JPH06317143A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PURPOSE:To regenerate an NOx absorber by switching the flow of exhaust into the plural NOx absorbers without using a device that has a movable member such as a shutoff valve and a switching valve. CONSTITUTION:The exhaust passage 2 of a diesel engine 1 branches into a plurality of passages, and the branch passages 2a, 2b are provided with respective particulate filters 3a, 3b, respective reducing agent supply nozzles 11a, 11b, and an NOx absorber 5a, 5b. The particulate filters are provided with heaters 4a, 4b which alternately burn collected particulates. After particulates on one of the filters have been burnt, the pressure loss of the filters is reduced and most of the exhaust is allowed to flow toward the filter where the particulates have been burnt, while little exhaust flows into the NOx absorber located downstream of the other filter. Therefore, the flow of exhaust into the NOx absorber can be switched without using any switching valve, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to an exhaust purifying apparatus for an internal combustion engine, in particular, to effectively removable exhaust purification apparatus NO _X in the exhaust gas of an internal combustion engine.

[0002]

2. Description of the Related Art An example of this type of exhaust emission control device is disclosed in Japanese Patent Application Laid-Open No. 62-106826. The apparatus of this publication is to connect a vessel containing an absorbent (catalyst) for absorbing NO _X in the presence of oxygen in an exhaust passage of a diesel engine, NO _X in the exhaust gas to the _the NO _X absorbent
Is absorbed, and when the NO _x absorption efficiency of the absorbent is reduced, the inflow of exhaust gas into the container is blocked, and a reducing agent is introduced into the container to generate a reducing atmosphere to release NO _x from the absorbent. , Which reduces and purifies the released NO _x .

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
6826 JP devices, NO _X released from _the NO _X absorbent by the inside of the container by introducing a reducing agent into the container housing the _the NO _X absorbent to a reducing atmosphere, reduction purification (hereinafter,
"Playback"). Further, since the exhaust gas of a diesel engine contains a large amount of oxygen, in order to reduce the amount of reducing agent required to create a reducing atmosphere in the container, the exhaust gas flowing into the container at the time of introducing the reducing agent should be blocked or It is necessary to reduce and prevent oxygen contained in the exhaust from flowing into the container. In the device of the above publication, when the reducing agent is introduced, the shut-off valve provided on the upstream side of the container is used to block the inflow of exhaust gas into the container to introduce the reducing agent, thereby reducing the consumption amount of the reducing agent.

[0004] Therefore, in order to perform exhaust purification during engine operation using the apparatus of JP-A Sho 62─106826 is a plurality of containers accommodating the _the NO _X absorbent is connected in parallel to the engine exhaust passage sequentially and then play back the blocking the flow of exhaust gas into _the NO _X absorbent by one, it is necessary to allow exhaust to flow through one of the NO _X absorbent regenerating operation in any other of the NO _X absorbent, providing a shut-off valve and switching valve for interrupting or reducing the flow of exhaust gas to each of the NO _X absorbent in the exhaust passage need arises.

However, since these shut-off valves and change-over valves operate intermittently with a relatively long operation interval in the exhaust gas, there is a tendency that the movable parts tend to stick due to fine particles or oil in the exhaust gas. There is. In particular, since the exhaust gas of a diesel engine contains a large amount of exhaust particulates (diesel particulates), when the above-mentioned exhaust gas purification device is applied to a diesel engine, malfunctions such as a shutoff valve are likely to occur and the reliability of the device is reduced. There is a problem that

[0006] The present invention has been made in view of the above problems, it blocked the flow of sequential exhaust by connecting a plurality of _the NO _X absorbent in the exhaust passage N
An object of the present invention is to provide an exhaust emission control device for an internal combustion engine having a simple structure in which malfunction of the movable member due to a stick does not occur when the O _X absorbent is regenerated.

[0007]

According to the present invention, in order to solve the problems] In the exhaust gas purifying apparatus for purifying NO _X components in the exhaust of a diesel engine, an exhaust passage which is branched into a plurality of passages, the arranged respective branch passages supply and _the NO _X absorbent the air-fuel ratio of exhaust gas oxygen concentration of the inflowing exhaust absorbs NO _X when the lean releases the absorbed NO _X when reduced, the reducing agent individually the each of the NO _X absorbent a reducing agent supply means for reducing and purifying the released NO _X with the release of absorbed NO _X from _the NO _X absorbent and, particulates in exhaust is disposed upstream of the reducing agent introduction means of each of said branch passages And a means for individually burning the particulates collected by the respective particulate filters, and the particulate filter The amount of particulates captured bets filter of the NO _X from the reducing agent supplying reducing agent from the supply means to the NO _X absorbent _the NO _X absorbent when the predetermined value or more release, reduction was carried out, the NO _X emissions, performs combustion of particulates captured in the particulate filter after completion of the reduction, a reducing agent at least another one of the feed to the one downstream side of the NO _X absorbent particulate filter There is provided an exhaust gas purification device for an internal combustion engine, characterized in that the combustion means of the particulates is controlled so that the particulate collection amount of the particulate filter is equal to or less than the predetermined amount.

[0008]

When the particulate collection amount of the particulate filter increases, the flow path resistance (pressure loss) of the particulate filter increases, and the exhaust gas passes through the particulate filter and becomes difficult to flow. Therefore, if the particulate collection amount of some of the particulate filters connected in parallel to the exhaust passage is large and the collection amount of other particulate filters is small, the amount of exhaust gas collected is small. less focused on (low resistance) particulate filter of flow, collecting a large amount of not almost the (resistance greater) particulate filter exhaust stream, most inflow exhaust on the downstream side of the NO _X absorbent Will not do.

[0009] In the present invention, by supplying the reducing agent to the NO _X absorbent in the state where the amount of exhaust gas flowing into the downstream side of the NO _X absorbent particulate collection amount of the particulate filter is increased is reduced NO _X Regenerate the absorbent. This reduces the amount of reducing agent consumed for regeneration of the NO _x absorbent. Further, after the regeneration of the NO _x absorbent is completed, the particulate matter trapped in the particulate filter is burned to reduce the flow path resistance of the particulate filter. Accordingly, _the NO _X absorbent to the flow rate of the exhaust gas flowing is completed regeneration increased in the NO _X absorbent absorbs NO _X in the exhaust gas.

The particulate filter sequentially burns particulates, and the timing of particulate burning is set so that a part of the particulate filters is in a state where the amount of trapped particulates is low (resistance is small). To be done. As a result, each NO _x
The flow rate of the exhaust gas flowing into the absorbent is repeatedly increased and decreased in accordance with the collected particulates and the combustion of upstream particulate filter, as in the case of using a shut-off valve and switching valve to the _the NO _X absorbent The exhaust gas is switched.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, 1 is a diesel engine and 2 is an exhaust passage of the engine 1. In this embodiment,
The exhaust passage 2 has two branch passages 2 on the downstream side of the exhaust manifold.
a, 2b, and the branch passages 2a, 2b from the upstream side to the particulate filters 3a, 3b, the reducing agent supply nozzles 11a, 11b of the reducing agent supply device 11, and NO.
_X absorbents 5a and 5b are arranged respectively.

NO_XThe absorbents 5a and 5b are, for example, alumina
As a carrier, and potassium K, sodium
Alkali such as Na, lithium Li, and cesium Cs
Metals, alkalis such as barium Ba, calcium Ca
Earth, lantern La, rare earth such as yttrium Y
At least one selected from the group and precious metals such as platinum Pt
And are carried. This NO_XAbsorbent 5a, 5b flow
NO if the air-fuel ratio of the incoming exhaust is lean_XAbsorb
However, if the oxygen concentration decreases, NO_XReleases NO _XSucking
Performs release action.

The above exhaust air-fuel ratio is N in this case.
It means the ratio of the total amount of air and the total amount of fuel supplied to the exhaust passage, engine combustion chamber, intake passage, etc. on the upstream side of the O _x absorbents 5a, 5b. Therefore, NO _X
When fuel, reducing agent, or air is not supplied to the exhaust passages or intake passages on the upstream side of the absorbents 5a and 5b, the exhaust air-fuel ratio becomes equal to the operating air-fuel ratio of the engine (air-fuel ratio in combustion in the engine combustion chamber).

In this embodiment, since the diesel engine is used, the exhaust air-fuel ratio during normal operation is lean, and the NO _X absorbents 5a and 5b absorb NO _{X in} the exhaust. In addition, the NO _x absorbents 5a, 5b are operated by the operation described later.
The flow rate of exhaust gas flowing into the reducing agent supply nozzle 11 is reduced.
When the reducing agent is supplied from a and 11b and the oxygen concentration in the exhaust gas decreases, the NO _x absorbents 5a and 5b absorb the absorbed NO _x.
Release.

The detailed mechanism of this absorption / release action is not clear in some parts. However, it is considered that this absorbing / releasing action is performed by the mechanism shown in FIG. Next, regarding this mechanism, platinum P on the carrier
The case of supporting t and barium Ba will be described as an example, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

That is, the inflow exhaust becomes considerably lean.
And the oxygen concentration in the exhaust gas increased significantly, as shown in Figure 2 (A).
As these oxygen O₂Is O₂ ^-Or O^2-In the form of
It adheres to the surface of platinum Pt. On the other hand, the NO in the exhaust gas is
This O on the surface of platinum Pt₂ ^-Or O^2-Reacts with N
O₂Becomes (2NO + O₂→ 2 NO₂ ). Then generated
NO₂Part of the inside of the absorbent while being oxidized on platinum Pt
2 while being absorbed by and bound to barium oxide BaO.
As shown in (A), nitrate ion NO₃ ^-Absorbent in the form of
Diffuse in. NO in this way_XIs NO_XAbsorbent 5
It is absorbed in a and 5b.

Therefore, NO ₂ is produced on the surface of platinum Pt as long as the oxygen concentration in the inflowing exhaust gas is high, and NO ₂ is absorbed in the absorbent and the nitrate ion NO ₃ unless the NO _X absorption capacity of the absorbent is saturated. ^- is generated. In contrast the reaction with the amount of NO ₂ oxygen concentration is lowered in the inflowing exhaust gas decreases the reverse (NO ₃ ^- → NO ₂₎ proceeds, the nitrate ions NO ₃ of the absorbent ^- is NO ₂ It is released from the absorbent in the form. That is, when the oxygen concentration in the inflowing exhaust gas decreases, NO
NO _X is released from the _X absorbents 5a and 5b.

On the other hand, when reducing components such as HC and CO are present in the inflowing exhaust gas, these components are oxygen O ₂ on platinum Pt.
^- or it is reacted with oxide and O ^2-, lowering the oxygen concentration in the exhaust to consume oxygen in the exhaust. Further, NO ₂ released from the NO _x absorbents 5a, 5b due to the decrease in oxygen concentration in the exhaust gas is reduced by reacting with HC and CO as shown in FIG. 2 (B). In this way, NO _{2 is} deposited on the surface of platinum Pt.
When NO is absent, the absorbent releases NO _{2 one} after another. Therefore, if there are HC and CO components in the inflowing exhaust gas, the NO _x absorbents 5a, 5b will be discharged from the NO _x absorbents 5a, 5b in a short time.
Will be released and reduced.

That is, HC and CO in the inflowing exhaust gas are
O on the platinum Pt₂ ^-Or O^2-Reacts with and oxidizes immediately
And then O on the platinum Pt₂ ^-Or O^2-Is consumed
However, if HC and CO still remain,
NO released from the absorbent_XAnd discharged from the agency
NO_XIs reduced. Therefore, N
O_XNO to release and reduce (regenerate)_XFor absorbent
The amount of reducing agent to be supplied depends on the consumption of oxygen due to oxidation.
The amount and NO necessary to sufficiently reduce the oxygen concentration in the air
_XTotal NO released from absorbents 5a, 5b _XReduce
It will be the total of the required amount and. But diesel engine
Since the air-fuel ratio of the exhaust is always lean in Gin, NO_X
NO while flowing a large amount of exhaust gas to the absorbents 5a, 5b_XRelease of
If you try to release or reduce it, you will consume oxygen in the exhaust gas.
The amount of reducing agent used for this purpose becomes very large. Therefore, this implementation
In the example, as described below, the particulate filters 3a, 3
Using the increase in pressure loss due to particulate collection of b, N
O_XAlternately lower the flow rate of exhaust gas flowing into the absorbents 5a, 5b.
NO after reducing_XSupply the reducing agent to the absorbents 5a, 5b
There is.

As the particulate filters 3a and 3b, cylindrical porous filters made of, for example, sintered metal, which have good heat conduction, are used in this embodiment. The normally used particulate filter is required to have a relatively small increase in pressure loss with respect to an increase in the amount of collected particulates, but the particulate filters 3a and 3b used in the present embodiment, conversely, are It has the characteristic that the pressure loss rapidly increases with an increase in the amount of collected curate. FIG. 3 shows a comparison of the pressure loss with respect to the collection amount of the normal particulate filter (broken line) and the particulate filters 3a and 3b (solid line) of this embodiment.

That is, the particulate filters 3a and 3b used in this embodiment are set in the shape, volume and pore size distribution of the filter so that a large pressure loss will occur in a short time (with a small amount of collected particulates) during use. There is. Further, in this embodiment, the particulate filter 3 is used.
Electric heaters 4a and 4b for burning the collected particulates are embedded in a and 3b over the entire length of the filter. In this embodiment, since the pressure loss increases and the amount of exhaust gas passing decreases when the amount of collected particulates is relatively small, when the amount of collected particulates reaches a certain amount, the amount of collected particles does not increase much thereafter, and the heat transfer Since a good metal filter of No. 3 is used, it is possible to reduce the pressure loss by burning the particulates collected in the filters 3a and 3b in an extremely short time by energizing the electric heaters 4a and 4b.

The reducing agent supply device 11 includes a reducing agent pressure supply source 11c such as a container and a pump, a reducing agent supply nozzle 11a,
Control valves 11d and 11 for controlling the reducing agent supply amount to 11b
e, and the control valve 11d, 11e is alternately opened by a control signal from the ECU 30 described later to open the nozzle 11
The reducing agent is supplied from a and 11b to the branch passages 2a and 2b on the upstream side of the NO _x absorbents 5a and 5b. As described above, in the present invention, a substance that generates a reducing component such as HC or CO can be used as the reducing agent, and for example, a gas such as hydrogen or carbon monoxide, a gas such as propane, propylene or butane, or a liquid hydrocarbon or gas oil. Liquid fuels such as kerosene can be used as the reducing agent.

Reference numeral 30 in the drawing denotes an electronic control unit (ECU) of the engine 1. ECU30 is CPU, RA
The M, ROM, and the input port and the output port are connected to each other by a bidirectional bus, which is a well-known digital computer, and performs basic control such as fuel injection amount control of the engine. In the present embodiment, the electric heater 4a, Switching of exhaust to the NO _x absorbents 5a, 5b by energizing 4b and regeneration of the NO _x absorbents 5a, 5b by supplying the reducing agent from the nozzles 11a, 11b of the reducing agent supply device 11 are performed.
For these controls, signals such as engine speed, accelerator opening, and exhaust temperature are input to the input ports of the ECU 30 from sensors (not shown).
The output ports of 30 are connected to the electric heaters 4a and 4b and the control valves 11d and 11e of the reducing agent supply device 11 via drive circuits (not shown), respectively, and control their operation.

Next, the operation of regenerating the NO _x absorbent of the exhaust gas purification device of this embodiment will be described. As described above, in the present embodiment, NO _X is utilized without using a device having a movable member such as a switching valve, by utilizing the increase in pressure loss due to particulate collection of the particulate filters 3a and 3b and the decrease in pressure loss due to particulate combustion. absorbent 5a, to reproduce _the NO _X absorbent by controlling the flow of exhaust gas into 5b.

FIG. 4 is a timing chart showing the regeneration operation of the NO _x absorbent of the present embodiment, and FIG. 4 (a) shows the time variation of the particulate collection amount of the particulate filters 3a, 3b. (B) is a particulate filter 3
3A and 3B show changes over time in the exhaust gas flow rates passing through a and 3b (that is, the exhaust gas flow rates flowing into the NO _x absorbents 5a and 5b).

In this embodiment, the ECU 30 energizes the electric heaters 4a and 4b of the particulate filters 3a and 3b at regular intervals to burn the particulates collected by the particulate filter. It should be noted that, as described above, when the particulate collection amount of the particulate filter increases to a certain extent, the pressure loss increases significantly, so that the exhaust gas hardly passes through the filter and the particulate collection amount does not increase any more (that is, The amount of curate collected is saturated). In the present embodiment, the energization interval of each of the electric heaters 4a and 4b is set to be longer than the use time from the state where the trapping amount is zero until the trapping amount of the particulate filter that has started to be used is saturated. . For this reason, as shown in FIG. 4A, the particulate trapped amounts of the particulate filters 3a and 3b are each a period (FIG. 4) in which the trapped amount increases with time.
(A), section), a period during which the trapped amount hardly increases (Fig. 4 (a), section), and a period during which the trapped amount decreases due to particulate combustion by energizing the heater (Fig. 4).
(A), section) is repeated three times.

In the electric heaters 4a and 4b, one of the particulate filters is in the above section (see FIG. 4).
In the case of (a)), the energization cycle is set so that the electric heater of the other particulate filter is energized. By setting the energization period so as to be shifted in this way, in the present embodiment, the amount of trapped particulates in one filter is saturated and the pressure loss is very large, and the pressure loss in the other filter is small due to particulate combustion. The state of being present is periodically and alternately repeated (see FIG. 4A).

As described above, when one of the particulate filters in the branch passages 2a and 2b has a large pressure loss and the other has a small pressure loss, the exhaust gas flows into the branch passage having the smaller pressure loss and the branch having the larger pressure loss. Almost no flow in the passage. Therefore, as described above, the electric heaters 4a, 4
When the energization period of b is set to be shifted, the exhaust flow rate passing through each particulate filter is as shown in FIG.
It changes as shown in (b).

For example, immediately after the heater 4a of the filter 3a is energized, the pressure loss of the filter 3a is small and the filter 3b is small.
Since the pressure loss is large, the exhaust gas flow rate on the filter 3a side greatly increases and the exhaust gas flow rate on the filter 3b side decreases to near zero (FIG. 4 (b), section I). After that, in the filter 3a, the pressure loss increases as the amount of collected particulates increases, so the exhaust flow rate starts to decrease on the filter 3a side, and conversely on the filter 3b side, the exhaust flow rate increases as the pressure loss of the filter 3a increases. When the amount of collected particulates in 3a approaches saturation, the exhaust flow rates of both filters become substantially equal (Fig. 4 (b), section II). Then, when the heater 4b of the filter 3b is energized, the particulate loss of the filter 3b is reduced by the particulate combustion of the filter 3b, and the exhaust flow rate is increased or decreased in the filters 3a and 3b (Fig. 4 (b), section III). , IV). Thus, by controlling the energization interval of the heater as described above, NO _X absorbent 5a, alternately 5b, the flow rate of the exhaust gas flowing it is possible to produce a state of substantially zero, by using a switching valve such as an exhaust It is possible to obtain the same effect as that of switching.

[0030] In this embodiment, a predetermined time when the exhaust flow rate is decreased in each of the NO _X absorbent (FIG. 4 (b), the period R) for supplying a reducing agent from the reducing agent supply device 11 to _the NO _X absorbent. As a result, it is possible to reduce the exhaust gas flow rate at the time of regeneration of the NO _X absorbent and reduce the amount of reducing agent required for regeneration without using a member having a movable part such as a switching valve.

Although the ECU 30 energizes the electric heaters 4a and 4 (b) at regular intervals in the above embodiment (for example, energization for about 1 minute every few minutes), for example, the particulates of the engine. You may make it change an electricity supply interval according to the generation amount. In this case, the amount of particulates generated per unit time of the engine is stored in advance in the ROM of the ECU 30 as a function of operating state parameters such as the number of revolutions, load (accelerator opening), and the amount of particulates generated is calculated at regular intervals. The energization interval may be calculated by performing integration and multiplying the time until the integrated value reaches a predetermined amount by a constant coefficient. This makes it possible to adjust the energization interval of the heater according to the change in the saturation time of the particulate collection amount of the filter due to the variation of the particulate generation amount of the engine.

In the above embodiment, the case where two branch passages are provided and the exhaust gas flow is alternately switched by energizing the heater of the particulate filter to regenerate the NO _x absorbent has been described. Three or more passages are provided, a particulate filter and a NO _x absorbent are arranged in each branch passage, and the heater of one particulate filter is sequentially energized and the NO _x absorbent on the downstream side of the other particulate filter is regenerated. You can also do

Further, in the above embodiment, the NO _x absorbents are installed independently of each other. However, the same number of independent flow passages as the exhaust branch passages are formed in a single NO _x absorbent, and the flow of each of them is reduced. It is also possible to connect the branch passage on the downstream side of the particulate filter to the passage. As a result, NO _X
The installation space for the absorbent can be reduced. Also,
In this case, NO in the order as a part that performs NO _X absorbent regeneration of the NO _X absorbent to complete the heater energizing portion and a particulate filter in the embodiment is always adjacent _X
If to perform a combustion of regeneration and particulates of the absorbent, it is possible to raise the temperature of the absorbent in heat in NO _X absorption generated by the combustion of the reducing agent during regeneration of the NO _X absorbent, NO _X even when the exhaust temperature is relatively low
It is possible to maintain the absorbing agent being absorbed at a temperature equal to or higher than the activation temperature and maintain a high NO _x purification efficiency.

[0034]

As described above, the exhaust emission control device of the present invention has the following features.
Each of the exhaust branch passages of the diesel engine is
A particulate filter is provided for each particulate.
Burning of particulates collected by the rate filter
By controlling the imming, shut-off valve, switching valve, etc.
To each branch passage without using a device with movable members
Exhaust is switched, and each particulate filter is
NO installed on the downstream side _XExhaust that flows in when the absorbent is regenerated
Since the air flow rate can be reduced, the stickiness of the movable member can be reduced.
NO while preventing malfunction due to locking_XAbsorbent regeneration
This has the effect of reducing the amount of reducing agent consumed at that time.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an exhaust gas purification device for an internal combustion engine according to the present invention.

FIG. 2 is a diagram illustrating the NO _X absorption and release action of the NO _X absorbent of the present invention.

FIG. 3 is a diagram showing pressure loss characteristics of the particulate filter of the embodiment of FIG.

FIG. 4 is a timing diagram illustrating the operation of the embodiment of FIG.

[Explanation of symbols]

1 ... diesel engine 2 ... exhaust passage 2a, 2b ... branch passages 3a, 3b ... particulate filter 4a, 4b ... electric heater 5a, 5b ... NO _X absorbent 11 ... reducing agent supply device 11a, 11b ... reducing agent feed nozzle 30 ... ECU

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display area F01N 3/08 H

Claims (1)

[Claims] 1. An exhaust emission control device for purifying NO _x components in the exhaust gas of a diesel engine, and an exhaust passage branched into a plurality of passages, and NO _x when the exhaust air-fuel ratio is lean disposed in each of the branch passages. NO the oxygen concentration of the absorbed inflowing exhaust releasing NO _X absorbed when lowering the
And _X absorbent, a reducing agent supply means for reducing and purifying the released NO _X with the release of NO _X absorbed from _the NO _X absorbent supplying reducing agent separately for the respective of the NO _X absorbent, the respective A particulate filter disposed upstream of the reducing agent introducing means in the branch passage for collecting particulates in the exhaust gas, and means for individually burning the particulates collected in the respective particulate filters. , release of the NO _X from the supplying reducing agent from the reducing agent supply means to the NO _X absorbent _the NO _X absorbent amount of particulates captured in the particulate filter when the predetermined value or more, reducing the performed, the NO _X release, performs combustion of the collected particulates in the particulate filter after completion of reduction, one Patikyu NO on the downstream side of the Tofiruta
During the supply of the reducing agent to the _X absorbent, at least one other particulate filter controls the combustion means of the particulates so that the particulate collection amount is equal to or less than the predetermined amount. Exhaust gas purification device for engines.