JP4483493B2 - Diesel engine exhaust purification system - Google Patents

Description

  The present invention relates to an exhaust gas purification technology for a diesel engine, and more particularly to an exhaust gas purification system in which a fuel addition valve is provided in the middle of an exhaust pipe to supply fuel to an exhaust gas purification catalyst to maintain its function.

  An exhaust gas purification system provided with an exhaust gas purification catalyst for exhaust gas purification is employed in the middle of the exhaust pipe of the diesel engine. As the exhaust purification catalyst used here, for example, when the exhaust air-fuel ratio is lean, NOx in the exhaust gas is oxidized and temporarily stored in the form of nitrate, and unburned when the oxygen concentration in the exhaust gas decreases. NOx storage and reduction catalysts that reduce and purify NOx through the intervention of HC, CO, and the like are known.

  However, the NOx occlusion reduction catalyst cannot occlude more NOx when the occlusion amount of NOx increases and reaches the saturation amount. Therefore, it is necessary to periodically reduce the oxygen concentration of the exhaust gas flowing into the NOx occlusion reduction catalyst so as to release the occluded NOx and maintain the catalytic function.

  In the case of a gasoline engine, by reducing the operating air-fuel ratio (A / F) (operating at a rich air-fuel ratio), the oxygen concentration in the exhaust gas is reduced and unburned HC (hydrocarbon) and CO in the exhaust gas are reduced. The reduction component such as NO can be increased to promote the release of NOx. However, in the case of a diesel engine, since it is difficult to operate at a rich air-fuel ratio, it is difficult to promote the release of NOx from the NOx storage reduction catalyst.

  In view of this, a technique has been conventionally proposed in which a fuel addition valve is provided in the exhaust pipe upstream of the NOx storage reduction catalyst, and fuel is added from the fuel addition valve to the NOx storage reduction catalyst to promote the release of NOx. When fuel is added to the exhaust gas upstream of the NOx storage reduction catalyst, the fuel is pyrolyzed in the high-temperature exhaust gas to generate a large amount of hydrocarbons. By reacting this hydrocarbon with oxygen on the NOx occlusion reduction catalyst using the hydrocarbon as a reducing agent, it is possible to reduce the oxygen concentration in the exhaust gas and promote the release of NOx.

  In addition, as a measure to reduce particulate matter (particulate matter) discharged from diesel engines, exhaust purification catalysts such as oxidation catalysts supported on particulate filters and flow-through oxidation catalysts are placed in the middle of the exhaust pipe. Has been deployed. If such an oxidation catalyst is used, it is possible to promote the oxidation reaction of the particulates collected in the particulate filter and the particulates in the exhaust gas and to reduce the particulates by combustion removal.

  However, since the oxidation catalyst has an activation temperature region, if the operation state at an exhaust temperature that falls below the activation lower limit temperature continues, the oxidation catalyst may not be activated and particulates may not be efficiently removed. Such a case can be dealt with by a technique in which a fuel addition valve is provided on the upstream side of the oxidation catalyst to add fuel to the exhaust gas as described above. In other words, the added fuel is pyrolyzed in high-temperature exhaust gas to produce a large amount of hydrocarbons, and the catalyst bed temperature is raised by the reaction heat generated when this hydrocarbon is oxidized on the oxidation catalyst. Curation can be reduced.

  In this way, the fuel addition valve is arranged upstream of the exhaust purification catalyst (NOx storage reduction catalyst, oxidation catalyst, or particulate filter carrying these) provided in the middle of the exhaust pipe to add fuel. Then, the function of the exhaust gas purification catalyst can be maintained. A plurality of improved techniques for arranging the fuel addition valve upstream of the exhaust purification catalyst have been proposed.

  Incidentally, in a passenger car equipped with a diesel engine, there may be a case where an exhaust purification catalyst can be arranged while securing a space immediately under the exhaust manifold and the turbocharger where the exhaust gas temperature is high. In this case, a fuel addition valve can be provided in the exhaust port of the cylinder head so that fuel can be added to the exhaust gas and supplied to the exhaust purification catalyst. However, in the case of a truck or the like equipped with a diesel engine, it is generally difficult to secure a space for installing an exhaust purification catalyst at the same position as a passenger car. Therefore, in the case of a truck equipped with a diesel engine, an exhaust purification catalyst is disposed in the middle of the exhaust pipe, and a fuel addition valve is disposed upstream of the exhaust purification catalyst to perform fuel addition. . For example, Patent Document 1 discloses an exhaust gas purification system suitable for a diesel engine in which an exhaust gas purification catalyst is arranged in the middle of an exhaust pipe due to the mounting space.

  FIG. 4 is a diagram showing the exhaust purification system 100 of Patent Document 1. In this exhaust purification system 100, a fuel addition valve 102 is provided along the exhaust pipe 101 outside the curved portion 101a of the exhaust pipe 101 located upstream from an exhaust purification catalyst (not shown). And the injection space 104 is formed toward the direction along the exhaust pipe 101 downstream from the curved part 101a from the front-end | tip part of the nozzle 103 of the fuel addition valve 102. As shown in FIG. This injection space 104 is formed in a boss portion 105 attached so as to protrude from the exhaust pipe 101. This exhaust purification system 100 injects fuel FE into the flow path in the exhaust pipe 101 downstream of the curved portion 101a via the injection space 104. In this purification system 100, since the boss portion 105 formed so as to protrude from the exhaust pipe 101 serves as an attachment portion of the fuel addition valve 102, the fuel addition valve 102 is not exposed to the exhaust gas EG. It is possible to prevent burning and burning of fuel on the tip of the nozzle 103.

  Further, a water jacket 106 having a cylindrical shape substantially concentric with the fuel addition valve 102 is provided inside the boss portion 105. A part of cooling water from a diesel engine (not shown) is supplied to the water jacket 106 to cool the fuel addition valve 102.

JP 2004-197635 A

  The exhaust purification system 100 of Patent Document 1 has an excellent structure that can prevent the fuel addition valve 102 from burning out or the fuel 103 from sticking to the tip of the nozzle 103 as compared with the exhaust purification system proposed previously. Yes. However, the exhaust purification system 100 still has a plurality of problems to be improved.

  For example, the boss 105 attached to the exhaust pipe 101 for holding the fuel addition valve 102 is formed of a casting. However, since castings are heavy, vibrations of diesel engines are promoted. In general, the casting surface has low smoothness and rough texture (rough surface roughness), so the added fuel injected from the fuel addition valve tends to adhere to the wall surface. When the fuel adheres to the wall surface in this manner, soot contained in the exhaust gas is easily deposited. When soot accumulates in this manner, the shape of fuel injected from the fuel addition valve deteriorates. Furthermore, fuel may be absorbed by the accumulated soot. In this case, there arises a problem that it becomes difficult for the added fuel necessary for maintaining the catalytic function to reach the purification catalyst.

  Further, the range cooled by the water jacket 106 extends to the boss portion and the exhaust pipe of the fuel addition valve peripheral portion, and if these are cooled too much, soot accumulation may be promoted. Further, since a piping system for supplying cooling water to the water jacket 106 is required, the structure becomes complicated.

  Accordingly, an object of the present invention is to provide an exhaust gas purification system for a diesel engine that can be reduced in weight and can suppress problems of soot accumulation and supercooling.

  An object of the present invention is to dispose an exhaust purification catalyst in an exhaust pipe of a diesel engine and dispose a fuel addition valve in a curved portion where the exhaust pipe is curved on the upstream side of the exhaust purification catalyst. An exhaust purification system for injecting additional fuel from the exhaust gas and supplying it to the exhaust purification catalyst, wherein the exhaust pipe is formed of a metal pipe, and a fuel addition valve holder is formed using a heat insulating material outside the curved portion Can be achieved by a diesel engine exhaust purification system in which the fuel addition valve holder is held in the fuel addition valve holder.

  According to the present invention, since the structure for fixing the fuel addition valve holder formed using the heat insulating material to the metal pipe is adopted, the structure portion for fixing the fuel addition valve can be reduced in weight as compared with the case of being made of casting, By using a heat insulating material, the fuel addition valve can be protected from the heat of the exhaust gas. Therefore, the structure which supplies and cools cooling water can be omitted. Moreover, since the fuel addition valve holder can be prepared separately from the metal pipe, it is easy to process the injected additive fuel so that it does not adhere to the wall surface. Therefore, it is possible to provide an exhaust gas purification system for a diesel engine that can reduce the weight and suppress the problems of soot accumulation and supercooling.

  In addition, the fuel addition valve holder may have a metal outer cylinder and an inner cylinder, and a ceramic material may be provided as the heat insulating material between the outer cylinder and the inner cylinder. And the said outer cylinder and the said inner cylinder may employ | adopt the structure joined through the said ceramic material and insert material.

  Further, the fuel addition valve holder includes a holder main body portion that holds the fuel addition valve and an adapter portion that fixes the holder main body portion to the curved portion, and at least one of the holder main body portion and the adapter portion includes the A structure in which a ceramic material is provided as a heat insulating material can be used.

  ADVANTAGE OF THE INVENTION According to this invention, the exhaust gas purification system of the diesel engine which can achieve weight reduction and can suppress soot accumulation and supercooling can be provided.

  A diesel engine exhaust purification system (hereinafter simply referred to as an exhaust purification system) according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a diesel engine to which an exhaust purification system is applied.

  The diesel engine 1 is equipped with a turbocharger 3. The intake air NA introduced through the air cleaner 4 is introduced into the compressor 3a of the turbocharger 3 through the intake pipe 5 and pressurized, and the pressurized intake air NA is supplied through the intercooler 6 to the intake manifold of the diesel engine 1. 7 and is distributed to each cylinder (not shown).

  The exhaust gas EG discharged from each cylinder of the diesel engine 1 through the exhaust manifold 8 is sent to the turbine 3b of the turbocharger 3 through the exhaust pipe 2, and is discharged after driving the turbine 3b. The exhaust pipe 2 is formed of a metal pipe such as stainless steel.

  The exhaust purification system applied to the diesel engine 1 includes an exhaust purification device 10 and a fuel addition device 20. The exhaust gas purification device 10 is disposed at a predetermined position of the exhaust pipe 2 so as to purify the exhaust gas EG after driving the turbine 3b and then exhaust it outside the apparatus. The fuel addition device 20 is disposed in a curved portion 2a where the exhaust pipe 2 is curved on the upstream side of the exhaust purification device 10 in the direction in which the exhaust gas EG flows. The fuel addition device 20 is fixed along the outside of the curved portion 2a, and a fuel addition valve 30 that injects the added fuel into the exhaust pipe 2 is held inside. The fuel addition valve 30 is disposed at a position where it is not exposed to the exhaust gas EG flowing through the exhaust pipe 2 as in the conventional fuel addition valve (see FIG. 4).

  An exhaust purification catalyst 11 that can maintain its function (or regenerate) by adding fuel is disposed inside the exhaust purification apparatus 10. Examples of such a regeneration type catalyst include a catalyst regeneration type particulate filter, a NOx reduction catalyst (selective reduction type catalyst), a NOx storage reduction catalyst, a catalyst in which a particulate filter is combined with a NOx storage reduction catalyst, an oxidation catalyst, and the like. Can be adopted.

  As described above, the fuel addition device 20 is attached in a state of protruding outward from the curved portion 2 a of the exhaust pipe 2. The fuel addition device 20 includes a fuel addition valve 30 and a fuel addition valve holder 21 that holds the fuel addition valve 30. The fuel addition valve holder 21 of the present embodiment is composed of two parts, a holder main body part 21a and an adapter part 21b. The holder main body 21a has a substantially cylindrical shape, and holds the fuel addition valve 30 by being inserted into a space formed in the central portion. The adapter portion 21b is a member for fastening the holder main body portion 21a to the exhaust pipe 2. FIG. 2 is an enlarged cross-sectional view taken along line AA in FIG. In FIG. 2, only the reference numeral 30 indicates the fuel addition valve in order to facilitate confirmation of the structure of the peripheral portion of the fuel addition valve 30.

  The holder main body 21 a includes an inner cylinder 22 that is in direct contact with the fuel addition valve 30, a heat insulating ceramic 23 disposed outside the inner cylinder 22, and an outer cylinder 24 that covers the ceramic 23 from the outside. Structure. The inner cylinder 22 is formed of a metal material such as stainless steel, and a space into which the fuel addition valve 30 is just inserted is formed in the center. The ceramic 23 is arranged in a cylindrical shape so as to wrap the inner cylinder 22 from the outside. Therefore, the heat transmitted from the exhaust pipe 2 can be blocked by the ceramic 23 and the fuel addition valve 30 can be protected. Further, the outer periphery of the ceramic 23 is covered with an outer cylinder 24 formed of a metal material such as stainless steel. Thus, the holder main body 21a realizes a structure having heat insulation and impact resistance by sandwiching the front and back of the brittle ceramic 23 between the inner and outer cylinders made of metal. Further, such a structure is lighter than a casting.

  The inner cylinder 22 and the ceramic 23 and the ceramic 23 and the outer cylinder 24 are connected by using insert materials 25 and 26 that join the metal material and the ceramic. Therefore, a structure in which the ceramic 23 is stably held between the inner and outer cylinders 22 and 24 made of metal can be obtained.

  The inner cylinder 22 and the ceramic 23 are substantially cylindrical, but the outer cylinder 24 is partially open on the adapter portion 21b side. Therefore, the ceramic 23 is projected outward in an arc shape. The adapter portion 21b side is molded so as to correspond to the protruding portion, and the ceramic 23 and the adapter portion 21b are connected. On the other hand, the outer cylinder 24 is provided with a connecting bracket portion 27 extending outward. The bracket portion 27 is fixed to the adapter portion 21b. The adapter part 21b is produced in a predetermined shape with a metal such as stainless steel. Therefore, by fixing the bracket portion 27 of the outer cylinder 24 to the adapter portion 21b with the bolt 28, the holder main body portion 21a and the adapter portion 21b can be fixed integrally.

  Further, the surface of the adapter portion 21 b opposite to the holder main body portion 21 a is formed in an arc shape so as to correspond to the exhaust pipe 2. The adapter part 21b is fixed to a predetermined position of the exhaust pipe 2 by welding, brazing or the like. In this way, the fuel addition valve holder 21 is fixed to the curved portion 2a of the exhaust pipe 2. In addition, the adapter part 21b may form the outer peripheral part with stainless steel, and may arrange | position the ceramic similar to the holder main-body-part 21a side inside. If a configuration in which ceramic is provided in the adapter portion 21b in this way is adopted, the heat transmitted from the exhaust pipe side can be more reliably cut off and the fuel addition valve 30 can be protected from heat loss.

  The exhaust pipe 2 at a position where the fuel addition device 20 is fixed is formed with an opening 2HL for introducing fuel into the inside. In the fuel addition device 20, a fuel spray passage 20HL is provided at a position corresponding to the opening 2HL, penetrating the holder main body portion 21a and the adapter portion 21b. The fuel spray passage 20HL has a cross-sectional shape of, for example, a circle or an ellipse, and can be formed as a substantially conical space in which the inner diameter increases as the distance from the exhaust pipe 2 increases. The fuel spray passage 20HL may be formed according to the spray shape of the added fuel injected from the fuel addition valve 30, and is designed to prevent the added fuel injected from the fuel addition valve 30 from adhering to the inner surface. It is more preferable. The fuel spray passage 20HL is also formed in the portion of the ceramic 23. However, the adhesion of the injected fuel can be suppressed by applying a mirror finish to the ceramic surface of this portion.

  FIG. 3 is a diagram showing an outline of the manufacturing process of the holder main body 21a. 3 shows the state of the process in the cross section taken along the line B-B in FIG. 2, (A) shows the state when the ceramic 23 is set in the outer cylinder 24, and (B) shows the inside of the ceramic 23. The state when setting the cylinder 22 is shown. In the step shown in FIG. 3 (A), an insert member 26 is interposed between the outer tube 24 and the ceramic 23 under vacuum heating, and the ceramic 23 is pushed (pressurized) into the outer tube 24, whereby the outer tube 24 and the ceramic 23 can be firmly joined. Further, in the step shown in FIG. 3B, the inner cylinder 22 is pushed into the ceramic 23 by inserting the insert material 25 between the inner cylinder 22 and the ceramic 23 under vacuum heating. 22 and the ceramic 23 can be firmly joined in the same manner. Then, the fuel addition device 20 can be completed by inserting the fuel addition valve 30 into the inner cylinder 22.

  As shown in FIG. 3B, the fuel addition valve 30 is disposed along the curved portion 2a of the exhaust pipe 2, and is installed with the tip of the fuel addition valve 30 facing downward. A part of the fuel guided from a fuel tank (not shown) or the like to the base end portion of the fuel addition valve 30 is injected from the distal end portion of the fuel addition valve 30 toward the direction along the exhaust pipe 2 downstream of the curved portion 2a. It has come to be. The fuel injected from the tip of the fuel addition valve 30 is introduced into the exhaust pipe 2 through the fuel spray passage 20HL described above. The added fuel that has entered the exhaust pipe 2 is supplied to the exhaust purification catalyst 11 and used for maintaining the function.

  In the exhaust gas purification system for a diesel engine described above, the exhaust pipe 2 and the fuel addition valve holder 21 can be manufactured separately, so that the fuel spray passage 20HL can be easily processed with high accuracy. Therefore, the wall surface in the fuel spray passage 20HL of the fuel addition valve holder 21 through which the added fuel injected from the fuel addition valve 30 passes can be formed with high smoothness. For example, as described above, the ceramic 23 portion is subjected to processing such as mirror finishing, so that the inner wall surface of the fuel spray passage 20HL can be formed smoothly to prevent soot accumulation. Moreover, the accumulation of soot on the wall surface can also be suppressed by making the exhaust pipe 2 a metal pipe such as stainless steel. Furthermore, since the fuel addition valve holder 21 of the present exhaust purification system is reduced in weight as compared with the fixed portion of the fuel addition valve that uses a conventional casting, the influence of vibration from the diesel engine can be reduced.

  Further, since the fuel addition valve 30 is held by the fuel addition valve holder 21 having a heat insulating structure, the heat transmitted from the outside of the fuel addition valve 30 can be cut off to prevent a failure due to overheating. Therefore, this exhaust purification system does not require a piping configuration for flowing cooling water in order to cool the fuel addition valve 30, and the configuration can be simplified and the cost can be reduced. Furthermore, the problem of the promotion of soot accumulation due to supercooling, which becomes a problem when cooling water is used, does not occur.

  Furthermore, in the embodiment described above, the fuel addition valve holder 21 is divided into the holder main body portion 21a and the adapter portion 21b, so that each processing can be easily performed and assembled. However, the fuel addition valve holder 21 may be integrally formed. When the fuel addition valve holder is integrally formed, the outer cylinder portion on the holder main body portion 21a side and the adapter portion 21b may be manufactured integrally. In this case, the number of parts can be reduced.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

It is a figure which shows the diesel engine to which the exhaust gas purification system is applied. It is an expanded sectional view by the AA arrow of FIG. It is the figure which showed the outline of the manufacturing process of a holder main-body part. It is the figure shown about the conventional exhaust gas purification system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Exhaust pipe 2a Curved part of exhaust pipe 10 Exhaust purification apparatus 11 Exhaust purification catalyst 20 Fuel addition apparatus 21 Fuel addition valve holder 21a Holder main body part 21b Adapter part 22 Inner cylinder 23 Ceramic 24 Outer cylinder 25, 26 Insert material 30 Fuel addition valve FE fuel (added fuel)
EG exhaust gas

Claims (2)

An exhaust purification catalyst is disposed in the exhaust pipe of the diesel engine, and a fuel addition valve is disposed in a curved portion where the exhaust pipe is curved on the upstream side of the exhaust purification catalyst, and the added fuel is supplied from the fuel addition valve. An exhaust gas purification system that injects and supplies the exhaust gas purification catalyst,
The exhaust pipe is formed of a metal pipe, and a fuel addition valve holder formed using a heat insulating material is fixed outside the curved portion, and the fuel addition valve is held in the fuel addition valve holder ,
The fuel addition valve holder has a metal outer cylinder and an inner cylinder, and a ceramic material is disposed as the heat insulating material between the outer cylinder and the inner cylinder, and the outer cylinder and the inner cylinder are the ceramic material. A diesel engine exhaust purification system characterized by being joined to each other via an insert material .   The fuel addition valve holder includes a holder main body portion that holds the fuel addition valve and an adapter portion that fixes the holder main body portion to the curved portion, and the heat insulating material is provided in at least one of the holder main body portion and the adapter portion. The exhaust gas purification system for a diesel engine according to claim 1, wherein a ceramic material is provided.

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