JP3642032B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine.
[0002]
[Prior art]
From the viewpoint of fuel economy, a lean burn engine has been developed in a gasoline engine, and the application range of a diesel engine is being expanded. In diesel engines and lean-burn gasoline engines, fuel is burned under a large excess of air, so emissions of incomplete combustion components HC (hydrocarbon) and CO (carbon monoxide) are low, but in the air nitrogen and burning and the rest of the oxygen becomes large emissions of the NO _X generated in response (nitrogen oxides) in the.
[0003]
In order to reduce the emission into the atmosphere of such harmful NO _X to be relatively large amounts produced, it is known to arrange the storage reduction NO _X catalyst exhaust system. NO storage reduction NO _X catalyst, while absorbing NO _X in the form of nitrate at high oxygen concentration in the exhaust gas, while releasing NO _X which the oxygen concentration in the exhaust gas absorbed to be lower, which released _X is reduced and purified by reducing components such as HC and CO in the exhaust gas. Thus, in the internal combustion engine having a storage reduction NO _X catalyst, favorably absorb NO _X from the exhaust gas of a high oxygen concentration lean combustion, by periodic rich mixture burn operation (rich spike operation) In addition, the oxygen concentration in the exhaust gas can be reduced and reducing components such as HC and CO can be present in the exhaust gas, so that the absorbed NO _x can be reduced and purified well without being released into the atmosphere.
[0004]
By the way, the fuel of the internal combustion engine contains sulfur, and SO _x is also generated during combustion. SO _X can be oxidized similarly to the NO _X is absorbed in the form of sulfate to storage reduction NO _X catalyst. Sulfates, in order to be stable substance, hardly released from the usual rich mixture be carried out-burn operation storage reduction NO _X catalyst, SO _X storage amount is increased gradually. For storable amount of nitrate or sulfate in the occlusion reduction type NO _X catalyst is finite, storage capacity increase of sulfate in the occlusion reduction type NO _X catalyst (hereinafter, referred to as SO _X poisoning) them if, since storable amount of nitrates is to be reduced by that amount, reducing the storage amount of sulfate in the occlusion reduction type NO _X catalyst (hereinafter, referred to as sO _X poisoning restoration or sulfur desorption regeneration) let be Eventually, NO _X cannot be absorbed at all.
[0005]
Sulfates, storage reduction NO _X catalyst becomes a high temperature of about 600 ° C, and, when the oxygen concentration of the ambient drops, can be released from the catalyst as a gas, for example, decomposed into SO _2. Thereby, the sulfur for removal of the release play (SO _X poisoning recovery), for example, must be by burning HC and CO on the storage reduction NO _X catalyst raising the temperature of the storage reduction NO _X catalyst is there. In order to carry out this, the operation at the rich air-fuel ratio is regularly performed.
[0006]
The sulfur desorption regeneration (SO _X poisoning recovery) aims to reduce and release K ₂ SO ₄ to SO ₂ . However, since the operation is performed with a strong rich air-fuel ratio, a reducing component such as H ₂ exists, and SO ₂ once desorbed may be further reduced to S or H ₂ S. This S or H ₂ S is occluded again in the form of K ₂ SO _{4 by} the catalyst, and the catalyst is poisoned. Thus, the next desorption is suppressed, and it takes a long time to completely release the sulfur component from the catalyst as SO ₂ . For this reason, the SO _X poisoning recovery process cannot be easily performed in normal traveling, and the NO _X purification rate decreases. Even if the SO _X poisoning recovery process can be performed, the fuel consumption is reduced. Has been worsening.
[0007]
In order to shorten the processing time for sulfur desorption regeneration (SO _X poisoning recovery), it has been proposed to suppress the reduction to S or H ₂ S by repeating lean / rich with the average air-fuel ratio made weakly rich. ing. However, microscopically, the regeneration time is only slightly shortened by repeating the poisoning and the poisoning recovery by reoxidation. In addition, in order to suppress re-poisoning, when attempting to desorb sulfur under an air-fuel ratio close to stoichiometry, the reducing power is weak and sulfur desorption hardly occurs.
[0008]
Meanwhile, in order to improve the NO _X purification rate by storage reduction NO _X catalyst, it is effective to oxidize advance to NO ₂ NOx stored difficult NO. Therefore, JP-A-11-324652 discloses a storage-reduction NO a plasma generator disposed upstream of the _X catalyst, exhaust gas purification device having improved storage capability by converting NO to NO ₂ . However, in this exhaust purification device, if the plasma generator is always operated to generate plasma, there is a problem that energy loss is large.
[0009]
[Problems to be solved by the invention]
The present invention has been made in view of the problems described above, efficiency in the purpose, an exhaust purification device arranged storage reduction NO _X catalyst and the plasma generating apparatus in an exhaust passage of an internal combustion engine, a plasma generator The aim is to improve the purification rate by expediting the release and reduction of harmful substances such as NO _x and SO _x stored in the catalyst while operating well to suppress energy consumption.
[0010]
[Means for Solving the Problems]
To achieve the above object, first, according to the aspect, in the exhaust passage upstream of the suction storage reduction NO _X catalyst with storage reduction NO _X catalyst is disposed in the exhaust passage or intake storehouse of the present invention in the exhaust purification device of reduced NO _X catalyst integrally with an internal combustion engine in which the plasma generator is located, the plasma generated when processing for releasing harmful substances occluded in the occlusion reduction type NO _X catalyst is performed An exhaust emission control device for an internal combustion engine is provided, characterized in that a control means for operating the device is provided.
[0011]
In this exhaust purification apparatus, when executing the process of releasing harmful substances occluded in the occlusion reduction type NO _X catalyst, i.e. for poisoning recovery of the rich spike operation during or SO _X for the reduction and purification of the NO _X During the rich operation, since the plasma generator is activated to generate plasma, the release of harmful substances and the reduction reaction proceed quickly, and the plasma generator does not operate in all regions, so that energy consumption is suppressed.
[0012]
Further, according to the second aspect of the present invention, preferably, the control means, the temperature of the occlusion reduction type NO _X catalyst is higher than the temperature or said first time is less than a predetermined first temperature Even when the temperature is equal to or higher than the predetermined second temperature, the plasma generator is further operated. When the catalyst temperature is high or low, the NO _x absorption rate is low. However, in this exhaust purification device, the plasma generation device operates to generate plasma even in such a case, so that the NO _x purification rate is improved. Is planned.
[0013]
Further, according to the third aspect of the present invention, preferably, the front oxidation catalyst of storage reduction NO _X catalyst is arranged, the plasma generating apparatus of said occlusion reduction type NO _X catalyst and the oxidation catalyst Arranged between. In this exhaust purification device, an oxidation catalyst is disposed in front of the plasma generator, so that excess reducing agent is consumed by the oxidation catalyst, and active species such as NO ₂ and active oxygen generated by the action of plasma are reduced. the amount is made to reduce that reacts with agents, so that the sufficient active species into storage reduction NO _X catalyst is sent.
[0014]
In addition, according to a fourth aspect of the present invention, the occlusion reduction type NO _X catalyst is supported particulate material capable collection filter.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0016]
FIG. 1 is a schematic diagram showing the overall configuration of an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention. Reference numeral 10 denotes a main body of a diesel engine or a lean burn gasoline engine. A generator 12 driven by the engine body 10 is connected to the engine body 10. The electricity generated by the generator 12 is stored in the battery 14.
[0017]
Two catalysts are arranged in the exhaust passage 20 extending from the engine body 10. Downstream of the catalyst is storage reduction NO _X catalyst 22, the upstream side of the catalyst is an oxidation catalyst 24. Further, between the oxidation catalyst 24 and the storage reduction NO _X catalyst 22, the plasma generator 26 is disposed. In the plasma generator 26 may be integrally mounted on the storage reduction NO _X catalyst 22.
[0018]
The plasma generator 26 is supplied with power from a power supply device 28. The power supply device 28 converts the DC voltage supplied from the battery 14 into an AC voltage, and adjusts the frequency and the AC voltage value to change the input power to the plasma generator 26.
[0019]
The electronic control unit (ECU) 30 controls the engine body 10 and the power supply device 28 and operates by receiving power supplied from the battery 14. Electronic control unit 30 detects the operating state of the engine body 10, the air-fuel ratio (A / F) sensor 32 provided upstream of the oxidation catalyst 24, the plasma generating apparatus 26 and the storage reduction NO _X catalyst 22 The output signals of various sensors such as the exhaust temperature sensor 34 provided between the two are received. Further, the electronic control unit 30 can detect a travel distance from a travel distance counter 36 provided in a vehicle on which the engine is mounted.
[0020]
FIG. 2 is a flowchart showing a procedure of exhaust purification processing executed by the ECU 30. First, in step 102, A / F sensor 32, respectively the air-fuel ratio from the output of the exhaust temperature sensor 34 and the travel distance counter 36, together with the exhaust temperature and the travel distance is detected, storage reduction NO _X catalyst from the engine operating condition A catalyst temperature of 22 is estimated.
[0021]
Next, at step 104, it is determined whether or not the travel distance from the previous execution of the SO _X poisoning recovery process is greater than or equal to a predetermined value. When the travel distance is equal to or greater than the predetermined value, the process proceeds to step 106, and the SO _X poisoning recovery process is executed. When the travel distance is less than the predetermined value, the process proceeds to step 108. Note that the execution timing of the recovery process may be determined based on a decrease in the NO _X storage amount of the NO _X catalyst 22.
[0022]
In step 106, the SO _X poisoning recovery process is executed while operating the plasma generator 26 by adjusting the frequency and voltage value of the supplied AC voltage according to the exhaust gas temperature and the air-fuel ratio. In the SO _X poisoning recovery process, control is performed so that the center of the air-fuel ratio becomes stoichiometric or weakly rich. For this reason, the amount of reducing components such as H ₂ and CO in the exhaust gas is small compared to the conventional SO _X poisoning recovery process performed under a strong rich air-fuel ratio. However, since the reducing component is activated by the operation of the plasma generator 26 and its reducing power is strong, sulfur can be desorbed from the catalyst in a short time even with a small amount of the reducing component.
[0023]
Since only a small amount of reducing component such as H ₂ is produced, the main component due to the decomposition of sulfate becomes SO ₂ , and re-poisoning of the catalyst is suppressed. That is, if there is an excess of hydrogen,
SO ₄ ^2- + (HC * or H ₂ or CO) → SO ₂ + CO ₂ , H ₂ O
SO ₂ + 2H ₂ → S + 2H ₂ O
SO ₂ + 3H ₂ → H ₂ S + 2H ₂ O
As a result of this reaction, S and H ₂ S are generated and re-poisoning occurs. However, in the present embodiment, because a SO _X poisoning restoration process by activating a small amount of reducing gas generated by the operation of the air-fuel ratio of near stoichiometric plasma to decompose the sulfate SO ₂ As a result, no further reduction to S or H ₂ S occurs and no re-poisoning occurs. After execution of step 106, the routine ends.
[0024]
In step 108 that is executed when the execution condition of the SO _X poisoning recovery process is not satisfied in step 104, it is determined whether or not the rich spike operation is being executed. That is, in this embodiment, the rich spike operation for reducing and purifying regularly NO _X have been made in the fuel injection control is separately performed, judging whether or not in such rich spike operation Is done.
[0025]
If the rich spike operation is being performed, the process proceeds to step 110, and the plasma generator 26 is operated while adjusting the frequency and voltage value of the supplied AC voltage in accordance with the exhaust temperature and the air-fuel ratio. Thus, reduction components in the exhaust gas (HC) is activated, reducing the occluded NO _X is promoted to the storage reduction NO _X catalyst 22. After execution of step 110, the routine ends.
[0026]
When it is determined that it is not during the rich spike operation in step 108, the process proceeds to step 112, the catalyst temperature TC of the occlusion reduction type NO _X catalyst 22 whether less than a predetermined temperature T ₁ is determined. In the catalyst low temperature region where TC <T ₁ is established, the routine proceeds to step 110 where the plasma generator 26 is operated. Thus,
NO + (1/2) O ₂ → NO ₂
Thus, NO is converted into NO ₂ that is easily stored in the NO _x catalyst 22.
[0027]
When it is determined that there is no low-temperature region in step 112, the process proceeds to step 114, the storage-reduction type NO _X temperature T ₂ the catalyst temperature TC is given catalyst 22 (T ₁ <T ₂₎ is determined is greater than or not is The In the catalyst high temperature region where T ₂ <TC is established, the routine proceeds to step 110 where the plasma generator 26 is operated. In the high temperature region of the catalyst, NO _x is hardly occluded, but the active oxygen generated in the plasma reacts with NO _x , whereby the oxidation of NO _x to NO ₂ is promoted and the occlusion in the catalyst proceeds. NO _X purification rate is improved.
[0028]
When the conditions are not satisfied in all of steps 104, 108, 112, and 114, the process proceeds to step 116, and the operation of the plasma generator 26 is stopped. Thus, since the plasma generator does not operate in all regions, energy consumption is suppressed.
[0029]
Incidentally, in order to operate the plasma generator 26, when the voltage value and frequency of the AC voltage supplied to the plasma generator 26 is adjusted in accordance with the exhaust temperature and the air-fuel ratio, the pre-warm-up of the occlusion reduction type NO _X catalyst 22 It is preferable to switch the control map between after and warm-up. FIGS. 3 and 4 are diagrams illustrating a map in which the voltage value and frequency of the AC voltage supplied to the plasma generator are determined according to the exhaust gas temperature and the air-fuel ratio (A / F). FIG. FIG. 4 is applied before the machine and after the catalyst is warmed up. According to these maps, the frequency is increased before catalyst warm-up compared to after catalyst warm-up, which corresponds to the fact that the catalyst is not activated before catalyst warm-up. It is.
[0030]
In the present embodiment, front to the oxidation catalyst 24 of the occlusion reduction type NO _X catalyst 22 is arranged, configured and the plasma generator 26 is disposed between the oxidation catalyst 24 and the storage reduction NO _X catalyst 22 It has become. Thus, excess reducing agent is consumed by the oxidation catalyst 24, active species such as NO ₂ and active oxygen produced by the action of the plasma is made to reduce the amount that reacts with the reducing agent, the storage reduction NO _X catalyst 22 Sufficient active species will be sent.
[0031]
It is also possible to adopt a configuration in which occlusion reduction type NO _X catalyst is supported particulate material capable collection filter. In other words, in diesel engines, the amount of particulates (particulates) emitted increases, but particulates cannot be reduced sufficiently by improving combustion alone. Therefore, particulates are trapped in the exhaust system as post-processing. In some cases, a filter is provided. In such a case, it is possible to carry the storage reduction NO _X catalyst to the particulate filter.
[0032]
【The invention's effect】
As described above, according to the present invention, the plasma generator is efficiently operated to suppress energy consumption, and the release and reduction of harmful substances such as NO _x and SO _x occluded in the catalyst are accelerated. As a result, the exhaust gas purification rate can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the overall configuration of an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a procedure of exhaust purification processing executed by an electronic control unit.
FIG. 3 is a diagram illustrating a map in which a voltage value and a frequency of an AC voltage supplied to a plasma generator are determined according to an exhaust gas temperature and an air-fuel ratio, and applied before catalyst warm-up.
FIG. 4 is a diagram illustrating a map in which a voltage value and a frequency of an alternating voltage supplied to a plasma generator are determined according to an exhaust gas temperature and an air-fuel ratio, and applied after catalyst warm-up.
[Explanation of symbols]
10 ... engine body 12 ... generator 14 ... battery 20 ... exhaust passage 22 ... storage reduction NO _X catalyst 24 ... oxidizing catalyst 26 ... plasma generator 28 ... power supply apparatus 30 ... electronic control unit (ECU)
32 ... Air-fuel ratio (A / F) sensor 34 ... Exhaust temperature sensor 36 ... Travel distance counter

Claims (5)

With storage reduction NO _X catalyst is disposed in an exhaust passage of absorbent storage reduction NO or the exhaust passage upstream of the _X catalyst absorbent storage reduction NO _X catalyst integrally with an internal combustion engine in which the plasma generator is located In the exhaust purification device,
An oxidation catalyst is disposed in the exhaust passage upstream of the plasma generator,
It said control means for actuating is provided the plasma generator when the storage reduction NO _X catalyst treatment to release the occluded hazardous substances is performed,
The control means operates the plasma generator and controls the center of the air-fuel ratio to be stoichiometric or weakly rich.
An exhaust emission control device for an internal combustion engine, characterized in that: Wherein, said when the temperature of the storage reduction NO _X catalyst is a second temperature above a higher predetermined than the temperature or said first time is less than a predetermined first temperature, further the plasma The exhaust emission control device for an internal combustion engine according to claim 1, wherein the generator is operated. 3. The exhaust gas of an internal combustion engine according to claim 1 , wherein the control means performs control to increase the frequency of the AC voltage supplied to the plasma generator before the catalyst warms up as compared to after the catalyst warms up. Purification equipment. The storage-reduction type NO _X catalyst is supported particulate material capable collection filter, the exhaust purification system of an internal combustion engine according to any one of claims 1 to 3. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 4, wherein the treatment for releasing the harmful substance is for sulfur content.

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