JP2012159054A - Exhaust gas purification system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas purification system for an internal combustion engine capable of making efficient use of exhaust gas heat, capable of being downsized while reducing the amount of hydrocarbon such as light oil supplied to an oxidation catalyst to increase the temperature of exhaust gas, and also capable of suppressing an EGR cooler and an EGR valve provided in an EGR passage from being clogged with SOF.SOLUTION: In an exhaust gas purification system 1, 1A for an internal combustion engine for purifying harmful substances in exhaust gas G of an internal combustion engine 10, a first oxidation catalyst 18 is placed between a discharge port and a discharge manifold 11a for every cylinder, and a second oxidation catalyst 19, an urea injection nozzle 20, a diesel particulate filter 21a and a selective reduction catalyst 21b are placed in a discharge passage 13, in this order from the side of the discharge manifold 11a.

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine that purifies harmful substances such as particulate matter, nitrogen oxides, carbon monoxide, and hydrocarbons in the exhaust gas of an internal combustion engine such as a diesel vehicle.

  For the purpose of purifying harmful substances such as particulate matter (PM), nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC) in the exhaust gas of engines such as diesel cars (internal combustion engines) Reduction of generation of harmful substances by improving the combustion state in the engine cylinder, oxidation catalyst device (DOC), diesel particulate filter device (DPF), urea selective reduction catalyst (urea SCR catalyst) provided in the exhaust passage of the engine ) Removal of harmful substances is progressing by an exhaust gas purification system configured by mounting a plurality of exhaust gas purification devices such as an apparatus.

  For example, an oxidation catalyst, a urea injection device, a diesel particulate filter device, a selective reduction type NOx catalytic converter, and an oxidation catalyst are arranged in this order from the upstream side of the exhaust passage, and the diesel particulate filter device has an oxidation function. An exhaust gas purification system that supports a urea decomposition catalyst without supporting a catalyst has been proposed (see, for example, Patent Document 1).

  However, as a result of improvements in the combustion state of the engine, the exhaust gas temperature has been decreasing at a temperature range of 30 ° C. to 50 ° C. or more than before, and multiple exhaust gas purification devices have become larger. Therefore, the heat capacity of the entire exhaust gas purification device in the exhaust gas purification system has increased, and it has become difficult to ensure the activation temperature of the catalyst. Further, since the exhaust gas purification device is disposed farther from the exhaust port of the engine due to the increase in size, it tends to be more difficult to maintain the catalyst at the activation temperature or higher. Therefore, there is a problem that the effect of reducing harmful substances in each exhaust gas purification device is reduced.

  In addition, in the urea selective reduction type catalyst (urea SCR) device, it is necessary to diffuse urea water uniformly and to promote the decomposition of urea into ammonia. It is difficult to shorten the distance to the selective catalytic reduction catalyst device, which is a major factor in increasing the size of the exhaust gas purification system.

JP 2010-242515 A

  The present invention has been made in view of the above situation, and an object of the present invention is to effectively use the heat of the exhaust gas and to supply the amount of hydrocarbons such as light oil supplied to the oxidation catalyst to increase the temperature of the exhaust gas. It is another object of the present invention to provide an exhaust gas purification system for an internal combustion engine that can reduce the size of the engine and reduce the size of the EGR passage, and can further prevent clogging caused by the SOF component of an EGR cooler and an EGR valve provided in an EGR passage.

  An exhaust gas purification system for an internal combustion engine according to the present invention for achieving the above-described object is an exhaust gas purification system for an internal combustion engine that purifies harmful substances in the exhaust gas of the internal combustion engine. Each cylinder is disposed between the exhaust manifolds, and a second oxidation catalyst, a urea injection nozzle, a diesel particulate filter, and a selective reduction catalyst are disposed in the exhaust passage sequentially from the exhaust manifold side.

  According to this configuration, since the first oxidation catalyst is arranged for each cylinder between the exhaust port and the exhaust manifold, the first oxidation is performed using the high-temperature exhaust gas before the exhaust gas is cooled and the temperature is lowered. It becomes easy to maintain the catalyst at or above the catalyst activation temperature, and the first oxidation catalyst can efficiently oxidize carbon monoxide and hydrocarbons in the exhaust gas. By these oxidations, the temperature of the exhaust gas flowing into the second oxidation catalyst can be increased, so that the second oxidation catalyst can be easily maintained at a temperature higher than the catalyst activation temperature.

  Therefore, the exhaust gas purification system can effectively use the heat of the exhaust gas, and the amount of hydrocarbons such as light oil supplied to the oxidation catalyst for increasing the temperature of the exhaust gas can be reduced, thereby reducing the fuel consumption. Further, the arrangement of the first oxidation catalyst can reduce the size of the entire exhaust gas purification system.

  Further, since the exhaust gas used in EGR is normally supplied from the exhaust manifold or the exhaust passage to the intake passage side, it passes through the first oxidation catalyst and is SOF (Soluble Organic Fraction: unburned substance) in the exhaust gas. , Liquid hydrocarbon fine particles) component-exhausted exhaust gas can be flowed through the EGR passage. Therefore, adverse effects such as clogging due to the SOF component of the EGR cooler and the EGR valve provided in the EGR passage can be suppressed.

  In the exhaust gas purification system for an internal combustion engine, a turbocharger turbine is arranged between the urea injection nozzle and the diesel particulate filter.

  According to this configuration, since the urea injected from the urea injection nozzle is stirred and diffused in the turbine, the thermal decomposition and hydrolysis of urea are promoted, and after passing through the turbine, the sprayed urea is in the exhaust pipe. Is evenly diffused. Therefore, the distance from the urea injection nozzle to the selective reduction catalyst can be shortened, and the exhaust gas purification system can be miniaturized. In addition, since ammonia can be generated from urea at a high conversion rate by promoting the thermal decomposition and hydrolysis of urea, the purification performance of the selective catalytic reduction catalyst on the downstream side can be improved.

  In addition, since sulfur oxides generated by high EGR combustion react with urea injected from the urea injection nozzle and are neutralized, corrosion or the like caused by sulfur oxide in the exhaust pipe or turbine downstream of the urea injection nozzle. Can be suppressed.

  In the exhaust gas purification system for an internal combustion engine, the first oxidation catalyst supports a catalyst in which an oxide having an oxygen storage ability and an oxide semiconductor are mixed, and the second oxidation catalyst has a noble metal catalyst or a hydrocarbon. A catalyst in which an adsorbent and a precious metal catalyst are mixed is supported. According to this configuration, the first oxidation catalyst becomes an exhaust gas purification device excellent in purifying carbon monoxide, and the second oxidation catalyst becomes an exhaust gas purification device excellent in hydrocarbon purification and low-temperature activity.

  According to the exhaust gas purification system for an internal combustion engine according to the present invention, since the first oxidation catalyst is provided between the exhaust port and the exhaust manifold, the heat of the exhaust gas can be used effectively and the temperature of the exhaust gas is increased. In addition, the amount of hydrocarbons such as light oil supplied to the oxidation catalyst can be reduced, and fuel consumption can be reduced. Further, the exhaust gas purification system can be reduced in size.

  Furthermore, since the exhaust gas that has passed through the first oxidation catalyst and has a reduced SOF component can flow into the EGR passage, clogging of the EGR cooler provided in the EGR passage and the SGR component of the EGR valve can be suppressed.

It is a figure which shows the structure of the exhaust-gas system of the internal combustion engine of the 1st Embodiment of this invention. It is a figure which shows the structure of the exhaust-gas system of the internal combustion engine of the 2nd Embodiment of this invention. It is a figure which shows the ammonia conversion rate of Examples 1-3. It is a figure which shows the NOx average purification rate in JE05 mode of Examples 1-3.

  Hereinafter, an exhaust gas purification system for an internal combustion engine according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, an exhaust gas purification system 1 for an internal combustion engine according to a first embodiment includes particulate matter (PM), nitrogen oxide (NOx) in exhaust gas G of an engine (internal combustion engine) 10, This is a system for purifying harmful substances such as carbon monoxide (CO) and hydrocarbons (HC).

  An engine 10 provided with the exhaust gas purification system 1 for an internal combustion engine includes an intake passage 12 connected to an intake manifold 11 a provided in the engine body 11 and an exhaust passage 13 connected to an exhaust manifold 11 b provided in the engine body 11. And is configured.

  In the intake passage 12, a low-pressure stage compressor 14 a of a low-pressure stage turbocharger 14 and a high-pressure stage compressor 15 a of a high-pressure stage turbocharger 15 are arranged in this order from the upstream side. A first oxidation catalyst 18 is disposed for each cylinder between the exhaust port and the exhaust manifold 11b.

  At the same time, in order from the exhaust manifold 11b side, the second oxidation catalyst 19, the high pressure turbine 15b of the high pressure turbocharger 15, the urea injection nozzle 20, the low pressure turbine 14b of the low pressure turbocharger 14, and the diesel particulate filter (DPF). 21a, a selective reduction catalyst (SCR) 21b, and a third oxidation catalyst 21c are arranged.

  In the configuration of FIG. 1, the diesel particulate filter (DPF) 21a, the selective reduction catalyst (SCR) 21b, and the third oxidation catalyst 21c are configured as an exhaust gas purification unit 21 disposed in the same container. The separate structure arrange | positioned at another container may be sufficient.

  Further, the EGR passage 16 is provided by connecting the exhaust manifold 11b on the downstream side of the first oxidation catalyst 18 and the intake passage 12 on the downstream side of the high pressure compressor 15a, and the exhaust gas Ge that has passed through the first oxidation catalyst 18 is provided. Configured for use in recirculation. An EGR valve 17 is disposed in the EGR passage 16. Thus, an HP-EGR system that recirculates high-pressure exhaust gas is configured.

  In the exhaust gas purification system 1 of the internal combustion engine, the first oxidation catalyst 18 and the second oxidation catalyst 19 constitute an upstream oxidation catalyst, and the first oxidation catalyst 18 is excellent in purifying carbon monoxide. In addition, a catalyst in which an oxide having an oxygen storage capacity (OSC) and an oxide semiconductor are mixed is supported.

Examples of the oxide having oxygen storage ability include oxide containing cerium (Ce), and examples of the oxide semiconductor include titanium oxide (TiO ₂ ), zinc oxide (ZnO), yttrium oxide (Y ₂ O ₃ ), and the like. is there. Preferably, a noble metal is supported on the oxide having oxygen storage capacity. In addition, the second oxidation catalyst 19 is configured to carry a catalyst that is excellent in hydrocarbon purification and is a mixture of a metal catalyst or a hydrocarbon adsorbent and a noble metal catalyst. Examples of the noble metal catalyst include platinum (Pt).

  As a result, the first oxidation catalyst becomes an exhaust gas purification device excellent in purifying carbon monoxide, and the second oxidation catalyst becomes an exhaust gas purification device excellent in hydrocarbon purification and low-temperature activity. As a result, it is possible to obtain an excellent catalyst structure and to reduce the size of the oxidation catalyst.

Since the urea injection nozzle 20 is installed between the second oxidation catalyst 19 and the turbine (in FIG. 1, the low-pressure turbine 14b), the injected urea is stirred and diffused in the low-pressure turbine 14b, so Hydrolysis and thermal decomposition are promoted. For this reason, the distance from the urea injection nozzle 20 to the selective catalytic reduction catalyst 21b can be shortened. Further, after the injected urea passes through the low-pressure turbine 14b, it is diffused into the exhaust pipe and becomes uniform. When urea is injected from the urea injection nozzle 20, sulfur oxide (SOx) generated by high EGR combustion reacts with the urea and is neutralized. That is, a reaction of “2NH ₃ + SO ₃ + H ₂ O → (NH ₄ ) ₂ SO ₄ ” is generated to produce ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) as a neutralized product. Therefore, corrosion and the like in the exhaust pipe and the turbine on the downstream side from the urea injection nozzle due to the sulfur oxide generated by the high EGR combustion can be suppressed. In the configuration of FIG. 1, the two low-pressure stage turbochargers 14 and the high-pressure stage turbocharger 15 are provided, but the turbocharger corresponding to the low-pressure stage turbocharger 14 may be a single configuration.

The diesel particulate filter 21a has a configuration in which noble metal catalyst is not applied in order to prevent the urea sprayed from the urea injection nozzle 20 on the flow side from being oxidized, and further, a hydrolysis catalyst layer is formed on the surface of the filtration wall. . That is, a porous layer formed of nano-order particles is used for urea hydrolysis. As the hydrolysis catalyst, titanium dioxide (TiO ₂ ), zirconium dioxide (ZrO ₂₎ , a rare earth oxide having a high basicity, or the like can be used.

  Moreover, it is preferable to use the diesel particulate filter 21a having a structure with high purification characteristics and low pressure loss by optimizing the porosity, pore diameter, and wall thickness. Further, the diesel particulate filter 21a can form a porous layer formed of nano-order particles on the filtration surface, and can exhibit effects such as reduction of pressure loss at the time of PM collection and reduction of variation in collection. It is preferable to do so.

The urea ((NH ₂ ) ₂ CO) sprayed into the exhaust gas upstream of the diesel particulate filter 21a mainly contains the thermal decomposition of urea and the hydrolysis of isocyanic acid (HCNO) generated by this thermal decomposition. It is converted to ammonia (NH ₃ ) by decomposition. Since the reaction rate of hydrolysis is slower than that of thermal decomposition, in an exhaust gas purification system that uses a selective catalytic reduction catalyst for vehicles with limited layout, ammonia is generated from urea simply by making the diffusion of urea uniform. The conversion rate to do is not enough.

However, due to the hydrolysis layer provided in the diesel particulate filter 21a, isocyanic acid generated by the thermal decomposition of urea ((NH ₂ ) ₂ CO → (NH ₃ ) + HNCO) is hydrolyzed “HCNO + H ₂ O → NH ₃ + CO _2. Can produce ammonia.

Furthermore, in this diesel particulate filter 21a, the ash component (calcium carbonate: CaCO ₃ ) generated after burning the particulate matter (PM) reacts with ammonium sulfate ((NH ₄ ) ₂ SO ₄ ), and “( NH ₄ ) ₂ SO 4 + CaCO ₃ → (NH ₄ ) ₂ CO ₃ + CaSO ₄ ”produces ammonium carbonate ((NH ₄ ) ₂ CO ₃ ). This ammonium carbonate undergoes thermal decomposition of “(NH ₄ ) ₂ CO ₃ → 2NH ₃ + H ₂ O + CO ₂ ” at 58 ° C. or higher to produce ammonia.

  Therefore, a sufficient ammonia conversion rate can be obtained by the diesel particulate filter 21a, and the converted ammonia is used for the NOx purification reaction in the downstream selective reduction catalyst 21b.

  The selective reduction catalyst 21b is formed using a catalyst carrier (monolith catalyst) or the like, but it is preferable to use a small catalyst having a reduced volume by increasing the amount of catalyst per specific volume.

  The third oxidation catalyst 21c is for decomposing ammonia that has not been consumed by the selective catalytic reduction catalyst 21b to prevent ammonia from flowing out (slipping), but depending on the use of the exhaust gas purification system 1. May be omitted.

  Next, an exhaust gas purification system for an internal combustion engine according to a second embodiment will be described. The exhaust gas purification system 1A of the second embodiment shown in FIG. 2 differs from the exhaust gas purification system 1 of the first embodiment of FIG. 1 in the positions of the urea injection nozzle 20 and the exhaust gas purification unit 21. Yes.

  In the exhaust gas purification system 1 of FIG. 1, the urea injection nozzle 20 is provided upstream of the low-pressure stage turbine 14b, and the exhaust gas purification unit 21 is disposed immediately after the low-pressure stage turbine 14b. In the exhaust gas purification system 1A shown in FIG. 2, the urea injection nozzle 20 is provided on the downstream side of the low-pressure turbine 14b, and at a position away from the urea injection nozzle 20 in contrast to the engine 10 disposed close to the engine 10. Is provided with an exhaust gas purification unit 21, and the exhaust gas purification unit 21 is disposed far from the engine 10.

According to the exhaust gas purification systems 1 and 1A of the internal combustion engine having the above-described configuration, ammonia (NH ₃ ) generated from urea and sulfur oxide (SOx) in the exhaust gas and “2NH ₃ + SO ₃ + H ₂ O → (NH ₄ ) ₂ SO ₄ ”reaction, and the ash component (CaCO ₃ ) and ammonium sulfate ((NH ₄ ) ₂ SO generated after the particulate matter (PM) is burned by the downstream diesel particulate filter 21a. ₄ ) causes a reaction of “(NH ₄ ) ₂ SO 4 + CaCO ₃ → (NH ₄ ) ₂ CO ₃ + CaSO ₄ ”, and the thermal decomposition of the produced ammonium carbonate ((NH ₄ ) ₂ CO ₃ ) “(NH ₄₎ captured by _{2 CO 3 → 2NH 3 + H} 2 O + CO 2 "in the resulting ammonia (downstream side of the selective reduction catalyst 21b of the NH ₃₎ a diesel particulate filter 21a, It can be used to Ox clean reaction.

  Therefore, according to the exhaust gas purification systems 1 and 1A for the internal combustion engine having the above-described configuration, the heat of the exhaust gas G can be effectively utilized because the first oxidation catalyst 18 is provided between the exhaust port and the exhaust manifold 11a. In addition, the amount of hydrocarbons such as light oil supplied to the oxidation catalyst for increasing the temperature of the exhaust gas G can be reduced, and fuel consumption can be reduced. Further, the exhaust gas purification systems 1 and 1A can be reduced in size.

  Further, since the exhaust gas G having a reduced SOF component passing through the first oxidation catalyst 18 can be flowed to the EGR passage 16, an EGR cooler (not shown) provided in the EGR passage 16 and the EGR valve 17 An adverse effect such as clogging due to the SOF component can be suppressed.

  Next, the test results in the JE05 mode by the exhaust gas purification systems 1 and 1A for the internal combustion engine will be described. In the configuration of the exhaust gas purification system 1 of the first embodiment of FIG. 1, the configuration in which the diesel particulate filter 21a is provided with a hydrolysis layer is referred to as Example 1, and the configuration in which the hydrolysis layer is not provided is referred to as Example 2. The configuration of the exhaust gas purification system 1A of the second embodiment in FIG. 2 is a configuration in which a hydrolysis layer is provided on the diesel particulate filter 21a as Example 3, and a JE05 mode test was conducted. The results are shown in FIG. And shown in FIG.

  In Example 1, the average inlet temperature during the JE05 mode was 200 ° C. at the inlet of the first oxidation catalyst 18, 175 ° C. at the inlet of the diesel particulate filter 21a, and 170 ° C. at the inlet of the selective catalytic reduction catalyst 21b. On the other hand, in Example 3, the average inlet temperature during JE05 mode was 150 ° C. at the inlet of the first oxidation catalyst 18, 140 ° C. at the inlet of the diesel particulate filter 21a, and 125 ° C. at the inlet of the selective catalytic reduction catalyst 21b. .

  3 shows the ammonia conversion rate at the inlet of the selective catalytic reduction catalyst 21b of Examples 1 to 3, and FIG. 4 shows the NOx average purification rate in the JE05 mode. Example 1 shows a high ammonia conversion rate even at 200 ° C., as shown in FIG. On the other hand, in Example 3, at 150 ° C., the hydrocarbon (HC) purification rate of the first oxidation catalyst 18 was 10% or less (the carbon monoxide (CO) purification rate was the same). Further, at 125 ° C., the NOx purification rate of the selective catalytic reduction catalyst 21b was 5% or less. Therefore, the average purification rate was 50% or less for hydrocarbons, carbon monoxide, and NOx. In the third embodiment, in order to inject and uniformly diffuse urea, a distance of 25 cm or more is required from the position of the urea injection nozzle 20 to the selective reduction catalyst 21b. To reduce the distance, It became necessary to provide a diffusion plate.

  According to the exhaust gas purification system for an internal combustion engine of the present invention, the heat of the exhaust gas can be used effectively, the amount of hydrocarbons such as light oil supplied to the oxidation catalyst for increasing the temperature of the exhaust gas can be reduced, and the exhaust gas Since the purification system can be reduced in size and clogging due to the SOF component of the EGR cooler and EGR valve provided in the EGR passage can be suppressed, it can be used as an exhaust gas purification system for an internal combustion engine mounted on an automobile or the like.

1, 1A Exhaust gas purification system for internal combustion engine 10 Engine (internal combustion engine)
11b Exhaust manifold 13 Exhaust passage 14 Low pressure turbocharger 14b Low pressure turbine 18 First oxidation catalyst 19 Second oxidation catalyst 20 Urea injection nozzle 21 Exhaust gas purification unit 21a Diesel particulate filter (DPF)
21b Selective reduction catalyst (SCR)
21c Third oxidation catalyst A Intake G Exhaust gas Ge EGR gas

Claims (3)

  In the exhaust gas purification system for an internal combustion engine that purifies harmful substances in the exhaust gas of the internal combustion engine, the first oxidation catalyst is disposed between the exhaust port and the exhaust manifold for each cylinder, and in order from the exhaust manifold side, the second An exhaust gas purification system for an internal combustion engine, wherein an oxidation catalyst, a urea injection nozzle, a diesel particulate filter, and a selective reduction catalyst are arranged in an exhaust passage.   The exhaust gas purification system for an internal combustion engine according to claim 1, wherein a turbine of a turbocharger is disposed between the urea injection nozzle and the diesel particulate filter.   The first oxidation catalyst carries a catalyst in which an oxide having an oxygen storage capability and an oxide semiconductor are mixed, and the second oxidation catalyst carries a catalyst in which a noble metal catalyst or a hydrocarbon adsorbent and a noble metal catalyst are mixed. The exhaust gas purification system for an internal combustion engine according to claim 1 or 2.

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