JPS6249451B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for reducing soot contained in exhaust gas from a combustion chamber of an internal combustion engine such as a diesel engine. Most of the soot, which is a component of black smoke generated from hydrocarbon flames, is fine particles with a diameter of 2 μm or less. Exhaust resistance becomes extremely large, and the size also increases. Therefore, it is almost impossible to use it to purify soot emitted from the combustion chamber of an internal combustion engine such as an automobile. Further, when the above-mentioned soot is collected by a filter device, there is a problem that the filter becomes clogged, resulting in an increase in back pressure.

Taking the above points into consideration, there is a method in which exhaust smoke is guided into an alternating, pulsed, or electrostatic field space to break down soot, which has a chain-like structure of fine particles connected, into individual fine particles. In addition, a combination has recently been developed in which the soot whose specific surface area has been increased by this operation is then oxidized by heating or catalytic action to remove it and purify the exhaust gas.

The present invention provides methods for preventing soot staining on electrode insulating parts in the first step, in which an alternating, pulsed or electrostatic voltage is applied to the soot-containing gas to decompose chain-like soot and convert it into fine particulate soot; It is related to maintaining durability. Soot particles become finer under the influence of an electric field. However, some of it is electrically charged, and this adheres to the surface of the electrode support, which also serves as an insulator, forming a soot deposit layer. However, the electrical resistance of these soots varies depending on the generation conditions, but is often on the order of MΩ-cm. Therefore, when a high voltage is applied between the electrodes to which this soot deposit layer is attached, the insulation between the electrodes decreases, leakage current increases, and
Initial clean performance is sometimes rapidly lost.

The present invention aims to improve the durability of the soot reduction device in exhaust gas as described above by preventing soot from adhering to the electrode insulation portion. That is, the present invention includes a casing formed as a part of an internal combustion engine exhaust gas flue or an exhaust gas flow path, and at least a pair of mutually insulated electrodes that form an electric field for soot atomization inside the casing. The present invention provides a soot reduction device characterized in that an air curtain is formed around a rod-shaped insulator that supports an electrode over the entire circumference and in the axial direction to prevent soot from adhering.

The present invention will be explained in detail below.

In the present invention, gas containing soot, such as combustion exhaust gas from an internal combustion engine, is guided through a flue or exhaust pipe to a predetermined electric field (alternating, pulsed is an electrostatic field) formed by at least a pair of electrodes. The aggregated particles of soot are made finer by the high-voltage electric field between the electrodes.
This soot atomization electric field has one pole (usually the ground pole) on the device casing (e.g. outer cylinder) or cylindrical mesh formed as part of the flue, and the other pole in an appropriate shape and arrangement. It is placed at the center of the flue and fixedly supported on the device outer cylinder via an insulator (center electrode). The shape of the support insulator for the center electrode is determined depending on the shape and arrangement of the center electrode, the shape of the device outer cylinder, and the like. In this application, as an example of the center electrode for the cylindrical outer cylinder ground electrode, a metal rod-shaped body arranged on the central axis of the device outer cylinder with many small protrusions formed thereon can be used, and the center electrode is supported by the center hole. A rod-shaped insulator, preferably an insulator, into which the center electrode is fitted can be fixed to a blind flange at one end of the device outer cylinder.
As the center electrode, a rod-like body without small protrusions or a net-like structure different from the rod-like body can be used. Opposing plane electrodes supported by rod-like supports, or a pair of electrodes of any other shape can also be used. .

The exhaust gas inlet to the outer cylinder is preferably disposed at the boundary between the insulator and the center electrode or near the starting point of the electrode section, orthogonal to the outer cylinder axis, or so that the inflow gas is directed obliquely to the outlet side. In other words, it is desirable to arrange the insulator in a portion that is recessed with respect to the exhaust gas flow path, for example, in a blind branch. The exhaust gas outlet is not particularly limited in the present invention, and it suffices to provide it as appropriate in the downstream region of the gas flow. As for the soot reduction device as a whole, the device of the present invention not only atomizes the soot, but also completely burns it depending on the purpose, so an active medium is usually arranged downstream of the soot atomization electric field area. An exhaust gas outlet may be located beyond that.

The clean gas blown onto the insulation can be clean air, optionally preheated air or part of cleaned exhaust gas, and optionally also the negative pressure suction of the internal combustion engine can be used. When the negative pressure suction of an internal combustion engine is used, no additional air pump is required, and there are great benefits in terms of device simplification and energy efficiency. For example, clean gas introduced from the air supply port of the blind flange can be blown onto the rod-shaped insulator for the rod-shaped center electrode along the surface of the insulator in a direction parallel to the axis. In this case, the clean gas flow can be in the form of a thin cylinder concentrically around the outer circumference of the insulator.
It is also preferable that the air be blown onto the insulator through a circumferential slit formed on the inner wall of an air supply chamber arranged around the insulator to form an air curtain. At this time, it is preferable to tilt the spraying angle appropriately in the exhaust gas flow direction and spray at least a portion including the tip of the insulator.

Note that the blown gas stream can also be blown by rotating around an axis, and can also be blown out from partial opening nozzles or other shaped nozzles appropriately arranged on the circumference, but in either case, the air Determine the nozzle arrangement and configuration to form a curtain.

In a preferred embodiment, the blown air can be sucked in from outside air through a backflow prevention device such as a reed valve using negative pressure when the engine is exhausted.

The specific configuration of the apparatus of the present invention will be described in detail below.

Configuration 1 (See Figure 1) The device casing consists of an outer cylinder 5 made of metal or a conductive material, and the exhaust gas inlet 15 is perpendicular to the outer cylinder 5 and opens near the inlet end of the outer cylinder. It is fixed and closed by a blind flange 11 with bolts, and the internal space forms a recess branching from the exhaust gas flow path. An appropriate number of air supply ports 8 are provided in the flange 11.
The air supply port 8 is connected to the outside air via an air supply pipe 25, a reed valve 7, and an air cleaner 30. Between the flange 11 and the end surface of the outer cylinder 5, a disc-shaped partition wall 13 of an appropriate thickness having a central opening 12 with a diameter slightly larger than the outer periphery of the insulator 4 is disposed at the center. It is fixed together with the flange 11 to form a.

The insulator 4 is fitted and fixed into the center hole 15 of the flange 11 via an insulator fixing fitting 16.
A supporting portion of a rod-shaped center electrode 3 is fitted and fixed into the center hole of the insulator, and the outer end of the insulator forms a terminal 10, which is connected to a high voltage power source _E1 . The outer periphery of the insulator 4 and the inner surface of the central opening 12 of the partition wall 13 form a nozzle 9 consisting of a thin-walled cylindrical space, and the insulator 4 extends further from the nozzle end to an extension of the exhaust gas inlet. However, the length of this insulator 4 can be adjusted as appropriate. Further, the inner end of the insulator 4 may be slightly tapered, and the central opening 12 of the partition wall 13 may be slightly tapered.
It can also be tapered as appropriate.

It is preferable to form an appropriate number of discharge protrusions 17 on the electrode portion of the center electrode 3. The outer cylinder 5 is grounded, and the inner surface of the outer cylinder 5 forms a ground electrode. When a high voltage is applied between the outer cylinder 5 and the center electrode, an electric field is formed in the inner space of the outer cylinder 5. If sufficient insulation is maintained, the center electrode protrusion Electric discharge occurs between 17 and the inner cylinder 5.

Exhaust gas is transferred, for example, from a silencer to exhaust gas inlet 1.
The soot flows in the direction of the arrow A, passes through the inner cylinder 5, and flows toward the exhaust gas outlet in the direction of the arrow B, and the contained soot is atomized as it passes through the electric field. At this time, the inner part of the outer cylinder of the insulator 4 is exposed to the soot-containing exhaust gas, and soot tends to adhere to its surface, but in this device,
Since clean air is blown around the outer periphery of the insulator 4 in the direction of arrow C, the surface of the insulator 4 is kept clean.

In addition, by disposing a backflow prevention valve such as a reed valve 7 in the air supply pipe, when the gas pressure in the exhaust pipe exceeds the blowing air pressure, the exhaust gas nozzle 9
backflow into the body can be prevented.

The shape of the insulator 4 can be such that the diameter tapers toward the tip or decreases (as shown in FIG. 2) like the insulator shown in FIG. 1. According to this configuration, the surface of the insulator is kept clean by the clean gas flow that is emitted from inside the insulator support portion and flows along the surface of the insulator in parallel with the axis.

Configuration 2 (See Figure 3) The exhaust gas inlet 1 for the outer cylinder 5 is opened downstream (inward) from the inner end of the insulator 4, and the exhaust gas flows in and out according to arrows A and B. be done. The inside diameters of the insulator 4 and the outer cylinder 5 are made to have the same outer diameter as shown in FIG. In this case, the blown gas flows in from the air supply port 8 of the flange 11 and moves along the insulator 4 along the arrow C or
Sprayed according to C′. Note that a conical guide as shown by a two-dot chain line 19 may also be provided. This guide can be fixed to the outer cylinder 5 together with the flange 11. A portion 24 of the insulator 4 (a branched portion when viewed from the flow path) is depressurized, and air flows in from the air supply port 8 to keep the insulator clean.

Configuration 3 (See Figure 4) The outer cylinder 5, center electrode 3, and insulator 4 are the same as those in Figure 1, and the entire circumference formed by being surrounded by a double outer cylinder instead of the flange and partition wall in the same figure. A cup-shaped blind flange 21 forming an air supply chamber 20 and a full-circumference slit-shaped nozzle 6 opening into the outer cylinder is fixed to the end of the outer cylinder 5 via a ring 23. The circumferential slit-shaped nozzle 6 is preferably formed in the shape of a conical shell so that the blown air can be ejected obliquely in the direction of the exhaust gas outlet. In this case, the air flow is ejected from the entire circumference of the nozzle 6 toward the center to form an air curtain. Note that a rotating vane can also be appropriately arranged inside the nozzle 6.

The flange 21 has a recessed space 24 in the cross section of the inner diameter of the outer cylinder to form a predetermined air chamber, has an air supply port 8 connected to the air supply chamber 20, and has an end that contacts the ring 23 on the entire circumference. It has a ring-shaped notch and forms an air supply chamber 20 (or a part thereof). ring 2
Another part of the ring-shaped air supply chamber 20 can also be formed at the end that contacts the flange 21 of No. 3. A gasket 22 corresponding to the width of the nozzle 6 is disposed between the ring 23 and the flange 21, and the gasket 22 is tightened and fixed with bolts, thereby forming a full circumference slit-shaped nozzle 6. The blown air is passed through the air cleaner 30 and the air pump 29 to the air supply pipe 25.
The air is guided to the air supply port 8 through the air.

Configuration 4 (See Figure 5) The same device as shown in Figure 4 is further provided with a heating means (heating element) around the outer periphery of the insulator in the recess 24 of the flange, so that it can be heated evenly by air blowing. It is possible to quickly burn off the soot that adheres to the engine and causes soot accumulation if left unattended during long-term operation. This heating element 26 is arranged in the form of a coil, for example, with an appropriate clearance around the outer periphery of the insulator 4, is hermetically fixed to the flange 21 via an insulator 27, is connected to a separate power source _E2, and is connected to one side. Ground the terminal. The spraying position should be on the electrode end side of the insulator relative to the heating element.

Configuration 5 (See Figure 6) An insulator 4 is used instead of the coiled heating element 26 in Figure 5.
It is also possible to use one in which the heating element 26a is placed inside the a itself. In this case, air is blown onto the insulator at a position inward (at the tip) of the enclosed portion of the heating element 26a. The portion of the insulator 4a in which the heating element is not enclosed can be appropriately shortened. In this case, as the insulator material, an insulator that has a high heat resistance chamber and can withstand thermal shock, such as an alumina sintered body, can be used.

Configuration 6 (See Figure 7) A blind flange 2 having a center electrode 3 and an insulator 4 inside a recess 28 in an outer cylinder 5 similar to that shown in Figure 1.
It is fixedly supported in the center hole 15 of 1a. This configuration does not have an air blowing port, but has a coiled heating element 26 around a predetermined insulator in the flange recess 28,
A heating element lead portion is hermetically fixed to the mirror surface of the flange 21a through an insulating material 27, passing through the mirror surface of the flange 21a. This heating element can be connected to a separate power source E ₂ and heated to burn off the attached soot and maintain insulation. The space in which the insulator 4 and the heating element 26 are arranged forms a branched recess with respect to the exhaust gas flow path.

Configuration 7 (See FIG. 8) An insulator having a device outer cylinder 5 similar to that shown in FIG. 7, a center electrode 3, a flange 21a having a recess 28, and incorporating a heating element 26a similar to that shown in FIG. By providing the body 4a, it is possible to burn off soot adhering to the surface of the insulator 4a and maintain insulation properties.

As the heating element, an electric heating element such as an electric resistance heating element can be used, and can be wound inside the insulator in the form of a double coil, for example.

Examples are described below.

Example 1 Diesel engine (Yanmar Diesel
A device with the structure shown in Figure 1 was installed 300 mm from the exhaust port of the NSC type (displacement 0.269).
A pulse voltage of 20KV250Hz was applied to the electrodes, and the center electrode was set as the negative pole.

The above engine was operated at 2000 rpm with no load, and the exhaust gas containing soot was flowed into the device to examine the state of soot adhering to the electrode insulator. In addition, before starting the engine, blow air from the nozzle at 10%
Min made me squirt. Changes in insulation resistance due to soot adhering to the insulator were continuously examined using an oscilloscope while the engine was running, and using an insulation resistance meter when the engine was stopped.

The results were as follows.

1. When air is not blown out from the nozzle; soot covers the insulator and also adheres to the inner wall of the nozzle hole, causing the insulation to break down about 10 seconds after the start of operation.

2 When air is blown out at 10/min; Even if the above operation is continued for 8 hours, and the cycle of running for 30 minutes and then stopping for 30 minutes is repeated 6 times (total running time is 3 hours), there is no abnormality in insulation. The device operated smoothly without any problems.

Example 2 A heating element was heated using the apparatus shown in Figures 7 and 8.
A voltage of 12 V was applied, and exhaust gas containing soot was caused to flow into the apparatus under the same engine operating conditions and pulse voltage application conditions as in Example 1. Simultaneously measuring the surface temperature of the insulator, we found that the surface temperature was approx.
It was confirmed that soot could be burned off at temperatures above 600°C. Then, when the insulator surface temperature was maintained at 600 to 700℃ and operated continuously for 3 hours, and when operated for 6 cycles every 30 minutes with 30 minute interval stops (operating time 3 hours), there was no abnormality in insulation and the equipment was running smoothly. It was activated.

As described above, the present invention can prevent the adhesion of soot by using a clean gas jetting means, a heating means, or a combination of these means.

The clean gas blowing means of the present invention can prevent soot from adhering to the entire surface of the insulator by forming an air curtain around the entire circumference of the rod-shaped insulator in the axial direction. As a result, the initial soot reduction performance can be maintained without deteriorating the insulation properties, contributing to improved durability of the device.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of an apparatus showing one embodiment of the present invention, FIG. 2 is a modification of FIG. 1, and FIG. 3 is another embodiment. 4 to 6 show other embodiments of the present invention, and FIGS. 7 and 8 show still further embodiments. 2... Electric field, 3... Center electrode, 4, 4a... Insulator, 5... Casing (outer cylinder), 8... Air supply port, 6, 9... Nozzle, 12... Opening, 13...
Partition wall, 14, 20...Air supply chamber, 17...Protrusion, 2
1...Flange, 23...Ring, 24...Recessed space, 25...Air supply pipe, 26, 26a...Heating element, 28...Flange recess, _E1 ...High voltage power supply,
_E2 ...Power supply.

Claims (1)

[Scope of Claims] 1. A casing formed as a part of a flow path for exhaust gas discharged from an internal combustion engine, and at least one pair of mutually insulated members forming an electric field for atomizing or collecting soot. A soot reduction device having an electrode disposed in a casing over a predetermined length in the axial direction of the exhaust gas flow path, the soot reduction device having an electrode disposed in the casing over a predetermined length in the axial direction of the exhaust gas flow path, the soot reduction device having an electrode disposed in the axial direction over the entire circumference around a rod-shaped insulator that supports at least one of the electrodes. A soot reduction device characterized by having a clean gas jetting means capable of forming an air curtain. 2. The clean gas blowing means connects the air supply chamber 14 communicating with the air supply port 8, the inner surface of the opening 12 of the partition wall 13, and the insulator 4.
2. Device according to claim 1, comprising a nozzle 9 formed by an outer periphery. 3. The clean gas blowing means comprises an air supply chamber 20 connected to the air supply port 8 and arranged around the insulator 4, and a full circumference nozzle 6 opening from the air supply chamber 20 toward the casing central axis. The device according to scope 1. 4. The device according to claim 1, wherein the insulator is supported by a wall portion forming a recess with respect to the exhaust gas flow path. 5. The soot reduction device according to claim 1, wherein the insulator supporting the electrode has heating means for burning off soot adhering to the insulator. 6. The device according to claim 5, wherein the insulator is supported by a wall portion forming a recess with respect to the exhaust gas flow path. 7. The device according to claim 5, wherein the clean gas jetting position is on the electrode end side of the insulator with respect to the heating means. 8. The device according to claim 5, wherein the heating means is an electric heating element disposed around the outer periphery of the insulator. 9. The device according to claim 5, wherein the heating means is an electric heating element disposed inside the insulator.