JP2845052B2 - 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.

[0002]

2. Description of the Related Art When the air-fuel ratio of exhaust gas is lean, the present applicant absorbs NOx, and the air-fuel ratio of exhaust gas becomes stoichiometric.
(Stoichiometric air-fuel ratio) or NOx absorbed when rich
A NOx absorption / release catalyst for releasing NOx and reducing the released NOx is disposed in a diesel engine exhaust passage;
NOx is released from the Ox absorption / release catalyst and the released N
There has been proposed an exhaust gas purifying apparatus for an internal combustion engine in which a reducing agent is supplied to a NOx absorption / release catalyst and burned when Ox is reduced.

[0003]

However, in this apparatus, when the exhaust gas temperature is low and the catalyst does not reach the activation temperature during the release and reduction of the NOx absorbed by the NOx absorption and release catalyst, the reducing agent is a catalyst. Since combustion does not occur, the amount of oxygen in the exhaust gas does not decrease. As a result, there is a problem that NOx is not released from the NOx absorption / release catalyst, or even if NOx is released, reduction and purification are not sufficiently performed.

[0004]

According to the present invention for solving the above problems, NOx is absorbed when the air-fuel ratio of exhaust gas is lean, and is absorbed when the air-fuel ratio of exhaust gas is stoichiometric or rich. A NOx absorption / release catalyst for releasing NOx and reducing the released NOx is disposed in the engine exhaust passage. When NOx is released and reduced from the NOx absorption / release catalyst, a reducing agent is supplied to the NOx absorption / release catalyst to burn it. , The upstream end of the NOx adsorbing / releasing catalyst to promote the start of combustion of the reducing agent on the NOx adsorbing / releasing catalyst.
The amount of platinum carried in
You have more than your holdings .

[0005]

When the NOx is released and reduced from the NOx absorption / release catalyst, a reducing agent is supplied to the NOx absorption / release catalyst and burned. As a result, oxygen in the exhaust gas in the NOx absorption / desorption catalyst is consumed and the oxygen concentration is reduced. Therefore, NOx is released from the NOx absorption / desorption catalyst and reduced by the reducing agent.

[0006] The white at the upstream end of the NOx absorption / desorption catalyst
The amount of supported gold is higher than the amount of supported platinum in other parts.
By increasing the number, the start of combustion of the reducing agent in the NOx adsorbing / releasing catalyst is promoted. Therefore, even when the exhaust gas is at a low temperature, the reducing agent is started to burn, so that NOx can be surely reduced.

[0007]

Referring to FIG. 1, reference numeral 2 denotes a diesel engine main body, 4 denotes an intake passage, and 6 denotes an exhaust passage. An intake throttle valve 8 is provided in the intake passage 4, and the intake throttle valve 8 is normally fully opened. In the middle of the exhaust passage 6, N
A casing 12 containing an Ox absorption / release catalyst 10 is provided. A fuel supply device 14 for supplying fuel as a reducing agent is disposed in the exhaust passage 6 upstream of the casing 12.

[0008] NOx contained in the casing 12
The adsorption / desorption catalyst 10 uses, for example, alumina as a carrier, and, for example, potassium K, sodium Na, lithium L
i, alkali metal such as cesium Cs, barium B
a, alkaline earth such as calcium Ca, lanthanum L
a, at least one selected from rare earths such as yttrium Y and a noble metal such as platinum Pt are supported. The NOx absorption / release catalyst 10 absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and performs an absorption / release operation of the NOx that releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases.

If the above-described NOx adsorbing / releasing catalyst 10 is disposed in the engine exhaust passage, the NOx adsorbing / releasing catalyst 10 actually
Ox is absorbed and released, but the detailed mechanism of the absorption and release 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 other noble metals, alkali metals,
The same mechanism can be obtained by using 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.
As shown in (A), these oxygens O ₂ adhere to the surface of platinum Pt in the form of O ₂ ⁻ . On the other hand, N
O is O ₂ on the surface of the platinum Pt ^- reacted with, and _{NO 2 (2NO + O 2 →} 2NO 2). NO ₂ generated
Is partially oxidized on platinum Pt while absorbing and releasing catalyst 10
Is absorbed while bonding with the barium oxide BaO within, nitrate ions NO ₃ as shown in FIG. 2 (A) ^- diffuses into absorbing and releasing catalyst 10 in the form of. In this way, NOx becomes N
It is absorbed in the Ox absorption / desorption catalyst 10.

As long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is generated on the surface of the platinum Pt,
As long as the x absorption capacity is not saturated, NO ₂ is absorbed in the absorption / desorption catalyst 10 to generate nitrate ions NO ₃ ⁻ . 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 opposite direction (NO ₃ ⁻ → NO ₂ ), and thus the nitrate ion NO ₃ ^-
There are released from the absorbent in the form of NO _2. That is, when the oxygen concentration in the inflowing exhaust gas decreases, NOx is released from the NOx absorption / release catalyst 10. If the degree of leanness of the inflowing exhaust gas decreases, the concentration of oxygen in the inflowing exhaust gas decreases. Therefore, if the degree of leanness of the inflowing exhaust gas decreases, NOx is released from the NOx absorption / release catalyst 10.

On the other hand, at this time, the air-fuel ratio of the inflowing exhaust gas is reset.
HC, CO is oxygen O on platinum Pt._Two ^-When
Reacts and oxidizes. Also, the air-fuel
When the ratio is made rich, the oxygen concentration in the inflow exhaust gas becomes extremely high.
NO from the adsorption / desorption catalyst 10_TwoIs released,
This NO_TwoAre the unburned HC and C as shown in FIG.
It reacts with O and is reduced and purified. White in this way
NO on the surface of gold Pt _TwoIs no longer present
NO from 10 to next from 10_TwoIs released. Therefore inflow
If the air-fuel ratio of the exhaust gas is made rich, NO
x NOx is released from the x absorption / desorption catalyst 10 and reduced and purified.
Will be.

As described above, when the air-fuel ratio of the inflowing exhaust gas becomes lean, NOx is absorbed by the NOx adsorbing / releasing catalyst 10, and when the air-fuel ratio of the inflowing exhaust gas is made rich, NOx is released from the NOx adsorbing / releasing catalyst 10 within a short time. Released and reduced. In a diesel engine, the exhaust gas is not always rich or stoichiometric, and is always lean. Therefore, when the NOx absorbed and released by the NOx absorption / desorption catalyst 10 is released and reduced, the fuel supply device 14 supplies the NOx to the exhaust passage 6.
The fuel is supplied inside. The supplied fuel is burned by the NOx adsorbing / releasing catalyst 10, whereby the oxygen in the exhaust gas in the NOx adsorbing / releasing catalyst 10 is consumed and the oxygen concentration is reduced.
NOx is released from the gas and is reduced and purified.

However, when the temperature of the exhaust gas is low and the NOx adsorbing / releasing catalyst 10 has not reached the activation temperature, the fuel supplied into the exhaust passage 6 does not burn in the NOx adsorbing / releasing catalyst 10, so that the As a result, there arises a problem that NOx is not released from the NOx adsorbing and releasing catalyst, or even if NOx is released, it is not sufficiently reduced and purified.

Therefore, in the first embodiment, as shown in FIG. 3, platinum Pt is carried on the upstream end portion 10a of the NOx adsorbing / releasing catalyst 10 at a high level, and platinum Pt is carried on the other portion 10b.
t is carried in an ordinary amount. As a result, the catalyst activation temperature at the upstream end portion 10a can be lowered, and therefore, even if the exhaust gas temperature is low, the fuel can be reduced to NO.
x The combustion can be started at the upstream end 10a of the adsorption / desorption catalyst 10. When the combustion of the fuel is started at the upstream end portion 10a, the NOx absorption / desorption catalyst 1 is generated by the generated heat.
The other portion 10b of 0 is also heated to a temperature equal to or higher than the catalyst activation temperature, and combustion of the fuel is started. As a result, NOx
Oxygen in the exhaust gas in the adsorption / desorption catalyst 10 is consumed and the oxygen concentration is reduced.
Ox is released and reduced and purified.

Next, a second embodiment will be described. Second
In the embodiment, the NOx absorbed and released by the
When the NOx adsorbing / releasing catalyst 10 has not reached the activation temperature in the case of reducing by releasing x, the intake throttle valve 8
Of the intake air is reduced, thereby reducing the intake air amount. As a result, the temperature of the exhaust gas flowing into the NOx adsorbing / releasing catalyst 10 is increased, the NOx adsorbing / releasing catalyst 10 reaches the activation temperature, and the fuel supplied to the exhaust passage is started to burn. When the fuel starts burning, the NOx adsorbing / releasing catalyst 10 is maintained at a temperature equal to or higher than the activation temperature by the generated heat. Therefore, the opening degree of the intake throttle valve 8 may be reduced only at the fuel combustion starting time. The throttle amount of the intake throttle valve 8 is set so that the intake air amount is reduced to such an extent that the operation of the engine is not hindered.

Next, a third embodiment will be described. Third
In the embodiment, the electric heater 16 is disposed in the casing 12 upstream of the NOx absorption / release catalyst 10. When the NOx absorbed and released by the NOx absorption and release catalyst 10 is released and reduced, and the NOx absorption and release catalyst 10 has not reached the activation temperature, the heater 16 is energized to activate the NOx absorption and release catalyst 10. It should be higher than the temperature. The heater 16 needs to be energized only when the fuel starts to be burned by the NOx absorption / release catalyst 10.

Note that the combustion promoting means is not limited to the above-described one, but is a case where the NOx absorbed and released by the NOx absorbing and releasing catalyst 10 is released and reduced, and the NOx absorbing and releasing catalyst 10 does not reach the activation temperature. A highly reactive gas such as hydrogen, propylene, propane, or a highly volatile liquid such as gasoline may be injected upstream of the NOx absorption / desorption catalyst 10, and an electric load (alternator, blower, etc.) )
Alternatively, the physical load (air conditioner, torque converter, etc.) may be increased to increase the exhaust gas temperature.

Although the present embodiment has been described with reference to a diesel engine, the present invention can also be applied to a gasoline engine.

[0020]

Effect of the Invention At the upstream end of the NOx absorption / release catalyst
The supported amount of platinum is calculated from the supported amount of platinum in other parts.
When the exhaust gas temperature is low, the start of combustion of the reducing agent is promoted, and NOx can be reliably reduced.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining an absorption / release effect of NOx.

FIG. 3 is a view showing a NOx absorption / release catalyst according to a first embodiment of the present invention.

FIG. 4 is a view showing a NOx storage / release catalyst according to a third embodiment of the present invention.

[Explanation of symbols]

 2: Diesel engine body 6: Exhaust passage 8: Intake throttle valve 10: NOx absorption / release catalyst 14: Fuel supply device

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F01N 3/08 F01N 3/18 F01N 3/28 301

Claims (1)

(57) [Claims] 1. When the air-fuel ratio of exhaust gas is lean, N
When the air-fuel ratio of the exhaust gas is stoichiometric or rich, a NOx absorbing / releasing catalyst for releasing the absorbed NOx and reducing the released NOx is disposed in the engine exhaust passage, and the NOx absorbing / releasing catalyst removes the NOx from the NOx absorbing / releasing catalyst. At the time of release and reduction, a reducing agent is supplied to the NOx absorption / release catalyst to burn it, and upstream of the NOx absorption / release catalyst to promote the start of combustion of the reducing agent at the NOx absorption / release catalyst.
The amount of platinum carried on the side
An exhaust gas purification device for an internal combustion engine that has a larger amount of gold carried .