Exhaust emission control device

Abstract

To properly oxidize soot in exhaust gas even when the performance of an oxidation catalyst is deteriorated.SOLUTION: An exhaust emission control system S comprises: an oxidation catalyst 20 provided in an exhaust passage 15 through which exhaust gas from an engine 10 flows; a first acquisition unit 122 that acquires a first concentration of carbon dioxide in the exhaust gas upstream of the oxidation catalyst 20 and a second concentration of carbon dioxide in the exhaust gas downstream of the oxidation catalyst 20; and an injection control unit 126 that injects ozone to the upstream side of the oxidation catalyst 20 in the exhaust passage 15 when the concentration difference between the first concentration and the second concentration is smaller than a first threshold value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an exhaust gas purification system that purifies exhaust gas from an internal combustion engine. [Background technology]

[0002] The exhaust purification system has an oxidation catalyst (DOC) installed in the exhaust passage through which the exhaust gas flows. The oxidation catalyst oxidizes the soot contained in the exhaust gas, thereby preventing soot from accumulating on the filter installed downstream. In addition, some exhaust purification systems have an ozone injection unit provided upstream of an oxidation catalyst that injects ozone to oxidize CO and NO (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-31928 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the oxidation performance of the oxidation catalyst may be reduced by the adhesion of sulfur, phosphorus, etc. to the surface of the oxidation catalyst. Even if the technology of Patent Document 1 is used as a countermeasure against this, the ozone injection unit will continue to inject ozone in the same manner as before the oxidation performance was reduced, so there is a risk that the oxidation of soot will be insufficient.

[0005] The present invention has been made in consideration of these points, and has an object to appropriately oxidize soot in exhaust gas even when the performance of the oxidation catalyst is deteriorated. [Means for solving the problem]

[0006] In one aspect of the present invention, an exhaust purification system is provided, comprising: an oxidation catalyst provided in an exhaust passage through which exhaust gas from an internal combustion engine flows; a first acquisition unit that acquires a first concentration of carbon dioxide in the exhaust gas upstream of the oxidation catalyst and a second concentration of carbon dioxide in the exhaust gas downstream of the oxidation catalyst; and an injection control unit that injects ozone into the exhaust passage upstream of the oxidation catalyst when a concentration difference between the first concentration and the second concentration is smaller than a first threshold value.

[0007] Furthermore, the injection control unit may be configured to inject a larger amount of ozone when the concentration difference is smaller than a second threshold value that is lower than the first threshold value, than when the concentration difference is equal to or greater than the second threshold value.

[0008] Furthermore, the injection control unit may stop the injection of the ozone when the concentration difference becomes equal to or greater than the first threshold value after the injection of the ozone.

[0009] The present invention may further include an ozone generating unit that generates the ozone, and when the concentration difference is smaller than the first threshold value, the injection control unit may cause the ozone generating unit to generate the ozone and inject the generated ozone into the exhaust passage.

[0010] In addition, the engine may further include a second acquisition unit that acquires the rotation speed of the internal combustion engine and the load acting on the internal combustion engine, and the injection control unit may identify the first threshold value corresponding to the rotation speed and the load acquired by the second acquisition unit.

[0011] The exhaust gas may further include an injection unit that injects the ozone, and a distance between the injection unit and the oxidation catalyst in the exhaust passage may be longer than a distance between the injection unit and the internal combustion engine.

[0012] The system may further include a first detection unit provided upstream of the oxidation catalyst and detecting the first concentration, and a second detection unit provided downstream of the oxidation catalyst and detecting the second concentration, wherein the first acquisition unit acquires the first concentration detected by the first detection unit and the second concentration detected by the second detection unit. Effect of the Invention

[0013] According to the present invention, there is an effect that soot in exhaust gas can be appropriately oxidized even if the performance of the oxidation catalyst is deteriorated. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic diagram showing a configuration of an exhaust gas purification system S according to one embodiment. [Diagram 2] FIG. 2 is a block diagram showing a detailed configuration of a control device 100. [Diagram 3] 4 is a flowchart illustrating an example of the operation of the control device 100. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] <Exhaust gas purification system configuration> Fig. 1 is a schematic diagram showing the configuration of an exhaust purification system S according to one embodiment. As shown in Fig. 1, the exhaust purification system S has an engine 10, an exhaust passage 15, an oxidation catalyst 20, a DPF (Diesel Particulate Filter) 25, a urea water injection unit 30, an agitation unit 35, a SCR (Selective Catalytic Reduction) catalyst 40, an ASC (Ammonia Slip Catalyst) 45, an ozone generation unit 50, an ozone injection unit 55, and a control device 100. The exhaust purification system S is mounted on a vehicle such as a truck, and purifies the exhaust gas of the engine 10.

[0016] The engine 10 is an internal combustion engine that generates power by burning and expanding a mixture of fuel and intake air (air). The engine 10 is, for example, a diesel engine. The exhaust passage 15 is an exhaust pipe connected to the engine 10. Exhaust gas from the engine 10 flows through the exhaust passage 15.

[0017] The oxidation catalyst 20 is provided in the exhaust passage 15 and oxidizes soot contained in the exhaust gas. For example, the oxidation catalyst 20 oxidizes HC to convert it into carbon dioxide (hereinafter referred to as CO2) and water. The oxidation catalyst 20 is configured, for example, such that catalytic components and the like are supported on the surface of a ceramic support.

[0018] The DPF 25 is a filter that collects particulate matter (PM) contained in exhaust gas. The DPF 25 is provided downstream of the oxidation catalyst 20. The DPF 25 is made of, for example, a honeycomb body made of metal or ceramics, and collects PM by the pores and surfaces of the partition walls.

[0019] The urea water injection unit 30 injects urea water into the exhaust passage 15. The urea water injection unit 30 is provided between the DPF 25 and the SCR catalyst 40. The urea water injected by the urea water injection unit 30 is hydrolyzed by the heat of the exhaust gas flowing through the exhaust passage 15, producing ammonia. The ammonia is used to cause a reduction reaction of NOx in the exhaust gas.

[0020] The stirring unit 35 stirs the urea water injected by the urea water injection unit 30. The provision of the stirring unit 35 makes it easier to disperse ammonia. The stirring unit 35 is provided between the urea water injection unit 30 and the SCR catalyst 40.

[0021] The SCR catalyst 40 is a reduction catalyst that promotes the reduction reaction of ammonia and NOx. Ammonia generated from the urea water is adsorbed onto the SCR catalyst 40. The SCR catalyst 40 reduces NOx to harmless nitrogen and water using the adsorbed ammonia, thereby reducing NOx emissions.

[0022] The ASC 45 is a catalyst that decomposes ammonia desorbed from the SCR catalyst 40. The ASC 45 converts ammonia into nitrogen or water, for example, thereby making it possible to suppress the emission of ammonia.

[0023] The ozone generating unit 50 generates ozone. As an example, the ozone generating unit 50 generates ozone by a silent discharge method. In the silent discharge method, an AC voltage is applied to parallel electrodes with a dielectric between them to generate ozone from oxygen. The ozone generating unit 50 supplies the generated ozone to the ozone spraying unit 55 via a supply path 52 by a pump or the like.

[0024] The ozone injector 55 injects ozone into the exhaust passage 15. The ozone injector 55 injects ozone generated by the ozone generator 50. The injected ozone oxidizes soot in the exhaust gas. In this embodiment, when the oxidation performance of the oxidation catalyst 20 is degraded, the ozone injector 55 injects ozone to oxidize soot.

[0025] The ozone injection unit 55 is located upstream of the oxidation catalyst 20 in the exhaust passage 15. For example, the distance between the ozone injection unit 55 and the oxidation catalyst 20 in the exhaust passage 15 may be longer than the distance between the ozone injection unit 55 and the engine 10. In this case, the distance that the ozone injected from the ozone injection unit 55 travels to pass through the oxidation catalyst 20 becomes longer, so that the soot is more easily oxidized by the ozone. However, this is not limited to the above, and the ozone injection unit 55 may be located closer to the oxidation catalyst 20 than the engine 10.

[0026] The concentration detection units 60 and 61 are provided in the exhaust passage 15 and are sensors that detect the concentration of CO2 in the exhaust gas. The concentration detection unit 60 is located upstream of the oxidation catalyst 20 in the exhaust passage 15, and the concentration detection unit 61 is located downstream of the oxidation catalyst 20 in the exhaust passage. Specifically, the concentration detection unit 60 is located between the ozone injection unit 55 and the oxidation catalyst 20, and the concentration detection unit 61 is located between the oxidation catalyst 20 and the DPF 25. The concentration detection unit 60 corresponds to a first detection unit that detects a first concentration of CO2, and the concentration detection unit 61 corresponds to a second detection unit that detects a second concentration of CO2.

[0027] The concentration detection unit 60 outputs a first concentration of the detected CO2 to the control device 100, and the concentration detection unit 60 outputs a second concentration of the detected CO2 to the control device 100. Since the oxidation catalyst 20 oxidizes CO, the second concentration detected by the concentration detection unit 61 located downstream of the oxidation catalyst 20 is higher than the first concentration detected by the concentration detection unit 60 located upstream of the oxidation catalyst 20.

[0028] The control device 100 controls the operation of the exhaust purification system S. For example, the control device 100 controls the detection of the CO2 concentration by the concentration detection units 60 and 61 and the injection of ozone by the ozone injection unit 55 after the engine 10 is started.

[0029] However, the oxidation performance of the oxidation catalyst 20 may be reduced when the active sites of the oxidation catalyst 20 are poisoned by sulfur, phosphorus, or the like in the exhaust gas. When the oxidation performance of the oxidation catalyst 20 is reduced, soot that has not been oxidized may accumulate in the DPF 25. In response to this, the control device 100 of this embodiment, which will be described in detail later, injects ozone into the exhaust passage 15 when the difference in concentration between the first and second concentrations of CO2 before and after the oxidation catalyst 20 is smaller than a threshold value. This allows soot to be appropriately oxidized by ozone when the oxidation performance of the oxidation catalyst 20 has deteriorated.

[0030] <Detailed configuration of the control device> 2 is a block diagram showing a detailed configuration of the control device 100. The control device 100 includes a storage unit 110 and a control unit 120.

[0031] The storage unit 110 includes, for example, a read only memory (ROM) and a random access memory (RAM). The storage unit 110 stores various data and programs executed by the control unit 120. For example, the storage unit 110 stores the rotation speed and load of the engine 10 in association with the first threshold value, which is the concentration difference of CO2 described above. That is, the storage unit 110 stores a map in which the first threshold value is determined for each rotation speed and load.

[0032] The control unit 120 is, for example, a CPU (Central Processing Unit). The control unit 120 executes the programs stored in the storage unit 110 to function as a first acquisition unit 122, a second acquisition unit 123, a determination unit 124, and an ejection control unit 126.

[0033] The first acquisition unit 122 acquires the concentration of CO2 in the exhaust gas. The first acquisition unit 122 acquires a first concentration of CO2 in the exhaust gas upstream of the oxidation catalyst 20 and a second concentration of CO2 in the exhaust gas downstream of the oxidation catalyst 20.

[0034] The first acquisition unit 122 acquires the CO2 concentration detected by the concentration detection units 60 and 61. Specifically, the first acquisition unit 122 acquires the first concentration detected by the concentration detection unit 60 and the second concentration detected by the concentration detection unit 61. The first acquisition unit 122 acquires the first concentration and the second concentration at a predetermined interval after the engine 10 starts operating. The first acquisition unit 122 outputs the first concentration and the second concentration acquired in sequence to the determination unit 124.

[0035] The second acquisition unit 123 acquires information on the state and operation of the engine 10. For example, the second acquisition unit 123 acquires information on the engine speed and the load acting on the engine 10 detected by the engine detection unit 70 including various sensors from the engine detection unit 70. For example, the second acquisition unit 123 acquires the engine speed and the load of the engine 10 when the engine 10 starts to operate. The second acquisition unit 123 identifies the load acting on the engine 10 from, for example, the depression amount of the accelerator pedal. Note that the second acquisition unit 123 may acquire the torque due to the rotation of the engine 10 instead of the load acting on the engine 10. The second acquisition unit 123 outputs the detection result to the determination unit 124.

[0036] The judgment unit 124 judges the state of the oxidation catalyst 20. Specifically, the judgment unit 124 judges whether the oxidation performance of the oxidation catalyst 20 has deteriorated. The judgment unit 124 judges whether the oxidation performance of the oxidation catalyst 20 has deteriorated based on the concentration difference between the first concentration and the second concentration of CO2 acquired by the first acquisition unit 122. For example, when the concentration difference of CO2 is equal to or greater than a first threshold, the judgment unit 124 judges that the oxidation performance of the oxidation catalyst 20 has not deteriorated. On the other hand, when the concentration difference of CO2 is smaller than the first threshold, the judgment unit 124 judges that the oxidation performance of the oxidation catalyst 20 has deteriorated. Here, the first threshold is a preset value, and is obtained from the first concentration and the second concentration when the oxidation catalyst 20 exhibits normal oxidation performance.

[0037] The determination unit 124 sets the first threshold value according to the rotation state of the engine 10 acquired by the second acquisition unit 123. For example, the determination unit 124 refers to a map stored in the storage unit 110 and sets the first threshold value corresponding to the rotation speed and load of the engine 10 acquired by the second acquisition unit 123. In this case, the determination unit 124 compares the concentration difference between the first concentration and the second concentration acquired by the first acquisition unit 122 with the set first threshold value to determine whether the oxidation performance of the oxidation catalyst 20 has deteriorated. Although the generation degree of soot in the exhaust gas varies depending on the rotation state of the engine 10, by setting the first threshold value as described above, it is possible to determine with high accuracy whether the oxidation performance of the oxidation catalyst 20 has deteriorated. Note that a function for identifying the first threshold value from the rotation speed and load of the engine 10 may be stored in the storage unit 110, and the determination unit 124 may identify the first threshold value using the function.

[0038] The injection control unit 126 controls the generation of ozone by the ozone generation unit 50 and the injection of ozone by the ozone injection unit 55. The injection control unit 126 controls the generation of ozone by the ozone generation unit 50 and the injection of ozone by the ozone injection unit 55 based on the determination result by the determination unit 124.

[0039] In this embodiment, the injection control unit 126 injects ozone upstream of the oxidation catalyst 20 in the exhaust passage 15 when the concentration difference between the first and second concentrations of CO2 is smaller than a first threshold value. When the oxidation performance of the oxidation catalyst 20 is degraded, the second concentration does not increase, and the concentration difference between the first and second concentrations becomes smaller than the first threshold value. Therefore, when the concentration difference is smaller than the first threshold value, the injection control unit 126 injects ozone upstream of the oxidation catalyst 20 to compensate for the insufficient oxidation of soot by the oxidation catalyst 20. The injected ozone oxidizes soot before passing through the oxidation catalyst 20, and can compensate for the performance degradation of the oxidation catalyst 20.

[0040] When the concentration difference is smaller than the first threshold, the injection control unit 126 performs both ozone generation by the ozone generating unit 50 and ozone injection by the ozone injection unit 55. Specifically, when the concentration difference is smaller than the first threshold, the injection control unit 126 first causes the ozone generating unit 50 to generate ozone. Then, the injection control unit 126 injects the ozone generated by the ozone generating unit 50 into the exhaust passage 15. This makes it possible to generate and inject a required amount of ozone. Furthermore, by performing both ozone generation and ozone injection, a storage unit for storing ozone is not required.

[0041] When the soot is oxidized by the injected ozone, the second concentration detected by the concentration detection unit 61 becomes high. Then, when the concentration difference becomes equal to or greater than the first threshold value after the injection of ozone, the injection control unit 126 stops the injection of ozone. This makes it possible to prevent the injection of excessive ozone.

[0042] The injection control unit 126 may change the injection amount of ozone according to the magnitude of the concentration difference between the first and second concentrations of CO2. For example, when the concentration difference of CO2 is smaller than a second threshold value that is lower than the first threshold value, the injection control unit 126 increases the injection amount of ozone. That is, the smaller the concentration difference between the first and second concentrations, the larger the injection amount of ozone is. Thereby, when the oxidation performance of the oxidation catalyst 20 is significantly reduced, the oxidation performance of the oxidation catalyst 20 can be compensated for by increasing the injection amount of ozone.

[0043] The injection control unit 126 refers to the storage unit 110 and identifies a first threshold value corresponding to the rotation speed and load of the engine 10 acquired by the second acquisition unit 123. Then, the injection control unit 126 injects ozone when the concentration difference between the first concentration and the second concentration is smaller than the identified first threshold value. By setting the first threshold value according to the rotation state of the engine 10 as described above, even if the degree of soot generation differs depending on the rotation state of the engine 10, ozone is injected when it is possible to determine with high accuracy that the performance of the oxidation catalyst 20 has deteriorated, so that unnecessary injection of ozone can be suppressed.

[0044] <Example of control device operation> Fig. 3 is a flowchart for explaining an example of the operation of the control device 100. The process shown in the flowchart of Fig. 3 starts when the engine 10 is started (step S102).

[0045] Next, the first acquisition unit 122 acquires a first concentration of CO2 upstream of the oxidation catalyst 20 and a second concentration of CO2 downstream of the oxidation catalyst 20 (step S104). Specifically, the first acquisition unit 122 acquires the first concentration detected by the concentration detection unit 60 and the second concentration detected by the concentration detection unit 61.

[0046] Next, the determination unit 124 determines whether the concentration difference between the first and second concentrations of CO2 is smaller than a first threshold value (step S106). When the oxidation performance of the oxidation catalyst 20 is not degraded, the concentration difference of CO2 is equal to or greater than the first threshold value, but when the oxidation performance of the oxidation catalyst 20 is degraded, the concentration difference of CO2 is smaller than the first threshold value.

[0047] When it is determined in step S106 that the concentration difference is smaller than the first threshold value (Yes), in other words when the oxidation performance of the oxidation catalyst 20 has deteriorated, the injection control unit 126 causes the ozone injector 55 to inject ozone into the exhaust passage 15 (step S108). Specifically, the injection control unit 126 causes the ozone generator 50 to generate ozone, and causes the ozone injector 55 to inject the generated ozone into the exhaust passage 15. As a result, the injected ozone oxidizes soot while passing through the oxidation catalyst 20, and the second concentration of CO2 increases.

[0048] After the injection of ozone, the first acquisition unit 122 again acquires the first concentration of CO2 upstream of the oxidation catalyst 20 and the second concentration of CO2 downstream of the oxidation catalyst 20 (step S110). Then, the determination unit 124 determines whether the concentration difference between the reacquired first concentration and second concentration is equal to or greater than the first threshold value (step S112).

[0049] If it is determined in step S112 that the concentration difference is smaller than the first threshold (No), the process returns to step S108, and the injection control unit 126 causes the ozone injection unit 55 to inject ozone again. On the other hand, if it is determined in step S112 that the concentration difference is equal to or greater than the first threshold (Yes), the injection control unit 126 does not inject ozone.

[0050] The control device 100 repeats the above-described processing of steps S104 to S112 until the engine 10 stops operating (step S114: No). As a result, even if the oxidation performance of the oxidation catalyst 20 decreases while the engine 10 is operating, the oxidation can be assisted by ozone. As a result, it is possible to suppress a decrease in the purification efficiency of NOx in the SCR catalyst downstream of the oxidation catalyst 20.

[0051] <Effects of this embodiment> The exhaust purification system S of the above-described embodiment acquires a first concentration of CO2 upstream of an oxidation catalyst 20 provided in an exhaust passage 15, and a second concentration of CO2 downstream of the oxidation catalyst 20. Then, when a concentration difference between the first concentration and the second concentration is smaller than a first threshold value, the exhaust purification system S injects ozone into the exhaust passage 15 upstream of the oxidation catalyst 20. As a result, when the oxidation performance of the oxidation catalyst 20 is degraded and the CO2 concentration difference becomes smaller than the first threshold value, ozone is injected into the exhaust passage 15. The injected ozone oxidizes soot, thereby compensating for the degraded oxidation performance of the oxidation catalyst 20. As a result, soot accumulation in the DPF 25 downstream of the oxidation catalyst 20 can be suppressed.

[0052] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. For example, all or part of the device can be configured by distributing or integrating functionally or physically in any unit. In addition, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effect of the new embodiment resulting from the combination combines the effect of the original embodiment. [Explanation of symbols]

[0053] 10 Engine 15 Exhaust passage 20 Oxidation Catalyst 50 Ozone generator 55 Ozone injection unit 60, 61 Concentration detection unit 110 Storage section 122 First acquisition part 123 Second Acquisition Department 126 Injection control unit S Exhaust purification system

Claims

1. an oxidation catalyst provided in an exhaust passage through which exhaust gas from an internal combustion engine flows; a first acquisition unit that acquires a first concentration of carbon dioxide in the exhaust gas upstream of the oxidation catalyst and a second concentration of carbon dioxide in the exhaust gas downstream of the oxidation catalyst; an injection control unit that injects ozone into the exhaust passage upstream of the oxidation catalyst when a concentration difference between the first concentration and the second concentration is smaller than a first threshold value; An exhaust purification system comprising:

2. The injection control unit increases the injection amount of the ozone when the concentration difference is smaller than a second threshold value that is lower than the first threshold value, compared to when the concentration difference is equal to or larger than the second threshold value.

2. The exhaust gas purification system according to claim 1.

3. The injection control unit stops the injection of the ozone when the concentration difference becomes equal to or greater than the first threshold value after the injection of the ozone.

2. The exhaust gas purification system according to claim 1.

4. The apparatus further includes an ozone generating unit that generates the ozone, When the concentration difference is smaller than the first threshold value, the injection control unit causes the ozone generating unit to generate the ozone and injects the generated ozone into the exhaust passage.

2. The exhaust gas purification system according to claim 1.

5. A second acquisition unit that acquires a rotation speed of the internal combustion engine and a load acting on the internal combustion engine, The injection control unit specifies the first threshold value corresponding to the rotation speed and the load acquired by the second acquisition unit.

2. The exhaust gas purification system according to claim 1.

6. The apparatus further includes an injection unit that injects the ozone, a distance between the injection part and the oxidation catalyst in the exhaust passage is longer than a distance between the injection part and the internal combustion engine; 2. The exhaust gas purification system according to claim 1.

7. a first detection unit provided upstream of the oxidation catalyst and configured to detect the first concentration; A second detection unit is provided downstream of the oxidation catalyst and detects the second concentration. The first acquisition unit acquires the first concentration detected by the first detection unit and the second concentration detected by the second detection unit.

2. The exhaust gas purification system according to claim 1.

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