JP2005113688A - Engine exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve NOx emission control efficiency by preventing choking in an injection nozzle to supply a reducing agent to the exhaust upstream side of a reduction catalyst. <P>SOLUTION: In a reducing agent supply device 6, a detection signal S1 for exhaust temperature from an exhaust temperature sensor 9 is used to set supply quantity of urea water to the injection nozzle 5 to be above the lowest limit value of supply quantity to cool the inside of the injection nozzle 5 at temperature less than urea water crystallizing temperature with the detected exhaust temperature. As urea water is supplied, the inside of the injection nozzle 5 is cooled to temperature less than urea water crystallizing temperature. Urea water is thus prevented from crystallizing in the injection nozzle 5, thereby choking in the injection nozzle 5 can be prevented. NOx emission control efficiency can thus be improved. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an exhaust purification device that reduces and removes nitrogen oxides (NOx) discharged from a diesel engine, a gasoline engine or the like mounted on a moving vehicle by using a reducing agent, and in particular, an exhaust upstream side of a reducing catalyst. The present invention relates to an exhaust emission control device for an engine which prevents clogging of an injection nozzle supplied to the engine and improves the efficiency of NOx purification processing.

Several exhaust emission control devices have been proposed as a system for purifying exhaust gas by removing NOx from particulate matter (PM) in exhaust gas discharged from the engine. This exhaust purification device places a reduction catalyst in an exhaust system of an engine, and injects and supplies a reducing agent into an exhaust passage upstream of the reduction catalyst, thereby causing NOx and reducing agent in the exhaust to undergo a catalytic reduction reaction, thereby reducing NOx. Is purified to harmless components. The reducing agent is stored in a storage tank in a liquid state at room temperature, and a required amount is injected and supplied from an injection nozzle. In the reduction reaction, ammonia having good reactivity with NOx is used, and as the reducing agent, an aqueous urea solution, an aqueous ammonia solution, or other reducing agent aqueous solution that easily generates ammonia by hydrolysis is used (for example, patents). Reference 1).
JP 2000-27627 A

  However, in the conventional exhaust purification device, the supply amount of the reducing agent is controlled in accordance with the engine operating state (exhaust temperature, NOx emission amount, etc.). However, depending on the engine operating state, it is provided in the exhaust passage. In some cases, the injection hole of the injection nozzle or the passage leading to the injection nozzle is clogged, and the reducing agent cannot be supplied sufficiently. As a result, the reduction reaction of NOx on the reduction catalyst does not proceed smoothly, and there is a possibility that NOx is discharged.

  The main cause of the clogging of the injection nozzle is that urea in an aqueous urea solution (hereinafter referred to as “urea water”) as a reducing agent crystallizes and adheres in an injection hole or a passage leading to it. This is because urea water condenses at 100 ° C., and when urea water is heated to 100 ° C. or higher, urea crystals are generated. Here, during normal injection supply of urea water by the injection nozzle, urea water supplied from the storage tank (in the case of a reducing agent supply system that supplies compressed air together with urea water to the injection nozzle, urea water and Even if the compressed air) cools the inside of the nozzle and the injection nozzle is heated by the exhaust from the engine, the urea water does not reach 100 ° C. However, when the supply amount of urea water decreases and the inside of the nozzle cannot be cooled completely, the urea water inside the nozzle becomes 100 ° C. or more, and urea crystals are generated, which may cause clogging.

  Accordingly, the present invention addresses such problems and prevents the clogging of the injection nozzle that supplies the reducing agent to the exhaust upstream side of the reduction catalyst, thereby improving the efficiency of the NOx purification process. The purpose is to provide.

  In the exhaust emission control device according to claim 1, a reduction catalyst disposed in an exhaust system of the engine for reducing and purifying nitrogen oxide in the exhaust gas with a reducing agent, and the reducing agent in the exhaust passage of the exhaust system. A reducing agent supply means having an injection nozzle for supplying the exhaust catalyst to the exhaust upstream side; and a temperature detection means provided near the exhaust upstream side of the injection nozzle for detecting the exhaust temperature in the exhaust passage. In the engine exhaust gas purification device, the reducing agent supply means cools the inside of the injection nozzle to a temperature below the temperature at which the reducing agent crystallizes at the exhaust temperature using an exhaust temperature detection signal from the temperature detecting means. It is set to be equal to or higher than the lower limit value of the supply amount to be supplied, and the reducing agent is supplied to the injection nozzle.

  With such a configuration, using the detection signal of the exhaust temperature from the temperature detection means, the reducing agent supply means cools the inside of the injection nozzle below the temperature at which the reducing agent crystallizes at the detected exhaust temperature. The reducing agent is supplied to the injection nozzle at the set supply amount. By supplying such a reducing agent, the inside of the injection nozzle is cooled below a temperature at which the reducing agent crystallizes.

  According to a second aspect of the present invention, the reducing agent supply means inputs an exhaust temperature detection signal from the temperature detection means and an engine operating state signal, and supplies the reducing agent in the engine operating state. Control which calculates | requires the amount, and calculates | requires the lower limit of the supply amount of the reducing agent which cools the inside of the said injection nozzle to less than the temperature which crystallizes the said injection nozzle in the exhaust temperature, compares both, and sets control agent supply amount A circuit is provided. Thus, the control circuit provided in the reducing agent supply means inputs the exhaust temperature detection signal from the temperature detection means and the engine operating state signal, and supplies the reducing agent in the engine operating state at that time. The lower limit of the supply amount of the reducing agent that cools the inside of the injection nozzle below the temperature at which the reducing agent crystallizes at the detected exhaust temperature is determined, and the supply amount of the reducing agent is set by comparing the two. .

  The invention as set forth in claim 3 is characterized in that the reducing agent supply means supplies compressed air together with the reducing agent to the injection nozzle, atomizes the reducing agent, and supplies it by injection. As a result, compressed air is supplied to the injection nozzle together with the reducing agent, the reducing agent is atomized with the compressed air, and is supplied to the exhaust upstream side of the reduction catalyst.

  The invention according to claim 4 is characterized in that the reducing agent is an aqueous urea solution. Thus, nitrogen oxides in the exhaust gas are reduced and purified using an aqueous urea solution that easily generates ammonia by hydrolysis as a reducing agent.

  According to the first aspect of the present invention, the supply of the reducing agent that is set to be equal to or higher than the lower limit of the supply amount that cools the inside of the injection nozzle below the temperature at which the reducing agent crystallizes at the detected exhaust temperature causes the inside of the injection nozzle to It is possible to prevent the reducing agent from being crystallized by cooling and preventing the injection nozzle from being clogged. Therefore, the efficiency of the NOx purification process can be improved.

  According to the second aspect of the present invention, the supply amount of the reducing agent in the engine operating state at that time and the supply amount of the reducing agent that cools the inside of the injection nozzle below the temperature at which the reducing agent crystallizes at the detected exhaust temperature. Is compared with the lower limit value, and the reducing agent can be supplied by always setting it to be equal to or higher than the lower limit value of the supply amount of the reducing agent at the exhaust temperature at that time. Therefore, the inside of the injection nozzle is cooled and the reducing agent is not crystallized, and the injection nozzle can be prevented from being clogged.

  Furthermore, according to the invention which concerns on Claim 3, the inside of an injection nozzle is efficiently cooled with a reducing agent and compressed air by supplying compressed air with a reducing agent with respect to an injection nozzle. Therefore, the reducing agent does not crystallize in the injection nozzle and can be prevented from being clogged.

  Furthermore, according to the invention of claim 4, NOx in the exhaust gas is made harmless by using a urea aqueous solution that easily generates ammonia by hydrolysis without directly using ammonia as a reducing agent. This can improve the efficiency of the NOx purification treatment.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a view showing an embodiment of an exhaust emission control device for an engine according to the present invention. This exhaust purification device is for reducing and removing NOx discharged from a diesel engine, a gasoline engine or the like mounted on a moving vehicle using a reducing agent. The exhaust of the engine 1 using gasoline or light oil as fuel is discharged from the exhaust manifold 2 to the atmosphere via an exhaust pipe 4 provided with a NOx reduction catalyst 3. Specifically, the exhaust pipe 4 serving as an exhaust passage is provided with three catalysts, a nitric oxide (NO) oxidation catalyst, a NOx reduction catalyst, and an ammonia oxidation catalyst, in that order from the upstream side of the exhaust. Although an exhaust system is configured by arranging sensors, NOx sensors, etc., the detailed configuration is not shown.

  The NOx reduction catalyst 3 reduces and purifies NOx in the exhaust gas passing through the exhaust pipe 4 with a reducing agent. The NOx reduction catalyst 3 has a honeycomb-shaped cross section made of ceramic cordierite or Fe-Cr-Al heat-resistant steel. For example, a zeolite-type active component is supported on the monolith type catalyst carrier. Then, the active component carried on the catalyst carrier is activated upon receiving the supply of the reducing agent, and effectively purifies NOx into a harmless substance.

  An injection nozzle 5 is disposed in the exhaust pipe 4 on the exhaust upstream side of the NOx reduction catalyst 3. The injection nozzle 5 supplies a reducing agent to the exhaust upstream side of the NOx reduction catalyst 3. Compressed air is supplied together with the reducing agent via the reducing agent supply device 6, and the reducing agent is atomized and injected. It comes to supply. Here, the injection nozzle 5 is disposed in the exhaust pipe 4 toward the downstream side substantially parallel to the flow direction A of the exhaust gas, or is inclined obliquely at an appropriate angle. The reducing agent supply device 6 is supplied with the reducing agent stored in the storage tank 7 through the supply pipe 8. The injection nozzle 5 and the reducing agent supply device 6 constitute reducing agent supply means for supplying the reducing agent to the exhaust upstream side of the NOx reduction catalyst 3.

  In this embodiment, a urea aqueous solution (urea water) is used as a reducing agent to be supplied by injection from the injection nozzle 5. In addition, an aqueous ammonia solution or the like may be used. The urea water injected and supplied from the injection nozzle 5 is hydrolyzed by the exhaust heat in the exhaust pipe 4 to easily generate ammonia. The obtained ammonia reacts with NOx in the exhaust gas in the NOx reduction catalyst 3 to be purified into water and harmless gas. The urea water is a solid or powdery urea aqueous solution, stored in the storage tank 7, and supplied to the reducing agent supply device 6 through the supply pipe 8.

  An exhaust temperature sensor 9 is provided in the vicinity of the upstream side of the exhaust of the injection nozzle 5 inside the exhaust pipe 4. The exhaust temperature sensor 9 serves as temperature detection means for detecting the exhaust temperature in the exhaust pipe 4, and in this embodiment, the exhaust temperature in the vicinity of the exhaust upstream side of the injection nozzle 5 is detected. . An exhaust gas temperature detection signal detected by the exhaust gas temperature sensor 9 is sent to the reducing agent supply device 6.

  Here, in the present invention, the reducing agent supply device 6 uses the detection signal of the exhaust temperature from the exhaust temperature sensor 9 and is less than the temperature at which urea water crystallizes inside the injection nozzle 5 at the exhaust temperature. The urea water is supplied to the injection nozzle 5 by setting it to be equal to or higher than the lower limit value of the supply amount to be cooled. That is, as shown in FIG. 2, a booster pump 10 provided in the middle of the supply pipe 8 from the storage tank 7 shown in FIG. 1 to raise the pressure of urea water, and a urea water provided downstream of the booster pump 10. A supply valve 11 that opens and closes the passage, an air supply valve 13 that opens and closes the passage of compressed air provided in the middle of an air supply pipe 12 from a compressed air source (not shown), and a reducing agent supply control circuit 14 are provided. .

The reducing agent supply control circuit 14 receives the exhaust gas temperature detection signal S ₁ from the exhaust gas temperature sensor 9 and the engine control circuit 15 receives the operation state signal S ₂ from the engine control circuit 15. The urea water supply amount in the operating state is obtained, and the lower limit value of the urea water supply amount for cooling the inside of the injection nozzle 5 below the temperature at which the urea water is crystallized at the exhaust temperature is obtained. For example, a control microcomputer (MPU) is used to set the supply amount of water, and control signals are supplied to the booster pump 10, supply valve 11, and air supply valve 13 in accordance with the set supply amount of urea water. And the supply amount of urea water and compressed air to the injection nozzle 5 is controlled.

The engine control circuit 15 includes a temperature sensor for detecting the exhaust temperature (engine exhaust temperature) of the exhaust manifold 2 shown in FIG. 1, a NOx sensor (not shown), an intake flow rate sensor, a rotational speed sensor, a load sensor, and the like. enter the detection signal controls the operating state of the engine 1, for example, a control microcomputer (MPU), the engine exhaust temperature and NOx emissions the reducing agent an operating condition signal S ₂ of the engine 1, such as the amount of feed The data is sent to the control circuit 14.

  Next, the operation of the exhaust emission control device configured as described above will be described with reference to FIGS. First, in FIG. 1, exhaust from the operation of the engine 1 passes through the exhaust manifold 2, the exhaust pipe 4, the NOx reduction catalyst 3 disposed in the exhaust pipe 4, and the exhaust pipe. 4 is discharged into the atmosphere from the end discharge port. At this time, urea water is injected from the injection nozzle 5 disposed upstream of the NOx reduction catalyst 3 in the exhaust pipe 4. After the urea water is supplied to the injection nozzle 5 from the urea water storage tank 7 through the supply pipe 8 to the reducing agent supply device 6, the urea water is supplied together with the compressed air by the operation of the reducing agent supply device 6. The injection nozzle 5 atomizes the urea water and supplies it by injection.

In this state, in FIG. 2, by detecting the exhaust temperature in the exhaust pipe 4 by the exhaust temperature sensor 9 provided near the exhaust upstream side of the injection nozzle 5, the detection signal S ₁ is the reducing agent supply device 6 To the reducing agent supply control circuit 14. Further, from the engine control circuit 15, a signal S ₂ of the operating state of the engine 1 such as the engine exhaust temperature and the NOx emission amount is also sent to the reducing agent supply control circuit 14.

Then, the reducing agent supply control circuit 14 obtains the urea water (reducing agent) supply amount V ₁ determined by the engine operating state by using the input signal S ₂ of the operating state of the engine 1 (step S1 in FIG. 3). . Further, the reducing agent supply control circuit 14 uses the detected exhaust gas temperature detection signal S ₁ in the exhaust pipe 4 to determine the temperature at which urea water is crystallized, which is determined by the exhaust gas temperature in the vicinity of the upstream side of the injection nozzle 5. A lower limit value V ₂ of the supply amount of urea water (reducing agent) to be cooled below is obtained (step S2). Then, by comparing the supply quantity of urea water determined the V ₁ and the lower limit V ₂ of that supply quantity, V ₁ determines whether V ₂ is smaller than (Step S3).

If V ₁ is equal to or greater than V ₂ , step S3 proceeds to “NO”, returns to step S1, and loops steps S1 → S2 → S3. In this case, the urea water supply amount V ₁ determined by the current engine operating condition is equal to or higher than the lower limit value V ₂ of the supply amount for cooling the inside of the injection nozzle 5 to a temperature lower than the temperature at which the urea water crystallizes. at a feed rate V ₁ of the urea water that is configured capable of cooling the interior of the injection nozzle 5. Therefore, the reducing agent supply control circuit 14 maintains the current urea water supply valve 11 and compressed air supply valve 13 opening, and the reducing agent supply device 6 injects the urea water supply amount V _{1 as} it is. Urea water is supplied to the nozzle 5.

Next, assuming that V ₁ becomes smaller than V ₂ , step S3 proceeds to “YES” and enters step S4. In this case, the supply amount V _{1 of} urea water determined by the current engine operating state is in a state smaller than the lower limit value V ₂ of the supply amount that cools the inside of the injection nozzle 5 below the temperature at which urea water crystallizes. , it is impossible to cool the interior of the supply amount V ₁ in the injection nozzle 5 of the urea water that is currently set. Therefore, the reducing agent supply control circuit 14 changes the current urea water supply valve 11 and the compressed air air supply valve 13 to increase the degree of opening, and the reducing agent supply device 6 changes the supply amount of urea water. The setting is changed to the lower limit V ₂ or more of the supply amount for cooling below the temperature at which the urea water is crystallized (step S4), and the urea water is supplied to the injection nozzle 5. Thereby, the inside of the injection nozzle 5 can be cooled by the supply of the urea water changed and set in step S4, and the clogging can be prevented and the efficiency of the NOx purification process can be improved.

  Thereafter, in order to end the injection of the urea water from the injection nozzle 5 by stopping the operation of the engine 1, the supply of the urea water from the storage tank 7 is first interrupted by the operation of the reducing agent supply device 6, and then for a while. Only compressed air is supplied to the injection nozzle 5. Thereby, urea water is expelled from the injection hole of the injection nozzle 5 or the passage leading to it, and the injection of urea water is terminated. In this way, the urea water is expelled from the injection nozzle 5, so that no urea water remains or so-called “post sagging” when the supply of the urea water to the injection nozzle 5 is stopped, and the urea in the injection hole or the passage leading to it. It is possible to prevent water from crystallizing and causing clogging.

  In the above description, the reducing agent supply device 6 and the injection nozzle 5 are reducing agent supply means for supplying compressed air together with urea water to the injection nozzle 5, but the present invention is not limited to this, and the injection Only the urea water may be supplied to the nozzle 5.

It is a conceptual diagram which shows embodiment of the exhaust emission purification device of the engine by this invention. It is a schematic diagram for demonstrating a structure and operation | movement of the reducing agent supply apparatus and injection nozzle in the said exhaust gas purification apparatus. It is a flowchart for demonstrating operation | movement of the said exhaust gas purification apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Engine 3 ... Reduction catalyst 4 ... Exhaust pipe 5 ... Injection nozzle 6 ... Reducing agent supply device 7 ... Storage tank 8 ... Supply piping 9 ... Exhaust temperature sensor 11 ... Urea water supply valve 13 ... Air supply valve 14 ... Reducing agent Supply control circuit 15 ... Engine control circuit

Claims (4)

A reduction catalyst disposed in the exhaust system of the engine for reducing and purifying nitrogen oxides in the exhaust with a reducing agent;
Reducing agent supply means having an injection nozzle for supplying the reducing agent to the exhaust upstream side of the reduction catalyst in the exhaust passage of the exhaust system;
A temperature detecting means provided in the vicinity of the exhaust upstream side of the injection nozzle for detecting the exhaust temperature in the exhaust passage;
An exhaust emission control device for an engine equipped with
The reducing agent supply means uses an exhaust temperature detection signal from the temperature detection means to set the supply temperature at which the inside of the injection nozzle is cooled below the temperature at which the reducing agent is crystallized at the exhaust temperature. And an exhaust purification device for an engine, wherein a reducing agent is supplied to the injection nozzle.   The reducing agent supply means inputs an exhaust temperature detection signal from the temperature detection means and also inputs an engine operating state signal to obtain a reducing agent supply amount in the engine operating state, and at the exhaust temperature. A control circuit is provided that obtains a lower limit value of a supply amount of the reducing agent that cools the inside of the injection nozzle to a temperature lower than a temperature at which the reducing agent crystallizes, and compares both to set a supply amount of the reducing agent. The exhaust emission control device for an engine according to claim 1.   The engine exhaust purification according to claim 1 or 2, wherein the reducing agent supply means supplies compressed air together with the reducing agent to the injection nozzle, and atomizes and supplies the reducing agent by injection. apparatus.   The engine exhaust gas purification apparatus according to any one of claims 1 to 3, wherein the reducing agent is an aqueous urea solution.

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