JPH03179120A - Exhaust gas purifying apparatus - Google Patents

Abstract

PURPOSE:To burn up soot captured by a filter quickly and efficiently by disposing a heat source on the upstream side or the like of a filter disposed in a passage of a casing connected to an exhaust passage of an internal combustion engine. CONSTITUTION:An exhaust gas purifying apparatus 1 is constructed so that a passage 2a of a metallic pipe casing 2 is connected to an exhaust pipeline Ea of an internal combustion engine. A filter 3 for purifying exhaust gas is disposed in the interior of the casing 2, and a heat insulation material 4 is interposed between the filter and the casing. An electric heater 7 as a heat source for oxidizing carbon is disposed in such a manner as to cover the inlet side of the casing 2 on the upstream side of the filter 3, that is, in the vicinity of the exhaust gas introduction side. Further, a heat insulation material 8 is disposed similarly in such a manner as to cover the inlet side of the casing 2 on the upstream side of the electric heater 7. By this arrangement, soot captured by the filter 3 can be burnt up quickly and efficiently the using the electric heater 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exhaust gas purification device for purifying exhaust gas in an internal combustion engine such as a diesel engine.

[Prior Art] Conventionally, as a method for removing soot mixed in the exhaust gas of a diesel engine, a filter made of porous silicon carbide sintered body formed in a honeycomb shape is connected to the exhaust side of the diesel engine. A method has been considered in which the soot mixed in the exhaust gas is collected by this filter and the soot is combusted within the filter.

In order to burn the soot collected within the filter, it is necessary to heat the inside of the filter to a temperature higher than the ignition temperature of the soot, and attempts have been made to use, for example, an electric heater as a relatively simple means.

[Problems to be Solved by the Invention] By the way, the filter made of porous silicon carbide sintered body has the following problems:
Because it has high thermal conductivity and a relatively large heat capacity, an electric heater that can generate a large amount of heat in a relatively short period of time was required to heat the inside of the filter above the ignition temperature of soot.

However, when attempting to use an electric heater that generates a large amount of heat, there are drawbacks such as the need for an extremely large battery to supply electricity commensurate with the amount of heat generated.

The present invention was made in view of the above circumstances, and its purpose is to efficiently burn the inside of the filter in a short time and with low power consumption by using an electric heater when burning the soot collected in the filter. An object of the present invention is to provide an exhaust gas purification device capable of heating soot to a temperature higher than its ignition temperature.

[Means and operations for solving the problems] In order to solve the above problems, the present invention includes: a casing provided with a passage communicating with the exhaust side of an internal combustion engine; a filter disposed in the passage; The device includes a heat source disposed on at least one of the upstream side and downstream side of the filter in the passage, and a heat insulating material disposed on the opposite side of the filter with the heat source in between.

According to this configuration, heat radiation to the outside of the passage on the upstream side or downstream side of the heat source is suppressed by the heat insulating material disposed on the opposite side of the filter with the heat source in between.

Therefore, the filter is efficiently heated by the heat source, and the carbon oxidation treatment is efficiently performed.

Moreover, by supplying secondary air toward the filter from the upstream side of the heat insulating material at the same time as heating by the heat source, heat from the heat source is efficiently supplied to the filter along with the flow of the secondary air. Therefore, by using a conventional heat source without using a heat source with a large calorific value, the filter can be heated to a temperature that allows carbon oxidation treatment in a short time, and the time required for carbon oxidation treatment is significantly reduced. be shortened. Furthermore, since rapid heating by a heat source with a large calorific value can be avoided, damage to the filter due to rapid thermal expansion can be prevented.

It is preferable that the filter is formed into a honeycomb shape using a porous silicon carbide sintered body.

This is because the porous silicon carbide sintered body has excellent heat resistance and mechanical strength, and has a high porosity, so it is suitable as a filter material.

The heat insulating material is preferably a heat insulating material provided with ventilation holes.

According to this configuration, the exhaust gas circulation path is ensured by the ventilation hole.

Alternatively, the heat insulating material is preferably a heat insulating material formed in a mesh shape using ceramic fibers.

This is because this configuration not only ensures a flow path for exhaust gas but also suppresses exhaust resistance to a low level.

Examples 1 to 3 embodying the present invention will be described below with reference to the drawings.

[Example 1] FIG. 1 is a diagram showing an exhaust gas purification device 1 and its experimental equipment, and FIG. 2 is a diagram showing the exhaust gas purification device 1 in an enlarged manner. The exhaust gas purification device l includes a casing 2 made of a metal pipe, and a passage 2a of the casing 2 is connected to the internal combustion engine E.
is connected to the exhaust pipe Ea. A filter 3 for purifying exhaust gas is disposed within the casing 2, and a heat insulating material 4 is provided between the filter 3 and the inner wall of the passage 2a of the casing 2.

As shown in FIGS. 4 and 5, the filter 3 is formed in a honeycomb shape from a porous silicon carbide sintered body, and has a columnar shape as a whole. This filter 3 is formed with a large number of gas passage holes 5 extending in parallel to the axial direction, and either one end of the supply side or the discharge side of each gas passage hole 5 is alternately sealed with small pieces 6 made of silicon carbide. has been done. Furthermore, on the inner wall surface of each gas passage hole 5 of the filter 3,
It is also possible to form an oxide film of alumina, silica, mullite, etc., and to support an oxidation catalyst made of platinum group elements, other metal elements, their oxides, etc.

Further, the heat insulating material 4 has a cylindrical shape and is formed with an appropriate thickness.

An electric heater 7 serving as a heat source for carbon oxidation treatment is disposed upstream of the filter 3, that is, near the exhaust gas introduction side, so as to cover the inlet side of the casing 2.

Furthermore, a heat insulating material 8 is disposed upstream of the electric heater 7 so as to cover the inlet side of the casing 2 as well.

As shown in FIGS. 2 and 3, the heat insulating material 8 has a disk shape, and is formed with a large number of gas passage holes 9 and communication holes 10 as ventilation holes communicating in the exhaust gas flow direction. It is desirable that the passage holes 9 and the communication holes 10 are designed to minimize the pressure loss of the flowing gas. This heat insulating material 8 is attached to the casing 2. The electric heater 7 has a spiral shape and is attached to the downstream wall surface of the heat insulating material 8.

Further, in this embodiment 1, both of the heat insulating materials 4.8 can be made of an inorganic or organic heat insulating material. As inorganic heat insulating materials, alumina-silica ceramic fiber, alumina fiber, zirconia fiber silica fiber, rock wool, asbestos, etc. can be used, and as organic heat insulating materials, fibers such as nylon and Kevlar, and foams such as urethane can be used. It is possible to use a molded article or a combination of these.

Preferably, inorganic fibers are used in part or in whole.

A pressure sensor Ps that detects the pressure is disposed in the exhaust pipe Ea connected to the internal combustion engine E, and a detection signal from the sensor Ps is input to the control device C via the piezoelectric transducer Pe, and the control device Device C allows pressure values to be monitored. Furthermore, a supply pipe Ca for supplying secondary air toward the inlet side of the casing 2 is connected to the exhaust pipe Ea, and secondary air from a compressor Co is introduced into the supply pipe Ca. It looks like this.

When the pressure monitored by the control device C reaches a predetermined value, the amount of carbon (soot) etc. collected by the filter 3 reaches a predetermined amount, and the carbon in the filter 3 needs to be oxidized. In order to control the carbon oxidation treatment, the controller C closes the switch S to start energizing the electric heater 7, and also operates the compressor Co to remove air from the air supply pipe Ca. Secondary air is supplied to the inlet side of the casing 2.

Therefore, in the exhaust gas purification device 1 of this embodiment, the heat resistance of the porous silicon carbide sintered body can be effectively utilized to form the filter 3 with excellent heat resistance. Then, the exhaust gas from the internal combustion engine E is passed from the inlet side of the casing 2 through the gas passage hole 9 and the communication hole 10 of the heat insulating material 8 to the filter 3.
When introduced into the exhaust gas, carbon in the exhaust gas is filtered by the wall of the gas passage hole 5 of the filter 3. When the filter 3 supports an oxidation catalyst, CO, HC, etc. are oxidized by the oxidation catalyst. The purified exhaust gas is then discharged from the filter 3.

Then, when the pressure value detected by the pressure sensor Ps reaches a predetermined value, it is assumed that the amount of carbon collected by the filter 3 has reached a predetermined amount that requires oxidation treatment, and the control device C oxidizes the carbon. Execute processing control. During this carbon oxidation treatment, with a predetermined amount of carbon remaining in the filter 3, the electric heater 7 starts heating the filter 3, and the compressor Co is operated to start supplying secondary air. Then, by continuing this process, carbon etc. in the filter 3 are burned and the filter 3 is regenerated.

In the exhaust gas purification device l of this embodiment 1, an electric heater 7 is disposed upstream of the filter 3, and a heat insulating material 8 is further disposed upstream of the electric heater 7. Heat radiation from 7 to the outside of the passage 2a on the upstream side thereof is suppressed by the heat insulating material 8. In addition, at the same time as the electric heater 7 is heated, secondary air is supplied from the upstream side of the insulation material 8 toward the fill and -3, so the heat from the electric heater 7 is carried by the flow of the secondary air. It is efficiently supplied to the filter 3. Furthermore, in the exhaust gas purification device 1 of this Q embodiment, since the heat insulating material 4 is provided between the filter 5 and the inner wall of the casing 2, light heat from the peripheral edge of the filter 3 is suppressed.

As a result, the temperature of the filter 3 can be raised to a temperature at which carbon oxidation treatment is sufficiently effective in a short period of time using the normal amount of heat, without having to specifically increase the amount of heat generated by the electric heater 7. , it is possible to perform carbon oxidation treatment in an extremely short time. In other words, the thermal energy/L energy from the electric heater 7 can be effectively used to efficiently regenerate the filter 3. Further, by saving power in the electric heater 7, the power consumption of the battery can be reduced, and a decrease in the service life of the battery can also be prevented.

In addition, since rapid heating is not performed by an electric heater that generates a large amount of heat, the temperature difference between each part of the filter 3 can be kept small, and the occurrence of cracks etc. due to rapid thermal expansion of the filter 3 can be kept small. Thus, damage to the filter 3 can be prevented.

Here, specific experimental data regarding regeneration processing of the filter 3 and comparative experimental data will be explained.

As experimental conditions, the filter 3 has a diameter of 140 mm, a length of 140 mm, and a thermal conductivity of 0.029 cal/cm.

sec, °C, specific heat 0.34 cal/g, 'C was used.

The heat insulating material 4 around the filter 3 is made of ceramic fiber, has a thickness of 25 mm, and has a thermal conductivity of 0.08 kcal/m.
hr, °C was used. The insulating material 8 on the upstream side of the filter 3 is made of ceramic fiber.

Thickness: 15 mm, thermal conductivity: 0.15 kcal/m
, hr, 'C's were used. Further, the electric heater 7 used was a 12V-2, 5kW electric heater. Furthermore, the amount of secondary air supplied from compressor Co is 501/m
It was set as in.

For carbon collection in exhaust gas, pressure sensor Ps
The collection operation was continued until the pressure detected at reached a predetermined value. Regarding the calculation of the amount of carbon captured during this period,
The volume of the filter 3 is the total volume of the gas passage hole 5,
The amount of carbon collected was determined based on the weight change before and after the collection process. Regarding the regeneration process time of the filter 3,
The center of the upstream side surface of the filter 3 was set as a measurement point P, and a thermocouple (not shown) was arranged to monitor temperature changes. Since the temperature at the measurement point P drops rapidly when the combustion of the carbon captured by the filter 3 ends, the time from the start of energization to the electric heater 7 to the time of temperature drop was measured as the regeneration processing time.

As a result, the regeneration processing time performed using the experimental apparatus of this example was 7 to 8 minutes.

On the other hand, as a comparative experiment to the above experiment, the insulating material 8 on the upstream side of the electric heater 7 was omitted, and only the electric heater 7 was used, and carbon collection was carried out under the same experimental conditions as the above experiment.
After obtaining the same amount of carbon as in the experiment, the carbon was oxidized and the regeneration time was measured.

As a result, the regeneration processing time was 18 minutes.

As is clear from the above results, in the experiment in which the heat insulating material 8 was provided upstream of the filter 3, the regeneration processing time was approximately half that of the comparative experiment in which the heat insulating material 8 was omitted, and carbon was efficiently You can see that it is burning.

Note that the configuration of the first embodiment can also be implemented by changing it as follows.

(1) In the above configuration, as shown in FIGS. 1 and 2, the heat insulating material 8
As shown in FIG. 6, a heat insulating material 12 may be fixed to the inner wall of the casing 2 on the upstream side of the electric heater 11 as a heat source.

(2) In the above configuration, as shown in FIGS. 1 and 2, a heat insulating material 8 with an electric heater 7 assembled on the upstream side of the filter 3;
Although a heat insulating material 4 around the outer periphery of the filter 3 is provided separately, as shown in FIG. An electric heater 14 can also be installed as a heat source.

(3) In the above configuration, the heat insulating material 4 is provided around the outer periphery of the filter 3, but the heat insulating material 4 may be omitted.

(4) In the above configuration, the electric heater 7 is provided as a heat source, but a heater that utilizes heat generated by an internal combustion engine may also be provided.

[Example 2] As shown in Fig. 8, in this example 2, an electric heater 7 as a heat source is provided upstream of the filter 3, and further upstream of the electric heater 7, heat-resistant fibers are used. A net-like heat insulating material 15 formed in a mesh shape is provided. Due to the presence of this net-like heat insulating material 15, the electric heater 7
Radiant heat from the filter 3 is suppressed from going in the opposite direction to the filter 3, and the filter 3 is efficiently heated.

In addition, since the reticulated heat insulating material 15 of the present Example 2 can secure a larger aperture ratio than the aperture ratio of the end face of the honeycomb-like filter 3, the heat insulating material 15 having the gas passage holes 9 used in the above-mentioned Example 1 can It has better air permeability than No. 8, and allows exhaust gas to pass through it smoothly without increasing exhaust resistance.

Here, as the heat-resistant fibers, ceramic fibers having heat resistance of 1000° C. or higher, such as alumina-silica ceramic fibers, alumina fibers, and silica fibers, can be used.

Further, the reticulated heat insulating material 15 has a thickness of, for example, 0.5 to
1. Omm heat-resistant thread with aperture of 1. 0-2. Omm
, it is desirable to form it in a mesh shape with an aperture ratio of 40 to 60%. By setting the mesh opening and opening ratio within this range, the reticulated heat insulating material 15 can have both high levels of heat insulation and air permeability.

Note that the electric heater 7 and the mesh heat insulating material 15 may be provided on the downstream side of the casing 2.

[Embodiment 3] As shown in FIG. 9, in this embodiment 3, the casing 2 is formed longer than in the embodiment 1.2, and inside the casing 2 there is a filter member 16a divided into three parts. 1
A filter 16 consisting of 6c is provided. 10th
As shown in the figure, these three filter members 16a~
16c is formed in a honeycomb shape, and each has a large number of gas passage holes 5 that communicate with each other. The supply end of the gas passage hole 5 provided in the filter member 16a disposed on the upstream side, and the discharge side end of the gas passage hole 5 provided in the filter member 16c disposed on the downstream side. , either the supply side or the discharge side of each gas passage hole 5 that communicates the three filter members with each other is sealed with a small piece 6 made of silicon carbide, and these three filter members 16a-16c are integrated into the filter 16
It functions as a.

Ceramic heaters 17 each having a mesh cross section are disposed on the upstream and downstream sides of the filter 16 and between each filter member 16a to 16c, and are wrapped in a cylindrical heat insulating material 4. It is arranged within the casing 2. Further, in the vicinity of the ceramic heaters 17 located at both ends of the filter 16, a reticulated heat insulating material 15 is disposed as in the second embodiment.

According to this configuration, the exhaust gas processing ability of the exhaust gas purification device can be improved, so that it can also be used in a diesel engine with a large displacement of 8000 cc or more. Further, since the filter area is secured by increasing the overall length of the filter 16 without increasing the cross-sectional area of the cage jig 2, it is extremely suitable as an exhaust gas purification device for use in a vehicle where space is limited.

Furthermore, the filter 16 is divided into three parts, and each filter member 1 is divided into three parts.
By providing the ceramic heater 17 between the filters 6a to 16c, the temperature distribution in the longitudinal direction of the entire filter can be made substantially uniform. Therefore, it is possible to prevent cracks from occurring due to non-uniform temperature distribution of the filter. In particular, filter 1
When 6 is made of a material with a large coefficient of thermal expansion, such as a silicon carbide sintered material, reliability can be improved more than before.

[Effects of the Invention] As detailed above, according to the present invention, when burning the soot collected in the filter, an electric heater is used to efficiently burn the inside of the filter in a short time and with low power consumption. It has the excellent effect of being able to heat soot above its ignition temperature.

[Brief explanation of drawings]

1 to 7 show a first embodiment embodying the present invention.
Figure 2 is a partial cross-sectional view showing an exhaust gas purification device and its experimental equipment, Figure 2 is an enlarged cross-sectional view of the exhaust gas purification device, Figure 3 is a front view showing the heat insulating material, and Figure 4 is a cross-sectional view of the filter. 5 is a front view of the filter, FIGS. 6 and 7 are sectional views showing the exhaust gas purification device turned sideways, and FIG. 8 is an exhaust gas purification device of Example 2 embodying the present invention. FIGS. 9 and 10 are sectional views showing a third embodiment of the present invention, FIG. 9 is a sectional view showing an exhaust gas purification device, and FIG.
The figure is a cross-sectional view of the split filter. 2... Casing, 2a... Passage, 3.16...
Filter 7.11.14...Electric heater as heat source, 8,12.13...Insulating material, 9...Gas passage hole as ventilation hole, lO...Communication hole as ventilation hole, 15 ...Mesh insulation material, 17...Ceramic heater as a heat source-1E...Internal combustion engine.

Claims (1)

[Claims] 1. A casing (2) equipped with a passage (2a) communicating with the exhaust side of the internal combustion engine (E), and a filter (3, 16) disposed in the passage (2a).
), and the filter (3, 16) in the passageway (2a).
) a heat source (7, 11, 14, 17) disposed on at least one of the upstream side or the downstream side of the heat source (7, 11,
14, 17); and a heat insulating material (8, 12, 13, 15) disposed on the opposite side of the filter (3, 16). 2. The exhaust gas purification device according to claim 1, wherein the filter (3, 16) is formed into a honeycomb shape of a porous silicon carbide sintered body. 3. The exhaust gas purification device according to claim 1 or 2, wherein the heat insulating material is a heat insulating material (8, 12, 13) provided with ventilation holes (9, 10). 4. The exhaust gas purification device according to claim 1 or 2, wherein the heat insulating material is a heat insulating material (15) formed in a mesh shape using ceramic fibers.