JP5516445B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine that purifies nitrogen oxides in exhaust gas discharged from the internal combustion engine.

  Conventionally, as an exhaust purification device that removes nitrogen oxides (NOx) in exhaust gas discharged from an internal combustion engine, for example, a NOx storage reduction catalyst and a urea selective reduction catalyst are known. Specifically, the NOx occlusion reduction type catalyst is a catalyst that reduces and purifies NOx occluded by itself using the unburned fuel HC as a reducing agent. In addition, the urea selective reduction catalyst is a catalyst that selectively reduces and purifies NOx in exhaust gas using urea as a reducing agent.

  However, in these devices, the purification capacity of the catalyst is low until the catalyst temperature rises to the activation temperature after the internal combustion engine is started and the catalyst is warmed up, and NOx in the exhaust gas is appropriately purified. I can't. For this reason, when a technique for improving the thermal efficiency of the internal combustion engine or the like is introduced for the purpose of improving the fuel consumption reduction effect of the internal combustion engine, the catalyst temperature does not easily rise, and the degree of NOx purification becomes remarkable. There is a fear.

  In order to solve such problems, a technique for removing nitrogen oxides as disclosed in Patent Document 1 below is also known. Specifically, in this technology, first, nitric oxide (NO) in exhaust gas is oxidized to be easily adsorbed nitrogen oxides (NO 2 and the like), and sprayed toward the modified nitrogen oxides. By spraying water from the apparatus, ionization of the modified nitrogen oxide is promoted. Then, the ionized nitrogen oxide is adsorbed by the adsorbent, and the nitrogen oxide ions are concentrated by electrophoresis by forming an electric field in a part of the adsorbent. Then, the nitrogen oxide ions are reduced and purified by reducing the concentrated nitrogen oxide ions with a three-way catalyst. This makes it possible to purify the nitrogen oxides in the exhaust regardless of the exhaust temperature.

JP 2005-233161 A

  However, even with the technique described in Patent Document 1, a situation in which nitrogen oxides in the exhaust gas cannot be appropriately purified may occur. As such a situation, for example, when water sprayed from a spraying device is reused, there is a situation where the concentration of nitrogen oxides contained in the water increases and ionization of nitrogen oxides cannot be promoted. At this time, the purification ability of nitrogen oxides decreases, and the exhaust characteristics of the internal combustion engine may be deteriorated.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can suitably suppress deterioration of exhaust characteristics of nitrogen oxides in exhaust gas. There is.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

The invention according to claim 1 is a first storage means for storing an absorbing liquid that absorbs nitrogen oxides in exhaust gas discharged from an internal combustion engine to an exhaust passage, and an absorbing liquid stored in the first storing means. Supply means for supplying to the exhaust passage, and second storage means for storing a storage liquid that is different from the absorption liquid and absorbs nitrogen oxide, wherein the storage liquid is nitrogen per unit amount. The nitrogen oxide absorption density, which is the amount of oxide absorbed, is higher than the nitrogen oxide absorption density of the absorbing liquid, and the first storage means and the second storage means are partitioned by a permeable membrane, The first storage means collects and stores the absorption liquid supplied to the exhaust passage by the supply means, and the permeable membrane contains nitrogen oxides absorbed in the absorption liquid on the storage liquid side. Transparent selectively That it is characterized by having a function of lowering the concentration of nitrogen oxides of the absorption liquid.

  In the above invention, the supply liquid is supplied to the exhaust passage by the supply means, so that nitrogen oxide in the exhaust is absorbed and deterioration of the exhaust characteristics is suppressed. Here, when the absorption liquid collected in the first storage means is used repeatedly, the concentration of nitrogen oxide in the absorption liquid increases, and the absorption amount (absorption rate) of nitrogen oxide by the absorption liquid per unit time and absorption There is a possibility that the absorption amount (absorption density) of nitrogen oxides per unit amount of the liquid may decrease. In this case, nitrogen oxides in the exhaust cannot be properly absorbed by the absorbing liquid, and the exhaust characteristics may be deteriorated.

  Here, in the said invention, the storage liquid which absorbs a nitrogen oxide is stored in the 2nd storage means partitioned off with the 1st storage means and the permeable membrane. Then, the permeable membrane has a function of selectively permeating nitrogen oxides absorbed by the absorbing liquid to the storage liquid side. For this reason, the raise of the density | concentration of the nitrogen oxide in an absorption liquid can be suppressed, and the fall of the absorption rate and absorption density of the nitrogen oxide by an absorption liquid can be suppressed. Thereby, deterioration of exhaust characteristics can be avoided appropriately.

  Furthermore, in the above invention, the absorbing liquid and the storage liquid are different liquids. For this reason, for example, when elements required for each of the absorption liquid and the storage liquid are different, it is possible to appropriately cope with this difference.

  According to a second aspect of the present invention, in the first aspect of the invention, electrical energy is supplied to the storage liquid by applying a voltage between the pair of electrodes, and nitrogen oxides absorbed in the storage liquid are reduced. And a reduction and purification means for purifying.

  In the said invention, by supplying an electrical energy to the storage liquid in the said aspect, the nitrogen oxides absorbed by the storage liquid can be reduced and purified. For this reason, the density | concentration of the nitrogen oxide in a storage liquid can be reduced, and the fall of the quantity of the nitrogen oxide which can be absorbed in a storage liquid can be avoided. Thereby, the raise of the density | concentration of the nitrogen oxide in an absorption liquid can be avoided, and the fall of the absorption rate and absorption density of the nitrogen oxide by an absorption liquid can be avoided more suitably.

  The invention according to claim 3 is the invention according to claim 2, wherein the reduction and purification means is absorbed in the storage liquid every time a specified period elapses after the nitrogen oxide is previously reduced by the reduction and purification means. It is characterized by reducing and purifying nitrogen oxides.

  If the time since the previous reduction of nitrogen oxides becomes longer, the total amount of nitrogen oxides that permeate from the absorbing liquid side through the permeable membrane to the storage liquid side increases, so that the absorption of nitrogen oxides in the storage liquid is increased. The amount increases. In view of this point, in the above invention, the nitrogen oxides in the stored liquid can be efficiently reduced and purified by reducing and purifying nitrogen oxides in the above embodiment.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the supply means holds an addition valve for adding the absorbing liquid to the exhaust passage and the absorbing liquid on the surface. And at least one of the contactors for contacting the exhaust gas.

  In the said invention, an absorption liquid can be appropriately supplied to an exhaust passage by using an addition valve and a contactor.

1 is a system configuration diagram according to a first embodiment. FIG. The figure shown about the permeation | transmission aspect of the nitrogen oxide through the permeable film concerning the embodiment. The figure which shows the density | concentration distribution of the absorption liquid and storage liquid through the permeable film concerning the embodiment. The system block diagram concerning 2nd Embodiment. The flowchart which shows the procedure of the reduction | restoration purification process concerning the embodiment. The time chart which shows an example of the reduction | restoration purification process concerning the embodiment. The system block diagram concerning 3rd Embodiment. The figure which shows the structure which supplies the absorption liquid concerning other embodiment. The figure which shows the structure which supplies the absorption liquid concerning other embodiment.

(First embodiment)
Hereinafter, a first embodiment in which an exhaust emission control device according to the present invention is applied to a vehicle on which only an engine is mounted as an in-vehicle main engine will be described with reference to the drawings.

  FIG. 1 shows a system configuration diagram according to the present embodiment.

  The illustrated engine 10 is a compression ignition internal combustion engine (diesel engine). The combustion chamber 12 of each cylinder of the engine 10 is provided with an electromagnetically driven fuel injection valve 14 protruding into the combustion chamber 12. High pressure fuel (light oil) is supplied to the fuel injection valve 14 from a pressure accumulation container (common rail) (not shown), and high pressure fuel is injected and supplied from the fuel injection valve 14 to the combustion chamber 12. The fuel injected and supplied to the combustion chamber 12 and the intake air introduced from the intake passage 16 into the combustion chamber 12 are used for combustion by compression of the combustion chamber 12. The energy generated by the combustion is extracted as rotational energy of the output shaft (crankshaft 18) of the engine 10. A crank angle sensor 20 that detects the rotation angle of the crankshaft 18 is provided in the vicinity of the crankshaft 18.

  The intake air and fuel used for combustion are discharged into the exhaust passage 22 as exhaust. In the exhaust passage 22, as an exhaust aftertreatment device, an oxidation catalyst (DOC 24) that oxidizes nitrogen oxides (NOx) contained in the exhaust and the particulate matter (PM) in the exhaust are captured in order from the upstream side. A diesel particulate filter (DPF 26) that collects and a NOx removal device 28 that removes NOx in the exhaust are provided. The DOC 24 is a member having a function of oxidizing nitrogen monoxide (NO) in the exhaust gas into nitrogen dioxide (NO 2). In the present embodiment, NOx includes at least one of nitric oxide NO, nitrogen dioxide NO2, and nitrate ions.

  The NOx removal device 28 includes a tank 30, a circulation pump 32, an addition valve 34, a contactor 36, and the like. Specifically, the inside of the tank 30 is partitioned by the permeable membrane 38 into an absorption liquid storage part 32a and a storage liquid storage part 32b. Each of the absorption liquid storage part 32a and the storage liquid storage part 32b stores the absorption liquid A and storage liquid B that absorb NOx.

  More specifically, as shown in FIG. 2, the permeable membrane 38 is made of, for example, an organic polymer, and is supported by a support 38a made of porous ceramic or the like to ensure strength. The permeable membrane 38 has a large number of pores penetrating in the thickness direction. Specifically, the diameters of these pores are larger than the size (for example, 0.22 nm) of NOx (for example, NO2 and nitrate ions, represented by “◯” in the figure) absorbed in the absorbing liquid A. And it is smaller than the molecular size of the absorption liquid A and the storage liquid B (for example, 0.3 nm). That is, the permeable membrane 38 has a function of selectively transmitting NOx absorbed in the absorption liquid A of the absorption liquid storage section 32a to the storage liquid B side through itself. Thereby, it is possible to transmit only NOx from the absorbing liquid A side to the storing liquid B side while partitioning the absorbing liquid A and the storing liquid B.

  In the present embodiment, the absorbing liquid A and the storage liquid B are ionic liquids, alkaline aqueous solutions (for example, NaOH aqueous solution, NH3 aqueous solution), water (for example, engine cooling water), and the like, with chemical changes. A substance that absorbs (chemical adsorption) NOx is assumed, and different substances are assumed for the absorbing liquid A and the storage liquid B. The reason why different kinds of substances are assumed here is to appropriately cope with different elements (NOx absorption ability) required for each of the absorption liquid A and the storage liquid B. The absorption capacity of NOx required for each of the absorption liquid A and the storage liquid B will be described. In this embodiment, the absorption liquid A has the capacity to absorb NOx in the exhaust gas in a shorter time than the storage liquid B. Is assumed. In order to realize this, for example, the absorption liquid A has a higher NOx absorption amount (NOx absorption rate) per unit time such as a higher mass transfer coefficient than the storage liquid B (for example, water) (for example, ionic liquid). ). In addition, it is assumed that the storage liquid B has the ability to have a larger maximum storage amount of NOx than the absorption liquid A. In order to realize this, for example, a storage liquid B having a higher NOx absorption amount (NOx absorption density) per unit amount than the absorbing liquid A (for example, ionic liquid) (for example, an alkaline aqueous solution) may be employed. .

  Returning to the description of FIG. 1, the absorbing liquid storage unit 32 a and the addition valve 34 are connected via a circulation passage 40, and a circulation pump 32 is provided on the circulation passage 40. Specifically, the circulation pump 32 is an electric type that pumps up the absorption liquid A stored in the absorption liquid storage section 32 a and pumps it to the addition valve 34.

  The addition valve 34 is an electromagnetically driven valve body that supplies the absorbing liquid A to the exhaust passage 22. Specifically, the addition valve 34 is provided so as to eject the absorbing liquid A toward the contactor 36.

  The contactor 36 includes a holding body 36a that holds the absorbing liquid A and a case 36b that accommodates the holding body 36a therein, and is a member that has a function of bringing the absorbing liquid A into contact with the exhaust gas. Specifically, the contactor 36 is provided on the downstream side of the addition valve 34 in the exhaust passage 22. Specifically, the case 36b included in the contactor 36 is connected to the exhaust passage 22 so that the exhaust gas flows through the case 36b. The holding body 36a has, for example, a plurality of walls extending in parallel with the flow direction of the exhaust gas and is configured to be able to flow the exhaust gas, and is exposed to the exhaust gas flowing through the case 36b. Has been placed.

  In such a configuration, when the absorbing liquid A is injected and supplied from the addition valve 34 to the exhaust passage 22, the absorbing liquid A and the exhaust come into contact with each other, so that NOx in the exhaust is absorbed by the absorbing liquid A. Specifically, NOx in the exhaust is directly absorbed by the absorbing liquid A supplied by injection. Further, the absorbed liquid A sprayed and supplied is held in contact with the holding body 36a, and NOx is absorbed by the exhaust gas coming into contact with the absorbing liquid A held in the holding body 36a.

  The absorbing liquid A injected and supplied from the addition valve 34 and absorbing NOx is recovered in the absorbing liquid storage portion 32a of the tank 30. Specifically, the absorbed liquid A after being sprayed is moved to the lower part of the case 36b or collected by the demister 42 provided on the exhaust downstream side in the case 36b, and then is absorbed in the lower part in the case 36b. It is recovered in the absorbing liquid storage part 32a through the provided recovery passage 44. The demister 42 is a member for avoiding the absorption liquid A from being released to the atmosphere.

  The electronic control unit (hereinafter referred to as ECU 46) is mainly composed of a microcomputer composed of a well-known CPU, ROM, RAM and the like. An output signal of the crank angle sensor 20 is input to the ECU 46. The ECU 46 performs combustion control of the engine 10 such as fuel injection control by the fuel injection valve 14 by executing various control programs stored in the ROM based on input signals from the respective sensors.

  In particular, the ECU 46 performs NOx purification control such as drive control of the circulation pump 32 and injection control by the addition valve 34. According to these controls, the absorption liquid A is circulated through the absorption liquid A through the absorption liquid A through the absorption liquid storage 32a → circulation passage 40 → addition valve 34 → contactor 36 → recovery passage 44 → absorption liquid storage 32a. NOx can be absorbed. According to such control, NOx in the exhaust can be appropriately removed in an operation region where the temperature of the exhaust system is low, for example, when the engine 10 is started.

  Here, when the state in which the absorbing liquid A circulates through the path and absorbs NOx in the exhaust gas is continued, the concentration of NOx in the absorbing liquid A increases. When the concentration of NOx in the absorption liquid A increases, the NOx absorption rate of the absorption liquid A and the NOx absorption density of the absorption liquid A decrease, so that the absorption liquid A can appropriately absorb NOx in the exhaust gas. There is concern about disappearing.

  In order to solve such a problem, in the present embodiment, NOx absorbed in the absorbing liquid A is moved to the storage liquid B side and stored, thereby suppressing an increase in the concentration of NOx in the absorbing liquid A. . Hereinafter, a mode of reducing the concentration of NOx in the absorbing liquid A will be described with reference to FIG.

  FIG. 3 shows an example of a state in which the concentration of NOx in the absorbing liquid A is lowered by moving NOx in the absorbing liquid A to the storage liquid B through the permeable membrane 38. Specifically, in the figure, the horizontal axis indicates the distance from the permeable membrane 38 to the absorption liquid A side and the storage liquid B side, and the vertical axis indicates the concentration of each NOx in the absorption liquid A and the storage liquid B. Yes.

  The example indicated by the broken line in the figure shows a case where the absorption liquid A is continuously used and the concentration of NOx in the absorption liquid A is increased more than the concentration of the storage liquid B. Here, due to the concentration difference between the absorbing liquid A and the storage liquid B, NOx in the absorbing liquid A permeates to the storage liquid B side through the permeable membrane 38, so that NOx diffuses into the storage liquid B. As a result, as shown by the solid line in the figure, the NOx concentrations of the absorbing liquid A and the storage liquid B are in an equilibrium state, and the NOx concentrations in these liquids are substantially the same. That is, the concentration of NOx in the absorbing liquid A decreases.

  According to the configuration described above, an increase in the concentration of NOx in the absorption liquid A can be suppressed, and a decrease in the NOx absorption rate of the absorption liquid A can be avoided. Thereby, deterioration of exhaust characteristics can be avoided.

  It is desirable that the ECU 46 performs a notification process for notifying the user that the storage liquid B should be replaced before the concentration of NOx in the storage liquid B becomes excessively high. As a result, the stored liquid B in the tank 30 is replaced by a user or the like, so that the exhaust characteristics can be maintained well. Here, the notification process may be performed, for example, when it is determined that the specified travel distance has elapsed since the storage liquid B was replaced last time.

  According to the embodiment described in detail above, the following effects can be obtained.

  (1) NOx in the exhaust gas was absorbed and removed by the absorbing liquid A, and the NOx absorbed in the absorbing liquid A via the permeable membrane 38 was moved to the storage liquid B. For this reason, an increase in the concentration of NOx in the absorption liquid A can be suppressed, and a decrease in the NOx absorption rate of the absorption liquid A can be avoided. Thereby, deterioration of exhaust characteristics can be avoided appropriately.

  Furthermore, even when the cost of the absorbing liquid A (ionic liquid) is high, for example, by using a low cost (water) as the storage liquid B, the amount of the absorbing liquid A used for NOx absorption is reduced. Therefore, an increase in cost due to the introduction of the NOx removing device 28 can be suitably suppressed.

(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  FIG. 4 shows a system configuration diagram according to the present embodiment. In FIG. 4, the same members as those in FIG. 1 are given the same numbers for the sake of convenience. Further, in FIG. 4, the configuration on the upstream side of the NOx removal device 28 in the exhaust passage 22 is omitted because it is the same configuration as in FIG.

  As shown in the figure, the NOx removal device 28 is further provided with a reduction purification device 48 having a function of reducing and purifying NOx. Specifically, the reduction and purification device 48 is a pair of the power supply device 50 and the power supply device 50 that is electrically connected to the storage liquid B of the storage liquid storage section 32b (or a part thereof). A pair of electrodes (a positive electrode 51a and a negative electrode 51b) are provided.

  In the storage liquid storage section 32b, a discharge passage 52 communicating with the exhaust downstream side of the case 36b in the exhaust passage 22 in order to release N2 and O2 generated when electrolysis, which will be described later, is performed by the reduction purification device 48. Is provided.

  In such a configuration, when a voltage is applied between the electrodes 51a and 51b by the power supply device 50, NOx absorbed in the storage liquid B by electrolysis is reduced, so that O2 is generated from the vicinity of the positive electrode 51a. N2 is generated from the negative electrode 51b. These O 2 and N 2 are discharged to the exhaust passage 22 through the discharge passage 52. Thereby, NOx in the storage liquid B is reduced and purified, and the concentration of NOx in the storage liquid B can be reduced.

  As the electrodes 51a and 51b, an ionization tendency is avoided in order to avoid a situation in which the electrode is corroded by the storage liquid B or a salt is generated by the reaction between the storage liquid B and the electrode, so that electrolysis is not promoted. It is desirable to use a metal with a small (for example, copper, silver, platinum, gold). Further, as the storage liquid B, it is desirable to employ a liquid whose NOx absorption capacity does not decrease by electrolysis (high withstand voltage).

  The ECU 46 performs a reduction purification process that manipulates the energized state between the electrodes 51a and 51b in order to reduce and purify NOx in the storage liquid B by electrolysis.

  FIG. 5 shows the procedure of reduction purification processing by electrolysis according to the present embodiment. This process is repeatedly executed by the ECU 46 at a predetermined cycle, for example.

  In this series of processes, first, in step S10, the total absorption of NOx by the storage liquid B is based on the engine speed NE calculated from the output value of the crank angle sensor 20 and the fuel injection amount Q from the fuel injection valve 14. The quantity Gtotal is calculated. In the present embodiment, the NOx absorption amount by the storage liquid B from the timing when the reduction purification process was executed to the present time is calculated as the total absorption amount Gtotal. Note that the engine rotational speed NE and the fuel injection amount Q are used in calculating the total NOx absorption amount Gtotal because it is possible to estimate the NOx emission amount from the engine 10 according to these parameters. .

  In the subsequent step S12, the concentration Cn of NOx in the storage liquid B is calculated based on the total NOx absorption amount Gtotal. Here, the NOx concentration Cn tends to increase as the total absorption amount Gtotal increases.

  In a succeeding step S14, it is determined whether or not an execution condition for the reduction and purification process is satisfied. In the present embodiment, the execution condition is a condition that the specified period has elapsed since the previous execution of the reduction purification process. This condition is a condition for efficiently reducing and purifying NOx in the storage liquid B. That is, when electrolysis is performed in a situation where a large amount of NOx exists in the vicinity of both electrodes 51a and 51b, for example, a larger amount of NOx can be reduced and purified than in a case where electrolysis is performed in a situation where there is little NOx near these electrodes. Can do.

  Here, in the present embodiment, the specified period is a period from the previous execution of the reduction purification process until the concentration of NOx in the stored liquid B becomes equal to or higher than the specified concentration α. The prescribed concentration α may be set as a value that can grasp that the NOx concentration of the storage liquid B has risen to such an extent that the absorption liquid A cannot properly absorb NOx in the exhaust gas.

  If an affirmative determination is made in step S14, the process proceeds to step S16 to perform reduction purification processing by electrolysis. Specifically, a voltage is applied between the electrodes 51a and 51b by the power supply device 50 to energize. Here, the period during which the reduction purification process is performed (purification process execution period) is determined in advance by experiments or the like as the time required to set the NOx concentration Cn to a threshold value (for example, a value close to 0) smaller than the specified concentration α. Just do it.

  When a negative determination is made in step S14 or when the process of step S16 is completed, the series of processes is temporarily terminated.

  FIG. 6 shows an example of the reduction and purification process according to the present embodiment.

  In the example shown in the figure, during the period from time t1 to time t2, NOx in the exhaust gas is removed by the NOx removal device 28, so that NOx is absorbed in the storage liquid B, and the concentration of NOx in the storage liquid B Rises. Thereafter, when it is determined that the concentration Cn of NOx in the storage liquid B has reached the specified concentration α at time t2, the reduction purification process is started. And this process is continued by the said purification process execution period T1 (time t2-t3), and the density | concentration Cn of NOx in the storage liquid B falls.

  As described above, in the present embodiment, reduction of NOx absorption rate and absorption density by the absorbing liquid A can be more preferably avoided by performing reduction purification treatment by electrolysis.

  According to the embodiment described above in detail, the following effects can be obtained in addition to the effects of the first embodiment.

  (2) NOx absorbed in the storage liquid B was reduced and purified by reduction and purification treatment by electrolysis. Accordingly, by avoiding a decrease in the NOx storage capacity of the stored liquid B, an increase in the NOx concentration in the absorbent liquid A can be avoided, and a decrease in the NOx absorption capacity by the absorbent liquid A can be more suitably avoided. be able to.

  Further, since NOx in the storage liquid B is automatically reduced and purified by the reduction and purification process, maintenance performance can be improved, for example, the frequency of replacement of the storage liquid B by a user or the like can be reduced.

  Furthermore, since the absorption liquid A does not require high electric resistance, a liquid having low electric resistance as compared with the storage liquid B can be adopted.

  (3) When it is determined that the concentration Cn of NOx in the storage liquid B is equal to or higher than the specified concentration α, a reduction purification process is performed. Thereby, for example, compared with the case where the control logic that always performs the reduction purification treatment is adopted, the reduction purification amount of NOx per unit electric energy required for the electrolysis can be increased. Reduction and purification can be performed efficiently.

(Third embodiment)
Hereinafter, the third embodiment will be described with reference to the drawings with a focus on differences from the second embodiment.

  FIG. 7 shows a system configuration diagram according to the present embodiment. In FIG. 7, the same members as those in FIG. 4 are given the same numbers for the sake of convenience.

  As illustrated, the reduction and purification device 54 according to the present embodiment includes a pair of electrodes 56a and 56b and a plasma generator 56 including a high voltage generator 56c that applies a high voltage to these electrodes, and an N2 separator 58. It is prepared for. Specifically, of the pair of electrodes 56a and 56b, the ground electrode 56a is immersed in the storage liquid B. Further, the discharge electrode 56b is exposed from the surface of the storage liquid B when the storage liquid B is stationary.

  The N2 separator 58 is connected to the exhaust downstream side of the case 36 b in the exhaust passage 22, and separates N2 in the exhaust and supplies it to the plasma generator 56.

  In such a configuration, when a high voltage is applied between the discharge electrode 56b and the ground electrode 56a by the high voltage generator 56c, streamer discharge occurs. When N2 is supplied from the N2 separator 58 to the plasma generator 56 in a state where this discharge occurs, N2 is dissociated by streamer discharge and N radicals are generated. Then, N radicals are sprayed onto the surface of the storage liquid B, whereby NOx is reduced and purified. Thereby, NOx in the storage liquid B is reduced and purified, and the concentration of NOx in the storage liquid B can be reduced.

  Thus, in this embodiment, NOx in the storage liquid B can be reduced and purified using the plasma generator 56.

(Other embodiments)
Each of the above embodiments may be modified as follows.

  The configuration for supplying the absorbing liquid A to the exhaust passage 22 is not limited to those exemplified in the above embodiments. For example, as shown in FIG. 8, it is good also as a structure which does not equip the case 36b of the contactor 36 with the holding body 36a. For example, as shown in FIG. 9, the addition liquid 34 may not be provided, and the absorbing liquid A may be directly supplied to the holding body 36 a in the case 36 b via the circulation passage 40. In this case, in order to allow exhaust to flow into the case 36b from vertically above, the case 36b is connected to the exhaust passage 22 so that the inlet of the case 36b faces vertically upward, and the circulation passage 40 from above vertically toward the inlet of the case 36b. It is desirable that the absorbing liquid A be supplied via Thereby, it can be expected that the supplied absorbing liquid A spreads so as to extend in the horizontal direction of the holding body 36a, so that the holding liquid 36a is appropriately held by the holding body 36a.

  The number of addition valves 34 provided in the exhaust passage 22 is not limited to one, and may be, for example, a plurality.

  The absorbing liquid A and the storage liquid B are not limited to those exemplified in the above embodiments. For example, it may be an ionic liquid, an alkaline aqueous solution, water, or the like, and a substance that absorbs NOx (physical adsorption) without chemical change.

  The method for calculating the total NOx absorption amount Gtotal is not limited to that exemplified in the second embodiment. For example, a NOx sensor that detects NOx is provided between the DPF 26 and the addition valve 34 in the exhaust passage 22, and the NOx emission amount of the engine 10 is directly detected using this sensor. The total absorption amount Gtotal may be calculated.

  The method for grasping the concentration Cn of NOx in the storage liquid B is not limited to the one exemplified in the second embodiment. For example, a sensor that detects the concentration of NOx in the storage liquid B may be provided in the storage liquid storage unit 32b, and the concentration Cn of NOx may be detected based on the output value of this sensor.

  The execution conditions for the reduction and purification process are not limited to those exemplified in the second embodiment. For example, it may be a condition that the total absorption amount Gtotal is equal to or greater than a specified amount. For example, it may be a condition that the travel distance of the vehicle becomes equal to or more than a specified distance since the reduction purification process was executed last time.

  Further, for example, the logical product of the execution condition and the condition that the specified period has elapsed since the previous execution of the reduction purification process and the condition that the vehicle is stopped (the vehicle traveling speed is 0) are true. It is good also as the condition. Here, the condition that the vehicle is stopped is for avoiding a situation in which NOx cannot be appropriately reduced and purified by the reduction and purification process. That is, for example, in the second embodiment described above, the behavior of the storage liquid B (behavior of the liquid and the liquid surface, such as a flow of the storage liquid B occurs between the electrodes 51a and 51b due to the vehicle shaking, etc.) ) May become unstable. In this case, electrophoresis of NOx absorbed and ionized in the storage liquid B is hindered, and there is a possibility that NOx in the storage liquid B cannot be appropriately reduced and purified by the reduction and purification treatment. For this reason, by providing the condition that the vehicle is stopped, a situation in which the reduction and purification cannot be appropriately performed is avoided.

  -The vehicle to which the present invention is applied is not limited to a vehicle equipped with only an engine as an in-vehicle main unit. For example, you may apply to a hybrid vehicle provided with a rotary machine with an engine as a vehicle-mounted main machine. Also, for example, a battery that includes only a rotating machine as an in-vehicle main machine and that serves as a power supply source for the rotating machine, an auxiliary generator for charging the battery, and an engine that serves as a power supply source for the auxiliary generator You may apply to the series hybrid vehicle (what is called a range extender vehicle) provided. In these cases, compared to a vehicle on which only the engine is mounted as the in-vehicle main machine, for example, the frequency of use of the engine is reduced in a low-speed traveling speed range, and it is likely that a situation in which the temperature of the exhaust system is difficult to rise is likely to occur. . For this reason, by applying the present invention in which appropriate purification can be expected from a region where the temperature of the exhaust system is low, deterioration of exhaust characteristics can be avoided.

  The plasma generator 56 is not limited to the one exemplified in the third embodiment. For example, an underwater discharge type in which both the pair of electrodes 56a and 56b are immersed in the stored liquid may be used.

  The difference in elements required for the absorption liquid A and the storage liquid B is not limited to those exemplified in the above embodiments (NOx absorption capacity, cost, electric resistance), but the fluidity of the liquid in the tank 30 Other differences in requirements are also possible. Even in this case, it can be expected that the above difference is appropriately handled by applying the present invention having a configuration in which the inside of the tank 30 is partitioned by the permeable membrane 38 and different kinds of liquid are stored.

  The engine 10 is not limited to a compression ignition type engine, but may be, for example, a direct injection type spark ignition type engine.

  DESCRIPTION OF SYMBOLS 10 ... Engine, 22 ... Exhaust passage, 28 ... NOx removal apparatus (one embodiment of exhaust gas purification apparatus of internal combustion engine), 30 ... Tank, 34 ... Addition valve, 36 ... Contactor, 38 ... Permeation membrane, 48, 54 ... Reduction purification device, A ... absorbing liquid, B ... storage liquid.

Claims (4)

First storage means for storing an absorbing liquid that absorbs nitrogen oxides in the exhaust gas discharged from the internal combustion engine into the exhaust passage;
Supply means for supplying the absorption liquid stored in the first storage means to the exhaust passage;
A second storage means for storing a storage liquid that is different from the absorption liquid and absorbs nitrogen oxides;
The storage liquid has a nitrogen oxide absorption density, which is an absorption amount of nitrogen oxide per unit amount, higher than the nitrogen oxide absorption density of the absorption liquid,
The first storage means and the second storage means are partitioned by a permeable membrane,
The first storage means collects and stores the absorbing liquid supplied to the exhaust passage by the supply means,
The permeable membrane has a function of reducing the concentration of nitrogen oxides in the absorbing liquid by selectively transmitting nitrogen oxides absorbed in the absorbing liquid to the storage liquid side. An exhaust purification device for an internal combustion engine.   The apparatus further comprises reduction purification means for supplying electric energy to the storage liquid by applying a voltage between a pair of electrodes and reducing and purifying nitrogen oxides absorbed in the storage liquid. Item 2. An exhaust emission control device for an internal combustion engine according to Item 1.   The reduction purification unit reduces and purifies nitrogen oxides absorbed in the stored liquid every time a predetermined period has elapsed since the previous reduction of nitrogen oxides by the reduction purification unit. 3. An exhaust emission control device for an internal combustion engine according to 2.   2. The supply means is at least one of an addition valve for adding the absorbing liquid to the exhaust passage, and a contactor for holding the absorbing liquid on the surface and bringing it into contact with exhaust gas. The exhaust gas purification device for an internal combustion engine according to any one of claims 3 to 4.

Images