WO2005073530A1

WO2005073530A1 - Engine exhaust emission control system

Info

Publication number: WO2005073530A1
Application number: PCT/JP2005/001532
Authority: WO
Inventors: Kiminobu Hirata; Nobuhiko Masaki; Hisashi Akagawa
Original assignee: Nissan Diesel Motor Co., Ltd.
Priority date: 2004-02-02
Filing date: 2005-02-02
Publication date: 2005-08-11
Also published as: JP4290026B2; JP2005214170A

Abstract

An engine exhaust emission control system comprising, respectively disposed in an engine exhaust system along an exhaust flowing direction, at least an oxidizing catalyst for oxidizing nitrogen monoxide into nitrogen dioxide, an injection nozzle for injecting and supplying a liquid reducing agent according to an engine operation condition, and reducing catalyst for reducing and purifying nitrogen oxides using the liquid reducing agent, wherein, since the oxidizing catalyst is disposed in an exhaust system fixed to the engine and the reducing catalyst is disposed in an exhaust system fixed to the chassis to thereby elongate the distance between the injection nozzle and the reducing catalyst, a sufficient time is ensured for diffusing and mixing a liquid reducing agent, injected and supplied from the injection nozzle, into/with the exhaust until it reaches the reducing catalyst to thereby facilitate the diffusion and mixing of the liquid reducing agent.

Description

Specification

Engine exhaust purification device

Technical field

[0001] The present invention relates to an engine exhaust purification device (hereinafter referred to as "exhaust exhaust device") for reducing and purifying nitrogen oxides (NOx) in exhaust using a liquid reducing agent. The present invention relates to a technique for promoting diffusion and mixing of a liquid reducing agent.

Background art

[0002] As a catalyst purification system for purifying NOx contained in exhaust gas of an engine, an exhaust purification device disclosed in Japanese Patent Application Laid-Open No. 2000-27627 (Patent Document 1) has been proposed.

[0003] A powerful exhaust gas purification device injects and supplies a required amount of liquid reducing agent according to the engine operating state to an exhaust gas upstream of a reduction catalyst provided in an engine exhaust system, thereby providing a high level of exhaust gas. NOx is subjected to a catalytic reduction reaction with a liquid reducing agent to purify NOx into harmless components. Here, the reduction reaction uses ammonia having a good reactivity with NOx. As the liquid reducing agent, an aqueous urea solution that generates ammonia by hydrolysis with exhaust heat and steam in the exhaust gas is used. In addition, an oxidation catalyst that oxidizes nitrogen monoxide (NO) to nitrogen dioxide (NO) in the exhaust system of the begging engine that improves the NOx purification rate of the reduction catalyst

2

A technique has been developed in which an injection nozzle for injecting and supplying a liquid reducing agent and a reduction catalyst are arranged in this order, respectively, and the ratio of NO to NO in exhaust gas is improved by an oxidation catalyst.

2

Patent Document 1: JP-A-2000-27627

Disclosure of the invention

Problems to be solved by the invention

[0004] By the way, if the liquid reducing agent injected and supplied from the injection nozzle is not sufficiently diffused and mixed in the exhaust gas until it reaches the reduction catalyst, the improvement of the NOx purification rate by the reduction catalyst cannot be expected. Would. On the other hand, if the diffusion and mixing of the liquid reducing agent is insufficient, and the injection and supply of the liquid reducing agent in the required amount or more in accordance with the operating state of the engine, the running cost is not only increased. The reducing agent component is deposited in the exhaust system located downstream of the exhaust gas. Therefore, the precipitation of the reducing agent component In order to promote the diffusion and mixing of the liquid reducing agent while suppressing the reduction, it is necessary to increase the distance between the injection nozzle and the reducing catalyst.

[0005] However, since the oxidation catalyst, the injection nozzle, and the reduction catalyst are disposed in the exhaust system on the chassis side, the distance between the oxidation catalyst and the reduction catalyst is limited due to the layout of the vehicle. I couldn't make it longer. In addition, if an injection nozzle is arranged upstream of the exhaust of the oxidation catalyst, sufficient time for the liquid reducing agent to diffuse and mix before reaching the reduction catalyst can be secured, but the oxidation catalyst oxidizes the liquid reducing agent. The meaning of providing an oxidation catalyst is diminished. Therefore, it is difficult to increase the distance between the injection nozzle and the reduction catalyst, and it has been difficult to say that the liquid reducing agent is effectively used. Note that a similar problem may occur in an exhaust gas purification apparatus using a fuel such as light oil, gasoline, or alcohol as a liquid reducing agent.

[0006] In view of the above-mentioned conventional problems, the present invention has reviewed the layout of the oxidation catalyst, the injection nozzle, the reduction catalyst, and the like provided in the engine exhaust system, and has discussed the relationship between the injection nozzle and the reduction catalyst. An object of the present invention is to provide an exhaust gas purifying apparatus that promotes diffusion and mixing of a liquid reducing agent by ensuring a sufficient distance.

Means for solving the problem

[0007] Accordingly, in the present invention, at least an oxidation catalyst for oxidizing nitrogen monoxide to nitrogen dioxide and a liquid reducing agent are injected and supplied to the engine exhaust system in the exhaust gas flow direction according to the operating state of the engine. In an exhaust gas purifying apparatus for an engine, each of which is provided with an injection nozzle for performing a reduction and a reduction catalyst for reducing and purifying nitrogen oxides using a liquid reducing agent, an exhaust gas in which the oxidation catalyst is fixed to the engine is provided. The reduction catalyst is arranged in the exhaust system fixed to the chassis while being arranged in the system. Here, the injection nozzle can be disposed in an exhaust system fixed to the chassis or the engine. Further, a turbocharger turbine that collects exhaust energy and supercharges intake air may be disposed in an exhaust system upstream of the reduction catalyst, that is, an exhaust system fixed to a chassis or an engine.

[0008] Furthermore, the oxidation catalyst is formed by a thin coat of a catalyst component on a honeycomb-type catalyst carrier in which a large number of cells formed along the exhaust gas flow direction have thin walls. Is desirable. In this way, even if the oxidation catalyst is miniaturized, the emission of the catalyst carrier is reduced. The gas flow passage area is sufficiently secured, the pressure loss can be suppressed as much as possible, and the cost can be reduced because the amount of the catalyst component is small. At this time, there is a concern that the oxidation catalyst may be reduced in size due to downsizing of the oxidation catalyst and reduction of the catalyst components. However, since the oxidation catalyst is disposed in the exhaust system fixed to the engine, the exhaust gas passing therethrough is exhausted. In addition to a sufficiently high temperature, a reduction in the amount of heat released from the peripheral wall due to the downsizing of the oxidation catalyst makes it possible to secure oxidation performance equivalent to that of the conventional configuration.

The invention's effect

According to the exhaust purification device of the present invention, since the oxidation catalyst is provided in the exhaust system fixed to the engine, it is possible to move the injection nozzle to the upstream of the exhaust gas. The distance between can be increased. As a result, sufficient time is allowed for the liquid reducing agent injected and supplied from the injection nozzle to diffuse and mix in the exhaust gas until the liquid reducing agent reaches the reduction catalyst, thereby promoting the diffusion and mixing of the liquid reducing agent. can do. Further, since the diffusion and mixing of the liquid reducing agent are promoted, the precipitation of the reducing agent component in the injection nozzle and the exhaust system located downstream of the exhaust nozzle can also be suppressed. At this time, if the exhaust gas of the engine is directly introduced into the oxidation catalyst, the oxidation catalyst can easily exhibit its oxidation ability easily at a temperature higher than the activation temperature.

Brief Description of Drawings

FIG. 1 is a configuration diagram showing a first embodiment of an exhaust gas purification apparatus according to the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of the exhaust gas purification apparatus according to the present invention.

FIG. 3 is a configuration diagram showing a third embodiment of the exhaust gas purification apparatus according to the present invention.

FIG. 4 is a configuration diagram showing a fourth embodiment of the exhaust gas purification apparatus according to the present invention.

FIG. 5 is a configuration diagram showing a fifth embodiment of the exhaust gas purification apparatus according to the present invention. Explanation of symbols

[0011] 10 engine

12 Exhaust manifold

14 Exhaust pipe

14A Upstream exhaust pipe

14B Downstream exhaust pipe 14C flexiv tube

16 Turbine

18 Oxidation catalyst

20 Injection nozzle

22 NOx reduction catalyst

BEST MODE FOR CARRYING OUT THE INVENTION

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

FIG. 1 shows the configuration of an exhaust gas purifying apparatus according to a first embodiment of the present invention.

An exhaust pipe 14 connected to an exhaust manifold 12 of the engine 10 includes at least a turbocharger bin 16 for collecting exhaust energy and supercharging intake air along an exhaust flow direction, An oxidation catalyst 18 that oxidizes NO to NO, and a liquid

2

An injection nozzle 20 for injecting and supplying a body reducing agent and a NOx reduction catalyst 22 for reducing and purifying NOx using a liquid reducing agent are provided respectively. More specifically, the turbine 16 and the oxidation catalyst 18 are respectively disposed in an upstream exhaust pipe 14A fixed to the engine 10 and the exhaust manifold 12, while the injection nozzle 20 and the NOx reduction catalyst 22 are mounted on a chassis (not shown). Each is fixed to the fixed downstream exhaust pipe 14B. The upstream exhaust pipe 14A and the downstream exhaust pipe 14B are connected to each other via a flexible tube 14C that absorbs the relative movement between the engine 10 and the chassis, thereby forming an exhaust system. Here, from the viewpoint of simplifying the in-vehicle layout, it is preferable that at least one of the turbine 16 and the oxidation catalyst 18 be directly supported by the engine 10 via a bracket. Reference numeral 24 in the drawing denotes a reducing agent oxidation catalyst that oxidizes and purifies the liquid reducing agent that has passed through the NOx reduction catalyst 22.

[0015] Further, since the oxidation catalyst 18 is provided in the engine room, it is desirable to reduce the size while minimizing the pressure loss due to the increase in exhaust resistance. For this reason, the oxidation catalyst 18 has a structure in which a large number of cells formed along the exhaust gas flow direction have a thin-walled honeycomb-type catalyst carrier, and a thin layer of a noble metal such as platinum as a catalyst component is wash-coated with a thin layer. Use something. In this way, despite the size reduction, the exhaust gas flow area in the catalyst carrier is sufficiently ensured, the pressure loss can be suppressed as much as possible, and the cost can be reduced because the catalyst component can be reduced. Can be done. At this time, There is a concern that the oxidation capacity may be reduced due to the downsizing of the medium 18 and the reduction of the catalyst components.However, since the oxidation catalyst 18 is provided in the engine room, the temperature of the exhaust passing therethrough is sufficiently high. The reduction in the amount of heat radiated from the peripheral wall due to the downsizing of the oxidation catalyst 18 makes it possible to ensure the same oxidation performance as in the conventional configuration.

[0016] According to the powerful configuration, the oxidation catalyst 18 is disposed in the engine room, so that the injection nozzle 20 can be moved upstream of the exhaust gas. The distance between them can be lengthened. For this reason, a sufficient time for the liquid reducing agent injected and supplied from the injection nozzle 20 to diffuse and mix in the exhaust gas until the liquid reducing agent reaches the NOx reduction catalyst 22 can be secured, and the diffusion and mixing of the liquid reducing agent can be performed. Can be promoted. Further, since the diffusion and mixing of the liquid reducing agent are promoted, the precipitation of the reducing agent component in the injection nozzle 20 and the downstream exhaust pipe 14B located downstream of the exhaust nozzle can be suppressed.

FIG. 2 shows a configuration of an exhaust gas purification apparatus according to a second embodiment of the present invention. Note that the following embodiments have the same basic configuration as the first embodiment, and therefore, the same components will be denoted by the same reference characters and description thereof will be omitted.

In the present embodiment, unlike the first embodiment, a configuration is adopted in which the oxidation catalyst 18 and the turbine 16 are arranged in this order along the exhaust gas flow direction in the upstream exhaust pipe 14A. In this way, the exhaust gas from the exhaust manifold 12 is directly introduced into the oxidation catalyst 18, so that the oxidation catalyst 18 can sufficiently exhibit its oxidizing ability so that the catalyst components easily reach the activation temperature or higher. . Note that other operations and effects are the same as those of the first embodiment, and a description thereof will be omitted (the same applies hereinafter).

FIG. 3 shows a configuration of a third embodiment of the exhaust gas purification apparatus according to the present invention.

[0020] An exhaust pipe 14 connected to an exhaust manifold 12 of the engine 10 has at least an oxidation catalyst 18, an injection nozzle 20, a turbine 16, a NOx reduction catalyst 22, , Respectively. Specifically, the oxidation catalyst 18 is provided in the upstream exhaust pipe 14A, while the injection nozzle 20, the turbine 16 and the NOx reduction catalyst 22 are provided in the downstream exhaust pipe 14B. With this configuration, the same operation and effect as those of the second embodiment can be obtained.

FIG. 4 shows the configuration of a fourth embodiment of the exhaust gas purification apparatus according to the present invention. [0022] In the present embodiment, unlike the third embodiment, the oxidation catalyst 18, the injection nozzle 20, and the turbine 16 are provided in the upstream exhaust pipe 14A along the exhaust gas flow direction, while the downstream exhaust pipe 14B is provided. In addition, a configuration in which a NOx reduction catalyst 22 is provided is adopted. This makes it possible to maximize the distance between the injection nozzle 20 and the NOx reduction catalyst 22 as much as possible while sufficiently exhibiting the oxidation ability of the oxidation catalyst 18 as in the second embodiment. The time required for the liquid reducing agent injected and supplied from to diffuse and mix can be maximized.

FIG. 5 shows the configuration of a fifth embodiment of the exhaust gas purification apparatus according to the present invention.

In the present embodiment, a configuration is adopted in which the turbine 16 provided in the upstream exhaust pipe 14A of the fourth embodiment is removed. That is, the present invention exerts its functions and effects even in a configuration in which the turbine 16 is not provided in the exhaust system. It goes without saying that the exhaust system power turbine 16 in the first to third embodiments may be removed.

[0025] In short, in the exhaust gas purification apparatus in which at least the oxidation catalyst 18, the injection nozzle 20 and the NOx reduction catalyst 22 are provided in the engine exhaust system along the exhaust gas flow direction, the oxidation catalyst 18 By disposing the NOx reduction catalyst 22 in the downstream exhaust pipe 14B while disposing the NOx reduction catalyst 22 in the upstream exhaust pipe 14A, the distance between the injection nozzle 20 and the NOx reduction catalyst 22 can be increased. Therefore, the time required for the liquid reducing agent injected and supplied from the injection nozzle 20 to reach the NOx reduction catalyst 22 becomes longer, and sufficient time for the liquid reducing agent to diffuse and mix is secured. By effectively utilizing the liquid reducing agent, NOx in exhaust gas can be purified. Further, since there is no need to inject and supply the liquid reducing agent more than necessary, it is also possible to suppress the deposition of the reducing agent component in the injection nozzle 20 and the downstream exhaust pipe 14B located downstream of the exhaust nozzle.

Claims

The scope of the claims

[1] An oxidation catalyst for oxidizing nitrogen monoxide to nitrogen dioxide at least along an exhaust gas flow direction to an engine exhaust system, an injection nozzle for injecting a liquid reducing agent according to an engine operating state, and a liquid reduction And a reduction catalyst that reduces and purifies nitrogen oxides using an agent.

An exhaust purification system for an engine, wherein the oxidation catalyst is provided in an exhaust system fixed to an engine, while the reduction catalyst is provided in an exhaust system fixed to a chain.

2. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the injection nozzle is disposed in an exhaust system fixed to a chassis.

3. The exhaust gas purification apparatus for an engine according to claim 1, wherein the injection nozzle is disposed in an exhaust system fixed to the engine.

4. The exhaust gas purifying apparatus for an engine according to claim 1, wherein a turbine of a turbocharger that collects exhaust energy and supercharges intake air is disposed in an exhaust system upstream of the reduction catalyst.

5. The exhaust gas purification device for an engine according to claim 4, wherein the turbine is disposed in an exhaust system fixed to the engine.

6. The exhaust emission control device for an engine according to claim 4, wherein the turbine is disposed in an exhaust system fixed to a chassis.

[7] The oxidation catalyst is characterized in that a honeycomb-type catalyst carrier in which a large number of cells are formed along the exhaust gas flow direction and the partition walls of which are formed of thin walls is wash-coated with a thin layer of a catalyst component. The exhaust purification device for an engine according to claim 1, wherein