JP4946725B2 - Exhaust gas purification method and exhaust gas purification device - Google Patents

Description

  The present invention relates to an exhaust gas purification method and an exhaust gas purification device, and more particularly, is configured to be able to supply active oxygen upstream of an exhaust gas purification catalyst disposed in an exhaust passage of an engine and an exhaust gas purification method using active oxygen. In addition, the present invention belongs to a technical field for improving exhaust emission.

  In general, in a vehicle such as an automobile using fossil fuel such as gasoline as an energy source, the exhaust gas temperature is relatively low for several tens of seconds immediately after the engine is started, and the exhaust gas purification catalyst disposed in the exhaust passage of the engine It is known that hydrocarbon (HC) and carbon monoxide (CO), which are unburned exhaust gas components, are difficult to purify because catalytic metals such as platinum (Pt) and palladium (Pd) are not activated. ing. As one method for improving this, conventionally, a manifold catalyst called “straight catalyzer” in which the catalyst is disposed directly under the exhaust manifold has been widely adopted. However, this method shortens the time until the catalyst temperature rises to the activation temperature, and is not a fundamental solution to the problem.

  Therefore, hydrocarbon adsorbents such as zeolite are used as the material for the manifold catalyst. That is, after the engine is started, when the exhaust gas temperature is relatively low, unburned hydrocarbons discharged from the engine are adsorbed in the pores of the hydrocarbon adsorbent, and when the exhaust gas temperature rises to about 200 ° C, Unburned hydrocarbons adsorbed on the hydrocarbon adsorbent are released and reacted with a catalytic metal activated to some extent at about 200 ° C. However, since aluminosilicate porous materials such as zeolite have the property that the crystal structure tends to collapse at high temperatures, this method has a problem that the purification performance of the catalyst gradually decreases with time. .

In order to cope with this problem, a method of oxidizing and purifying unburned exhaust gas components using active oxygen such as ozone (O ₃ ) without using a hydrocarbon adsorbent such as zeolite has been proposed. For example, Patent Document 1 discloses that ozone, which is active oxygen, is generated by applying a high voltage to air, and this ozone is supplied upstream of the catalyst in the exhaust passage, and one of the HC contained in the exhaust gas. A technique is disclosed in which a part is converted to CO, and this CO is further oxidized to CO ₂ with a catalyst at a later stage.

Patent Document 2 also discloses a means for generating and supplying active oxygen. That is, in Patent Document 2, a discharge unit and a hydrogen supply unit are provided on the upstream side of the NOx occlusion reduction catalyst disposed in the exhaust pipe of the engine, and it is easy to occlude NO by oxygen radicals or ozone generated by the discharge unit. An exhaust emission control device configured to reduce and purify NO ₂ that is oxidized to NO ₂ and stored in a NOx storage reduction catalyst, and NO ₂ released from the NOx storage reduction catalyst by hydrogen supplied to an exhaust pipe by a hydrogen supply means. It is disclosed.

  Here, in general, active oxygen such as ozone has a strong oxidizing power and has a relatively long life from generation to decomposition at a relatively low temperature of about room temperature. Supplying active oxygen to the exhaust passage upstream of the catalyst until reaching the activation temperature is considered to be one of the effective methods for oxidizing and purifying unburned exhaust gas components of HC and CO. .

JP-A-2005-207316 (paragraphs 0046 to 0050) JP-A-2005-344688 (paragraphs 0005 to 0007)

  As described above, supplying active oxygen such as ozone to the exhaust gas until the exhaust gas temperature rises to the catalyst activation temperature after engine startup is one effective purification method for unburned exhaust gas components. However, on the other hand, the present inventors have studied the effect of active oxygen by changing the composition of the exhaust gas in various ways, and obtained the following knowledge.

That is, when comparing the case where HC is present and the case where HC and NOx coexist as the composition of the exhaust gas, the active oxygen is not supplied at a low temperature until the catalyst is activated. Below, it has been found that the HC purification rate decreases in the latter case (details will be described later with reference to FIG. 8, but the former corresponds to reference C in FIG. 8 and the latter corresponds to reference A). This is only the presence of normal oxygen, it takes precedence of NO of the NOx is oxidized to NO _2, HC is considered to be because it is delayed to oxidize into water and carbon dioxide. In this case, the present inventors have found that when the active oxygen is supplied, the purification rate of HC is significantly improved even when HC and NOx coexist (reference B in FIG. 8). Fall under). This is in addition to the oxidation purify HC by active oxygen, NO is NO ₃ by the active oxygen ^- converted to the active species, the NO ₃ ^- active species is believed to be due to contribute to the oxidation of HC with the active oxygen .

  In the exhaust gas purification method using active oxygen, the present invention reliably improves the purification rate of HC even in the presence of nitrogen oxides in which the oxidation of HC is delayed only by the presence of normal oxygen, and In an exhaust gas purifying apparatus capable of supplying active oxygen to the exhaust passage upstream of the catalyst, after the engine is started, when the exhaust gas temperature is equal to or lower than the catalyst activation temperature, nitrogen oxides that HC oxidation is delayed only by the presence of normal oxygen It is an object to reliably improve the HC purification rate even under the coexistence.

  In order to solve the above problems, the present invention uses the following means.

That is, the invention according to claim 1 of the present application is an exhaust gas purification method using active oxygen, which detects the concentration of nitrogen oxide contained in the exhaust gas in the exhaust passage and detects the detected concentration of nitrogen oxide. when is equal to or higher than the predetermined concentration, by supplying active oxygen to the exhaust gas, nitrogen oxides NO ₃ ^- converted to the active species, the NO ₃ ^- active species, downstream of the supply of the active oxygen of the exhaust passage in the three-way catalyst including at least one catalytic metal of the arranged platinum or palladium bound to the catalyst metal, NO ₃ bound to the catalytic metal ^- oxidizing hydrocarbons contained in the exhaust gas by the active species It is characterized by purifying.

Next, an invention according to claim 2 of the present application is an exhaust gas purification apparatus having active oxygen supply means capable of supplying active oxygen to an exhaust passage upstream of an exhaust gas purification catalyst disposed in an exhaust passage of an engine. Exhaust gas temperature detecting means for detecting the temperature of the exhaust gas upstream of the exhaust gas purification catalyst, and nitrogen oxide for detecting the concentration of nitrogen oxide contained in the exhaust gas upstream of the exhaust gas purification catalyst. The exhaust gas temperature detected by the exhaust gas temperature detecting means after the engine is started is equal to or lower than a predetermined temperature and the nitrogen oxide concentration detected by the nitrogen oxide concentration detecting means is equal to or higher than the predetermined concentration. wherein the active oxygen supply active oxygen supply control means for operating the means provided in the case, and the exhaust gas purifying catalyst, at least one catalytic metal of the platinum or palladium Seen, the nitrogen oxide in the exhaust gas by supplying active oxygen is formed by conversion NO ₃ ^- by the active species bound to the catalytic metal, NO ₃ bound to the catalytic metal ^- active species included in the exhaust gas It is a three-way catalyst for oxidizing and purifying hydrocarbons .

  Next, the invention according to claim 3 of the present application is the exhaust gas purifying apparatus according to claim 2, further comprising engine load detecting means for detecting engine load, wherein the nitrogen oxide concentration detecting means comprises: The nitrogen oxide concentration is detected based on the engine load detected by the engine load detecting means.

  Next, the invention according to claim 4 of the present application is the exhaust gas purifying apparatus according to claim 3, wherein the engine load detecting means is configured to take an intake air amount, a throttle opening, and an engine speed as an engine load. It is characterized by detecting at least one of them.

  The invention according to claim 5 of the present application is the exhaust gas purifying apparatus according to any one of claims 2 to 4, wherein the concentration of nitrogen oxides detected by the nitrogen oxide concentration detection means And an active oxygen supply amount changing means for changing the amount of active oxygen supplied by the active oxygen supply means.

First, according to the first aspect of the invention, in the exhaust gas purification method using active oxygen, the concentration of nitrogen oxide contained in the exhaust gas is detected, and the detected concentration of nitrogen oxide is equal to or higher than a predetermined concentration. , that is, when a relatively high NOx concentration by supplying active oxygen to the exhaust gas, the NO of nitrogen oxides NO ₃ ^- converted to the active species, the NO ₃ ^- in the exhaust gas using an active species Since the contained HC was oxidized and purified, even if the NOx concentration is relatively high, and therefore nitrogen oxides containing NO, which is one factor that delays HC oxidation, coexist with HC in the exhaust gas. Even if it exists, the purification rate of HC will improve reliably.

On the other hand, according to the second aspect of the present invention, in the exhaust gas purifying apparatus capable of supplying active oxygen to the exhaust passage upstream of the catalyst, the temperature of the exhaust gas upstream of the catalyst is equal to or lower than a predetermined temperature after the engine is started. When the concentration of nitrogen oxides contained in the exhaust gas upstream of the catalyst is not lower than the predetermined concentration, that is, when the NOx concentration is relatively high, the active oxygen supply means is operated to move the active oxygen to the upstream of the catalyst. it is so arranged to supply to, by the active oxygen, NO of nitrogen oxides NO ₃ ^- converted to the active species, the NO ₃ ^- so that the active species to oxidize purifies HC contained in the exhaust gas . As a result, even if the NOx concentration is relatively high and therefore nitrogen oxides containing NO, which is one factor that delays the oxidation of HC, coexist with HC in the exhaust gas, the HC purification rate is high. It will definitely improve.

  In that case, according to the invention described in claim 3, the engine load detecting means for detecting the engine load is provided, and the concentration of nitrogen oxide is detected based on the engine load detected by the engine load detecting means. Therefore, it is not necessary to newly provide a dedicated device such as a NOx sensor for detecting the NOx concentration in the exhaust gas. Here, it is generally known that the NOx concentration in the exhaust gas is greatly influenced by the engine load, that is, has a predetermined correlation with the engine load.

  Further, in this case, according to the invention described in claim 4, since at least one of the intake air amount, the throttle opening degree, and the engine speed is detected as the engine load, the air-fuel ratio of the engine The engine load and thus the NOx concentration is detected using parameters generally used in control and output control, and it is not necessary to newly provide a device for detecting the engine load for NOx concentration detection.

Then, according to the invention described in claim 5, it is so arranged to change the supply amount of the active oxygen according to the concentration of nitrogen oxides, NO ₃ from NO ^- proper good conversion to the active species in just proportion done, the result, NO ₃ ^- so that the oxidation purify HC with active species can be reliably and smoothly achieved. Hereinafter, the present invention will be described in more detail through the best mode of the present invention.

  FIG. 1 is an overall configuration diagram including a control system of an exhaust gas purification device 10 according to a first embodiment of the present invention. In the present embodiment, the control operation performed by the control unit 20 constitutes an embodiment of the exhaust gas purification method of the present invention.

  The engine 1 has an intake passage 2 and an exhaust passage 3. The exhaust passage 3 has catalytic metals such as platinum (Pt), palladium (Pd), rhodium (Rh), and oxide carriers carrying these catalytic metals. A three-way catalyst 11 having a structure containing activated alumina, cerium (Ce) -based composite oxide (oxygen storage material), and the like is disposed as an exhaust gas purification catalyst.

An ozone supply device 12 is disposed in the exhaust passage 3 upstream from the three-way catalyst 11 as active oxygen supply means. That is, the ozone supply passage 4 joins immediately upstream of the three-way catalyst 11, and the air supply pump 13 for sending air toward the exhaust passage 3 through the passage 4 on the ozone supply passage 4 An ozone generation device (ozonizer) 14 for generating ozone (O ₃ ) as active oxygen using air sent by the pump 13 as a raw material is disposed. For example, the ozone generator 14 generates ozone by silently discharging air.

  Further, in the exhaust passage 3, the temperature of the exhaust gas in the exhaust passage 3 is located upstream of the three-way catalyst 11 and downstream of the junction of the ozone supply passage 4 (the portion where the ozone supply device 12 supplies ozone). An exhaust gas temperature sensor 15 for detecting NOx is provided, upstream of the junction of the ozone supply passage 4, NOx for detecting the concentration of nitrogen oxide (NOx concentration) contained in the exhaust gas in the exhaust passage 3. A sensor 16 is provided.

  The control unit 20 of the exhaust gas purifying apparatus 10 inputs an exhaust gas temperature signal from the exhaust gas temperature sensor 15 and a NOx concentration signal from the NOx sensor 16, and based on the input result, controls the engine 1. In addition to fuel injection control, ozone supply control for the ozone supply device 12 (that is, the air supply pump 13 and the ozone generation device 14) is executed.

  In the present embodiment, the control unit 20 performs ozone supply control for the following purpose.

That is, as shown in FIG. 2, when HC and NOx coexist in the exhaust gas in the exhaust passage 3 upstream from the three-way catalyst 11, the ozone supply device 12 is operated to exhaust from the ozone supply passage 4. Ozone is supplied to the passage 3. Then, NO of NOx is NO ₃ by ozone ^- are converted to the active species. Then, the NO ₃ ^- together with the active species oxidizes purify HC to water and carbon dioxide, NO ₃ ^- active species itself is reduced and purified into nitrogen. By such a series of reactions, the purification rate of HC in the exhaust gas is improved.

Note that the series of reactions described above can occur in the exhaust passage 3 upstream of the three-way catalyst 11 or also in the catalyst 11. However, NO ₃ ^- active species, since easily ties stable to catalytic metals such as platinum and palladium, and to work more effectively as a strong oxidizing agent of HC in the catalyst 11.

  FIG. 3 is a flowchart showing an example of a specific operation of the ozone supply control performed immediately after the engine 1 is started by the control unit 20 according to the first embodiment. That is, after confirming that it is a cold start in step S11, the control unit 20 detects the NOx concentration in step S12, and determines in step S13 whether the NOx concentration is a predetermined value or more. In step S11, whether or not the engine is cold started is determined by a cooling water temperature signal from a cooling water temperature sensor (not shown) that detects the temperature of the cooling water of the engine 1 or the exhaust gas temperature sensor. 15 on the basis of an exhaust gas temperature signal from 15 or the like.

  As a result, when the NOx concentration is equal to or higher than the predetermined value, that is, when the NOx concentration is relatively high, the ozone supply amount is set according to the NOx concentration in step S14. Here, as illustrated in FIG. 4, the ozone supply amount is set so as to increase as the NO concentration increases.

  FIG. 4 shows an example that is preferably used when the size of the catalyst 11 is 1.0 L. In the illustrated example, a NO concentration of 50 ppm is used as the predetermined value for determination in step S13.

  Next, in step S15, the ozone supply device 12 is operated. In other words, ozone is supplied to the exhaust passage 3 upstream of the three-way catalyst 11 (corresponding to symbol B in FIG. 8). At this time, the amount of ozone set in step S14 is supplied to the exhaust passage 3. This is achieved, for example, by increasing or decreasing the air supply pump 13 of the ozone supply device 12 to increase or decrease the amount of air sent to the ozone generation device 14. Alternatively, it is achieved by increasing or decreasing the applied voltage when silently discharging air and adjusting the ozone generation rate in the ozone generator 14 to increase or decrease.

  Next, in step S16, it is determined whether the exhaust gas temperature T is equal to or lower than the activation temperature TH of the catalyst 11. As a result, while the exhaust gas temperature T is equal to or lower than the catalyst activation temperature TH, the above steps S12 to S15 are repeated. That is, the supply of ozone in an amount corresponding to the NOx concentration is continued.

  Then, when the exhaust gas temperature T becomes higher than the catalyst activation temperature TH, the process proceeds to step S17, the ozone supply device 12 is stopped, and this ozone supply control is ended.

  On the other hand, when the NOx concentration is less than the predetermined value in step S13, that is, when the NOx concentration is relatively low, even if the exhaust gas temperature T is equal to or lower than the catalyst activation temperature TH (YES in step S16) The process immediately proceeds to step S17, and the ozone supply device 12 is stopped (corresponding to the reference C in FIG. 8). Alternatively, although not shown, when the NOx concentration is less than the predetermined value in step S13, a predetermined amount of ozone may be supplied until the exhaust gas temperature T exceeds the catalyst activation temperature TH ( This corresponds to the symbol D in Fig. 8. In this case, by supplying ozone regardless of the NOx concentration, HC in the exhaust gas is oxidized and purified with ozone.

  Moreover, when it determines with not being a cold start by step S11, this control is complete | finished, without operating the ozone supply apparatus 12. FIG.

  As described above, the exhaust gas purification apparatus 10 according to the present embodiment has an ozone supply device 12 (that is, an air supply pump 13 and an ozone generation device 14) upstream of the three-way catalyst 11 disposed in the exhaust passage 3 of the engine 1. ) Is configured to be able to supply ozone.

After the cold start of the engine 1 (YES in step S11), the temperature T of the exhaust gas upstream from the catalyst 11 is equal to or lower than the activation temperature TH of the catalyst 11 (YES in step S16), that is, the catalyst 11 has not been activated. And the ozone supply device 12 is operated only when the NOx concentration contained in the exhaust gas upstream of the catalyst 11 is equal to or higher than the predetermined concentration (YES in step S13), that is, when the NOx concentration is relatively high (step S15), ozone it is so arranged that the supply upstream of the catalyst 11, as described with reference to FIG. 2, this ozone, NO of NOx is NO ₃ ^- converted to the active species, the NO ₃ ^- active species Oxidizes and purifies HC contained in the exhaust gas. As a result, even if the NOx concentration is relatively high and therefore NOx containing NO, which is one factor that delays the oxidation of HC, coexists with HC in the exhaust gas, the HC purification rate is ensured. Will be improved.

Moreover, since the supply amount of ozone was set to be changed according to the NOx concentration (step S14), NO from NO ₃ ^- conversion to the active species are carried out in just proportion properly good result, NO ₃ ^- activity Thus, the oxidative purification of HC using seeds is reliably and smoothly achieved.

  Next, a second embodiment of the present invention will be described. However, the description of the same or similar parts as those in the first embodiment will be omitted, and only the characteristic parts of the second embodiment will be described. The same reference numerals are used for the same or similar components as those in the first embodiment.

  FIG. 5 is an overall configuration diagram including a control system of the exhaust gas purifying apparatus 10 according to the second embodiment of the present invention. The difference from FIG. 1 is that the NOx sensor 16 is not provided in the exhaust passage 3, but instead, an air flow meter 17 for detecting the intake air amount and a throttle for detecting the opening of the throttle valve are provided in the intake passage 2. An opening sensor 18 is provided, and the engine 1 is provided with an engine speed sensor 19 for detecting the engine speed.

  The control unit 20 of the exhaust gas purifying apparatus 10 includes an exhaust gas temperature signal from the exhaust gas temperature sensor 15, an intake air amount signal from the air flow meter 17, and a throttle opening from the throttle opening sensor 18. A signal and an engine speed signal from the engine speed sensor 19 are input, and on the basis of the input result, in addition to the fuel injection control for the engine 1, the ozone supply device 12 (that is, the air supply pump 13 and the ozone generation device). The ozone supply control for 14) is executed.

  That is, in the second embodiment, the NOx concentration in the exhaust passage 3 upstream from the catalyst 11 is not directly detected by the NOx sensor, but at least one of the intake air amount, the throttle opening, and the engine speed is used. From this, the NOx concentration is indirectly estimated.

  FIG. 6 is a flowchart showing an example of a specific operation of ozone supply control performed immediately after the engine 1 is started by the control unit 20 according to the second embodiment. In FIG. 6, steps S21 and S24 to S28 are the same as steps S11 and S13 to S17 of FIG.

  In this second embodiment, the control unit 20 confirms that the engine is cold start in step S21, and then in step S22, the intake air amount detected by the air flow meter 17 and the throttle opening sensor. The throttle opening detected at 18 and the engine speed detected by the engine speed sensor 19 are read as engine loads.

  In step S23, the NOx concentration in the exhaust passage 3 upstream from the catalyst 11 is estimated based on the read engine load. Here, the NOx concentration in the exhaust gas is greatly influenced by the engine load and has a predetermined correlation with the engine load. For example, as shown in FIG. 7, the NOx concentration becomes high in the middle load region. Thus, it is estimated that the NOx concentration becomes lower as it goes to the low load side and the high load side.

  In step S24, it is determined whether the NOx concentration estimated in this way is equal to or higher than a predetermined value.

  As described above, the second embodiment includes the engine load detection means 17 to 19 for detecting the engine load, and detects (estimates) the NOx concentration based on the engine load detected by the engine load detection means 17 to 19. (Step S23), it is not necessary to newly provide a dedicated device such as the NOx sensor 16 of the first embodiment for detecting the NOx concentration in the exhaust gas.

  In this case, since at least one of the intake air amount, the throttle opening degree, and the engine speed is detected as the engine load (step S22), it is generally used for air-fuel ratio control and output control of the engine 1. Thus, the engine load and thus the NOx concentration are detected using the parameters, and it is not necessary to provide a new device for detecting the engine load for detecting the NOx concentration.

  FIG. 8 is a graph showing the experimental results of the exhaust gas purification rate (HC purification rate) performed by changing the composition of the exhaust gas.

That is, an exhaust gas purification performance test (HC purification performance test) was conducted by passing a simulated exhaust gas through an exhaust gas purification catalyst generally used for gasoline engines. The catalyst used had a total amount of catalyst noble metals of 7.0 g / L, and the breakdown was Pt: Pd: Rh in a mass ratio of 1: 30: 2. Further, Ce, Zr, and Nd composite oxide for supporting Pd (that is, an oxygen storage material having a composition of Ce of 50 to 70% by weight, Zr of 20 to 30% by weight and the balance of Nd) is 100 g / L, Rh The supporting OSC material (oxygen storage material including ceria) was 70 g / L, and Pt supporting Al ₂ O ₃ was 60 g / L.

The composition of the simulated gas used is experimental example A, in which propylene (C ₃ H ₆ ) is 700 ppmC, nitric oxide (NO) is 1000 ppm, oxygen (O ₂ ) is 1.0 vol%, and the rest is nitrogen. B was propylene (C ₃ H ₆ ) 700 ppmC, nitric oxide (NO) 1000 ppm, ozone (O ₃ ) 0.3 vol%, oxygen (O ₂ ) 0.7 vol%, and the rest nitrogen. In Example C, propylene (C ₃ H ₆ ) was 700 ppmC, oxygen (O ₂ ) was 1.0 vol%, and the remainder was nitrogen. Experimental Example D was propylene (C ₃ H ₆ ) 700 ppmC, ozone (O ₃ ) Was 0.3 vol%, oxygen (O ₂ ) was 0.7 vol%, and the rest was nitrogen.

  The flow rate of the simulation gas was 20 L / min, and the temperature of the simulation gas was started from 70 ° C. (cold start) and was raised at 10 ° C./min.

  The results are shown in FIG. In FIG. 8, the vertical axis represents the propylene concentration in the simulated gas after passing through the catalyst, that is, the HC purification rate. As is clear from this, it can be seen that the HC purification rate is good in the order of Experimental Examples A, B, C, and D.

In other words, Experimental Example B in which ozone was supplied in the presence of C ₃ H ₆ as HC and NO (corresponding to YES in steps S13 and S24), usually in the presence of only C ₃ H ₆ as HC Example C in which only oxygen was supplied (corresponding to NO in steps S13 and S24), and Example D in which ozone was supplied in the presence of only C ₃ H ₆ as HC (NO in steps S13 and S24) In this case, the HC purification rate increases steadily as the simulated gas temperature and, consequently, the catalyst temperature rises. In Experimental Example D, which was the best, the simulated gas temperature was about 150 ° C. In Experimental Example C, in which the HC purification rate reached approximately 100% at the next stage, and the second best test example C, the HC purification rate reached approximately 100% when the simulated gas temperature reached about 165 ° C., and then Experimental example B was good Is, HC purification rate reaches approximately 100% at the stage where the simulant gas temperature was about 190 ° C..

In particular, in Examples B, NO ₃ were converted from NO with ozone ^- is considered that the active species contributed to the oxidation of HC with ozone.

In contrast to this, in Example A in which only normal oxygen was supplied without supplying ozone in the coexistence of C ₃ H ₆ as HC and NO, HC purification was performed until the simulated gas temperature was about 150 ° C. Although the rate increased, the HC purification rate decreased on the contrary, and the HC purification rate did not reach 100%. This is, in the presence of only normal oxygen, NO can be precedence to oxidize to NO _2, presumably because HC is delayed be oxidized to water and carbon dioxide.

  The above embodiment is the best embodiment of the present invention, but it goes without saying that various modifications and changes may be made without departing from the scope of the claims. For example, in the above-described embodiment, the exhaust gas temperature is directly detected by the exhaust gas temperature sensor 15 disposed in the exhaust passage 3, but the present invention is not limited to this, and it can also be estimated indirectly based on the engine load. It is.

  In the second embodiment, the characteristics of the engine load and the NOx concentration illustrated in FIG. 7 may be different depending on the type of engine load, that is, the intake air amount, the throttle opening, or the engine speed. Good.

  As described above in detail with reference to specific examples, the present invention reliably improves the HC purification rate even in the presence of nitrogen oxides in which HC oxidation is delayed only by the presence of normal oxygen. Therefore, it is possible to supply active oxygen upstream of an exhaust gas purification method and an exhaust gas purification device, in particular, an exhaust gas purification method using active oxygen and an exhaust gas purification catalyst disposed in the exhaust passage of the engine. Extensive industrial applicability is expected in the technical field of the exhaust gas purification apparatus constructed as described above.

1 is an overall configuration diagram including a control system for an exhaust gas purifying apparatus according to a first embodiment of the present invention. It is explanatory drawing which shows reaction when supplying active oxygen to the exhaust gas in which HC and NOx coexist. It is a flowchart which shows an example of the specific operation | movement of the ozone supply control which the control unit which concerns on 1st Embodiment performs immediately after starting of an engine. It is a characteristic view used when setting ozone supply amount by the said control action. It is a whole block diagram containing the control system of the exhaust-gas purification apparatus which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows an example of the specific operation | movement of ozone supply control which the control unit which concerns on 2nd Embodiment performs immediately after starting of an engine. It is a characteristic view used when estimating NOx concentration by the control operation. It is a graph which shows the experimental result of the exhaust gas purification rate performed by changing the composition of exhaust gas.

Explanation of symbols

1 Engine 3 Exhaust passage 10 Exhaust gas purification device 11 Exhaust gas purification catalyst (three-way catalyst)
12 Ozone supply device (active oxygen supply means)
13 Air supply pump 14 Ozone generator 15 Exhaust gas temperature sensor (exhaust gas temperature detection means)
16 NOx sensor (nitrogen oxide concentration detection means)
17 Air flow meter (engine load detection means)
18 Throttle opening sensor (engine load detection means)
19 Engine speed sensor (engine load detection means)
20 Control unit (active oxygen supply control means, active oxygen supply amount changing means)

Claims (5)

An exhaust gas purification method using active oxygen,
Detect the concentration of nitrogen oxides contained in the exhaust gas in the exhaust passage ,
When the concentration of the detected nitrogen oxide is equal to or higher than the predetermined concentration, by supplying active oxygen to the exhaust gas, nitrogen oxides NO ₃ ^- converted to the active species,
The NO ₃ ^- the active species, is bound to the active oxygen the catalyst metal in the three-way catalyst comprising at least one catalytic metal of the arranged platinum or palladium downstream of the supply portion of the exhaust passage,
NO ₃ bound to the catalytic metal ^- exhaust gas purification method, characterized in that the oxidation purifying hydrocarbons contained in the exhaust gas in the active species. An exhaust gas purification apparatus having active oxygen supply means capable of supplying active oxygen to an exhaust passage upstream of an exhaust gas purification catalyst disposed in an exhaust passage of an engine,
Exhaust gas temperature detection means for detecting the temperature of the exhaust gas upstream of the exhaust gas purification catalyst;
Nitrogen oxide concentration detecting means for detecting the concentration of nitrogen oxide contained in the exhaust gas upstream of the exhaust gas purification catalyst,
The active oxygen is detected when the temperature of the exhaust gas detected by the exhaust gas temperature detecting means is not more than a predetermined temperature and the concentration of nitrogen oxide detected by the nitrogen oxide concentration detecting means is not less than a predetermined concentration after the engine is started. Active oxygen supply control means for operating the supply means ,
And, wherein the exhaust gas purifying catalyst comprises at least one catalytic metal of the platinum or palladium, NO ₃ nitrogen oxides in the exhaust gas by the supply of the active oxygen is formed by the conversion ^- active species of the catalytic metal by binding to, NO ₃ bound to the catalytic metal ^- exhaust gas purification device, wherein the active species is a three-way catalyst for oxidizing purifying hydrocarbons contained in the exhaust gas. The exhaust gas purification device according to claim 2,
Engine load detection means for detecting engine load is provided,
The exhaust gas purifier according to claim 1, wherein the nitrogen oxide concentration detecting means detects the concentration of nitrogen oxide based on the engine load detected by the engine load detecting means. An exhaust gas purification device according to claim 3,
The engine load detecting means detects at least one of an intake air amount, a throttle opening degree, and an engine speed as an engine load. The exhaust gas purifying device according to any one of claims 2 to 4,
Exhaust gas provided with active oxygen supply amount changing means for changing the supply amount of active oxygen by the active oxygen supply means according to the concentration of nitrogen oxides detected by the nitrogen oxide concentration detection means Gas purification device.

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