JP2021028482A - Exhaust emission control device - Google Patents

Abstract

To provide an exhaust emission control device capable of reducing inflow amount of particulate matters to a filter while effectively using heat of exhaust gas without adding a catalyst on which Pt, etc. is supported.SOLUTION: An exhaust emission control device 100 includes: a DPF 8a provided in an exhaust passage 3 of an engine 1 and collecting particulate matters included in exhaust gas of the engine 1; and a PM combustion catalyst 7 that is provided on the upstream side of the DPF 8a in the exhaust passage 3 and can burn a part of the particulate matters without largely depending on oxidation reaction with NO2. A passage length from an upstream end of the exhaust passage 3 to the PM combustion catalyst 7 is shorter than that from the PM combustion catalyst 7 to the DPF 8a.SELECTED DRAWING: Figure 1

Description

The present invention relates to an exhaust gas purification device.

Conventionally, there is known an exhaust treatment device in which a fine particle removing filter for collecting particulate matter [PM: Particulate Matter] contained in exhaust gas is arranged in an exhaust passage of an internal combustion engine (for example, Patent Document 1). In the exhaust treatment apparatus described in Patent Document 1, the combustion catalyst and the fine particle removing filter are housed in the housing of the fine particle removing filter in this order.

Japanese Unexamined Patent Publication No. 2010-229988

In recent years, exhaust gas regulations, including reduction of particulate matter emissions, have been strengthened. In the present technical field, in order to reduce the emission amount of particulate matter, for example, it is possible to suppress an increase in the size of a filter for collecting particulate matter, an increase in the burden on the filter due to the regeneration of the filter, and an increase in cost. It is desired.

The present invention provides an exhaust purification device capable of reducing the inflow of particulate matter into a filter while effectively utilizing the heat of exhaust gas without adding a catalyst carrying Pt or the like. With the goal.

The exhaust purification device according to one aspect of the present invention is provided in the exhaust passage of the internal combustion engine, is provided with a filter for collecting particulate matter contained in the exhaust gas of the internal combustion engine, and is provided on the upstream side of the filter in the exhaust passage. It _{is equipped with a combustion catalyst capable of burning a part of particulate matter without the main cause of oxidation reaction by NO 2} , and the flow path length from the upstream end of the exhaust passage to the combustion catalyst is the flow path from the combustion catalyst to the filter. Shorter than long.

In the exhaust purification device according to one aspect of the present invention, a combustion catalyst is provided on the upstream side of the filter in the exhaust passage. Since the combustion catalyst can burn a part of the particulate matter, it is possible to reduce the amount of the particulate matter flowing into the filter. The combustion catalyst for a portion of the particulate matter can be combusted without mainly due to oxidation reaction with NO _2, a catalyst obtained by loading Pt or the like for generating NO ₂ on the upstream side of the combustion catalyst You do not have to add it. Further, since the flow path length from the upstream end of the exhaust passage to the combustion catalyst is shorter than the flow path length from the combustion catalyst to the filter, the heat of the exhaust gas is generated in order to burn a part of the particulate matter in the combustion catalyst. Is effectively used. Therefore, according to the exhaust gas purification device, it is possible to reduce the amount of particulate matter flowing into the filter while effectively utilizing the heat of the exhaust gas without adding a catalyst supporting Pt or the like.

In one embodiment, the exhaust purification device is provided on the upstream side of the exhaust gas in the exhaust passage to raise the temperature of the exhaust gas flowing into the combustion catalyst and the temperature of the exhaust gas flowing into the combustion catalyst. A temperature sensor for detection and a temperature rise control unit for controlling the temperature rise unit so as to raise the temperature when the temperature is less than a predetermined temperature threshold based on the detection result of the temperature sensor may be further provided. .. In this case, the exhaust gas flowing into the combustion catalyst is heated by using the temperature raising unit, so that a part of the particulate matter can be effectively burned in the combustion catalyst.

According to the present invention, it is possible to reduce the inflow of particulate matter into the filter while effectively utilizing the heat of the exhaust gas without adding a catalyst carrying Pt or the like.

It is a schematic block diagram of the engine system provided with the exhaust gas purification device of embodiment. It is a figure which illustrates the characteristic of a combustion catalyst. It is a flowchart which illustrates the process of the ECU of FIG. It is a schematic block diagram of the engine system provided with the exhaust gas purification device of a modification.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent elements are designated by the same reference numerals, and duplicate description will be omitted.

[Engine system configuration]
FIG. 1 is a schematic configuration diagram of an engine system including the exhaust gas purification device of the embodiment. As shown in FIG. 1, the exhaust gas purification device 100 is mounted on a vehicle such as a truck and purifies the exhaust gas discharged from a diesel engine (hereinafter, simply referred to as an engine) 1 which is an internal combustion engine. The engine 1 has a plurality of injectors (heating units) 2 that inject fuel into a plurality of cylinders. The vehicle on which the exhaust gas purification device 100 is mounted may be a large vehicle such as a tractor or a bus, a medium-sized vehicle, a small vehicle, and a light vehicle, in addition to a truck.

The engine 1 is connected to each injector 2 and includes a common rail (not shown) that stores high-pressure fuel and supplies high-pressure fuel to each injector. Each injector 2 injects fuel, for example, a main injection, a pilot injection that injects a minute amount of fuel before the main injection, an after-injection that injects a minute amount of fuel after the main injection, and an injection after the after-injection. Post-injection can be performed.

An exhaust passage 3 for exhausting the exhaust gas generated in the combustion chamber is connected to the engine 1. The exhaust purification device 100 includes a turbine 5 of a turbocharger 4, an ATC (heating unit) [After Turbo Catalyst] 6, and a PM combustion catalyst (combustion) arranged in order from the upstream side to the downstream side in the exhaust passage 3. The catalyst) 7 and the post-treatment unit 8 are provided. Further, the engine 1 includes an EGR unit 9 that recirculates a part of the exhaust gas as EGR (exhaust gas recirculation) gas.

The ATC 6 is a small oxidation catalyst provided on the upstream side of the PM combustion catalyst 7 in the exhaust passage 3. The ATC 6 raises the temperature of the exhaust gas flowing into the PM combustion catalyst 7 by the heat of reaction when oxidizing HC or CO contained in the exhaust gas.

The PM combustion catalyst 7 is provided on the upstream side of the aftertreatment unit 8 in the exhaust passage 3. The PM combustion catalyst 7 is configured to be able to burn a part of particulate matter without mainly causing an oxidation reaction by _{NO 2.}

The PM combustion catalyst 7 has, for example, a flow-through type carrier. On the wall surface of the carrier, protrusions for making it easier for PM to come into contact with and be captured may be formed so as to intersect the flow direction of the exhaust gas in the carrier.

The PM combustion catalyst 7 is, for example, a catalyst in which a catalyst component containing a metal such as Ag or a metal oxide is supported on a carrier made of a cerium-zirconium composite oxide (for example, an Ag / CeO _2- based composite oxide catalyst). You may. Alternatively, the PM combustion catalyst 7 is a catalyst in which, for example, a catalyst component containing a copper-vanadium composite oxide, an alkali metal element, and an alkaline earth metal element is supported on a carrier made of a heat-resistant inorganic oxide ( For example, it may be a V—Cs-based composite oxide catalyst).

Here, FIG. 2 is a diagram illustrating the characteristics of the PM combustion catalyst 7. In FIG. 2, the horizontal axis represents time and the vertical axis represents temperature and combustion rate, and PM in the PM combustion catalyst 7 as the temperature of the exhaust gas flowing into the PM combustion catalyst 7 (hereinafter referred to as inlet temperature Tin) rises. The characteristic curve U of the combustion rate of the above is illustrated. The characteristic curve U as shown in FIG. 2 can be experimentally obtained by using, for example, a sample in which soot imitating PM and a catalyst component are mixed.

In the example of FIG. 2, the temperature of the PM combustion catalyst 7 is raised from the temperature of the PM combustion catalyst 7 lower than the first temperature T1 with a substantially constant temperature gradient. The inlet temperature Tin reaches the first temperature T1 at time t1. At the first temperature T1, the combustion speed of PM in the PM combustion catalyst 7 rises. That is, the first temperature T1 is a temperature at which PM combustion substantially starts in the PM combustion catalyst 7. The first temperature T1 belongs to the temperature range of 200 ° C. to 250 ° C. The first temperature T1 can be set to 200 ° C. as an example.

The inlet temperature Tin reaches the second temperature T2 at time t2. At the second temperature T2, the combustion rate of PM in the PM combustion catalyst 7 is maximum. That is, in the temperature range of the first temperature T1 to the second temperature T2, the gradient of the combustion rate is positive, so that the PM combustion rate in the PM combustion catalyst 7 can be increased by raising the temperature of the PM combustion catalyst 7. .. The second temperature T2 belongs to the temperature range of 250 ° C to 400 ° C. The second temperature T2 can be set to 300 ° C. as an example.

Here, the flow path length from the upstream end of the exhaust passage 3 (here, the position of the turbine 5 of the turbocharger 4) to the PM combustion catalyst 7 is from the flow path length from the PM combustion catalyst 7 to the post-processing unit 8. Is also short. Specifically, the PM combustion catalyst 7 is arranged together with the ATC 6 directly under the turbine 5 of the turbocharger 4 in which the temperature of the exhaust gas is relatively high in the exhaust passage 3. Immediately below the turbine 5 means a position in a range in which the cooling of the exhaust gas flowing out of the turbine 5 is substantially negligible. The position directly below the turbine 5 may be, for example, a position in the exhaust passage 3 such that the inlet temperature Tin becomes the first temperature T1 or higher during the operation of the engine 1. The position directly below the turbine 5 may be, for example, a position within 30 cm from the position of the turbine 5 along the flow path of the exhaust gas.

The post-treatment unit 8 includes, for example, a catalytic converter, and is provided with a DPF (filter) [Diesel Particulate Filter] 8a and an SCR [Selective Catalytic Reduction] 9c. The DPF8a collects PM (particulate matter) contained in the exhaust gas of the engine 1. The SCR9c reduces NOx contained in the exhaust gas using, for example, urea water added on the upstream side.

A fuel addition valve and a DOC [Diesel Oxidation Catalyst] may be provided on the upstream side of the DPF 8a in the aftertreatment unit 8. In this case, PTF for _{oxidizing NO to NO 2} may be supported on DPF8a. The PM collected by DPF8a is continuously oxidized by using the heat generated in DOC by the oxidation of the fuel added by the fuel addition valve and NO _2. Alternatively, a burner for burning the PM collected by the DPF 8a may be provided on the upstream side of the DPF 8a in the post-treatment unit 8 instead of the fuel addition valve and the DOC.

Further, the exhaust gas purification device 100 includes a temperature sensor 14, each injector 2, and an ECU [Electronic Control Unit] 10 connected to the temperature sensor 14.

The ECU 10 is an electronic control unit having a CPU [Central Processing Unit], a ROM [Read Only Memory], a RAM [Random Access Memory], a CAN [Controller Area Network] communication circuit, and the like. In the ECU 10, various functions are realized by loading the program stored in the ROM into the RAM and executing the program loaded in the RAM in the CPU. The ECU 10 may be composed of a plurality of electronic control units.

The temperature sensor 14 is a detector that detects the inlet temperature Tin of the exhaust gas flowing into the PM combustion catalyst 7. More specifically, the temperature sensor 14 is provided between the ATC 6 and the PM combustion catalyst 7 in the exhaust passage 3 and detects the inlet temperature Tin of the exhaust gas between the ATC 6 and the PM combustion catalyst 7. The temperature sensor 14 transmits a detection signal of the detected temperature to the ECU 10.

Next, the functional configuration of the ECU 10 will be described. The ECU 10 includes a temperature acquisition unit 11, a temperature determination unit 12, and a temperature rise control unit 13.

The temperature acquisition unit 11 acquires the inlet temperature Tin of the exhaust gas, for example, based on the detection signal from the temperature sensor 14. The temperature acquisition unit 11 may acquire the exhaust gas inlet temperature Tin by estimation based on the operating state of the engine 1 without using the temperature sensor 14. In this case, the temperature sensor 14 may be omitted.

The temperature determination unit 12 determines whether or not the inlet temperature Tin of the exhaust gas is less than a predetermined temperature threshold value. The temperature threshold value is a threshold value of the inlet temperature Tin of the exhaust gas for determining whether or not to perform temperature rise control for raising the temperature of the exhaust gas flowing into the PM combustion catalyst 7. The temperature threshold can be, for example, the above-mentioned second temperature T2. Alternatively, the temperature threshold value may be a temperature equal to or higher than the above-mentioned first temperature T1 and lower than the second temperature T2.

The temperature determination unit 12 may determine whether or not the inlet temperature Tin of the exhaust gas exceeds a predetermined temperature lower limit value. The lower temperature lower limit is a threshold value of the further exhaust gas inlet temperature Tin for determining whether or not to control the temperature rise. The lower limit of the temperature can be, for example, the above-mentioned first temperature T1. Alternatively, the lower limit of temperature may be a predetermined temperature lower than the above-mentioned first temperature T1.

The temperature rise control unit 13 executes the temperature rise control when the inlet temperature Tin is less than the above-mentioned temperature threshold value based on the detection result of the temperature sensor 14. Specifically, the temperature rise control unit 13 controls the injector 2 so as to perform post-injection when the temperature determination unit 12 determines that the inlet temperature Tin is lower than the second temperature T2. That is, the temperature rise control unit 13 raises the temperature of the exhaust gas flowing into the PM combustion catalyst 7 by using the oxidation reaction heat generated in the ATC 6 by performing the post injection. Further, the temperature rise control unit 13 controls the injector 2 so as not to perform post injection when the temperature determination unit 12 determines that the inlet temperature Tin is not less than the second temperature T2.

The temperature rise control unit 13 does not have to execute the temperature rise control when the inlet temperature Tin does not exceed the above-mentioned lower limit of the temperature based on the detection result of the temperature sensor 14. Specifically, the temperature rise control unit 13 may control the injector 2 so as not to perform post injection when the temperature determination unit 12 determines that the inlet temperature Tin does not exceed the first temperature T1. .. When the temperature determination unit 12 determines that the inlet temperature Tin does not exceed the first temperature T1, for example, the engine 1 is in a situation such as idling stop or engine braking, and the exhaust gas of the engine 1 is heated by combustion. Corresponds to the case where it is not done. That is, in such a situation, the execution of the temperature rise control can be omitted. On the other hand, the temperature rise control unit 13 causes the injector 2 to perform post-injection when the temperature determination unit 12 determines that the inlet temperature Tin exceeds the first temperature T1 and is lower than the second temperature T2. You may control it. In this case, the PM combustion catalyst 7 is heated so that the inlet temperature Tin reaches the first temperature T1 by effectively utilizing the heat of the exhaust gas of the engine 1 and the combustion rate is more suitable by the temperature rise control. Can be done.

Next, an example of processing by the ECU 10 will be described with reference to FIG. FIG. 3 is a flowchart illustrating the processing of the ECU 10 of FIG. The processing of the flowchart of FIG. 3 is repeatedly executed at a predetermined cycle, for example, during the operation of the engine 1.

As shown in FIG. 3, the ECU 10 acquires the inlet temperature Tin by the temperature acquisition unit 11 in S01. In S02, the ECU 10 determines whether or not the inlet temperature Tin exceeds the first temperature T1 by the temperature determination unit 12. When the temperature determination unit 12 determines that the inlet temperature Tin does not exceed the first temperature T1 (S02: NO), the ECU 10 ends the process of FIG.

When the temperature determination unit 12 determines that the inlet temperature Tin exceeds the first temperature T1 (S02: YES), the ECU 10 determines that the inlet temperature Tin is less than the second temperature T2 by the temperature determination unit 12 in S03. Judge whether or not there is. When the temperature determination unit 12 determines that the inlet temperature Tin is not less than the second temperature T2 (S03: NO), the ECU 10 ends the process of FIG.

When the temperature determination unit 12 determines that the inlet temperature Tin is less than the second temperature T2 (S03: YES), the ECU 10 executes the temperature rise control by the temperature rise control unit 13 in S02. The temperature rise control unit 13 controls the injector 2 so as to perform post injection, for example. After that, the ECU 10 ends the process of FIG.

[Action and effect]
As described above, according to the exhaust gas purification device 100 according to the present embodiment, the PM combustion catalyst 7 is provided on the upstream side of the DPF 8a in the exhaust passage 3. Since the PM combustion catalyst 7 can burn a part of PM, it is possible to reduce the inflow amount of PM into DPF8a. Further, since the PM combustion catalyst 7 can burn a part of PM without the main cause of the oxidation reaction by _{NO 2} , Pt or the like for generating _{NO 2 is supported on the upstream side of the PM combustion catalyst 7.} It is not necessary to add a catalyst. Further, since the flow path length from the upstream end of the exhaust passage 3 to the PM combustion catalyst 7 is shorter than the flow path length from the PM combustion catalyst 7 to the DPF 8a, a part of PM is burned in the PM combustion catalyst 7 (PM). The heat of the exhaust gas is effectively used to assist the combustion of the exhaust gas. Therefore, according to the exhaust gas purification device, it is possible to reduce the inflow amount of PM into the DPF 8a while effectively utilizing the heat of the exhaust gas without adding a catalyst carrying Pt or the like. As a result, it is possible to suppress the increase in size of DPF8a and the increase in the regeneration frequency of DPF8a, reduce the burden of collecting and regenerating PM in DPF8a of the post-processing unit 8, and reduce the amount of PM emitted. ..

According to the exhaust purification device 100, the ATC 6 provided on the upstream side of the PM combustion catalyst 7 in the exhaust passage 3 and raising the temperature of the exhaust gas flowing into the PM combustion catalyst 7 and the exhaust gas flowing into the PM combustion catalyst 7 An injector that raises the inlet temperature Tin when the inlet temperature Tin is less than a predetermined temperature threshold (second temperature T2) based on the detection result of the temperature sensor 14 and the temperature sensor 14 that detects the inlet temperature Tin. Further includes a temperature rise control unit 13 for controlling 2. As a result, the exhaust gas flowing into the PM combustion catalyst 7 is heated by using the ATC 6 and the injector 2, so that a part of PM can be effectively burned in the PM combustion catalyst 7.

[Modification example]
Although the embodiments according to the present invention have been described above, the present invention is not limited to the above-described embodiments.

In the above embodiment, the ATC 6 and the injector 2 are exemplified as the temperature raising unit, but the temperature rising unit is not limited to this. For example, as shown in the exhaust gas purification device 100A of FIG. 4, a heater 15 can be used as the temperature raising unit instead of the ATC 6 and the injector 2. The heater 15 is, for example, an electric heater for heating the PM combustion catalyst 7. In this case, when the temperature determination unit 12 determines that the inlet temperature Tin exceeds the first temperature T1 and is less than the second temperature T2, the temperature rise control unit 13 energizes the heater 15 as temperature rise control. You may.

In addition, even if FIG. 1 and FIG. 4 are combined, the temperature rise control by the temperature rise control unit 13 using the ATC 6 and the injector 2 and the temperature rise control by the temperature rise control unit 13 using the heater are used in combination. Good.

In the above embodiment, the temperature rise control is executed based on the temperature determination result using the temperature lower limit value and the temperature threshold value, but the temperature rise control unit 13 raises the inlet temperature Tin by various other methods. May be good. For example, the temperature rise control unit 13 may omit the determination of the temperature using the lower limit of the temperature.

The temperature rise control unit 13 that controls the temperature rise unit based on the detection result of the temperature sensor 14 may be omitted. In this case, for example, the temperature sensor 14 may be omitted, and a heater that is constantly energized may be provided as a temperature raising unit. Alternatively, both the temperature sensor 14 and the temperature raising unit may be omitted.

In the above embodiment, the diesel engine 1 is exemplified as the internal combustion engine, but other internal combustion engines such as a gasoline engine may be used. Further, in the above embodiment, the upstream end of the exhaust passage 3 corresponds to the position of the turbine 5 of the turbocharger 4, but when the turbocharger is provided in a plurality of stages, the turbine in the last stage It may correspond to the position of the exhaust manifold or the exhaust port when the turbocharger is not provided.

2 ... Injector (heating unit), 3 ... Exhaust passage, 6 ... ATC (heating unit), 7 ... PM combustion catalyst (combustion catalyst), 8a ... DPF (filter), 13 ... Temperature control unit, 14 ... Temperature Sensor, 15 ... heater (heating part), 100, 100A ... exhaust purification device.

Claims (2)

A filter provided in the exhaust passage of the internal combustion engine and collecting particulate matter contained in the exhaust gas of the internal combustion engine.
A combustion catalyst provided on the upstream side of the filter in the exhaust passage and capable of burning a part of the particulate matter without being mainly caused by an oxidation reaction by _{NO 2 is provided.}
An exhaust purification device in which the flow path length from the upstream end of the exhaust passage to the combustion catalyst is shorter than the flow path length from the combustion catalyst to the filter. A temperature raising unit provided on the upstream side of the combustion catalyst in the exhaust passage and raising the temperature of the exhaust gas flowing into the combustion catalyst.
A temperature sensor that detects the temperature of the exhaust gas flowing into the combustion catalyst, and
The first aspect of the present invention further includes a temperature rise control unit that controls the temperature rise unit so as to raise the temperature when the temperature is less than a predetermined temperature threshold value based on the detection result of the temperature sensor. The exhaust purification device described.

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