JPH0598944A - Device for reducing nitrogen oxides of diesel engine - Google Patents

Abstract

PURPOSE:To reduce the total quantity of NOx even if the exhaust temperature is changed with the fluctuation of an engine load. CONSTITUTION:A nitrogen oxides reducing device is provided with multiple catalyst carrying filters 2a-2c, which are arranged separately inside of an exhaust pipe 1 of an engine, a temperature sensor 7 provided inside of the exhaust pipe, and means 5a, 5b for passing the exhaust selectively to the multiple catalyst carrying filters 2a-2c. The exhaust flow quantity per a volume occupied with the catalyst is changed by the exhaust temperature.

Description

Detailed Description of the Invention

[0001]

The present invention relates, in a diesel engine, an apparatus for reducing the NO _X (nitrogen oxides).

[0002]

2. Description of the Related Art Conventionally, as one of the methods for reducing NO _x contained in the exhaust gas of a diesel engine, there is a method of connecting a catalytic converter to the engine exhaust system and reducing the NO _x by a reduction catalyst. At present, as this reduction catalyst, a method of using a zeolite-based catalyst with a hydrocarbon as a reducing agent is drawing attention.

[0003]

By the way, when the above zeolite-based catalyst is used, the NO _X reduction rate depends on the exhaust temperature and the exhaust gas flow rate (SV: space velocity) per volume occupied by the catalyst, as shown in FIG. Change. That is, when the exhaust gas flow rate (SV) per volume is fixed, the maximum NO _X reduction rate is exhibited at a certain exhaust temperature, and the NO _X reduction rate is lowered below that temperature, and this NO _X reduction rate is also higher. The curve shows the exhaust gas flow rate (S
V), and when SV is increased, the NO _X reduction rate tends to decrease.

However, in the conventional catalytic converter, since the volume occupied by the catalyst is fixed, when the exhaust gas temperature greatly changes due to the engine load, NO _x is generated.
The reduction rate will be greatly influenced. For example, when the exhaust gas flow rate SV = a ₂ per volume, the exhaust temperature is 500
The NO _x reduction rate is 65% at ℃, but the exhaust temperature is 30
At 0 ° C., the NO _X reduction rate is 10%, and there is a problem that the NO _X reduction rate is significantly reduced due to the engine load.

The present invention solves the above problems and provides a nitrogen oxide reducing apparatus for a diesel engine, which can reduce the total NO _x even if the exhaust temperature changes due to changes in the engine load. With the goal.

[0006]

To this end, a nitrogen oxide reduction apparatus for a diesel engine according to the present invention comprises a plurality of catalyst-carrying filters 2 which are arranged separately in an exhaust pipe 1 of the engine.
a, 2b, 2c and the temperature sensor 7 provided in the exhaust pipe
And means 5a, 5b for selectively passing the exhaust gas through the plurality of catalyst-carrying filters 2a, 2b, 2c, and changing the exhaust gas flow rate per volume occupied by the catalyst depending on the exhaust gas temperature. The numbers added to the above-mentioned configurations are for comparison with the drawings for easy understanding, and the configurations of the present invention are not limited thereto.

[0007]

In the present invention, for example, as shown in FIG.
If the exhaust gas temperature T ₀ is less than T _1, the NO _X removal along the NO _X reduction rate curve of the exhaust gas flow rate per volume occupied by the catalyst as a SV = a _1, the exhaust gas temperature T
₀ above T _1, if T ₂ or less, the exhaust gas flow rate per volume is increased with SV = a _2, the NO _X removal along the NO _X reduction rate curve, the exhaust gas temperature T ₀ is T ₂ if more greater, the exhaust gas flow rate per volume is increased with SV = a _3, to remove the NO _X along the NO _X reduction curve.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing one embodiment of a nitrogen oxide reduction device for a diesel engine of the present invention.

In the present embodiment, the catalyst-carrying filters 2a, 2b, 2c are arranged in the exhaust pipe 1 connected to the engine in three divided parts, but the number is not limited to three. Instead, it may be divided into two or several. Between the catalyst supporting filters 2a and 2b and between the catalyst supporting filters 2b and 2c
A bypass pipe 3 is connected between them and is connected to the outlet of the exhaust pipe 1, and a valve 5 is provided at the inlet of the bypass pipe 3, respectively.
a and 5b are provided. These valves 5a, 5b
Is driven to open and close to the positions of θ ₀ and θ ₁ by the actuators 6a and 6b. An exhaust gas temperature sensor 7 is provided on the inlet side of the exhaust pipe 1, and a detection signal of the exhaust gas temperature sensor 7 is input to an electronic control unit 8 and, after being processed based on the control data stored here, The output signal is output to the actuators 6a and 6b.

FIG. 2 is a diagram for explaining the control data, showing the relationship between the NO _x reduction rate, the exhaust temperature and the exhaust gas flow rate SV per volume occupied by the catalyst. SV = a
₁ is the exhaust gas flow rate per volume when the exhaust gas flows through all of the catalyst-carrying filters 2a, 2b, 2c, SV = a
₂ is a gas flow rate per volume when the exhaust gas catalyst carrying filter 2a, 2b flows, SV = a ₃ is the exhaust gas flow rate per volume when the exhaust gas flows through the catalyst-carrying filter 2a. The temperature at the intersection of the NO _X reduction rate curve at SV = a _{1 and} the NO _X reduction rate curve at SV = a ₂ is T _1, and the NO _X reduction rate curve at SV = a ₂ and NO at SV = a ₃ . The temperature at the intersection with the _X reduction rate curve is T ₂ .

FIG. 3 is a diagram for explaining the control flow. First, in step S1, the current exhaust gas temperature T ₀
Is read, and the current exhaust gas temperature T ₀ is read in step S2.
Is smaller than T ₁ , and if smaller, a signal is sent to the actuators 6a and 6b so as to set the positions of the valves 5a and 5b to θ ₀ in step S5. If T ₀ is equal to or greater than T ₁ in step S2, the process proceeds to step S3. If T ₀ is equal to or less than T ₂ , the position of valve 5a is θ ₀ and the position of valve 5b is θ _{1 in} step S7.
To the actuators 6a and 6b. If T ₀ is larger than T ₂ in step S3, the process proceeds to steps S4 and S6, where the position of the valve 5a is θ ₁ and the valve 5 is
The actuators 6a, 6 are arranged so that the position of b is θ _0.
send a signal to b.

The above operations are summarized in Table 1 below. The catalyst-carrying filters 2a, 2b, 2
The volumes of c are V ₁ , V ₂ , and V ₃ , respectively.

[0013]

[Table 1]

Therefore, if the exhaust gas temperature T ₀ is lower than T ₁ , the exhaust gas flows through all of the catalyst-carrying filters 2a, 2b, 2c, the exhaust gas flow rate per volume becomes SV = a ₁ , and SV = shown in FIG. NO _x is removed along the NO _x reduction rate curve in a ₁ (for example, 50% NO _x reduction rate when exhaust temperature is 300 ° C.), and exhaust temperature T ₀ is T ₁ or more,
If T ₂ or less, the exhaust gas is the catalyst-carrying filter 2a,
2b, the exhaust gas flow rate per volume becomes SV = a ₂ , and NO _X is removed along the NO _X reduction rate curve at SV = a ₂ shown in FIG. 2 (for example, when the exhaust temperature is 500 ° C., NO of 65% is obtained). _X reduction rate), and the exhaust temperature T ₀ is T
Is greater than _2, the exhaust gas only flows catalyst-carrying filter 2a, the exhaust gas flow rate per volume SV = a _3, and the the NO _X along the NO _X reduction rate curve at SV = a ₃ shown in FIG. 2 are removed (For example, when the exhaust temperature is 600 ° C., the NO _X reduction rate is 55%). As a result, even if the exhaust gas temperature changes, the exhaust gas flow rate SV is changed by changing the exhaust gas flow rate SV per volume occupied by the catalyst.
In order to shift to a curve with a high NO _x reduction rate corresponding to
It is possible to reduce the total NO _x .

The present invention is not limited to the above embodiment, but various modifications can be made. For example, in the above embodiment, the catalyst-carrying filters 2a, 2b, 2c are connected in series, but divided catalyst-carrying filters may be arranged in parallel and switched by a switching valve.

[0016]

As is apparent from the above description, according to the present invention, a plurality of catalyst-carrying filters arranged separately in the exhaust pipe of the engine, a temperature sensor provided in the exhaust pipe, and a plurality of the above-mentioned plurality of temperature sensors are provided. The catalyst-carrying filter is provided with means for selectively passing exhaust gas, and the exhaust gas flow rate per volume occupied by the catalyst is changed depending on the exhaust temperature, so that the exhaust gas per volume occupied by the catalyst is changed even if the exhaust temperature changes. By changing the flow rate SV, the curve shifts to a curve with a high NO _X reduction rate corresponding to the exhaust gas flow rate SV, so that the total NO _X can be reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a nitrogen oxide reduction device for a diesel engine of the present invention.

FIG. 2 is a diagram for explaining control data, showing the relationship between the NO _X reduction rate, the exhaust gas temperature, and the exhaust gas flow rate per volume occupied by the catalyst.

FIG. 3 is a diagram for explaining a control flow.

[Explanation of symbols]

1 ... Exhaust pipe, 2a, 2b, 2c ... Catalyst carrying filter, 3
... bypass pipe 5a, 5b ... valve, 6a, 6b ... actuator, 7
... Exhaust temperature sensor 8 ... Electronic control unit, SV ... Exhaust gas flow rate per volume occupied by catalyst

Claims (1)

[Claims] 1. A plurality of catalyst-carrying filters arranged separately in an exhaust pipe of an engine, a temperature sensor provided in the exhaust pipe, and means for selectively passing the exhaust gas through the plurality of catalyst-carrying filters. A nitrogen oxide reduction device for a diesel engine, which is equipped with and changes the flow rate of exhaust gas per volume occupied by the catalyst according to the exhaust temperature.