JP2006170049A - Exhaust emission control device and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device and its control method for effectively burning or oxidizing and removing PM by relatively small energy consumption. <P>SOLUTION: This exhaust emission control device 10 collects a particulate (the PM) in exhaust gas by arranging a particulate filter 1 in an exhaust gas flow. The exhaust emission control device 10 has a plasma generator 2 for jetting fuel (4) to the upstream side of this filter by turning the fuel into plasma. The control method of this exhaust emission control device is provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purification apparatus that purifies exhaust gas using a particulate filter that collects particulates in an exhaust gas flow, and a control method thereof.

  Internal combustion engines such as automobiles, especially diesel engines, contain particulates mainly composed of carbon (hereinafter referred to as “PM (Particulate Matter)”), which causes exhaust black smoke. . From the viewpoint of environmental pollution, it is desirable to collect and remove this PM. For this purpose, a ceramic particulate filter (hereinafter referred to as “PM filter”) is arranged in the exhaust passage of the diesel engine, and PM is collected and removed by this filter, and the PM collected by this filter is collected. An exhaust gas purification device that regenerates a filter by burning the gas intermittently or continuously has been proposed.

  Here, in order to burn and remove the PM collected by the PM filter, the exhaust temperature is generally increased by adding fuel to the exhaust pipe, rich control of the engine, or the like. A conventional injector used for adding fuel to the exhaust pipe is, for example, as shown in FIG. The injector 100 includes a substantially cylindrical nozzle 12 having a hollow space 13 therein, and a substantially cylindrical needle valve 14 that slides (moves) in the hollow space 13 of the nozzle 12. The nozzle 12 and the needle valve 14 are arranged so that their axes A are coaxial. The nozzle 12 is provided with a supply passage 15 that communicates with the hollow space 13. The supply passage 15 is connected to a fuel supply source (not shown), and high-pressure fuel is supplied into the hollow space 13 through the supply passage 15. The supplied fuel flows to the tip portion of the nozzle 12 via the annular flow path 16 between the needle valve 14 and the inner wall surface of the nozzle 12 and is injected from the injection hole 19 at the tip portion of the nozzle 12. Here, the needle valve 14 is slid in the hollow space 13, and the tip of the needle valve 14 is brought into contact with the inner wall surface of the nozzle tip, thereby opening and closing the inlet of the injection hole 19, and Control the injection.

  It has also been proposed to use plasma for combustion removal of PM collected by a filter. For example, in Patent Document 1, PM in exhaust gas discharged from a diesel engine is collected by a filter, and this filter is used. An exhaust gas purifying apparatus is disclosed in which discharge is performed between electrodes arranged so as to be sandwiched to generate plasma, and PM is oxidized and removed by this plasma energy.

Patent Document 2 discloses an exhaust gas purifying apparatus that collects PM in exhaust discharged from a diesel engine with a filter, generates NO ₂ with a catalyst on the upstream side of the filter, and oxidizes and removes PM by the NO ₂ . It is disclosed. Here, it is disclosed that combustion removal of PM is achieved from a relatively low temperature of 250 ° C. when NO ₂ is supplied to a filter that collects PM.

JP 2001-295629 A Japanese Patent No. 3012249

  In order to burn and remove PM trapped in the PM filter, when fuel is added to the exhaust pipe by a conventional injector, particularly when the exhaust gas is at a relatively low temperature, the oxidation reaction of the fuel added initially proceeds. It is difficult, and it is conceivable that a part of the added fuel newly forms PM, and the added fuel is directly released into the atmosphere.

The exhaust gas purification devices described in Patent Documents 1 and 2 partially achieve the purpose of burning or oxidizing and removing PM collected by a filter. However, the exhaust gas purification device of Patent Document 1 may require a relatively large amount of electric energy for generating plasma, and the exhaust gas purification device of Patent Document 2 generates a sufficient amount of NO ₂ . Therefore, sufficient PM burn-off may not be achieved.

  Therefore, the present invention provides an exhaust gas purifying apparatus that effectively burns or oxidizes and removes PM with relatively little energy consumption, and a control method therefor.

  The exhaust gas purifying apparatus of the present invention is an exhaust gas purifying apparatus that arranges a PM filter in an exhaust gas flow and collects PM in the exhaust gas. It has a plasma generator that is ejected directly into the exhaust gas flow upstream of the filter without being interposed.

  According to the exhaust gas purifying apparatus of the present invention, the oxidation of the added fuel can be promoted even when the exhaust gas is at a relatively low temperature by converting the fuel into plasma by the plasma generator and ejecting the fuel into the exhaust gas flow. Therefore, it is possible to suppress the added fuel from newly forming PM, and the added fuel from being unreacted and released into the atmosphere.

  In the exhaust gas purifying apparatus of the present invention, the entire exhaust gas flow supplied with fuel is not converted into plasma, but the fuel is converted into plasma by the plasma generator and then injected into the exhaust gas flow. Accordingly, it is possible to obtain a large plasma density with a relatively narrow space for plasma formation, that is, with relatively little energy consumption.

  In one aspect of the exhaust gas purifying apparatus of the present invention, the plasma generator converts water into plasma together with fuel.

  According to this aspect, OH radicals, O radicals, and the like can be generated by converting water into plasma together with fuel. These OH radicals, O radicals, etc. promote the oxidation reaction of the fuel, and bind to the end of the molecular chain of the fuel cut by the plasma to prevent the generation of unsaturated hydrocarbons and suppress the generation of soot. be able to.

  Moreover, in one aspect of the exhaust gas purifying apparatus of the present invention, the plasma generator converts a part of the exhaust gas or air into plasma together with the fuel.

When the plasma generator generates a part of the exhaust gas together with the fuel, especially the recirculated exhaust gas, it promotes the production of NO ₂ , ozone, O radical, etc. with high oxidation activity, and burns the PM collected in the PM filter Removal can be promoted.

  When the plasma generator converts the air together with the fuel into plasma, the generation of ozone, O radicals and the like having high oxidation activity can be promoted, and combustion removal of PM collected by the PM filter can be promoted. Further, since air has a higher oxygen concentration than exhaust gas, it is possible to promote the oxidation reaction of the fuel, and hence the exhaust gas temperature.

  In the control method of the exhaust gas purifying apparatus of the present invention, the temperature of the exhaust gas in the filter is set to be higher than 500 ° C., in particular, higher than 600 ° C. by converting the fuel into plasma using the plasma generator and ejecting the fuel into the exhaust gas flow. The collected PM is burned and removed.

  As described above, in the exhaust gas purification apparatus of the present invention, the oxidation reaction of the added fuel is efficiently performed with relatively little energy consumption, the temperature of the downstream filter is raised, and the collected PM is combusted. Can be removed.

In another method for controlling an exhaust gas purification apparatus of the present invention, a plasma generation device is used to convert a part of the exhaust gas or air together with fuel into a plasma to be ejected into the exhaust gas stream, whereby an oxidizing component, for example, Ozone, oxygen radicals, and NO ₂ are generated, and the temperature of the exhaust gas in the filter is collected by the filter in a state of less than 450 ° C., for example, 250 ° C. to 450 ° C., particularly less than 400 ° C., for example, 250 to 400 ° C. PM is burned off.

  According to this method of the present invention, by generating an oxidizing component in the exhaust gas stream, a relatively low exhaust gas temperature, such as less than 450 ° C., that is, a temperature lower than the temperature at which the PM is substantially burned and removed by heat. The PM collected by the filter can be removed by combustion. When performing this method, a relatively small amount of fuel can be continuously added over a relatively long period in the plasma generator.

  In the following, the present invention will be described in detail with reference to FIG. 1, but this figure is a diagram showing an outline of the present invention, and the present invention is not limited to this embodiment.

  The exhaust gas purification device 10 of the present invention is an exhaust gas purification device that collects PM in exhaust gas by arranging the PM filter 1 in the exhaust gas flow. Here, the fuel is converted into plasma by the plasma generator 2 and ejected 4 into the exhaust gas flow 9 on the upstream side of the exhaust gas flow of the PM filter 1.

  The PM filter that can be used in the present invention is an arbitrary filter that can be used for collecting PM in exhaust gas, and in particular, a ceramic wall flow honeycomb filter such as cordierite can be used.

  The fuel that can be used in the present invention may also be any hydrocarbon compound and a hydrocarbon-based compound optionally having other atoms such as oxygen, such as ether. Therefore, the fuel that can be used in the present invention may be gasoline or light oil used to generate power energy of the internal combustion engine, or may be different from the fuel as the power source of the internal combustion engine. Good.

  When the plasma generator converts the water together with the fuel into plasma, the water is supplied to the plasma generator together with the fuel, injected into the plasma generated by the plasma generator, etc. It can be turned into plasma.

  In addition, when the plasma generator converts a part of the exhaust gas or air together with the fuel into a plasma, the exhaust gas part or air is supplied to the plasma generator together with the fuel, or converted into a plasma converted into a plasma by the plasma generator. On the other hand, a part of the exhaust gas or air can be converted into plasma by injecting the fuel into the plasma generator, and the fuel can be injected into the plasma.

  Below, the plasma generator which can be used with the exhaust gas purification apparatus of this invention is illustrated.

<Discharge plasma generator>
A plasma generator that can be used in the present invention is, for example, a discharge plasma generator as shown in FIG.

  In the discharge plasma generator 20 shown in FIG. 2, a cylindrical body 22 is disposed at the tip of the nozzle 12 of the injector 100 as shown in FIG. The cylindrical body 22 and the tip end portion of the nozzle 12 are electrically insulated by an insulating material 23, and the cylindrical body 22 is connected to a power source 28 so that each becomes a counter electrode. The part is grounded. Either the cylindrical body 22 or the tip portion of the nozzle 12 can be a cathode or an anode. In FIG. 2, the tip of the nozzle 12 is grounded, but it may be connected to the power source 28 and applied with a voltage opposite to that of the cylindrical body 22.

  In the use of the discharge plasma generator 20, when fuel is injected from the nozzle 12, a discharge is generated between the cylindrical body 22 and the nozzle tip portion 18 by the power source 28, thereby causing the inside of the cylindrical body 22 and the vicinity thereof. To generate a plasma 29.

  The plasma generator that can be used in the present invention may be, for example, a discharge plasma generator as shown in FIG.

  In the discharge plasma generator 30 shown in FIG. 3, a discharge electrode 36 is disposed on the central axis of a conductive cylindrical conduit 32 through which a part of exhaust gas or air flows, and these conduit 32 and discharge electrode 36 are arranged. An insulating material 34 is disposed between the two. The conduit 32 and the discharge electrode 36 are respectively connected to the ground and the power source 38 so as to be counter electrodes. Either the conduit 32 or the discharge electrode 36 can be a cathode or an anode. Further, either the conduit 32 or the discharge electrode 36 can be grounded.

  In the use of the discharge plasma generator 30, a power source 38 generates a discharge between the tip 32 a of the conduit 32 and the tip 36 a of the discharge electrode 36, thereby supplying the discharge through the flow path in the discharge plasma generator 30. Part of the exhaust gas or air 33 to be converted into plasma 39. The fuel is injected from the injector 100 into a part of the plasmad exhaust gas or air.

  In FIG. 3, the conduit is used as one electrode, but it is naturally possible to use a separate electrode that is paired with the discharge electrode 36.

  Further, as shown in FIG. 4, the injection nozzle of the injector 100 for injecting fuel is disposed in the flow path of the discharge plasma generator 30 ′, and between the inner wall of the discharge plasma generator 30 ′ and the injection nozzle of the injector 100. Further, the gas 33 to be plasma can be circulated, and the injection nozzle of the injector 100 can be used as one electrode.

  Furthermore, when further water is supplied to the region where the plasma is generated, an additional injector for injecting water is used in the same manner as injecting fuel in the discharge plasma generators 30 and 30 ′ of FIGS. Thus, it is possible to inject water into a part of the exhaust gas converted into plasma or air.

  The portion used as an electrode in the discharge plasma generator can be manufactured from a material that can be used as a discharge electrode by applying a voltage between the electrodes. As such a material, a conductive material or a semiconductor material can be used, but a metal material such as copper, tungsten, stainless steel, iron, aluminum, or the like is preferable. However, particularly in arc discharge, the electrode becomes hot, so it is preferable to use a high melting point material such as tungsten. Moreover, in order to use barrier discharge, an insulating material can also be arrange | positioned on these electroconductive or semiconductive materials.

  The discharge plasma generated here refers to plasma generated by causing high-energy electrons generated by discharge between electrodes to collide with gas molecules, thereby changing the gas molecules into positive ions and negative ions. In order to generate this discharge plasma, any discharge mode can be used, but arc discharge or corona discharge, for example, barrier discharge can be used.

  When plasma is generated by a discharge plasma generator using arc discharge, the power supply can supply a voltage of 1 to 50 V and a current of 5 to 500 A, for example. In this arc discharge, the discharge is sustained by electrons emitted from the cathode. As a current for causing arc discharge, not only direct current but also alternating current can be used.

  Arc discharge is advantageous in that the output can be easily increased by increasing the discharge current and discharge voltage, and stable discharge can be sustained for a long time. Moreover, arc discharge is advantageous in that the apparatus and technology for generating arc discharge are simple and the equipment cost is relatively low.

  When plasma is generated by a discharge plasma generator using corona discharge, the power source may supply a pulsed direct current or alternating voltage. In general, a voltage of 1 kV to 100 kV, for example, 5 kV to 20 kV can be used as an applied voltage between the electrodes. The pulse width of the applied voltage can be 0.1 μs to 10 ms, particularly 0.1 to 10 μs.

  In addition, it is preferable to arrange an insulating material on the electrode to perform barrier discharge in terms of plasma stability, electrode durability, and the like.

<Coupled induction plasma generator>
A coupled induction plasma generator that generates plasma by coupled induction has, for example, an induction coil disposed around a space to be plasmatized, supplies a high-frequency current to the induction coil, and generates a magnetic field in a gas flow path. And generating an eddy current to generate coupled induction plasma.

  This may be, for example, as shown in FIG. In this coupled induction plasma generating device 40, a part of the exhaust gas to be converted into plasma or a tip part of a conduit 42 for circulating air is made of a material that transmits electromagnetic waves, for example, an insulating material such as quartz. An induction coil 44 for generating an induction electric field is disposed around the portion. A high frequency power supply 48 is connected to one end of the induction coil 44 via a matching box 47, and the other end is grounded.

  In the use of this fuel addition device, the impedance is adjusted by the matching box 47 and a high frequency current is passed from the high frequency power supply 48 to the induction coil 44, a magnetic field is generated inside the distal end portion of the conduit 42, an eddy current is generated, Thereby, a plasma 49 is inductively generated in and around the conduit 42. The fuel is injected from the injector 100 into a part of the plasmad exhaust gas or air. As the high-frequency current used here, for example, a frequency of 2 to 50 MHz, particularly 3 to 40 MHz can be used.

  This coupled induction plasma is preferable in terms of durability because the electrode (metal part) can not be directly exposed to the high temperature plasma.

  In the coupled induction plasma generator, as in the discharge plasma generator shown in FIGS. 2 and 4, the fuel is directly converted into plasma, and the injection nozzle of the injector 100 for injecting fuel is placed in the gas flow path for generating plasma. It can also be arranged.

<Microwave plasma generator>
A microwave plasma generator that generates plasma by using a microwave has, for example, a plasma exciter disposed in a flow path of a gas to be converted into plasma, and this plasma exciter is irradiated with microwaves to excite plasma. Plasma is generated around the body.

  This may be, for example, as shown in FIG. In the microwave plasma generator 50 shown in FIG. 6, plasma excitation that promotes excitation of the plasma 59 around the irradiation of the microwave 54 in a part of the exhaust gas to be converted into plasma or in a conduit that circulates air. A body 52, for example a conductive ceramic, in particular a conductive ceramic sintered body such as a SiC sintered body, is arranged.

  In the use of the microwave plasma generator 50, a microwave 54 generated by a microwave generator such as a magnetron, for example, a microwave having a frequency of about 2.54 GHz is converted into plasma from an antenna via a waveguide. The plasma 49 is generated by irradiating a part of the exhaust gas or the air 33 to increase the electric field strength. The fuel is injected from the injector 100 into a part of the plasmad exhaust gas or air.

  In particular, when generating a microwave plasma at atmospheric pressure or higher, the plasma exciter 52 is generally used, and the plasma is irradiated around the plasma exciter by irradiating the plasma exciter with microwaves. It is advantageous to generate it.

  The use of microwave plasma is preferable with respect to durability because the electrode (metal part) can not be directly exposed to the high temperature plasma.

  In the microwave plasma generator 50, as in the discharge plasma generator shown in FIGS. 2 and 4, the fuel is directly converted into plasma, and the injection nozzle of the injector 100 that injects fuel is converted into plasma in the gas flow path. It is also possible to arrange them.

<Plasma>
As is generally known, plasma means a material state in which two or more kinds of charged particles having positive and negative charges that freely move coexist. Therefore, in the plasma state, the substance present has high potential energy, and when the fuel is brought into the plasma state, radicalization and cracking can be performed and converted into a low molecular weight component having high reactivity.

In the following examples, an effect of generating an oxidizing component, particularly NO ₂ when a plasma is applied to an exhaust gas accompanied by a fuel component using a discharge plasma generator of the type shown in FIG. NO ₂ generated here is a relatively low exhaust gas temperature, such as less than 450 ° C., that is, a temperature lower than the temperature at which PM is substantially removed by heat. Can be promoted.

  In the discharge plasma generator shown in FIG. 8, a cylindrical electrode 84 is disposed so as to surround the center electrode 82, and the central electrode 82 and the cylindrical electrode 84 are connected and grounded to a power source 86, respectively. The model gas converted into plasma in the discharge plasma generator 80 passes through the space surrounded by the cylindrical electrode 84 from the left side to the right side in FIG. In using this discharge reactor, a voltage is applied between the center electrode 82 and the cylindrical electrode 84 by the power source 86, thereby causing a discharge between these power sources. Here, an insulating material layer is disposed inside the cylindrical electrode 84 to generate a barrier discharge.

The composition of the model gas to be circulated in the discharge plasma generator was as shown in Table 1.

As a result of the experiment, when 80 ppm of C ₃ H ₈ is present in the model gas, the NO ₂ generation rate is 82%, and when C ₃ H ₈ is not present in the model gas, the NO ₂ generation rate is It was 8%. That is, it was shown that the presence of C ₃ H ₈ as a fuel component promotes the generation of NO ₂ as an oxidizing component when plasma is applied to exhaust gas.

Here, whether the NO incoming gas is changed to how much NO ₂ is defined as a "generation rate NO _{2" (NO + O → NO 2)} . Therefore, the NO ₂ production rate = (NO ₂ concentration in the outgas) / (NO concentration in the incoming gas). That is, for example, the NO ₂ production rate of 60% indicates a state in which when 100 ppm of NO is supplied as an input gas, 60 ppm changes to NO ₂ and the remaining 40 ppm remains NO. Here, the gas concentration is expressed by volume (number of moles).

It is a figure which shows one aspect | mode of the exhaust gas purification apparatus of this invention. It is sectional drawing which shows the discharge plasma generator which can be used with the fuel addition apparatus of this invention. It is sectional drawing which shows the other discharge plasma generator which can be used with the fuel addition apparatus of this invention. It is sectional drawing which shows the further another discharge plasma generator which can be used with the fuel addition apparatus of this invention. It is sectional drawing which shows the coupling induction plasma generator which can be used with the fuel addition apparatus of this invention. It is sectional drawing which shows the microwave plasma generator which can be used with the fuel addition apparatus of this invention. It is an expanded sectional view of the conventional injector. It is a perspective view of the discharge plasma generator used in the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 PM filter 2 Plasma generator 4 Plasma-ized fuel 9 Exhaust gas flow 10 Exhaust gas purification apparatus 20, 30, 30 'of this invention Discharge plasma generator 33 Arrow 29, 39, 39' which shows the flow of the gas converted into plasma , 49, 59 Plasma 40 Coupling induction plasma generator 50 Microwave plasma generator 80 Discharge plasma generator 100 used in the embodiment 100 Conventional injector

Claims (5)

An exhaust gas purification device that collects particulates in exhaust gas by disposing a particulate filter in the exhaust gas flow,
An exhaust gas purifying apparatus comprising a plasma generator for converting fuel into plasma and ejecting the fuel into the exhaust gas flow upstream of the filter.   The exhaust gas purification apparatus according to claim 1, wherein the plasma generation device converts water into plasma together with fuel.   The exhaust gas purifying apparatus according to claim 1 or 2, wherein the plasma generator converts a part of the exhaust gas or air into a plasma together with the fuel.   The fuel is converted into plasma using the plasma generator and ejected into the exhaust gas flow, whereby the temperature of the exhaust gas in the filter exceeds 500 ° C., and the particulates collected in the filter are burned and removed. Item 4. A method for controlling an exhaust gas purifying apparatus according to any one of Items 1 to 3.   Using the plasma generator, a part of the exhaust gas or air together with the fuel is converted into plasma and ejected into the exhaust gas stream to generate an oxidizing component in the exhaust gas stream, and the temperature of the exhaust gas in the filter is less than 450 ° C. The control method of the exhaust gas purifying apparatus according to claim 3, wherein the particulates collected by the filter are burned and removed in the state.

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