JP5878336B2 - Exhaust gas purification device - Google Patents

Description

  The present invention relates to an apparatus for purifying exhaust gas by reducing nitrogen oxide (hereinafter referred to as NOx) contained in exhaust gas of an engine such as a diesel engine.

  Conventionally, a fuel addition valve for injecting fuel into the exhaust manifold is provided, and the fuel injected from the fuel addition valve serves as a reducing agent for the NOx storage-type NOx catalyst provided in the exhaust pipe on the downstream side of the supercharger, There has been disclosed an exhaust emission control device provided with a fuel reforming catalyst for reforming fuel injected by a fuel addition valve upstream of a supercharger (see, for example, Patent Document 1). In this exhaust purification device, the fuel reforming catalyst is disposed in the exhaust passage from the collecting portion of the exhaust manifold to the supercharger, and the central axis thereof is disposed substantially parallel to the direction of the exhaust gas flow. The fuel reforming catalyst has a catalyst carrier formed by winding a base material around the core member so that the core member is at the center, and an outer cylinder that houses the catalyst carrier. The base material is formed by joining the metal corrugated plates between two metal plate materials, and platinum or the like is supported on the base material. In addition, the core member has a collision portion at its tip that diffuses the collided fuel around. The collision portion is formed with a tapered surface so that its cross section expands along the longitudinal direction of the core member, and this tapered surface is configured to be exposed from the catalyst carrier. Further, the end face of the catalyst carrier is formed in a conical surface projecting in the vicinity of the collision portion. Further, the fuel reforming catalyst has a function of oxidizing the injected fuel, and the reformed fuel becomes a reducing agent for the NOx catalyst.

In the exhaust purification apparatus configured as described above, when fuel is sprayed on the collision portion of the fuel reforming catalyst, the fuel atomizes and diffuses so that the entire catalyst carrier is used. Further, since the end face of the catalyst carrier is formed in a conical surface projecting in the vicinity of the collision portion, the injected fuel spreads well over the entire catalyst carrier. As a result, the fuel reforming catalyst is excellent in the ability to atomize the injected fuel, and the fuel reforming efficiency is good. The reformed fuel is supplied to the NOx catalyst and functions as a reducing agent for the NOx catalyst. That is, the NOx catalyst absorbs NOx when the air-fuel ratio of the exhaust gas is lean, releases the absorbed NOx when the oxygen concentration of the exhaust gas decreases, and reduces it to N ₂ using the reformed fuel as a reducing agent. It is supposed to be.

JP 2005-76530 A (paragraphs [0017], [0018] [0022], [0024], FIGS. 1 to 4)

  However, in the above-described conventional exhaust purification device disclosed in Patent Document 1, after the fuel injected from the fuel addition valve is sprayed on the collision portion of the fuel reforming catalyst and atomized and diffused, the fuel reforming catalyst is Although the injected fuel is reformed, heat is generated at this time, and the temperature of the exhaust gas rises together with the combustion reforming catalyst. If this exhaust gas temperature rises too much, this exhaust gas flows into the turbine housing of the turbocharger. When the turbine rotor blades rotate at a high speed, the turbine rotor blades may be damaged by rotating at the high speed with the heat.

  The object of the present invention is to prevent damage to the turbine rotor blades of the turbocharger, and to add a relatively small amount of fuel from the fuel addition means to the reforming catalyst. It is another object of the present invention to provide an exhaust gas purification device that can be efficiently modified.

As shown in FIG. 1, the first aspect of the present invention is that the fuel 25 of the engine 11 is made hydrogen by being provided in the collecting pipe portion 17b of the exhaust manifold 17 connected to the exhaust port of the engine 11 with the turbocharger 19. A reforming catalyst 22 for reforming, a fuel adding means 23 for supplying the fuel 25 to the reforming catalyst 22 by adding the fuel 25 to the exhaust manifold 17, and a downstream side of the exhaust gas from the turbine housing 19b of the turbocharger 19 A platinum-based catalyst 36 that generates ammonia from NOx contained in the exhaust gas in a fuel-rich state provided in the exhaust pipe 18 and hydrogen generated by the reforming catalyst 22, and the exhaust pipe 18 downstream of the exhaust gas from the platinum-based catalyst 36. Provided in a selective reduction catalyst 37 for reducing NOx in exhaust gas using ammonia as a reducing agent, and a bypass pipe 38 for bypassing the turbine housing 19b Based on the waste gate valve 39 that adjusts the opening of the bypass pipe 38 and adjusts the flow rate of the exhaust gas flowing to the turbine housing 19b, the temperature sensor 47 that detects the inlet temperature of the turbine housing 19b, and the operating conditions of the engine 11. What exhaust gas purifying apparatus der provided with a controller 54 for controlling the waste gate valve 39 based on the detection output of the temperature sensor 47 and controls the fuel adding means 23, a mass flow for detecting an amount of air taken into the engine 11 A sensor 48 is provided in the engine 11, an O ₂ sensor 49 for detecting the oxygen concentration in the exhaust gas is provided in the exhaust manifold 17 upstream of the reforming catalyst 22, and an exhaust pipe downstream of the exhaust gas from the selective reduction catalyst 37. 18 or upstream of the exhaust gas from the selective catalytic reduction catalyst 37 and from the platinum-based catalyst 36. The NOx sensor 51 for detecting the concentration of NOx in the exhaust gas is provided in one or both of the exhaust pipes 18 on the downstream side of the exhaust pipe 18, and the NOx concentration in the exhaust gas becomes a predetermined value or more. When the NOx sensor 51 detects this, the controller 54 is configured to control the fuel addition means 23 based on the detection outputs of the NOx sensor 51, the mass flow sensor 48, and the O ₂ sensor 49. To do .

  In the present specification, the mixing ratio of oxygen and fuel in the exhaust gas is defined as the air-fuel ratio, and the mixing ratio of oxygen and fuel when the oxygen and fuel in the mixture reacts without excess or deficiency in the engine is defined as the stoichiometric air-fuel ratio. The ratio between the air-fuel ratio and the stoichiometric air-fuel ratio is referred to as an excess air ratio λ, and the “fuel-rich exhaust gas” refers to an exhaust gas in which the excess air ratio λ is less than 1.

  The second aspect of the present invention is an invention based on the first aspect, and further, as shown in FIG. 1, the fuel addition means 23 is provided in the collecting pipe portion 17 b on the exhaust gas upstream side of the reforming catalyst 22. A fuel addition nozzle 24 for adding fuel 25 to the collecting pipe portion 17b upstream of the reforming catalyst 22 and a fuel supply means 26 for supplying the fuel 25 to the fuel addition nozzle 24 are provided.

  A third aspect of the present invention is an invention based on the first aspect, wherein the fuel addition means further includes a plurality of fuel injection nozzles for injecting fuel into each cylinder of the engine, and fuel to these fuel injection nozzles. And a fuel supply means for supplying fuel, wherein the fuel is injected from a plurality of fuel injection nozzles in an amount exceeding the amount of fuel combusted by the engine.

  A fourth aspect of the present invention is an invention based on the first or second aspect, and as shown in FIG. 1, the reforming catalyst 22 is selected from the group consisting of rhodium, palladium and platinum. A honeycomb carrier is coated with zeolite or alumina to which seeds or two or more metals are added.

  In the exhaust gas purifying apparatus according to the first aspect of the present invention, fuel is added to the exhaust manifold from the fuel adding means, and a part of the fuel raises the temperature of the reforming catalyst, and the temperature of the reforming catalyst raises another fuel. Some are reformed to hydrogen. At this time, the exhaust gas is immediately after being discharged from the engine and is at a relatively high temperature. Therefore, the reforming catalyst can be heated to a temperature at which the reforming catalyst can be reformed with a relatively small amount of fuel. As a result, by adding a relatively small amount of fuel from the fuel addition means to the reforming catalyst, a part of the fuel can be efficiently reformed to hydrogen in the reforming catalyst. In addition, when the remaining portion of the fuel that has passed through the reforming catalyst without being reformed into hydrogen by the reforming catalyst and the hydrogen reformed by the reforming catalyst flow into the platinum-based catalyst, that is, in a fuel-rich state, the hydrogen is When flowing into the platinum-based catalyst, ammonia is generated from the NOx contained in the exhaust gas by the platinum-based catalyst and the hydrogen generated by the reforming catalyst. When the exhaust gas containing ammonia flows into the selective catalytic reduction catalyst, ammonia and NOx react on the selective catalytic reduction catalyst, and the NOx reduction reaction and the ammonia oxidation reaction are promoted. Reduced. As a result, it is possible to prevent ammonia from being released into the atmosphere and to efficiently reduce NOx in the exhaust gas. Further, when the temperature sensor detects that the exhaust gas temperature has become equal to or higher than a predetermined value, the controller opens the waste gate valve and allows a part of the exhaust gas to flow through the bypass pipe. As a result, the flow rate of the exhaust gas flowing into the turbine housing of the turbocharger is reduced, energy for driving the turbine rotor blades is reduced, and it is possible to suppress an excessive increase in the rotational speed of the turbine rotor blades. The turbine rotor blades can be prevented from being damaged by the high speed rotation of the turbine rotor blades.

  In the exhaust gas purifying apparatus according to the second aspect of the present invention, fuel is added from the fuel addition nozzle to the exhaust manifold, so that it is necessary to newly add a fuel addition nozzle, and the number of parts increases, but the combustion of fuel in the engine Fuel can be added to the exhaust manifold without affecting the engine.

  In the exhaust gas purifying apparatus according to the third aspect of the present invention, fuel exceeding the amount of fuel combusted in the engine is injected from a plurality of fuel injection nozzles that inject fuel into each cylinder of the engine. However, it is not necessary to newly add a fuel addition nozzle, and an increase in the number of parts can be avoided.

It is a block diagram which shows the exhaust gas purification apparatus of this invention embodiment. (A) is a figure which shows the change with respect to the time of the fuel flow rate when adding fuel toward the reforming catalyst provided in the exhaust pipe of the comparative example 1, (b) is provided in the exhaust manifold of the first embodiment. It is a figure which shows the change with respect to time of the fuel flow volume when fuel is added toward the reforming catalyst.

  Next, an embodiment for carrying out the present invention will be described with reference to the drawings. As shown in FIG. 1, an intake pipe 14 is connected to an intake port of a diesel engine 11 via an intake manifold 13, and an exhaust pipe 18 is connected to an exhaust port via an exhaust manifold 17. The intake manifold 13 and the intake pipe 14 constitute an intake passage 12, and the exhaust manifold 17 and the exhaust pipe 18 constitute an exhaust passage 16. The intake passage 12 is provided with a compressor housing 19a of the turbocharger 19 and an intercooler 21 for cooling the intake air compressed by the turbocharger 19, and the exhaust passage 16 is provided with the turbocharger 19 of the turbocharger 19. A turbine housing 19b is provided. Specifically, the compressor housing 19a is provided in the middle of the intake pipe 14, and the intercooler 21 is provided in the middle of the intake pipe 14 on the downstream side of the intake air from the compressor housing 19a. The turbine housing 19 b is interposed between the exhaust manifold 17 and the exhaust pipe 18. A compressor rotor blade (not shown) is rotatably accommodated in the compressor housing 19a, and a turbine rotor blade (not shown) is rotatably accommodated in the turbine housing 19b. The compressor rotor blades and the turbine rotor blades are connected by a shaft (not shown), and the compressor rotor blades are rotated via the turbine rotor blades and the shaft by the energy of the exhaust gas discharged from the engine 11, and the compressor rotor blades are rotated. Thus, the intake air in the intake pipe 14 is compressed.

  On the other hand, the exhaust manifold 17 includes a plurality of branch pipe portions 17a each having one end connected to a plurality of exhaust ports, and a single collection pipe portion 17b formed by collecting the other ends of the branch pipe portions 17a. Have A reforming catalyst 22 for reforming the fuel (light oil) 25 of the engine 11 into hydrogen is provided in the middle of the collecting pipe portion 17b. The reforming catalyst 22 is configured by coating a honeycomb carrier with zeolite or alumina to which one or more metals selected from the group consisting of rhodium, palladium and platinum are added. Specifically, the reforming catalyst 22 made of zeolite to which a metal such as rhodium is added is configured by coating a honeycomb carrier with a slurry containing zeolite powder obtained by ion exchange of a metal such as rhodium. The reforming catalyst 22 made of alumina to which a metal such as rhodium is added is configured by coating a honeycomb carrier with a slurry containing γ-alumina powder or θ-alumina powder carrying a metal such as rhodium.

  On the other hand, the exhaust manifold 17 is provided with fuel addition means 23. The fuel addition means 23 includes a fuel addition nozzle 24 provided in the collecting pipe portion 17 b on the exhaust gas upstream side of the reforming catalyst 22, and a fuel supply means 26 that supplies the fuel 25 to the fuel addition nozzle 24. The fuel addition nozzle 24 is configured to supply the fuel 25 to the reforming catalyst 22 by adding the fuel 25 to the collecting pipe portion 17 b on the exhaust gas upstream side of the reforming catalyst 22. The fuel supply means 26 includes a fuel supply pipe 27 having a tip connected to the fuel addition nozzle 24, a fuel tank 28 connected to the base end of the fuel supply pipe 27 and storing the fuel 25, and an inside of the fuel tank 28. A fuel pump 29 that pumps the fuel 25 to the fuel addition nozzle 24, and a fuel supply amount adjustment valve 31 that adjusts the supply amount (injection amount) of the fuel 25 injected from the fuel addition nozzle 24. The fuel tank 28 can also be used as a fuel tank of the engine 11. The fuel pump 29 is provided in a fuel supply pipe 27 between the fuel addition nozzle 24 and the fuel tank 28, and the fuel supply amount adjustment valve 31 is provided in the fuel supply pipe 27 between the fuel addition nozzle 24 and the fuel pump 29. Provided. Further, the fuel supply amount adjustment valve 31 is provided in the fuel supply pipe 27 to adjust the supply pressure of the fuel 25 to the fuel addition nozzle 24, and the fuel addition nozzle 24 is provided at the base end of the fuel addition nozzle 24. And a fuel on-off valve 33 that opens and closes the base end of 24.

  The fuel pressure regulating valve 32 is a three-way valve having first to third ports 32 a to 32 c, the first port 32 a is connected to the discharge port of the fuel pump 29, and the second port 32 b is connected to the fuel on-off valve 33. The third port 32 c is connected to the fuel tank 28 via the return pipe 34. When the fuel pressure adjustment valve 32 is driven, the fuel 25 pumped by the fuel pump 29 flows into the fuel pressure adjustment valve 32 from the first port 32a, and after the fuel pressure adjustment valve 32 has adjusted to a predetermined pressure, The pressure is fed from the 2 port 32 b to the fuel on-off valve 33. When the drive of the fuel pressure adjustment valve 32 is stopped, the fuel 25 pumped by the fuel pump 29 flows into the fuel pressure adjustment valve 32 from the first port 32a, and then passes through the return pipe 34 from the third port 32c. Returned to 29.

  A platinum-based catalyst 36 is provided in the exhaust pipe 18, that is, in the exhaust pipe 18 on the exhaust gas downstream side of the turbine housing 19 b of the turbocharger 19. The platinum catalyst 36 is accommodated in a first case 41 having a larger diameter than the exhaust pipe 18. The platinum-based catalyst 36 is a monolithic catalyst, and a zeolite carrier or a cordierite-made honeycomb carrier or platinum added with only platinum, or platinum and a metal composed of either palladium or rhodium or both. The metal honeycomb carrier is coated. Specifically, the platinum-based catalyst 36 made of zeolite to which a metal such as platinum is added is configured by coating a honeycomb carrier with a slurry containing zeolite powder obtained by ion exchange of a metal such as platinum. The platinum catalyst 36 made of alumina to which a metal such as platinum is added is formed by coating a honeycomb carrier with a slurry containing γ-alumina powder or θ-alumina powder carrying a metal such as platinum. The platinum-based catalyst 36 is configured to generate ammonia from NOx contained in the fuel-rich exhaust gas and hydrogen generated by the reforming catalyst 22.

  A selective reduction catalyst 37 is provided in the exhaust pipe 18 on the downstream side of the exhaust gas from the platinum-based catalyst 36. The selective catalytic reduction catalyst 37 is accommodated in a second case 42 having a larger diameter than the exhaust pipe 18. The selective catalytic reduction catalyst 37 is a monolithic catalyst, in which a honeycomb carrier made of cordierite is coated with zeolite or alumina to which one or more metals selected from the group consisting of iron, vanadium and copper are added. Composed. Specifically, the selective reduction catalyst 37 made of zeolite to which a metal such as iron is added is configured by coating a honeycomb carrier with a slurry containing zeolite powder obtained by ion exchange of a metal such as iron. The selective reduction catalyst 37 made of alumina to which a metal such as iron is added is configured by coating a honeycomb carrier with a slurry containing γ-alumina powder or θ-alumina powder supporting a metal such as iron. The selective reduction catalyst 37 is configured to reduce NOx in the exhaust gas using ammonia as a reducing agent.

  On the other hand, the exhaust manifold 17 and the exhaust pipe 18 are connected to bypass the turbine housing 19 b of the turbocharger 19 by a bypass pipe 38. That is, one end of the bypass pipe 38 is connected to the collecting pipe portion 17b of the exhaust manifold 17 on the exhaust gas downstream side of the reforming catalyst 22, and the other end of the bypass pipe 38 is on the exhaust gas downstream side of the turbine housing 19b and the platinum-based catalyst 36. The exhaust pipe 18 is connected to the exhaust gas upstream side. The bypass pipe 38 is provided with a waste gate valve 39. The valve 39 is configured to adjust the flow rate of the exhaust gas flowing through the turbine housing 19b by adjusting the opening of the bypass pipe 38. Further, the exhaust manifold 17 and the intake pipe 14 are connected to bypass the engine 11 through the EGR pipe 43. That is, the EGR pipe 43 branches from the branch pipe portion 17 a of the exhaust manifold 17 and joins the intake pipe 14 on the intake downstream side of the intercooler 21. The EGR pipe 43 is provided with an EGR valve 44 for adjusting the flow rate of exhaust gas (EGR gas) recirculated from the EGR pipe 43 to the intake pipe 14. In addition, the code | symbol 46 of FIG. 1 is an EGR cooler which cools the waste gas (EGR gas) which passes the EGR pipe | tube 43. FIG.

On the other hand, a temperature sensor 47 for detecting the inlet temperature of the turbine housing 19b is provided in the collecting pipe portion 17b of the exhaust manifold 17 downstream of the reforming catalyst 22 and upstream of the turbine housing 19b. The engine 11 is provided with a mass flow sensor 48 for detecting the amount of air sucked into the engine 11, and an O ₂ sensor 49 for detecting the oxygen concentration in the exhaust gas in the exhaust manifold 17 upstream of the reforming catalyst 22. And an NOx sensor 51 for detecting the concentration of NOx in the exhaust gas is provided in the exhaust pipe 18 on the downstream side of the exhaust gas from the selective catalytic reduction catalyst 37. Further, the rotation speed of the engine 11 is detected by the rotation sensor 52, and the load of the engine 11 is detected by the load sensor 53. The detection outputs of the temperature sensor 47, the mass flow sensor 48, the O ₂ sensor 49, the NOx sensor 51, the rotation sensor 52 and the load sensor 53 are connected to the control input of the controller 54. The control output of the controller 54 includes the fuel pump 29, the fuel The pressure control valve 32, the fuel on-off valve 33, the waste gate valve 39 and the EGR valve 44 are connected. A memory 56 is connected to the engine 11. In this memory 56, the opening degree of the waste gate valve 39 corresponding to the inlet temperature of the turbine housing 19b and the exhaust gas flow rate is stored in advance. The memory 56 stores in advance the on / off state of the fuel pump 29, the opening degree of the fuel pressure adjustment valve 32, and the opening / closing interval of the fuel on-off valve 33 in accordance with the intake air amount, the oxygen concentration in the exhaust gas, and the NOx concentration. . Furthermore, the opening degree of the EGR valve 44 corresponding to the engine speed and the engine load is stored in the memory 56 in advance.

The operation of the exhaust gas purification apparatus configured as described above will be described. During the operation of the engine 11, the controller 54 determines that the NOx concentration in the exhaust gas has reached a predetermined value or more based on the detection output of the NOx sensor 51 and the like. Specifically, the controller 54 turns on the fuel pump 29 based on the detection output of the NOx sensor 51 and the like, and opens the fuel pressure adjustment valve 32 based on the detection outputs of the mass flow sensor 48 and the O ₂ sensor 49. At the same time, the opening / closing interval of the fuel on-off valve 33 is adjusted to a predetermined interval, the fuel pressure adjusting valve 32 is closed after a predetermined time has passed, the opening / closing of the fuel on-off valve 33 is stopped, and the fuel pump 29 is turned off. Turn off. As a result, a required amount of fuel 25 is added to the exhaust manifold 17 from the fuel addition nozzle 24. A part of the fuel 25 added from the fuel addition nozzle 24 raises the temperature of the reforming catalyst 22 and rises to a predetermined temperature (for example, 600 ° C. in the case of the reforming catalyst 22 to which rhodium and palladium are added as added metals). Another part of the fuel 25 is reformed to hydrogen by the warmed reforming catalyst 22. At this time, the exhaust gas is immediately after being discharged from the engine 11 and is at a relatively high temperature. Therefore, the reforming catalyst 22 can be heated to a temperature at which the reforming catalyst 22 can be reformed with a relatively small amount of fuel 25. As a result, by adding a relatively small amount of fuel 25 from the fuel addition nozzle 24 to the reforming catalyst 22, a part of the fuel 25 can be efficiently reformed into hydrogen in the reforming catalyst 22.

  When the remaining portion of the fuel 25 that has passed through the reforming catalyst 22 without being reformed into hydrogen by the reforming catalyst 22 and the hydrogen reformed by the reforming catalyst 22 flow into the platinum-based catalyst 36, that is, exhaust gas is generated. When hydrogen flows into the platinum-based catalyst 36 in a fuel-rich state (a state where the excess air ratio λ of the exhaust gas is less than 1), the platinum-based catalyst 36 is changed to NOx contained in the exhaust gas at a predetermined temperature or higher (eg, 300 ° C. or higher). Ammonia is produced from the hydrogen produced by the catalyst 22. When the exhaust gas containing ammonia generated by the platinum-based catalyst 36 flows into the selective reduction catalyst 37, ammonia is adsorbed by the selective reduction catalyst 37. The ammonia and NOx adsorbed on the selective catalytic reduction catalyst 37 react at a predetermined temperature or higher (for example, 180 ° C. or higher), and the NOx reduction reaction and ammonia oxidation reaction are promoted. Reduced. As a result, it is possible to prevent ammonia from being released into the atmosphere and to efficiently reduce NOx in the exhaust gas. Note that if the ammonia adsorbed on the selective reduction catalyst 37 is completely consumed for the reduction of NOx, the NOx in the exhaust gas passes through the selective reduction catalyst 37. At this time, since the NOx sensor 51 detects that the NOx concentration has reached a predetermined value or more, the controller 54 repeats the same operation as the above operation.

  On the other hand, when the temperature sensor 47 detects that the exhaust gas temperature has become equal to or higher than a predetermined value, the controller 54 opens the waste gate valve 39 based on the detection output of the temperature sensor 47 and allows a part of the exhaust gas to flow to the bypass pipe 38. As a result, the flow rate of the exhaust gas flowing into the turbine housing 19b of the turbocharger 19 is reduced, energy for driving the turbine rotor blades is reduced, and an excessive increase in the rotational speed of the turbine rotor blades is suppressed. Therefore, damage to the turbine rotor blade due to the high-speed rotation of the turbine rotor blade can be prevented.

  In the above embodiment, the exhaust gas purification apparatus of the present invention is applied to a diesel engine. However, the exhaust gas purification apparatus of the present invention may be applied to a gasoline engine. Further, in the above embodiment, the fuel addition means is provided in the collecting pipe part upstream of the reforming catalyst and adds fuel to the collecting pipe part upstream of the reforming catalyst, and the fuel The fuel supply means supplies fuel to the addition nozzle. The fuel addition means supplies a plurality of fuel injection nozzles that inject fuel to each cylinder of the engine, and supplies fuel to these fuel injection nozzles. The fuel supply means may be provided, and a plurality of fuel injection nozzles may be configured to inject an amount of fuel that exceeds the amount of fuel combusted by the engine. In this case, since the amount of fuel exceeding the amount of fuel combusted in the engine is injected from a plurality of fuel injection nozzles, although there is some influence on the fuel combustion in the engine, it is necessary to newly add a fuel addition nozzle. And an increase in the number of parts can be avoided.

  In the above embodiment, the NOx sensor 51 is provided in the exhaust pipe 18 on the exhaust gas downstream side of the selective reduction catalyst 37, but the NOx sensor 51 provided in the exhaust pipe 18 on the exhaust gas downstream side of the selective reduction catalyst 37. Alternatively, or in addition to this NOx sensor 51, another NOx sensor may be provided in the exhaust pipe 18 on the exhaust gas upstream side of the selective catalytic reduction catalyst 37 and on the exhaust gas downstream side of the platinum-based catalyst 36. In this case, the controller controls the fuel pump 29, the fuel pressure adjustment valve 32, the fuel on-off valve 33, the waste gate valve 39, and the EGR valve 44 based on the detection output of the other NOx sensor, thereby reforming. The platinum catalyst 36 generates ammonia from the hydrogen produced by the catalyst 22 and NOx contained in the exhaust gas, and the remainder of the NOx that passes through the platinum catalyst 36 without being reformed to ammonia by the platinum catalyst 36 is selected. Reduction can be achieved with the reduced catalyst 37. In other words, the NOx concentration in the exhaust gas is detected by the other NOx sensor, and the concentration of NOx that has passed through the platinum catalyst 36 without being reformed to ammonia by the platinum catalyst 36 is selectively reduced. The concentration can be limited to a reducible level. As a result, emission of NOx into the atmosphere can be suppressed. Furthermore, another NOx sensor may be provided in the exhaust pipe 18 on the exhaust gas upstream side of the platinum-based catalyst 36 and on the exhaust gas downstream side of the connection portion to the exhaust pipe 18 at the other end of the bypass pipe 38. In this case, the controller controls the fuel pump 29, the fuel pressure adjusting valve 32, the fuel on-off valve 33, the waste gate valve 39, and the EGR valve 44 based on the detection output of the further NOx sensor. The platinum catalyst 36 generates ammonia from the hydrogen produced by the catalyst 22 and NOx contained in the exhaust gas, and the platinum catalyst 36 does not reform the ammonia and eliminates the NOx that passes through the platinum catalyst 36 as it is. Can do.

  Next, examples of the present invention will be described in detail together with comparative examples.

<Example 1>
As shown in FIG. 1, the reforming catalyst 22 is provided in the collecting pipe portion 17b of the exhaust manifold 17 of the in-line six-cylinder turbocharged diesel engine 11 having a displacement of 8000 cc. Further, a fuel addition nozzle 24 for supplying fuel (light oil) 25 is provided in the collecting pipe portion 17 b upstream of the reforming catalyst 22, and the fuel supply means 26 supplies fuel 25 to the fuel addition nozzle 24. did. Here, the reforming catalyst 22 was a catalyst prepared by coating a honeycomb carrier with a slurry containing zeolite powder obtained by ion exchange of rhodium. On the other hand, the compressor housing 19a of the turbocharger 19 is provided in the middle of the intake pipe 14, and the intercooler 21 is provided in the middle of the intake pipe 14 on the downstream side of the intake air from the compressor housing 19a. A turbine housing 19 b is interposed between the exhaust manifold 17 and the exhaust pipe 18. Further, a platinum-based catalyst 36 and a selective reduction catalyst 37 were provided in the exhaust pipe 18 in order from the exhaust gas upstream side. Here, the platinum-based catalyst 36 is a catalyst produced by coating a honeycomb carrier with a slurry containing platinum-ion-exchanged zeolite powder, and the selective reduction catalyst 37 is a slurry containing iron-ion-exchanged zeolite powder. The catalyst was prepared by coating a honeycomb carrier. This exhaust gas purification apparatus was designated as Example 1.

<Comparative Example 1>
The reforming catalyst is provided in the exhaust pipe downstream of the turbocharger turbine housing and upstream of the platinum-based catalyst, and the fuel addition nozzle is provided downstream of the turbocharger turbine housing. The configuration was the same as that of Example 1 except that it was provided in the exhaust pipe upstream of the reforming catalyst. This exhaust gas purification apparatus was designated as Comparative Example 1.

<Comparative test 1 and evaluation>
Fuel was added from the fuel addition nozzles of the exhaust gas purifying apparatuses of Example 1 and Comparative Example 1, and the fuel was supplied to the reforming catalyst. The fuel was reformed to hydrogen by the reforming catalyst. At this time, the amount of fuel added from the fuel addition nozzle was controlled so that the reformed hydrogen became a predetermined amount. Specifically, as shown in FIGS. 2A and 2B, the flow rate and supply time of the fuel for raising the temperature of the reforming catalyst are Q ₁ and T ₁ , respectively, and hydrogen is generated by the reforming catalyst. The fuel flow rate and the supply time for (reforming) were Q ₂ and T ₂ , respectively. In Example 1 and Comparative Example 1, while keeping Q ₁ , Q ₂ and T _{2 the} same, T ₁ is changed so that the hydrogen reformed by the reforming catalyst becomes a predetermined amount. The amount of fuel added from the fuel addition nozzle was controlled. As a result, when the exhaust gas temperature in the collecting pipe portion of the exhaust manifold is 500 ° C. and the exhaust gas temperature upstream of the platinum-based catalyst is 300 ° C., the fuel for raising the temperature of the reforming catalyst of Comparative Example 1 Assuming that the supply time T ₁ is 100%, the fuel supply time T ₁ for raising the temperature of the reforming catalyst of Example 1 is as short as 35%. As a result, it was found that the exhaust gas purification apparatus of Example 1 can be reformed to hydrogen in the reforming catalyst with less fuel addition than the exhaust gas purification apparatus of Comparative Example 1.

11 Diesel engine (engine)
DESCRIPTION OF SYMBOLS 17 Exhaust manifold 17b Collecting pipe part 18 Exhaust pipe 19 Turbocharger 19b Turbine housing 22 Reforming catalyst 23 Fuel addition means 24 Fuel addition nozzle 25 Fuel 26 Fuel supply means 36 Platinum catalyst 37 Selective reduction catalyst 38 Bypass pipe 39 Waste Gate valve 47 Temperature sensor 54 Controller

Claims (4)

The fuel (25) of the engine (11) is reformed to hydrogen provided in the collecting pipe (17b) of the exhaust manifold (17) connected to the exhaust port of the engine (11) with the turbocharger (19). A reforming catalyst (22);
Fuel addition means (23) for supplying the fuel (25) to the reforming catalyst (22) by adding the fuel (25) to the exhaust manifold (17);
NOx contained in the exhaust pipe (18) downstream of the exhaust gas from the turbine housing (19b) of the turbocharger (19) and contained in the exhaust gas in a fuel-rich state and hydrogen generated by the reforming catalyst (22) A platinum-based catalyst (36) for producing ammonia from
A selective reduction catalyst (37) provided in an exhaust pipe (18) downstream of the platinum-based catalyst (36) for reducing NOx in the exhaust gas using the ammonia as a reducing agent;
A waste gate valve (39) that is provided in a bypass pipe (38) that bypasses the turbine housing (19b) and adjusts an opening degree of the bypass pipe (38) to adjust a flow rate of exhaust gas flowing to the turbine housing (19b). When,
A temperature sensor (47) for detecting the inlet temperature of the turbine housing (19b);
A controller (54) for controlling the fuel addition means (23) based on an operating condition of the engine (11) and for controlling the waste gate valve (39) based on a detection output of the temperature sensor (47). An exhaust gas purification device provided ,
A mass flow sensor (48) for detecting the amount of air sucked into the engine (11) is provided in the engine (11),
The exhaust manifold (17) upstream of the reforming catalyst (22 ) is provided with an O ₂ sensor (49) for detecting the oxygen concentration in the exhaust gas ,
An exhaust pipe (18) on the exhaust gas downstream side of the selective reduction catalyst (37) or an exhaust pipe (18) on the exhaust gas upstream side of the selective reduction catalyst (37) and on the exhaust gas downstream side of the platinum-based catalyst (36) NOx sensor (51) for detecting the concentration of NOx in the exhaust gas is provided in either or both of the exhaust pipe (18) of
When the NOx sensor (51) detects that the NOx concentration in the exhaust gas has reached a predetermined value or more, the controller (54) detects the NOx sensor (51), the mass flow sensor (48), and the O ₂ An exhaust gas purification apparatus configured to control the fuel addition means (23) based on each detection output of the sensor (49) .   The fuel addition means (23) is provided in the collecting pipe portion (17b) upstream of the reforming catalyst (22) and the exhaust pipe upstream of the reforming catalyst (22). The exhaust gas purification device according to claim 1, further comprising: a fuel addition nozzle (24) for adding fuel (25); and a fuel supply means (26) for supplying the fuel (25) to the fuel addition nozzle (24).   The fuel addition means has a plurality of fuel injection nozzles for injecting fuel into each cylinder of the engine, and a fuel supply means for supplying the fuel to these fuel injection nozzles. The exhaust gas purifying apparatus according to claim 1, wherein the exhaust gas purifying apparatus is configured to inject an amount of fuel exceeding an amount of fuel combusted by the engine.   The said reforming catalyst (22) is formed by coating a honeycomb carrier with zeolite or alumina to which one or more metals selected from the group consisting of rhodium, palladium and platinum are added. The exhaust gas purification apparatus as described.

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