function carried on the surface of the filter base provided on the exhaust passage of the internal combustion engine. Therefore, contact between the particulates and the catalyst is avoided, and even with a catalyst-carrying filter, combustion of particulates due to oxygen is not promoted at high temperatures. In other words, by suppressing the particulate combustion rate, the self-ignition of particulates can be suppressed, the excessive temperature rise can be reduced, and the number of forced regenerations can be reduced even in a filter device carrying a catalyst. And the durability of the filter base material is improved.
According to the present invention, since the filter base material has an oxidizing function, NO ₂ generated by the catalytic action on the filter passes through the heat-resistant oxide layer and comes into contact with the particulates. The particulates can be continuously burned in the region, and the continuous regeneration performance can be improved while improving the durability of the filter base material with fuel efficiency.
According to the present invention, the filter base material is loaded with a NOx occlusion type catalyst that occludes NOx during lean operation and exhausts NOx during reduction operation, or a catalyst that reduces NOx using urea or ammonia as a reducing agent. Thus, it is a small device having NOx purification performance while improving the durability of the filter base material with fuel efficiency.

  FIG. 1 shows an exhaust gas purification apparatus 1 as an embodiment of the present invention. The exhaust gas purification device 1 purifies exhaust gas discharged from a diesel engine (hereinafter simply referred to as an engine) 2 as an internal combustion engine. The exhaust gas purification device 1 is provided in the exhaust passage R, and a filter device 220 that collects particulates in the exhaust gas flowing through the exhaust passage R, and an oxidation as a catalyst device disposed on the upstream side of the filter device 220. A catalyst 21 and an injection nozzle 30 are provided as a supply device for supplying fuel containing hydrocarbon (HC) as an additive into an exhaust passage upstream of the oxidation catalyst 21.

  The exhaust passage R is composed of an exhaust manifold 4 communicating with the combustion chamber 3 of the engine 2 and an exhaust pipe 5 connected to the exhaust manifold 4. The engine 2 is an in-line four-cylinder engine, and an injector 8 is provided in each cylinder. Each injector 8 is provided with a fuel supply section 9 for supplying fuel to the injector 8 and a fuel injection section 11 for injecting fuel into each combustion chamber 3 by each injector 8, and these are driven and controlled by the engine ECU 12.

  The fuel supply unit 9 makes the high-pressure fuel of the high-pressure fuel pump 13 driven by the engine 2 constant by the fuel pressure adjusting unit 14 controlled by the fuel pressure control unit 121 in the engine ECU 12, and then guides it to the common rail 15. The fuel is supplied to each injector 8 through a fuel pipe 16 that branches and extends. The electromagnetic valve 17 included in the injector 8 is connected to the injection control unit 122.

  The engine ECU 12 includes a vehicle speed sensor 7 that detects a vehicle speed Vc, an accelerator pedal opening sensor 24 that detects an accelerator pedal opening θa of the engine 2, a crank angle sensor 25 that detects crank angle information Δθ, and an exhaust temperature gt. An exhaust gas temperature sensor 26 for detecting, a water temperature sensor 27 for detecting the water temperature wt, and an atmospheric pressure sensor 28 for outputting the atmospheric pressure pa are connected. The crank angle information Δθ is used for derivation of the engine speed Ne in the engine ECU 12 and fuel injection timing control.

  The engine ECU 12 includes a fuel pressure control unit 121 and an injection control unit 122. The injection control unit 122 calculates the basic fuel injection amount according to the engine speed Ne and the accelerator pedal depression amount a, and adds correction values of, for example, the water temperature wt, the atmospheric pressure pa, and the vehicle speed information Vc according to the driving conditions. Deriving the fuel injection amount. The injection timing is derived by adding a correction corresponding to the operating condition to a known basic advance value. Then, an output signal corresponding to the calculated injection timing and fuel injection amount is set in an injector driver (not shown), and is output to the electromagnetic valve 17 of the fuel injection unit 11 to control fuel injection of the injector 8.

  The oxidation catalyst 21 and the filter device 220 are arranged in series in the order of the oxidation catalyst 21 and the filter device 220 on the exhaust pipe 5 in a metal cylindrical casing 18 through a support member 19 made of a bulky metal net. It is arranged and stored. The oxidation catalyst 21 has a catalyst supported on a catalyst support 211. The catalyst carrier 211 is a monolith type made of ceramic and having a honeycomb structure in cross section, and a large number of exhaust gas passages r1 having both ends opened therein are formed therein. The catalyst component is supported on the passage-facing wall surfaces of the multiple exhaust gas passages r1. In this embodiment, a catalyst having platinum (Pt) as a main component is attached as a catalyst component.

  The filter device 220 includes a DPF 22 as a filter base material carrying a catalyst having an oxidation function on the surface. For example, the DPF 22 is made of a ceramic such as cordierite mainly composed of Mg, Al, and Si, and is formed as a honeycomb structure in which a large number of exhaust gas passages r2 are laminated in parallel in the direction of the exhaust passage R. ing. Here, the exhaust gas passages r2 adjacent to each other are formed so that either the upstream side or the downstream side of the exhaust passage R are alternately closed by the seal portions 23. In this embodiment, the DPF 22 has a function of collecting particulates (PM) in the exhaust gas in the exhaust gas and a function of oxidizing.

As shown in FIG. 2, on the surface of the catalyst layer (hereinafter referred to as “oxidation catalyst layer”) 221 supported on the DPF 22, a layer of the heat-resistant oxide 222 that does not contribute to the combustion of particulates (PM) in the exhaust gas. (Hereinafter referred to as “heat-resistant oxide layer” 222). That is, the heat-resistant oxide layer 222 is laminated on the surface of the oxidation catalyst layer 221. In FIG. 2, the white arrow schematically shows the flow of the exhaust gas. An oxidation catalyst is used as the catalyst of the oxidation catalyst layer 221. That is, DF is used for the DPF 22, and the supported catalyst surface is coated with the heat-resistant oxide layer 222. As the heat-resistant oxide, alumina (Al ₂ O ₃ ), titania (TiO ₂ ), or the like is used.

  The injection nozzle 30 is attached to the exhaust pipe 5 upstream of the oxidation catalyst 21 and is connected to a fuel storage section (not shown) via a pipe 32. The pipe 32 is provided with an electromagnetic valve 31 that controls fuel supply to the injection nozzle 30. The electromagnetic valve 31 is connected to the engine ECU 12, and its opening / closing is controlled by the injection control unit 123. The injection control unit 123 is configured to open the electromagnetic valve 31 and inject fuel from the injection nozzle 30 to perform a regeneration operation when the trapped amount exceeds a predetermined value and the exhaust gas temperature is equal to or higher than the predetermined temperature. Has been. The amount of fuel supplied into the exhaust pipe 5 is regulated such that the exhaust temperature to the DPF 22 is 600 ° C. or higher.

  Next, the operation and purification function of the exhaust gas purification device 1 will be described. When the engine 2 is started and the exhaust process starts, exhaust gas is discharged from the combustion chamber 3. This exhaust gas flows into the DPF 22 through the exhaust passage R and the oxidation catalyst 21. The exhaust gas that has flowed in passes through the passage-facing wall b of each exhaust gas passage r2-1 and reaches each exhaust gas passage r2-2 that has an outlet formed downstream of the exhaust passage R, and is discharged. (PM) is collected by filtration. The exhaust gas thus purified is discharged into the atmosphere. By passing the exhaust gas, the oxidation catalyst 21 and the DPF 22 are respectively heated and continuously regenerated to the catalyst activation temperature.

At this time, in the oxidation catalyst 21,
2NO + O ₂ → 2NO ₂ (1) occurs.
In the DPF 22, since the oxidation catalyst layer (catalyst having an oxidation function) 221 is supported, as shown in FIG. 3, there is a reaction of the formula (1), coupled with NO ₂ generated by the oxidation catalyst 21,
PM + NO ₂ → CO + NO (2) reaction occurs.
At this time, particulates (PM) in the exhaust gas are collected in the heat-resistant oxide layer 222 on the surface of the oxidation catalyst layer 221, but the generated NO ₂ passes through the heat-resistant oxide layer 222. Thus, the particulate (PM) can be continuously burned in the normal temperature range because it is in contact with the particulate.

  When the particulate (PM) trapped amount in the DPF 22 exceeds a predetermined value and the exhaust temperature gt from the exhaust temperature sensor 26 is equal to or higher than the predetermined temperature, the injection control unit 123 drives the electromagnetic valve 31 to inject the injection nozzle 30. The fuel is sprayed into the exhaust gas from the catalyst toward the oxidation catalyst 21 to perform forced regeneration.

During forced regeneration, the oxidation catalyst
While the reaction of fuel (HC) + O ₂ → CO ₂ + H ₂ O + heat (3) is performed,
In the DPF 22, a reaction of PM + O ₂ → COX (4) is performed.

  As described above, even when forced regeneration is performed, the heat-resistant oxide layer 222 is coded on the surface of the oxidation catalyst layer 221, so that the particulate (PM) and the oxidation catalyst layer 221 are formed as shown in FIG. And the combustion rate of particulates (PM) is suppressed even with CSF which is a catalyst-carrying filter. For this reason, the occurrence of self-loading of particulates (PM) can be suppressed, the excessive temperature rise can be reduced, and even the CSF (DPF) 22 can reduce the number of times of forced regeneration, and the fuel efficiency can be reduced. The durability of the material can be improved.

  In this embodiment, the oxidation catalyst layer 221 is formed on the inner wall surface 22a of the DPF 22 that is inside each exhaust gas passage r2-1, and the heat-resistant oxide layer 222 is formed on the surface thereof. It is not limited to. For example, as shown in FIG. 5, an oxidation catalyst layer 221 may be formed on the outer wall surface 22 b of the DPF 22. In this case, the catalyst that forms the oxidation catalyst layer 221 often passes through the filter and oozes out to the inner wall surface 22a. Therefore, if the surface of the oxidization catalyst 221 that leaks out is coated with the heat-resistant oxide layer 222, Good.

  In the present embodiment, the oxidation catalyst 221 is exemplified as the catalyst having an oxidation function, but is not limited to this, and the NOx is occluded during the lean operation of the engine 2 and the NOx is discharged during the rich operation and reduced. It may be a NOx occlusion type catalyst or a catalyst that reduces NOx using urea or ammonia as a reducing agent. In this way, the DPF 22 carries a NOx occlusion type catalyst or a catalyst for reducing NOx using urea or ammonia as a reducing agent, and the surface of the particulate (PM) and the catalyst can be contacted by coating the surface with a heat-resistant oxide. This can be avoided, and self-ignition of particulates (PM) can be suppressed. Further, by supporting the NOx storage type catalyst on the DPF 22, the number of parts and space can be reduced and the apparatus can be reduced in size as compared with the case where the NOx storage type catalyst is provided separately from the DPF 22.

It is a schematic block diagram of the exhaust-gas purification apparatus and filter apparatus as one Embodiment of this invention. It is an expanded sectional view showing the composition of the principal part of a filter device. It is an expanded sectional view which shows the collection state of the particulates of the filter apparatus which has a heat resistant oxide. It is an expanded sectional view which shows the collection state of the particulates of the filter apparatus which does not have a heat resistant oxide. It is an expanded sectional view which shows the structure of the principal part of the filter apparatus of a form different from the filter apparatus shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust-gas purification apparatus 2 Internal combustion engine 21 Catalyst catalyst 22 Filter base material 221 Catalyst which has an oxidation function 222 Heat resistant oxide R Exhaust passage PM particulate

Claims (5)

A filter base material provided in an exhaust passage of an internal combustion engine and carrying a catalyst having an oxidation function on its surface;
A filter device characterized in that a heat-resistant oxide that does not contribute to combustion of particulates in exhaust gas is coded on the surface of the catalyst. The filter device according to claim 1, wherein
The filter device, wherein the catalyst having an oxidation function is a NOx occlusion type catalyst that occludes NOx during lean operation of the internal combustion engine and exhausts and reduces NOx during rich operation. The filter device according to claim 1, wherein
The filter device, wherein the catalyst having an oxidation function is a catalyst that reduces NOx using urea or ammonia as a reducing agent. The filter apparatus according to claim 1, 2, or 3, wherein an oxidation catalyst is disposed upstream of the filter base material. A filter device that is provided in an exhaust passage of an internal combustion engine and collects particulates in exhaust gas flowing through the exhaust passage; and a supply device that supplies fuel into the exhaust passage upstream of the filter device. In the exhaust gas purification device,
An exhaust gas purification device comprising the filter device according to any one of claims 1 to 4 as the filter device.

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