JPH06272539A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To enable the use of a liquid reducing agent for an NOx absorbent regenerating operation by solving problems of activity degradation and low temperature toxic damage of NOx absorbent caused by the deposition of ungasified component when the NOx absorbent is regenerated by the use of the liquid reducing agent. CONSTITUTION:An NOx absorbent 5 is disposed in an exhaust pipe 3 of an internal combustion engine and a reducing agent supply device 11 for supplying a liquid reducing agent like light oil is disposed in the upstream of the NOx absorbent 5. A heat exchange section 13a for preheating the liquid reducing agent with the heat of exhaust gas in the exhaust pipe is provided in a supply path 13 for supplying the reducing agent to a reducing agent injection valve 12 of the reducing agent supply device 11. Since the liquid reducing agent is gasified by the preheating section 13a, an amount of ungasified component reaching the NOx absorbent is reduced.

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 internal combustion engine that burns at a lean air-fuel ratio in most operating regions such as a diesel engine and a gasoline engine that performs lean combustion. The present invention relates to an exhaust gas purification device that can effectively remove NO _X in exhaust gas.

[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 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 In such a case, when exhaust gas is blocked from flowing into the absorbent and a gaseous reducing agent is supplied to the absorbent, NO _x is released from the absorbent and the released NO _x is reduced and purified. Is.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the exhaust gas purification device of Japanese Patent No. 6826, a gaseous reducing agent such as hydrogen is supplied to the NO _X absorbent in order to perform NO _X release from the NO _X absorbent and reduction purification (hereinafter referred to as “regeneration”). There is. However, a 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 particularly when used in an internal combustion engine for vehicles.

Therefore, it is preferable to use a liquid reducing agent which is easy to handle as the reducing agent used for regenerating the NO _x absorbent. Further, in order to eliminate 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 a liquid reducing agent, if possible. However, especially liquid fuels such as light oil contain many components having different boiling points, and also contain components that are difficult to vaporize when the exhaust temperature is low. For this reason, these liquid fuels are directly used for NO
_When injected into the exhaust passage on the upstream side of the _X absorbent, the component with a high boiling point is not vaporized and remains in a mist state with the exhaust flow.
_It may reach the _X absorbent. In this case NO _X
The fuel that has reached the absorbent adheres to the absorbent surface in a liquid state and forms a layer covering the absorbent surface.

The liquid fuel adhering to the surface of the NO _x absorbent is
When the temperature of the absorbent is high to some extent, it receives the heat of the absorbent to be vaporized and acts 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 fall below the activation temperature. Therefore, if liquid fuel such as light oil is used as the 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, when the temperature of the NO _x absorbent falls below the vaporization temperature of the fuel, the fuel adhering to the absorbent no longer vaporizes and covers the surface of the NO _x absorbent, reducing the effective surface area and reducing the amount of NO _x . absorption, release effect is inhibited, in some cases problems of cold poisoning called _the NO _X absorbent occurs. For the above reasons, conventionally, when liquid fuel such as light oil is used as a reducing agent, a burner or the like is provided in the exhaust passage to incompletely burn the liquid fuel and the generated gas such as HC or CO is used as the reducing agent. _X absorbent had to be supplied. However, it is not preferable from a safety point of view to provide a burner or the like in the exhaust passage for combustion, and there is a problem that the structure becomes complicated because the burner and its auxiliary equipment are provided in the exhaust passage.

An object of the present invention is to solve the above problems and to provide an exhaust gas purifying apparatus for an internal combustion engine which can use a liquid fuel such as light oil as a reducing agent for an NO _X absorbent.

[0008]

According to the present invention SUMMARY OF], in an exhaust passage of an internal combustion engine capable of performing combustion of the lean air-fuel ratio, the air-fuel ratio of the inflowing exhaust is absorbed inflowing exhaust the NO _X when the lean oxygen concentration place _the NO _X absorbent to release the absorbed NO _X when lowered, the NO _X in the exhaust gas is absorbed, by supplying the liquid reducing agent to the _the NO _X absorbent after NO _X absorbing NO _X the NO _X absorbed from the absorbent causes release in the exhaust purification system for an internal combustion engine to reduce and purify the NO _X, characterized in that it comprises a reducing agent preheating means for preheating the supply liquid reducing agent to the _the NO _X absorbent An exhaust gas purification device for an internal combustion engine is provided.

[0009]

The liquid fuel supplied to the exhaust passage on the upstream side of the NO _x absorbent is preheated and vaporized by the preheating means before being supplied, so that the liquid fuel that reaches the NO _x absorbent in a liquid state is reduced and the NO _x absorbent is absorbed. The temperature drop of the agent is prevented. For this reason,
There is no problem of reduced activity of the NO _x absorbent and low temperature poisoning.

[0010]

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

[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
The valve is closed to a predetermined opening when the O _X is regenerated, and the exhaust pipe 3 is throttled to reduce the amount of exhaust gas passing through the NO _X absorbent 5. Reference numeral 7 is an actuator of an appropriate type 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. Reference numeral 20 in the drawing denotes an electronic control unit (ECU) of the engine 1. The ECU 20 is a CPU,
The RAM, the ROM, the input port, and the output port are connected to each other by a bidirectional bus, and are composed of known digital computers to perform basic control such as fuel injection amount control of the engine. In this embodiment, an exhaust shutter valve is also provided. The opening / closing control of 6 and the reducing agent supply control from the reducing agent supply device 11 are performed. For these controls, signals such as exhaust temperature, engine speed, accelerator opening, etc. are input to the input ports of the ECU 20 from sensors not shown.

As the NO _x absorbent 5, for example, a carrier such as alumina is used, and on this carrier, an alkali metal such as potassium K, sodium Na, lithium Li, cesium Cs, or an alkaline earth such as barium Ba or calcium Ca is used. At least one selected from rare earths such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt are supported. 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 exhaust air-fuel ratio is N in this case.
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 fuel, reducing agent or air is not supplied to the upstream side exhaust passage of, 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 absorbent 5 absorbs NO _{X in} the exhaust. Further, when the reducing agent is introduced into the exhaust gas from the reducing agent supply device 11 and the oxygen concentration is reduced, the NO _x absorbent 5 releases the absorbed reducing agent. There are some points where the detailed mechanism of this absorption / release action is not clear. However, it is considered that this absorbing / releasing action is performed by the mechanism shown in FIG. Next, this mechanism will be described by taking as an example the 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 inflow exhaust becomes considerably lean, the oxygen concentration in the inflow exhaust greatly increases, and as shown in FIG. 7 (A), the oxygen O ₂ is in the form of 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 to generate NO ₂
(2NO + O ₂ → 2NO ₂ ). Next, a part of the generated NO ₂ is oxidized on the platinum Pt, absorbed in the absorbent and bonded to the barium oxide BaO, and as shown in FIG.
As shown in ( ₃ ), it diffuses into the absorbent in the form of nitrate ion NO ₃ ⁻ . In this way, NO _X is absorbed in the NO _X absorbent 5.

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 oxygen concentration decreases and the amount of NO ₂ is reduced by reaction backward in the inflowing exhaust gas (NO ₃ ^- → NO ₂₎ proceeds to thus of the absorbent and nitrate ions NO ₃ ^- is NO ₂ Is 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, 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. In addition, NO ₂ released from the NO _X absorbent 5 due to a decrease in 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 platinum Pt in this manner, 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. As the reducing agent used for the NO _x releasing and reducing operation (regenerating operation) of the NO _x absorbent 5,
It is sufficient if it produces a reducing component such as hydrocarbon or carbon monoxide in exhaust gas, hydrogen, gas such as carbon monoxide, liquid or gaseous hydrocarbon such as propane, propylene, butane,
Liquid fuels such as gasoline, light oil, and kerosene can be used,
In this embodiment, as described above, light oil, which is the fuel of the diesel engine 1, is used as the reducing agent in order to avoid the complexity of storage, replenishment, and the like.

Next, the reducing agent supply device 11 of this embodiment will be described with reference to FIG. As described above, when light oil is used as the reducing agent, there arises a problem that the high boiling point components in the light oil adhere to the NO _X absorbent 5 in a liquid state. In the present embodiment, as described below, the problem of the liquid fuel adhesion is solved by preheating the light oil supplied from the reducing agent supply device 11.

In FIG. 2, the reducing agent supply device 11 includes an injection valve 12 disposed upstream of the NO _x absorbent 5 in the exhaust pipe 3.
Is equipped with. 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 the fuel supply device 14 of the diesel engine 1 to a shutoff valve 15 which opens and closes in response to a control signal from the ECU 20.
Pressure is supplied to the injection valve 12 through the fuel passage 13 and the fuel passage 13. In the present embodiment, the fuel passage 13 is provided with a heat exchange section 13a wound around the exhaust pipe 3 so that the heat of the exhaust gas in the exhaust pipe 3 preheats the light oil in the heat exchange section 13a. It has become.

In this embodiment, when the regeneration operation of the NO _x absorbent 5 is completed (that is, the injection of the light oil is completed and the injection valve 12 is closed), the shutoff valve 1 is triggered by a signal from the ECU 20.
5 opens. As a result, 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. When a predetermined time has elapsed, the shutoff valve 15 is closed, and the fuel passage 13 between the shutoff valve 15 and the injection valve 12 is closed.
Is kept sealed at both ends.

The light oil held in the fuel passage 13 is heated by receiving the heat of the exhaust gas via the heat exchanging portion 13a in this sealed state until the next regeneration operation is started. Therefore, the temperature of the light oil in the fuel passage 13 rises, and the pressure rises due to the rise of the vapor pressure, so that the high temperature,
High pressure. Next, when the regeneration condition of the NO _X absorbent 5 is satisfied, the injection valve 12 is opened by the signal of the ECU 20. As a result, 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 point component has already vaporized, but the high-boiling point component that remains in the liquid state also remains in the fuel passage 13.
The inside is rapidly depressurized from the high pressure state due to the opening of the injection valve 12, so that it is instantly vaporized. Therefore, only the gaseous light oil is supplied to the NO _x absorbent 5, and the above-mentioned problems due to the arrival of the liquid component of the light oil are prevented.

In the above embodiment, the fuel supply system 1
4 and the fuel passage 13 are provided with a shut-off valve 15 which opens and closes in response to a signal from the ECU 20, but instead of the shut-off valve 15, a non-return valve for preventing back flow of light oil from the fuel passage 13 to the fuel supply device 14. A valve may be provided. In this case, when the injection valve 12 is opened during the regeneration operation and the pressure in the fuel passage 13 drops below the fuel supply pressure, the fuel oil is automatically fed from the fuel supply device 14 into the fuel passage 13 through the check valve. Therefore, it is not necessary to open / close the shutoff valve 15.

In this embodiment, the amount of light oil supplied to the NO _x absorbent 5 is controlled by 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. Further, in the present embodiment, the heat exchange portion 13a of the fuel passage 13 is provided around the exhaust pipe 3, but if the heat exchange portion 13a is arranged in the exhaust pipe 3 as shown in FIG. Can be maintained in a high temperature and high pressure state.

Next, FIG. 4 shows another embodiment of the present invention.
In this embodiment, the heat exchange portion 13a of the fuel passage 13 is in the form of a container formed around the exhaust pipe 3 and having a relatively large capacity. Further, 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 the present embodiment, when the light oil in the heat exchange section 13a is heated to a high temperature and high pressure state, the vaporized low boiling point component of the light oil is transferred to the heat exchange section 1
A high-boiling component that fills the upper part of 3a and does not vaporize remains in the lower part as a liquid. When the injection valve 12 opens, the light oil in the heat exchange part 13 is injected into the exhaust pipe 3, but since the injection valve 12 is connected to the upper part of the heat exchange part 13a, the upper part of the injection valve 12 vaporizes. Low boiling point component and heat exchange part 1
Only the high boiling point component vaporized by the pressure reduction in 3 is injected. For this reason, since only the gaseous light oil is injected from the injection valve 12, it is possible to more reliably prevent the liquid component from adhering to the NO _X absorbent 5.

In this embodiment, after the regeneration operation is completed, the shutoff valve 16 below the heat exchange section 13a is opened, and the heat exchange section 13a is opened.
The high boiling point component that remains as a liquid inside the recovery passageway 17
And the upper cutoff valve 15 opens simultaneously with the opening of the lower cutoff valve 16, and the light oil is supplied from the fuel supply device 14 to the heat exchange section 13a to collect the heat in the heat exchange section 13a. Light oil is replaced. The upper cutoff valve 15 is closed after a predetermined time has elapsed after the lower cutoff valve 16 was closed, and during that time, the heat exchange section 13a is filled with a predetermined amount of new light oil.

Next, FIG. 5 shows still another embodiment of the present invention. In the present embodiment, the reducing agent supply device 11 is not provided with the heat exchange portion as in the above-described embodiment, and the preheating chamber 18 in which the vaporization heat storage body 18a is built in the exhaust passage 3 on the downstream side of the injection valve 12 is provided. The difference is that is provided. Heat storage body 18
Reference symbol a is made of a porous material such as a ceramic sintered material, and as shown in FIG. 6, a passage 19 in the exhaust flow direction is formed inside. The passage 19 is a passage 19 whose downstream end is closed.
a and a 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 do.

[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. During the regeneration operation of the NO _x absorbent 5, the mist-like light oil injected from the injection valve 12 flows into the heat storage body 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 in a liquid state, but the exhaust wall surface 19c that separates the passages 19a and 19b of the heat storage body 18a.
Since it is trapped when passing through the exhaust gas, only the exhaust gas and the vaporized component of light oil reach the NO _X absorbent 5 on the downstream side of the heat storage body 18a. Further, since the high boiling point component of the light oil trapped in the heat storage body 18a deprives the heat of vaporization from the high temperature heat storage body 18a and is vaporized, the temperature of the NO _x absorbent 5 does not drop when the high boiling point component is vaporized. Further, when the exhaust gas temperature is low, a part of the high boiling point component of the light oil trapped in the heat storage material 18a remains in the heat storage material 18a in a liquid state, but the engine load increases and the exhaust gas temperature rises. When it does, it vaporizes and flows out from the heat storage body 18a, and the NO _x absorbent 5
Since it is oxidized by the catalytic action of the above, the exhaust passage of the heat storage body 18a is not blocked, and the emissions of HC, CO, etc. do not deteriorate. In this embodiment, a heat insulating material 18b is provided outside the preheating chamber 18 to prevent heat from being dissipated from the heat storage body 18a and to keep the heat storage body 18a at a high temperature.

In the embodiment described above, when the exhaust temperature is relatively low, it is possible that a part of the high boiling point component of the light oil reaches the NO _x absorbent 5 in a liquid state.
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 The liquid component that has reached the point (3) is also promptly vaporized, and the activity of the NO _x absorbent 5 and low temperature poisoning do not occur.

[0031]

According to the present invention, N
O_XNO when regenerating the absorbent _XSupply to absorbent
By providing a means for preheating the liquid reducing agent before
NO_XDue to the reducing agent reaching the absorbent in a liquid state
NO_XPrevents the activity of the absorbent from decreasing 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 drawings]

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

FIG. 2 is a diagram showing an example of a configuration of the reducing agent supply device of FIG.

FIG. 3 is a diagram showing an example of a configuration of the reducing agent supply device of FIG.

FIG. 4 is a diagram showing an example of a configuration of the reducing agent supply device of FIG.

FIG. 5 is a diagram showing a second embodiment of the exhaust emission control device of the present invention.

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

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

[Explanation of symbols]

DESCRIPTION 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 valve 13 ... Fuel passage 13a ... Heat exchange part 14 ... Fuel supply device 15 ... shut-off valve 16 ... shut-off valve 17 ... recovery passage 18 ... preheating chamber 18a ... heat storage body 19 ... exhaust passage 20 ... ECU

Claims (1)

[Claims] In an exhaust passage of claim 1 an internal combustion engine capable of performing combustion of the lean air-fuel ratio, the air-fuel ratio of the inflowing exhaust gas is the oxygen concentration of the inflowing exhaust absorbs NO _X when the lean absorbed when reduced NO place _the NO _X absorbent to release the _X, the NO _X in the exhaust gas is absorbed to release the _the NO _X absorbent NO _X which the liquid reducing agent is supplied and absorbed from _the NO _X absorbent in after NO _X absorbent the in the exhaust purification device for an internal combustion engine NO _X to reduce and purify the _the NO _X absorbent exhaust purification system of an internal combustion engine, characterized in that it comprises a reducing agent preheating means for preheating the supply liquid reducing agent together.