JP2005105913A - 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 14 for reducing and purifying NOx in exhaust gas by using a liquid reducing agent such as a ureal aqueous solution, a reducing agent supply device 18 for controlling a flow rate of the liquid reducing agent supplied to the NOx reducing catalyst 14 in response to an engine operation state, an injection nozzle 22 for injecting and supplying the liquid reducing agent into the exhaust gas upstream side of the NOx reducing catalyst 14, and a pipe 20 for communicating and connecting the reducing agent supply device 18 with and to the injection nozzle 22. The pipe 20 is composed of a ceramic material having small heat conductivity being a thermal property. This constitution can reduce quantity of heat transmitted to the reducing agent supply device 18 via the injection nozzle 22 and the pipe 20 from an exhaust pipe 16, and can allow the reducing agent supply device 18 to approach the exhaust pipe 16. Thus, the length of the pipe 20 is shortened, and the clogging is little caused by reducing an absolute quantity of the liquid reducing agent sticking to its inner wall. <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 purification device has a reduction catalyst disposed in an exhaust system of an 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 reducing 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 a small amount of NOx in the exhaust gas, and there is a case where NOx purification by the reduction catalyst is unnecessary. 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. 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. 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.

  In order to solve such a problem, it is conceivable to shorten the distance between the reducing agent supply device that injects and supplies the liquid reducing agent upstream of the NOx reduction catalyst and the injection nozzle. The use temperature is required to be within a predetermined range. Since the exhaust pipe is heated to a high temperature by the exhaust heat, and the exhaust heat is transmitted to the reducing agent supply device through the injection nozzle and its piping, the reducing agent supply device, the injection nozzle, The distance could not be shortened.

  Accordingly, in view of the above-described conventional problems, the present invention reduces the volume unrelated to the liquid reducing agent injection supply, by reducing the distance between the reducing agent supply device and the injection nozzle. An object of the present invention is to provide an exhaust emission control device in which clogging in a nozzle and its piping is less likely to occur.

  Therefore, according to the first aspect of the present invention, a reduction catalyst that is disposed in the engine exhaust system and that reduces and purifies nitrogen oxides with a liquid reducing agent, and a liquid reducing agent that is supplied to the reduction catalyst according to engine operating conditions. A reductant supply device that controls the flow rate of the reductant, an injection nozzle that is fixed to the exhaust system via a flange and that injects a liquid reductant upstream of the exhaust of the reduction catalyst, the reductant supply device, and the injection nozzle, And an exhaust gas purification apparatus for an engine comprising a pipe for connecting the pipes to each other, wherein the pipe is made of a ceramic material.

The invention according to claim 2 is characterized in that a radiating fin is arranged in the flange.
The invention according to claim 3 is characterized in that a refrigerant is passed through the flange.
According to a fourth aspect of the present invention, a heat insulating gasket is interposed between the exhaust system and the flange.

  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. At this time, since the piping connecting the reducing agent supply device and the injection nozzle is made of a ceramic material, the heat transfer coefficient, which is a thermal characteristic thereof, is small, so the heat of the exhaust system supplies the reducing agent. It becomes difficult to be transmitted to the device. For this reason, even if the reducing agent supply device is brought close to the exhaust system, an increase in the use temperature is suppressed and a predetermined use environment can be satisfied. As a result, the length of the pipe can be shortened and the volume unrelated to the injection and supply of the liquid reducing agent is reduced. The liquid reducing agent adhering to the piping and the inner wall of the injection nozzle immediately after the stop of the injection supply is reduced. Therefore, even if moisture is evaporated from the liquid reducing agent due to the exhaust heat and the components are deposited, the absolute amount thereof is small, so that the pipe and the injection nozzle are not clogged.

  On the other hand, when the supply of the liquid reducing agent is restarted, the liquid reducing agent passes through the pipe and the injection nozzle vigorously, so that the solidified component is dissolved and discharged to the exhaust system. Therefore, even if the liquid reducing agent is supplied and supplied intermittently, the components of the liquid reducing agent do not gradually accumulate on the inner walls of the pipe and the injection nozzle, and the required nitrogen oxide purification is achieved. Efficiency can be maintained over a long period of time.

  According to the invention described in claim 2 or claim 3, the exhaust heat transmitted from the exhaust system to the flange radiates heat or exchanges heat with the refrigerant by the heat radiating fin, and from the flange to the reducing agent supply device via the pipe. The amount of heat transferred is reduced. For this reason, since the use temperature of the reducing agent supply device is lowered, the reducing agent supply device can be brought closer to the exhaust system, and the volume unrelated to the injection supply of the liquid reducing agent can be further reduced. And since the absolute amount of the liquid reducing agent adhering to the piping and the inner wall of the injection nozzle immediately after stopping the supply of the liquid reducing agent is further reduced, the clogging can be effectively prevented.

  According to the invention of claim 4, since the heat insulating material gasket is interposed between the exhaust system and the flange, it is difficult for heat of the exhaust system to be transmitted to the flange, and the same as in claim 2 or claim 3. The effect can be demonstrated.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows the configuration of an exhaust emission control device embodying the present invention.
Exhaust gas from the engine 10 is discharged from the exhaust manifold 12 to the atmosphere via an exhaust pipe 16 in which a NOx reduction catalyst 14 is provided. More specifically, the exhaust pipe 16 is provided with a nitric oxide (NO) oxidation catalyst, a NOx reduction catalyst, and a slip ammonia oxidation catalyst in that order from the exhaust upstream side. Although an exhaust system is configured by being arranged, it is not shown in detail.

  The liquid reducing agent is injected and supplied together with air from the reducing agent supply device 18 to the upstream side of the exhaust of the NOx reduction catalyst 14 via the pipe 20 and the injection nozzle 22. That is, as shown in FIG. 2, the exhaust pipe 16 positioned upstream of the NOx reduction catalyst 14 has a flange 24 to which an injection nozzle 22 is coupled by a bolt 26 so as to close an opening 16 </ b> A opened in the peripheral wall. It is concluded. The reducing agent supply device 18 and the injection nozzle 22 are connected in communication via a ceramic pipe 20. 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 aqueous urea solution injected and supplied upstream of the NOx reduction catalyst 14 is hydrolyzed by the exhaust heat and water vapor in the exhaust, and ammonia is easily generated. It is known that the generated ammonia reacts with NOx in the exhaust gas in the NOx reduction catalyst 14 and is purified into water and harmless gas. The urea aqueous solution is an aqueous solution in which solid or powdered urea is dissolved, and is supplied to the reducing agent supply device 18 from a storage tank (not shown).

In addition, a control unit 28 with a built-in computer is provided to control the injection supply amount of the urea aqueous solution according to the engine operating state. The control unit 28 controls the reducing agent supply device 18 in accordance with the engine speed and the fuel injection amount input via a CAN (Controller Area Network).
According to such a configuration, since the reducing agent supply device 18 and the injection nozzle 22 are connected to each other via the ceramic pipe 20, the heat conductivity, which is the thermal characteristic, is small, so that the heat of the exhaust pipe 16 is reduced. It becomes difficult to be transmitted to the agent supply device 18. For this reason, even if the reducing agent supply device 18 is brought close to the exhaust pipe 16, an increase in the use temperature is suppressed and a predetermined use environment can be satisfied. Since the reducing agent supply device 18 can be brought closer to the exhaust pipe 16, the length of the pipe 20 can be shortened and the volume unrelated to the injection supply of the urea aqueous solution is reduced. The urea aqueous solution adhering to the pipe 20 and the inner wall of the injection nozzle 22 immediately after the supply of the injection is stopped is reduced. Therefore, even if moisture evaporates from the urea aqueous solution adhering to the inner wall due to the exhaust heat and urea is deposited, the absolute amount thereof is small, so that the pipe 20 and the injection nozzle 22 are not clogged.

  On the other hand, when the engine operating state changes and the supply of urea aqueous solution is resumed, the urea aqueous solution and air pass through the pipe 20 and the injection nozzle 22 vigorously. Then, it is discharged to the exhaust pipe 16. Therefore, even if the urea aqueous solution injection is intermittently performed, urea does not gradually accumulate on the inner wall of the pipe 20 and the injection nozzle 22, 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.

  Further, in order to further reduce the amount of heat transferred from the exhaust pipe 16 to the reducing agent supply device 18, as shown in FIG. An air cooling structure in which heat radiating fins 30 made of good copper or the like are arranged may be employed. Furthermore, a cooling water passage may be formed inside the flange 24, and a water cooling structure that allows engine cooling water or the like as a refrigerant to pass therethrough may be employed as shown in FIG. Both of the air cooling structure and the water cooling structure in the flange 24 may be adopted.

  When such a configuration is adopted, the exhaust heat transmitted from the exhaust pipe 16 to the flange 24 is radiated or heat-exchanged with the cooling water by the radiating fins 30, and the amount of heat transmitted to the pipe 20 is reduced. For this reason, since the operating temperature of the reducing agent supply device 18 is lowered, the reducing agent supply device 18 can be brought closer to the exhaust pipe 16, and the volume unrelated to the injection supply of the urea aqueous solution is further reduced. And since the absolute amount of the urea aqueous solution adhering to the inner wall of the piping 20 and the injection nozzle 22 further decreases, the clogging can be effectively prevented.

  Further, instead of the air cooling structure or the water cooling structure, a heat insulating material gasket may be interposed between the opening 16A of the exhaust pipe 16 and the flange 24. If it does in this way, it will become difficult to transmit the heat of the exhaust pipe 16 to the flange 24, and the effect similar to the said effect can be exhibited. In particular, if an insulating gasket is interposed between the opening 16A and the flange 24 in addition to the air cooling structure and / or the water cooling structure, the amount of heat transferred from the exhaust pipe 16 to the reducing agent supply device 18. Is effectively reduced, and the reducing agent supply device 18 can be made closer to the exhaust pipe 16.

Configuration diagram of an exhaust emission control device embodying the present invention The elements on larger scale near the injection nozzle concerning a 1st embodiment of the present invention. The elements on larger scale near the injection nozzle concerning a 2nd embodiment of the present invention. The elements on larger scale near the injection nozzle concerning a 3rd embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 14 NOx reduction catalyst 16 Exhaust pipe 16A Opening 18 Reducing agent supply apparatus 20 Piping 22 Injection nozzle 24 Flange 30 Radiation fin

Claims (4)

A reduction catalyst disposed in the engine exhaust system 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 fixed to the exhaust system via a flange and supplying a liquid reducing agent to the exhaust upstream 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 emission control device for an engine, wherein the pipe is made of a ceramic material.   2. The exhaust emission control device for an engine according to claim 1, wherein heat dissipating fins are arranged on the flange.   The engine exhaust gas purification apparatus according to claim 1 or 2, wherein a refrigerant is passed through the flange.   The engine exhaust gas purification apparatus according to any one of claims 1 to 3, wherein a heat insulating material gasket is interposed between the exhaust system and the flange.

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