JPH1162558A - Regenerating system for exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the incineration time of particulates by providing a heater regenerating the filter in front of an exhaust emission control device provided with a honeycomb filter for exhaust emission control made of a porous silicon carbide sintered body, and the inflow port of combustion improving air in front of the heater, and controlling the heater and the combustion improving air. SOLUTION: A heater is made ON, the inflow side end face of a honeycomb filter 12 for exhaust emission control made of a porous silicon carbide sintered body is heated, and after the lapse of a fixed time, combustion improving air is supplied to the gas inflow side end face of the filter 12 through a gas inflow port 16. In this case, a position of the highest temperature heated by the heater 13 is the front end face, and by supplying the combustion improving air in this condition, combustion is begun. In this way, the highest temperature position in the honeycomb filter 12 for exhaust emission control is conformed to the combustion beginning point, and hence a temperature rising time is remarkably shortened. Further, conduction of heat from the heater 13 in the honeycomb filter 12 for exhaust emission control is performed along the lengthwise direction of the filter 12, and combustion can be efficiently propagated.

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 purifying exhaust gas discharged from an internal combustion engine such as a diesel engine. It relates to a reproduction system.

[0002]

2. Description of the Related Art There is known an exhaust gas purifying apparatus provided with an exhaust gas purifying honeycomb filter used for removing NOx (nitrogen oxide), HC (hydrocarbon) and the like discharged from an internal combustion engine such as a diesel engine. is there. This filter removes NOx, HC, and the like, and at the same time, captures particulates (particulate matter) contained in the exhaust gas. Therefore, as the operating time increases, the filter efficiency decreases due to accumulation of the particulates. These phenomena are
For example, it is prominent in diesel vehicles such as buses, trucks and forklifts.

[0003] Therefore, by burning the particulates captured by the honeycomb filter for exhaust gas purification,
Although it is necessary to regenerate the filter, cordierite used in a conventional honeycomb filter for purifying exhaust gas has a problem in terms of durability due to poor maximum operating temperature and thermal conductivity.

The applicant of the present invention has disclosed an exhaust gas purifying apparatus using a porous silicon carbide sintered body having a high maximum operating temperature and a high thermal conductivity in a honeycomb filter for purifying exhaust gas in Japanese Patent Application Laid-Open No. Hei 3-23307. It has been proposed. This is shown in FIG.
As shown in FIG. 1, in an exhaust gas purifying apparatus 1 provided in an exhaust passage 3, a heater 4 is provided on the outer periphery of an exhaust gas purifying honeycomb filter 2. The regeneration of the exhaust gas purifying honeycomb filter 2 is performed by the heater 4.
Is heated and auxiliary combustion air is supplied from an inflow port 5 provided in front of the exhaust gas purification device 1 to incinerate the particulates.

However, according to this device, since the heater 4 is provided on the outer periphery of the honeycomb filter 2 for purifying exhaust gas, the temperature distribution when the particulates start to burn is along the outer peripheral surface of the filter 2. However, it takes a long time (heating time) to heat the entire filter 2 to the particulate combustion temperature. In addition, when the combustion assist air is supplied to the heated filter, the combustion starts.However, when the amount of the trapped particulates is large, when the combustion proceeds in the latter half of the combustion, the front surface is cooled by the combustion assist air. As a result, a situation in which the temperature becomes high in the rear of the filter is formed. The stress distribution generated by this temperature distribution sometimes exceeds the allowable stress of the filter, and the upper limit of the amount of incineration is reduced in consideration of the case where cracks are generated in the filter.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has been developed in order to regenerate a honeycomb filter for purifying an exhaust gas which captures particulates in exhaust gas discharged from an internal combustion engine. It is an object of the present invention to provide a regeneration system for an exhaust gas purifying apparatus capable of reducing the time required for incineration of curate and increasing the amount of incineration.

[0007]

According to a first aspect of the present invention, there is provided a regeneration system for an exhaust gas purifying apparatus, which is provided in an exhaust passage of an internal combustion engine and comprises a porous silicon carbide sintered body. An exhaust gas purifier provided with a gas purifying honeycomb filter, a heater disposed in front of the filter on the gas inflow side to regenerate the filter, and a flow of auxiliary combustion air provided in the purifier in front of the heater Entrance and
It is characterized by comprising a control unit for controlling the supply of the electric power supplied to the heater and the auxiliary combustion air.

In the reproducing system of the present invention, the position of the highest temperature heated by the heater is the front end,
In this state, combustion starts when supplementary air is supplied. As described above, since the highest temperature position in the filter and the combustion start point coincide with each other, the temperature rise time is significantly shortened. Also,
Conduction of heat from the heater in the exhaust gas purifying honeycomb filter is performed along the longitudinal direction of the filter, so that combustion propagation is efficiently performed, and the front end is not cooled by the auxiliary combustion air. It becomes uniform in the longitudinal direction, resulting in combustion propagation in which stress distribution hardly occurs. As a result, the amount of particulates that can be incinerated is significantly increased, and a system that can be safely recycled in a short time can be configured.

As a configuration for achieving the excellent combustion mechanism of the regeneration system, the present invention employs a porous silicon carbide sintered body as a material for a honeycomb filter for purifying exhaust gas. This material has very high thermal conductivity,
The amount of heat directly from the heater and the amount of heat exchanged by the auxiliary air passing through the heater surface help to efficiently propagate the heat exchanged behind the filter and in the radial direction, and safely diffuse heat even if local excessive combustion occurs. Can be like this,
Regardless of whether the amount of particulates is large or small, regeneration can be completely and safely achieved in a short time. For this reason, the variation in the temperature distribution occurring when burning the particulates is eliminated, and the time required for burning the particulates can be further reduced, and the amount of the particulates that can be burned can be increased.

According to a second aspect of the present invention, there is provided a regeneration system for an exhaust gas purifying apparatus according to the first aspect, wherein the heater is disposed between the exhaust gas purifying honeycomb filter and the gas inlet side end face of the filter by 0.2 to 15 cm. Are arranged at an interval of.

In this case, since the gas inlet side end face of the exhaust gas purifying honeycomb filter is not in direct contact with the heater, the gas inlet side end face of the exhaust gas purifying honeycomb filter may exhibit an abnormally high temperature due to the heating of the heater. Absent. Thus, it is possible to prevent a crack from being generated near the gas inlet side end face of the exhaust gas purifying honeycomb filter due to a rapid temperature change. Further, since the front end of the filter is not blocked, the pressure loss does not increase, and when the regenerating system is mounted on a vehicle, the heater and the front end of the filter are brought into contact with each other due to vibration, so that damage is not caused.

It is particularly desirable that the separation distance be limited to the range of 0.2 to 15 cm, because the balance between heat propagation to the filter, heat exchange with the combustion assisting air, and avoidance of contact vibration is good.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an embodiment of a regeneration system for an exhaust gas purifying apparatus according to the present invention. The exhaust gas purifying device 10 is a device for purifying exhaust gas discharged from an internal combustion engine (in this embodiment, a diesel engine), and is provided in the middle of an exhaust passage 11 from the internal combustion engine. As shown in FIG. 2, the exhaust gas purifying apparatus 10 includes an exhaust gas purifying honeycomb filter 12 made of a sintered body of porous silicon carbide (SiC), and a gas inflow side of the filter 12 for heating the filter 12. And a heater 13 disposed in front of the end face. The pump unit 14 mounted on the vehicle is connected to the exhaust gas purifying device 10 via a pipe 15, and the auxiliary combustion air is supplied from the inlet 16 provided in the exhaust gas purifying device 10 via the pipe 15 into the exhaust gas purifying device 10. Supply. The degree of clogging due to particulates in the exhaust gas purification device 10 can be known by monitoring a change in pressure during operation transmitted to the monitor box 18 via the air tube 17. Reference numeral 19 denotes a check valve for preventing gas from flowing back from inside the exhaust gas purifying apparatus 10.
The arrangement of 9 is not limited to this mode, and may be provided in the pipe 15.

The controller unit 20 (200 V AC power supply in this embodiment) is connected to circuits R 1, R 2, R 3 via a connector box 21. Circuit R1
Monitors a rapid rise in the temperature inside the exhaust gas purification device 10 due to gas discharged based on an output signal from a temperature sensor (for example, a thermocouple) provided in the exhaust gas purification device 10. The circuit R2 is connected to the heater 13 and controls the heater temperature as described later. The circuit R3 is connected to the pump unit 14 and controls the supply of the auxiliary combustion air as described later.

The heater 13 is a spiral ceramic heater disposed at a predetermined distance from the end face of the filter 12 on the gas inflow side. The shape of the heater 13 is not limited to a spiral shape, and any shape may be used as long as the heater 13 allows the supplied auxiliary combustion air to pass through when disposed in front of the filter 12.

In this case, the gas inlet side end face of the exhaust gas purifying honeycomb filter 12 is not in direct contact with the heater 13, so that the gas inlet side end face of the filter 12 does not exhibit an abnormally high temperature due to the heating of the heater 13. . Thereby, it is possible to prevent a crack from being generated near the gas inlet side end face of the exhaust gas purifying honeycomb filter 12 due to a rapid temperature change. Further, since the front end of the filter 12 is not blocked, the pressure loss does not increase, and when the regeneration system is mounted on a vehicle, the vibration causes the heater 13 and the front end of the filter 12 to contact and vibrate, leading to damage. I can't do that.

In particular, if the heater 13 is arranged at a distance of 0.2 to 15 cm from the end face of the exhaust gas purifying honeycomb filter 12 on the gas inflow side of the filter 12, heat transmission to the filter 12, It is desirable to have a good balance between heat exchange with the substrate and avoidance of contact vibration.

The honeycomb filter 12 for purifying exhaust gas includes:
The porous silicon carbide sintered body is formed in a honeycomb shape and has a substantially columnar shape as a whole. The filter 12 has a plurality of exhaust gas passage holes 12a extending in parallel with the longitudinal direction thereof.
Either one end of the gas inflow side and the discharge side of 2a is alternately sealed with small pieces 12b of a porous silicon carbide sintered body.
In this way, the flow holes on the gas inflow side end face and the gas discharge side end face of the filter 12 have a checkered pattern. Further, an oxidation catalyst can be carried on the inner wall surface of the exhaust gas passage hole 12a. The exhaust gas purifying honeycomb filter 12 is tightly held in a casing of the exhaust gas purifying apparatus 10 via a heat insulating material 23 provided on an outer peripheral surface thereof.

The operation of the exhaust gas purifying honeycomb filter 12 will now be described. As shown in FIG. 2, when the exhaust gas (arrow A) discharged from the diesel engine flows into the exhaust gas purifying honeycomb filter 12, the particulate matter (such as soot) in the exhaust gas is formed on the surface of the exhaust gas flow hole 12a. Particulate matter) and HC are filtered and oxidized by the oxidation catalyst. The purified exhaust gas (arrow B) passing through the exhaust gas purifying honeycomb filter 12 is discharged to the outside of the vehicle through the exhaust passage 11.

However, when the diesel engine is operated for a long time, particulates accumulate on the inner wall surface of each flow hole, and the filter efficiency of the filter 12 is reduced.
For this reason, after stopping the operation of the diesel engine, the filter 12 in the exhaust gas purification device 10 is regenerated by using the regeneration system according to the present invention.

First, the control unit 20 is turned on, and the heater 13 is turned on via the circuit R2, thereby heating the end face of the exhaust gas purifying honeycomb filter 12 on the gas inflow side. After a lapse of a predetermined time, the circuit R3 is turned on. The pump unit 14 is operated via the gas supply line to supply auxiliary combustion air to the gas inlet side end face of the filter 12 via the pipe 15 and the gas inlet 16. In this case, the hottest position heated by the heater 13 is the front end, and in this state,
Combustion starts when supplementary air is supplied. As described above, the position of the highest temperature in the exhaust gas purifying honeycomb filter 12 coincides with the combustion start point, so that the temperature rise time is significantly shortened. In addition, since the heat from the heater 13 is transmitted in the exhaust gas purifying honeycomb filter 12 along the longitudinal direction of the filter 12, combustion propagation is efficiently performed,
The front end is not cooled by the auxiliary combustion air, becomes uniform in the longitudinal direction, and becomes a combustion propagation in which a stress distribution hardly occurs. As a result, the amount of particulates that can be incinerated is significantly increased, and a system that can be safely recycled in a short time can be configured.

As a configuration for achieving the excellent combustion mechanism of the regeneration system, the present invention employs a porous silicon carbide sintered body as a material of the exhaust gas purifying honeycomb filter 12. This material has a very high thermal conductivity and helps to efficiently propagate the heat exchanged by the direct heat from the heater 13 and the heat exchanged by the auxiliary combustion air passing through the heater surface to the rear and radial direction of the filter. Even if excessive combustion occurs, heat can be safely diffused, and regeneration can be achieved completely safely in a short time regardless of whether the amount of particulates is large or small. . For this reason, the variation in the temperature distribution that occurs when burning the particulates is eliminated, and the time required for burning the particulates can be further reduced, and the amount of the particulates that can be burned can be increased. The exhaust gas purifying honeycomb filter 12
When the auxiliary combustion air is supplied to the inside, the heater 13 is turned off.
N may be simultaneous.

FIG. 3 shows a comparison between the temperature distribution in the filter in the regeneration system of the present invention and the temperature distribution in the filter in the conventional purification device disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 3-23307. However, the timing for turning on the heater and the timing for supplying the auxiliary combustion air are as follows.
The reproduction system according to the present invention is operated at the timing shown in FIG. 4A, and the conventional apparatus is operated at the timing shown in FIG. 4B.

FIGS. 3A, 3B and 3C show data relating to the reproduction system of the present invention. FIG.
(A) shows the temperature measurement points in this system,
Temperature measurement is performed at six points up to six. FIG. 3 (b)
FIG. 3 shows the temperature distribution at six measurement points when the particulates start burning, and FIG. 3C shows the temperature distribution at the six measurement points when the particulates are burning. 3 (d), (e), and (f) are data relating to the conventional device, respectively.
3 (a), 3 (b), and 3 (b) in the reproduction system of the present invention.
Since the relationship corresponds to (c), a detailed description is omitted. The asterisks in FIGS. 3B, 3C, 3E, and 3F indicate the temperatures at six measurement points, that is, the heater temperatures.

First, the system of the present invention is shown in FIG.
This will be discussed with reference to (b) and (c). At this time, the heater 13 is turned on for a time t2 (2
0 to 45 min).

The temperature distribution in the filter 12 from the time when the heater 13 is turned on until the predetermined time t1 shows a characteristic as shown in FIG. 3B, and the temperature near the inflow side end face of the filter 12 is high. However, the temperature distribution in the filter 2 from the start of the supply of the auxiliary combustion air at the predetermined time t1 (20 min) to the time t3 (45 min) shows a characteristic as shown in FIG. Is substantially uniform in the longitudinal direction during the burning of the particulates. FIG.
When the regeneration system of the present invention is operated in accordance with the sequence shown in (a), the accumulated particulates are incinerated and the filter 12 is regenerated in about 45 minutes. The amount of particulates that can be incinerated during this period is 50 g.

Next, the conventional device is shown in FIGS. 3 (d), (e),
Consider with reference to (f). The heater 4 is shown in FIG.
As shown in (b), the ON state is maintained until time t4. In this case, the time t4 is a time when the temperature in the filter 2 rises to a temperature at which the particulates can be burned (a temperature of 630 ° C. or higher).

The temperature distribution between the time when the heater 4 is turned on and the predetermined time t4 shows the characteristic shown in FIG. 3 (e), and the temperature distribution in the filter 2 is substantially uniform. However, the temperature distribution in the filter 2 after supplying the auxiliary combustion air beyond the time t4 shows the characteristic as shown in FIG.
The temperature increases as it approaches the gas discharge side of the filter 2,
There is variation in the temperature distribution. In this conventional apparatus, the time required to regenerate the filter 2 fluctuates at a predetermined time t4 of the sequence shown in FIG. 4B, but is usually about 65 minutes, during which the amount of particulates that can be incinerated is increased. Is 40 g.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As a honeycomb filter for purifying exhaust gas, a cell structure: 14/200 and a size: φ140 × 15
A first filter made of a 0 L silicon carbide sintered body, and
Cell structure: 14/200 and size: φ165 × 1
A regeneration system according to the present invention is provided by using a second filter made of a 50 L silicon carbide sintered body.
No. 307 was compared with the exhaust gas purifying apparatus according to the regeneration rate (%) when 40 g of the particulate matter was burned.

Regarding the first filter, the regeneration system of the present invention was operated while controlling the heating temperature of the heater and the supply amount of the auxiliary air (35 L / min) by the control unit according to the sequence shown in FIG. ,
The reproduction time was 45 (minutes) and the reproduction rate was 100%.
On the other hand, in the conventional apparatus, the same auxiliary air supply amount was used as shown in FIG.
When operated according to the sequence shown in (b),
The reproduction time was 70 (minutes) and the reproduction rate was 98%.

With respect to the second filter, when the supply amount of auxiliary combustion air is set to 48 L / min, the regeneration system of the present invention has a regeneration time of 35 minutes and a regeneration rate of 100%. The reproduction time was 75 (minutes) and the reproduction rate was 96%.

As is clear from the above results, the regeneration system of the present invention has a longer heating time (heat-up time) for heating the entire exhaust gas purifying honeycomb filter to the particulate combustion temperature than the conventional exhaust gas purifying apparatus. Time) and the time required to regenerate the filter. Further, when the amount of particulate burned when the allowable temperature gradient in the filter due to the heating of the heater was set to 70 ° C./cm was actually measured, the regeneration system of the present invention shortened the regeneration time compared to the above-mentioned conventional apparatus. About 15-20
g It was confirmed that extra incineration was possible.

FIG. 5 shows another embodiment of the present invention, in which the regeneration system of the present invention is employed in each of the bifurcated exhaust passages 11a and 11b. In this embodiment, each of the exhaust passages 11a and 11b has an opening / closing valve 24, and the controller unit 20 controls one of the exhaust passages 11a and 11b to open and the other to close, thereby purifying the exhaust gas. The honeycomb filters 12 can be separately regenerated.

The above is only a preferred embodiment of the present invention, and various changes can be made within the scope of the present invention. For example, the regeneration system of the present invention can be applied to a gasoline engine instead of a diesel engine. In the illustrated example, all the members except the control unit are used in a vehicle-mounted state. However, the control unit may be mounted in a vehicle-mounted state, and a power supply wire may be simply connected through a connector.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a reproduction system of the present invention.

FIG. 2 is an enlarged partial cross-sectional view showing a main part of a reproduction system according to the present invention.

FIG. 3 is a diagram for comparing a temperature distribution in a filter in a regeneration system of the present invention with a temperature distribution in a filter in a conventional exhaust gas purification device.

FIG. 4 is a time chart showing operating states of the regeneration system of the present invention and a conventional exhaust gas purification device, respectively.

FIG. 5 is a diagram showing another example of the reproduction system of the present invention.

FIG. 6 is a diagram showing an example of a conventional exhaust gas purification device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1,10 Exhaust gas purifying device 2,12 Exhaust gas purifying honeycomb filter 3,11 Exhaust passage 4,13 Heater 12a Exhaust gas circulation hole 12b SiC small piece 14 Pump unit 15 Supply pipe 16 Gas inlet 17 Air tube 18 Monitor box 19 Check valve 20 Controller unit 21 Connector box 23 Insulation material 24 Open / close valve R1 circuit (thermocouple) R2 circuit (heater) R3 circuit (pump)

Claims (2)

[Claims] 1. An exhaust gas purifying apparatus provided in an exhaust passage of an internal combustion engine and provided with an exhaust gas purifying honeycomb filter made of a porous silicon carbide sintered body, and a gas inflow of the filter for regenerating the filter. And a control unit that controls the supply of electric power to the heater and the supply of auxiliary air provided to the purification device in front of the heater. The exhaust gas purification system regeneration system. 2. The exhaust gas purifying honeycomb filter according to claim 1, wherein the heater is arranged at a distance of 0.2 to 15 cm from an end face on the gas inflow side of the filter. Regeneration system for exhaust gas purification device.