JP2008208749A - Soot purifying device for diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soot purifying device for a diesel engine capable of enlarging the self-reproduction domain of a particulate filter. <P>SOLUTION: The soot purifying device for a diesel engine 20 comprises either one or both of an oxidation catalyst 4 and a particulate filter 1 in the inside. Without uniformizing the catalyst density distribution in the cross-sectional view of the oxidation catalyst 4 or the particulate filter 1, the catalyst density distribution in the central portion is higher than that in the outer peripheral portion. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technology for a black smoke purification device for a diesel engine that reduces emission of black smoke.

  In recent years, environmental concerns and health effects are concerned, so black smoke (PM) and PM (Particulate Matter) in exhaust gas discharged from diesel engines such as automobiles, ships, and generators. Development of a device that removes water is in progress. In some areas, regulations are being reinforced more specifically, and it is urgently necessary to deal with them. As technical methods for dealing with these, there are a method for preventing black smoke emission by measures such as fuel injection timing and mixing ratio on the engine side, and a method for dealing with exhaust system post-treatment. As a method for dealing with exhaust system after-treatment, for example, a technology for attaching a black smoke removal device (DPF: Diesel Particulate Filter) to an exhaust device such as a diesel engine is already known, and a commercially available retrofit type black As a smoke removing device, a ceramic filter system in which a ceramic is formed into a honeycomb shape is the mainstream. Various methods for regenerating the clogging of black smoke have been studied for these devices, but they are not yet technically sufficient.

As a conventional technique, in Patent Document 1, a larger amount of catalyst metal is distributed on the filter outer periphery side than the filter center side of the DPF, and the combustion of particulates on the filter outer periphery side is promoted, so that the filter center portion and the outer periphery portion are separated. The technique of eliminating the temperature gradient between them is known.
JP 2006-88027 A

  In industrial institutions, they are used in various ways depending on the application and operator. Further, the diesel particulate filter has a self-regeneration difficult region as shown in FIG. The definition of the self-regeneration region here refers to an operation region in which the amount of soot entering the particulate filter is lower than the amount of soot oxidized on the particulate filter. This state is a region where the soot amount accumulated at the balance point is sufficiently lower than the reference value of the differential pressure and pool soot, although it varies depending on other factors such as the pool state of soot and the outside temperature.

In general, it is said that the oxidation reaction by oxygen is dominant on the particulate filter in the exhaust gas temperature range of 450 ° C. or higher. This oxidation rate is greatly influenced by temperature. Oxidation by oxygen is considered to be slow and slow to accumulate soot unless there is a temperature of 600 ° C. or higher. If the amount of oxygen suddenly becomes sufficient from a state where the temperature is 600 ° C. or more with a large amount of soot accumulated, for example, when idling is suddenly dropped, the oxidation rapidly proceeds to a temperature exceeding 1000 ° C. and the filter melts down. Oxygen oxidation is difficult to control because it causes so-called runaway regeneration. When the exhaust gas temperature is in the range of 250 ° C. to 350 ° C., NO 2 is generated on the preceding oxidation catalyst or particulate filter, and this NO 2 returns to NO and oxidizes soot on the catalyst on the particulate filter. This oxidation is governed not only by the temperature but also by the amount of NO 2, that is, the amount of the oxidation catalyst and the amount of catalyst on the particulate filter. There is no runaway for this. When the exhaust gas temperature is 250 ° C. or lower, self-regeneration is difficult. In a region where self-regeneration is difficult, it is necessary to perform so-called forced regeneration in which the exhaust gas temperature is forcibly increased.
In addition, it is necessary to enlarge the self-regeneration area as much as possible in order to reduce the cost and size of the particulate filter regeneration assisting device. In addition, as shown in FIG. 7, the low temperature region is generally a low load and low rotation region, and the gas temperature is lowered, and the gas volume flow rate is greatly reduced from the rated value.
This invention is made | formed in view of the said actual condition, The place made into the objective is providing the black smoke purification apparatus for diesel engines which can expand the self regeneration area | region of a particulate filter.

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

  That is, in claim 1, in the black smoke purification device for a diesel engine having either or both of the oxidation catalyst and the particulate filter inside, the catalyst density of the particulate filter is not uniform, but the central side rather than the outer peripheral side. The catalyst density is increased.

  According to the second aspect of the present invention, the oxidation catalyst density of the oxidation catalyst arranged to face the portion where the catalyst density is increased on the center side rather than the outer peripheral side of the particulate filter is increased.

  In claim 3, the carrier shape of the oxidation catalyst or the particulate filter is substantially cylindrical, and the maximum exhaust gas flow rate outside the self-regeneration area set by the area ratio is divided by the gas flow rate at the maximum output. In a large range, the catalyst density on the center side of the oxidation catalyst or the particulate filter is increased.

  According to a fourth aspect of the present invention, when the flow rate of the exhaust gas is small, the exhaust gas passage is throttled so that the exhaust gas flows intensively in the vicinity of the center of the oxidation catalyst or the particulate filter.

  As effects of the present invention, the following effects can be obtained.

  In claim 1, the total amount of catalyst is the same, and the self-regeneration area can be expanded.

  In claim 2, the total amount of catalyst is the same, and the self-regeneration area can be expanded. In addition, the density of the catalyst supported on the particulate filter carrier and the oxidation catalyst carrier can be set as appropriate, and the self-regeneration region can be further easily expanded.

  In the third aspect, in the case of self-reproducible margin, the regeneration is promoted near the center of the highest temperature, and the balance is maintained in a state where the regeneration is not sufficiently performed on the outer periphery, and this balanced state is maintained. Since the exhaust gas temperature can be shifted to the low temperature side, the self-regeneration area can be expanded. In this balanced state, the self-regeneration region can be expanded without increasing the overall exhaust resistance.

  In claim 4, by restricting the exhaust gas inlet and guiding the exhaust gas to the vicinity of the center of the filter, the gas flow in the low speed region is further concentrated near the center, and the temperature of the center is kept relatively high. The self-reproducing area can be expanded.

Next, embodiments of the invention will be described.
1 is a schematic view showing a black smoke purification device for a diesel engine according to the present invention, FIG. 2 is a cross-sectional view taken along the line AA of FIG. 1, and FIG. 3 is a schematic view showing the black smoke purification device for a diesel engine in Example 2. FIG. 4, FIG. 4 is a cross-sectional view taken along the line BB of FIG. 3, FIG. 5 is a schematic diagram showing a black smoke purification device for a diesel engine in Example 3, and FIG. 6 is a diagram showing a self-regeneration region according to the present invention. 7 is a diagram showing a conventional self-reproducing area.

The whole structure of the black smoke purification apparatus for diesel engines which concerns on this invention using FIG. 1 is demonstrated.
As shown in FIG. 1, the diesel engine black smoke purification device 20 (hereinafter referred to as a black smoke purification device) includes an inlet portion 2, a particulate filter 1, and an outlet portion 3. The inlet portion 2 and the outlet portion 3 are formed in the housings 7a and 7b, respectively. The particulate filter 1 is disposed in the installation portion 1a between the housings 7a and 7b. The particulate filter 1 is kept airtight with both the housings 7a and 7b and the gasket 15, and is integrated with the V-shaped band 12. It is fixed to. A heat insulating sound absorbing material 8 is disposed in the inlet portion 2, and the heat insulating sound absorbing material 8 is pressed against the inner wall of the inlet portion 2 by heat insulating sound absorbing material pressing plates 13 and 16.
The particulate filter 1 can be attached to and detached from the installation portion 1a.

  An inlet pipe 6 that guides exhaust gas 10 from an engine (not shown) is disposed at the inlet 2. The inlet pipe 6 is inserted through the inlet portion 2 in a substantially vertical direction, and has an opening for connecting to an engine through an exhaust pipe (not shown) at one end, and the other end is sealed. . A number of small holes 6 a are provided in the cylindrical side wall of the inlet pipe 6. The exhaust gas 10 enters the inlet portion 2 from the inlet pipe 6 through the small hole 6a. Further, the outlet portion 3 is provided with an outlet pipe 14 for discharging the exhaust gas 10 and a resonance pipe 25 for reducing noise during exhaust gas discharge in parallel with the outlet pipe 14.

Thus, the exhaust gas 10 is introduced into the inlet portion 2 through the small hole 6 a of the inlet pipe 6, and subsequently passes (purifies) the particulate filter 1 before entering the outlet pipe 14, from the outlet pipe 14. Discharged.
In this embodiment, only the particulate filter 1 is arranged inside the black smoke purification device 20. However, the combination of the oxidation catalyst and the particulate filter or only the oxidation catalyst is used as in the second embodiment described later. It does not matter as a configuration arranged in the black smoke purification device.

  Next, the particulate filter 1 disposed in the black smoke purification device 20 will be described with reference to FIGS. 1 and 2.

The particulate filter 1 is a substantially cylindrical honeycomb filter having a polygonal section partitioned by porous partition walls made of ceramics such as cordierite (see FIG. 2). Although not shown, the particulate filter 1 is configured by substantially sealing the adjacent inlet portions and outlet portions of a large number of through holes formed in parallel with each other by these partition walls. The partition walls are coated with a catalytic metal such as Pt to carry the catalytic function. In the particulate filter 1, when the exhaust gas 10 of the engine introduced from the inlet side of the filter 1 passes through the porous partition wall, PM composed of fine particles contained in the exhaust gas 10 is filtered, and PM The exhaust gas 10 is removed from the outlet pipe 14.
In this embodiment, Pt or the like is used as the catalyst metal, but it is not particularly limited, and Pd, Rh, Ir, or the like may be used.

Further, as shown in FIG. 2, the particulate filter 1 in the present embodiment increases the catalyst density on the center side rather than the outer peripheral side without making the catalyst distribution density uniform. That is, when the catalyst metal is coated, the filter carrier is treated so that the density of the catalyst metal at the center is increased. Specifically, as shown in FIG. 2, as the catalyst distribution in the filter 1, the amount of catalyst supported is increased inside the boundary L1 in the sectional view of the particulate filter 1, and the amount of catalyst supported is decreased outside the boundary L1. Yes. Further, the particulate filter 1 as a whole is configured such that a large amount of catalyst is concentrated in the central portion and a small amount of catalyst is formed on the outside.
In the present embodiment, the total amount of the catalyst coated on the particulate filter 1 is configured so that a large amount of catalyst is distributed in the center without changing from the conventional one, but the present invention is particularly limited to this. The total amount of catalyst to be used can be set as appropriate in consideration of the self-regeneration capability of the filter.

  In such a configuration, the exhaust gas 10 is introduced into the inlet portion 2 through the small hole 6 a of the inlet pipe 6, subsequently passes through the particulate filter 1, enters the outlet pipe 14, and is discharged from the outlet pipe 14. Is done. As shown in FIG. 2, in the configuration of the particulate filter 1 in cross-sectional view, the amount of catalyst when the operating state approaches the non-regeneration region of the particulate filter 1 by making the catalyst density higher on the center side than on the outer peripheral side. When there is little (outer peripheral side), soot accumulation exceeds oxidation and soot accumulates. When this happens, the ventilation resistance of the portion where the soot accumulates (outer peripheral side) increases, and the amount of exhaust gas flowing in the outer peripheral portion decreases, and concentrates on the center side of the filter 1 where the amount of catalyst is large. Since the central portion of the filter 1 has a large amount of catalyst, the soot oxidation speed is fast and the amount of heat of the exhaust gas 10 is concentrated, so that the temperature also rises, and self-regeneration is continued considering only the balance of this portion. That is, by continuing this self-regeneration, the self-regeneration area is expanded as shown in FIG. 6 as compared with the conventional self-regeneration area shown in FIG. Further, since the gas flow rate at this time is small, the total exhaust resistance can be reduced below the standard.

  Thus, in the black smoke purification apparatus 20 for diesel engines that has either or both of the oxidation catalyst and the particulate filter 1 inside, the catalyst density of the particulate filter 1 is not uniform and is more central than the outer peripheral side. By increasing the catalyst density, the total catalyst amount is the same and the regeneration range can be expanded.

Next, another embodiment of the black smoke purification apparatus provided with an oxidation catalyst and a particulate filter will be described with reference to FIG.
As shown in FIG. 3, the black smoke purification apparatus 40 of the present embodiment is the same as that of the first embodiment except that the oxidation catalyst 4 is arranged at the rear stage of the inlet portion 2 in the black smoke purification apparatus 20 shown in the first embodiment. It is comprised similarly to.

The oxidation catalyst 4 has a substantially cylindrical shape, and has a monolith support (material: cordierite) (not shown) in which grid-like (honeycomb-shaped) passages are formed in the direction in which the exhaust gas 10 flows. It is formed by supporting a catalytic metal such as platinum, rhodium or palladium. By supporting such a catalyst metal, the oxidizing power of CO or hydrocarbon (HC or the like) is imparted to the oxidation catalyst 4.
The material of the monolith carrier is not limited to cordierite, and silicon carbide, stainless steel or the like may be used.

Further, as shown in FIG. 4, the oxidation catalyst 4 in this example has a high catalyst distribution density on the center side shown in Example 1 without making the catalyst distribution density (oxidation catalyst density) uniform in a cross-sectional view. Opposite to the curate filter 1 (FIG. 2), the catalyst distribution density is increased in a portion that is substantially the same region. That is, the catalyst distribution density on the center side is higher than that on the outer periphery side, as is the case with the particulate filter 1. Such an oxidation catalyst 4 is formed by applying a treatment to the filter carrier so that the density of the catalyst metal at the center is increased during the coating of the catalyst metal. Specifically, as shown in FIG. 4, as the catalyst distribution in the oxidation catalyst 4, the amount of catalyst supported is increased inside the boundary L2 in the cross section of the oxidation catalyst 4, and the amount of catalyst supported is decreased outside the boundary L2. Yes. Thus, the oxidation catalyst 4 as a whole is configured such that a large amount of catalyst is concentrated in the central portion and the amount of catalyst is reduced on the outside.
In the present embodiment, the total amount of the catalyst coated on the oxidation catalyst 4 is not changed, and more catalyst is distributed to the center side than the outer peripheral side. However, the present invention is particularly limited to this. The total amount of the catalyst to be supported can be appropriately set in consideration of the oxidation ability of the catalyst metal to be used.

In such a configuration, the exhaust gas 10 is introduced from the inlet pipe 6 to the inlet portion 2 through the small hole 6 a, passes through the oxidation catalyst 4 from the inlet portion 2, and then continues to the subsequent stage of the oxidation catalyst 4. It passes through the particulate filter 1, enters the outlet pipe 14, and is discharged from the outlet pipe 14.
As shown in FIG. 4, in the cross-sectional view of the oxidation catalyst 4, the catalyst distribution density is made higher in the center side than in the outer peripheral side, and the particulate filter 1 in the subsequent stage of the oxidation catalyst 4 is made the same as in the first embodiment. That is, the particulate filter 1 is the same as in the first embodiment in which the oxidation catalyst 4 and the particulate filter 1 in which the catalyst metal is made dense in the central portion are arranged to face each other. When the operating state approaches the non-regeneration region, the soot accumulation exceeds the oxidation and the soot accumulates when the amount of the catalyst is small (outside). As a result, the ventilation resistance of the portion where the soot has accumulated (outer peripheral side) is increased, and the amount of exhaust gas flowing in the outer peripheral portion is reduced and concentrated on the central side of the oxidation catalyst 4 and the particulate filter 1 which are the portions with a large amount of catalyst. The central part of the oxidation catalyst 4 and the particulate filter 1 has a large amount of catalyst, so that the oxidation speed of the soot is fast and the amount of heat of the exhaust gas 10 is concentrated, so the temperature also rises. Playback continues. That is, by continuing this self-regeneration, the self-regeneration area is expanded as shown in FIG. 6 as compared with the conventional self-regeneration area shown in FIG. Further, since the gas flow rate at this time is small, the total exhaust resistance can be reduced below the standard.

  In this way, by increasing the oxidation catalyst density of the oxidation catalyst 4 arranged opposite to the part where the catalyst density is increased on the center side rather than the outer peripheral side of the particulate filter 1, the total catalyst amount is the same and self The playback area can be expanded. In addition, the density of the catalyst supported on the particulate filter carrier and the oxidation catalyst carrier can be set as appropriate, and the self-regeneration region can be further easily expanded.

Next, the range setting of the high-density region of the catalyst will be described in detail with reference to FIG.
In general, the temperature of the particulate filter and the oxidation catalyst is highest near the center and decreases as it goes to the outer periphery in a donut shape. In the case of self-regenerative margin, the balance is achieved in a state where it is regenerated in the vicinity of the center where the temperature is highest and is not sufficiently regenerated on the outer periphery. Therefore, by carrying the catalyst metal intensively in the vicinity of the central portion as in the present invention, the self-regeneration region can be expanded in the direction of the arrow shown in FIG.
Further, the maximum gas flow rate outside the self-regeneration range set by the area ratio (dhc ² / dtc ² ; FIG. 4) from the center of the oxidation catalyst 4 and the particulate filter 1 (Gvo; FIG. 6) gas flow rate at the maximum output (Gvmax Expanding the self-regeneration area without increasing the exhaust resistance at the balance point by widening the high catalyst density area (the high density area on the center side shown in FIG. 4) in a range larger than the value divided by FIG. Can do. The gas flow rate at each rotational load can be accurately calculated from fuel consumption, intake air amount, and exhaust gas temperature. The calculation formula of the gas flow rate is shown below.
<Calculation formula of gas flow rate>
Gv = (f · Pe · Vo + Va) · Tg / 300
Gv (m ^ 3 / h): Gas volume flow rate at that point f (kg / (kw · h)): Fuel consumption at that point Pe (kw): Output Vo at that point Vo (m ^ 3 / kg): combustion gas amount of 1 kg of fuel at 300 ° K, 100 kPa,
Va (m ^ 3 / kg): Value of intake air at that point converted to 300 ° K and 100 kPa Tg (K): Exhaust gas temperature at that point Based on the gas flow rate thus calculated or measured (Dhc ² / dtc ² ) ≧ Gvo / Gvmax
Since the gas flow resistance depends on the gas flow velocity, the gas flow velocity can be made lower than a certain value, so that the back pressure can also be made lower than a certain value. The gas flow rate is obtained by subtracting the consumed oxygen amount from the intake air amount and the combustion gas amount per unit time at the exhaust gas temperature. As shown in FIG. 6, the maximum gas flow rate (Gvmax) is generally maximum at the maximum rotational load. The maximum gas flow rate (Gvo) at the time of self-regeneration is almost equal to the maximum gas flow rate outside the self-regeneration region, and is generally the gas flow rate at the lower right corner in the self-regeneration region.

  As described above, the carrier shape of the oxidation catalyst 4 or the particulate filter 1 is substantially cylindrical, and the maximum exhaust gas flow rate outside the self-regeneration area set by the area ratio is divided by the gas flow rate at the maximum output. By increasing the catalyst density on the central side of the oxidation catalyst 4 or the particulate filter 1 within a large range, the exhaust gas temperature that maintains the balance state that is self-regenerative can be shifted to the low temperature side, so that self-regeneration is possible. The area can be expanded. In addition, the self-regeneration area can be expanded without increasing the overall exhaust resistance in the balanced state.

Next, another embodiment of the black smoke purification apparatus provided with a flow dividing valve will be described with reference to FIG.
5A is a front view showing the inlet pipe 26, and FIG. 5B is a schematic view showing the black smoke purification device for a diesel engine in the third embodiment.
The black smoke purification apparatus 60 shown in the present embodiment includes an inlet portion 22, a particulate filter 1, and an outlet portion 3 as shown in FIG. The inlet portion 2 and the outlet portion 3 are formed in the housings 27a and 27b, respectively. A particulate filter 1 is disposed in an installation portion 1a between the housings 27a and 27b. The particulate filter 1 is kept airtight with both the housings 27a and 27b and the gasket 15, and is integrated with the V-shaped band 12. It is fixed to. The heat insulating sound absorbing material 8 is disposed in the inlet portion 22, and the heat insulating sound absorbing material 8 is pressed against the inner wall of the inlet portion 22 by the heat insulating sound absorbing material pressing plates 13 and 16.
The particulate filter 1 can be attached to and detached from the installation portion 1a.
In addition, the catalyst distribution density in the particulate filter 1, the outlet portion 3, and the particulate filter 1 is configured in the same manner as in Example 1, and detailed description thereof is omitted.

An inlet pipe 26 that guides the exhaust gas 10 from an engine (not shown) is disposed at the inlet portion 22. The inlet pipe 26 communicates with the inlet portion 22 in the housing 27a. A front end portion of a cylindrical guide tube 30 is disposed at the front end of the inlet tube 26, and the guide tube 30 extends rearward and passes through the inlet portion 22. The middle part of the guide tube 30 is bent so that the rear end of the guide tube 30 is guided near the center of the particulate filter 1. A diversion valve 32 is provided in the inlet pipe 26. The shunt valve 32 includes a butterfly valve 32a. One end of the butterfly valve 32a has a substantially U-shaped notch as shown in FIG. The inlet pipe 26 reaching the inlet portion 22 is configured to be openable and closable so as to abut the portion.
The diversion valve 32 is connected to a control means via an actuator (not shown) so as to perform opening / closing control. The rotation speed detecting means or the exhaust gas flow rate detecting means is connected to the control means.

  When the diversion valve 32 is open, the exhaust gas 10 is introduced into the particulate filter 1 from the inlet pipe 26 through the inlet portion 22, and the exhaust gas 10 is also introduced from the induction pipe 30 into the particulate filter. 1 Enters the vicinity of the center. On the other hand, when the flow dividing valve 32 is closed, the exhaust gas 10 is introduced from only the induction pipe 30 to the vicinity of the center of the particulate filter 1.

  In such a configuration, when the operating state of the engine is in the low speed range, that is, when the flow rate of the exhaust gas 10 is small, the control means controls the diverter valve 32 to close and serves as the inlet of the exhaust gas 10. By narrowing the inlet pipe 26 and guiding the exhaust gas 10 to the center of the particulate filter 1 only through the induction pipe 30, the exhaust gas flow is further concentrated near the center of the filter 1, and the temperature at the center is compared. The self-regeneration area is expanded by maintaining a high temperature. In the present embodiment, as described above, in the particulate filter 1, the catalyst density is higher in the center side than in the outer peripheral side in the sectional view of the particulate filter 1 as in the first embodiment, and the effect obtained by using such a filter. With this, the effect of further expanding the self-reproducing area can be obtained.

  As described above, when the flow rate of the exhaust gas 10 is small, the exhaust gas flow path is throttled so that the exhaust gas 10 flows intensively in the vicinity of the center of the filter 1. The gas flow in the low speed region is further concentrated near the center by guiding the filter to the vicinity of the center of the filter, and the self-regeneration region can be expanded by keeping the temperature of the center portion at a relatively high temperature.

Schematic which shows the black smoke purification apparatus for diesel engines which concerns on this invention. FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. Schematic which shows the black smoke purification apparatus for diesel engines in Example 2. FIG. The BB cross-section arrow figure of FIG. Schematic which shows the black smoke purification apparatus for diesel engines in Example 3. FIG. The figure which shows the self reproduction | regeneration area | region which concerns on this invention. The figure which shows the conventional self reproduction | regeneration area | region.

Explanation of symbols

1 Particulate Filter 4 Oxidation Catalyst 10 Exhaust Gas 20 Black Smoke Purifier

Claims (4)

  In the black smoke purification device for diesel engines having either or both of an oxidation catalyst and a particulate filter inside, the catalyst density on the center side is increased from the outer peripheral side without making the catalyst density of the particulate filter uniform. A black smoke purification device for diesel engines.   2. The black smoke purification for a diesel engine according to claim 1, wherein the oxidation catalyst density of the oxidation catalyst disposed opposite to the portion where the catalyst density on the center side is increased from the outer peripheral side of the particulate filter is increased. apparatus.   The oxidation catalyst or particulate filter has a substantially cylindrical carrier shape, and the oxidation catalyst is in a range larger than the value obtained by dividing the maximum gas flow rate outside the self-regeneration area set by the area ratio by the gas flow rate at the maximum output. 3. The black smoke purification device for a diesel engine according to claim 1, wherein the catalyst density on the center side of the particulate filter is increased.   The exhaust gas passage is throttled when the flow rate of the exhaust gas is small, and the exhaust gas is configured to flow intensively in the vicinity of the center of the oxidation catalyst or the particulate filter. Black smoke purification device for diesel engines.

Images