JP2023035098A - Exhaust purification device - Google Patents

Abstract

To provide an exhaust purification device capable of preventing defective electric discharge with an electrode discharging electricity inside the exhaust purification device exposed to moisture.SOLUTION: A catalyst converter 16 which is installed in an exhaust passage of an internal combustion engine comprises: a honeycomb catalyst 16a with a catalyst purifying exhaust supported therein; and a high-voltage electrode 16b which is inserted into the honeycomb catalyst 16a from a downstream side in an exhaust flow direction and discharges electricity inside the honeycomb catalyst 16a with high voltage applied thereto. The high-voltage electrode 16b is arranged at a position away from a moisture exposed region 10, on the honeycomb catalyst 16a, exposed to moisture flowing into the honeycomb catalyst 16a.SELECTED DRAWING: Figure 4

Description

The present invention relates to an exhaust purification device.

Conventionally, in detecting an abnormality in an exhaust gas purification device (plasma reactor) that purifies exhaust gas using plasma generated by applying an AC voltage to a pair of facing electrodes, an abnormality in the plasma reactor is detected based on an increase in discharge current. is detected, and insulation failure may occur temporarily when there is a lot of moisture, such as immediately after starting, so it is known to stop abnormality determination while the exhaust temperature is low (for example, Patent Document 1) .

Japanese Patent Application Laid-Open No. 2004-340037

Under conditions where the exhaust temperature is low, such as immediately after starting the internal combustion engine, part of the moisture discharged from the engine body exists as a condensed liquid, and when this moisture adheres to the electrodes of the plasma reactor, plasma generation is suppressed. , there is a problem that purification of exhaust gas by plasma is hindered. In particular, when a plasma reactor is provided with a catalyst carrier that supports a catalyst, and electrodes are inserted into the catalyst carrier, water is taken into the cells of the catalyst carrier and tends to adhere to the electrodes.

In the technology described in the above patent document, while the exhaust temperature is low, such as immediately after starting, the abnormality determination based on the discharge current is stopped. not, and there is room for improvement.

In view of the above problems, an object of the present disclosure is to provide an exhaust gas purification device capable of suppressing interference with discharge due to water exposure of electrodes that generate discharge inside the exhaust gas purification device. be.

The gist of the present disclosure is as follows.
(1) An exhaust purification device provided in an exhaust passage of an internal combustion engine,
a catalyst carrier on which a catalyst for purifying exhaust gas is carried;
an electrode that is inserted into the catalyst carrier from the downstream side in the direction of flow of the exhaust gas and that is applied with a high voltage to generate electric discharge inside the catalyst carrier;
with
The exhaust purification device, wherein the electrode is arranged to avoid a region where the catalyst carrier is wetted by moisture flowing into the catalyst carrier from the upstream side in the exhaust gas flow direction.

Advantageous Effects of Invention According to the present disclosure, it is possible to prevent the discharge from being hindered due to the electrodes that generate discharge inside the exhaust purification device being wet.

1 is a schematic diagram showing a schematic configuration of an internal combustion engine and its surroundings according to an embodiment; FIG. 1 is a perspective view showing the configuration of a catalytic converter; FIG. FIG. 4 is a schematic cross-sectional view showing a state in which the high voltage electrode and the ground electrode are short-circuited due to the catalytic converter getting wet with water discharged from the engine body and the water adhering to the high voltage electrode and the ground electrode. FIG. 4 is a schematic cross-sectional view showing an example in which high-voltage electrodes are arranged so as to avoid the wet area when the wet area occurs as shown in FIG. 3 ; FIG. 4 is a characteristic diagram showing the waveform of a discharge current flowing between a high voltage electrode and a ground electrode; FIG. 4 is a schematic cross-sectional view showing a case in which a wet area is unevenly generated in a direction perpendicular to the flow direction of exhaust gas; FIG. 7 is a schematic cross-sectional view showing an example in which high-voltage electrodes are arranged so as to avoid the wet area when the wet area occurs as shown in FIG. 6 ; FIG. 4 is a schematic cross-sectional view showing an example in which a plurality of high voltage electrodes are provided; FIG. 4 is a schematic diagram for explaining control for switching ON/OFF of the voltage to the high-voltage electrode according to the size of the wetted area;

Hereinafter, embodiments will be described in detail with reference to the drawings. In the following description, the same reference numerals are given to the same constituent elements.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a schematic configuration of an internal combustion engine and its surroundings according to this embodiment. Referring to FIG. 1, 1 indicates an engine body, 2 indicates a combustion chamber of each cylinder, and 3 indicates an exhaust manifold. An outlet of the exhaust manifold 3 is connected to a catalytic converter 16 via an exhaust pipe 4a. An outlet of the catalytic converter 16 is open to the atmosphere through an exhaust pipe 4b. In this embodiment, the catalytic converter 16 is equipped with a plasma generator, and a high voltage electrode 16b is inserted into the catalytic converter 16 . An electronic control unit (ECU) 18 controls the voltage applied to the high voltage electrode 16b by controlling the high frequency power supply 16d.

FIG. 2 is a perspective view showing the configuration of the catalytic converter 16. As shown in FIG. The catalytic converter 16 is one aspect of an exhaust purification device provided in the exhaust passage. FIG. 2 schematically shows a state in which the honeycomb catalyst 16a is inserted into the catalytic converter 16. As shown in FIG. A high voltage electrode 16b is inserted in the honeycomb catalyst 16a. A high frequency voltage is applied to the high voltage electrode 16b from a high frequency power source 16d. On the other hand, the outer cylinder of the catalytic converter 16 into which the honeycomb catalyst 16a is inserted is grounded and serves as a ground electrode 16c. A plasma generation device 50 is composed of the high-voltage electrode 16b, the ground electrode 16c, and the high-frequency power source 16d. The high-voltage electrode 16b is inserted into the honeycomb catalyst 16a from the downstream side in the exhaust flow direction, and a high voltage is applied to the honeycomb catalyst 16a to generate electric discharge inside the honeycomb catalyst 16a.

The honeycomb catalyst 16a has a normal catalyst for exhaust purification, oxidizes HC to water and carbon dioxide, oxidizes CO to carbon dioxide, and reduces NOx to nitrogen and oxygen, respectively. do. Therefore, the honeycomb catalyst 16a has noble metals such as Pt (platinum), Pd (palladium), and Rh (rhodium) as catalyst components.

When a high frequency high voltage is applied to the high voltage electrode 16b, a discharge current 30 flows between the high voltage electrode 16b and the ground electrode 16c toward the outside of the high voltage electrode 16b, generating plasma. Nitrogen oxides (NOx) in the exhaust gas are decomposed into nitrogen and oxygen by the plasma, and the exhaust purification performance is improved. In particular, under conditions where the exhaust gas temperature is low (for example, 100° C. or lower) such as immediately after the start of the internal combustion engine, the honeycomb catalyst 16a cannot sufficiently purify the exhaust gas. Since the exhaust gas is purified even before the internal combustion engine is warmed up, the exhaust gas purification performance is improved especially when the internal combustion engine is started.

More specifically, when a high-frequency high voltage is applied between the high-voltage electrode 16b and the ground electrode 16c, electrons are ejected from the atoms of the material forming the electrodes due to discharge, and the electrons diffuse in the honeycomb catalyst 16a. It collides with purification target gas such as NOx flowing in the honeycomb catalyst 16a. Due to the collision of electrons, the state of gas components such as NOx becomes unstable, and they are decomposed into radical species such as N and O according to the following equations (1) and (2). Radical species such as hydroxyl radicals are generated by the action of electrons on moisture present in the exhaust gas.

O ₂ +e ⁻ →O ⁻ +O (1)
NO + e ^- → N + O ^- (2)

Oxygen and nitrogen are generated from the generated radical species by the catalytic action of the honeycomb catalyst 16a, for example, according to the following formulas (3) and (4). As a result, NOx in the exhaust is reduced. In formulas (3) and (4), M represents a catalyst. Also, hydroxyl radicals oxidize HC in the exhaust.

O+O→O ₂ (3)
M.

N+N→N ₂ (4)
M.

However, under conditions where the exhaust temperature is low, such as immediately after starting the internal combustion engine, part of the moisture discharged from the engine body 1 exists as a condensed liquid, and the moisture adheres to the high voltage electrode 16b and the ground electrode 16c. , Plasma may not be generated normally. In such a case, the plasma generator 50 cannot purify the exhaust.

FIG. 3 shows a state in which the catalyst converter 16 is exposed to moisture discharged from the engine body 1, and the moisture adheres to the high voltage electrode 16b and the ground electrode 16c, causing a short circuit between the high voltage electrode 16b and the ground electrode 16c. It is a schematic sectional view showing. As shown in FIG. 3 , since water flows from the engine body 1 , the upstream side of the catalytic converter 16 in the flow direction of the exhaust is wet. More specifically, in the example shown in FIG. 3 , in the flow direction of the exhaust gas, a region at a distance A from the upstream end of the catalytic converter 16 is wet, and is the wet region 10 . In the flow direction of the exhaust gas, a region of distance B downstream of the wet region 10 is a dry region that is not wet. In the wet region 10, the high voltage electrode 16b and the ground electrode 16c are short-circuited by being wetted. FIG. 3 shows a state in which an unintended discharge (spark 20) occurs due to a short circuit between the high voltage electrode 16b and the ground electrode 16c.

The honeycomb catalyst 16a is one embodiment of a catalyst carrier that has a plurality of cells through which exhaust gas flows and carries a catalyst that purifies the exhaust gas. configured. A cell is an air layer through which the exhaust gas passes, and the inner wall of the cell is provided with pores. For this reason, when liquid moisture flows from the upstream side, the liquid moisture is taken into the pores of the inner walls of the cells, and furthermore, the liquid moisture is taken into the cells, thereby generating the wet area 10 . If a pair of electrodes to which a high voltage is applied is inserted in the wetted region 10, the electrodes will be short-circuited and a large current will flow. The flow of such a large current causes problems such as no current flowing to a portion (catalyst cell) to be discharged, overloading the power supply, and possibly breaking the power supply.

If the high-voltage electrode 16b and the ground electrode 16c are short-circuited due to exposure to water, plasma cannot be generated. Also, even if the high voltage electrode 16b and the ground electrode 16c are not completely short-circuited, when the high voltage electrode 16b is wet, the generation of plasma is suppressed and the plasma is not normally generated. Therefore, the exhaust purification performance is degraded due to exposure to water.

In this embodiment, the arrangement of the electrodes with respect to the wetted region 10 is optimized, and the high-voltage electrode 16b is a wetted region where the honeycomb catalyst 16a is wetted by moisture flowing into the honeycomb catalyst 16a from the upstream side in the exhaust flow direction. It is arranged avoiding 10. FIG. 4 is a schematic cross-sectional view showing an example in which the high-voltage electrode 16b is arranged so as to avoid the wet area 10 when the wet area 10 is generated as shown in FIG. In the example shown in FIG. 4, the length of the high voltage electrode 16b is shorter than in the example shown in FIG. More specifically, the tip of the high-voltage electrode 16b is positioned downstream of the wet area 10 . The range (distance A) of the wetted area 10 in the catalytic converter 16 can be determined at the design stage, or can be determined through experiments.

As described above, the catalytic converter 16 is exposed to water when the exhaust gas temperature is low, such as immediately after starting the internal combustion engine. Although the amount of water that flows as a liquid from the engine body 1 immediately after starting may vary depending on the operating conditions (exhaust temperature, fuel injection amount, etc.), it can be determined as a general water content according to a certain operating condition. , the range of the wetted area 10 is determined in advance by design or experiment based on this. When the internal combustion engine is warmed up and the temperature of the exhaust gas rises, the moisture flowing from the engine body 1 becomes water vapor. Therefore, when the exhaust gas temperature rises, the catalytic converter 16 will not be newly exposed to water. Also, even in the wet region 10 where liquid moisture has already adhered, when the temperature of the exhaust gas rises, the moisture becomes water vapor and flows downstream. Therefore, the range of the wetted area 10 (distance A shown in FIG. 4) determined in advance by design or experiment does not expand further downstream.

Therefore, by inserting the high-voltage electrode 16b from the downstream side in the flow direction of the exhaust gas and arranging the tip of the high-voltage electrode 16b downstream of the water-receiving region 10, the high-voltage electrode 16b is positioned so as to avoid the water-receiving region 10. 16b can be placed. As a result, the high-voltage electrode 16b is not wetted, and plasma is normally generated.

FIG. 5 is a characteristic diagram showing the waveform of the discharge current flowing between the high voltage electrode 16b and the ground electrode 16c. Here, a characteristic C1 indicated by a solid line indicates a discharge current waveform when the high-voltage electrode 16b is arranged so as to avoid the wet area 10 of the catalytic converter 16 (FIG. 4), and a characteristic C2 indicated by a broken line indicates a high-voltage electrode. It shows a discharge current waveform when the voltage electrode 16b is wet.

As shown by the solid line characteristic C1 in FIG. 5, when the high voltage electrode 16b is not wet, the discharge current waveform is pulse-shaped. In this case, plasma is normally generated.

On the other hand, when the high-voltage electrode 16b is wet, as indicated by the dashed line characteristic C2 in FIG. 5, the discharge current waveform does not become pulsed, and no plasma is generated. Therefore, it can be seen that plasma can be generated if the high-voltage electrode 16b is not wet.

As described above, whether or not the high-voltage electrode 16b is wet can be determined from the waveform of the discharge current flowing between the high-voltage electrode 16b and the ground electrode 16c. If so, it can be determined that the high voltage electrode 16b is not wet. If the high-voltage electrode 16b is wetted and the high-voltage electrode 16b and the ground electrode 16c are short-circuited, the discharge current flowing between the high-voltage electrode 16b and the ground electrode 16c excessively increases. Whether or not 16b is wet can also be determined based on whether the value of the discharge current exceeds a predetermined value.

3 and 4 show the case where the wet area 10 is generated evenly in the direction orthogonal to the flow direction of the exhaust gas, but the wet area 10 may be affected by gravity or between the engine body 1 and the catalytic converter 16. Depending on the shape of the exhaust pipe 4a (the degree of curvature of the exhaust pipe 4a) that connects the , there is a case where it is biased toward the outer peripheral side from the central axis of the catalytic converter 16 in the direction perpendicular to the flow direction of the exhaust gas. More specifically, wetted region 10 may occur downward in the direction of gravity within catalytic converter 16 . Also, the wetted region 10 may occur in a direction perpendicular to the flow direction of the exhaust gas, in a direction corresponding to the bent outer side of the exhaust pipe 4a on the upstream side of the catalytic converter 16 .

FIG. 6 is a schematic cross-sectional view showing a case where the wetted area 10 is unevenly generated in the direction perpendicular to the flow direction of the exhaust gas. In the example shown in FIG. 6, the wetted area 10 is biased downward in the direction orthogonal to the flow direction of the exhaust gas. Even in this case, if the high-voltage electrode 16b is wet, plasma will not be generated normally.

FIG. 7 is a schematic cross-sectional view showing an example in which the high-voltage electrode 16b is arranged so as to avoid the wet area 10 when the wet area 10 is generated as shown in FIG. Since the wetted region 10 is biased downward in the direction perpendicular to the flow direction of the exhaust gas, the high-voltage electrode 16b is arranged on the outer circumference so as to be away from the wetted region 10 in the direction perpendicular to the flow direction of the exhaust gas. It is arranged offset in the direction (upward). As a result, the high voltage electrode 16b is not exposed to water, and the high voltage electrode 16b and the ground electrode 16c are not short-circuited. Therefore, plasma is normally generated. In the example shown in FIG. 7, since the high-voltage electrode 16b is not exposed to water by arranging the high-voltage electrode 16b above the wet area 10, the length of the high-voltage electrode 16b is reduced as in the example of FIG. length must not be shortened.

FIG. 8 is a schematic cross-sectional view showing an example in which a plurality of high voltage electrodes are provided. 8, in the example of FIG. 7, in addition to the high voltage electrode 16b arranged above the wetted area 10 in the direction orthogonal to the flow direction of the exhaust gas, the high voltage electrode 16b is arranged below the high voltage electrode 16b. 16b' are arranged. The length of the high voltage electrode 16b' is shorter than that of the upper high voltage electrode 16b so that the high voltage electrode 16b' does not enter the wet area 10. As shown in FIG. As a result, the high voltage electrode 16b' is not exposed to water, and the high voltage electrode 16b' and the ground electrode 16c are not short-circuited. Therefore, plasma is normally generated. Thus, when a plurality of high voltage electrodes are provided, each high voltage electrode is arranged so as to avoid the wetted area 10 . When the plasma generator 50 has a plurality of high-voltage electrodes, the distance between each high-voltage electrode and the ground electrode 16c is shortened, so the voltage required for discharge can be reduced.

FIG. 9 is a schematic diagram for explaining the control of switching ON/OFF of the voltage to the high voltage electrode 16b according to the size of the wetted area 10. As shown in FIG. The high-voltage electrode 16b is arranged to avoid the wet area 10 determined from the general amount of water flowing from the engine body 1 described above. Even if the wet region 10 reaches the high-voltage electrode 16b, voltage application to the high-voltage electrode 16b is stopped while the high-voltage electrode 16b is wet.

FIG. 9 shows, in order from the top, the catalyst temperature, the size of the wetted area 10, and ON/OFF control of voltage application to the high voltage electrode 16b. In addition, the bottom part of FIG. 9 illustrates how the state of water exposure in the catalytic converter 16 changes over time.

In FIG. 9, the internal combustion engine is started at time _t0 . A high voltage is applied to the high voltage electrode 16b of the plasma generation device 50 immediately after the internal combustion engine is started, and the plasma generated by the plasma generation device 50 purifies the exhaust gas passing through the catalytic converter 16 .

At time _t0 when the internal combustion engine is started, the wet region 10 does not occur, but the wet region 10 expands as time elapses. Moreover, the temperature of the honeycomb catalyst 16a rises with the lapse of time after time _t0 .

At time t1, the size of the wet region 10 is small, and the wet region 10 does not reach the tip of the high voltage electrode 16b. Therefore, the application of the high voltage to the high voltage electrode 16b continues.

At time t2, the size of the wet region 10 increases, and the wet region 10 reaches the tip of the high voltage electrode 16b. As described above, when the high-voltage electrode 16b is not wetted, the waveform of the current flowing between the high-voltage electrode 16b and the ground electrode 6c is pulse-shaped. The waveform of the current flowing between the electrode 16b and the ground electrode 6c is not pulsed.

Therefore, the ECU 18 acquires the current flowing between the high-voltage electrode 16b and the ground electrode 6c, and stops applying the high voltage to the high-voltage electrode 16b when the waveform of the current ceases to be pulse-like at time t2. . The current flowing between the high voltage electrode 16b and the ground electrode 6c is detected by an ammeter.

Further, as described above, when the high voltage electrode 16b is wet and the high voltage electrode 16b and the ground electrode 16c are short-circuited, the discharge current flowing between the high voltage electrode 16b and the ground electrode 16c excessively increases. . Therefore, the ECU 18 may stop applying the high voltage to the high voltage electrode 16b when the current flowing between the high voltage electrode 16b and the ground electrode 6c exceeds a predetermined value.

After that, when the catalyst temperature reaches about 100° C., the moisture in the wet area 10 evaporates. As a result, the size of the wetted region 0 is reduced, and at time t3, the high-voltage electrode 16b is not wetted.

Therefore, when the catalyst temperature reaches 100.degree. C. or when a predetermined time elapses after the catalyst temperature reaches 100.degree. Note that the catalyst temperature is detected by a catalyst temperature sensor that detects the temperature of the catalytic converter 16 . After stopping the application of the high voltage to the high voltage electrode 16b, the ECU 18 may restart the application of the high voltage to the high voltage electrode 16b after a predetermined time has elapsed.

After time t3, since the catalyst temperature is 100° C. or higher, wet region 10 does not occur. Therefore, after time t3, the state in which the high voltage is applied to the high voltage electrode 16b is continued.

As described above, by switching on/off the voltage to the high voltage electrode 16b immediately after starting the internal combustion engine, it is possible to stop the application of the high voltage when the high voltage electrode 16b is wet. Further, when the moisture in the wet region 10 evaporates and the wetness disappears, the application of the high voltage to the high voltage electrode 16b can be resumed.

As described above, according to the present embodiment, the high-voltage electrode 16b of the plasma generation device 50 is inserted into the honeycomb catalyst 16a from the downstream side in the exhaust flow direction, avoiding the wet region 10 on the upstream side of the honeycomb catalyst 16a. are placed. Therefore, the high-voltage electrode 16b is prevented from being exposed to water flowing from the engine body 1 when the internal combustion engine is started. This makes it possible to generate a plasma when starting the internal combustion engine.

Further, since the high-voltage electrode 16b is arranged so as to avoid the wetted area 10, it is possible to determine the abnormality of the plasma generation device 50 based on the discharge current immediately after starting the internal combustion engine, thereby generating plasma. When the device 50 has an abnormality, it becomes possible to stop the energization to the high voltage electrode 16b.

(Modification)
In the embodiment described above, the high voltage electrode 16b is arranged so as to avoid the wet area 10 in order to prevent the high voltage electrode 16b from being wet. On the other hand, an adsorbent that adsorbs moisture may be provided upstream of the catalytic converter 16 in order to prevent the high-voltage electrode 16b from being exposed to water. In this case, the moisture flowing from the engine body 1 to the catalytic converter 16 is absorbed by the adsorbent, so that the high voltage electrode 16b in the catalytic converter 16 is prevented from getting wet.

Reference Signs List 1 engine body 3 exhaust manifold 4a exhaust pipe 4b exhaust pipe 6c ground electrode 10 wet area 16 catalytic converter 16a honeycomb catalyst 16b high voltage electrode 16b' high voltage electrode 16c ground electrode 16d high frequency power supply 18 electronic control unit (ECU)
20 spark 30 discharge current 50 plasma generator

Claims (1)

An exhaust purification device provided in an exhaust passage of an internal combustion engine,
a catalyst carrier on which a catalyst for purifying exhaust gas is carried;
an electrode that is inserted into the catalyst carrier from the downstream side in the direction of flow of the exhaust gas and that is applied with a high voltage to generate electric discharge inside the catalyst carrier;
with
The exhaust purification device, wherein the electrode is arranged to avoid a region where the catalyst carrier is wetted by moisture flowing into the catalyst carrier from the upstream side in the exhaust gas flow direction.

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