JPH0673316U - Exhaust gas purification device for diesel engine - Google Patents

Abstract

(57) [Summary] [Purpose] In an exhaust emission control device for a diesel engine, it is possible to prevent the reducing agent from being discharged unreacted during warm-up of the reduction catalyst. [Structure] A reduction catalyst 3 interposed in the middle of an exhaust passage 2 of a diesel engine 1, an addition device 5 for adding a reducing agent to the upstream side of the reduction catalyst 3, and a downstream side of the reduction catalyst 3 in the exhaust passage 2 And an oxidation catalyst 6 interposed.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an improvement in an exhaust emission control device for a diesel engine.

[0002]

[Prior art]

 As a device for purifying nitrogen oxides discharged from a diesel engine, a reduction catalyst is provided in the middle of an exhaust passage as seen in, for example, JP-A-2-149317 and JP-A-63-110919. In some cases, a reducing agent is added on the upstream side of the reduction catalyst.

As such an exhaust emission control device, as shown in FIG. 4, for example, a reduction catalyst 3 is interposed in the middle of an exhaust passage 2 of a diesel engine 1 and a part of light oil stored in a fuel tank 4 is stored. In some cases, an addition device 5 is added as a reducing agent on the upstream side of the reduction catalyst 3 in the exhaust passage 2. The reduction catalyst 3 is adapted to decompose the nitrogen oxides in the exhaust gas into nitrogen and oxygen by contacting the exhaust gas containing nitrogen oxides in an oxidizing atmosphere or in the presence of hydrocarbons (Japanese Patent Laid-Open No. Hei 10-1999) No. 1-118009).

[0004]

[Problems to be solved by the device]

 However, in such a conventional diesel engine exhaust emission control device, when the reducing agent is injected during the warm-up that rises to the temperature at which the catalyst is activated, as shown by the solid line in FIG. However, there is a problem that it is discharged unreacted.

The present invention focuses on the above-mentioned problems, and an object thereof is to prevent the reducing agent from being discharged unreacted during the warm-up of the reduction catalyst.

[0006]

Means for Solving the Problems The present invention is directed to a reduction catalyst interposed in the exhaust passage of a diesel engine, a means for adding a reducing agent to the upstream side of the reduction catalyst, and a reduction catalyst in the exhaust passage. And an oxidation catalyst installed on the downstream side.

[0007]

[Action]

 By adding the reducing agent in a state where the reducing catalyst is not activated, the reducing agent passes through the reducing catalyst unreacted, but the unreacted reducing agent is oxidized by passing through the oxidizing catalyst and is not treated. It is possible to prevent the reaction from being discharged to the outside through the exhaust passage.

[0008]

【Example】

 Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

As shown in FIG. 1, a reduction catalyst 3 is interposed in the exhaust passage 2 of a diesel engine 1. The reduction catalyst 3 has, for example, a structure in which a base material such as alumina, silica, or zeolite and a catalyst material made of a metal such as copper are supported on a honeycomb-shaped carrier, and has a structure in which copper is supported. By contacting exhaust gas containing nitrogen oxides (NO x) in the presence of hydrocarbons, the nitrogen oxides in the exhaust gas are decomposed into nitrogen and oxygen.

As a means for adding the reducing agent to the upstream side of the reduction catalyst 3, an addition device 5 for adding a part of the light oil stored in the fuel tank 4 to the upstream side of the reduction catalyst 3 in the exhaust passage 2 is provided. .

An oxidation catalyst 6 is provided in the exhaust passage 2 immediately downstream of the reduction catalyst 3. The oxidation catalyst 6 has, for example, a structure in which a base material made of alumina or the like and a catalyst substance made of a metal such as platinum or palladium are carried on a honeycomb-shaped carrier. , CO is oxidized and purified.

The temperature at which the oxidation catalyst 6 is activated is formed to be lower than the temperature at which the reduction catalyst 3 is activated.

In this embodiment, a reduction catalyst 3 and an oxidation catalyst 6 are provided inside a cylindrical casing 7 with a space therebetween.

Next, the operation will be described.

By adding the reducing agent in a state where the catalyst of the reducing catalyst 3 is not activated, the reducing agent passes through the reducing catalyst 3 unreacted, but the unreacted reducing agent passes through the oxidation catalyst 6. By doing so, as shown by the broken line in FIG. 2, the total hydrocarbon (THC) emission amount is rapidly reduced, and the reducing agent is discharged to the outside through the exhaust passage 2 without reaction. Can be suppressed.

As another embodiment, as shown in FIG. 3, the reduction catalyst section 13 and the oxidation catalyst section 16 may be integrated and housed inside a cylindrical casing 17.

[0017]

[Effect of device]

 As described above, the present invention has a reduction catalyst installed in the middle of the exhaust passage of a diesel engine, a means for adding a reducing agent to the upstream side of the reduction catalyst, and a downstream side of the reduction catalyst in the exhaust passage. Since the catalyst is equipped with an oxidation catalyst, it is possible to prevent the reducing agent from being discharged unreacted during warm-up of the catalyst.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing the same operation.

FIG. 3 is a configuration diagram showing another embodiment.

FIG. 4 is a configuration diagram showing a conventional example.

[Explanation of symbols]

 1 Diesel engine 2 Exhaust passage 3 Reduction catalyst 5 Addition device (addition means) 6 Oxidation catalyst

Claims (1)

[Scope of utility model registration request] 1. A reduction catalyst provided in the middle of the exhaust passage, means for adding a reducing agent to the upstream side of the reduction catalyst, and an oxidation catalyst provided downstream of the reduction catalyst in the exhaust passage. Exhaust gas purification device for diesel engines.