JP5517781B2 - Exhaust gas purification device - Google Patents

Description

  The present invention relates to an apparatus for purifying nitrogen oxides (hereinafter referred to as NOx) contained in exhaust gas from a diesel engine and reducing NOx emissions.

  Conventionally, as this type of exhaust gas purification device, a NOx occlusion reduction catalyst is provided in the middle of an exhaust pipe through which exhaust gas from an engine flows, and an oxidation catalyst is provided in an exhaust pipe upstream of the NOx occlusion reduction catalyst. Fuel addition means for adding fuel is inserted into the exhaust pipe upstream of the exhaust gas from the oxidation catalyst, and the reducing agent addition means adds the reducing agent to the exhaust gas between the oxidation catalyst and the NOx storage reduction catalyst. A configured exhaust purification device is disclosed (for example, see Patent Document 1).

  In the exhaust emission control device configured as described above, for example, when the fuel is added by the fuel addition means in a state where the temperature of the NOx occlusion reduction catalyst is low such that the vehicle travels on a congested road and the exhaust gas temperature falls below 200 ° C. In addition, the combustion of the fuel in the oxidation catalyst raises the temperature of the exhaust gas. At the same time, the reducing agent is added to the upstream side of the NOx occlusion reduction catalyst by the reducing agent addition means, and the reducing fuel and the reducing agent flow into the NOx occlusion reduction catalyst. Make the amount optimal. As a result, even if the fuel added by the fuel addition means burns by the oxidation catalyst and the inflow amount of the fuel to the NOx storage reduction catalyst decreases, the reducing agent is directly added to the NOx storage reduction catalyst by the reducing agent addition means. While improving the regeneration efficiency of the NOx occlusion reduction catalyst, it is possible to suppress the addition of excessive fuel from the fuel addition means and prevent deterioration of fuel consumption. The amount of fuel added by the fuel adding means is calculated by a predetermined function process or map process by the control device in accordance with the temperature of the exhaust gas, the load of the diesel engine and the rotational speed. Further, the amount of reducing agent added by the reducing agent adding means is calculated by a predetermined function process or map process by the control device in accordance with the amount of fuel added, the temperature of the exhaust gas, the load and the rotational speed of the diesel engine.

JP 2008-25438 A (Claim 1, paragraphs [0033] to [0035])

However, since the exhaust gas purification apparatus disclosed in the above-mentioned conventional Patent Document 1 does not detect the exhaust gas flow rate, the fuel and reducing agent addition timing and addition amount by the fuel addition means and the reducing agent addition means are optimally controlled. It is difficult. For this reason, the inside of the exhaust pipe becomes an incomplete reduction atmosphere, and NOx stored in the NOx storage reduction catalyst is released, which may reduce the NOx reduction performance of the NOx storage reduction catalyst. Further, in the exhaust emission control device disclosed in the above-mentioned conventional patent document 1, since the fuel and reducing agent are not added by the fuel adding means and the reducing agent adding means at the time of high rotation and high load operation of the engine having a large exhaust gas flow rate, It becomes an exhaust gas atmosphere in which the oxygen in the interior increases and the air-fuel ratio becomes lean. That is, there is a problem that the NOx reduction performance of the NOx occlusion reduction catalyst is deteriorated because the exhaust gas atmosphere in which the fuel in the exhaust gas is not sufficiently increased and the air-fuel ratio is sufficiently rich cannot be obtained. Note that when the exhaust pipe is in an incomplete reducing atmosphere, the NOx stored by the NOx storage reduction catalyst is released because the fuel and reducing agent that have flowed into the NOx storage reduction catalyst are collected by this catalyst. This is because NOx is peeled off from the catalyst as it is without causing the reaction of NOx to N ₂ , CO ₂ or the like.

  The object of the present invention is to store the NOx occlusion reduction catalyst by optimally controlling the injection timing and the injection flow rate of the hydrocarbon-based liquid from the first and second liquid injection nozzles based on the exhaust gas flow rate detected with high accuracy. An object of the present invention is to provide an exhaust gas purification device that can suppress the release of NOx that has been performed and can improve the NOx reduction performance of the NOx storage reduction catalyst. Another object of the present invention is to provide an exhaust gas in which the air-fuel ratio becomes sufficiently rich by sufficiently increasing the amount of hydrocarbon-based liquid (fuel) in the exhaust gas when the engine with a large exhaust gas flow rate is operated at high speed and high load. An object of the present invention is to provide an exhaust gas purifying apparatus capable of improving the NOx reduction performance of a NOx occlusion reduction catalyst by obtaining an atmosphere.

As shown in FIGS. 1 and 2 , the first aspect of the present invention is a NOx occlusion reduction catalyst 24 provided in the exhaust pipe 16 of the engine 11 and carrying an NOx absorbent and an active metal, and an NOx occlusion reduction catalyst 24. An oxidation catalyst 23 provided in the exhaust pipe 16 on the exhaust gas upstream side, and a first liquid injection capable of injecting the hydrocarbon-based liquid 28 into the exhaust pipe 16 inserted into the exhaust gas upstream side of the oxidation catalyst 23 toward the oxidation catalyst 23 A nozzle 21, a second liquid injection nozzle 22 inserted into the exhaust pipe 16 between the NOx storage reduction catalyst 24 and the oxidation catalyst 23 and capable of injecting a hydrocarbon-based liquid 28 toward the NOx storage reduction catalyst 24, a first Hydrocarbon-based liquid supply means 30 for supplying the liquid 28 to the liquid injection nozzle 21 via the first liquid adjustment valve 31 and supplying the liquid 28 to the second liquid injection nozzle 22 via the second liquid adjustment valve 32; An exhaust gas purifying apparatus comprising temperature sensors 61 and 62 for detecting the temperature of exhaust gas flowing through the trachea 16 and a controller 38 for controlling the first and second liquid regulating valves 31 and 32 based on detection outputs of the temperature sensors 61 and 62. The exhaust gas flow rate detecting means 44 for detecting the exhaust gas flow rate in the exhaust gas is further provided, and the controller 38 controls the first and second liquid regulating valves 31, based on the detection outputs of the temperature sensors 61 and 62 and the exhaust gas flow rate detecting means 44. 32, the exhaust gas temperature detected by the temperature sensors 61 and 62 is higher than a predetermined temperature, and the exhaust gas flow rate detected by the exhaust gas flow rate detection means 44 is less than the first predetermined flow rate, the controller 38. Controls the first and second liquid regulating valves 31 and 32 to inject the liquid 28 from both the first and second liquid ejecting nozzles 21 and 22. The exhaust gas temperature detected by the temperature sensors 61 and 62 is higher than a predetermined temperature, and the exhaust gas flow rate detected by the exhaust gas flow rate detecting means 44 is greater than the first predetermined flow rate and is controlled to be second. When the flow rate is equal to or lower than the predetermined flow rate, the controller 38 controls the first and second liquid regulating valves 31 and 32 so that the liquid 28 is ejected only from the first liquid ejecting nozzle 21 and the liquid 28 is ejected from the second liquid ejecting nozzle 22. Control is performed to give priority to the reduction of NOx without injection, the exhaust gas temperature detected by the temperature sensors 61 and 62 is higher than a predetermined temperature, and the exhaust gas flow rate detected by the exhaust gas flow rate detection means 44 is higher than the second predetermined flow rate. In many cases, the controller 38 controls the first and second liquid regulating valves 31 and 32 to eject the liquid 28 from both the first and second liquid injection nozzles 21 and 22, and NOx It is characterized by performing control giving priority to the reduction of .

The second aspect of the present invention is an invention based on the first aspect, further shown in FIGS. 1 and 2, when the displacement of the engine 11 is 4-5 liters predetermined temperature 180 ° C. The first predetermined flow rate is 30 g / second, and the second predetermined flow rate is 80 g / second.

A third aspect of the present invention is an invention based on the first or second aspect , and further, as shown in FIG. 1, the exhaust gas flow rate detection means 44 determines the air flow rate flowing into the intake pipe 13 of the engine 11. It has an air flow rate sensor 37 for detection, and the controller 38 is configured to calculate the exhaust gas flow rate based on the detection output of the air flow rate sensor 37.

  In the exhaust gas purifying apparatus according to the first aspect of the present invention, the controller controls the first and second liquid regulating valves based on the detection outputs of the temperature sensor and the exhaust gas flow rate detecting means, so that the exhaust gas flow rate detecting means detects the accuracy. Based on the exhaust gas flow rate, the first and second liquid injection nozzles inject the hydrocarbon-based liquid with the optimal flow rate at the optimal timing. As a result, the release of NOx stored in the NOx storage reduction catalyst can be suppressed, and the NOx reduction performance of the NOx storage reduction catalyst can be improved.

Further, when the exhaust gas temperature detected by the temperature sensor is higher than the predetermined temperature and the exhaust gas flow rate detected by the exhaust gas flow rate detecting means is less than the first predetermined flow rate, the liquid is injected from both the first and second liquid injection nozzles. Then, since the control for suppressing the release of NOx is performed, the hydrocarbon-based liquid injected from the second liquid injection nozzle is discharged from the first liquid injection nozzle even during the low rotation and low load operation with a small exhaust gas flow rate. By supplementing the injected hydrocarbon-based liquid, the hydrocarbon-based liquid is uniformly dispersed in the exhaust gas immediately before flowing into the NOx storage reduction catalyst. As a result, since the distribution of the hydrocarbon-based liquid on the NOx storage reduction catalyst becomes uniform, the release of NOx stored in the NOx storage reduction catalyst can be suppressed, and the NOx reduction performance of the NOx storage reduction catalyst can be improved.

  Further, when the exhaust gas temperature detected by the temperature sensor is higher than a predetermined temperature and the exhaust gas flow rate detected by the exhaust gas flow rate detecting means is greater than the first predetermined flow rate and lower than the second predetermined flow rate, only from the first liquid injection nozzle. Since control is performed so that NOx reduction is prioritized without injecting liquid from the second liquid injection nozzle, it is injected from the first liquid injection nozzle during medium rotation and medium load operation where the exhaust gas flow rate is appropriate. Even if a portion of the hydrocarbon liquid burns with the oxidation catalyst, the amount of the remaining hydrocarbon liquid discharged from the oxidation catalyst is relatively large, and the hydrocarbon liquid just before flowing into the NOx storage reduction catalyst. Evenly dispersed in the exhaust gas. As a result, the hydrocarbon liquid flowing into the NOx occlusion reduction catalyst does not become excessive, and is uniformly distributed on the NOx occlusion reduction catalyst, so that the release of NOx occluded in the NOx occlusion reduction catalyst can be suppressed, and the NOx occlusion reduction is achieved. The NOx reduction performance of the reduction catalyst can be improved.

  Further, when the exhaust gas temperature detected by the temperature sensor is higher than the predetermined temperature and the exhaust gas flow rate detected by the exhaust gas flow rate detecting means is higher than the second predetermined flow rate, liquid is ejected from both the first and second liquid ejection nozzles. Since the NOx reduction is prioritized, the hydrocarbon-based liquid injected from the second liquid injection nozzle is used in the first liquid injection nozzle even during high-speed and high-load operation of the engine with a large exhaust gas flow rate. By supplementing the hydrocarbon-based liquid injected from the exhaust gas, it is possible to sufficiently increase the hydrocarbon-based liquid in the exhaust gas immediately before flowing into the NOx storage-reduction catalyst and to obtain an exhaust gas atmosphere in which the air-fuel ratio is sufficiently rich. . As a result, the release of NOx stored in the NOx storage reduction catalyst can be suppressed, and the NOx reduction performance of the NOx storage reduction catalyst can be improved.

It is a block diagram which shows the exhaust gas purification apparatus of this invention embodiment. It is a flowchart which performs discharge | emission suppression of NOx and reduction priority of NOx by controlling the 1st and 2nd liquid injection nozzle using the exhaust gas purification apparatus. It is a figure which shows NOx reduction rate when exhaust gas is purified in the predetermined mode using the exhaust gas purification apparatus of Example 1 and Comparative Example 1. It is a flowchart which performs NOx reduction | restoration by controlling a 1st liquid injection nozzle using the exhaust gas purification apparatus of the comparative example 1.

  Next, an embodiment for carrying out the present invention will be described with reference to the drawings. As shown in FIG. 1, an intake pipe 13 is connected to an intake port of a diesel engine 11 via an intake manifold 12, and an exhaust pipe 16 is connected to an exhaust port via an exhaust manifold 14. The intake pipe 13 is provided with a compressor housing 17a that rotatably accommodates a compressor wheel (not shown) of the turbocharger 17 and an intercooler 18 that cools the intake air compressed by the turbocharger 17. The exhaust pipe 16 is provided with a turbine housing 17b that rotatably accommodates a turbine wheel (not shown) of the turbocharger 17. The compressor wheel and the turbine wheel are connected by a shaft (not shown). The compressor wheel is rotated via the turbine wheel and the shaft by the energy of the exhaust gas discharged from the engine 11, and the intake air (intake air) in the intake pipe 13 is compressed by the rotation of the compressor wheel. Reference numeral 19 in FIG. 1 denotes an air cleaner attached to the intake upstream end of the intake pipe 13.

  On the other hand, in the middle of the exhaust pipe 16, an oxidation catalyst 23 and a NOx storage reduction catalyst 24 are provided in this order from the engine side (exhaust gas upstream side). The oxidation catalyst 23 is accommodated in a cylindrical upstream converter 26 in which the diameter of the exhaust pipe 16 is enlarged, and the NOx storage reduction catalyst 24 is accommodated in a cylindrical downstream converter 27 in which the diameter of the exhaust pipe 16 is enlarged. The oxidation catalyst 23 is a monolith catalyst, which is a cordierite honeycomb carrier coated with platinum-alumina, platinum-palladium-alumina, platinum-zeolite, platinum-palladium-zeolite, platinum-zeolite-alumina, or the like. . The platinum-zeolite is configured by coating a slurry containing hydrogen ion exchanged zeolite powder and then supporting Pt. Platinum-zeolite-alumina is constituted by supporting Pt after coating a slurry containing the hydrogen ion-exchanged zeolite powder and γ-alumina powder. The oxidation catalyst 23 has a function of increasing the exhaust gas temperature by burning a hydrocarbon-based liquid 28 injected from a first liquid injection nozzle 21 described later.

  The NOx occlusion reduction catalyst 24 occludes NOx in the exhaust gas flowing into the exhaust pipe 16, and releases the occluded NOx when the hydrocarbon (HC) concentration in the exhaust gas increases, and is regenerated by platinum-barium. -Alumina catalyst. The NOx occlusion reduction catalyst 24 is not shown, but a monolith carrier (material: cordierite) in which a grid-like (honeycomb-like) passage is formed in the flow direction of exhaust gas, and a noble metal (active cord) formed on the monolith carrier. Metal) and a coating layer on which a NOx absorbent is supported. The noble metal is platinum (Pt), and the NOx absorbent is barium (Ba). The NOx absorbent is supported by 2 to 50% by weight, preferably 5 to 20% by weight, based on the total weight of the NOx occlusion reduction catalyst 24. The coat layer is alumina.

  On the other hand, a first liquid injection nozzle 21 capable of injecting a hydrocarbon-based liquid 28 is provided in the exhaust pipe 16 on the exhaust gas upstream side of the oxidation catalyst 23 and on the exhaust gas downstream side of the turbine housing 17a of the turbocharger 17. 23 is inserted. A second liquid injection nozzle 22 capable of injecting the hydrocarbon-based liquid 28 is inserted into the exhaust pipe 16 between the NOx storage reduction catalyst 24 and the oxidation catalyst 23 toward the NOx storage reduction catalyst 24. The first and second liquid injection nozzles 21 and 22 are connected to the hydrocarbon-based liquid supply means 30. The hydrocarbon-based liquid supply means 30 includes a liquid tank 33 that stores the hydrocarbon-based liquid 28, a pump 34 that supplies the liquid 28 in the liquid tank 33 to the first and second liquid injection nozzles 21 and 22, and a first The first liquid regulating valve 31 that adjusts the flow rate of the liquid 28 supplied to the liquid ejecting nozzle 21 and the second liquid adjusting valve 32 that adjusts the flow rate of the liquid 28 supplied to the second liquid ejecting nozzle 22 are provided. One end of a first branch pipe 41 is connected to the first liquid jet nozzle 21, and one end of a second branch pipe 42 is connected to the second liquid jet nozzle 22. The other ends of the first and second branch pipes 41 and 42 are connected to one end of the supply pipe 36, and the other end of the supply pipe 36 is connected to the liquid tank 33.

  The pump 34 is provided in the supply pipe 36, the first flow rate adjustment valve 31 is provided in the first branch pipe 41, and the second flow rate adjustment valve 32 is provided in the second branch pipe 42. The first liquid regulating valve 31 is a three-way two-position switching electromagnetic valve having first to third ports 31a to 31c. The first port 31a is connected to the discharge port of the pump 34 through the first branch pipe 41. The second port 31 b is connected to the first liquid jet nozzle 21 through the first branch pipe 41, and the third port 31 c is connected to the liquid tank 33 through the first return pipe 51. The second liquid regulating valve 32 is a three-way two-position switching electromagnetic valve having first to third ports 32a to 32c. The first port 32a communicates with the discharge port of the pump 34 through the second branch pipe 42. The second port 32 b is connected to the second liquid jet nozzle 22 through the second branch pipe 42, and the third port 32 c is connected to the liquid tank 33 through the second return pipe 52.

  The hydrocarbon-based liquid 28 is a fuel such as light oil. When the first liquid regulating valve 31 is turned on while the pump 34 is operating, the first port 31a and the second port 31b are connected in communication, and the liquid 28 is supplied to the first liquid ejecting nozzle 21. When the first liquid regulating valve 31 is turned off, the first port 31 a and the third port 31 c are connected in communication, and the liquid 28 returns to the liquid tank 33 through the first return pipe 51. Further, when the second liquid regulating valve 32 is turned on while the pump 34 is operating, the first port 32a and the second port 32b are connected in communication, and the liquid 28 is supplied to the second liquid jet nozzle 22, When the second liquid regulating valve 32 is turned off, the first port 32 a and the third port 32 c are connected in communication, so that the liquid 28 returns to the liquid tank 33 through the second return pipe 52.

  The exhaust pipe 16 between the first liquid injection nozzle 21 and the oxidation catalyst 23 is provided with a first temperature sensor 61 that detects the exhaust gas temperature near the inlet of the oxidation catalyst 23. The exhaust pipe 16 between the second liquid injection nozzle 22 and the NOx storage reduction catalyst 24 is provided with a second temperature sensor 62 that detects the exhaust gas temperature near the inlet of the NOx storage reduction catalyst 24. An air flow sensor 37 is provided in the intake pipe 13 between the air cleaner 19 and the compressor housing 17 a of the turbocharger 17. The air flow sensor 37 is a thermal flow meter. A voltage is applied to the thermal flow meter to heat it to a predetermined temperature, and the detection element of the thermal flow meter is cooled by the intake air flowing through the intake pipe 13. Accordingly, a voltage signal corresponding to the intake flow rate is output. Further, a pair of NOx sensors (not shown) for detecting the NOx concentration in the exhaust gas are inserted into the exhaust pipe 16 before and after the NOx storage reduction catalyst 24. The detection outputs of the first temperature sensor 61, the second temperature sensor 62, the air flow rate sensor 37, and the pair of NOx sensors are respectively connected to control inputs of a controller 38 composed of a microcomputer, and the control output of the controller 38 includes a pump 34, The first liquid regulating valve 31 and the second liquid regulating valve 32 are connected to each other.

  The controller 38 is provided with a memory 43. The memory 43 stores a formula for converting the voltage signal detected by the air flow rate sensor 37 into an air flow rate, and a formula for converting the air flow rate into an exhaust gas flow rate. Then, the controller 38 calculates the exhaust gas flow rate by substituting the voltage signal into these equations for calculation. In other words, the exhaust gas flow rate detection means 44 is configured by the air flow rate sensor 37, the controller 38 and the memory 43. Further, the memory 43 stores the ON time of the first and second liquid regulating valves 31 and 32 according to the exhaust gas flow rate, the exhaust gas temperature at the oxidation catalyst 23 inlet, and the temperature at the NOx storage reduction catalyst 24 inlet, The operation timing of the pump 34 is stored as a map.

  Specifically, the controller 38 is configured to control the first and second liquid regulating valves 31 and 32 in the following three control patterns. In the first control pattern, the first and second exhaust gas temperatures detected by the temperature sensors 61 and 62 are higher than a predetermined temperature, and the exhaust gas flow rate detected by the exhaust gas flow rate detecting means 44 is less than the first predetermined flow rate. This is a control pattern in which the liquid 28 is ejected from both the liquid ejection nozzles 21 and 22 to suppress the release of NOx. The second control pattern is when the exhaust gas temperature detected by the temperature sensors 61 and 62 is higher than a predetermined temperature, and the exhaust gas flow rate detected by the exhaust gas flow rate detecting means 44 is greater than the first predetermined flow rate and lower than the second predetermined flow rate. Furthermore, the control pattern prioritizes the reduction of NOx without ejecting the liquid 28 only from the first liquid ejecting nozzle 21 and ejecting the liquid 28 from the second liquid ejecting nozzle 22. When the exhaust gas temperature detected by the temperature sensors 61 and 62 is higher than a predetermined temperature and the exhaust gas flow rate detected by the exhaust gas flow rate detecting means 44 is higher than the second predetermined flow rate, the third control pattern is the first and second control patterns. This is a control pattern in which the liquid 28 is ejected from both the liquid ejection nozzles 21 and 22 and NOx reduction is prioritized. However, in each control pattern, the injection flow rate of the liquid 28 from each injection nozzle 21, 22 corresponding to the exhaust gas flow rate is stored as a map. The total ejection amount of the liquid 28 in the third control pattern is set to be larger than the total ejection amount of the liquid 28 in the first control pattern. When the displacement of the engine 11 is 4 to 5 liters, the memory 43 stores 180 ° C. as the predetermined temperature, 30 g / second as the first predetermined flow rate, and 80 g / second as the second predetermined flow rate. Is preferably stored.

The operation of the exhaust gas purification apparatus configured as described above will be described with reference to FIGS. When the engine 11 is operating at a low speed and under a low load, the pair of NOx sensors detect that a predetermined amount or more of NOx has been stored in the NOx storage reduction catalyst 24, and the temperature sensors 61 and 62 are higher than 180 ° C. (predetermined temperature). When the exhaust gas temperature is detected, the controller 38 takes in the voltage signal detected by the air flow sensor 37, substitutes the electric signal into the conversion formula to the air flow rate stored in the memory 43, calculates the air flow rate, and then the memory 43. The exhaust gas flow rate is calculated by substituting the air amount into the conversion formula for the air flow rate stored in the above to the exhaust gas flow rate. If the exhaust gas flow rate is less than 30 g / second (first predetermined flow rate), the controller 38 controls the first and second liquid regulating valves 31, 32 to control the first and second liquid injection nozzles 21, The hydrocarbon-based liquid 28 is jetted from both sides 22 to control NOx release. At this time, since the engine 11 is operating at a low speed and a low load with a small exhaust gas flow rate, most of the hydrocarbon-based liquid 28 injected from the first liquid injection nozzle 21 is burned by the oxidation catalyst 23 and oxidized. Although the amount of the hydrocarbon liquid 28 discharged from the catalyst 23 decreases, the hydrocarbon liquid 28 injected from the second liquid injection nozzle 22 supplements the hydrocarbon liquid 28 injected from the first liquid injection nozzle 21. Therefore, the hydrocarbon-based liquid 28 is uniformly dispersed in the exhaust gas immediately before flowing into the NOx storage reduction catalyst 24. As a result, the distribution of the hydrocarbon-based liquid 28 on the NOx storage-reduction catalyst 24 becomes uniform, and the dispersion flow rate of the hydrocarbon-based liquid 28 is sufficient, so the NOx trapped in the NOx storage-reduction catalyst 24 is obtained. Reaction to N ₂ , CO _2, etc. occurs promptly and is peeled off from the NOx storage reduction catalyst 24. Therefore, the release of NOx stored in the NOx storage reduction catalyst 24 can be suppressed, and the NOx reduction performance of the NOx storage reduction catalyst 24 can be improved.

  Further, during the middle rotation and medium load operation of the engine 11, the pair of NOx sensors detect that a predetermined amount or more of NOx is occluded in the NOx occlusion reduction catalyst 24, and the temperature sensors 61 and 62 detect the temperature from 180 ° C. (predetermined temperature). When a high exhaust gas temperature is detected, the controller 38 takes in the voltage signal detected by the air flow sensor 37, calculates the air flow rate by substituting the electric signal into the conversion formula for the air flow rate stored in the memory 43, The exhaust gas flow rate is calculated by substituting the air amount into the conversion formula of the air flow rate stored in 43 to the exhaust gas flow rate. If the exhaust gas flow rate is higher than 30 g / second (first predetermined flow rate) and 80 g / second (second predetermined flow rate) or less, the controller 38 controls the first and second liquid regulating valves 31. , 32 is controlled so that the hydrocarbon liquid 28 is injected only from the first liquid injection nozzle 21 and the hydrocarbon liquid 28 is not injected from the second liquid injection nozzle 22 and priority is given to the reduction of NOx. Do. At this time, since the engine 11 performs a medium rotation and medium load operation in which the exhaust gas flow rate is an appropriate amount, even if a part of the hydrocarbon liquid 28 injected from the first liquid injection nozzle 21 burns in the oxidation catalyst 23, The amount of the remaining hydrocarbon liquid 28 discharged from the oxidation catalyst 23 is relatively large, and the hydrocarbon liquid 28 is uniformly dispersed in the exhaust gas immediately before flowing into the NOx storage reduction catalyst 24. As a result, the hydrocarbon-based liquid 28 flowing into the NOx occlusion reduction catalyst 24 is not excessively distributed, but is uniformly distributed on the NOx occlusion reduction catalyst 24, so that the NOx occlusion reduction catalyst 24 is occluded in the same manner as described above. The release of NOx can be suppressed, and the NOx reduction performance of the NOx storage reduction catalyst 24 can be improved.

  Further, when the engine 11 is operated at a high speed and a high load, the pair of NOx sensors detects that a predetermined amount or more of NOx is occluded in the NOx occlusion reduction catalyst 24, and the temperature sensors 61 and 62 detect the temperature from 180 ° C. (predetermined temperature). When a high exhaust gas temperature is detected, the controller 38 takes in the voltage signal detected by the air flow sensor 37, calculates the air flow rate by substituting the electric signal into the conversion formula for the air flow rate stored in the memory 43, The exhaust gas flow rate is calculated by substituting the air amount into the conversion formula of the air flow rate stored in 43 to the exhaust gas flow rate. If the exhaust gas flow rate is higher than 80 g / second (second predetermined flow rate), the controller 38 controls the first and second liquid regulating valves 31 and 32 to thereby control the first and second liquid injection nozzles 21 and 32. The hydrocarbon-based liquid 28 is injected from both of the two, and control is performed to give priority to the reduction of NOx. At this time, since the engine 11 is operating at a high speed and a high load with a large exhaust gas flow rate, most of the hydrocarbon-based liquid 28 injected from the first liquid injection nozzle 21 is combusted by the oxidation catalyst 23 and is oxidized. Although the amount of the hydrocarbon liquid 28 discharged from the catalyst 23 decreases, the hydrocarbon liquid 28 injected from the second liquid injection nozzle 22 supplements the hydrocarbon liquid 28 injected from the first liquid injection nozzle 21. Therefore, the hydrocarbon-based liquid 28 in the exhaust gas immediately before flowing into the NOx occlusion reduction catalyst 24 is sufficiently increased, resulting in an exhaust gas atmosphere in which the air-fuel ratio becomes sufficiently rich. As a result, similarly to the above, the release of NOx stored in the NOx storage reduction catalyst 24 can be suppressed, and the NOx reduction performance of the NOx storage reduction catalyst 24 can be improved.

  In this embodiment, a particulate filter is not provided in the exhaust pipe, but a particulate filter may be provided in the exhaust pipe on the downstream side of the exhaust gas from the NOx storage reduction catalyst. Thereby, the particulates contained in exhaust gas can be reduced. In this embodiment, a pair of NOx sensors are provided in the exhaust pipes before and after the NOx storage reduction catalyst. However, an air concentration sensor may be provided before and after the oxidation catalyst and before and after the NOx storage reduction catalyst. Thereby, since the air concentration in the exhaust gas can be detected with high accuracy, the injection timing and the injection flow rate of the hydrocarbon-based liquid from the first and second liquid injection nozzles can be further optimally controlled. As a result, the release of NOx stored in the NOx storage reduction catalyst can be further suppressed, and the NOx reduction performance of the NOx storage reduction catalyst can be further improved. Furthermore, in this embodiment, a diesel engine with a turbocharger is cited as the engine, but the exhaust gas purification apparatus of the present invention may be applied to a naturally aspirated diesel engine.

Next, examples of the present invention will be described in detail together with comparative examples.
<Example 1>
As shown in FIG. 1, an exhaust gas purification device was attached to a diesel engine 11 with a turbocharger 17 having a displacement of 5120 cc. The exhaust gas purifying apparatus includes a NOx occlusion reduction catalyst 24 provided in the exhaust pipe 16 of the engine 11, an oxidation catalyst 23 provided in the exhaust pipe 16 upstream of the exhaust gas from the NOx occlusion reduction catalyst 24, and an exhaust gas from the oxidation catalyst 23. A first liquid injection nozzle 21 inserted in the upstream exhaust pipe 16, a second liquid injection nozzle 22 inserted in the exhaust pipe 16 between the NOx storage reduction catalyst 24 and the oxidation catalyst 23, and a first liquid injection. Hydrocarbon liquid supply for supplying the hydrocarbon liquid 28 to the nozzle 21 via the first liquid regulating valve 31 and for supplying the hydrocarbon liquid 28 to the second liquid injection nozzle 22 via the second liquid regulating valve 32 Means 30. Further, the first temperature sensor 61 is inserted into the exhaust pipe 16 near the inlet of the oxidation catalyst 23, and the second temperature sensor 62 is inserted into the exhaust pipe 16 near the inlet of the NOx storage reduction catalyst 24, so that the compressor of the turbocharger 17. An air flow sensor 37 was inserted into the intake pipe 13 on the intake upstream side of the housing 17a. Further, the hydrocarbon-based liquid supply means 30 includes a liquid tank 33 that stores the hydrocarbon-based liquid 28, a pump 34 that supplies the liquid 28 in the liquid tank 33 to the first and second liquid injection nozzles 21, 22, A first liquid regulating valve 31 for adjusting the flow rate of the liquid 28 supplied to the first liquid ejecting nozzle 21; and a second liquid adjusting valve 32 for adjusting the flow rate of the liquid 28 supplied to the second liquid ejecting nozzle 22. did. The detection outputs of the first temperature sensor 61, the second temperature sensor 62, and the air flow rate sensor 37 are connected to the control input of the controller 38, and the pump 34, the first liquid regulating valve 31, and the second output are connected to the control output of the controller 38. Liquid regulating valves 32 were connected to each other. In the NOx storage reduction catalyst 24, the coat layer was alumina, the noble metal (active metal) was platinum (Pt), and the NOx absorbent was barium (Ba). The oxidation catalyst 23 was a honeycomb carrier coated with platinum-palladium-alumina. When the pair of NOx sensors detect that a predetermined amount or more of NOx is occluded in the NOx occlusion reduction catalyst 24 during the operation of the engine 11, the controller 38 operates the exhaust gas purifying device according to the procedure shown in the flowchart of FIG. Controlled.

<Comparative Example 1>
Except that the second liquid injection nozzle, the second liquid regulating valve, the first temperature sensor, and the air flow rate sensor were not provided, the configuration was the same as that of the exhaust gas purification apparatus of Example 1. Then, when the pair of NOx sensors detect that a predetermined amount or more of NOx is occluded in the NOx occlusion reduction catalyst during the operation of the engine, the controller controls the exhaust gas purifying apparatus according to the procedure shown in the flowchart of FIG. . Specifically, when the temperature sensor detects the exhaust gas temperature exceeding 180 ° C., the controller operates the first liquid injection nozzle to perform NOx reduction.

<Comparative test 1 and evaluation>
The engine equipped with the exhaust gas purifying apparatus of Example 1 and Comparative Example 1 is combined with idling and fine acceleration / deceleration driving based on an average driving pattern based on the average driving pattern in the domestic exhaust gas regulation mode: Japan. Mode). After measuring the NOx emission amount at this time, the reduction rate of NOx was calculated. The result is shown in FIG. In addition, the NOx reduction rate (%) of FIG. 3 was calculated | required as follows. The emission amount of NOx from the diesel engine not equipped with the exhaust gas purification device is X (g), and the emission amount of NOx from the diesel engine equipped with the exhaust gas purification device of Example 1 and Comparative Example 1 is Y (g ), And when the NOx reduction rate is Z (%), it was obtained from the equation Z = [(X−Y) / X] × 100. As apparent from FIG. 3, the NOx reduction rate of the engine with the exhaust gas purification device of Comparative Example 1 was as low as 49%, while the NOx reduction rate of the engine with the exhaust gas purification device of Example 1 was low. Increased to 70%.

DESCRIPTION OF SYMBOLS 11 Diesel engine 13 Intake pipe 16 Exhaust pipe 21 1st liquid injection nozzle 22 2nd liquid injection nozzle 23 Oxidation catalyst 24 NOx occlusion reduction catalyst 28 Hydrocarbon liquid 30 Hydrocarbon liquid supply means 31 1st liquid adjustment valve 32 2nd Liquid regulating valve 37 Air flow sensor 38 Controller 44 Exhaust gas flow rate detecting means 61 First temperature sensor 62 Second temperature sensor

Claims (3)

A NOx occlusion reduction catalyst (24) provided in the exhaust pipe (16) of the engine (11) and carrying an NOx absorbent and an active metal, and an exhaust pipe (16) upstream of the exhaust gas from the NOx occlusion reduction catalyst (24) An oxidation catalyst (23) provided on the exhaust gas and a hydrocarbon liquid (28) that is inserted into the exhaust pipe (16) upstream of the exhaust gas from the oxidation catalyst (23) toward the oxidation catalyst (23). The first liquid injection nozzle (21) is inserted into an exhaust pipe (16) between the NOx occlusion reduction catalyst (24) and the oxidation catalyst (23), and is carbonized toward the NOx occlusion reduction catalyst (24). A second liquid injection nozzle (22) capable of injecting a hydrogen-based liquid (28), and supplying the liquid (28) to the first liquid injection nozzle (21) via a first liquid regulating valve (31); A hydrocarbon-based liquid supply means (30) for supplying the liquid (28) to the second liquid injection nozzle (22) via a second liquid regulating valve (32), and an exhaust gas temperature flowing through the exhaust pipe (16) Detect Exhaust gas provided with a temperature sensor (61, 62) for controlling and a controller (38) for controlling the first and second liquid regulating valves (31, 32) based on the detection output of the temperature sensor (61, 62) In the purification device,
Further comprising an exhaust gas flow rate detecting means (44) for detecting the exhaust gas flow rate in the exhaust gas,
The controller (38) is configured to control the first and second liquid regulating valves (31, 32) based on the detection outputs of the temperature sensors (61, 62) and the exhaust gas flow rate detection means (44). It is,
When the exhaust gas temperature detected by the temperature sensor (61, 62) is higher than a predetermined temperature and the exhaust gas flow rate detected by the exhaust gas flow rate detecting means (44) is less than a first predetermined flow rate, the controller (38) Controls the first and second liquid regulating valves (31, 32) to inject the liquid (28) from both the first and second liquid injection nozzles (21, 22), thereby releasing NOx. Control to suppress,
The exhaust gas temperature detected by the temperature sensor (61, 62) is higher than a predetermined temperature, and the exhaust gas flow rate detected by the exhaust gas flow rate detecting means (44) is greater than the first predetermined flow rate and less than a second predetermined flow rate. When the controller (38) controls the first and second liquid regulating valves (31, 32), the liquid (28) is ejected only from the first liquid ejecting nozzle (21), and the second Without injecting the liquid (28) from the liquid injection nozzle (22), control to give priority to the reduction of NOx,
When the exhaust gas temperature detected by the temperature sensor (61, 62) is higher than a predetermined temperature and the exhaust gas flow rate detected by the exhaust gas flow rate detecting means (44) is larger than the second predetermined flow rate, the controller (38 ) Controls the first and second liquid regulating valves (31, 32), injects the liquid (28) from both the first and second liquid injection nozzles (21, 22), and reduces NOx. An exhaust gas purification device configured to perform control giving priority to the above . When the displacement of the engine (11) is 4 to 5 liters, the predetermined temperature is 180 ° C., the first predetermined flow rate is 30 g / second, and the second predetermined flow rate is 80 g / second. Item 1. An exhaust gas purifying apparatus according to Item 1 . The exhaust gas flow rate detection means (44) has an air flow rate sensor (37) for detecting the flow rate of air flowing into the intake pipe (13) of the engine (11), and the controller (38) is the air flow rate sensor (37 The exhaust gas purifying apparatus according to claim 1 or 2, wherein the exhaust gas flow rate is calculated on the basis of a detection output.

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