JP2006090259A - Exhaust emission control system of diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control system of a diesel engine capable of suppressing soot deposition onto an inner wall surface of a spray passage when cooling a fuel adding valve. <P>SOLUTION: In the exhaust emission control system of a diesel engine, an exhaust emission control catalyst is arranged in an exhaust pipe 2 of a diesel engine. A valve mounting part 40 is provided to a bending outer side of a bend 2a disposed upstream from the exhaust emission control catalyst. A fuel loading valve 30 is held in the valve mounting part. While a cooling water passage 41 through which cooling water for cooling the fuel loading valve is fed is formed in the valve mounting part, a spray passage 44 is formed in the valve mounting part facing the exhaust pipe. The fuel loading valve 30 is arranged in the spray passage facing an injection hole 32. The loaded fuel FE is sprayed through the injection hole 32 to be supplied to the exhaust emission control catalyst. A heat insulating layer 45 is provided between the cooling water passage 41 and the spray passage 44. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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) emitted 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 exhaust pipes. 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. Moreover, the exhaust purification catalyst can be maintained within the activation temperature by providing a fuel addition valve and adding fuel. Therefore, there have conventionally been a plurality of proposals regarding the technology for disposing the fuel addition valve upstream of the exhaust purification catalyst.

  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). A spray passage 104 is formed from the tip of the nozzle 103 of the fuel addition valve 102 toward the direction along the exhaust pipe 101 downstream of the curved portion 101a. The spray passage 104 is formed in a boss portion 105 that is integrally formed 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 through the spray passage 104. In this purification system 100, a boss portion 105 provided so as to protrude from the exhaust pipe 101 serves as a valve mounting portion of the fuel addition valve 102, and the fuel addition valve 102 is not exposed to the exhaust gas EG. In addition, it is possible to prevent the fuel from sticking to 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 problems to be improved.

  In the exhaust purification system 100, a water jacket 106 is provided on the boss portion 105 serving as a valve mounting portion to prevent burning of the fuel addition valve 102 and burning of fuel to the tip of the nozzle 103. However, the boss portion 105 is formed of a material having high thermal conductivity such as a casting. Therefore, the cooling effect by the water jacket 106 extends to the periphery other than the fuel addition valve 102. In order to efficiently use the fuel FE injected from the nozzle 103 by the exhaust purification catalyst, it is desirable to maintain the exhaust pipe 2 and the spray passage 104 at a certain high temperature without cooling, but the water jacket 106 cools the fuel FE. It will be.

  In particular, when the spray passage 104 is cooled, soot SM or HC (hereinafter simply referred to as soot SM) is easily deposited on the inner wall surface. When soot SM accumulates in this manner, the injection shape of the fuel injected from the fuel addition valve 102 deteriorates. Further, the accumulated soot SM may clog the nozzle hole of the fuel addition valve 102. In this case, the added fuel necessary for maintaining the catalyst function cannot be supplied to the purification catalyst, so that the function of the catalyst is not fully exhibited, leading to deterioration of emission and fuel consumption. In particular, in order to protect the fuel addition valve from burning or the like, the configuration in which the nozzle 103 of the fuel addition valve 102 faces the spray passage 104 as shown in the figure is easily affected by the accumulation of soot SM.

  Accordingly, an object of the present invention is to provide an exhaust gas purification system for a diesel engine that can suppress the accumulation of soot on the inner wall surface of the spray passage when the fuel addition valve is cooled.

  The above object is to arrange an exhaust purification catalyst in the exhaust pipe of a diesel engine, provide a valve mounting portion outside the curved portion upstream of the exhaust purification catalyst, and hold the fuel addition valve at the valve mounting portion. A cooling water passage for flowing cooling water for cooling the fuel addition valve is formed in the valve mounting portion, a spray passage is formed in the valve mounting portion toward the exhaust pipe, and an injection hole faces the spray passage. An exhaust purification system for a diesel engine, in which the fuel addition valve is disposed, and the added fuel is injected from the nozzle hole and supplied to the exhaust purification catalyst, and is provided between the cooling water passage and the spray passage. This can be achieved by an exhaust gas purification system for a diesel engine provided with a heat insulating layer.

  According to the present invention, since the heat insulating layer is provided between the cooling water passage and the spray passage, the cooling effect (endothermic effect) generated when the cooling water flows in the cooling water passage is the spray passage that does not require cooling. It can be prevented from spreading to. Therefore, it is possible to suppress the accumulation of soot on the inner wall surface of the spray passage even when the fuel addition valve is cooled. As a result, the fuel can be stably supplied from the fuel addition valve, so that the function of the exhaust purification catalyst can be maintained and the emission and fuel consumption of the diesel engine can be improved.

  Moreover, you may employ | adopt the structure which further provided the heat insulation layer in alignment with the said exhaust pipe in the said valve attachment part of the said exhaust pipe side from the said cooling water channel | path. Moreover, it is good also as a structure where the said heat insulation layer forms a part of said cooling water channel | path. Furthermore, the cooling water passage is configured to supply a part of the cooling water of the diesel engine, the cooling water of the diesel engine is not higher than a predetermined water temperature, and the exhaust gas flowing in the exhaust pipe is not higher than the predetermined gas temperature. In some cases, the supply of cooling water to the cooling water passage may be restricted.

  According to the exhaust purification system for a diesel engine of the present invention, the cooling effect when the fuel addition valve is cooled can be prevented from spreading to the periphery of the fuel addition valve. Therefore, it is possible to provide a diesel engine exhaust purification system that can suppress the generation of soot when the fuel addition valve is cooled.

  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. 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 to the intake manifold 7 through the intercooler 6. The cylinders 8a to 8d are formed so as to be distributed.

  The exhaust gas EG discharged from the cylinders 8a to 8d of the diesel engine 1 through the exhaust manifold 9 is sent to the turbine 3b of the turbocharger 3 through the exhaust pipe 2, and is discharged after driving the turbine 3b. It is configured. The diesel engine 1 includes an EGR (exhaust gas recirculation) device 10 that promotes exhaust purification. The EGR device 10 includes an EGR passage 11 that recirculates a part of the exhaust gas EG from the exhaust manifold 9 to the intake manifold 7, and an EGR cooler 12 and an EGR valve 13 provided in the EGR passage 11. The fuel FE stored in the fuel tank 21 is supplied to the common rail 23 by the fuel pump 22. The common rail 23 is connected to injectors 24a to 24d disposed in the respective cylinders 8a to 8d.

  In addition, the diesel engine 1 includes an exhaust purification device 50 disposed on the downstream side of the exhaust pipe 2 and an exhaust purification system 30 that adds fuel to an exhaust purification catalyst 51 in the exhaust purification device 50. Is included. The exhaust purification device 50 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 valve 30 is disposed outside in the bending direction of the curved portion 2a where the exhaust pipe 2 is curved on the upstream side of the exhaust purification device 50 in the direction in which the exhaust gas EG flows. The fuel addition valve 30 is attached at a position where it is not exposed to the exhaust gas EG flowing in the exhaust pipe 2 as in the conventional fuel addition valve (see FIG. 4).

  An exhaust purification catalyst 51 that can maintain its function (or regenerate) by adding fuel is disposed inside the exhaust purification device 50. Examples of such regeneration-type catalysts include catalyst regeneration-type particulate filters, NOx reduction catalysts (selective reduction catalysts), NOx storage-reduction catalysts, particulate filters carrying NOx storage-reduction catalysts, and oxidation catalysts. it can.

  In addition, a water jacket 41 as a cooling water passage is disposed to cool the fuel addition valve 30. As the cooling water used in the water jacket 41, a part of the cooling water for the diesel engine 1 is used. That is, the feed pipe 26 and the return pipe 27 are connected to a predetermined position of the cylinder head 25 so that cooling water in a water jacket (not shown) provided in the cylinder head 25 of the diesel engine 1 can be used. A water jacket 41 on the fuel addition valve 30 side is connected to the other ends of the pipes 26 and 27. A water temperature sensor 28 that detects the temperature of the cooling water and a valve 29 that opens and closes the feed pipe 26 are disposed on the feed pipe 26 side.

  FIG. 2 is an enlarged view of the periphery of the curved portion 2a of the exhaust pipe 2 to which the fuel addition valve 30 is fixed. A boss portion 40 as a valve attachment portion is integrally formed on the outer side portion of the bending portion 2a in the bending direction. The fuel addition valve 30 is held by the boss portion 40. The boss 40 has the same outer shape as the conventional boss shown in FIG. A substantially conical spray passage 44 is formed in the boss portion 40 so as to be out of the region through which the exhaust gas EG passes (so as to protrude outward). The fuel addition valve 30 is fixed to the boss portion 40 such that the injection hole 32 faces the spray passage 44. That is, the fuel addition valve 30 is fixed to the boss portion 40 with a part of the nozzle portion 31 in which the injection hole 32 is formed protruding into the spray passage 44. In the example shown in the figure, the nozzle portion 31 is disposed at a deep position in the spray passage 44. If the fuel addition valve 30 is arranged on the back side of the spray passage 44 in this way, the fuel addition valve 30 can be more reliably protected from heat loss and fuel burn-in. The base end portion 30a of the fuel addition valve 30 is connected to a fuel pump 22 that pumps the fuel FE, and is configured so that a part of the fuel FE can be used as the added fuel (see FIG. 1). Although FIG. 2 shows a structural example in which the boss portion 40 is formed integrally with the exhaust pipe 2, the boss portion 40 may be formed separately and fixed to the exhaust pipe 2.

  Inside the boss portion 40, the above-described water jacket 41 is disposed to cool the fuel addition valve 30. The water jacket 41 is arranged in a ring shape so as to surround the fuel addition valve 30. The cooling water supply port 43 of the water jacket 41 is connected to the feed pipe 26 described above, and the cooling water discharge port 42 is connected to the return pipe 27 described above (see FIG. 1).

  When the water jacket 41 is provided and the fuel addition valve 30 is cooled, the cooling effect reaches the peripheral portion of the fuel addition valve 30 as pointed out as a problem, and the accumulation of soot on the wall surface 44WA of the spray passage 44 is promoted. May be. Therefore, a heat insulating layer 45 is provided inside the boss portion 40 in order to suppress unnecessary cooling to the spray passage 44. The heat insulating layer 45 is formed as a layer having a heat insulating action such as an air layer or a ceramic layer. For example, an air layer can be formed by providing a predetermined space along the spray passage 44 in the boss portion 40. Moreover, a ceramic layer can be formed by accommodating a ceramic material in the space.

  In addition, in FIG. 2, the case where the heat insulation layer 45 was provided along the exhaust pipe 2 in the exhaust pipe 2 side rather than the water jacket 41 as a preferable structural example is shown. The boss portion 40 is formed using a metal material such as a casting or stainless steel. Since such a material has high thermal conductivity, the generation of soot on the wall surface 44WA of the spray passage 44 can be more reliably suppressed by disposing the heat insulating layer 45 on the exhaust pipe 2 side as well as the spray passage 44 side. However, it is good also as a structure which forms the heat insulation layer 45 only in the part along the wall surface 44WA of the spraying passage 44 from a viewpoint of simplifying a structure.

  2 shows an example in which the heat insulating layer 45 is formed in an independent region. However, when the heat insulating layer 45 is formed using ceramic, the surface of the ceramic is used. The water jacket 41 may be formed by using it. When such a structure is employed, the heat insulating layer 45 becomes a part of the configuration of the water jacket 41, so that the structure of the boss portion 40 can be simplified and downsized.

  Furthermore, the exhaust gas purification system applied to the diesel engine 1 (hereinafter simply referred to as the engine 1) suppresses soot generation by warming up early when the peripheral portion of the fuel addition valve 30 is at a low temperature. It is configured to be able to. This point will be described. When cold, the engine coolant temperature and the exhaust gas temperature are low. Further, the temperature of the engine cooling water and the temperature of the exhaust gas are relatively low even during low load operation such as idling. At these times, the peripheral portion of the fuel addition valve 30 is also at a low temperature, and soot is likely to accumulate on the wall surface 44WA of the spray passage 44. If the cooling water is allowed to flow through the water jacket 41 in such a situation, accumulation of soot on the wall surface 44WA is promoted. Therefore, the exhaust purification system applied to the engine 1 has a more preferable configuration in which the supply of the cooling water to the water jacket 41 is restricted when the peripheral portion of the fuel addition valve 30 is assumed to be low temperature. I have.

  Reference is again made to FIG. As described above, the water temperature sensor 28 for detecting the temperature of the cooling water passing through the cooling water feed pipe 26 is provided. A gas temperature sensor 14 that detects the gas temperature of the exhaust gas EG passing through the exhaust pipe 2 is disposed in the exhaust pipe 2 upstream of the exhaust purification catalyst 51. Output signals from the water temperature sensor 28 and the gas temperature sensor 14 are supplied to an ECU (electronic control unit) 20. The ECU 20 determines whether or not the peripheral portion of the fuel addition valve 30 is in a low temperature state based on the output signals of the water temperature sensor 28 and the gas temperature sensor 14, and when determining that the temperature is low, closes the valve 29 and closes the water. It is set to stop the supply of cooling water to the jacket 41. With this configuration, the peripheral portion of the fuel addition valve 30 can be warmed up early, and soot accumulation can be more reliably suppressed. Further, when the peripheral portion of the fuel addition valve 30 is in a low temperature state, it can be assumed that the temperature of the exhaust purification catalyst 51 is also low. Therefore, the exhaust purification catalyst 51 side can be activated at an early stage by the cooling water supply control performed by the ECU 20. If the peripheral portion of the fuel addition valve 30 and the exhaust purification catalyst 51 are thus warmed up early and the fuel FE is injected from the fuel addition valve 30, the exhaust purification catalyst 51 can be operated efficiently. .

  FIG. 3 is a flowchart showing a routine example of the cooling water supply control executed by the ECU 20. For example, the ECU 20 activates this routine when the ignition key of the engine 1 is turned on. First, the ECU 20 checks whether or not the cooling water temperature of the engine 1 is equal to or lower than a predetermined temperature from the output signal of the water temperature sensor 28 (S101). Here, the predetermined temperature used for the determination by the ECU 20 can be appropriately determined. For example, refer to the cooling water temperature (for example, 60 to 70 degrees) detected by the water temperature sensor 28 when the engine 1 is stably operated at a medium load. To set.

  The ECU 20 opens the valve 29 and supplies the cooling water to the water jacket 41 when the cooling water temperature of the engine 1 exceeds the predetermined temperature, that is, when it is determined that the engine 1 is sufficiently heated (S101). Then, the fuel addition valve 30 is cooled (S103). On the other hand, when the cooling water temperature of the engine is equal to or lower than the predetermined temperature in step 101 (S101), the ECU 20 further confirms whether the gas temperature of the exhaust gas EG is equal to or lower than the predetermined temperature based on the output signal of the gas temperature sensor 14. Perform (S102). The predetermined temperature here may also be set with reference to the exhaust gas temperature (for example, 200 to 220 degrees) detected by the gas temperature sensor 14 when the engine 1 is stably operated at a medium load.

  When the gas temperature exceeds the predetermined temperature, that is, when the ECU 20 determines that the peripheral portion of the fuel addition valve 30 is sufficiently heated, the ECU 20 opens the valve 29 and supplies the water jacket 41 with cooling water to supply fuel. The addition valve 30 is cooled (S103). On the other hand, when the exhaust gas temperature is equal to or lower than the predetermined temperature in step 102 (S102), the engine 1 is in a low load operation such as when it is cold or idle, and the periphery of the fuel addition valve 30 is also at a low temperature. is assumed. Therefore, the ECU 20 closes the valve 29 and stops the supply of cooling water to the water jacket 41 (S104). As described above, when the peripheral portion of the fuel addition valve 30 is at a low temperature, the supply of the cooling water to the water jacket 41 is stopped to synergize with the structure of the boss portion 40 including the heat insulating layer 45 described above. As a result, accumulation of soot on the wall surface 44WA can be reliably prevented.

  In the above-described example, the ECU 20 performs the cooling water supply control using the output signal from the gas temperature sensor 14 disposed in the exhaust pipe 2 upstream of the exhaust purification catalyst 51. When the gas temperature sensor 15 is arranged further downstream, an output signal from the gas temperature sensor 15 may be used (see FIG. 1). In this case, the predetermined temperature used by the ECU 20 for determination can be, for example, a catalyst outlet temperature detected by the gas temperature sensor 15 when the engine 1 is stably operated at a medium load. When the cooling water supply control is performed using the catalyst outlet temperature, it is possible to simultaneously realize the suppression of the soot generation around the fuel addition valve 30 and the early warm-up of the exhaust purification catalyst 51.

  As described above, according to the exhaust purification system applied to the engine 1, even if the fuel addition valve 30 is cooled by the water jacket 41, the cooling effect does not reach the spray passage 44, and soot is accumulated on the wall surface 44 WA. Can be suppressed. Therefore, the fuel FE can be stably injected by the fuel addition valve 30 disposed so that the injection hole 32 faces the spray passage 44 formed in the boss portion 40. As a result, the function of the exhaust purification catalyst 51 is sufficiently exerted, so that the emission and fuel consumption of the engine 1 are improved.

  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 the figure shown about the diesel engine to which the exhaust gas purification system is applied. It is the figure which expanded and showed the periphery of the curved part of the exhaust pipe to which a fuel addition valve is fixed. It is the flowchart which showed the example of a routine of the cooling water supply control performed by ECU. 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 30 Fuel addition valve 31 Nozzle part 32 Injection hole 40 Boss part (valve attachment part)
41 Water jacket (cooling water passage)
44 Spray passage 45 Heat insulation layer 50 Exhaust purification device 51 Exhaust purification catalyst FE Fuel (added fuel)
EG exhaust gas SM soot

Claims (4)

An exhaust purification catalyst is disposed in the exhaust pipe of the diesel engine, a valve mounting portion is provided outside the curved portion upstream of the exhaust purification catalyst, and a fuel addition valve is held by the valve mounting portion,
Forming a cooling water passage for flowing cooling water for cooling the fuel addition valve in the valve attachment portion, and forming a spray passage in the valve attachment portion toward the exhaust pipe;
An exhaust purification system for a diesel engine, in which the fuel addition valve is disposed with the injection hole facing the spray passage, and the added fuel is injected from the injection hole and supplied to the exhaust purification catalyst,
An exhaust gas purification system for a diesel engine, wherein a heat insulating layer is provided between the cooling water passage and the spray passage. 2. The exhaust purification system for a diesel engine according to claim 1, wherein the valve mounting portion further includes a heat insulating layer provided along the exhaust pipe on the exhaust pipe side from the cooling water passage. The exhaust gas purification system for a diesel engine according to claim 1 or 2, wherein the heat insulating layer forms a part of the cooling water passage. When the cooling water passage is configured to supply a part of the cooling water of the diesel engine, the cooling water of the diesel engine is equal to or lower than a predetermined water temperature, and the exhaust gas flowing through the exhaust pipe is equal to or lower than the predetermined gas temperature The exhaust purification system for a diesel engine according to any one of claims 1 to 3, wherein supply of cooling water to the cooling water passage is restricted.

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