JPH08260946A - Dpf regenerating system using heater - Google Patents

Abstract

PURPOSE: To prevent generation of a leak even when the DPF regenerating system is heated by arranging a ceramics layer provided with a DPF consisting of the porous carbide-silicon sintered body, and having high insulation resistance excellent in the heat conductivity between the DPF and a heater. CONSTITUTION: An exhaust emission control device is provided with a casing 2 of metallic pipes, and a passage 2a is connected to an exhaust pipe passage of an internal combustion engine. A DPF(diesel particulate filter) 3 to carry the catalyst to purify the exhaust gas is arranged in the casing 2. A ceramics layer 4 having high insulation resistance excellent in the heat conductivity is closely attached to the outer circumference of the DPF 3, and regenerating heaters 5 consisting of one ceramics heating wire are arranged in a surrounding manner with the prescribed intervals vertically to the axis of the DPF 3. In regenerating the DPF 3, no leak is generated even when the DPF is heated to the high temperature, and the insulation resistance of the DPF 3 consisting of the porous carbide and silicon sintered body is deteriorated, and the particulates are burned at the high temperature to allow the regeneration of the DPF 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DPF regeneration system using a heater in an exhaust gas purifying apparatus for purifying exhaust gas discharged from an internal combustion engine such as a diesel engine.

[0002]

2. Description of the Related Art Conventionally, when purifying particulates (particulate matter) in exhaust gas of a diesel engine or the like, a filter (diesel particulate filter; DPF) formed by cordierite is used for diesel engines. This is done by connecting to the exhaust side and collecting particulates on the surface of the filter.

When such a DPF is used for a long time, particulates containing black smoke as a main component are deposited on the filter, pressure loss increases, and a load is applied to the engine. Then, ignite with a burner, etc.
For example, by heating F to a high temperature, the accumulated particulates are burned to be removed, and the DPF must be regenerated.

However, this DPF has a melting point (1200-1200).
(1300 ° C.), the DPF regeneration treatment by ignition does not produce DPF.
After igniting particulates at one end of the
If air is supplied to the ignition position side from the ignition position side, non-uniform combustion of particulates occurs and a local temperature rise occurs. If the regeneration process is repeated, the DPF is melted and cannot be reused. There was a problem.

There is also a method of embedding a heater wire in the DPF to heat it to a high temperature, but it is impossible to maintain a sufficient temperature for combustion due to the thermal conductivity of cordierite, or a long time is required. There was a problem I needed.

In order to solve such a problem, it has been proposed to use a silicon carbide sintered body having excellent heat resistance and thermal conductivity as the DPF. However, in this method, since the thermal conductivity of the material is too high, there is a drawback in that a considerable amount of heat is transmitted in the radial direction of the DPF, that is, in the casing direction on the outer periphery of the DPF to generate heat.

[0007]

[Problems to be Solved by the Invention]
In the publication, as shown in FIG. 2, a heater wire 5 is provided on the outer periphery of the DPF, and a high heat insulating material layer 6 is provided between the heater wire 5 and the inner wall of the passage 2a. A technique of heating to a temperature that allows uniform and short-term regeneration is disclosed.

However, when the DPF is loaded with a catalytic metal that burns particulates at a low temperature, 4
Although it is possible to burn the particulates by heating at about 00 ° C, there is a structural problem in supporting the catalyst metal. If such a catalyst is not supported, the catalyst will be heated to 600 ° C or higher. Therefore, the insulating property of the material becomes a problem. Generally, a non-oxide ceramic material such as silicon carbide has a low insulation resistance value with temperature. Therefore, when the heater is brought into contact with the DPF to increase the thermal efficiency by electric heating, leakage occurs at high temperatures, and there are major obstacles such as failure to meet the withstand voltage standard.

Further, the DPF in which the heater wire is divided into a plurality of pieces
By embedding in the inside and disposing the high heat insulating material layer between the DPF and the inner wall of the passage, the temperature distribution in each divided portion becomes small, the generated stress is low, and the occurrence of cracks is prevented in advance. There was a problem that the temperature near the outer peripheral portion of the DPF did not rise and regeneration was incomplete.

The present invention has been made in order to solve these problems, and DP which does not cause leakage even when heated to a high temperature.
It is intended to provide an F reproduction system.

[0011]

In order to solve the above-mentioned problems, the present invention provides a casing having a passage connected to the exhaust side of an internal combustion engine, a DPF disposed in the passage, and a DPF. DPF equipped with a heater arranged on the outer periphery
In the reproduction system, the DPF is made of a porous silicon carbide sintered body, and a ceramic layer having a high insulation resistance with excellent thermal conductivity is disposed between the DPF and the heater. It is something.

As the ceramic layer having excellent thermal conductivity and high insulation resistance, one having high bending strength and excellent punching workability is preferable. Examples of the ceramic layer having high thermal conductivity and high insulation resistance include, for example, a mica plate for electric heating (Z523, soft mica manufactured by Nippon Mica Mfg. Co., Ltd.)
Etc. can be mentioned. As the above-mentioned mica plate for electric heating, one having a silicon resin as a main component as an adhesive is preferable. The thickness of the mica plate for electric heating is 0.3 to 1.0 m.
m is preferred.

The DPF regeneration system of the present invention is the above DP.
In order to heat F to a high temperature, it is preferable that a high heat insulating material layer is provided between the heater and the inner wall of the passage.

Examples of the high heat insulating material layer include inorganic fibers such as alumina-silica ceramic fibers, alumina fibers, zirconia fibers, silica fibers, rock wool and asbestos; organic fibers such as nylon and Kevlar; foams such as urethane. A molded body of the above; a combination thereof, and the like. Preferably, the inorganic fiber is used partially or entirely. Further, a space may be formed in a part between the DPF and the inner wall of the passage so that the air layer is a part of the high heat insulating material layer.

[0015]

In the DPF regeneration system of the present invention, by arranging a ceramic layer having a high insulation resistance with excellent thermal conductivity between the DPF and the heater, it is heated to a high temperature of 600 ° C. or higher, DPF made of porous silicon carbide sintered body
The leakage resistance does not occur even if the insulation resistance value of is reduced. Therefore,
The DPF regeneration system of the present invention is 600 ° C. without supporting a catalyst for burning particulates at low temperature on the DPF.
The DPF regeneration process can be performed by burning the particulates at the above high temperature. Further, in the DPF regeneration system of the present invention, by disposing the high heat insulating material layer between the heater and the inner wall of the passage, the DPF can be uniformly heated to a high temperature to completely burn the particulates. it can.

[0016]

【Example】

First Embodiment Hereinafter, a DPF regeneration system that is a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of the DPF regeneration system in the first embodiment, and FIG. 3 is the first embodiment.
3 is a schematic view and a partial cross-sectional view of the exhaust gas purification device in FIG. By assigning the same reference numerals to the same components,
Overlapping description is omitted.

In FIG. 3, the exhaust gas purifying apparatus 1 includes a casing 2 made of a metal pipe, and a passage 2a of the casing 2 is connected to an exhaust pipe Ea of the internal combustion engine E. A DPF 3 carrying a catalyst for purifying exhaust gas is arranged in the casing 2. In FIG. 1, a ceramic layer 4 having a high insulation resistance with excellent thermal conductivity is closely attached to the outer periphery of the DPF 3, and a regeneration heater 5 composed of a single ceramic heater wire is provided on the outer periphery of the ceramic layer 4. Are arranged so as to be lined up at a predetermined interval perpendicular to the axis of the DPF. A high heat insulating material layer 6 that covers the heater 5 is attached to the inner wall of the passage 2 a of the casing 2.

The DPF 3 is formed of a porous silicon carbide sintered body into a honeycomb shape and has a prismatic shape as a whole. A large number of gas passage holes extending parallel to the axial direction are formed in the DPF 3, and one end of each of the gas passage holes on the supply side or the discharge side is alternately sealed with a small piece of silicon carbide.

As shown in FIG. 3, when the exhaust gas of the internal combustion engine E is introduced into the DPF 3 from the supply side of the casing 2,
Particulates in the exhaust gas are collected by the wall portion of the gas passage hole. And the purified exhaust gas is DP
Emitted from F3.

When the regeneration process of the DPF 3 used in this way is performed, the heating of the DPF 3 by the heater 5 is started in a state where a predetermined amount of particulates are collected in the DPF 3. Then, the temperature of the DPF 3 is a predetermined temperature (400
Up to 800 ° C.), supply of secondary air for promoting combustion to the casing 2 is started. Then, by continuing this process, the particulates in the DPF 3 are burned and the DPF 3 is regenerated.

Here, concrete experimental data regarding the reproduction processing of the DPF 3 will be described. As an experimental condition, D
PF3 has a diameter of 140 mm, a length of 140 mm, a thermal conductivity of 0.029 cal / cm · sec · ° C., and a specific heat of 0.22 c.
Al / g · ° C was used. The heat insulating material 4 on the outer periphery of the DPF 3 was made of ceramic fiber and had a thickness of 25 mm and a thermal conductivity of 0.08 kcal / m · hr · ° C. For the ceramic layer 4 having high insulation resistance with excellent thermal conductivity on the outer periphery of the DPF 3, a mica plate for electric heating (manufactured by Japan Mica Mfg. Co., Ltd., Z523, soft mica) was used. The heater 5 used was 12V-2.5kW. In addition, the secondary air supply from the compressor is 50L /
It was set to min.

The particulate collection in the exhaust gas continued the collection operation until the pressure detected by the pressure sensor Ps reached a predetermined amount. In the calculation of the particulate collection amount during this period, the volume of the DPF 3 was used as the total amount of the gas passage holes, and the particulate collection amount was obtained based on the weight change before and after the collection process.

The leakage current from the DPF 3 was measured with a micro ammeter or a leakage current meter. Regarding the regeneration processing time of the DPF 3, the center of the upstream side surface of the DPF 3 is measured at the measurement point P.
As a result, a thermocouple was placed and the temperature change was monitored. Since the temperature at the measurement point P sharply drops at the end of combustion of the particulates collected in the DPF 3, the time from the start of energization of the heater 5 to the temperature drop time was measured as the regeneration processing time.

As a result, using the apparatus of Example 1, 60
When regenerated by heating with an electric heater at 0 ° C., leakage was 0 A, which was not observed. The required regeneration processing time was 32 minutes.

Comparative Example 1 Hereinafter, a DPF regeneration system which is Comparative Example 1 will be described with reference to the drawings. FIG. 2 is a DPF in Comparative Example 1.
It is sectional drawing of a reproduction | regeneration system. The same components will be assigned the same reference numerals and overlapping description will be omitted.

In FIG. 2, the same experiment was conducted with the same configuration as in Example 1 except that a ceramic layer having high thermal conductivity and high insulation resistance was not used on the outer periphery of the DPF 3.

As a result, using the apparatus of Comparative Example 1, 60
When regenerated by heating with an electric heater at 0 ° C., the leakage current was about 0.1 mA. The required regeneration processing time was 33 minutes.

[0028]

Since the DPF regenerating system of the present invention has the above-mentioned structure, it is heated to a high temperature of 600 ° C. or higher in the regenerating process and is made of a porous silicon carbide sintered body
Even if the insulation resistance value of the PF is reduced, leakage does not occur. Therefore, the DPF regeneration process is performed by burning the particulate matter at a high temperature of 600 ° C. or higher without supporting the catalyst for burning the particulate matter at a low temperature on the DPF. can do.

[Brief description of drawings]

FIG. 1 is a sectional view of a DPF regeneration system according to a first embodiment.

FIG. 2 is a sectional view of a DPF regeneration system of Comparative Example 1.

3A and 3B are a schematic view and a partial cross-sectional view of the exhaust gas purifying apparatus according to the first embodiment.

[Explanation of symbols]

 1 Exhaust Gas Purification Device 2 Casing 2a Passage 3 DPF 4 Ceramic Layer 5 Heater 6 High Insulation Material Layer

Claims (2)

[Claims] 1. A DPF including a casing having a passage connected to an exhaust side of an internal combustion engine, a DPF arranged in the passage, and a heater arranged on an outer periphery of the DPF.
In the regeneration system, the DPF is made of a porous silicon carbide sintered body, and a ceramic layer having a high insulation resistance with excellent thermal conductivity is disposed between the DPF and the heater. Characteristic DPF regeneration system. 2. The DPF regeneration system according to claim 1, wherein a high heat insulating material layer is disposed between the heater and the inner wall of the passage.