JP2002276341A - Diesel exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diesel exhaust emission control device to purify particulate matter of both exhaust gas (composed mainly of burnable organic matter) at idling and a low load and exhaust gas (composed mainly of particulate matter) at a heavy load. SOLUTION: A first purifier 16 to capture particulate matter in the exhaust gas of diesel engine 3 at a PM filter 2 for oxidizing and removing and a second purifier 17 to remove soluble organic matter in the exhaust gas are connected with an exhaust gas passage 4 of the engine in parallel. The purifier 17 comprises a heater 19 for heating the exhaust gas and a catalyst. Exhaust gas flow resistance of the purifier 17 side is set larger than that of the purifier 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel exhaust gas purification device, and more particularly, to a method for efficiently removing particulate matter suspended in exhaust gas of a diesel engine in a wide range from idle to high load. The present invention relates to a purifying device described in US Pat.

[0002]

2. Description of the Related Art The regulation of particulate matter (PM) discharged from a diesel engine has been strengthened year by year along with nitrogen oxide (NOx), carbon monoxide (CO), unburned hydrocarbon (HC), and the like. At the same time, it is no longer possible to meet the regulation values only by improving the engine. Therefore, a technique of reducing the amount of particulate matter discharged into the atmosphere by collecting the particulate matter with a particulate matter filter (DPF) discharged from the engine is about to be adopted.

A conventional filter for trapping particulate matter requires heat resistance due to the high temperature of the exhaust gas.
There are a ceramic monolithic honeycomb type wall flow type and a fiber type filter type in which ceramic or metal is made into a fibrous form to make a filter.

[0004] The main component of the particulate matter is that the soot component generally increases as the load on the diesel engine increases, and the soluble organic matter (SO
F) accounts for most.

[0005]

By the way, when the particulate matter filter collects the particulate matter, the pressure loss increases in proportion to the amount of the collected particulate matter. Therefore, it is necessary to regenerate the filter by removing the particulate matter captured by the filter by burning or the like.

[0006] As a method for regenerating a filter by burning the above-mentioned particulate matter, various proposals have been made, such as an electric heater heating type, a burner heating type and a back washing type. However, these methods have a drawback in that energy must be externally applied in order to burn the particulate matter, so that fuel consumption is deteriorated and the size of the apparatus is increased. On the other hand, there is a device called a continuous regeneration type DPF, which basically can continuously collect particulate matter and regenerate a filter by the heat energy of exhaust gas. Can be simplified as a filter system,
There is an advantage that control of fuel consumption can be reduced and control can be simplified. Specifically, the following has been proposed.

In the NO ₂ regeneration type DPF device shown in FIG. 1, a NO oxidation reactor 1 for oxidizing nitrogen monoxide NO to nitrogen dioxide NO ₂ is arranged on the upstream side of the exhaust gas flow, and P NO
The one with the M filter 2 is the diesel engine 3
In the exhaust gas passage 4 of FIG. In addition,
Reference numeral 5 shown in FIG. 1 is a muffler, 6 is a battery, 7 is a fuel injection system, and 8 is a fuel tank.

[0008] The NO oxidation reactor 1 has a honeycomb structure made of porous ceramic and carries an oxidation catalyst, and the PM filter 2 is a normal wall flow filter made of ceramic. When the high-temperature exhaust gas passes through the NO oxidation reactor 1, NO in the exhaust gas is oxidized to NO ₂ , so most of the NOx in the exhaust gas downstream of the NO oxidation reactor 1 becomes NO ₂ . Become. Since NO ₂ has a smaller energy barrier than oxygen (O ₂ ), it lowers the temperature at which the particulate matter trapped by the PM filter 2 is burned and removed,
The PM filter 2 can be regenerated without supplying external energy.

The NO shown in FIG._TwoFigure of regeneration type DPF device
NO shown in 1_TwoIt is an improved regenerative DPF device.
As shown in FIG. 2A, the oxidation catalyst 9 is
Wall surface of PM filter 2 consisting of flow type filter
To NO oxidation and NO _TwoOf particulate matter by
Oxidation and removal at once in PM filter 2
Is simplified. In this method, the catalyst is
To apply to the surface of the filter 2, put the catalyst on the filter
Initial filter pressure due to the residue of the components
Loss tends to increase.

The wall flow filter is, as shown in FIG. 2A, a honeycomb structure made of porous ceramic similarly to the oxidation reactor, and has a cell on both sides of a wall 10 constituting the honeycomb. 11-1 and 11-2 have a structure in which one opening is alternately closed with a ceramic material 11.

The regenerative DPF device shown in FIG.
The filter 12 is coated with a catalyst 12 for directly oxidizing the particulate matter captured by the filter 2 with O ₂ . Here, the structure of the wall flow type filter will be described with reference to a partially enlarged sectional view A of FIG.

That is, the exhaust gas G flowing into the cell 11-1 is:
When passing through the inside of the wall 10 and flowing out of the cell 11-2 to the downstream side, the wall 10 has a structure in which particulate matter is captured by the PM filter 2. Method for oxidizing particulate matter directly O ₂ Thus, by applying the catalyst 12 on the exhaust gas inlet side surface of the wall portion 10, removing the particulate matter trapped on the portion directly oxidized by O ₂ can do.

Each of the above-mentioned catalysts has a function of lowering the oxidation start temperature of the particulate matter. However, in the case of a catalyst which can be supplied industrially at present, the exhaust gas temperature is 35%.
A temperature of about 0 ° C. is required. Therefore, when the engine is idling or operating at a low load, the exhaust gas temperature is 350
If the temperature does not reach ℃, the collected particulate matter cannot be removed from the PM filter 2 and regenerated.

As a result, if idling or low-load operation is continued, particulate matter accumulates on the filter surface, increasing the back pressure, deteriorating fuel economy, and eventually stopping the engine.

As a proposal for solving this problem, for example, a method disclosed in Japanese Patent Application Laid-Open No. 7-109917 is disclosed.
An oxidation catalyst provided with a wall flow type filter provided with an electric heater on the inlet side of the exhaust gas to burn the collected particulate matter without propagating and to burn soluble organic components (SOF) downstream thereof And supported SO
An F filter is provided, and a bypass with a switching valve is attached in parallel with the wall flow type filter, so that exhaust gas is directly passed to the catalytic reactor through the bypass at a low load. This method has a disadvantage in that a large amount of exhaust gas discharged during a high-load operation flows into the SOF filter, and thus becomes large.

The present invention has been made in view of the above problems, and purifies exhaust gas during idling and low load conditions where the discharge of flammable organic substances increases, and at high load conditions where the discharge of particulate matter increases. It is an object of the present invention to provide a diesel exhaust gas purifying apparatus capable of achieving both of the above purifying.

[0017]

According to the present invention, there is provided a diesel exhaust gas purifying apparatus for achieving the above object, in which a particulate matter in exhaust gas of a diesel engine is captured by a filter and oxidized to remove the particulate matter. A filter and a second purifier for capturing and oxidizing and removing particulate matter in the exhaust gas of the engine mainly composed of soluble organic matter, in parallel with the exhaust gas passage of the engine, The purifier includes a heater for heating the exhaust gas and the catalyst, and the second purifier-side exhaust gas flow resistance is formed to be larger than the first purifier-side exhaust gas flow resistance.

The second purifier is required to maintain the exhaust gas temperature at the catalyst activation temperature in order to exert the purifying function mainly at the time of low load operation with a small amount of exhaust gas. Therefore, the temperature of the heater is preferably controlled by a controller. The heating method is not particularly limited, but usually an electric heater is used.

According to the above configuration, the exhaust gas flows more in the direction in which the first purifier and the second purifier easily flow. Therefore, during a high-load operation, a large amount flows into the first purifier having a small flow resistance, but a small amount also flows into the second purifier. In this case, since the second purifier is provided with the heater, the trapped particulate matter can be oxidized and removed, and there is no risk of clogging the filter.

On the other hand, during idling and low load operation, the amount of exhaust gas changes, so that the exhaust gas naturally flows into the first purifier having a small flow resistance. However, since the first purifier does not have a heater, soluble organic matter cannot be oxidized and removed, and the flow resistance gradually increases. On the other hand, the second purifier has a heater so that purification is performed.

By the way, when the operation is switched from the low load operation to the high load operation, the flow resistance of the first purifier is increased for the above-mentioned reason, so that the first purifier cannot sufficiently exhibit the purifying function. Purification is performed by a vessel. However,
The purification function is restored by the inflow of the high-temperature exhaust gas, and the exhaust gas is eventually purified mainly by the first purifier.

The operation of the present invention described above can be efficiently generated by designing the flow resistance between the first purifier and the second purifier in a well-balanced manner for each target engine, and the load resistance against load fluctuation can be improved. It is possible to prevent the occurrence of engine trouble due to the reduction of the purification function and the generation of back pressure.

In the present invention, "low load" refers to a load state in which most of the particulate matter in the exhaust gas becomes soluble organic matter (SOF), and "high load" refers to a load state in which the soot component is increased.

According to the present invention, a switching valve may be provided at a branching portion that connects exhaust gas to the first purifier and the second purifier, and exhaust gas may be selectively supplied to one of the purifiers. it can. In this case, the switching valve can be controlled by detecting the load of the engine and the like.

[0025] The purifying means of the first purifier used in the present invention is characterized in that the particulate matter in the exhaust gas is trapped on the downstream side of the exhaust gas of a reactor carrying an oxidation catalyst for nitric oxide in the exhaust gas. One or more means selected from a means for disposing a filter, a means for supporting an oxidation catalyst for nitric oxide on the surface of the filter, and a means for supporting an oxidation catalyst for the particulate matter on the surface of the filter are employed. can do.

The oxidation catalyst used in the present invention may be any commonly used oxidation catalyst. However, since the oxidation catalyst for soluble organic substances is used at a low exhaust gas temperature, it is preferable to use a platinum (Pt) -based strong oxidation catalyst. In this case, the oxidation can be removed at a relatively low exhaust gas temperature of about 150 ° C., and the consumption of exhaust gas heating energy can be reduced.

[0027]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a diesel exhaust gas purifying apparatus according to an embodiment of the present invention.

The diesel exhaust gas purifying apparatus 15 of this embodiment shown in FIG. 4 branches the exhaust gas passage 4 of the diesel engine 3, one of which is connected to the first purifier 16 and the other is connected to the second purifier 17. It is intended to be connected. Reference numeral 18 in FIG. 4 is a controller by electronic control.

The first purifier 16 converts NO in exhaust gas to NO.
_In order to oxidize to ₂ , the honeycomb-structured NO oxidation reactor 1 supporting an oxidation catalyst (not shown) is arranged on the upstream side, and on the downstream side, the particulate matter is captured on the filter surface of the wall flow type filter. A collecting PM filter 2 is arranged to provide a sufficient cross-sectional area and a filtration area for each part to allow a large amount of exhaust gas discharged when the engine 3 is under a high load.

In order to oxidize soluble organic substances in the exhaust gas of the engine 3, the second purifier 17 is provided with a filter 18 of a wall flow type filter having a soluble organic substance oxidation catalyst (not shown) supported on the filter surface. And a heater 19 composed of an electric heater for heating the catalyst and the exhaust gas was arranged around and upstream of the heater. The cross-sectional area and the filtration area of each part adapted to the amount of exhaust gas discharged when the engine 3 is idle and at low load are set to have a flow resistance higher than the exhaust gas flow resistance of the first purifier 16.

The controller 20 energizes the heater 19 based on input data such as the exhaust gas temperature detected by the engine rotation sensor, the load state sensor (not shown), and the temperature sensor 21 to the second purifier. The temperature of the incoming exhaust gas is maintained at the activation temperature of the oxidation catalyst.

Therefore, the exhaust gas is distributed and flows based on the respective flow resistances of the first purifier 16 and the second purifier 17. In this case, the exhaust gas temperature decreases during idling or low load operation, so that the oxidizing function of the first purifier 16 decreases and the PM filter 2 becomes clogged, but the second purifier 17 maintains a sufficient regeneration function. Since it is made, it does not affect the purification function.

When the operation is switched from the low-load operation to the high-load operation, the flow resistance of the first purifier 16 is increased due to clogging, but since the second purifier 17 has a purifying ability, the purification is performed. Function can be maintained. During that time, the high-temperature exhaust gas also flows into the first purifier 16, so that the filter regeneration function is quickly restored. Therefore, there is no possibility that the back pressure increases due to a large amount of exhaust gas flowing in and the engine 3 is not hindered.

As another embodiment of the present invention, a switching valve is provided at a portion where the exhaust gas passage 4 is branched into the first purifier 16 and the second purifier 17, and the exhaust gas is adjusted according to the load condition of the engine 3. The flow can also be controlled.

The first purifier 16 can be implemented not only by the means shown in FIG. 4 but also by another method, for example, the method of capturing and regenerating particulate matter having the structure described with reference to FIGS.

[0036]

As described above, the diesel exhaust gas purifying apparatus of the present invention is suitable for high-load operation and continuously purifies particulate matter (PM) in exhaust gas. Purification is performed by arranging in parallel a second purifier that continuously purifies particulate matter (PM) in exhaust gas, which is suitable for idling or low-load operation. It is possible to stably perform particulate matter in exhaust gas over a wide range from idling to high-load operation without causing problems and without performing complicated control for filter function regeneration. Since the vessel can be realized with a small size, a highly reliable purification device can be supplied at low cost.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a conventional method for capturing and regenerating particulate matter in diesel exhaust gas.

FIG. 2 is a schematic explanatory view of a conventional method of capturing and regenerating particulate matter in diesel exhaust gas by a method different from that of FIG.

FIG. 3 is a schematic explanatory view of a conventional method of capturing and regenerating particulate matter in diesel exhaust gas, which is different from FIGS. 1 and 2.

FIG. 4 is a schematic explanatory view of a diesel exhaust gas purifying apparatus according to an embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 NO oxidation reactor 2 PM filter 3 Diesel engine 4 Exhaust gas passage 15 Diesel exhaust gas purifier 16 First purifier 17 Second purifier 18 Filter 19 Heater (heater)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/24 F01N 3/24 EF Term (Reference) 3G090 AA04 BA04 CB11 DA04 DA12 DA18 DA20 DB06 DB07 EA02 3G091 AA18 AB02 AB13 BA01 CA03 EA32 FA13 FA14 FB02 FB03 GA06 HA15

Claims (2)

[Claims] A first purifier for trapping and oxidizing and removing particulate matter in exhaust gas of a diesel engine; and a filter for filtering particulate matter in exhaust gas of the engine mainly composed of soluble organic matter. A second purifier for capturing, oxidizing and removing the exhaust gas and a catalyst connected in parallel to the exhaust gas passage of the engine, the second purifier including a heater for heating exhaust gas and a catalyst; A diesel exhaust gas purifying device in which the side exhaust gas flow resistance is made larger than the first purifier side exhaust gas flow resistance. 2. The purifying means of the first purifier is provided with a filter that captures particulate matter in exhaust gas on a downstream side of an exhaust gas of a reactor supporting an oxidation catalyst for nitric oxide in the exhaust gas. At least one member selected from a disposing means, a means for supporting an oxidation catalyst for nitric oxide on the surface of the filter, and a means for supporting an oxidation catalyst for the particulate matter on the surface of the filter. 2. The diesel exhaust gas purifying apparatus according to 1.