Exhaust system

Abstract

To provide an exhaust system having excellent exhaust emission control performance.SOLUTION: An exhaust system 1 includes: an exhaust pipe 2 for discharging exhaust gas discharged from an engine 101; a plasma reactor 3 interposed in the middle of the exhaust pipe 2 and adsorbing and decomposing hydrocarbon (HC) included in the exhaust gas; and an HC storage device 4 interposed on the upstream side of the plasma reactor 3 in the exhaust pipe 2 and adsorbing and emitting hydrocarbon (HC). The plasma reactor 3 includes first zeolite that adsorbs hydrocarbon (HC), and the HC storage device 4 includes second zeolite that adsorbs hydrocarbon (HC). Either one of the first zeolite or the second zeolite contains metal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to exhaust systems. [Background technology]

[0002] Conventionally, plasma reactors have been known as devices for decomposing hydrocarbons (HC) contained in exhaust gases. In plasma reactors, a voltage is applied to multiple electrode panels to generate plasma between the electrode panels, and the hydrocarbons (HC) can be decomposed by the plasma (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-90400 A Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, there is a limit to the decomposition performance of plasma reactors. Therefore, if an amount of hydrocarbons (HC) that exceeds the limit of the decomposition performance is supplied to a plasma reactor, some of the hydrocarbons (HC) may be released into the atmosphere without being decomposed. Therefore, there is a demand for plasma reactors to have improved exhaust gas purification performance.

[0005] The present invention is an exhaust system having excellent exhaust gas purification performance. [Means for solving the problem]

[0006] The present invention [1] includes an exhaust system comprising: an exhaust pipe for discharging exhaust gas discharged from an engine; a plasma reactor disposed in the exhaust pipe for adsorbing and decomposing hydrocarbons (HC) contained in the exhaust gas; and an HC storage device disposed in the exhaust pipe upstream of the plasma reactor for adsorbing and releasing the hydrocarbons (HC), wherein the plasma reactor comprises a first zeolite that adsorbs hydrocarbons (HC), and the HC storage device comprises a second zeolite that adsorbs hydrocarbons (HC), and either the first zeolite or the second zeolite contains a metal.

[0007] The present invention [2] includes an exhaust system comprising an exhaust pipe for discharging exhaust gas discharged from an engine, a plasma reactor disposed in the exhaust pipe for adsorbing and decomposing hydrocarbons (HC) contained in the exhaust gas, and an HC storage device disposed in the exhaust pipe upstream of the plasma reactor for adsorbing and releasing the hydrocarbons (HC), wherein the plasma reactor comprises a first zeolite for adsorbing hydrocarbons (HC), and the HC storage device comprises a second zeolite for adsorbing hydrocarbons (HC), wherein either the first zeolite or the second zeolite contains a first metal, and the other of the first zeolite or the second zeolite contains a second metal having a composition different from that of the first metal. Effect of the Invention

[0008] In the exhaust system of the present invention [1], only one of the plasma reactor and the HC storage device is equipped with a zeolite containing a metal, and the other is equipped with a zeolite not containing a metal. Therefore, among the hydrocarbons (HC) passing through the exhaust pipe, either the hydrocarbons (HC) with a relatively small carbon number or the hydrocarbons (HC) with a relatively large carbon number is adsorbed by the second zeolite of the HC storage device arranged on the more upstream side. Also, the other is adsorbed by the first zeolite of the plasma reactor arranged on the more downstream side. That is, when the engine starts, a part of the hydrocarbons (HC) passing through the exhaust pipe is adsorbed by the HC storage device, and only the remaining part is decomposed by the plasma reactor. Also, when the exhaust gas temperature rises due to the continuous operation of the engine, the hydrocarbons (HC) adsorbed by the HC storage device are released and decomposed by the plasma reactor. That is, the hydrocarbons (HC) are divided and supplied to the plasma reactor. Therefore, according to the above configuration, it is possible to suppress the supply of an amount of hydrocarbons (HC) exceeding the limit of the decomposition performance of the plasma reactor to the plasma reactor, and the hydrocarbons (HC) can be efficiently decomposed by the plasma reactor. Therefore, the above exhaust system has excellent exhaust gas purification performance.

[0009] In the exhaust system of the present invention [2], either the plasma reactor or the HC storage device is provided with a zeolite containing a first metal, and the other is provided with a zeolite containing a second metal having a composition different from that of the first metal. Therefore, among the hydrocarbons (HC) passing through the exhaust pipe, either the hydrocarbons (HC) with a relatively small carbon number or the hydrocarbons (HC) with a relatively large carbon number is adsorbed by the second zeolite of the HC storage device arranged on the more upstream side. Also, the other is adsorbed by the first zeolite of the plasma reactor arranged on the more downstream side. In other words, when the engine starts, a part of the hydrocarbons (HC) passing through the exhaust pipe is adsorbed by the HC storage device, and only the remainder is decomposed by the plasma reactor. In addition, when the exhaust gas temperature rises due to the continuous operation of the engine, the hydrocarbons (HC) adsorbed by the HC storage device are released and decomposed by the plasma reactor. In other words, the hydrocarbons (HC) are divided and supplied to the plasma reactor. Therefore, according to the above configuration, it is possible to prevent the supply of an amount of hydrocarbons (HC) that exceeds the limit of the decomposition performance of the plasma reactor from being supplied to the plasma reactor, and the hydrocarbons (HC) can be efficiently decomposed in the plasma reactor. Therefore, the above exhaust system has excellent exhaust gas purification performance. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of an exhaust system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram of an exhaust system according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] 1. Exhaust system configuration As shown in FIG. 1, the exhaust system 1 is mounted on a vehicle 100, for example.

[0012] The vehicle 100 includes an engine 101, an electrical system including a battery 102, an intake system (not shown) for drawing air into the engine 101, a fuel injection system (not shown) for supplying fuel to the engine 101, and an exhaust system 1 for exhausting air from the engine 101.

[0013] The exhaust system 1 includes an exhaust pipe 2 , a plasma reactor 3 , an HC storage device 4 , a valve 5 , and a control unit 6 .

[0014] (1) Exhaust pipe The exhaust pipe 2 includes a main pipe 21 and a bypass pipe 22 that bypasses the main pipe 21 .

[0015] The main pipe 21 is a pipe for discharging exhaust gas discharged from the engine 101. The main pipe 21 is connected to the engine 101. The exhaust gas that passes through the main pipe 21 is discharged outside the vehicle. A plasma reactor 3, which will be described later, is interposed in the main pipe 21.

[0016] The bypass pipe 22 is a pipe that bypasses the main pipe 21 upstream of the plasma reactor 3 (described later). The bypass pipe 22 branches off from the main pipe 21 between the engine 101 and the plasma reactor 3, and further merges with the main pipe 21 between the engine 101 and the plasma reactor 3.

[0017] Specifically, the bypass pipe 22 has an upstream end 2A and a downstream end 2B in the direction in which the exhaust gas passes. Both the upstream end 2A and the downstream end 2B are connected to the main pipe 21 on the upstream side of a plasma reactor 3 (described later). As a result, the bypass pipe 22 branches off the exhaust gas from the main pipe 21 on the upstream side of the plasma reactor 3 (described later), passes the exhaust gas, and merges with the main pipe 21. An HC storage device 4 (described later) is interposed in the bypass pipe 22.

[0018] (2) Plasma Reactor The plasma reactor 3 is a device that decomposes hydrocarbons (HC) contained in exhaust gas. The plasma reactor 3 can also decompose particulate matter (PM) contained in exhaust gas. The plasma reactor 3 is disposed in the middle of the exhaust pipe 2. More specifically, the plasma reactor 3 is disposed in the main pipe 21 downstream of the bypass pipe 22.

[0019] The plasma reactor 3 has an inlet 3A and an outlet 3B. Exhaust gas discharged from the engine 101 passes through the exhaust pipe 2 and is introduced into the inside of the plasma reactor 3 from the inlet 3A. The exhaust gas that has passed through the inside of the plasma reactor 3 is discharged from the outlet 3B and discharged outside the vehicle.

[0020] The plasma reactor 3 has a plurality of electrodes 7. The plurality of electrodes 7 are provided inside the plasma reactor 3. Each electrode 7 extends from the inlet 3A toward the outlet 3B. Each electrode 7 is composed of a conductor (e.g., a metal such as tungsten) and a dielectric covering the conductor (e.g., a ceramic such as aluminum oxide). Each electrode 7 has a flat plate shape. The plurality of electrodes 7 are arranged at intervals from each other in a direction perpendicular to the direction from the inlet 3A toward the outlet 3B. The plasma reactor 3 is electrically connected to a battery 102 via a power supply wiring 8.

[0021] When power is supplied to the plasma reactor 3 from the battery 102 via the power supply wiring 8, a discharge occurs between the electrodes 7. As a result, the gas between the electrodes 7 becomes a plasma state. That is, plasma is generated within the plasma reactor 3.

[0022] As a result, hydrocarbons (HC) contained in the exhaust gas introduced into the plasma reactor 3 are decomposed by the plasma in the plasma reactor 3. The exhaust gas that has passed through the plasma reactor 3 is exhausted outside the vehicle via the exhaust pipe 2.

[0023] Moreover, the plasma reactor 3 is provided with a first zeolite, and is capable of adsorbing hydrocarbons (HC) contained in the exhaust gas.

[0024] The first zeolite is an adsorbent that adsorbs hydrocarbons (HC). The first zeolite includes known zeolites. Examples of zeolites include natural zeolites and synthetic zeolites. Examples of natural zeolites include analcime, chalcocite, erionite, natrolite, mordenite, heulandite, stilbite, and laumontite. Examples of synthetic zeolites include A-type zeolite, Y-type zeolite, X-type zeolite, L-type zeolite, erionite, mordenite, β-zeolite, and ZSM-5-type zeolite. These can be used alone or in combination of two or more. Zeolites can contain metals, which will be described in detail later. Examples of metals include transition metals (excluding noble metals). More specifically, examples of metals include silver, iron, manganese, and copper. These can be used alone or in combination of two or more. A preferable example of the metal is silver. The metals may, for example, be supported on or contained in the zeolite in a known manner.

[0025] The first zeolite, for example, coats the surface of each electrode 7 to form a zeolite layer. As a result, hydrocarbons (HC) contained in the exhaust gas introduced into the plasma reactor 3 are adsorbed by the first zeolite on the surface of the electrode 7 and decomposed by the plasma.

[0026] Furthermore, in the plasma reactor 3, for example, a switch (not shown) is interposed in the middle of the power supply wiring 8. The switch is electrically connected to the control unit 6 via a signal wiring (not shown). The control unit 6 controls the power supply from the battery 102 to the plasma reactor 3. In detail, the control unit 6 supplies power from the battery 102 to the plasma reactor 3 by turning on the switch. Furthermore, the control unit 6 stops the power supply from the battery 102 to the plasma reactor 3 by turning off the switch.

[0027] (3)HC storage device The HC storage device 4 is a device for temporarily storing the hydrocarbons (HC) contained in the exhaust gas. The HC storage device 4 includes a second zeolite that adsorbs the hydrocarbons (HC). More specifically, the HC storage device 4 includes, for example, a second zeolite and a carrier coated with the second zeolite.

[0028] The second zeolite is an adsorbent that adsorbs hydrocarbons (HC). The second zeolite includes known zeolites. Examples of the zeolite include the above-mentioned natural zeolites and the above-mentioned synthetic zeolites. The zeolite can also contain the above-mentioned metals. The metals are, for example, supported on the zeolite or contained as a component by a known method.

[0029] The carrier is not particularly limited, but may be, for example, a monolith carrier made of cordierite. The monolith carrier has, for example, a honeycomb shape. The second zeolite is prepared, for example, as a slurry, and applied to the carrier and dried. This provides an HC storage device 4 including the second zeolite and the carrier.

[0030] The HC storage device 4 is interposed in the bypass pipe 22. The HC storage device 4 has an inlet 4A and an outlet 4B. Exhaust gas discharged from the engine 101 passes through the bypass pipe 22 and is introduced into the inside of the HC storage device 4 from the inlet 4A. In addition, exhaust gas that has passed through the inside of the HC storage device 4 is discharged from the outlet 4B and merges with the main pipe 21. At this time, a portion of the hydrocarbons (HC) contained in the exhaust gas is adsorbed by the second zeolite in the HC storage device 4.

[0031] (4) Valve The valve 5 is a member that adjusts the flow rate of exhaust gas flowing through the main pipe 21 and the flow rate of exhaust gas flowing through the bypass pipe 22 in the exhaust pipe 2. More specifically, the valve 5 is interposed in the connection portion between the main pipe 21 and the downstream end 2B of the bypass pipe 22. An example of the valve 5 is a three-way valve.

[0032] The valve 5 is movable between a main position (hereinafter, position A) where the opening of the bypass pipe 22 is 0% and the opening of the main pipe is 100% and a bypass position (hereinafter, position B) where the opening of the bypass pipe 22 is 100% and the opening of the main pipe is 0%, and the above opening can be adjusted to an arbitrary value. That is, the valve 5 is preferably a flow rate adjustment valve whose opening can be adjusted between position A and position B. Note that the valve 5 may be an opening / closing valve whose opening cannot be adjusted.

[0033] When the valve 5 is moved from position A to position B, the flow rate of exhaust gas flowing into the bypass pipe 22 and the HC storage device 4 increases. When the valve 5 is moved from position B to position A, the flow rate of exhaust gas flowing into the bypass pipe 22 and the HC storage device 4 decreases.

[0034] The arrangement of the valve 5 is not limited to the above, and may be any arrangement as long as it can adjust the flow rate of exhaust gas branching from the main pipe 21 to the bypass pipe 22. For example, the valve 5 may be disposed in the bypass pipe 22 on the upstream side of the HC storage device 4. The valve 5 may be disposed in the main pipe 21, instead of at the connection between the main pipe 21 and the bypass pipe 22, or may be disposed in the bypass pipe 22.

[0035] (5) Control section The control unit 6 is an ECU (Electronic Control Unit) that executes electrical control in the vehicle 100, and includes a CPU, a ROM, and a RAM. The control unit 6 is connected to a battery 102 via a power supply line 10. When the ignition switch of the vehicle 100 is turned on, the control unit 6 is started up by being supplied with power from the battery 102 via the power supply line 10.

[0036] The control unit 6 is electrically connected to the valve 5 via a signal wiring 9. The control unit 6 controls the opening degree of the valve 5 by sending an electrical signal to the valve 5 via the signal wiring 9.

[0037] In addition, the control unit 6 is electrically connected to an accelerator pedal (not shown) and is capable of receiving an electrical signal in response to starting and stopping of the engine 101 .

[0038] (6) Catalyst unit The exhaust system 1 further includes a catalytic unit 12. The catalytic unit 12 is disposed in the exhaust pipe 2, upstream of the upstream end 2A of the bypass pipe 22. That is, the exhaust gas discharged from the engine 101 first passes through the catalytic unit 12, then passes through the main pipe 21 or the bypass pipe 22, and is introduced into the plasma reactor 3, and is then discharged outside the vehicle.

[0039] The catalyst unit 12 includes a known exhaust gas purification catalyst. More specifically, the catalyst unit 12 includes, for example, an exhaust gas purification catalyst and a catalyst carrier that supports the exhaust gas purification catalyst.

[0040] The exhaust gas purification catalyst may be a known three-way catalyst. The three-way catalyst may be, for example, an oxide containing a precious metal. Examples of the precious metal include platinum, palladium, and rhodium. The exhaust gas purification catalyst is usually heated to oxidize and detoxify the hydrocarbons (HC) contained in the exhaust gas.

[0041] The catalyst carrier is not particularly limited, but may be, for example, a monolith carrier made of cordierite. The monolith carrier has, for example, a honeycomb shape. The exhaust gas purification catalyst is prepared, for example, as a slurry, and is applied to the catalyst carrier and dried. This results in a catalyst carrier carrying the exhaust gas purification catalyst.

[0042] 2. Zeolite As described above, the plasma reactor 3 and the HC storage device 4 are equipped with zeolite. Zeolite is a compound capable of adsorbing and releasing hydrocarbons (HC). More specifically, zeolite adsorbs hydrocarbons (HC) at relatively low temperatures (e.g., below 300°C). Zeolite also releases hydrocarbons (HC) at relatively high temperatures (e.g., above 300°C).

[0043] In addition, the carbon number of hydrocarbons (HC) that zeolites can absorb and release varies depending on the type of zeolite.

[0044] More specifically, metal-containing zeolites chemically adsorb hydrocarbons (HC) due to the influence of the metal. Therefore, metal-containing zeolites have the property of easily adsorbing and releasing hydrocarbons (HC) with a relatively small carbon number (e.g., less than 5 carbon atoms) and having difficulty adsorbing and releasing hydrocarbons (HC) with a relatively large carbon number (e.g., 5 or more carbon atoms).

[0045] Moreover, metal-free zeolites physically adsorb hydrocarbons (HC) in the pores of the zeolites. Therefore, metal-free zeolites have the property of easily adsorbing and releasing hydrocarbons (HC) with a relatively large carbon number (e.g., carbon number of 5 or more) and not easily adsorbing and releasing hydrocarbons (HC) with a relatively small carbon number (e.g., carbon number less than 5).

[0046] In the above exhaust system, only one of the first zeolite in the plasma reactor 3 and the second zeolite in the HC storage device 4 contains a metal, and the other does not contain a metal. In other words, either the first zeolite or the second zeolite is a zeolite that contains a metal, and the other is a zeolite that does not contain a metal.

[0047] For example, when the first zeolite in the plasma reactor 3 contains a metal, the second zeolite in the HC storage device 4 does not contain a metal. Also, when the first zeolite in the plasma reactor 3 does not contain a metal, the second zeolite in the HC storage device 4 contains a metal.

[0048] Preferably, the first zeolite in the plasma reactor 3 contains a metal, and the second zeolite in the HC storage device 4 does not contain a metal. More preferably, the first zeolite in the plasma reactor 3 contains silver (Ag), and the second zeolite in the HC storage device 4 does not contain a metal.

[0049] As described above, if only one of the first zeolite and the second zeolite contains a metal, the metal-containing zeolite can preferentially adsorb and release hydrocarbons (HC) with a relatively small carbon number, while the metal-free zeolite can preferentially adsorb and release hydrocarbons (HC) with a relatively large carbon number.

[0050] Therefore, if only one of the first zeolite and the second zeolite contains a metal and the other does not, it is possible to selectively adsorb and release either the hydrocarbons (HC) with a relatively high carbon number or the hydrocarbons (HC) with a relatively low carbon number onto the first zeolite of the plasma reactor 3. Also, it is possible to selectively adsorb and release the other of the hydrocarbons (HC) with a relatively high carbon number or the hydrocarbons (HC) with a relatively low carbon number onto the second zeolite of the HC storage device 4.

[0051] The content of the metal in the first zeolite or the second zeolite is appropriately set depending on the purpose and application, and is, for example, 1 mass % or more and 10 mass % or less of the metal relative to the total amount of the metal and zeolite.

[0052] 3. Exhaust gas purification During operation of the vehicle 100, exhaust gas generated in the engine 101 is first supplied to the catalyst unit 12. Then, when the vehicle 100 is continuously operated, the exhaust gas purification catalyst in the catalyst unit 12 is heated and activated by the relatively high-temperature exhaust gas. Therefore, the hydrocarbons (HC) contained in the exhaust gas are purified and rendered harmless by the exhaust gas purification catalyst. The rendered harmless exhaust gas then passes through the plasma reactor 3 and is discharged outside the vehicle.

[0053] On the other hand, immediately after starting the engine 101, the exhaust gas supplied to the catalyst unit 12 is at a relatively low temperature (for example, less than 300°C). Therefore, the exhaust gas purification catalyst may not be sufficiently heated and activated. In this case, the hydrocarbons (HC) contained in the exhaust gas may not be purified by the exhaust gas purification catalyst.

[0054] In such a case, exhaust gas containing hydrocarbons (HC) passes through the catalyst unit 12 and is introduced into the plasma reactor 3. Then, the control unit 6 applies a voltage to the electrode 7 of the plasma reactor 3 to generate plasma within the plasma reactor 3. As a result, the hydrocarbons (HC) are oxidized and rendered harmless by the plasma. The exhaust gas is then exhausted from the plasma reactor 3 and released into the atmosphere.

[0055] However, in the exhaust system 1, there is a limit to the decomposition performance of the plasma reactor 3. Therefore, when an amount of hydrocarbons (HC) exceeding the limit of the decomposition performance is supplied to the plasma reactor 3, there is a problem that some of the hydrocarbons (HC) are not decomposed and are released into the atmosphere. Therefore, the above exhaust system 1 controls the exhaust system 1 in the following manner.

[0056] 4. Exhaust system control The following describes the control of the exhaust system 1. The following also describes an embodiment in which the first zeolite in the plasma reactor 3 contains a metal, and the second zeolite in the HC storage device 4 does not contain a metal.

[0057] When the engine 101 is started, the control unit 6 first fixes the valve 5 to position B. That is, the opening degree of the bypass pipe 22 is set to 100%, and the opening degree of the main pipe 21 is set to 0%.

[0058] As a result, exhaust gas generated in the engine 101 passes through the catalytic unit 12, the HC storage device 4, and the plasma reactor 3 in this order. At this time, if the engine 101 has just started, the exhaust gas supplied to the catalytic unit 12 is at a relatively low temperature (for example, less than 300°C). Therefore, in the catalytic unit 12, the exhaust gas purification catalyst is not sufficiently heated, and the hydrocarbons (HC) contained in the exhaust gas are not sufficiently decomposed. As a result, the exhaust gas containing the hydrocarbons (HC) is introduced into the HC storage device 4.

[0059] The HC storage device 4 is equipped with a second zeolite. The second zeolite does not contain metal and has the property of preferentially adsorbing hydrocarbons (HC) with a relatively large carbon number. Therefore, when exhaust gas is supplied to the HC storage device 4, the hydrocarbons (HC) with a relatively large carbon number among the hydrocarbons (HC) contained in the exhaust gas are adsorbed by the second zeolite. On the other hand, the hydrocarbons (HC) with a relatively small carbon number are difficult to adsorb by the second zeolite, and are therefore discharged from the HC storage device 4 and introduced into the plasma reactor 3.

[0060] The plasma reactor 3 is equipped with a first zeolite. The first zeolite contains metal and has the property of preferentially adsorbing hydrocarbons (HC) with a relatively small carbon number. Therefore, when exhaust gas is supplied to the plasma reactor 3, the hydrocarbons (HC) with a relatively small carbon number are adsorbed by the first zeolite and remain in the plasma reactor 3.

[0061] Furthermore, the control unit 6 applies a voltage to the electrode 7 to generate plasma within the plasma reactor 3. As a result, hydrocarbons (HC) having a relatively small number of carbon atoms are decomposed by the plasma.

[0062] In the exhaust system 1, the control unit 6 holds the valve 5 in the above state (position B) for a predetermined time. The holding time is, for example, 10 to 50 seconds, or preferably 20 to 40 seconds.

[0063] After the above-mentioned retention time has elapsed, the temperature of the exhaust gas supplied to the catalytic unit 12 becomes relatively high (for example, 300°C or higher). As a result, the three-way catalyst in the catalytic unit 12 is heated and activated, and the hydrocarbons (HC) contained in the exhaust gas are decomposed in the catalytic unit 12.

[0064] Therefore, after the above-mentioned holding time has elapsed, the control unit 6 changes the valve 5 to position A. That is, the opening degree of the bypass pipe 22 is set to 0%, and the opening degree of the main pipe 21 is set to 100%. As a result, the exhaust gas that has passed through the catalyst unit 12 passes through the main pipe 21 and the plasma reactor 3, and is discharged outside the vehicle.

[0065] At this time, the control unit 6 applies a voltage to the electrode 7 of the plasma reactor 3 to generate plasma within the plasma reactor 3. As a result, the hydrocarbons (HC) with a relatively small carbon number that are retained within the plasma reactor 3 are continuously decomposed.

[0066] In the exhaust system 1, the control unit 6 holds the valve 5 in the above state (position A) for a predetermined time. The holding time is, for example, 10 to 120 seconds, or preferably 30 to 60 seconds.

[0067] When the above-mentioned holding time has elapsed, decomposition of hydrocarbons (HC) having a relatively small carbon number progresses in the plasma reactor 3, and the decomposition capacity of the plasma reactor 3 becomes sufficient.

[0068] Therefore, after the above-mentioned holding time has elapsed, the control unit 6 changes the valve 5 to position B. That is, the opening degree of the bypass pipe 22 is set to 100%, and the opening degree of the main pipe 21 is set to 0%. As a result, the exhaust gas that has passed through the catalyst unit 12 is introduced into the plasma reactor 3 via the bypass pipe 22 and the HC storage device 4.

[0069] At this time, in the HC storage device 4, the second zeolite is heated by the exhaust gas, and the hydrocarbons (HC) having a relatively large carbon number that were adsorbed on the second zeolite are desorbed from the second zeolite. As a result, the hydrocarbons (HC) having a relatively large carbon number are introduced into the plasma reactor 3 and decomposed by the plasma.

[0070] By such control, either the hydrocarbons (HC) with a relatively low carbon number or the hydrocarbons (HC) with a relatively high carbon number can be temporarily stored in the HC storage device 4, and the other can be plasma decomposed in the plasma reactor 3.

[0071] Furthermore, according to the above control, after the decomposition of hydrocarbons (HC) progresses and the plasma reactor 3 has an excess in its decomposition capacity, the hydrocarbons (HC) temporarily stored in the HC storage device 4 can be plasma decomposed in the plasma reactor 3.

[0072] In the above description, the first zeolite of the plasma reactor 3 contains a metal, and the second zeolite of the HC storage device 4 does not contain a metal. However, for example, the first zeolite of the plasma reactor 3 may not contain a metal, and the second zeolite of the HC storage device 4 may contain a metal. In such a case, immediately after the start of the engine 101, the hydrocarbons (HC) having a relatively large carbon number are adsorbed by the second zeolite of the HC storage device 4, and the hydrocarbons (HC) having a relatively small carbon number are adsorbed by the first zeolite of the plasma reactor 3. Then, after the hydrocarbons (HC) having a relatively small carbon number are decomposed in the plasma reactor 3, the hydrocarbons (HC) having a relatively large carbon number are desorbed from the second zeolite and introduced into the plasma reactor 3, where they are decomposed by the plasma.

[0073] 5. Effects In the above exhaust system 1, only one of the plasma reactor 3 and the HC storage device 4 is equipped with zeolite containing metal, and the other is equipped with zeolite not containing metal. Therefore, among the hydrocarbons (HC) passing through the exhaust pipe, either the hydrocarbons (HC) with a relatively small carbon number or the hydrocarbons (HC) with a relatively large carbon number is adsorbed by the second zeolite of the HC storage device 4 arranged on the more upstream side. The other is adsorbed by the first zeolite of the plasma reactor 3 arranged on the more downstream side. In other words, when the engine starts, a part of the hydrocarbons (HC) passing through the exhaust pipe 2 is adsorbed by the HC storage device 4, and only the remainder is decomposed by the plasma reactor 3. In addition, when the exhaust gas temperature rises due to the continuous operation of the engine, the hydrocarbons (HC) adsorbed by the HC storage device 4 are released and decomposed by the plasma reactor 3. In other words, the hydrocarbons (HC) are divided and supplied to the plasma reactor 3. Therefore, according to the above configuration, it is possible to prevent an amount of hydrocarbons (HC) exceeding the limit of the decomposition performance of the plasma reactor 3 from being supplied to the plasma reactor 3, and the hydrocarbons (HC) can be efficiently decomposed in the plasma reactor 3. Therefore, the above exhaust system 1 has excellent exhaust gas purification performance.

[0074] 6. Variations In the above description, the exhaust pipe 2 includes the main pipe 21 and the bypass pipe 22, but as shown in Fig. 2, the exhaust pipe 2 does not need to include the bypass pipe 22. In this case, the plasma reactor 3 is interposed in the main pipe 21, and the HC storage device 4 is interposed in the main pipe 21 on the upstream side of the plasma reactor 3.

[0075] Even in such an embodiment, immediately after the start of the engine 101, of the hydrocarbons (HC) contained in the exhaust gas, either the hydrocarbons (HC) with a relatively low carbon number or the hydrocarbons (HC) with a relatively high carbon number is adsorbed by the second zeolite in the HC storage device 4 and temporarily stored therein, and the other is plasma decomposed in the plasma reactor 3.

[0076] Then, when the temperature of the exhaust gas becomes relatively high (for example, 300° C. or higher), the hydrocarbons (HC) adsorbed in the second zeolite in the HC storage device 4 are released and introduced into the plasma reactor 3 where they are decomposed by plasma.

[0077] That is, according to the above exhaust system 1, hydrocarbons (HC) with a relatively low carbon number and hydrocarbons (HC) with a relatively high carbon number can be sequentially introduced into the plasma reactor 3 and decomposed by plasma. Therefore, the above exhaust system 1 has excellent exhaust gas purification performance.

[0078] Preferably, the exhaust pipe 2 includes a main pipe 21 and a bypass pipe 22, and the HC storage device 4 is disposed in the bypass pipe 22. With such a configuration, the amount of hydrocarbons (HC) introduced into the plasma reactor 3 can be adjusted as desired by controlling the opening and closing of the valve 5, thereby improving the efficiency of exhaust gas purification.

[0079] In addition, the first zeolite and / or the second zeolite can contain a precious metal in addition to the above-mentioned metals (transition metals). Examples of the precious metal include platinum, palladium, and rhodium. If the first zeolite and / or the second zeolite contain a precious metal, the exhaust gas purification performance can be improved in the plasma reactor 3 and / or the HC storage device 4.

[0080] In the above exhaust system 1, only one of the first zeolite (plasma reactor 3) and the second zeolite (HC storage device 4) contains a metal, and the other does not contain the first metal. However, for example, either the first zeolite (plasma reactor 3) or the second zeolite (HC storage device 4) may contain a first metal, and the other of the first zeolite or the second zeolite may contain a second metal having a composition different from that of the first metal.

[0081] The first metal and the second metal are not particularly limited as long as they are metals with different compositions. Examples of the metal include the above-mentioned transition metals and the above-mentioned noble metals. The first metal and the second metal may be a metal element or a metal composition. These may be used alone or in combination of two or more kinds.

[0082] For example, when the first zeolite (plasma reactor 3) contains only the above-mentioned transition metal as the first metal, the second zeolite (HC storage device 4) can contain, as the second metal, a metal composition containing the above-mentioned transition metal and the above-mentioned precious metal.

[0083] In addition, when the first zeolite (plasma reactor 3) contains only the above transition metal as the first metal, the second zeolite (HC storage device 4) can contain the above noble metal as the second metal without containing the above transition metal.

[0084] In the above-mentioned case, both the first zeolite and the second zeolite chemically adsorb the hydrocarbons (HC) due to the influence of the metal. The carbon number of the chemically adsorbed hydrocarbons (HC) differs depending on the type of metal contained in the zeolite. In other words, the carbon number of the hydrocarbons that are easily adsorbed by the zeolite containing the first metal is different from the carbon number of the hydrocarbons that are easily adsorbed by the zeolite containing the second metal.

[0085] Therefore, in the above-described exhaust system 1, one of the first zeolite and the second zeolite is more likely to adsorb and release hydrocarbons (HC) with a relatively small carbon number, and the other is more likely to adsorb and release hydrocarbons (HC) with a relatively large carbon number.

[0086] That is, in the above exhaust system 1, either the plasma reactor 3 (first zeolite) or the HC storage device 4 (second zeolite) is provided with a zeolite containing a first metal, and the other is provided with a zeolite containing a second metal having a composition different from that of the first metal. Therefore, among the hydrocarbons (HC) passing through the exhaust pipe, either one of the hydrocarbons (HC) having a relatively small carbon number is adsorbed by the second zeolite of the HC storage device 4 arranged on the more upstream side. Also, the other is adsorbed by the first zeolite of the plasma reactor 3 arranged on the more downstream side. That is, when the engine starts, a part of the hydrocarbons (HC) passing through the exhaust pipe 2 is adsorbed by the HC storage device 4, and only the remainder is decomposed by the plasma reactor 3. Also, when the exhaust gas temperature rises due to the continuous operation of the engine, the hydrocarbons (HC) adsorbed by the HC storage device 4 are released and decomposed by the plasma reactor 3. That is, the hydrocarbons (HC) are divided and supplied to the plasma reactor 3. Therefore, according to the above configuration, it is possible to prevent an amount of hydrocarbons (HC) exceeding the limit of the decomposition performance of the plasma reactor 3 from being supplied to the plasma reactor 3, and the hydrocarbons (HC) can be efficiently decomposed in the plasma reactor 3. Therefore, the above exhaust system 1 has excellent exhaust gas purification performance.

[0087] Furthermore, the combination of the first metal and the second metal is not limited to the above.For example, when the second zeolite (HC storage device 4) contains only the above transition metal as the first metal, the first zeolite (plasma reactor 3) can contain a metal composition containing the above transition metal and the above precious metal as the second metal.

[0088] In addition, when the second zeolite (HC storage device 4) contains only the above transition metal as the first metal, the first zeolite (plasma reactor 3) can contain the above noble metal as the second metal without containing the above transition metal.

[0089] Furthermore, for example, when the first zeolite (plasma reactor 3) contains a metal composition containing a transition metal and a precious metal as the first metal, the second zeolite (HC storage device 4) can contain only a precious metal as the second metal without containing a transition metal.

[0090] In addition, when the second zeolite (HC storage device 4) contains a metal composition containing a transition metal and a precious metal as the first metal, the first zeolite (plasma reactor 3) can contain only a precious metal as the second metal without containing a transition metal.

[0091] In these embodiments, either the plasma reactor 3 or the HC storage device 4 includes a zeolite containing a first metal, and the other includes a zeolite containing a second metal having a composition different from that of the first metal. Therefore, among the hydrocarbons (HC) passing through the exhaust pipe, either one of the hydrocarbons (HC) having a relatively small carbon number is adsorbed by the second zeolite of the HC storage device 4 arranged on the more upstream side. Also, the other is adsorbed by the first zeolite of the plasma reactor 3 arranged on the more downstream side. That is, when the engine is started, a part of the hydrocarbons (HC) passing through the exhaust pipe 2 is adsorbed by the HC storage device 4, and only the remainder is decomposed by the plasma reactor 3. Also, when the exhaust gas temperature rises due to the continuous operation of the engine, the hydrocarbons (HC) adsorbed by the HC storage device 4 are released and decomposed by the plasma reactor 3. That is, the hydrocarbons (HC) are divided and supplied to the plasma reactor 3. Therefore, according to the above configuration, it is possible to prevent an amount of hydrocarbons (HC) exceeding the limit of the decomposition performance of the plasma reactor 3 from being supplied to the plasma reactor 3, and the hydrocarbons (HC) can be efficiently decomposed in the plasma reactor 3. Therefore, the above exhaust system 1 has excellent exhaust gas purification performance. [Explanation of symbols]

[0092] 1 Exhaust system 2 Exhaust pipe 3. Plasma Reactor 4. Bypass pipe 5 Valve 6. Control Unit

Claims

1. an exhaust pipe for discharging exhaust gas discharged from the engine; a plasma reactor disposed in the exhaust pipe to adsorb and decompose hydrocarbons (HC) contained in the exhaust gas; a hydrocarbon (HC) storage device disposed in the exhaust pipe upstream of the plasma reactor and configured to adsorb and release hydrocarbons (HC); a valve for adjusting the flow rate of the exhaust gas; Equipped with The exhaust pipe is A main pipe for discharging exhaust gas discharged from the engine; a bypass pipe branching off from the main pipe between the engine and the plasma reactor and bypassing the main pipe; Equipped with the plasma reactor comprises a first zeolite that adsorbs hydrocarbons (HC); The HC storage device includes a second zeolite interposed in the bypass pipe and configured to adsorb hydrocarbons (HC); the valve is disposed in the exhaust pipe so as to be capable of adjusting a flow rate of exhaust gas flowing through the bypass pipe, An exhaust system, wherein either the first zeolite or the second zeolite contains a metal.

2. an exhaust pipe for discharging exhaust gas discharged from the engine; a plasma reactor disposed in the exhaust pipe to adsorb and decompose hydrocarbons (HC) contained in the exhaust gas; a hydrocarbon (HC) storage device disposed in the exhaust pipe upstream of the plasma reactor and configured to adsorb and release hydrocarbons (HC); a valve for adjusting the flow rate of the exhaust gas; Equipped with The exhaust pipe is A main pipe for discharging exhaust gas discharged from the engine; a bypass pipe branching off from the main pipe between the engine and the plasma reactor and bypassing the main pipe; Equipped with the plasma reactor comprises a first zeolite that adsorbs hydrocarbons (HC); The HC storage device includes a second zeolite interposed in the bypass pipe and configured to adsorb hydrocarbons (HC); the valve is disposed in the exhaust pipe so as to be capable of adjusting a flow rate of exhaust gas flowing through the bypass pipe, Either the first zeolite or the second zeolite contains a first metal; an exhaust system, wherein the other of said first zeolite or said second zeolite contains a second metal having a composition different from that of said first metal;

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