JP2005240738A - Power source for plasma reactor, plasma reactor, exhaust emission control device and exhaust emission control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power source for a plasma reactor, the plasma reactor, an exhaust emission control device and an exhaust emission control method, realizing both PM collection and combustion/removal. <P>SOLUTION: This power source for the plasma reactor is constituted so as to generate superimposed voltage (c) having a DC voltage component (a) and a pulse voltage component (b). The plasma reactor has a pair of electrodes sandwiching an exhaust gas flow passage, and is constituted such that voltage is applied to the electrodes by the power source for the plasma reactor. The exhaust emission control device is provided with the plasma reactor and a PM collection part in the downstream side of an exhaust gas flow. In the exhaust emission control method, the superimposed voltage (c) having the DC voltage component (a) and the pulse voltage component (b) is applied to an electrode of the plasma reactor with the pair of electrodes sandwiching the exhaust gas flow passage. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to purification of exhaust gas from an internal combustion engine or the like, and more particularly to removal of particulate matter (particulate: hereinafter referred to as “PM”) discharged from a diesel engine.

  Diesel engines are often installed in automobiles, particularly large vehicles. Recently, it has been strongly desired to reduce PM emissions together with nitrogen oxides, carbon monoxide, hydrocarbons, and the like in the exhaust gas in recent years. Therefore, it is desired to establish a technique for efficiently removing PM in the exhaust gas as well as technical development for fundamentally reducing PM by improving the engine or optimizing combustion conditions.

  Generally, a ceramic honeycomb filter, an alloy filter, and a ceramic fiber filter are used for removing PM in the exhaust gas. However, with these techniques, as the usage time elapses, the trapped PM causes the filter to become clogged, increasing the airflow resistance, and placing a burden on the engine. Further, even when PM is collected by a conventional filter, sufficient oxidation removal of PM cannot be expected by the action of exhaust heat alone.

  As an exhaust emission control device for a diesel engine, a device using discharge has been conventionally known. For example, Patent Document 1 discloses that two sets of plasma processing electrodes are provided across a filter element of a ceramic filter, and a high frequency voltage or a pulse high voltage is applied between these electrodes to generate a discharge. According to this, it is said that PM deposited on the ceramic filter can always be removed by low-temperature oxidation with plasma to prevent an increase in pressure loss.

JP-A-6-146852

  That is, the conventional exhaust gas purification apparatus using discharge discloses that PM collected by a ceramic filter is oxidized and removed by discharge at low temperature. However, since PM collection depends on the filter, the essential problem regarding pressure loss has not been solved.

  Therefore, the present invention provides a power source for a plasma reactor, a plasma reactor, an exhaust gas purification device, and an exhaust gas purification method that can achieve both PM collection and combustion removal. The present invention is particularly suitable for purifying exhaust gas from a diesel engine, but can also be used for purifying other exhaust gas, for example, exhaust gas from an internal combustion engine such as a gasoline engine.

  The plasma reactor power supply of the present invention is characterized by generating a superimposed voltage having a DC voltage component and a pulse voltage component.

  According to the power source for the plasma reactor of the present invention, the charging and electrostatic collection of PM can be promoted by the DC voltage component, and the activation of the exhaust gas component and the combustion removal of PM can be promoted by the pulse voltage component. .

  Here, “DC voltage component” in the present invention means that a voltage is applied in a constant direction at least over the residence time of the exhaust gas in the plasma reactor, and it does not deny that the direction of the applied voltage changes. Therefore, in the present invention, the DC voltage component may be any voltage that applies a voltage in a certain direction over a certain period, for example, 10 minutes. Of course, the DC voltage component may always be in a fixed direction.

  In the present invention, the “pulse voltage component” means a voltage that shows a waveform that rapidly increases and then decreases rapidly, and includes not only DC pulses but also AC pulses. For example, the pulse width of the pulse voltage component may be 10 nsec to 10 μsec.

  In one aspect, the power source for the plasma reactor of the present invention can alternately switch the direction of the DC voltage component, particularly both the DC voltage component and the pulse voltage component.

  According to this aspect, the direction of the electric field in the plasma reactor can be switched to switch the direction in which the charged PM is attracted by the Coulomb force. Therefore, PM deposition in the plasma reactor can be made relatively uniform.

  The plasma reactor of the present invention is a plasma reactor having an electrode pair sandwiching an exhaust gas flow channel, and is characterized in that a voltage is applied to the electrode pair by the plasma reactor power source of the present invention.

  According to the plasma reactor of the present invention, the charging and electrostatic collection of PM are promoted by the DC voltage component applied to the electrode pair, and the activation of the exhaust gas component and the combustion removal of PM are promoted by the pulse voltage component. can do.

  In one aspect, the plasma reactor according to the present invention has an electrode pair sandwiching the exhaust gas flow channel at an electric field that is non-parallel to the exhaust gas flow direction, particularly at an angle greater than 45 ° or 60 ° with respect to the exhaust gas flow direction. An electric field, more particularly an electric field perpendicular to the direction of the exhaust gas flow, can be created.

  According to this aspect, the deposition of relatively uniform PM in the plasma reactor can be promoted by making the exhaust gas flow direction different from the direction in which the charged PM is attracted by the Coulomb force due to the effect of the electric field.

  In one aspect, the plasma reactor of the present invention is characterized in that a PM collection structure is disposed in an exhaust gas flow passage between electrode pairs.

According to this aspect, the charging and electrostatic collection of the PM are promoted by the DC voltage component, and the active PM (for example, oxygen radical, ozone, NO _x radical) generated by the pulse voltage component is used to collect the PM. Can promote combustion removal.

Here, this PM collection structure has an arbitrary structure used for collecting PM in exhaust gas, such as a honeycomb structure or a packed bed of pellets, and particularly an exhaust gas purification catalyst or NO. _x is a honeycomb structure on which at least one of the occlusion materials is supported.

The exhaust gas purification catalyst may be a catalyst that promotes purification of exhaust gas, particularly purification of PM, NO _x , CO, and HC in the exhaust gas. For example, PM oxidation catalyst, three-way catalyst, NO _x storage reduction catalyst, or NO _x selective reduction What is called a catalyst may be sufficient. The NO _x storage material is an element selected from the group consisting of alkali metal elements, alkaline earth metal elements, and rare earth elements.

  The exhaust gas purifying apparatus of the present invention includes the plasma reactor of the present invention and a PM trapping portion on the downstream side of the exhaust gas flow.

According to the exhaust gas purifying apparatus of the present invention, in the plasma reactor of the present invention, it is possible to charge the PM with the DC voltage component and activate the exhaust gas component with the pulse voltage component. In addition, in the PM collection section on the downstream side of the exhaust flow, the collection of PM charged in the plasma reactor, the oxidation of PM by the active component of the exhaust gas generated in the plasma reactor, and the purification of NO _x , CO and HC It can be carried out.

Here, the PM trapping part has an arbitrary structure used for trapping PM in exhaust gas, such as a honeycomb structure or a packed bed of pellets, and in particular, an exhaust gas purification catalyst or NO _x. A honeycomb structure on which at least one of the occlusion materials is supported. Further, a plasma reactor having a honeycomb structure as shown in FIGS. 3 and 4 can also be used as the PM collecting part.

The exhaust gas purification catalyst may be a catalyst that promotes purification of exhaust gas, particularly purification of PM, NO _x , CO, and HC in the exhaust gas. For example, PM oxidation catalyst, three-way catalyst, NO _x storage reduction catalyst, or NO _x selective reduction What is called a catalyst may be sufficient. The NO _x storage material is an element selected from the group consisting of alkali metal elements, alkaline earth metal elements, and rare earth elements.

  The exhaust gas purification method of the present invention is characterized in that a superimposed voltage having a DC voltage component and a pulse voltage component is applied to an electrode of a plasma reactor having an electrode pair sandwiching an exhaust gas flow channel.

  According to the exhaust gas purification method of the present invention, the charging and electrostatic collection of PM can be promoted by the pulse voltage component and the DC voltage component, and the activation of the exhaust gas component and the combustion removal of PM can be promoted.

  According to the power source for plasma reactor, the plasma reactor, the exhaust gas purification apparatus, and the exhaust gas purification method of the present invention, the charging and electrostatic collection of PM are promoted by the pulse voltage component, the DC voltage component, and the exhaust gas component is activated. In addition, combustion removal of PM can be promoted.

  In the following, the present invention will be specifically described based on the embodiments shown in the drawings. However, these drawings show an outline of the present invention and are not limited to the present invention.

“Power supply for plasma reactor”
An example of the superimposed voltage applied by the plasma reactor power source of the present invention will be described with reference to FIG.

  In the plasma reactor power source of the present invention, as shown in FIG. 1, a superimposed voltage (c) of a DC voltage (a) and a pulse voltage (b) is applied to the plasma reactor.

  As described above, the application of the pulse voltage (b) is unsuitable for PM charging and electrostatic collection. This is because the period during which the electric field is generated is short. However, the application of a pulse voltage is suitable for activation of exhaust gas components and PM removal by combustion because the discharge energy supplied instantaneously increases. In addition, since an electric field is always generated when a DC voltage (a) is applied, it is optimally suited for PM charging and electrostatic collection, but is not suitable for activation of exhaust gas components.

  Therefore, as in the plasma reactor power source of the present invention, when the superimposed voltage (c) of the DC voltage (a) and the pulse voltage (b) is applied to the plasma reactor, the activation of the exhaust gas component and the effect of the pulse voltage component are achieved. The combustion removal of PM can be promoted, and the charging and electrostatic collection of PM can be promoted by the DC voltage component.

  In the plasma reactor power source of the present invention, as shown in FIG. 2, a superimposed voltage (c) of a DC voltage (a) switching between positive and negative directions and a pulse voltage (b) switching similarly between positive and negative directions. It can be applied to the plasma reactor.

  The DC voltage component that can be applied by the plasma reactor power source of the present invention can be set as a voltage that can charge the PM and electrostatically collect it. This DC voltage can be, for example, a DC voltage of 1 to 50 kV, particularly 20 to 40 kV. The DC voltage component also applies a voltage in a constant direction over at least the residence time of the exhaust gas in the plasma reactor, for example, for at least 1 second, at least 10 seconds, at least 1 minute, at least 10 minutes, or at least 1 hour. Anything is acceptable. Of course, the DC voltage component may always be in a fixed direction.

  The pulse voltage component that can be applied by the power source for the plasma reactor of the present invention can be set as a pulse frequency, a pulse width, and a pulse voltage that can generate corona discharge. These pulse frequencies and the like may be subject to certain restrictions from the design of the apparatus and the economy, but a high voltage and a short pulse are desirable from the viewpoint of generating corona discharge satisfactorily. The pulse frequency, pulse width and pulse voltage are 0.5 kHz to 50 kHz, especially 2 kHz to 20 kHz, 10 nsec to 10 μsec, especially 1 μsec to 5 μsec, and 100 V to 50 kV, especially 5 kV to 30 kV. The pulse voltage can be as follows.

  In the operation of the power source for the plasma reactor of the present invention, it is possible to always apply a superimposed voltage having a DC voltage component and a pulse voltage component, but normally, a DC voltage is applied to collect PM. If necessary, a pulse voltage component can be added as a superimposed voltage to promote activation of exhaust gas components and oxidation of PM.

  In the plasma reactor power source of the present invention, a positive voltage or a negative voltage can be applied, but it is preferable to apply a negative voltage. This is because it is more energetically advantageous to apply a negative voltage to give electrons than to apply a positive voltage to extract electrons from PM or gas.

[Plasma reactor]
The psmariaactor of the present invention may be as shown in FIG. Here, FIG. 3 is a side view of the first embodiment of the plasma reactor of the present invention, and FIG. 3B is a sectional view of the plasma reactor.

  In the plasma reactor 30, an outer peripheral electrode 34 is disposed around a cylindrical honeycomb structure 32, and a rod-shaped electrode 36 that is paired with the outer peripheral electrode 34 is disposed on the central axis of the honeycomb structure 32. . The outer peripheral electrode 34 is grounded, and the rod-shaped electrode 36 is connected to the plasma reactor power source 38 of the present invention. This plasma reactor 30 is used so that the exhaust gas flows in the honeycomb structure 32 in the direction indicated by the arrow 39.

  In the use of the plasma reactor 30 shown in FIG. 3, an electric field is generated between the outer peripheral electrode 34 and the rod-shaped electrode 36 by operating the plasma reactor power source 38. This electric field is transverse to the flow direction of the exhaust gas flowing in the flow path of the honeycomb structure 32. Therefore, the charged PM is pressed against the honeycomb wall surface of the honeycomb structure 32 by the Coulomb force generated by the electric field, and the collection of PM is promoted.

  The psmariacter to which a voltage is applied by the plasma reactor power source of the present invention may be as shown in FIG. Here, FIG. 4 is a side view of the second embodiment of the plasma reactor of the present invention, and FIG. 4B is a sectional view of the plasma reactor.

  In this plasma reactor 40, plate electrodes 44 and 46 are disposed on the upper and lower surfaces of a rectangular honeycomb structure 42, respectively. Here, the upper electrode 44 is grounded, and the lower electrode 46 is connected to the plasma reactor power supply 48 of the present invention. The plasma reactor 40 is used so that the exhaust gas circulates in the honeycomb structure 42 in the direction indicated by the arrow 49.

  In the use of the plasma reactor 40 shown in FIG. 4, an electric field is created between the upper electrode 44 and the lower electrode 46 by operating the plasma reactor power supply 48. This electric field is transverse to the flow direction of the exhaust gas flowing in the flow path of the honeycomb structure 42. Therefore, the charged PM is pressed against the honeycomb wall surface of the honeycomb structure 42 by the Coulomb force generated by the electric field, and the collection of PM is promoted.

  Hereinafter, each part constituting the plasma reactor of the present invention shown in FIGS. 3 and 4 will be described in detail.

  The honeycomb structure 32 (42) may be a ceramic honeycomb structure such as a cordierite honeycomb structure. The honeycomb structure may be a straight flow type or a wall flow type. However, the straight flow type is preferable from the viewpoint of ventilation resistance, and a good PM can be obtained even if a straight flow type honeycomb structure is used. Capture can be achieved.

The honeycomb structure 32 (42) may carry a PM oxidation catalyst for burning PM. Here, as the _catalyst, mention may be made of _{CeO 2, Fe / CeO 2,} Pt / CeO 2, Pt / Al 2 O 3, Mn / CeO 2, or CeO ₂ which carries an alkali metal or alkaline earth metal . Further, this CeO ₂ may be replaced with CeO ₂ —ZrO ₂ solid solution or Fe ₂ O ₃ . One or more of these metal oxides can be used in combination. In order to carry this metal oxide on the honeycomb structure 32 (42), an arbitrary method such as wash coating and subsequent firing can be used.

In these embodiments, the honeycomb structure 32 (42) is disposed between the outer peripheral electrode 34 and the rod-shaped electrode 36 (between the upper electrode 44 and the lower electrode 46). Alternatively, these electrodes may directly face each other without being arranged, and a space in which exhaust gas flows may be provided between these electrodes. In this case, an insulating material such as Al ₂ O ₃ is coated on the inner side of the outer peripheral electrode 34 (the exhaust gas flow channel side of the upper electrode 44 and the lower electrode 46), and stable barrier discharge occurs between the electrodes. Can be.

  The electrodes 34 and 36 (44 and 46) can be made of a material capable of applying a voltage between these electrodes. As the material, a conductive material or a material such as a semiconductor can be used, but a metal material is preferable. Specifically, copper, tungsten, stainless steel, iron, platinum, aluminum or the like can be used as the metal material, and stainless steel is particularly preferable from the viewpoint of cost and durability. The rod-shaped electrode 36 that can be used in the present invention is generally a metal wire, but a hollow rod-shaped electrode can also be used. The outer peripheral electrode 34 (the upper electrode 44 and the lower electrode 46) can be made by winding or pasting these materials as a metal mesh or metal foil around the honeycomb structure 32 (42), and forming the conductive paste into the honeycomb. It can be made by applying to the structure 32 (42). In the embodiment shown in FIG. 4, the upper electrode 44 and the lower electrode 46 can be made of metal meshes having different roughnesses to promote discharge.

  Here, the electrode 36 (44) is connected to the plasma reactor power source 38 (48) and the other electrode 34 (48) is grounded, but this can of course be reversed. Instead of grounding one of the electrodes, both electrodes may be connected to the plasma reactor power source to apply the opposite voltage. Furthermore, any electrode can be a cathode or an anode.

[Usage of plasma reactor]
The plasma reactor of the present invention can be used as shown in FIG. In other words, it is used on the downstream side of the engine to mainly charge the PM and activate the exhaust gas component, and further supports a PM trapping part, particularly a catalyst for purifying PM, NO _x , HC and CO further downstream. By arranging the honeycomb structure, it is possible to purify exhaust gas components and collect and oxidize PM.

  When using the arrangement of FIG. 5 (a), the electrodes of the plasma reactor of the present invention are made to face each other directly or through an insulating coating on at least one surface of these electrodes. It is preferable to allow exhaust gas to circulate between them.

The plasma reactor of the present invention can also be used as shown in FIG. That is, the plasma reactor of the present invention can be used not only to charge the PM and activate the exhaust gas components, but also to purify NO _x , HC and CO, and collect and oxidize PM.

When the arrangement shown in FIG. 5B is used, an insulating honeycomb structure such as a ceramic honeycomb is arranged between the electrodes of the plasma reactor of the present invention, and an exhaust purification catalyst such as a ternary element is arranged on the honeycomb structure. It is particularly preferable to support a catalyst, a NO _x purification catalyst such as a NO _x storage reduction catalyst and a NO _x selective reduction catalyst, and / or a PM oxidation catalyst.

  The present invention will be described below based on examples, but the present invention is not limited thereto.

As shown in FIG. 6, an exhaust gas purification test was conducted by flowing exhaust gas from a 2.2 L diesel engine through a plasma reactor. Here, a part of the exhaust gas from the plasma reactor was supplied to the exhaust gas analyzer, and the purification rates of HC, CO and NO _x were measured. Further, the other part of the exhaust gas from the plasma reactor was passed through a full tunnel, and a part was supplied to a quartz collection filter, and the PM collection efficiency was measured by a gravimetric method.

  A schematic diagram of the plasma reactor used in the experiment is shown in FIG.

In the plasma reactor 70, a converter vessel 74 that holds a ceramic honeycomb structure 76 is disposed on the downstream side of an exhaust pipe 72 and a cone 73 having an alumina cylinder on the inner periphery. Here, the exhaust pipe 72, the cone 73, and the converter container 74 are all made of stainless steel. The ceramic honeycomb structure 76 was a cylinder having a diameter of 103 mm and a length of 155 mm, and was coated with 240 g / honeycomb structure-L of Al ₂ O ₃ and 0.2 mol / honeycomb structure-L of K. Between the ceramic honeycomb structure 76 and the converter vessel 74, a ceramic fiber cushioning material having a thickness of about 5 mm was disposed.

  A rod-like electrode 75 is disposed on the central axis of the exhaust pipe 72, the cone 73, the converter container 74, and the ceramic honeycomb structure 76. The rod-like electrode 75 is connected to a power source 78, and the stainless steel exhaust pipe 72 and the converter container 74 are grounded to serve as a counter electrode.

[Comparative Example 1]
In Comparative Example 1, a DC voltage as shown in FIG. 1A was applied from the power source 78 to the rod-like electrode 75 with a magnitude of −30 kV. That is, V ₀ was set to −30 kV in FIG.

[Comparative Example 2]
In Comparative Example 2, a pulse voltage as shown in FIG. 1B was applied from the power source 78 to the rod-shaped electrode 75 at a magnitude of −30 kV. That is, in FIG. 1B, V _i is set to −30 kV. Here, the pulse width is 2 μs and the frequency is 10 kHz.

[Example]
In the example, a superimposed voltage as shown in FIG. 1C was applied from the power source 78 to the rod-shaped electrode 75. Here, both the DC voltage component and the pulse voltage component were set to −30 kV. That is, in FIG. 1C, V ₀ is set to −30 kV, and V ₀ + V _i is set to −60 kV. Here, the pulse width is 2 μs and the frequency is 10 kHz.

  In any of Comparative Examples 1 and 2 and Examples, discharge was mainly generated between the stainless steel exhaust pipe 72 having an alumina cylinder on the inner periphery and the rod-like electrode 75.

[PM collection rate test]
The engine speed was 2000 rpm and the torque was 30 Nm. The inlet gas temperature at this time was about 200 ° C. Without installing the plasma reactor 70, PM in the exhaust gas was collected with a quartz collection filter for 3 minutes, and the amount thereof was measured. Then, the plasma reactor 70 was installed, PM in exhaust gas was collected with the quartz collection filter using the three types of applied voltages of Comparative Examples 1 and 2, and the Example, and the quantity was measured. The measurement was performed 12 times every 10 minutes. Based on the amount of PM collected when the plasma reactor 70 was not installed, the PM collection rate in Comparative Examples 1 and 2 and Examples was determined.

  The PM collection rates obtained in Comparative Examples 1 and 2 and Examples are shown in FIG.

  As is apparent from FIG. 8, in Comparative Example 1 using a direct current, the PM collection rate decreased with the passage of time, and became approximately 0% after 90 minutes. This is considered to be due to the separation of the deposited PM accompanying the deposition of PM, the current flowing through the PM due to the deposition of PM, and the electric field strength in the honeycomb structure 76 being lowered.

  In Comparative Example 2 using a pulse voltage, the PM collection rate was initially lower than that in Comparative Example 1. This is considered to be due to the fact that the effect of charging and electrostatic collection of PM is less likely to occur compared to Comparative Example 1 because the voltage is applied only momentarily. However, in Comparative Example 2, unlike Comparative Example 1, the PM collection rate did not decrease with time. This is considered to be due to the fact that the PM on which the exhaust gas component activated by the pulse voltage was deposited was continuously oxidized, and thus the collected PM was prevented from being peeled off and energized to the deposited PM.

  In the example using the superimposed voltage, the PM collection rate was high from the beginning, and this collection rate could be maintained until the end. This is because the charging and collection of the PM can be achieved by the DC voltage component, and the PM deposited by the pulse voltage component can be continuously oxidized, thus preventing the collected PM from peeling and energizing the deposited PM. it is conceivable that.

[NO → NO ₂ conversion test]
This test was performed in a state where K / Al ₂ O ₃ was not coated on the honeycomb structure. The NO → NO ₂ conversion obtained in Comparative Examples 1 and 2 and the Examples is shown in FIG.

As is clear from FIG. 9, it was confirmed that the NO → NO ₂ conversion rate test was high in Comparative Example 2 using a pulse voltage and Example using a superimposed voltage having a pulse voltage component. The NO ₂ obtained here is an important component regarding the oxidation of PM. Therefore, in the PM collection rate test regarding Comparative Example 2 and Examples, it is considered that the oxidation of the deposited PM was promoted even by the presence of NO _{2 in} the exhaust gas. Further, in this experiment in addition to NO ₂ O _3, O ₂ ^- there is a high possibility that the like are generated, these production of order is believed to be the same as the rank NO _2.

[Exhaust gas purification test]
The engine speed was 2000 rpm and the torque was 30 Nm. The inlet gas temperature at this time was about 200 ° C. Without installing the plasma reactor 70, the amounts of NO _x , HC and CO in the exhaust gas were measured by the exhaust gas analyzer 66. A plasma reactor 70 was installed, and the amounts of NO _x , HC and CO in the exhaust gas were measured with an exhaust gas analyzer using the three types of applied voltages of Comparative Examples 1 and 2 and the Example. Based on the amounts of NO _x , HC and CO in the exhaust gas when the plasma reactor 70 was not installed, the purification rates of NO _x , HC and CO in Comparative Examples 1 and 2 and the examples were determined.

The purification rates of NO _x , HC and CO obtained in Comparative Examples 1 and 2 and the examples are shown in FIG.

  As can be seen from FIG. 10, when compared with Comparative Example 1 in which no pulse voltage is used, Comparative Example 2 and Example showed a high exhaust gas purification rate. This is believed to be due to the pulse voltage activating the exhaust gas component. Even in comparison with Comparative Example 2, the exhaust gas purification rate was high in the Examples. This is considered to be due to maintaining a higher electric field strength in the examples.

It is a figure showing the example of the superimposed voltage applied with the power supply for plasma reactors of this invention. It is a figure showing the other example of the superimposed voltage applied with the power supply for plasma reactors of this invention. It is the perspective view and sectional drawing showing the plasma reactor of this invention. It is the perspective view and sectional drawing showing the other plasma reactor of this invention. It is a figure which shows the usage condition of the plasma reactor of this invention. It is a flowchart of the apparatus used by the Example and the comparative example. It is a partial see-through | perspective perspective view of the plasma reactor used by the Example and the comparative example. It is a figure which shows the PM collection rate obtained by the Example and the comparative example. Shows the resulting NO → NO ₂ conversion in Examples and Comparative Examples. It is a figure which shows the exhaust gas purification rate obtained by the Example and the comparative example.

Explanation of symbols

30, 40 ... Plasma reactors 32, 42 ... Honeycomb structure 34 ... Peripheral electrode 36 ... Rod electrodes 38, 48 ... Power source 39, 49 ... Plasma reactor direction arrow 44 ... Upper electrode 46 ... Lower electrode 70 ... Plasma reactor 72 ... exhaust pipe 73 ... cone 74 ... converter vessel 75 ... rod electrode 76 ... ceramic honeycomb structure 76

Claims (8)

  A power source for a plasma reactor, characterized by generating a superimposed voltage having a DC voltage component and a pulse voltage component.   The power supply for a plasma reactor according to claim 1, wherein the direction of the DC voltage component is maintained in a constant direction, and the pulse width of the pulse voltage component is 10 nsec to 10 µsec.   The power source for a plasma reactor according to claim 1 or 2, wherein the direction of the DC voltage component is alternately switched.   A plasma reactor having an electrode pair sandwiching an exhaust gas flow channel, wherein a voltage is applied to the electrode pair by the plasma reactor power source according to any one of claims 1 to 3.   The plasma reactor according to claim 4, wherein the electrode pair creates an electric field that is non-parallel to the exhaust gas flow direction.   6. The plasma reactor according to claim 4, wherein a PM trapping structure is disposed in the exhaust gas flow passage between the electrode pairs.   An exhaust gas purification apparatus comprising: the plasma reactor according to any one of claims 4 to 6; and a PM trapping portion downstream of the exhaust gas flow.   An exhaust gas purification method, comprising applying a superimposed voltage having a DC voltage component and a pulse voltage component to an electrode of a plasma reactor having an electrode pair sandwiching an exhaust gas flow channel.

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