JP3093905B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly, to an exhaust gas purifying apparatus for an internal combustion engine, such as a diesel engine or a lean-burn gasoline engine, which burns at a lean air-fuel ratio in most operating regions. of the NO _X in the exhaust gas effectively removable it relates to an exhaust purification device.

[0002]

2. Description of the Related Art An example of this type of exhaust gas purifying apparatus is disclosed, for example, in Japanese Patent Application Laid-Open No. 62-106826. The apparatus of this publication is to place the absorbent to absorb NO _X in the presence of oxygen in an exhaust passage of a diesel engine (catalyst) to absorb the NO _X in the exhaust gas, lowering the NO _X absorption efficiency of the absorbent By shutting off the inflow of exhaust gas into the absorbent and supplying a gaseous reducing agent to the absorbent, NO _X is released from the absorbent and the released NO _X is reduced and purified. It is.

[0003]

Problems to be Solved by the Invention
In the exhaust gas purifying apparatus disclosed in Japanese Patent No. 6826, a gaseous reducing agent such as hydrogen is supplied to the NO _X absorbent in order to release NO _X from the NO _X absorbent and perform reduction purification (hereinafter referred to as “regeneration”). I have. However, the gaseous reducing agent such as hydrogen has a problem that it is difficult to handle such as requiring a special container for storage, and causes various problems especially when it is used for a vehicle internal combustion engine.

[0004] Thus, the reducing agent used for regeneration of _the NO _X absorbent, it is preferred that the handling is using a reducing agent simple liquid. In addition, in order to reduce the complexity of replenishment and storage, it is desirable to use the fuel of the vehicle, such as gasoline or light oil, as it is as the liquid reducing agent. However, liquid fuel such as light oil in particular contains many components having different boiling points, and also contains components that are difficult to vaporize when the exhaust temperature is low. For this reason, these liquid fuels are
_When injected into the exhaust passage on the upstream side of the _X absorbent, components having a high boiling point do not evaporate and remain in the form of a mist together with the exhaust gas.
_It may reach the _X absorbent. In this case NO _X
The fuel that has reached the absorbent adheres to the surface of the absorbent in a liquid state, and forms a layer covering the surface of the absorbent.

[0005] Liquid fuel adhering to _the NO _X absorbent surface,
When the temperature of the absorbent is high to some extent, the heat of the absorbent is vaporized by the heat of the absorbent to act as a reducing agent. However, since the evaporation heat considerable heat is lost from _the NO _X absorbent when the fuel is vaporized, will be the temperature of the NO _X absorbent is lowered, NO _X absorption and greater the amount of fuel to reach a liquid state The temperature of the agent may drop below the activation temperature. Therefore, when a liquid fuel such as light oil is used as a reducing agent,
It decreases the activity of _the NO _X absorbent caused the reduction of the NO _X purification rate, which may cause a problem leading to deterioration of the emission.

Further, it will cover the surface of the NO _X absorbent fuel temperature is attached to the absorbent and lower than the vaporization temperature of the fuel no longer vaporization without _the NO _X absorbent, of the NO _X by reduction of the effective surface area absorption, release effect is inhibited, in some cases problems of cold poisoning called _the NO _X absorbent occurs. For the above reasons, conventionally, when a liquid fuel such as light oil is used as a reducing agent, a burner or the like is provided in an exhaust passage to incompletely burn the liquid fuel, and the generated gas such as HC and CO is used as a reducing agent. _It had to be supplied to the _X absorbent. However, it is not preferable from the viewpoint of safety to provide a burner or the like in the exhaust passage from the viewpoint of safety, and there is a problem that the structure becomes complicated because the burner and its auxiliary equipment are provided in the exhaust passage.

[0007] The present invention is intended to provide an exhaust purification system of an internal combustion engine which can solve the above problems, to use a liquid fuel such as light oil as the reducing agent of the NO _X absorbent.

[0008]

According to the present invention, an inflow
Absorbed NO _X when the air-fuel ratio of the exhaust gas that is lean
And reduce the oxygen concentration in the incoming exhaust gas
The _the NO _X absorbent in the engine exhaust passage that releases the NO _X
With placing, always _the NO _X absorbent during the operation of the engine exhaust gas
Scan allowed to flow through the exhaust gas flowing into the NO _X absorbent
N but the NO _X absorbed in the NO _X absorbent when the lean
Oxygen concentration in the exhaust gas flowing into the O _X absorbent Shi lowered
Among which is adapted to release from _the NO _X absorbent when is because
In the exhaust purification system of combustion engine, the liquid in the _the NO _X absorbent
Exhaust gas which is supplied to the body reducing agent flowing into _the NO _X absorbent
Absorption in _the NO _X absorbent by allowed to lower the oxygen concentration
Co when releasing the NO _X that is yield from _the NO _X absorbent
To, to preheat the supplied liquid reducing agent to the _the NO _X absorbent
An exhaust gas purification device for an internal combustion engine, provided with a reducing agent preheating means, is provided .

[0009]

[Action] for liquid fuel supplied to the exhaust passage of the NO _X absorbent upstream vaporized is preheated by preheating means before supplying liquid fuel to reach the left _the NO _X absorbent liquid is reduced, NO _X absorption The temperature drop of the agent is prevented. For this reason,
_The NO _X absorbent decreased activity or cold poisoning problem does not occur.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, reference numeral 1 denotes a diesel engine, 2 denotes an intake pipe of the engine, and 3 denotes an exhaust pipe of the engine. Reference numeral 5 denotes a NO _X absorbent 5 described later connected to the exhaust pipe 3. In this embodiment, the _the NO _X absorbent 5 upstream of the engine exhaust pipe 3 and an exhaust shutter valve 6 is provided.

[0011] The shutter valve 6 is in the form of exhaust resistance less butterfly valve fully open state during normal operation of the engine is held fully opened, N from _the NO _X absorbent 5
O _X is closed to the predetermined opening degree at the time of the regenerating operation, reduce the amount of exhaust gas passing through the _the NO _X absorbent 5 squeezing exhaust pipe 3. Reference numeral 7 denotes an appropriate type of actuator such as a negative pressure actuator that drives the shutter valve 6 to open and close.

Further, _the NO _X absorbent when is disposed a reducing agent supply device 11 to be described later, the regenerating operation of the NO _X absorbent 5 is provided between the shutter valve 6 and _the NO _X absorbent 5 of the engine exhaust pipe 3 The reducing agent is supplied to the exhaust pipe on the upstream side of the exhaust pipe. In the figure, reference numeral 20 denotes an electronic control unit (ECU) of the engine 1. The ECU 20 is a CPU,
A known digital computer having a configuration in which a RAM, a ROM, and an input port and an output port are connected to each other via a bidirectional bus, performs basic control such as fuel injection amount control of an engine, and in this embodiment, an exhaust shutter valve. 6 and the control of the supply of the reducing agent from the reducing agent supply device 11. For these controls, input ports of the ECU 20 are supplied with signals such as exhaust temperature, engine speed, and accelerator opening from sensors (not shown).

[0013] _the NO _X absorbent 5 uses a carrier such as alumina or the like, the carrier on, for example potassium K, sodium Na, alkali metal, barium Ba, alkaline earth such as calcium Ca, such as lithium Li, cesium Cs And at least one selected from rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt. This _the NO _X absorbent 5 absorbs NO _X in the case the air-fuel ratio of the exhaust gas flowing is lean, the oxygen concentration is carried out to absorbing and releasing action of the NO _X that releases NO _X when lowered.

The above-described exhaust air-fuel ratio is defined as N
O _X absorbent upstream of 5 exhaust passage and the engine combustion chamber is intended to mean the ratio of the total sum and the fuel respectively supplied amount of air in the intake passage or the like. Therefore, NO _X absorbent 5
When no fuel, reducing agent or air is supplied to the upstream exhaust passage of the engine, 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).

[0015] In this embodiment, since the diesel engine is used, the exhaust air-fuel ratio during normal operation is lean, NO _X absorbent 5 performs absorption of the NO _X in the exhaust gas. Also, when a reducing agent is introduced into the exhaust oxygen concentration is lowered, the release of _the NO _X absorbent 5 absorbs reducing agent performs a reducing agent supply device 11. The detailed mechanism of this absorption / release action is not clear in some parts. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, this mechanism will be described by taking as an example a case where platinum Pt and barium Ba are supported on a carrier, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

That is, when the inflowing exhaust gas becomes considerably lean, the oxygen concentration in the inflowing exhaust gas greatly increases, and as shown in FIG. 7A, the oxygen O ₂ is converted into O ₂ ⁻ or O ²⁻ . It adheres to the surface of platinum Pt. On the other hand, NO in the inflowing exhaust gas reacts with this O ₂ ^- or O ^2- on the surface of platinum Pt, and NO ₂
(2NO + O ₂ → 2NO ₂ ). Next, a part of the generated NO ₂ is absorbed in the absorbent while being oxidized on the platinum Pt, and is combined with the barium oxide BaO.
It is diffused in the absorbent in the form of nitrate ions NO ₃ ^- as shown in the. In this way, NO _X is absorbed in the NO _X absorbent 5.

Accordingly, as long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is generated on the surface of the platinum Pt, and as long as the NO _x absorption capacity of the absorbent is not saturated, NO ₂ is absorbed in the absorbent and nitrate ions NO ₃ ^- is generated. On the other hand, when the oxygen concentration in the inflowing exhaust gas decreases and the amount of generated NO ₂ decreases, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and thus the nitrate ion NO ₃ ⁻ in the absorbent becomes NO ₂ Released from the absorbent in the form of That is, the oxygen concentration in the inflowing exhaust gas is released NO _X from _the NO _X absorbent 5 when lowered.

On the other hand, if reducing components such as HC and CO are present in the inflowing exhaust gas, these components become 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, the NO ₂ released from the NO _X absorbent 5 due to a decrease in the oxygen concentration in the exhaust gas
Is reduced by reacting with HC and CO as shown in FIG. 7 (B). When NO ₂ is no longer present on the surface of the platinum Pt, NO ₂ is released from the absorbent one after another.

[0019] That is, HC in the inflowing exhaust gas, CO, first O ₂ on the platinum Pt ^- immediately react with oxidized or O ^2-, and then on the platinum Pt O ₂ ^- or O ^2- is consumed the HC, NO _X discharged from the released NO _X and the engine from the absorbent by CO is reduced even yet HC, any remaining CO is. _The NO _X absorbent 5 of the NO _X emission, the reducing agent used for reduction operation (reproducing operation),
Any substance that generates a reducing component such as hydrocarbon or carbon monoxide in the exhaust gas may be used.Hydrogen, gas such as carbon monoxide, liquid or gaseous hydrocarbon such as propane, propylene, and butane,
Liquid fuels such as gasoline, light oil and kerosene can be used,
In this embodiment, light oil, which is the fuel of the diesel engine 1, is used as a reducing agent in order to avoid complications in storage and replenishment as described above.

Next, the reducing agent supply device 11 of this embodiment will be described with reference to FIG. When used as a reducing agent to gas oil as described above causes a problem that high-boiling component in the diesel fuel from adhering to leave _the NO _X absorbent 5 in a liquid. In this embodiment, as described below, the problem of the adhesion of the liquid fuel is solved by preheating the light oil supplied from the reducing agent supply device 11.

[0021] In FIG. 2, the reducing agent supply device 11 is arranged in _the NO _X absorbent 5 upstream side of the exhaust pipe 3 injectors 12
It has. Injection valve 12 injects a reducing agent (light oil) to _the NO _X absorbent 5 upstream opening and closing in response to a control signal from the above-mentioned ECU 20, performs the regenerating operation of the NO _X absorbent 5. Light oil is supplied from a fuel supply device 14 of the diesel engine 1 to a shut-off valve 15 which opens and closes in response to a control signal from the ECU 20.
Pressure is supplied to the injection valve 12 via the fuel passage 13 and the fuel passage 13. In the present embodiment, the fuel passage 13 includes a heat exchange portion 13a wound around the exhaust pipe 3, and the heat of the exhaust gas in the exhaust pipe 3 preheats the light oil in the heat exchange portion 13a. It has become.

[0022] In this embodiment, the regenerating operation of the NO _X absorbent 5 is completed (i.e., the injection valve 12 to complete the injection of diesel fuel is closed), the shut-off valve by ECU20 signals 1
5 opens. Thus, the fuel passage 13 up to the injection valve 12 is filled with light oil having a pressure equivalent to the outlet pressure of the fuel supply device 14. After a lapse of a predetermined time, the shutoff valve 15 is closed, and the fuel passage 13 between the shutoff valve 15 and the injection valve 12 is closed.
Are kept closed at both ends.

The light oil held in the fuel passage 13 is heated by receiving the heat of the exhaust gas through the heat exchange section 13a in this sealed state until the next regeneration operation is started. For this reason, the temperature of the light oil in the fuel passage 13 increases, and the pressure increases due to the increase of the vapor pressure.
High pressure condition. Then, the injection valve 12 by ECU20 signal when the reproduction condition is satisfied in _the NO _X absorbent 5 is opened. Accordingly, the high-pressure light oil in the fuel passage 13 is injected from the injection valve 12 into the exhaust passage 3. The light oil has a high temperature in the fuel passage 13 and the low-boiling components have already been vaporized.
The inside is rapidly reduced in pressure from the high pressure state by the opening of the injection valve 12, so that the gas instantaneously evaporates. Therefore, the NO _X absorbent 5 only gaseous diesel fuel is supplied, the foregoing by the arrival of the liquid component of the diesel fuel problems are prevented.

In the above embodiment, the fuel supply device 1
A shutoff valve 15 that opens and closes in response to a signal from the ECU 20 is provided between the fuel passage 4 and the fuel passage 13, but instead of the shutoff valve 15, a check valve that prevents backflow of light oil from the fuel passage 13 to the fuel supply device 14. It is good also as composition provided with a valve. In this case, when the injection valve 12 is opened during the regeneration operation and the pressure in the fuel passage 13 falls below the fuel supply pressure, light oil is automatically fed from the fuel supply device 14 into the fuel passage 13 through the check valve. , The opening and closing operation of the shut-off valve 15 becomes unnecessary.

In the present embodiment, the amount of light oil supplied to the NO _X absorbent 5 depends on the fuel passage 1 between the shutoff valve 15 and the injection valve 12.
3 and the fuel supply pressure of the fuel supply device 14. In this embodiment, the heat exchange portion 13a of the fuel passage 13 is provided around the exhaust pipe 3. However, if the heat exchange portion 13a is arranged in the exhaust pipe 3 as shown in FIG. Can be maintained at a higher temperature and a higher pressure.

Next, FIG. 4 shows another embodiment of the present invention.
In the present embodiment, the heat exchange portion 13a of the fuel passage 13 is in the form of a container having a relatively large capacity formed around the exhaust pipe 3. A fuel recovery passage 17 is connected to a lower part of the heat exchange part 13a via a shutoff valve 16, and the injection valve 12 is connected to an upper part of the heat exchange part 13a. In this embodiment, when the light oil in the heat exchange unit 13a is heated to a high-temperature and high-pressure state, the gasified low-boiling component of the light oil is removed from the heat exchange unit 1a.
A high boiling point component that fills the upper part of 3a and does not evaporate remains in the lower part as a liquid. When the injection valve 12 is opened, light oil in the heat exchange section 13 is injected into the exhaust pipe 3, but since the injection valve 12 is connected to the upper part of the heat exchange section 13 a, the upper part is vaporized from the injection valve 12. Low boiling point component and heat exchange unit 1
Only high-boiling components vaporized by the reduced pressure in 3 are injected. Thus, the adhesion of the liquid component into _the NO _X absorbent 5 since only gaseous diesel fuel is injected can be more reliably prevented from the injection valve 12.

In this embodiment, after the regeneration operation is completed, the shut-off valve 16 below the heat exchange section 13a is opened, and the heat exchange section 13a is opened.
The high-boiling components remaining as liquid in the recovery passage 17
And the upper shutoff valve 15 is opened simultaneously with the opening of the lower shutoff valve 16, and light oil is supplied from the fuel supply device 14 to the heat exchange unit 13 a, and The replacement of light oil is performed. The upper shut-off valve 15 closes a predetermined time after the lower shut-off valve 16 closes, during which time the heat exchange unit 13a is filled with a predetermined amount of fresh light oil.

FIG. 5 shows still another embodiment of the present invention. In this embodiment, the reducing agent supply device 11 is not provided with the heat exchange unit as in the above-described embodiment, and the preheating chamber 18 in which the heat storage body 18a for vaporization is built in the exhaust passage 3 downstream of the injection valve 12 is provided. Is provided. Heat storage 18
“a” is made of a porous material such as a ceramic sintered material, and has a passage 19 in the exhaust flow direction formed therein as shown in FIG. The passage 19 is a passage 19 whose downstream end is closed.
a and the passage 19b whose upstream end is closed are alternately arranged, and the exhaust gas flows into the heat storage body 18a from the passage 19a, passes through the wall surface 19c separating the passages 19a and 19b, and flows out from the passage 19b. It is supposed to.

[0029] In this embodiment, the regenerator 18a becomes a high temperature is heated by the exhaust gas passing through when _the NO _X absorbent 5 is performing the absorption of NO _X. NO During _X regenerating operation of the absorber 5, the atomized gas oil injected from the injection valve 12 flows into the regenerator 18a together with the exhaust gas. At this time, the high boiling point component of the light oil flows into the heat storage body 18a as it is in a liquid state, but the exhaust gas flows through the wall surface 19c separating the passages 19a and 19b of the heat storage body 18a.
Because it is trapped when passing through the, and exhaust in the NO _X absorbent 5 on the downstream side of the regenerator 18a, only the vaporized component of the gas oil arrives. The high-boiling components of the gas oil trapped in the regenerator 18a in order to vaporize depriving heat of vaporization from the hot regenerator 18a, the temperature of the NO _X absorbent 5 is not lowered during vaporization of high boiling components. When the exhaust gas temperature is low, a part of the high boiling point component of the light oil trapped in the heat storage element 18a remains in the heat storage element 18a in a liquid state, but the load on the engine increases and the exhaust temperature increases. It flows out vaporized by the regenerator 18a when, NO _X absorbent 5
Therefore, the exhaust passage of the heat storage body 18a is not blocked, and the emission of HC, CO, etc. does not deteriorate. In this embodiment, the heat insulating material 18b is provided on the outside of the preheating chamber 18 to prevent heat dissipation from the regenerator 18a, it has been to maintain a high-temperature regenerator 18a
You .

[0030] In the embodiments described above, when the exhaust temperature is relatively low is considered is a case where part of the high-boiling components of the gas oil to reach the left _the NO _X absorbent 5 in a liquid,
The amount of the liquid component to arrive as described above is small, also, _the NO _X absorbent and the temperature of the NO _X absorbent 5 is raised by heat generated by the oxidation reaction of the vaporized component having reached prior to the liquid components 5 liquid components reaching the even vaporized rapidly, does not lead to results in decreased activity or low poisoning of the NO _X absorbent 5.

[0031]

According to the present invention, N is reduced by using a liquid reducing agent.
O_XWhen regenerating the absorbent, NO _XSupply to absorbent
Means to preheat the liquid reducing agent before
NO_XDue to the fact that the reducing agent reaches the absorbent in a liquid state
NO_XPrevents a decrease in the activity of the absorbent and the occurrence of low-temperature poisoning.
NO by simple means using body reducing agent_XRegeneration operation of absorbent
It can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of an exhaust gas purification device of the present invention.

FIG. 2 is a diagram illustrating an example of a configuration of a reducing agent supply device in FIG. 1;

FIG. 3 is a diagram illustrating an example of a configuration of a reducing agent supply device in FIG. 1;

FIG. 4 is a diagram illustrating an example of a configuration of a reducing agent supply device in FIG. 1;

FIG. 5 is a view showing a second embodiment of the exhaust gas purification apparatus of the present invention.

FIG. 6 is a diagram showing a configuration of a heat storage body of FIG.

FIG. 7 is a diagram illustrating the NO _X absorption / release action of the NO _X absorbent.

[Explanation of symbols]

1 ... diesel engine 2 ... intake pipe 3 ... exhaust pipe 5 ... NO _X absorbent 6 ... shutter valve 7 ... actuator 11 ... reducing agent supply device 12 ... injection valves 13 ... fuel passage 13a ... heat exchange portion 14 ... Fuel supply device 15 ... Shutoff valve 16 ... Shutoff valve 17 ... Recovery passage 18 ... Preheating chamber 18a ... Regenerator 19 ... Exhaust passage 20 ... ECU

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-62-106826 (JP, A) JP-A-4-54926 (JP, U) Patent 2600492 (JP, B2)

Claims (1)

(57) [Claims] An air-fuel ratio of an inflowing exhaust gas is lean.
Absorbs NO _X in Rutoki, concentrated oxygen in the exhaust gas flowing
NO _X absorbent to release the NO _X absorbed to decrease the degree
Place the engine in the engine exhaust passage, and
The NO _X absorbent allowed to flow through the exhaust gas, NO _X absorption
The NO _X absorbent when the exhaust gas flowing into the lean to agent
In the exhaust gas that flows the absorbed NO _X into the NO _X absorbent
From _the NO _X absorbent when the oxygen concentration was allowed to decrease
In the exhaust purification system of an internal combustion engine which is adapted to emit, _the NO _X absorbent by supplying a liquid reducing agent to the _the NO _X absorbent
To reduce the oxygen concentration in the exhaust gas flowing into the
NO _X absorbed NO _X absorbed in the more _the NO _X absorbent
Together to release from the dosage, supplied to the _the NO _X absorbent
An exhaust gas purification device for an internal combustion engine, further comprising a reductant preheating means for preheating a liquid reductant .