JP2021088964A - Exhaust purification system and exhaust purification method - Google Patents

Abstract

To provide an exhaust purification system and an exhaust purification method capable of effectively reducing emissions of nitrogen monoxide (N2O) in exhaust into the atmosphere.SOLUTION: An exhaust purification system comprises: an exhaust passage 34 which distributes exhaust discharged from an engine 10; and an N2O decomposition processing section 80 which is installed in the exhaust passage 34 and includes an emission unit emitting ultraviolet light having a predetermined wavelength capable of decomposing at least nitrogen monoxide (N2O) toward the exhaust flowing in the exhaust passage 34. The N2O decomposition processing section 80 also has a mirror member which extends an optical path length by refracting the ultraviolet light emitted from the emission unit. The N2O decomposition processing section 80 is arranged at a downstream side of an aqueous vapor elimination processing section 71 capable of eliminating aqueous vapor from the exhaust flowing in the exhaust passage 34. The N2O decomposition processing section 80 is arranged at the downstream side of an ammonia slip catalyst 68 which eliminates ammonia slipped through a selective reducing catalyst performing reduction purification of nitrogen compounds in the exhaust with ammonia as a reducing agent.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an exhaust gas purification system and an exhaust gas purification method, and more particularly to a technique suitable for purifying N2O (nitrous oxide) contained in exhaust gas.

As an example of this type of exhaust purification system, a selective reduction type that reduces and purifies NOx (nitrogen oxides) in the exhaust by using ammonia produced by hydrolysis of urea water by exhaust heat in order from the upstream side of the exhaust as a reducing agent. A configuration in which a catalyst (Selective Catalytic Reduction: hereinafter, SCR catalyst) and an ammonia slip catalyst that decomposes ammonia slipped from the SCR catalyst are arranged has been widely put into practical use (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2011-122552

The target of decomposition of the ammonia slip catalyst is ammonia, and depending on the operating conditions, N2O in the exhaust may be discharged to the atmosphere. For example, N2O is likely to be generated in an exhaust gas atmosphere in a state of low NO concentration or high NO concentration in the process of decomposing ammonia, and reduction of N2O having a high global warming potential is an issue. As a method for decomposing N2O, it is conceivable to use pulse corona discharge or the like, but there is a problem that new NOx is generated by the reaction between N radicals and oxygen in the exhaust gas.

The technique of the present disclosure has been made in view of the above circumstances, and an object of the present invention is to provide an exhaust gas purification system and an exhaust gas purification method capable of effectively reducing the emission of N2O to the atmosphere.

The apparatus of the present disclosure is provided in an exhaust passage through which exhaust gas discharged from the engine is circulated, and an ultraviolet ray having a predetermined wavelength capable of decomposing at least sulfite nitrogen toward the exhaust gas flowing through the exhaust passage. It is characterized by comprising an irradiation device for irradiating light.

Moreover, it is preferable that the predetermined wavelength is 172 nm.

Further, a steam removal processing unit provided on the upstream side of the exhaust gas of the exhaust passage and capable of removing water vapor from the exhaust flowing through the exhaust passage is further provided, and the irradiation device is the water vapor removal processing unit. It is preferable to irradiate the ultraviolet light toward the dry exhaust from which water vapor has been removed.

Further, the exhaust passage is provided obliquely with respect to the axial direction of the exhaust passage, and the optical path length of the ultraviolet light in the exhaust passage is obtained by refracting the ultraviolet light emitted from the irradiation device. It is preferable that at least one or more mirror members are further provided.

Further, a selective reduction catalyst provided in the exhaust passage and using ammonia generated by hydrolysis of urea water by exhaust heat as a reducing agent to reduce and purify the nitrogen compound in the exhaust, and the selection of the exhaust passage. The irradiation device is further provided with an ammonia slip catalyst which is provided on the downstream side of the exhaust from the reduction catalyst and removes the ammonia slipped from the selective reduction catalyst, and the irradiation device is more than the ammonia slip catalyst in the exhaust passage. It is preferably arranged on the downstream side.

Further, an upstream index value acquisition means for acquiring a concentration index value of nitrous oxide in the exhaust flowing upstream of the irradiation device of the exhaust passage and an exhaust flowing downstream of the irradiation device of the exhaust passage. The irradiation device further includes a downstream index value acquisition means for acquiring the nitrous oxide concentration index value of the above, and the irradiation device has a nitrous oxide concentration index value acquired by the upstream index value acquisition means exceeding a predetermined threshold value. It is preferable to irradiate the ultraviolet light and stop the irradiation of the nitrous oxide when the concentration index value of nitrous oxide acquired by the downstream index value acquisition means drops below the threshold value.

The method of the present disclosure is characterized by irradiating the exhaust gas flowing through the exhaust passage of the engine with ultraviolet light having at least a predetermined wavelength capable of decomposing nitrous oxide.

According to the technique of the present disclosure, the emission of N2O to the atmosphere can be effectively reduced.

It is a schematic overall block diagram which shows the intake / exhaust system of the engine which concerns on this embodiment. It is a schematic block diagram which shows an example of the steam removal processing part which concerns on this embodiment. It is a schematic block diagram which shows an example of the N2O decomposition processing part which concerns on this embodiment. It is a schematic functional block diagram which shows the control device which concerns on this embodiment, and the related peripheral configuration. It is a flowchart explaining the process flow of steam removal control and N2O decomposition control which concerns on this Embodiment. It is a schematic block diagram which shows an example of the N2O decomposition processing part which concerns on another embodiment.

Hereinafter, the exhaust gas purification system and the exhaust gas purification method according to the present embodiment will be described with reference to the attached drawings. The same parts have the same reference numerals, and their names and functions are also the same. Therefore, detailed explanations about them will not be repeated.

[overall structure]
FIG. 1 is a schematic overall configuration diagram showing an intake / exhaust system of the engine 10 according to the present embodiment.

The engine 10 mainly has a cylinder head CH and an engine main body portion each of which is composed of a cylinder block, a crankcase, or the like (not shown). A plurality of cylinders C are provided in the cylinder block, and a piston (not shown) is housed in each cylinder C so as to be reciprocating.

The engine 10 is not limited to the 4-cylinder engine shown in the illustrated example, and may be a single-cylinder engine or a multi-cylinder engine other than the 4-cylinder engine. Further, the engine 10 is not limited to the in-line multi-cylinder engine shown in the illustrated example, and may be a V-type engine, a horizontally opposed engine, or the like.

An intake manifold 20 that distributes intake air to an intake port (not shown) is provided on the side portion of the cylinder head CH on the intake side. The air cleaner 21, the upstream intake passage 22, the compressor 42 of the supercharger 40, the downstream intake passage 23, and the like are connected to the intake manifold 20 in this order from the intake upstream side. The downstream intake passage 23 is provided with an intercooler 24 for cooling the intake air pumped by the compressor 42. The intercooler 24 may be either a water-cooled type or an air-cooled type.

An exhaust manifold 30 is provided on the exhaust side of the cylinder head CH to collect the exhaust gas discharged from each cylinder C via the exhaust port. In the exhaust manifold 30, in order from the exhaust upstream side, the upstream exhaust passage 31, the turbine 41 of the supercharger 40, the first connection exhaust passage 32, the front stage post-treatment device 50, the second connection exhaust passage 33, and the middle stage post-treatment device 60 , Downstream exhaust passage 34 and the like are connected. The downstream exhaust passage 34 is provided with a post-stage post-processing device 70, such as a silencer and a tail pipe (not shown). When the turbine housing of the turbocharger 40 is directly connected to the exhaust manifold 30, the upstream exhaust passage 31 may be omitted.

The supercharger 40 includes a turbine 41 driven by exhaust gas and a compressor 42 integrally rotatably connected to the turbine 41 by a turbo shaft 43. The supercharger 40 is not limited to the conventional type shown in the illustrated example, and may be a variable capacitance type having variable wings.

The pretreatment device 50 has an oxidation catalyst 52 and a filter 53 in this order from the upstream side of the exhaust gas.

The oxidation catalyst 52 is formed by supporting a catalyst component or the like on the surface of a ceramic carrier such as a cordierite honeycomb structure, and oxidizes HC and CO contained in the exhaust gas. When fuel (HC) is supplied by the post-injection by the in-cylinder injector (not shown) of the engine 10 or the exhaust pipe injection of the exhaust pipe injector (not shown), the oxidation catalyst 52 oxidizes the fuel (HC) to reduce the exhaust temperature. Raise.

The filter 53 is formed, for example, by arranging a large number of cells partitioned by a porous partition wall along the flow direction of exhaust gas, and alternately sealing the upstream side and the downstream side of these cells. .. The filter 53 collects particulate matter (PM) in the exhaust gas in the pores and surface of the partition wall, and when the amount of PM deposited reaches a predetermined amount, the filter regeneration is carried out to burn and remove the particulate matter (PM). Will be done. Note that the filter regeneration may be performed at predetermined intervals, such as when the cumulative mileage from the previous filter regeneration execution reaches a predetermined threshold distance.

The middle stage aftertreatment device 60 has a urea water injection device 61, an SCR catalyst 67, and an ammonia slip catalyst 68 in this order from the upstream side of the exhaust gas.

The urea water injection device 61 supplies the urea water tank 62 for storing the urea water, the strainer 63 which is immersed in the urea water in the urea water tank 62 to remove foreign matter, and the supply pipe 64 connected to the strainer 63. It includes a urea water pump 65 that is provided in the pipe 64 and pumps urea water from the urea water tank 62, and a urea water injector 66 that injects the urea water supplied from the supply pipe 64 into the second connection exhaust passage 33. ..

The urea water injected from the urea water injector 66 is hydrolyzed by exhaust heat and water vapor in the exhaust to produce ammonia (NH3), which is supplied to the SCR catalyst 67 on the downstream side as a reducing agent.

The SCR catalyst 67 is formed by supporting zeolite or the like on a porous ceramic carrier, for example. The SCR catalyst 67 adsorbs ammonia supplied as a reducing agent from the urea water injector 66, and selectively reduces and purifies NOx from the exhaust gas passing by the adsorbed ammonia.

The ammonia slip catalyst 68 is formed by supporting an oxidation catalyst component or the like on the surface of a ceramic carrier such as a honeycomb structure, and has a function of decomposing (oxidizing) ammonia slipped downstream from the SCR catalyst 67. ing.

The post-stage post-treatment device 70 is provided in the downstream exhaust passage 34, and includes a steam removal processing unit 71 and an N2O decomposition processing unit 80 in this order from the exhaust upstream side. Details of the steam removal processing unit 71 and the N2O decomposition processing unit 80 will be described later.

Various sensors are provided in the exhaust system of the engine 10. The exhaust temperature sensor 90 is provided immediately downstream of the oxidation catalyst 52, and acquires the temperature of the exhaust gas flowing through the oxidation catalyst 52 (oxidation catalyst outlet temperature). The differential pressure sensor 91 is provided upstream and downstream of the filter 53, and acquires the front-rear differential pressure of the filter 53. The NOx sensor 92 is provided immediately downstream of the SCR catalyst 67, and acquires the NOx value of the exhaust gas flowing through the SCR catalyst 67. The humidity sensor 93 is provided immediately downstream of the ammonia slip catalyst 68, and acquires the humidity of the exhaust gas flowing through the ammonia slip catalyst 68. The upstream N2O sensor 94 (an example of the upstream index value acquisition means) is provided immediately upstream of the N2O decomposition processing unit 80, and acquires the N2O concentration value of the exhaust gas flowing into the N2O decomposition processing unit 80. The downstream N2O sensor 95 (an example of the downstream index value acquisition means) is provided immediately downstream of the N2O decomposition processing unit 80, and acquires the N2O concentration value of the exhaust gas flowing through the N2O decomposition processing unit 80. The sensor values of each of these sensors 90 to 95 are transmitted to the electrically connected control device 100.

[Water vapor removal processing unit]
FIG. 2 is a schematic configuration diagram showing an example of the steam removal processing unit 71 according to the present embodiment.

As shown in FIG. 2, the water vapor removal processing unit 71 has a lead-out passage 72 that draws out exhaust gas containing water vapor from the downstream exhaust passage 34, a cooler 73 provided in the lead-out passage 72, and a lead-out passage 72 to the inlet port 74A. It is provided with an air compressor 74 to which the downstream end of the air compressor 74 is connected, a return passage 75 connecting the outlet port 74B of the air compressor 74 and the downstream exhaust passage 34, and a tank 76 provided in the return passage 75.

The cooler 73 cools the high-temperature exhaust taken into the outlet passage 72 from the downstream exhaust passage 34. The cooler 73 may be either an air-cooled type or a water-cooled type. When the cooler 73 is an air-cooled type, the high-temperature exhaust gas may be cooled by exchanging heat with running air or cooling air pumped by a fan or the like. In the case of the air-cooled type, it is preferable to provide a plurality of heat exchange fins on the outer periphery of the cooler 73 main body. When the cooler 73 is a water-cooled type, the high-temperature exhaust may be cooled by exchanging heat with engine cooling water (or engine oil, mission oil, or the like). If the cooler 73 is a water-cooled type using engine cooling water, warming up of the engine 10 (see FIG. 1) can be promoted. The arrangement position of the cooler 73 is not limited to the illustrated example, and may be provided in the return passage 75 as long as it is on the upstream side of the tank 76.

The air compressor 74 is an electric or mechanical compressor, and pumps the exhaust gas taken in from the downstream exhaust passage 34 through the lead-out passage 72 to the return passage 75. When the air compressor 74 is an electric type, a motor driven by electric power supplied from a battery (not shown) may be used as a drive source. When the air compressor 74 is a mechanical type, the power taken from the engine 10 (see FIG. 1) or the like may be used as the drive source. In the case of the mechanical type, it is preferable to provide a clutch capable of connecting and disconnecting the power transmission between the air compressor 74 and the drive source.

The tank 76 is provided in the return passage 75, and stores the water cooled by the cooler 73 and separated from the exhaust gas. That is, the water separated from the exhaust gas is stored in the tank 76, and the dry exhaust gas from which the water has been removed is returned to the downstream exhaust passage 34 via the return passage 75. The water vapor removal processing unit 71 is not limited to the configuration shown in the illustrated example, and other configurations can be applied as long as it functions as a separator capable of separating and removing water vapor from the exhaust gas.

[N2O decomposition processing unit]
FIG. 3 is a schematic configuration diagram showing an example of the N2O decomposition processing unit 80 according to the present embodiment.

As shown in FIG. 3, the N2O decomposition processing unit 80 has a first bent passage portion 81 that bends the flow path of the exhaust flowing from the downstream exhaust passage 34 in a substantially L shape, and an exhaust flowing from the first bent passage portion 81. A second bent passage portion 82 that bends the flow path in a substantially L shape, a linear passage portion 83 that extends substantially linearly from the downstream end of the second bent passage portion 82, and an exhaust flow that flows from the linear passage portion 83. It includes a third bending passage portion 84 that bends the path in a substantially L shape, an irradiation device 85 that can irradiate ultraviolet light, and a plurality of mirror members 86A and 86B that refract the ultraviolet light.

The irradiation device 85 is, for example, an excimer laser device capable of pulse-irradiating ultraviolet laser light, and is provided in the second bending passage portion 82. Specifically, the irradiation device 85 is attached to the outside of the bending of the second bending passage portion 82 so that the laser beam of ultraviolet light can be irradiated into the linear passage portion 83 in the substantially axial direction.

The plurality of mirror members 86A and 86B are arranged in the linear passage portion 83 at predetermined intervals, and the mirror surface is provided so as to be inclined at a predetermined angle with respect to the axial direction of the linear passage portion 83. That is, the linear passage portion 83 is made longer than necessary by refracting the ultraviolet light emitted from the irradiation device 85 at a plurality of locations on the inner peripheral surfaces of the mirror members 86A and 86B and the linear passage portion 83. It is configured so that the optical path length of ultraviolet light can be effectively secured. The number, arrangement position, and angle of the mirror members 86A and 86B are not limited to the illustrated examples, and can be appropriately set according to the diameter, shaft length, and the like of the linear passage portion 83. Further, as shown in FIG. 6, the irradiation device 85 may be attached so as to obliquely irradiate the linear passage portion 83 with ultraviolet light.

In the present embodiment, a light source capable of irradiating ultraviolet light in a predetermined wavelength band (preferably within the range of 172 nm ± 100 nm) including at least a wavelength of 172 nm is selected for the irradiation device 85. Here, the reason for selecting the wavelength of 172 nm is described. N2O absorbs ultraviolet light having a wavelength of 172 nm, and ultraviolet light having a wavelength of 172 nm has an energy of 7.2 eV. Further, since the binding energy of N2-O is 1.67 eV and the binding energy of N-NO is 4.99 eV, N2O can be decomposed by irradiating the exhaust with ultraviolet light having a wavelength of 172 nm. Furthermore, since N2 does not absorb ultraviolet light having a wavelength of 172 nm, it does not generate N radicals. That is, by irradiating ultraviolet light having a wavelength of 172 nm, N2O contained in the exhaust can be effectively treated by photodecomposition without generating new NOx in the exhaust that has passed through the SCR catalyst 67. ..

In the present embodiment, the ultraviolet light emitted from the irradiation device 85 is refracted by the inner peripheral surfaces of the mirror members 86A and 86B and the linear passage portion 83, so that the optical path length can be secured for a long time. Further, the dry exhaust gas from which water has been removed by the steam removal processing unit 71 (see FIG. 2 for details) on the upstream side flows into the linear passage portion 83.

That is, the ultraviolet light emitted from the irradiation device 85 is configured to be effectively absorbed by N2O with a long optical path length without being deprived of energy by the moisture in the exhaust. As a result, the ammonia slip catalyst 68 can efficiently decompose N2O that is likely to be generated in the process of decomposing ammonia, and it is possible to effectively reduce the emission of N2O into the atmosphere.

[Control device]
FIG. 4 is a schematic functional block diagram showing the control device 100 according to the present embodiment and related peripheral configurations.

The control device 100 is, for example, a device that performs calculations such as a computer, and is a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input port, and an output port connected to each other by a bus or the like. Etc., and execute the program.

Further, the control device 100 includes the exhaust humidity acquisition unit 110, the inlet N2O concentration value acquisition unit 120, the outlet N2O concentration value acquisition unit 130, the water vapor removal control unit 140, and the N2O decomposition control unit 150 by executing the program. Functions as a device equipped with. Each of these functional elements will be described as being included in the control device 100, which is integrated hardware in the present embodiment, but any part of these may be provided in separate hardware.

The exhaust humidity acquisition unit 110 acquires the humidity of the exhaust gas flowing through the ammonia slip catalyst 68 (hereinafter referred to as the slip catalyst outlet humidity) based on the sensor value of the humidity sensor 93. The slip catalyst outlet humidity may be estimated and acquired based on the operating state of the engine 10 and the exhaust state amount such as the exhaust temperature. The slip catalyst outlet humidity acquired by the exhaust humidity acquisition unit 110 is transmitted to the water vapor removal control unit 140.

The inlet N2O concentration value acquisition unit 120 acquires the N2O concentration value of the exhaust flowing into the N2O decomposition processing unit 80 (hereinafter, the inlet N2O concentration value) based on the sensor value of the upstream N2O sensor 94. The inlet N2O concentration value may be estimated and acquired based on the operating state of the engine 10 and the exhaust state amount such as the exhaust temperature. The inlet N2O concentration value acquired by the inlet N2O concentration value acquisition unit 120 is transmitted to the N2O decomposition control unit 150.

The outlet N2O concentration value acquisition unit 130 acquires the N2O concentration value of the exhaust flowing through the N2O decomposition processing unit 80 (hereinafter, the outlet N2O concentration value) based on the sensor value of the downstream N2O sensor 95. The outlet N2O concentration value may be estimated and acquired based on the operating state of the engine 10 and the exhaust state amount such as the exhaust temperature. The outlet N2O concentration value acquired by the outlet N2O concentration value acquisition unit 130 is transmitted to the N2O decomposition control unit 150.

The water vapor removal control unit 140 operates the air compressor 74 of the water vapor removal processing unit 71 to perform water vapor removal control for removing water vapor in the exhaust gas flowing into the N2O decomposition processing unit 80. Specifically, when the slip catalyst outlet humidity transmitted from the exhaust humidity acquisition unit 110 exceeds a predetermined threshold humidity (for example, about 10%), the water vapor removal control unit 140 has the air compressor 74 of the water vapor removal processing unit 71. The water vapor removal control is executed by transmitting an operation instruction signal to. When the water vapor removal control is executed, the dry exhaust gas from which the water vapor has been removed is sent to the N2O decomposition processing unit 80 on the downstream side.

The N2O decomposition control unit 150 performs N2O decomposition control for decomposing N2O by operating the irradiation device 85 and irradiating the exhaust with ultraviolet light. Specifically, the N2O decomposition control unit 150 is an irradiation device when the inlet N2O concentration value of the N2O decomposition processing unit 80 transmitted from the inlet N2O concentration value acquisition unit 120 exceeds a predetermined threshold concentration value (for example, 5 ppm). By transmitting an operation instruction signal to the 85, the irradiating device 85 irradiates nitrous oxide light. Further, when the outlet N2O concentration value of the outlet N2O decomposition processing unit 80 transmitted from the outlet N2O concentration value acquisition unit 130 drops to a predetermined threshold concentration value (for example, 5 ppm) or less, the N2O decomposition control unit 150 sends the irradiation device 85. By transmitting a stop instruction signal, the irradiation of nitrous oxide from the irradiation device 85 is stopped.

In this way, by controlling the irradiation / stopping of the nitrous oxide from the irradiation device 85 based on the inlet N2O concentration value and the outlet N2O concentration value of the N2O decomposition processing unit 80, the N2O contained in the exhaust is in a dry atmosphere. It will be possible to reliably reduce N2O emissions while efficiently disassembling underneath.

Next, the processing flow of the steam removal control and the N2O decomposition control according to the present embodiment will be described with reference to FIG. This routine is preferably started by starting the engine 10.

In step S100, it is determined whether or not the slip catalyst outlet humidity exceeds a predetermined threshold humidity. When the slip catalyst outlet humidity exceeds a predetermined threshold humidity (Yes), this control proceeds to the process of step S110. On the other hand, when the slip catalyst outlet humidity does not exceed a predetermined threshold humidity (No), this control repeats the determination process of step S100.

In step S110, the steam removal control is executed by operating the air compressor 74 of the steam removal processing unit 71.

Next, in step S120, it is determined whether or not the inlet N2O concentration value of the N2O decomposition processing unit 80 exceeds a predetermined threshold concentration value. When the inlet N2O concentration value exceeds a predetermined threshold concentration value (Yes), this control proceeds to the process of step S130. On the other hand, when the inlet N2O concentration value does not exceed the threshold concentration value (No), this control is returned to the determination process in step S100.

In step S130, the N2O decomposition control for decomposing N2O is executed by operating the irradiation device 85 and irradiating the exhaust with ultraviolet light.

Next, in step S140, it is determined whether or not the outlet N2O concentration value of the N2O decomposition processing unit 80 has decreased to a predetermined threshold concentration value or less. If the outlet N2O concentration value is not lowered below the predetermined threshold concentration value (No), this control is returned to the process of step S130. That is, the N2O decomposition control is continuously executed until the outlet N2O concentration value drops below the predetermined threshold concentration value. On the other hand, when the outlet N2O concentration value drops below the threshold concentration value (Yes), this control proceeds to the process of step S150.

In step S150, the operation of the irradiation device 85 (irradiation of ultraviolet light) is stopped, and then this control is returned. After that, each of the above steps S100 to 150 is repeatedly executed until the engine 10 is stopped.

According to the present embodiment described in detail above, the exhaust passage 34 (linear passage portion 83) on the downstream side of the ammonia slip catalyst 68 is absorbed by N2O toward the exhaust flowing through the exhaust passage 34, and is 7 An irradiation device 85 for irradiating ultraviolet light having a wavelength of 172 nm having an energy of .2 eV is provided. As a result, when ultraviolet light is irradiated from the irradiation device 85, N2O contained in the exhaust can be efficiently decomposed, and N2O discharged to the atmosphere can be reliably reduced.

Further, the linear passage portion 83 to which the ultraviolet light is irradiated from the irradiation device 85 is configured so that the dry exhaust from which the water vapor has been removed by the steam removal processing portion 71 on the upstream side flows into the linear passage portion 83, and the irradiation device 85 linearly flows. The ultraviolet light irradiated to the passage portion 83 is refracted by the mirror members 86A, 86B, etc., so that the optical path length can be secured for a long time. As a result, the ultraviolet light emitted from the irradiation device 85 is effectively absorbed by N2O with a long optical path length without being deprived of energy by the moisture in the exhaust, and the decomposition efficiency of N2O is ensured. It becomes possible to improve.

Further, the water vapor removal processing unit 71 operates when the slip catalyst outlet humidity exceeds a predetermined threshold humidity (for example, about 10%), and the irradiation device 85 operates when the outlet N2O concentration value of the N2O decomposition processing unit 80 exceeds a predetermined threshold value. When the concentration value (for example, 5 ppm) or less is lowered, the irradiation of ultraviolet light is stopped. As a result, wasteful power consumption can be suppressed, and deterioration of the fuel efficiency performance of the engine 10 can be effectively prevented.

[Other]
The present disclosure is not limited to the above-described embodiment, and can be appropriately modified and implemented without departing from the spirit of the present disclosure.

For example, although the post-stage post-treatment device 70 has been described as including the steam removal treatment unit 71, the steam removal treatment unit 71 may be omitted. Further, although the N2O decomposition processing unit 80 has been described as including the mirror members 86A and 86B, these mirror members 86A and 86B may be omitted.

Further, the irradiation device 85 has been described as irradiating ultraviolet light in a predetermined wavelength band including a wavelength of 172 nm, but if it is a wavelength band that is absorbed by N2O and can decompose N2O, ultraviolet light in another wavelength band is used. It may be configured to irradiate. Further, the irradiation device 85 is not limited to the excimer laser device, and other light source devices can be widely applied.

10 Engine 30 Exhaust manifold 31 Upstream exhaust passage 32 1st connection exhaust passage 33 2nd connection exhaust passage 34 Downstream exhaust passage 52 Oxidation catalyst 53 Filter 67 SCR catalyst 68 Ammonia slip catalyst 71 Steam removal processing unit 72 Derivation passage 73 Cooler 74 Air Compressor 75 Return passage 76 Tank 80 N2O decomposition processing unit 85 Irradiator 86A, 86B Mirror member 94 Upstream N2O sensor (upstream index value acquisition means)
95 Downstream N2O sensor (downstream index value acquisition means)
100 Control device 110 Exhaust humidity acquisition unit 120 Inlet N2O concentration value acquisition unit 130 Outlet N2O concentration value acquisition unit 140 Water vapor removal control unit 150 N2O decomposition control unit

Claims (7)

An exhaust passage that circulates the exhaust discharged from the engine,
An exhaust purification system provided in the exhaust passage, comprising an irradiation device that irradiates at least ultraviolet light having a predetermined wavelength capable of decomposing nitrous oxide toward the exhaust flowing through the exhaust passage. The exhaust gas purification system according to claim 1, wherein the predetermined wavelength is 172 nm. It is further provided with a water vapor removal processing unit which is provided on the exhaust upstream side of the exhaust passage with respect to the irradiation device and can remove water vapor from the exhaust flowing through the exhaust passage.
The exhaust purification system according to claim 1 or 2, wherein the irradiation device irradiates the ultraviolet light toward the dry exhaust from which water vapor has been removed by the water vapor removal processing unit. It is provided in the exhaust passage at an angle with respect to the axial direction of the exhaust passage, and by refracting the ultraviolet light emitted from the irradiation device, the optical path length of the ultraviolet light in the exhaust passage is lengthened. The exhaust purification system according to any one of claims 1 to 3, further comprising at least one mirror member. A selective reduction catalyst provided in the exhaust passage and reducing and purifying nitrogen compounds in the exhaust using ammonia generated by hydrolysis of urea water by exhaust heat as a reducing agent.
An ammonia slip catalyst provided on the downstream side of the exhaust gas of the exhaust passage with respect to the selective reduction catalyst and for removing the ammonia slipped from the selective reduction catalyst is further provided.
The exhaust purification system according to any one of claims 1 to 4, wherein the irradiation device is arranged downstream of the ammonia slip catalyst in the exhaust passage. An upstream index value acquisition means for acquiring a concentration index value of nitrous oxide in an exhaust gas flowing upstream of the irradiation device in the exhaust passage, and an upstream index value acquisition means.
Further provided with a downstream index value acquisition means for acquiring a concentration index value of nitrous oxide in the exhaust gas flowing downstream of the irradiation device of the exhaust passage.
When the concentration index value of nitrous oxide acquired by the upstream index value acquisition means exceeds a predetermined threshold value, the irradiation device irradiates the ultraviolet light and the nitrous oxide acquired by the downstream index value acquisition means. The exhaust purification system according to any one of claims 1 to 5, wherein when the concentration index value of is lowered to the threshold value or less, the irradiation of the ultraviolet light is stopped. An exhaust purification method characterized by irradiating the exhaust gas flowing through the exhaust passage of an engine with ultraviolet light having a predetermined wavelength capable of decomposing at least nitrous oxide.

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