JPH08200046A - Exhaust emission control device for engine - Google Patents

Abstract

PURPOSE: To prevent reduction of an exhaust temperature caused by compressed air which is supplied when a reducer is added on a catalyst, prevent the catalyst from interfering with activating, and prevent reduction of NOx reducing capacity of the catalyst. CONSTITUTION: A nozzle 3 for adding light oil as reducer is arranged in the exhaust pipe 1 which is arranged upstream from a catalyst 2, and a compressed air leading-in device 7 is arranged so as to led compressed air for spraying light oil to the nozzle 3. The compressed air leading-in device 7 is composed of a compressor 8 formed as a compressed air supplying source, and a compressed air leading-in passage for leading compressed air supplied from the compressor 8 into the nozzle 3, and a part of the compressed air leading-in passage is formed of a cylindrical passage 15 formed between an exhaust pipe 1 arranged downstream from the catalyst 2 and an outer circumferential pipe 14 arranged on the outer circumferential side of the exhaust pipe 1. Compressed air is heated by heat of exhaust gas passed the catalyst 2 while compressed air is passed the cylindrical passage 15, and then compressed air is led in the nozzle 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust emission control system for an engine, and more particularly to a reducing agent for an exhaust emission control system for removing nitrogen oxides contained in exhaust gas of an engine with a catalyst interposed in an exhaust passage. Related to atomization supply technology.

[0002]

Background Art Exhaust gas recirculation (EGR) is well known as an effective means for reducing the concentration of nitrogen oxides (NOx) contained in the exhaust gas of an engine. A method of interposing and treating NOx with this catalyst is also conceivable. In this case, in order to efficiently reduce NOx, it has been proposed to provide a device for adding light oil as a reducing agent in the exhaust passage on the upstream side of the catalyst (see Japanese Utility Model Laid-Open No. 5-87218).

[0003]

By the way, in such an exhaust emission control device, since the light oil, which is the reducing agent of the catalyst, is evenly added to the front surface of the catalyst, the atomization of the light oil is promoted and its vaporization It is necessary to provide means for improving the mixing property. There is a method of atomizing light oil by using compressed air (assist air) for atomization of light oil, but since the air temperature is low, the exhaust temperature decreases, which hinders the activation of the catalyst. However, there is a problem in that the NOx reduction ability of the catalyst is reduced.

In view of the above-mentioned conventional problems, the present invention therefore eliminates nitrogen oxides contained in the exhaust gas of an engine.
In an exhaust gas purification device that removes with a catalyst installed in an exhaust passage, the exhaust gas temperature is prevented from lowering due to compressed air supplied when a reducing agent is added, and activation of the catalyst is not hindered. The purpose is to prevent the reduction ability from decreasing.

[0005]

Therefore, according to the present invention, in an exhaust gas purifying apparatus for removing nitrogen oxides contained in the exhaust gas of an engine by a catalyst interposed in an exhaust passage, the exhaust gas purifying apparatus is provided on the upstream side of the catalyst. A nozzle for adding a reducing agent to the exhaust passage, and a compressed air introducing device for introducing compressed air for reducing agent spraying to the nozzle, the compressed air introducing device, a compressed air supply source And a compressed air introduction passage for introducing compressed air supplied from the compressed air supply source to the nozzle, and a part of the compressed air introduction passage,
It is formed by a tubular passage formed between an exhaust pipe that constitutes the exhaust passage on the catalyst downstream side and an outer peripheral pipe arranged on the outer peripheral portion of the exhaust pipe.

[0006]

In the present invention, compressed air is introduced to the nozzle,
A reducing agent such as light oil is sprayed on the front surface of the catalyst. Therefore, atomization of the reducing agent such as light oil is promoted, the vaporization and mixing properties thereof are improved, and the reducing agent such as light oil can be uniformly added to the front surface of the catalyst. Then, the compressed air passes through the tubular passage formed between the exhaust pipe that constitutes the exhaust passage on the catalyst downstream side and the outer peripheral pipe arranged at the outer peripheral portion of the exhaust pipe, so that the compressed air after passing through the catalyst It is heated by the heat of the exhaust gas, the temperature of the compressed air rises, and the decrease of the exhaust gas temperature can be prevented. Therefore,
The catalyst can be activated and the NOx reduction ability of the catalyst can be improved.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, a catalyst 2 for purifying NOx is provided in an exhaust pipe 1 which constitutes an exhaust passage of a diesel engine. A nozzle 3 for adding light oil as a reducing agent is arranged in the exhaust pipe 1 on the upstream side of the catalyst 2.

A light oil supply pipe 4 is connected to the nozzle 3, and the light oil supply pipe 4 communicates with a light oil tank 5. or,
A light oil injection pump 6 is interposed in the light oil supply pipe 4. On the other hand, the nozzle 3 is provided with a compressed air introduction device 7 for introducing compressed air for spraying light oil. The compressed air introduction device 7 includes a compressor 8 as a compressed air supply source,
And a compressed air introduction passage for introducing the compressed air supplied from the compressor 8 into the nozzle 3.

That is, in the first air introducing pipe 9 forming a part of the compressed air introducing passage, the filter 10, the compressor 8 and the buffer tank 1 for storing air are arranged in this order from the upstream side.
1 and an on-off valve 12 are provided respectively. The buffer tank 11 is provided with a pressure gauge 13. Further, a part of the compressed air introducing passage is provided in the exhaust pipe 1 downstream of the catalyst 2.
And the outer peripheral pipe 14 disposed on the outer peripheral portion of the exhaust pipe 1 are formed by a cylindrical passage 15, and the first air introducing pipe 9 is connected to the cylindrical passage 15 for communication. To be done.

Further, one end of a second air introducing pipe 16 is connected to the cylindrical passage 15 and the other end of the second air introducing pipe 16 is connected to the nozzle 3. The light oil injection pump 6 and the opening / closing valve 12 are respectively controlled according to the engine operating state to properly adjust the addition timing and the addition amount of the light oil. That is, a rotation speed sensor 17 for detecting an engine speed and a load sensor 18 for detecting an engine load (for example, a control rack position of a fuel injection pump) are provided, and a pump for controlling the light oil injection pump 6 is provided. A controller 19 for valves and a valve controller 20 for controlling the on-off valve 12 are provided. The detection signals output from the rotation speed sensor 17 and the load sensor 18 are input to the controllers 19 and 20, respectively, and the controllers 19 and 20 detect the light oil injection pump based on the engine rotation speed and the load, respectively. 6
And the on-off valve 12 are controlled respectively.

FIG. 2 is a flow chart for explaining the light oil addition control, which is executed when the engine is started, reads the engine speed and the load from the detection signals of the rotation speed sensor 17 and the load sensor 18, and adds the light oil corresponding thereto. The amount is obtained from the data map, and the pump 6 and the on-off valve 1 are operated by the pump driving voltage and the valve opening / closing operation corresponding to these values
2 are operated to inject light oil from the nozzle 3 to the catalyst 2 under high pressure (S1 to S4).

With such a configuration, light oil as a reducing agent for the catalyst 2 is added from the nozzle 3 to the front surface of the catalyst 2.
It should be noted that the optimum amount of light oil addition need not necessarily be proportionally increased in accordance with the engine operating state, and is decreased when the engine exhaust temperature exceeds a predetermined value to suppress excessive temperature rise of the catalyst. It is also necessary.

According to this structure, the compressed air from the compressor 8 passes through the first air introduction pipe 9 and the exhaust pipe 1
To the cylindrical passage 15 formed between the outer peripheral tube 14 and
Through the tubular passage 15, it reaches the second air introducing pipe 16 and is introduced into the nozzle 3. Therefore, the compressed air is heated by the heat of the exhaust gas that has passed through the catalyst 2 and is introduced into the nozzle 3 while passing through the tubular passage 15.

Therefore, the temperature of the compressed air introduced into the nozzle 3 becomes high, and the exhaust temperature can be prevented from lowering.
The catalyst 2 can be activated and the NOx reduction ability of the catalyst 2 can be improved. In particular, since the compressed air is heated by effectively utilizing the exhaust heat, it is not necessary to separately provide an air heating means, and only the outer peripheral pipe 14 is added to the exhaust pipe 1,
The structure can be simplified and the cost can be reduced.

[0015]

As described above, according to the present invention,
Since the compressed air from the compressed air supply source is introduced into the nozzle by passing through the cylindrical passage formed between the exhaust pipe and the outer peripheral pipe, In addition, the heat of the exhaust gas that has passed through the catalyst can be heated and introduced into the nozzle, so that the exhaust gas temperature can be prevented from lowering, the catalyst can be activated, and the NOx reduction capability of the catalyst can be improved.

In particular, since the compressed air is heated by effectively utilizing the exhaust heat, it is not necessary to separately provide an air heating means, the structure can be simplified, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a system configuration diagram of an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of the above embodiment.

[Explanation of symbols]

 1 Exhaust Pipe 2 Catalyst 3 Nozzle 7 Compressed Air Introducing Device 8 Compressor 9 First Air Introducing Pipe 14 Outer Pipe 15 Cylindrical Passage

Front Page Continuation (72) Inventor Hisashi Akagawa 1-chome, Io-chome, Ageo City, Saitama Prefecture Nissan Diesel Industry Co., Ltd.

Claims (1)

[Claims] 1. An exhaust emission control device for removing nitrogen oxides contained in exhaust gas of an engine with a catalyst interposed in an exhaust passage, wherein a nozzle for adding a reducing agent to an exhaust passage upstream of the catalyst. And a compressed air introducing device for introducing compressed air for spraying a reducing agent to the nozzle, wherein the compressed air introducing device is a compressed air supply source and a compressed air supplied from the compressed air supply source. A compressed air introduction passage for introducing air into the nozzle is included, and a part of the compressed air introduction passage is arranged in an exhaust pipe constituting the catalyst downstream side exhaust passage and an outer peripheral portion of the exhaust pipe. An exhaust gas purifying apparatus for an engine, which is formed by a cylindrical passage formed between the outer peripheral pipe and the outer peripheral pipe.