JP2005105969A - Exhaust emission control device of engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of clogging of an injection nozzle and its pipe. <P>SOLUTION: This exhaust emission control device comprises a NOx reducing catalyst 3 arranged in an exhaust pipe 2 of an engine 1, and reducing and purifying NOx by a liquid reducing agent such as a ureal aqueous solution, a reducing agent supply device 16 for controlling a flow rate of the liquid reducing agent supplied to the NOx reducing catalyst 3 in response to an engine operation state, an injection nozzle 5 for injecting and supplying the liquid reducing agent into the exhaust gas upstream side of the NOx reducing catalyst 3, and a pipe 15 for communicating and connecting the reducing agent supply device 16 with and to the injection nozzle 5. Water repellent treatment is applied to at least one inner wall among the injection nozzle 5 and the pipe 15. Thus, when injection supply of the liquid reducing agent stops, since the liquid reducing agent sticking to the inner wall of the injection nozzle 5 and the pipe 15 reduces, even if a component such as urea is deposited by exhaust heat, since its absolute quantity is little, the occurrence of clogging of the injection nozzle 5 and the pipe 15 can be prevented. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an exhaust purification device for an engine (hereinafter referred to as “exhaust purification device”) that uses a liquid reducing agent to reduce and remove nitrogen oxides (NOx) in exhaust gas, and in particular, an injection nozzle and its piping are clogged. It relates to technology that makes it difficult to get up

  As a catalyst purification system for removing NOx contained in engine exhaust, an exhaust purification device disclosed in Japanese Patent Laid-Open No. 2000-27627 (Patent Document 1) has been proposed.

Such an exhaust emission control device arranges a reduction catalyst in the exhaust passage of the engine and injects and supplies a reducing agent upstream of the exhaust of the reduction catalyst to cause a catalytic reduction reaction between NOx in the exhaust and the reducing agent, thereby converting NOx. It purifies to harmless components. The reducing agent is stored in a storage tank in a liquid state at room temperature, and a required amount corresponding to the engine operating state is injected and supplied from the injection nozzle. Here, as the reducing agent, a liquid reducing agent such as an aqueous urea solution, an aqueous ammonia solution, or light oil mainly composed of hydrocarbon is used.
JP 2000-27627 A

  By the way, depending on the engine operating state, there is an operating state where the exhaust temperature is low and the reduction catalyst does not function sufficiently. For this reason, from the viewpoint of preventing unnecessary consumption of the liquid reducing agent, a configuration is adopted in which the liquid reducing agent is intermittently injected and supplied upstream of the reduction catalyst according to the engine operating state and the exhaust temperature. . When such a configuration is adopted, there is a possibility that after the supply of liquid reducing agent stops, the liquid reducing agent coagulates in the injection nozzle and its piping, causing clogging, and the liquid reducing agent cannot be supplied. is there. That is, immediately after the supply of the liquid reducing agent is stopped, the liquid reducing agent droplets adhere to the injection nozzle and its piping. And since the injection nozzle and its piping are directly exposed to the high-temperature exhaust gas, the temperature rises due to the exhaust heat, the moisture of the liquid reducing agent evaporates, and its components are deposited. Further, if the engine is stopped when the injection nozzle and its piping are at a high temperature, clogging may occur in the same manner, and there is a possibility that the liquid reducing agent cannot be supplied by injection. If injection of the liquid reducing agent cannot be performed, NOx purification by the reduction catalyst cannot be expected, and exhaust gas containing a large amount of NOx will be released into the atmosphere.

  Accordingly, in view of the above-described conventional problems, the present invention provides an exhaust purification device that makes water-repellent treatment on the inner wall of at least one of the injection nozzle and its piping so that the injection nozzle and its piping are not easily clogged. The purpose is to provide.

  For this reason, the invention described in claim 1 is a reduction catalyst that is disposed in an engine exhaust passage and that reduces and purifies nitrogen oxides with a liquid reducing agent, and a liquid reducing agent that is supplied to the reduction catalyst in accordance with an engine operating state. A reducing agent supply device that controls the flow rate of the reducing catalyst, an injection nozzle that injects and supplies a liquid reducing agent upstream of the exhaust of the reduction catalyst, and a pipe that communicates the reducing agent supply device and the injection nozzle. In the engine exhaust gas purification apparatus, at least one of the injection nozzle and the pipe has a water repellent finish.

  The invention according to claim 2 is characterized in that the water repellent finish is a fluororesin finish.

  The invention according to claim 3 is characterized in that the water repellent finish is an organic plating finish.

  The invention according to claim 4 is characterized in that the pipe extends in a substantially vertical direction and the nozzle is connected to a lower end.

  According to the first aspect of the present invention, nitrogen oxides contained in the exhaust of the engine are reduced and removed by the reduction catalyst using the liquid reducing agent supplied by the reducing agent supply device. Since at least one inner wall of the injection nozzle and its piping is water-repellent, when the supply of the liquid reducing agent is stopped, the injection nozzle and the liquid reducing agent in the piping flow down vertically. The liquid reducing agent adhering to the inner wall is reduced. Therefore, even if moisture is evaporated from the liquid reducing agent due to the exhaust heat and a solid component is deposited, the absolute amount thereof is small, so that the injection nozzle and the pipe are not clogged.

  On the other hand, when the liquid supply of the liquid reducing agent is resumed, the liquid reducing agent passes through the injection nozzle and its piping vigorously, so even if the liquid reducing agent is solidified and adhered to the inner wall, it dissolves. And easily discharged into the exhaust pipe. Accordingly, even if the liquid supply of the liquid reducing agent is intermittently supplied, the solidified component does not gradually accumulate on the inner wall of the pipe and the injection nozzle, and the liquid reducing agent according to the engine operating state Therefore, the required NOx purification efficiency can be maintained over a long period of time.

  According to the invention of claim 2, since the fluororesin processing is used as the water-repellent processing applied to at least one inner wall of the injection nozzle and its piping, even if the injection nozzle and the piping are heated by the exhaust of the engine, A decrease in water repellency can be suppressed.

  According to the invention of claim 3, as the water-repellent process applied to at least one inner wall of the spray nozzle and its pipe, since the organic plating process is used, the water-repellent layer formed on the inner wall is difficult to peel off, Water repellency is improved.

  According to the invention described in claim 4, since the injection nozzle is connected to the lower end of the pipe extending in the substantially vertical direction, the liquid reducing agent in the pipe is caused by gravity when the injection of the liquid reducing agent is stopped. It flows down and is discharged from the injection nozzle. As a result, the liquid reducing agent adhering to the inner wall of the pipe decreases, so even if moisture is evaporated from the liquid reducing agent due to the exhaust heat and a solid component is deposited, the absolute amount of the liquid reducing agent is small. It can make clogging difficult.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a configuration diagram of an exhaust emission control device for an engine according to the present invention.

  An exhaust pipe 2 that is an exhaust passage of the engine 1 is provided with a NOx reduction catalyst 3 that reduces and purifies NOx. An injection nozzle 5 is provided on the upstream side of the NOx reduction catalyst 3 to inject and supply urea aqueous solution as a liquid reducing agent from an injection hole 4 opened in the exhaust pipe 2. In this embodiment, an aqueous urea solution is used as the liquid reducing agent, but an aqueous ammonia solution, light oil mainly composed of hydrocarbons, or the like may be used.

  The injection nozzle 5 is fixed to the exhaust pipe 2 by fixing the flange 11 provided so as to close the opening 10 opened in the peripheral wall of the exhaust pipe 2 with the bolt 12 and is reduced through the pipe 15. The agent supply device 16 is connected in communication.

  The reducing agent supply device 16 is supplied with an aqueous urea solution and compressed air, and the aqueous urea solution is injected and supplied from the injection nozzle 5 into the exhaust pipe 2 together with the compressed air. Further, in order to control the flow rate of the urea aqueous solution supplied to the NOx reduction catalyst 3 according to the engine operating state, a controller 20 incorporating a computer is provided. The controller 20 controls the reducing agent supply device 16 according to the engine operating state, that is, the engine rotation speed and the fuel injection amount input via the CAN (Controller Area Network).

  As shown in FIG. 2, the inner wall 15 a of the pipe 15 is subjected to a fluororesin process as a water repellent process to form a water repellent layer 30. The inner wall of the injection nozzle 5 is similarly subjected to fluororesin processing.

  According to the above configuration, the exhaust of the engine 1 passes through the exhaust pipe 2 and is guided to the NOx reduction catalyst 3. At this time, the controller 20 controls the operation of the reducing agent supply device 16 based on the rotation speed of the engine 1 and the fuel injection amount, so that an optimal amount of urea aqueous solution suitable for the engine operating state is supplied together with the compressed air to the pipe 15. And is injected and supplied from the injection nozzle 5 into the exhaust pipe 2 upstream of the NOx reduction catalyst 3. The urea aqueous solution supplied into the exhaust pipe 2 is hydrolyzed by exhaust heat and water vapor in the exhaust, and ammonia is easily generated. The generated ammonia reacts with NOx in the exhaust gas in the NOx reduction catalyst 3 to be purified into water and harmless gas.

  Since the water repellent finish is applied to the inner walls of the injection nozzle 5 and the pipe 15, the liquid reducing agent in the injection nozzle 5 and the pipe 15 flows down vertically when the injection supply of the urea aqueous solution is stopped. 5 and the urea aqueous solution adhering to the inner wall of the pipe 15 is reduced. Therefore, even if moisture evaporates from the urea aqueous solution adhering to the inner wall of the injection nozzle 5 and the pipe 15 due to the exhaust heat of the engine 1 and urea is deposited, the absolute amount thereof is small. It does not lead to clogging.

  On the other hand, when the engine operating state changes and the supply of urea aqueous solution is restarted, the urea aqueous solution and compressed air pass through the pipe 15 and the injection nozzle 5. For this reason, even if urea coagulates and adheres on the inner wall, it is dissolved and easily discharged to the exhaust pipe 2. Therefore, even if the urea aqueous solution injection is intermittently performed, urea does not gradually accumulate on the inner wall of the pipe 15 and the injection nozzle 5, and the urea aqueous solution is injected according to the engine operating state. Since the supply is possible, the required NOx purification efficiency can be maintained over a long period of time.

  In addition, since the fluororesin processing is used as the water repellent process applied to the inner walls of the injection nozzle 5 and the pipe 15, even if the injection nozzle 5 and the pipe 15 are heated by the exhaust of the engine 1, A decrease in water repellency can be suppressed.

  In addition to the fluororesin process, an organic plating process may be used as the water repellent process. If the organic plating process is used, the water repellent layer formed on the inner wall becomes difficult to peel off from the inner wall, and the water repellent performance in the injection nozzle 5 and the pipe 15 is improved.

  Further, it is desirable that the pipe 15 extends in a substantially vertical direction, and the injection nozzle 5 is connected to the lower end thereof. With such a configuration, when the urea aqueous solution injection stops, the urea aqueous solution in the pipe 15 flows down vertically due to gravity and is discharged from the injection port 4 of the injection nozzle 5 into the exhaust pipe 2. The urea aqueous solution adhering to the inner wall 15a of the pipe 15 is reduced. For this reason, even if moisture evaporates from the urea aqueous solution due to the exhaust heat and urea is deposited, the absolute amount thereof is small, so that the pipe 15 can be more easily clogged.

  In the above embodiment, both the spray nozzle 5 and the pipe 15 are subjected to water repellent treatment. However, only one of the nozzle nozzles 5 and the pipe 15 where clogging is likely to occur may be subjected to water repellent finish. If the inner wall 15a of the pipe 15 is subjected to water repellent treatment only on a portion that may be heated to a temperature at which the urea aqueous solution is solidified by exhaust, clogging of the pipe 15 is less likely to occur.

Configuration diagram of the exhaust emission control device of the present invention Cross section of the same piping

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Exhaust pipe 3 NOx reduction catalyst 5 Injection nozzle 15 Piping 15a Inner wall 16 Reducing agent supply apparatus 30 Water repellent layer

Claims (4)

A reduction catalyst disposed in the engine exhaust passage for reducing and purifying nitrogen oxides with a liquid reducing agent;
A reducing agent supply device for controlling a flow rate of the liquid reducing agent supplied to the reduction catalyst according to an engine operating state;
An injection nozzle for injecting and supplying a liquid reducing agent upstream of the exhaust of the reduction catalyst;
Piping for connecting the reducing agent supply device and the injection nozzle in communication with each other;
In an exhaust emission control device for an engine comprising:
An exhaust purification device for an engine, wherein a water repellent finish is applied to at least one inner wall of the injection nozzle and the pipe.   2. The engine exhaust gas purification apparatus according to claim 1, wherein the water repellent process is a fluororesin process.   2. The engine exhaust gas purification apparatus according to claim 1, wherein the water repellent process is an organic plating process.   The exhaust purification device for an engine according to any one of claims 1 to 3, wherein the pipe extends in a substantially vertical direction, and the injection nozzle is connected to a lower end.

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