JPH07293223A - Exhaust emission control device for diesel engine - Google Patents

Abstract

PURPOSE:To efficiently collect exhausted fine particles by means of two kinds exhausted fine particle filters according to the amount of exhaustion so as not to damage the exhausted fine particle filters. CONSTITUTION:The exhaust passage of a diesel engine is divided into main and sub exhaust routes A and B, a route switching valve 16 whose opening and closing are controlled according to the amount of exhaust gas is provided in the vicinity of a branching part, a felt-like main exhaust fine particle filter 22 made of inorganic fiber whose pore diameter is small and having a electrification heating wire netting on both surfaces is provided in the main exhaust route A and a sub exhaust fine particle filter 16 whose pore diameter is larger than that of the main exhaust fine particle filter 22 is provided on the sub- exhaust route B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for a diesel engine, which uses two kinds of exhaust particle filters corresponding to exhaust gas flow rates to efficiently collect exhaust particles.

[0002]

2. Description of the Related Art As an exhaust particulate filter for collecting particulates such as graphite called particulates in the exhaust of a diesel engine, a cordierite ceramic or a porous honeycomb body made of silicon carbide is used. Known are ones that use foam-like pores, ones that use a woven fabric made of inorganic fibers, and the like.

As a method of regenerating the exhaust particulate filter made of ceramics, the exhaust particulates collected on the surface are
There are those that ignite and burn with the flame of a burner, those that utilize combustion propagation, and those that ignite and burn with electric heat. Further, there is one in which air is caused to flow in the exhaust particulate filter in the direction opposite to the exhaust flow, and the exhaust particulates collected on the surface of the exhaust particulate filter are dropped and then burned.

The exhaust particulate filter made of the above-mentioned ceramic requires a considerably large surface area corresponding to the exhaust gas flow rate of the diesel engine since the pore diameter of the surface for collecting the exhaust particulate is smaller than that of the exhaust particulate. Further, in the above exhaust particulate filter, when the exhaust particulates are collected on the surface of the exhaust particulate filter, the pore size of the exhaust particulate filter becomes smaller and smaller, and the exhaust particulates are accumulated on the surface of the exhaust particulate filter, and the exhaust particulates The pressure loss due to the fluid resistance of the filter suddenly increases.

Further, when the exhaust particulate filter is regenerated by combustion, the combustion temperature may reach 1400 ° C. in the portion where the exhaust particulate is abnormally accumulated, and the exhaust particulate filter may be damaged or melted. Even if the combustion temperature is 1400 ° C. or lower, the combustion is not uniformly propagated, and cracks may occur in the exhaust particulate filter due to thermal stress. A conventional exhaust particle filter made of inorganic fibers also has a large surface area because it collects exhaust particles only on the surface.

[0006]

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to prevent the exhaust particulate filter from being damaged.
An object of the present invention is to provide an exhaust emission control device for a diesel engine in which exhaust particulates are efficiently collected by two types of exhaust particulate filters corresponding to the exhaust flow rate.

[0007]

In order to achieve the above object, the structure of the present invention divides the exhaust passage of a diesel engine into a main exhaust passage and a sub-exhaust passage, and an exhaust flow rate near the branch portion. Is equipped with a flow path switching valve that is controlled to open and close, and a main exhaust fine particle filter in the form of a felt made of inorganic fibers with a small pore size that has a wire mesh for electric heating on both sides is installed in the main exhaust flow path. An auxiliary exhaust particulate filter having a larger pore size than the main exhaust particulate filter is arranged in the exhaust passage.

[0008]

[Function] When the exhaust gas flow rate of the engine is low, the exhaust gas is efficiently collected by passing the exhaust gas through the main exhaust particle filter consisting of a felt-like body of inorganic fibers having a small pore diameter, and when the exhaust gas flow rate is high, The exhaust particulates are collected by passing through an auxiliary exhaust particulate filter made of a metal porous body having a large pore diameter, and the pressure loss is reduced.

The felt-like material having the optimum pore size between the inorganic fibers efficiently collects exhaust particulates not only on the surface but also on the inside of the surface.

The heat-resistant wire nets laminated on both sides of the felt-like body burn the collected exhaust fine particles by energizing the wire nets.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a side view showing a schematic structure of an exhaust gas purification apparatus for a diesel engine according to the present invention, and FIG. 2 is a side sectional view of the same exhaust gas purification apparatus. As shown in FIG. 2, in the exhaust gas purification device, a heat insulating material 6 is attached to the inner peripheral surface of a cylindrical container 5,
A partition cylinder 23 is concentrically arranged inside the partition wall, a main exhaust passage A is defined between the container 5 and the partition cylinder 23, and a sub exhaust passage B is defined inside the partition cylinder 23.

A double-cylinder-shaped main exhaust particulate filter made of a filter-like body of inorganic fiber having a small pore size and provided with a wire mesh for electric heating on both sides in an annular main exhaust passage A between the container 5 and the partition tube 23. 22 is provided. However, the main exhaust particulate filter 22 is composed of a plurality of elongated cup-shaped ones.
You may arrange | position in the annular space between the partition tube 23 at equal intervals in the circumferential direction. The main exhaust fine particle filter 22 having a double cylindrical shape with the right end wall 25 closed is provided with a wire mesh for electrically heating Fe-Cr-Al-Y alloy or the like on the surface on the exhaust inlet side and a catalytic action on the surface on the exhaust outlet side. Wire meshes such as platinum are polymerized and bonded. The left end of the main exhaust particulate filter 22 is supported by the annular plate 21, and the annular plate 21 is provided with a large number of openings communicating with the left end inlet 24 of the main exhaust particulate filter 22 at equal intervals in the circumferential direction.

In the sub-exhaust passage B inside the partition tube 23, a filter-like body of inorganic fibers having a pore size larger than that of the main exhaust fine particle filter 22 or aluminum, alumina on the surface thereof,
A cylindrical auxiliary exhaust particulate filter 16 made of a metal porous body coated with cordierite or the like is provided. Cylindrical auxiliary exhaust particulate filter 16
Also, wire mesh for electric heating such as Fe-Cr-Al-Y alloy on the inner peripheral surface,
Wire meshes such as platinum that act as a catalyst are polymerized and bonded to the outer peripheral surface. Secondary exhaust particulate filter 16 and partition tube 23
Is also supported by the annular plate 21 arranged at the inlet end (left end) of the container 5.

A flow passage switching valve 1 which is controlled to open and close in the vicinity of a branch portion between the main exhaust flow passage A and the sub exhaust flow passage B in accordance with the exhaust flow rate.
4 are provided. Therefore, the auxiliary exhaust particulate filter 16
A tube 12 is coupled to the left end of the, and a butterfly-shaped flow path switching valve 14 is rotatably supported inside the tube 12 by a support shaft 15. The support shaft 15 is projected to the outside of the container 5 and is connected with the lever 51. As shown in FIG. 1, the lever 51 is connected to the plunger 52 of the electromagnetic actuator 53. The cylinder 17 is connected to the right end portion of the auxiliary exhaust particulate filter 16,
The relief valve 19 made of a disc that opens and closes the end of the
Is pulled and brought into contact with the end of the cylinder 17.

The left end of the container 5 is connected to the inlet cylinder 2 via the conical cylinder 3.
The inlet tube 2 has a flange 2a joined to the upstream end of the exhaust pipe. The right end of the container 5 is connected to the outlet cylinder 8 via the conical cylinder 7, and the outlet cylinder 8 is connected to the downstream end of the exhaust pipe that communicates the flange 8a with the exhaust muffler.

The conical cylinder 3 has electrodes 41, 4 via an insulator.
2 and 43 are supported, and similarly the conical cylinder 7 is supported by the electrode 44. The electrodes 43 and 41 are energized to the metal nets superposed on the inner surface of the main exhaust particulate filter 22, and the electrodes 42 and 44 are energized to the metal nets superposed on the inner surface of the auxiliary exhaust particulate filter 16, respectively. The collected exhaust particulates are burned to regenerate the exhaust particulate filters 16 and 22.

In the exhaust particulate filter of the diesel engine described above, the flow path switching valve 14 is closed as shown in FIG. 2 when the flow rate of the exhaust gas is medium or less. Exhaust gas enters from the inlet pipe 2 through the conical cylinder 3 into the inside of the main exhaust fine particle filter 22 having a double cylindrical shape, and when passing through the main exhaust fine particle filter 22 inward or outward, the particles are filtered.
The filtered exhaust gas flows through the conical cylinder 7 and the outlet cylinder 8 to the exhaust muffler.

When the exhaust flow rate is medium or more, the electronic control unit 54 based on the signal of the sensor 55 for detecting the exhaust flow rate.
The electromagnetic actuator 53 is excited by the output of.
The plunger 52 of the magnetic actuator 53 projects to the left, and the flow path switching valve 14 rotates clockwise about the support shaft 15 to open. At this time, half of the exhaust flow rate passes through the main exhaust particulate filter 22 and flows through the conical cylinder 7 to the outlet cylinder 8 as described above. The remaining part of the exhaust flow rate is filtered by the fine particles when passing through the auxiliary exhaust fine particle filter 16 radially outward. The filtered exhaust gas flows through the partition cylinder 23 and the conical cylinder 7 to the outlet cylinder 8. When the flow rate of exhaust gas becomes moderate or less, the electromagnetic actuator 53 is demagnetized, the plunger 52 moves to the right,
The flow path switching valve 14 is closed.

When the exhaust gas pressure inside the auxiliary exhaust particle filter 16 becomes high when the auxiliary exhaust particle filter 16 is clogged, the relief valve 19 opens against the force of the spring 18 and the exhaust particle filters 16, 22 of each exhaust particle filter 16 and 22 are opened. Prevent damage. At this time,
A part of the exhaust gas flows directly from the inside of the auxiliary exhaust fine particle filter 16 to the outlet tube 8.

When the exhaust pressure inside the exhaust particulate filters 22 and 16 becomes high, the exhaust particulate filters 2 are exhausted.
The output of the electronic control unit 54 based on the signal of the sensor 56 that detects the exhaust pressure inside the electrodes 2, 16
Is energized to. That is, an energizing circuit is formed from the power source to the electrode 43, the wire mesh of the main exhaust particulate filter 22, the electrode 41, and the power source. When the wire net is heated, exhaust particulates such as graphite collected on the inner surface of the main exhaust particulate filter 22 are burned to regenerate the main exhaust particulate filter 22. at the same time,
From the power source to the electrode 42, the auxiliary exhaust particulate filter 16 wire mesh,
An energizing circuit is formed to the electrode 44 and the power source. When the wire net is heated, exhaust particulates such as graphite collected on the inner surface of the sub exhaust particulate filter 16 are burned, and the sub exhaust particulate filter 16 is regenerated. When the exhaust pressure inside each exhaust particulate filter 22, 16 falls below a predetermined value, the relief valve 19 is closed by the force of the spring 18, and each exhaust particulate filter 22, 1 is exhausted.
The power supply to 6 is also cut off.

As shown in FIG. 3, in order to improve the efficiency of collecting the exhaust particulates of the main exhaust particulate filter 22, the main exhaust particulate filter 22 has a felt-like body 32 made of a heat-resistant inorganic fiber on both sides thereof for conducting electricity. It is configured by superposing 31, 31a and catching with a thread 33. For inorganic fibers
Si-Ti-CO ceramics, Si-CO ceramics, Si
-N-based ceramics, Si-O-based ceramics, or fibers made of metal are used, and the surface of these inorganic fibers is coated with aluminum, alumina, or cordierite. In the wire mesh 31 for electric heating which becomes the surface on the exhaust inlet side
An Fe-Cr-Al-Y alloy is used, and a platinum wire is used for the metal net 31a that acts as a catalyst on the exhaust outlet side surface.

In order to manufacture the felt-like body 32, inorganic fibers are irregularly oriented in the horizontal direction by a carding machine, laminated and entangled with each other, and then needle-punched to make the inorganic fibers in the vertical direction (thickness direction). Also entwined with. An inorganic fiber having an outer diameter of 8 to 15 μm and a length of 30 to 100 mm is suitable, and if laminated with a thickness of 2 to 10 mm and needle punching at a needle punching interval of about 4 mm, the porosity is 90 to 99%. , Elongated elongated complex pores are formed between the inorganic fibers that are sufficient to trap the exhaust particulates. If the inorganic fibers are shorter than a predetermined size, the entanglement is poor, and if they are too long, it becomes difficult to orient them irregularly in the horizontal direction. It is appropriate that the needle spacing is about 4 mm, and it is adjusted by the laminated thickness of the inorganic fibers. If the thickness of the felt-like body 32 is 2 mm or less, the exhaust particulates pass through, and if the thickness exceeds 10 mm, the porosity increases, the collection efficiency decreases, and the regeneration time increases.

A specific example of the main exhaust particulate filter 22 is as follows. An inorganic fiber (trade name: Tyranno fiber) having an outer diameter of 8.5 μm and made of elements of silicon, titanium, carbon, and oxygen is cut into a length of 50 mm, and the cut inorganic fiber is horizontally and irregularly oriented by a carding machine. They were entwined while being entwined and laminated to have a uniform thickness. Next, the needles are struck in the vertical (thickness) direction at a needle spacing of 4 mm to pull up the inorganic fibers from the back surface or the intermediate layer, and the thickness is 3 mm and the basis weight is 200 g / m
^Two felt-like bodies 32 were formed. One side of the felt-like body 32 made of inorganic fiber is made of Fe-Cr-Al-Y alloy 35
The mesh metal mesh 31 was superposed on the other surface of the felt-like body 32 and the mesh metal mesh 31a made of platinum was polymerized and bonded to each other to form the double cylindrical exhaust particulate filter 22.

The auxiliary exhaust fine particle filter 16 has a porous metal body (Ni-Cr type metal home) having a pore diameter of 300 to 50.
Since it is as large as 0 μm and the collection efficiency of exhaust particulates is low at about 20%, aluminum paste is impregnated and applied to adjust the particle size to be collected and improve corrosion resistance, and the pore size is 250 to 300 μm. Adjusted to.

Although the metal porous body of the sub exhaust particulate filter 16 is adjusted to 250 to 300 μm in the above-mentioned specific example, it may be adjusted to about 100 μm. Further, instead of the porous metal body, as in the case of the porous body made of cordierite ceramics or the main exhaust fine particle filter 22, the felt-like body made of inorganic fibers is controlled to control the porosity. A larger one may be used.

As a comparative example of the main exhaust fine particle filter 22 according to the present invention, one in which the entire exhaust fine particle filter is made of a metal porous body is produced, and the collection efficiency of each of the main exhaust fine particle filter 22 according to the present invention and the comparative example. Is shown in Table 1. As is clear from the test results, the main exhaust fine particles 22 according to the present invention
The collection efficiency is very high and the pressure loss is small.

Table 1 Exhaust particulates Exhaust particulates Pressure loss (mmHg) Pressure loss (mmHg) Filter collection efficiency (%) Flow rate 20 ^m3 / min. Flow rate 20 ^m3 / min. Collection rate 0 when collected 45 g / m2 At the time of the present invention 80 4 120 Comparative example 50 0 40 The pressure loss of the exhaust particulate filter acceptable in the current diesel engine is 150 mmHg or less, and the exhaust particulate collection efficiency is desired to be 50% or more. The felt-like body 32 of the main exhaust particulate filter 22 has a high porosity so that the pressure loss is small, the exhaust particulate collection efficiency is high, and the surface area of the main exhaust particulate filter 22 is narrowed to about 1/3 that of the conventional honeycomb type. it can. The reason for this is that the felt-like body 32 made of an inorganic fiber has a mixture of a dense portion of fibers and a coarse portion of fibers, and large exhaust fine particles are collected in the coarse portion of the fibers near the surface, so that the fibers inside the surface are covered. This is because small exhaust particles are collected in the honey part.

[0028]

As described above, according to the present invention, the exhaust passage of the diesel engine is branched into the main exhaust passage and the sub-exhaust passage, and the flow is controlled to be opened and closed in the vicinity of the branch portion according to the exhaust flow rate. A flow switching valve is provided, and a main exhaust particulate filter is provided in the main exhaust channel, which is made of inorganic fiber with a small pore size and has wire mesh for electric heating on both sides.The main exhaust particulate filter is provided in the auxiliary exhaust channel. A secondary exhaust fine particle filter having a larger pore diameter is arranged, and when the exhaust flow rate is small, the exhaust particulate can be efficiently collected by the main exhaust fine particle filter made of a felt-like body of inorganic fibers having a small pore diameter, When the flow rate of exhaust gas is large, the exhaust gas particles can be collected by using the auxiliary exhaust gas particle filter made of a felt-like body of inorganic fibers or a porous metal body (metal home) having a large pore diameter to reduce the pressure loss.

In particular, since the main exhaust particulate filter is collected not only on the surface of the felt-like body made of inorganic fibers but also inside, a high exhaust particulate collection efficiency can be obtained.

[Brief description of drawings]

FIG. 1 is a side view showing a schematic configuration of an exhaust emission control device for a diesel engine according to the present invention.

FIG. 2 is a side sectional view of the exhaust emission control device.

FIG. 3 is a side sectional view of a main exhaust particulate filter in the exhaust emission control device.

[Explanation of symbols]

A: Main exhaust flow passage B: Sub exhaust flow passage 16: Sub exhaust particulate filter 22: Main exhaust particulate filter 31, 31
a: wire mesh 32: felt-like body 33: thread

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B01D 46/30 B 7446-4D

Claims (4)

[Claims] An exhaust passage of a diesel engine is branched into a main exhaust passage and a sub-exhaust passage, and a passage switching valve that is controlled to open and close according to an exhaust flow rate is provided near the branch portion, and a main exhaust passage is provided. A felt-like main exhaust particulate filter made of inorganic fiber with a small pore size, which has wire mesh for electric heating on both sides, is installed in the flow passage, and a sub-exhaust passage has a larger pore diameter than the main exhaust particulate filter. An exhaust emission control device for a diesel engine, which is provided with a fine particle filter. 2. The secondary exhaust particulate filter has a porosity of 98.
The exhaust gas purification device for a diesel engine according to claim 1, wherein the exhaust gas purification device is made of an inorganic fiber of not more than%. 3. The exhaust purification system for a diesel engine according to claim 1, wherein the auxiliary exhaust particulate filter is made of a conductive metal porous body. 4. The auxiliary exhaust fine particle filter is formed by impregnating and coating aluminum porous paste on a conductive metal porous body.
An exhaust emission control device for a diesel engine according to claim 1.