JP2006070771A - Exhaust emission control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control system by which NOx is reduced by controlling the ratio of NO to NOx in the state of a particulate filter being provided. <P>SOLUTION: The exhaust emission control system comprises a selective reduction catalyst 16, an aqueous urea-adding means 22, the particulate filter 28, a plasma generator 25, and a controller 32. The selective reduction catalyst 16 is placed midway on an exhaust pipe 11 of an engine 1 for selectively reacting NOx with ammonia. The aqueous urea-adding means 22 is for adding aqueous urea 21 as a reducing agent in the exhaust gas 9 on the entry side of the selective reduction catalyst 16. The particulate filter 28 is placed upstream of the addition point of the aqueous urea-adding means 22 in order to capture soot in the exhaust gas 9. The plasma generator 25 generating NO<SB>2</SB>upstream of the particulate filter 28 by discharging electricity in the exhaust gas 9. The controller 32 controls the plasma generator 25 in every temperature-region so as to adjust the NO/NO<SB>2</SB>ratio in the exhaust gas 9, and allows the aqueous urea-adding means 22 to make addition of the aqueous urea to oxidize the soot in the particulate filter 28. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust purification device applied to an engine such as a diesel engine.

  Particulate matter (particulate matter) discharged from a diesel engine is mainly composed of soot made of carbonaceous matter and SOF content (Soluble Organic Fraction) made of high-boiling hydrocarbon components. The composition contains a small amount of sulfate (mist-like sulfuric acid component). As a measure to reduce this type of particulates, a particulate filter is installed in the middle of the exhaust pipe through which the exhaust gas flows. It has been done conventionally.

  This type of particulate filter has a porous honeycomb structure made of a ceramic such as cordierite, and the inlets of the flow paths partitioned in a lattice pattern are alternately sealed, and the inlets are not sealed. About the flow path, the exit is sealed, and only the exhaust gas which permeate | transmitted the porous thin wall which divides each flow path is discharged | emitted downstream.

  Then, the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, so that the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging. Although it is necessary to regenerate, in normal diesel engine operation conditions, there are few opportunities to obtain exhaust temperatures that are high enough to cause the particulates to self-combust. It has been studied to adopt a catalyst regeneration type particulate filter in which an oxidation catalyst is separately provided in front of the particulate filter or an oxidation catalyst is disposed separately from the particulate filter.

  That is, if such a catalyst regeneration type particulate filter is employed, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates can be burned and removed even at an exhaust temperature lower than the conventional one. It becomes possible.

  Further, as a measure for reducing NOx in exhaust gas, a selective reduction type catalyst having a property of selectively reacting NOx with a reducing agent even in the presence of oxygen is provided in the middle of an exhaust pipe through which exhaust gas circulates. A necessary amount of reducing agent is added upstream of the selective catalytic reduction catalyst, and the reducing agent is reacted with NOx (nitrogen oxide) in the exhaust gas on the selective catalytic reduction catalyst, thereby reducing the NOx emission concentration. There is something that can be done.

  For example, as this type of selective reduction catalyst, noble metal catalysts such as platinum and palladium and base metal catalysts such as vanadium, copper and iron oxides are already known as having the above-described properties. The active temperature range of the selective catalytic reduction catalyst is generally narrow, and NOx can be purified only in a part of the exhaust temperature range of the diesel engine. Improvement of low-temperature activity will be a major issue in the future.

Therefore, the present inventors have arranged an oxidation catalyst in the preceding stage of the selective catalytic reduction catalyst to oxidize NO in the exhaust gas by the oxidation catalyst to generate strong oxidizing power NO ₂ , By introducing strong NO ₂ to the selective catalytic reduction catalyst, the reduction reaction by the reducing agent on the selective catalytic reduction catalyst is promoted, so that the reduction reaction starts from a lower temperature range than in the case of normal use of the selective catalytic reduction catalyst alone. (See, for example, Patent Document 1).
JP 2002-161732 A

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

However, for the reduction reaction that reduces and purifies NOx using ammonia (NH ₃ ) as the reducing agent,
[Chemical 1]
NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O
[Chemical formula 2]
4NO + 4NH ₃ + O ₂ → 3N ₂ + 6H ₂ O
[Chemical formula 3]
2NO ₂ + 4NH ₃ + O ₂ → 3N ₂ + 6H ₂ O
[Chemical formula 4]
8NH ₃ + 6NO ₂ → 7N ₂ + 12H ₂ O
Since the reaction rate decreases in order from top to bottom, the ratio of NO to NO ₂ in the exhaust gas is close to about 1: 1 so that the reaction can be performed by the reduction reaction with the fastest reaction rate [Chemical Formula 1]. Therefore, it is required to reduce NOx well even at low temperatures.

On the other hand, even if the ratio of NO to NO ₂ in the exhaust gas is controlled to be close to about 1: 1, when the exhaust gas is treated with the particulate filter, the particulate matter accumulated in the particulate filter is reduced. balance ratio of nO ₂ and react nO and nO ₂ is lost, there is a problem that it is impossible to properly perform the reduction of NOx with.

The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an exhaust purification device that reduces NOx by controlling the ratio of NO and NO ₂ with a particulate filter. Yes.

The present invention relates to a selective reduction catalyst that is provided in the middle of an exhaust pipe of an engine and can selectively react NOx with ammonia even in the presence of oxygen, and urea as a reducing agent in the exhaust gas on the inlet side of the selective reduction catalyst. Urea water adding means for adding water, a particulate filter installed upstream from the addition of the urea water adding means for capturing soot in the exhaust gas, and discharging into the exhaust gas upstream from the particulate filter. A plasma generator for generating NO ₂ , and the plasma generator is controlled for each temperature region so as to adjust the ratio of NO and NO ₂ in the exhaust gas, so that urea water is added to the urea water adding means. The present invention also relates to an exhaust emission control device comprising a control device capable of oxidizing soot in a particulate filter.

In the present invention, the control of the plasma generator is preferably configured to oxidize soot in the particulate filter and maintain the balance of the ratio of NO and NO ₂ .

  The present invention further includes a rotation sensor that detects the engine speed, a temperature sensor that detects the exhaust temperature, and a NOx sensor that detects the NOx concentration, and the detected values from the rotation sensor, the temperature sensor, and the NOx sensor. It is preferable that the plasma generator is controlled based on the above.

  Furthermore, in the present invention, it is preferable to provide an oxidation catalyst upstream of the plasma generator.

Thus, in this case, NO in the exhaust gas is oxidized to NO ₂ by the plasma generator and the ratio of NO and NO ₂ is controlled, so that urea water is added by the urea water adding means. However, NOx can be reduced. At the same time, even if a particulate filter is provided, the ratio of NO to NO ₂ in the exhaust gas is adjusted to oxidize the particulate filter soot by NO _2. It is possible to suppress and reduce NOx. Furthermore, since the plasma generator is controlled for each temperature region, NOx reduction and soot oxidation treatment can be performed in consideration of the influence of temperature in each temperature region.

Further, the control of the plasma generator oxidizes soot in the particulate filter and maintains the balance of the ratio of NO and NO ₂ to further suppress the effect of soot on the particulate filter, Can be suitably reduced.

Furthermore, a rotation sensor that detects the engine speed, a temperature sensor that detects the exhaust temperature, and a NOx sensor that detects the NOx concentration are provided, and plasma is generated based on detection values from the rotation sensor, the temperature sensor, and the NOx sensor. If the apparatus is configured to control, it can be processed appropriately in consideration of the ratio of NO to NO ₂ and the influence of temperature, so the plasma generator and / or urea water addition means can be easily controlled to reduce NOx. Can be more suitably performed.

Furthermore, if an oxidation catalyst is installed upstream of the plasma generator, NO ₂ is generated by the oxidation catalyst and flows down to the selective catalytic reduction catalyst, so the ratio of NO and NO ₂ can be easily controlled to reduce NOx. It can carry out more suitably.

According to the exhaust gas purification apparatus of the present invention described above, since the ratio of NO and NO ₂ is controlled by the plasma generator, NOx can be reduced even if urea water is added by the urea water adding means. At the same time, the particulate filter soot is oxidized by NO _2, so that the influence of the particulate filter soot can be suppressed. Furthermore, since the plasma generator is controlled for each temperature region, it is possible to achieve an excellent effect that NOx reduction and soot oxidation treatment can be performed in consideration of the temperature influence in each temperature region.

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

  1 to 4 show an example of an embodiment of the present invention. Reference numeral 1 in FIG. 1 denotes a diesel engine which is a diesel engine. In the engine 1 shown here, a turbocharger 2 is provided. The intake air 4 guided from the air cleaner 3 is sent to the compressor 2a of the turbocharger 2 through the intake pipe 5, and the intake air 4 pressurized by the compressor 2a is further sent to the intercooler 6 for cooling. Then, the intake air 4 is further guided from the intercooler 6 to the intake manifold 7 and is distributed to each cylinder 8 of the diesel engine 1 (the case of in-line 6 cylinders is illustrated in FIG. 1). .

  Further, the exhaust gas 9 discharged from each cylinder 8 of the diesel engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 10, and the exhaust gas 9 that has driven the turbine 2b passes through the exhaust pipe 11. It is designed to be discharged outside the vehicle.

  Further, an exhaust gas extracted from the exhaust manifold 10 is connected between the one end portion of the exhaust manifold 10 in the arrangement direction of the cylinders 8 and one end portion of the intake pipe 5 connected to the intake manifold 7 by the EGR pipe 12. 9 is recirculated to the intake pipe 5 through the water-cooled EGR cooler 13 and the EGR valve 14, and the exhaust gas 9 recirculated from the exhaust side to the intake side in each cylinder 8. The generation of NOx can be reduced by suppressing the combustion of the fuel and lowering the combustion temperature.

Further, a selective reduction catalyst 16 held by a casing 15 is provided in the middle of the exhaust pipe 11, and this selective reduction catalyst 16 is formed as a flow-through type honeycomb structure and coexists with oxygen. However, it has the property of selectively reacting NOx with ammonia. Here, the selective reduction catalyst 16, platinum, or a noble metal catalyst such as palladium, vanadium, copper, it is possible to adopt a conventionally known catalyst such as a base metal catalyst of oxides of iron, SO ₂ It is more preferable to employ a base metal catalyst having a relatively weak oxidizing power than to employ a noble metal catalyst that easily oxidizes to sulfate (sulfate).

  An injection nozzle 17 is installed in the exhaust pipe 11 upstream of the casing 15, and a urea water supply line 19 connects between the injection nozzle 17 and a urea water tank 18 provided at a required location. The urea water 21 (reducing agent) in the urea water tank 18 can be added to the upstream side of the selective catalytic reduction catalyst 16 via the injection nozzle 17 by driving the supply pump 20 provided in the middle of the water supply line 19. The injection nozzle 17, the urea water tank 18, the urea water supply line 19, and the supply pump 20 constitute a urea water addition device 22.

A mixer 23 for uniformly diffusing the spray of the urea water 21 is provided between the casing 15 and the addition position of the urea water 21 (opening position of the injection nozzle 17) by the urea water addition device 22. Further, immediately after the selective reduction catalyst 16 in the casing 15, an NH ₃ slip catalyst 24 that oxidizes surplus ammonia as a countermeasure against leakage ammonia is provided.

On the other hand, in the exhaust pipe 11 upstream of the urea water 21 addition position (opening position of the injection nozzle 17), a plasma generator 25 that discharges into the exhaust gas 9 to generate plasma is disposed. The generator 25 has a structure in which a plurality of electrodes (not shown) connected to the power source 26 are arranged to face each other and can discharge between each other, and NO is oxidized to NO ₂ by generating plasma. ing. Here, as shown in FIG. 2, the amount of NO ₂ generated can be controlled by adjusting the amount of electric power for generating plasma.

Further, the plasma generator 25 may be switched like a pulse with an ON-OFF switch having an electrical or mechanical contact in order to facilitate control of the power source for plasma generation. The amount of electricity is adjusted by controlling the switching interval and plasma is generated. As the power source 26, a DC power source, a high frequency power source, or a pulse power source can be applied. Furthermore, in order to increase the production rate of NO ₂ , it is preferable to attach an oxidation catalyst to the electrodes and sandwich a dielectric (not shown) coated with the oxidation catalyst between the electrodes. Furthermore, it is preferable that the power source 26 of the plasma generator 25 has a computer built therein so that the instructed power can be supplied. Further, the electrodes of the plasma generator 25 may have various shapes such as a plate shape, a rod shape, and a cylindrical shape as long as the distance between them can be set almost uniformly.

  Further, the exhaust pipe 11 between the plasma generator 25 and the urea water 21 addition position (opening position of the injection nozzle 17) is provided with a particulate filter 28 held in a casing 27. The curate filter 28 has a porous honeycomb structure made of ceramic such as cordierite, and the inlets of the respective flow paths partitioned in a lattice shape are alternately sealed, and the flow paths in which the inlets are not sealed are as follows. The outlet is sealed, and only the exhaust gas that has permeated through the porous thin wall that defines each flow path is discharged downstream.

  Furthermore, the exhaust pipe 11 between the plasma generator 25 and the turbine 2b of the turbocharger 2 is equipped with a casing 29 so as to improve the low-temperature activity of the selective catalytic reduction catalyst 16 that is installed upstream of the plasma generator 25. An embraced oxidation catalyst 30 is provided. The oxidation catalyst 30 has a structure in which aluminum oxide (alumina) is mixed with platinum and supported on a stainless steel metal carrier or the like. Here, the oxidation catalyst 30 and the plasma generator 25 may be provided separately as shown in FIG. 1, but the oxidation catalyst may be attached to the plasma generator 25 to form a plasma generator with an oxidation catalyst. Furthermore, a particulate filter 28 may be additionally provided to be combined into an oxidation catalyst and a plasma generator with a particulate filter (plasma DPF with an oxidation catalyst).

  Here, the operation of the plasma generator 25, the operation of the urea water addition device 22, the operation of the EGR valve 14 for recirculating the exhaust gas 9, and the operation of the fuel injection device 31 for injecting fuel into each cylinder 8 are performed by the engine. It is configured to receive command signals 26a, 22a, 14a, 31a from a control device 32 constituting a control computer (ECU: Electronic Control Unit).

  On the other hand, in the control device 32, a rotation speed signal 33a from the rotation sensor 33 in the engine 1, a load signal 34a from an accelerator sensor 34 (load sensor) for detecting the accelerator opening as a load of the engine 1, Detection signals 35a, 36a from NOx sensors 35, 36 for detecting the NOx concentration in the exhaust gas 9 between the casing 27 and the addition position of the urea water 21 and at an appropriate position downstream of the casing 15; Detection signals 37a, 38a from the temperature sensors 37, 38 for detecting the exhaust temperature on the exhaust side and the exhaust side, detection signals 39a from the temperature sensor 39 for detecting the intake air temperature on the inlet side of the intake manifold 7, The detection signal 40a from the supercharging pressure sensor 40 that detects the supercharging pressure on the inlet side, and the suction between the air cleaner 3 and the compressor 2a. A detection signal 41a from the air flow meter 41 for measuring the amount of air are inputted. Here, the control device 32 may further receive a detection signal from an outside air temperature sensor (not shown) arranged outside.

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

  When purifying NOx in the exhaust gas 9, first, the current rotational speed of the engine 1 is read based on the rotational speed signal 33 a from the rotational sensor 33, and the detection signal 35 a from the NOx sensors 35 and 36. 36a, the NOx concentration is read out, and the exhaust gas temperature is read out based on the detection signals 37a, 38a from the temperature sensors 37, 38, and the engine speed, NOx concentration, as shown in FIG. Plasma power for generating plasma in the plasma generator 25 is determined by a 3D map (three-dimensional map) composed of the exhaust temperature.

  Here, the control method of the control device differs depending on the temperature region for the determined plasma power. An example of a specific control method in the temperature region is as follows. The temperature region is a temperature region from the lower limit temperature to 130 ° C. In FIG. 4, the temperature range of I), the temperature range from 130 ° C. to 180 ° C. (the temperature range of II in FIG. 4), the temperature range of 180 ° C. to 270 ° C. (the temperature range of III in FIG. 4), from 270 ° C. Temperature range up to 450 ° C. (temperature range IV in FIG. 4), temperature range from 450 ° C. to 600 ° C. (temperature range V in FIG. 4), temperature range from 600 ° C. to upper limit temperature (in FIG. Temperature range).

The temperature range from the lower limit temperature to 130 ° C. (the temperature range I in FIG. 4) is a region that does not contribute to NOx reduction even when plasma is generated by the plasma generator 25, and power is not supplied. The temperature region from 130 ° C. to 180 ° C. (the temperature region II in FIG. 4) is a region that does not contribute to NOx reduction even when plasma is generated by the plasma generator 25 as in the previous temperature region. Then, electric power is supplied to maintain the temperature of the exhaust gas at a predetermined temperature so that the selective catalytic reduction catalyst 16 is brought into the active temperature region by the heat of plasma generation. Furthermore, in the temperature range from 180 ° C. to 270 ° C. (the temperature range of III in FIG. 4), it is not necessary to oxidize soot, but urea water 21 is added by the urea water addition device 22 to improve NOx reduction. This is a necessary region, and power for generating NO ₂ is supplied by the plasma generator 25 in order to reduce NOx. Further, in the temperature range from 270 ° C. to 450 ° C. (the temperature range IV in FIG. 4), the activity of the selective catalytic reduction catalyst 16 is high, and the production of NO ₂ is less than the selective catalytic reduction catalyst 16. good, a region that needs to oxidize soot, supplies power for generating NO ₂ by the plasma generating device 25 in order to oxidize the soot by NO _2. Note that the temperature range from 270 ° C. to 450 ° C. requires less power than the temperature range from 180 ° C. to 270 ° C. shown in FIG. In addition, in the temperature range from 450 ° C. to 600 ° C. (the temperature range of V in the figure), the activity of the selective catalytic reduction catalyst 16 is further higher, and NO ₂ generation is not required for the selective catalytic reduction catalyst 16. an area that needs to be reliably oxidized soot, supplies power for generating NO ₂ by the plasma generating device 25 in order to promote the oxidation of soot by NO _2. Further, the temperature range from 600 ° C. to the upper limit temperature (VI temperature range in the figure) is a region where soot naturally oxidizes, and NO ₂ is unnecessary, so power is not supplied.

In these temperature regions, NO ₂ is appropriately generated by the plasma generator 25, and a specific example will be described in the case of a temperature region from 180 ° C. to 270 ° C. (temperature region III in the figure). When NO ₂ is generated at 25, the current rotational speed of the engine 1 is read based on the rotational speed signal 33 a from the rotational sensor 33, and the current fuel injection is performed based on the load signal 34 a from the accelerator sensor 34. The amount is converted, and based on the detection signals 35a and 36a from the NOx sensors 35 and 36 and the detection signals 37a and 38a from the temperature sensors 37 and 38, the temperature, flow rate, NO concentration, N ₂ concentration, O ₂ concentration, etc. presume. Here, the rotation sensor 33, the accelerator sensor 34, the NOx sensors 35 and 36, the temperature sensors 37 and 38, etc. update and detect data at any time, so that the temperature, flow velocity, NO. Even if there is a change in the concentration, N ₂ concentration, O ₂ concentration, etc., it can be dealt with. Further, when the exhaust gas 9 is recirculated by the EGR valve 14, the amount of NO ₂ also changes at the outlet of the engine 1, but similarly, the data can be updated and detected.

After estimating the temperature, flow velocity, NO concentration, N ₂ concentration, O ₂ concentration, etc., the control device 32 causes the rotation of the engine 1 via the detection signals (detected values) 35a, 36a of the NOx sensors 35, 36. It is determined how much NO ₂ is generated and the ratio of NO to NO ₂ in the exhaust gas 9 is about 1: 1 through a map in which the number and the accelerator opening (fuel injection amount) are input. The power of the generator 25 is adjusted to generate plasma, and a predetermined amount of NO is oxidized to NO ₂ .

Here, the generation of NO ₂ by the plasma generator 25 is as follows.
[Equation 1]
NO ₂ generation = f (plasma energy, temperature, flow rate, NO concentration, N ₂ concentration, O ₂ concentration)
Since the temperature, flow velocity, NO concentration, N ₂ concentration, and O ₂ concentration vary depending on the operating state of the engine 1, the plasma energy is adjusted as appropriate.
The energy of plasma is
[Equation 2]
Plasma energy = f (power, distance between electrode plates, dielectric constant (body))
The distance between electrode plates and the dielectric constant (body) are invariable numbers depending on the setting of the apparatus.
In addition, the power is
[Equation 3]
Power = f (applied voltage, frequency (current amount))
It is. That is, the plasma energy can be controlled by changing the voltage and frequency. Here, the power source may use a high frequency pulse.

For this reason, the amount of NO ₂ generated is determined by adjusting the power, that is, the voltage and frequency (current amount) according to the temperature, flow rate, NO concentration, N ₂ concentration, and O ₂ concentration.

The ratio of NO and NO ₂ in the exhaust gas 9 by oxidizing NO to NO ₂ by the plasma generator 25 to about 1: After 1, the detection signal 35a from the NOx sensor 35, etc., based on 36a While calculating the addition amount of the urea water 21, it is confirmed by the detection signals 37a, 38a from the temperature sensors 37, 38, etc. that the exhaust temperature is in the active temperature region of the selective catalytic reduction catalyst 16, and the command from the control device 32 The urea water 21 is injected from the injection nozzle 17 of the urea water adding device 22 by the signal 22a, and NOx is reduced.

Thus, if the exhaust gas purification device is configured in this way, the plasma generator 25 oxidizes NO in the exhaust gas to NO ₂ to control the ratio of NO and NO ₂ , so the urea water addition device 22 controls the urea. Even when water is added, NOx can be reduced. At the same time, even if the particulate filter 28 is provided, the ratio of NO and NO ₂ in the exhaust gas is adjusted by dividing the temperature region and the soot of the particulate filter 28 is oxidized by NO _2. The influence of soot on the curate filter 28 can be suppressed, and NOx can be reduced. Further, since the plasma generator 25 is controlled for each temperature region, NOx reduction and soot oxidation treatment can be performed and power consumption can be reduced in consideration of the influence of temperature in each temperature region.

Further, the control of the plasma generator 25 oxidizes the soot in the particulate filter 28 and further suppresses the influence of the soot on the particulate filter 28 when configured to maintain the balance of the ratio of NO and NO _2. In addition, NOx can be suitably reduced.

Furthermore, a rotation sensor 33 for detecting the rotational speed of the engine 1, temperature sensors 37 and 38 for detecting the temperature of the exhaust gas, and NOx sensors 35 and 36 for detecting the NOx concentration are provided. 37 and 38 as well as when configured to control the plasma generator 25 on the basis of the detection value from the NOx sensor 35, because it can properly handle in consideration of the influence of the ratio and the temperature of the NO and NO _2, the plasma generating The device 25 and / or the urea water addition device 22 can be easily controlled to reduce NOx more suitably.

Furthermore, if the oxidation catalyst 30 provided upstream of the plasma generator 25 is provided, NO ₂ is generated by the oxidation catalyst 30 and flows down to the selective reduction catalyst 16, so that the ratio of NO and NO ₂ can be easily controlled. In addition, NOx can be reduced more suitably.

The exhaust emission control device of the present invention is not limited to the above-described embodiment. If the soot is oxidized by plasma and the ratio of NO and NO ₂ is controlled, a control method, a plasma generation method, and The processing procedure of NOx is not particularly limited, the control of the plasma generator and the urea water addition device may be controlled by a command signal from another sensor, and the scope not departing from the gist of the present invention Of course, various changes can be made.

It is the schematic which shows the embodiment which implements this invention. It is a graph showing the relationship between power and NO ₂ generation amount. It is a conceptual diagram which shows the 3D map which calculates | requires plasma electric power. It is a graph which shows the change of the control method by a temperature area.

Explanation of symbols

1 Diesel engine (engine)
9 Exhaust gas 11 Exhaust pipe 16 Selective reduction catalyst 21 Urea water (reducing agent)
22 Urea water addition device (urea water addition means)
25 Plasma generator 28 Particulate filter 30 Oxidation catalyst 32 Controller 33 Rotation sensor 33a Rotation speed signal (detection value)
34 Accelerator sensor (load sensor)
34a Load signal (detected value)
35 NOx sensor 35a Detection signal (detection value)
36 NOx sensor 36a Detection signal (detection value)
37 Temperature sensor 37a Detection signal (detection value)
38 Temperature sensor 38a Detection signal (detection value)
39 Temperature sensor 39a Detection signal (detection value)

Claims (4)

A selective reduction catalyst that is installed in the exhaust pipe of the engine and can selectively react NOx with ammonia even in the presence of oxygen, and urea water as a reducing agent is added to the exhaust gas on the inlet side of the selective reduction catalyst Urea water addition means, a particulate filter installed upstream from the addition of the urea water addition means to capture soot in the exhaust gas, and discharge into the exhaust gas upstream from the particulate filter to generate NO ₂ And a particulate filter that controls the plasma generator for each temperature region so as to adjust the ratio of NO and NO ₂ in the exhaust gas, and adds urea water to the urea water addition means. An exhaust emission control device comprising a control device capable of oxidizing the soot inside. _2. The exhaust emission control device according to claim 1, wherein the control of the plasma generator is configured to oxidize soot in the particulate filter and maintain a balance of the ratio of NO and NO2.   A rotation sensor that detects the number of revolutions of the engine, a temperature sensor that detects the exhaust temperature, and a NOx sensor that detects the NOx concentration, and a plasma generator based on detection values from the rotation sensor, the temperature sensor, and the NOx sensor The exhaust emission control device according to claim 1, wherein the exhaust gas purification device is configured to be controlled.   The exhaust emission control device according to any one of claims 1 to 3, further comprising an oxidation catalyst upstream of the plasma generator.

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