JP2953409B2 - Particulate trap for diesel engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an embodiment of a regenerative heater in which fine particles such as carbon (hereinafter referred to as "particulates") in exhaust gas of a diesel engine are collected by a filter and heated and burned. The present invention relates to a particulate trap for a diesel engine (hereinafter, referred to as DPF) using the DPF.

[0002]

2. Description of the Related Art Diesel engine exhaust gas contains
It contains particulates mainly composed of carbon called particulates. DPFs have been developed to remove these from exhaust gases. The DPF is configured by combining a filter portion for collecting particulates and a heating element for regeneration for burning and removing the collected particulates.

[0003] Porous ceramics and metallic porous bodies are used for the filter for collection. Porous ceramics have very small voids and can reliably trap particulates in exhaust gas. Therefore, a large pressure loss is required due to a large pressure loss of the exhaust gas, and cracks, cracks, and erosion due to local heating are liable to occur due to poor thermal conductivity. In particular, heat spots due to non-uniform heating are likely to be generated during regeneration, which is likely to cause damage to the filter.
The porous metal can control the size of the voids as compared with the ceramic, and has good thermal conductivity, so that a heat spot is hardly generated, and it is easy to maintain a uniform temperature distribution during reproduction.

As a means for burning and removing particulates, there is a method in which an electric heater is energized to heat and burn. Japanese Patent Application Laid-Open No. 6-257422 proposes an embodiment in which filters having different diameters are combined in a multilayer structure and a plate-shaped regenerative heater is disposed in the middle of the filter so as not to contact the filter. In this application, FIG. 7 is a conceptual diagram showing a state in which this is mounted on a DPF.

[0005] Exhaust gas of the diesel engine flows into the casing 105 from the flange connected to the exhaust pipe in the direction of arrow A on the left side, and when passing through the gap of the cylindrical filter 102, particulates are collected. . A regeneration heater 103 is disposed in the middle of the cylindrical filter 102, and is provided with an air inlet 106 and an air outlet 107 for taking in oxygen in the atmosphere to efficiently heat and burn the particulates. In order to more positively supply oxygen, there are a method of providing a blower fan and a method of using oxygen in exhaust gas. The purified gas is released into the atmosphere in the direction of arrow B on the left.

[0006]

With the prior art configuration, the collected particulates are directly heated so that efficient regeneration is possible. However, when the filter has a multi-layer structure, the heat capacity differs between the outer and inner cylinder sides of the multi-layer, and when looking at each cylindrical electric heater individually, the inner circular space surrounded by the heater is Although there is almost no flow and a constant temperature is maintained, the outer space is D
Since the heat flow to the outside of the PF is active, heat is easily radiated. Therefore, in a filter composed of a multilayer cylinder, the temperature of the center cylinder tends to be high.

Furthermore, the ambient atmosphere near the filter tends to cause a sharp rise in temperature from around 600 ° C. where the trapped carbon burns, and eventually reaches a temperature that induces deterioration of the filter due to oxidation. Shorten filter life.

In view of the above, the present invention provides a regenerative heater configuration in which the temperature distribution of a multilayer cylindrical filter is uniform within a range from a particulate combustion temperature of about 600 ° C. to a filter heat-resistant temperature of 1000 ° C. or less, and a control method therefor. The task was to do.

[0009]

Means for Solving the Problems A thin plate-shaped electric heater is provided between a multilayer cylindrical filter for collecting particulates without contacting the filter, and as the filter approaches the multilayer central side cylindrical filter. The power supplied to the heater is reduced to lower the temperature of the central cylinder, which tends to be high, to balance with the temperature of the outer cylinder.

As means for reducing the electric power supplied to the heater, it is practical to change the thickness of the thin plate-shaped electric heater and the geometrical pattern of the energizing path to preset the resistance value of the heater.

As a method of reducing the electric power supplied to the heater, the amount of electricity supplied to the heater is selectively reduced as the heater approaches the center cylinder, thereby controlling the balance with the temperature of the outer cylinder.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

The heater according to the present invention is a component corresponding to the reference numeral 103 in FIG. 7, which is a conceptual diagram of a conventional DPF.

When the filter is a porous metal body having conductivity, the heater is provided at a position not in contact with the filter. Therefore, the heater to be inserted into the narrow gap is preferably a thin plate, and the conductor pattern is conveniently formed by press punching or etching. The conductor pattern may be various geometric patterns, or may be formed of a punched metal or a dense and dense net of a conductor.

As the material of the heater, it is convenient to use a material mainly composed of Ni--Cr to which Al is added, or a material mainly composed of Fe--Cr having a higher resistance value to which Al is added.

The material of the filter is described in Japanese Patent Publication No. 57-393.
No. 17, the metal skeleton of the three-dimensional network structure manufactured by the manufacturing method described in JP-A No. 17 is 5 to 100 μm in thickness, and the pore size is 150 to
It is preferable to use a metal porous body made of Ni having a communication hole of 400 μm as a main raw material and diffusion and infiltration of Cr and Al.

In order to maintain the temperature inside the casing 105 of the DPF uniform, it is necessary to use a filter close to the center cylinder of the filter.
The amount of heat generated is limited by increasing the thickness of the heater as the heater becomes thicker to lower the resistance value, or by lowering the resistance value in combination with a material having good conductivity. Alternatively, when the specifications of the heaters are the same, the power supply may be reduced as the heater is closer to the center cylinder.

FIG. 1 shows a specific configuration diagram. When the exhaust gas of the diesel engine flows into the casing 105 from the flange connected to the exhaust pipe in the direction of arrow A on the left side and passes through the gaps of the cylindrical filters 4, 5, 6, and 7,
Particulates are collected. Cylindrical filter 4,
Regeneration heaters 2 and 3 are arranged between 5, 6 and 7. Thermocouples A, B, C, and D are installed on the outer circumference of the filter 4, the inner circumference of the filter 5, the outer circumference of the filter 6, and the inner circumference of the filter 7 at the midpoint of the collection length of the filter to monitor the temperature change of the filter. To detect. Reference numerals 8 and 9 are shielding plates for controlling the flow of exhaust gas. Regeneration heater 2,
Power is supplied to the power supply 3 from the power supply 11 via the variable resistors 12 and 13. Air inlet 1 for taking in atmospheric oxygen to heat and burn particulates efficiently
06 or the air outlet 107 may be provided.

[0019]

EXAMPLE The experimental apparatus shown in FIG. 6 evaluates the performance of a DPF. The configuration of the experimental apparatus is the same as that of a passenger car equipped with a 3400 cc, 4-cylinder direct injection diesel engine installed on a chassis dynamometer. The DPF 100 is arranged in the middle of introducing gas into the dilution tunnel. The specifications of the regenerative heater in which the DPF 100 was configured as shown in FIG. 1 were prepared as shown in the table.

[0020]

【table】

The heaters used in the table each have an energization path of a uniform geometric pattern formed with a uniform thickness, and all heaters are loaded with a voltage under the same conditions.

(Comparative Example 1) The materials of the heaters 2 and 3 of the DPF shown in FIG.
Electric power of 500 W is supplied together with 2 mm. After the start of regeneration, the burning of the particulates is started, and after about 25 minutes, the regeneration is finished. FIG.

The rate of temperature rise is such that the thermocouple at the outermost periphery rises more rapidly like the temperature of the thermocouple A until the particulate self-combustion temperature reaches 600 ° C., and the particulate self-combustion temperature 600 ° C. After that, the temperature of all the thermocouples rises discontinuously, and then the temperature of the thermocouple located closer to the center suddenly rises to a region exceeding the oxidation temperature of the filter, 1000 ° C, like the temperature of the thermocouple d. You can see that it is rising. In other words, it was proved that the filter 7 closer to the center was exposed to a higher temperature.

Comparative Example 2 Electric power of 1000 W was supplied to the heater 2 of the DPF shown in FIG. 1 and power was not supplied to the heater 3, and the regeneration was terminated about 25 minutes after the start of particulate combustion after the start of regeneration. FIG. 3 shows the temperature changes of the thermocouples A, B, C, and D with the lapse of time until the power supply is interrupted.

Contrary to Comparative Example 1, the rate of temperature rise is slower as the thermocouple d, which is the thermocouple located farthest from the heater 2, has a lower temperature rise and exceeds the self-combustion temperature of particulates of 600 ° C. It can be seen that after the temperature of all the thermocouples rises discontinuously, even the temperature of the outermost thermocouple a, which reaches the highest temperature, stays below 1000 ° C., which is the oxidation temperature of the filter. This phenomenon suggests that the temperature in the casing 105 can be balanced by controlling the temperature of the heater in the center cylinder. However, temperature variation between thermocouples is large, and efficient combustion has not been achieved.

(Example 1) Except that the materials of the heaters 2 and 3 of the DPF shown in FIG. 1 are unified to Ni-Cr-Al, the resistance is reduced to 0 by setting the plate thickness to 0.12 mm and 0.28 mm. After changing to .83 ohm and 0.36 ohm, 30
0 W and 700 W of electric power are supplied. After the start of regeneration, the burning of the particulates is started, and after about 25 minutes, the regeneration is terminated.
FIG. 4 shows the temperature changes of C and D.

The rate of temperature rise is as high as the temperature of the thermocouple A as the thermocouples present on the outermost periphery reach the self-combustion temperature of particulates of 600 ° C., but the temperature variation between the thermocouples is as follows. When the temperature exceeds the self-combustion temperature of particulates of 600 ° C. as compared with Comparative Example 1 or 2, even after the temperature of all thermocouples rises discontinuously, 80
It converges around 0 ° C.

(Example 2) Except that the thicknesses of the heaters 2 and 3 of the DPF shown in FIG.
Al and Ni-Cr-Al are used to set the resistance to 0.1.
After changing to 83 ohm and 0.36 ohm, 300W
And 700 W of electric power, and after the start of the regeneration, the burning of the particulates is started, and after about 25 minutes, the regeneration is completed. The thermocouples A, B, C,
FIG. 5 shows the temperature change of D.

The rate of temperature rise is almost the same as that of the first embodiment, and the thermocouple existing at the outermost periphery rises like the temperature of the thermocouple a until the self-combustion temperature of particulates reaches 600 ° C. The variation in the temperature between the pairs is smaller than that in Comparative Example 1 or 2, and exceeds the self-combustion temperature of particulates of 600 ° C., and converges to around 800 ° C. even after all the thermocouples rise discontinuously. doing.

[0030]

According to the present invention, a regeneration filter is arranged at a position not in contact with a filter between multilayer cylindrical filters for collecting particulates, and a heater closer to a center cylinder of the filter has a larger thickness. The amount of heat generated was controlled by lowering the resistance value, lowering the resistance value in combination with a material having good conductivity, or reducing the power supply as the heater was closer to the center cylinder. 10 to 25 minutes after the start of regeneration, the temperature distribution of each filter was from 600 ° C., which is the self-combustion temperature of particulates, to 1000 ° C., which is the heat resistant temperature of the filter.
It can be converged in the range of ° C. Therefore, a durable DPF with good regeneration efficiency can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a DPF of the present invention.

FIG. 2 shows a transition of a temperature change of a heater during a regeneration time of Comparative Example 1 for explaining an effect of the present invention.

FIG. 3 shows a transition of a temperature change of a heater during a regeneration time of Comparative Example 2 for explaining an effect of the present invention.

FIG. 4 shows a transition of a temperature change of a heater during a regeneration time according to the first embodiment of the present invention.

FIG. 5 shows a transition of a temperature change of a heater during a regeneration time according to a second embodiment of the present invention.

FIG. 6 is a configuration diagram of a DPF experimental apparatus.

FIG. 7 is a conceptual diagram of a conventional DPF.

[Explanation of symbols]

 2, 3: regenerative heater 4, 5, 6, 7: filter 8, 9: shielding plate 11: power supply 12, 13: variable resistor 100: DPF 105: casing 106: air inlet 107: air outlet

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-257422 (JP, A) JP-A-5-106425 (JP, A) JP-A-5-125925 (JP, A) JP-A-8- 193509 (JP, A) JP-A-7-310530 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F01N 3/02

Claims (3)

(57) [Claims] 1. A thin plate-shaped electric heater is provided between a multilayer cylindrical filter for collecting particulates without contacting the filter, and a heater closer to the multilayer central-side cylindrical filter has a higher temperature. A particulate trap for a diesel engine, characterized in that the supply power is reduced . 2. The diesel engine patty according to claim 1, wherein the means for reducing the electric power supplied to the heater reduces the resistance value of the heater toward a heater closer to a filter having a multilayered central cylinder. Cured trap. 3. The device according to claim 1, wherein the means for reducing the power supplied to the heater reduces the amount of power supplied to the heater as the heater is closer to a filter having a multilayered central cylinder. Particulate trap for diesel engines.