JP2001234732A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of purifying by continuous regeneration, avoiding thermal deterioration and thermal damage in a wide engine operation area. SOLUTION: In this exhaust emission control device, a continuous regeneration trap structure in which an oxidation catalyst 22 for oxidizing nitrogen monoxide into nitrogen dioxide and a filter 23 for trapping particulate matters are combined is combined with an introduction structure 26 for introducing air into the upstream side of oxidation catalyst 22, a temperature sensor 24 for detecting exhaust gas temperature in the upstream side of the oxidation catalyst 22, a nitrogen dioxide sensor 25 for detecting concentration of nitrogen dioxide directing to the filter 23, and an ECU 30 for allowing to introduce air when the detected temperature of the temperature sensor 24 is above a prescribed value and detected concentration by the nitrogen dioxide sensor 25 is below a prescribed value. Thus, sufficient oxidation removal of particulate matters is proceeded, which maintaining a conversion ratio from nitrogen monoxide to nitrogen dioxide high, even if the temperature of exhaust gas is high.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for removing particulate matter contained in exhaust gas discharged from an engine.

[0002]

2. Description of the Related Art Exhaust gas emitted from a diesel engine mounted on an automobile contains particulate matter (hereinafter, referred to as PM).
PM is a flammable substance such as soot and unburned carbonized compound.

[0003] Therefore, in automobiles, research is being conducted to remove particulate matter in exhaust gas discharged from an engine using an exhaust gas purifying apparatus for oxidizing PM.

Many of the exhaust gas purifying apparatuses are disclosed in
As disclosed in Japanese Patent Application Publication No. 1-93219, a structure has been proposed in which a diesel particulate oxidodaza (hereinafter, referred to as DPO) with a catalyst is disposed in an exhaust gas passage from which exhaust gas of an engine is discharged. The device captures PM emitted from the engine by DPO while the vehicle is running. Then, at the time of a high load at which a sufficient exhaust gas temperature necessary for PM combustion is secured, a part of the supercharged air is supplied to the DPO, and the collected PM is utilized by utilizing the oxygen of the intake air and the heat of the exhaust gas. Is burned to regenerate DPO.

The temperature of the exhaust gas discharged from the engine varies in a wide range from a low temperature to a high temperature depending on the driving condition of the vehicle. Therefore, the exhaust gas purifying apparatus can oxidize and remove PM from a region as low as possible. Desired.

[0006] However, the exhaust gas purifying apparatus is a DPO
With the catalyst attached to, the PM can be oxidized and removed in a relatively low temperature range, but the oxidation temperature of PM is still 45 ° C.
If the temperature is not higher than 0 ° C., sufficient regeneration of the filter cannot be obtained, and PM combustion in a desired low temperature range cannot be expected (according to a test).

Therefore, an exhaust gas purifying apparatus has been proposed in which PM is not oxidized and removed by nitrogen dioxide (NO ₂ ), instead of oxidizing PM by oxygen (O ₂ ).

[0008] As shown in Japanese Patent Application Laid-Open No. 1-318715, this is because nitrogen monoxide in the exhaust gas (hereinafter referred to as
NO) is oxidized into nitrogen dioxide (hereinafter referred to as NO ₂ ), and a DP that captures PM is disposed at a subsequent stage.
This is a two-stage exhaust gas purifying apparatus in which F is disposed. This device converts NO in exhaust gas to NO ₂ by the oxidation catalyst in the preceding stage.
Oxidation reaction (NO + 1 / 2O ₂ → NO ₂ )
Utilizing O ₂ , the PM collected by the latter DPF is caused to undergo a combustion reaction (oxidation reaction: C + 2NO ₂ → CO ₂ + 2NO),
It oxidizes and removes PM.

According to this technique, the above oxidation reaction causes 250
PM can be continuously oxidized and removed from a low temperature range of about 300 ° C. (continuous regeneration).

[0010]

However, when NO is changed to NO
Oxidation catalysts that oxidize to ₂ are currently 30
In a temperature range of 0 ° C. or higher, a phenomenon occurs in which the ability to convert NO into NO ₂ is reduced. Further, in a temperature range higher than that, NO ₂ obtained by the oxidation reaction using the oxidation catalyst causes a decomposition reaction (2NO ₂ → 2NO + O ₂ ) and returns to NO.

In this case, in the high temperature region, some NO
₂ decomposes and returns to NO, NO ₂ required for oxidative removal of PM
Is insufficient (conversion rate of NO → NO ₂ is reduced).

That is, the continuous regeneration type exhaust gas purification apparatus has a problem that the temperature range in which the DPF can be continuously regenerated is narrow.

For this reason, the PM purification rate of the exhaust gas purifying device shows a good value in a limited temperature range where continuous regeneration is possible, but is low in other temperature ranges, and the PM purification rate is reduced to an operating state as seen in an automobile. Accordingly, it is very difficult to regenerate the DPF in a temperature range where the temperature of the exhaust gas varies widely from a low temperature to a high temperature.

In addition, if the oxidation catalyst is in a temperature range of 500 ° C. or more, thermal degradation of the catalyst starts, and if the temperature of the DPF becomes 1000 ° C. or more, it may be damaged.
It was not enough to just add _2, and it was not easy to apply the continuous regeneration type exhaust gas purification device to exhaust gas purification of automobile engines.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a wide range of exhaust gas temperatures from a low temperature to a high temperature while avoiding thermal deterioration and damage due to heat while ensuring sufficient regeneration by continuous regeneration. It is an object of the present invention to provide an exhaust gas purification device capable of performing various purifications.

[0016]

In order to achieve the above object, an exhaust gas purifying apparatus according to the first aspect of the present invention comprises a nitric oxide (N
An oxidation catalyst for oxidizing O) to nitrogen dioxide (NO ₂ );
Air introduction means for introducing air to the upstream of the oxidation catalyst in a continuous regeneration trap structure combining a filter for collecting particulate matter (PM) in exhaust gas, and a temperature sensor for detecting the temperature of exhaust gas upstream of the oxidation catalyst A nitrogen dioxide sensor for detecting the concentration of nitrogen dioxide flowing from the oxidation catalyst to the filter, and air introduction so that air is introduced when the temperature detected by the temperature sensor is higher than a predetermined value and the detection concentration of the nitrogen dioxide sensor is lower than a predetermined value. By combining control means for controlling the means, air is introduced upstream of the oxidation catalyst when the exhaust gas temperature exceeds the optimum catalyst activation temperature for the oxidation reaction of the oxidation catalyst.

According to this configuration, when the continuous regeneration type exhaust gas purifying apparatus is in a state where continuous regeneration of the filter cannot be expected due to lack of nitrogen dioxide, the oxidation catalyst is cooled by the introduced air. Then, the oxidation catalyst is maintained at an optimal catalyst activation temperature (for example, around 300 ° C.) for oxidizing nitrogen monoxide in the exhaust gas to nitrogen dioxide. Moreover, the oxidation catalyst not only promotes the oxidation reaction but also suppresses the decomposition reaction of nitrogen dioxide by the addition of oxygen contained in the air. By such an oxidation reaction in which the catalyst temperature is kept almost constant, the oxidation catalyst performs an oxidation reaction from nitrogen monoxide to nitrogen dioxide at a high conversion rate even when the exhaust gas temperature is high.

Decomposition of nitrogen dioxide toward the subsequent filter is suppressed by cooling caused by the introduction of air and oxygen of the air. As a result, an optimum concentration of nitrogen dioxide for burning (oxidizing) the particulate matter of the filter is ensured, so that the particulate matter attached to the filter is sufficiently oxidized and removed.

Thus, by introducing air, even if the temperature of the exhaust gas is high, the particulate matter can be sufficiently oxidized and removed while the conversion of nitrogen monoxide to nitrogen dioxide is maintained at a high level. Can be improved.

In addition, since the oxidation catalyst and the filter are cooled by the introduced air, thermal deterioration and damage due to heat are avoided, so that the durability can be improved.

In the exhaust gas purifying apparatus according to the second aspect of the present invention, in addition to the above object, a supercharging device is provided so that air can be introduced while using an accessory attached to the engine while suppressing cost burden. And a valve for opening and closing the air passage for introducing a part of the supercharged air of the supercharging device to the upstream of the oxidation catalyst as an air introduction means on the premise that a supercharged engine having the above is adopted. The combination with the device was adopted.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to one embodiment shown in FIGS.

In FIG. 1, reference numeral 1 denotes a traveling diesel engine mounted on an automobile. The diesel engine 1 reciprocates a piston 7 in a cylinder 6 having intake and exhaust ports 2 and 3, intake and exhaust valves 4 and 5 for opening and closing the intake and exhaust ports 2 and 3, and a fuel injection nozzle (not shown). It is configured to be movable. Then, the engine 1 follows the reciprocating motion of the piston 7 and, at a predetermined timing, the intake / exhaust valve 4,
5 is opened and closed, and furthermore, fuel is injected from the fuel injection nozzle into the combustion chamber at a predetermined timing, so that a suction stroke, a compression stroke, a combustion stroke, and an exhaust stroke are periodically performed in the cylinder 6, and the piston 2 Power is output from a crankshaft (not shown) connected to the motor.

The intake port 2 of the diesel engine 1
Is connected to an outlet 11b of a compressor 11 constituting a supercharger, for example, a turbocharger 10. The exhaust port 3 is connected to an inlet 12 a of a turbine 12 of a turbocharger 10 that is coaxially connected to the compressor 11. By attaching this turbocharger 10,
The intake air is supercharged into the combustion chamber of the diesel engine 1 with the exhaust energy of the exhaust gas. That is, it is a supercharged diesel engine. The inlet 11a of the compressor 11 is connected to an air cleaner (not shown).

An exhaust pipe 15 (exhaust gas passage) is connected to the outlet 12 b of the turbine 12.
The exhaust gas of the diesel engine 1 is discharged to the outside (atmosphere).

An exhaust gas purifying device 20 for oxidizing and removing particulate matter in the exhaust gas is interposed in the exhaust pipe 15.

The apparatus has, for example, one common elongated case 21 having an inlet 21a connected to the upstream side of the exhaust pipe 15 at one end and an outlet 21b connected to the downstream side of the exhaust pipe 15 at the other end. have. An oxidation catalyst 22 for oxidizing nitrogen monoxide (hereinafter, referred to as NO) to nitrogen dioxide (hereinafter, referred to as NO ₂ ) is accommodated on the upstream side (previous stage) in the case 21. Further, the downstream side (the latter stage) in the case 21.
Contains particulate matter (PM)
A diesel particulate filter 23 (hereinafter, referred to as DPF 23: corresponding to the filter of the present application) that collects the dust is stored. The oxidation catalyst 22 and DPF arranged in series
23 constitutes a two-stage continuous regeneration trap. Then, the NO in the exhaust gas is oxidized to NO ₂ by the oxidation catalyst 22 in the preceding stage by the continuous regeneration type trap (NO + 1 / 2O ₂ → NO ₂ ), and this NO ₂ is utilized.
In the latter DPF, the captured PM is caused to undergo a combustion reaction (oxidation reaction: C + 2NO ₂ → CO ₂ + 2NO), and P in the exhaust gas is discharged.
M can be removed by oxidation.

In this exhaust gas purifying apparatus 20, case 2
A temperature sensor 24 for detecting an exhaust gas temperature on the upstream side of the oxidation catalyst 22 is mounted on the upstream side of the first catalyst 1. Further, a nitrogen dioxide sensor 25 for detecting the concentration of NO ₂ from the oxidation catalyst 22 to the DPF 23 is provided at an intermediate portion of the case 21.
(Hereinafter, referred to as NO ₂ sensor 25).

At a point upstream of the oxidation catalyst 22, for example, at a portion of the exhaust pipe 15 immediately before the inlet 21a, an air introduction pipe 2 is provided.
6 (corresponding to an air passage) is connected to one end. The other end of the air introduction pipe 26 is connected to a part of an intake passage 13 that connects the intake port 2 of the diesel engine 1 and the outlet 11b of the compressor 11, thereby supercharging the turbocharger 10. Part of the air can be introduced upstream of the oxidation catalyst 22. An actuator that controls the introduction of air, for example, a valve device 27 that is driven to open and close by a solenoid 27a is installed in the path of the air introduction pipe 26. The valve device 27 can open and close the air introduction pipe 26. (In this embodiment, the normally closed valve device 2
5).

Then, the temperature sensor 24, NO_TwoSensor 2
5. The solenoid 27a of the valve device 27 is, for example, a micro
ECU 30 (comprising control means)
Connected). The ECU 30 includes an automobile
During traveling, the temperature of the exhaust gas going to the oxidation catalyst 22 is
Less than 22 optimum activation temperature (predetermined value: 300 ° C, for example)
Above, that is, when the optimal activation temperature can no longer be maintained
NO to DPF23 _TwoIf the concentration is
Necessary for oxidizing and removing PM set from the operating state of engine 1
Concentration [for example, twice the PM molar concentration (predetermined value: oxidation reaction)
According to the equation)], that is, N required for oxidative removal of PM
O_TwoWhen the pressure is insufficient, the normally closed valve device 27 is opened.
Function is set. That is, the engine operating state
Only when is the low-temperature intake air containing a lot of oxygen
It is introduced from the upstream side of the oxidation catalyst 22.

By the introduction of the intake air, in the continuous regeneration trap, the PM can be sufficiently oxidized by continuous regeneration regardless of the exhaust gas temperature. The flowchart of FIG. 2 shows the control of the continuous regeneration trap.

The operation of the continuous regenerative trap will be described with reference to the flowchart. It is assumed that the diesel engine 1 is being driven as the automobile is running.

At this time, the exhaust gas discharged from the cylinder 6 is supplied to the turbine 12, the exhaust pipe 15,
Through the exhaust gas purification device 20 (continuous regeneration trap)
It is exhausted to the outside (atmosphere). The turbocharger 10
Are supercharging the intake air by driving the compressor 11 by the turbine 12.

When the exhaust gas passes through the exhaust gas purifying device 20, PM in the exhaust gas is collected by the DPF 23 at the subsequent stage, and the PM is generated by the oxidation catalyst 23 at the preceding stage.
_{At 2,} it is continuously burned (oxidized and removed).

That is, the exhaust gas temperature T (the temperature detected by the temperature sensor 24) is maintained in the optimum activation temperature range (for example, a temperature range below 300 ° C.) of the oxidation catalyst 22 (step S1), and the DPF 23 NO ₂ flowing into the inlet of the
The concentration R (the concentration detected by the NO ₂ sensor 25) exceeds a set NO ₂ concentration ([NO ₂ ]: twice the PM molar concentration obtained from the engine operating state) preset according to the engine operating state. It is assumed that the density is maintained (step S2).

Then, the ECU 30 determines that the current engine operating state is in a state of maintaining the continuous regeneration temperature range of the DPF 23, and closes the valve device 27 (step S).
3).

At this time, since the temperature of the exhaust gas is low, (3
(Less than 00 ° C.), the exhaust gas purifying apparatus 20 performs a sufficient reaction of oxidizing NO in exhaust gas to NO ₂ (NO + 1 / 2O ₂ → NO ₂ ) in the oxidation catalyst 22 in the former stage. Then, the trapped PM is subjected to a combustion reaction (oxidation reaction: C + 2N) in the subsequent DPF 23 by the NO _2.
O ₂ → CO ₂ + 2NO), which is a continuous oxidation and removal of PM.

On the other hand, depending on the operating condition of the automobile, the exhaust gas temperature T rises above the set exhaust gas temperature (300 ° C.), the reaction of oxidizing NO in the oxidation catalyst 22 to NO ₂ decreases (step S1), and the PM It is assumed that the NO ₂ concentration required for the oxidation removal has not been secured (step S2).

At this time, the ECU 30 determines that continuous regeneration of the DPF 23 cannot be expected due to the shortage of nitrogen dioxide, and opens the valve device 1 (step S).
4).

Then, a part of the supercharged air supercharged by the turbocharger 10 (air at a low temperature and containing a large amount of oxygen)
Is introduced upstream of the oxidation catalyst 22 through the air introduction pipe 26.

As a result, the oxidation catalyst 22 is cooled by the introduced air, and is maintained at an optimum catalyst activation temperature (for example, about 300 ° C.) for oxidizing NO to NO ₂ .
At the same time, the above oxidation reaction is promoted by the addition of oxygen contained in the air. Of course, the decomposition reaction of NO ₂ to NO is suppressed.

By maintaining such a catalyst temperature substantially constant, even if the exhaust gas temperature T is high, the oxidation catalyst 22
The oxidation reaction of NO to NO ₂ is performed at a high conversion.

Then, the NO ₂ is supplied to the DPF 23 at the subsequent stage.
Led to. The decomposition of this NO ₂ is suppressed by cooling by the introduced air and stabilization by the oxygen in the air. As a result, a decrease in NO ₂ concentration is suppressed, and an optimal NO ₂ concentration for burning (oxidizing) PM is secured. This N
O ₂ sufficiently oxidizes and removes PM attached to the DPF 23.

Thus, by the introduction of air, even if the temperature of the exhaust gas is high, the DPF 23 can sufficiently oxidize and remove PM with the DPF 23 while maintaining a high conversion rate from NO to NO ₂ (maintenance of continuous regeneration).

Thus, in the continuous regeneration temperature range of the DPF 23, PM can be efficiently purified not only in a limited operation state but also in an operation state of discharging high-temperature exhaust gas.

In particular, due to the coexistence effect of the cooling effect of the introduced air and the addition of oxygen to the introduced air,
It is possible to obtain a higher PM purification rate than that obtained simply by combining the two reaction systems of the oxidation catalyst 22 and the DPF 23 (improvement in purification ability). That is, FIG.
Is a graph of the same effect obtained by the rig test, and FIG. 3A shows PM in the reaction between PM (C) and NO _2.
(B) shows the purification rate of PM performed by the reaction between PM (C) and O _2, and (c) shows the purification rate of PM when air is introduced into both reaction systems. Shows the rate. By comparing (c) with the other (a) and (b), simply adding (a) and (b) from the effectiveness of cooling and oxygen addition that O ₂ brings to both the oxidation catalyst 22 and the DPF 23. It was found that a PM purification rate (PM purification ability) higher than that obtained was obtained, and it was confirmed that the purification ability of the continuous regeneration trap was promoted (by a rig test). However, PM
The purification rate is calculated as “the difference A between the PM accumulation amounts before and after heating / PM before heating.
This is a parameter represented by the “deposition amount B”.

In addition, the oxidation catalyst 22 and DPF 23
Cooling with the introduced air avoids thermal degradation and damage due to heat, and is therefore excellent in durability.

The introduced air is supplied to the turbocharger 10, which is an accessory attached to the diesel engine 1, as it is.
Since it is used as a supply source for supplying air containing a low temperature and a large amount of oxygen and is introduced upstream of the oxidation catalyst 22, a separate air supply source is not required, and the cost burden can be reduced.

The present invention is not limited to the above-described embodiment, but may be implemented with various modifications without departing from the gist of the present invention. For example, in the above-described embodiment, a part of the supercharged air of the turbocharger is introduced upstream of the oxidation catalyst, but air is introduced upstream of the oxidation catalyst by using another supercharger. You may make it do.

[0050]

As described above, according to the first aspect of the present invention, even if the temperature of the exhaust gas is high, the conversion of nitrogen monoxide to nitrogen dioxide is high even if the temperature of the exhaust gas is high. While oxidizing and removing the particulate matter (PM).

Therefore, while particulate matter can be efficiently burned and removed only in a predetermined operating region (operating region where the exhaust gas temperature is around 300 ° C.), in the present invention, the exhaust gas temperature is 300 ° C. Since the temperature of the oxidation catalyst can be maintained at the optimum temperature even in a higher operation state, the filter can be continuously regenerated in a wide operation range.
In addition, the exhaust gas purifying device including the continuous regeneration trap can further improve the purifying ability by cooling and oxygen addition that the introduced air brings to both the oxidation catalyst and the filter. In addition, the oxidation catalyst and the filter can be prevented from being thermally degraded or damaged by heat by cooling with the introduced air, so that they are excellent in durability.

According to the second aspect of the present invention, in addition to the above effects, a part of the supercharged air of the supercharger, which is an auxiliary device attached to the engine, is introduced upstream of the oxidation catalyst. In addition, when introducing air from the outside, it is not necessary to separately provide an air supply source, and an effect that air can be introduced while suppressing a burden on costs is achieved.

[Brief description of the drawings]

FIG. 1 shows an exhaust gas purifying apparatus according to an embodiment of the present invention.
The figure shown with the engine which assembled the same device.

FIG. 2 is a flowchart for explaining control for exerting the continuous regeneration capability of the exhaust gas purifying device regardless of the temperature of exhaust gas.

FIG. 3 is a diagram for explaining that the continuous regeneration ability is promoted by introduced air in a rig test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Diesel engine (engine) 10 ... Turbocharger (supercharger) 15 ... Exhaust pipe (exhaust gas passage) 21 ... Case 22 ... Oxidation catalyst 23 ... Particulate filter (filter) 24 ... Temperature sensor 25 ... Nitrogen dioxide Sensors 26, 27: air introduction pipe, valve device (air introduction means) 30: ECU (control means).

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G005 DA02 EA04 EA14 EA16 FA35 GB17 HA18 HA19 JA16 JA35 3G090 AA01 BA01 CB18 DA10 DA12 EA02 EA05

Claims (2)

[Claims] 1. An oxidation catalyst disposed in an exhaust gas passage for discharging exhaust gas from an engine for oxidizing nitrogen monoxide in the exhaust gas to nitrogen dioxide, and a particulate matter contained in the exhaust gas disposed downstream of the oxidation catalyst. A filter for collecting matter, an air introducing means for introducing air upstream of the oxidation catalyst, a temperature sensor for detecting an exhaust gas temperature upstream of the oxidation catalyst, and a filter for the nitrogen dioxide flowing from the oxidation catalyst to the filter. A nitrogen dioxide sensor for detecting a concentration, and controlling the air introduction means so that the air is introduced when a detection temperature of the temperature sensor is equal to or higher than a predetermined value and a detection concentration of the nitrogen dioxide sensor is equal to or lower than a predetermined value. An exhaust gas purifying apparatus comprising a control unit. 2. The exhaust gas purifying apparatus according to claim 1, wherein the engine is a supercharged engine having a supercharging device for supercharging intake air, and wherein the air introducing means includes a supercharging device. An exhaust gas purifying apparatus comprising: an air passage for introducing a part of the supercharged air upstream of the oxidation catalyst; and a valve device for opening and closing the air passage.