JP2012012952A - Exhaust purification system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust purification system that improves a purification performance at a low temperature right after an internal combustion engine is started in a plasma generation device and a fuel reformer in the exhaust purification system including an NOx adsorption catalyst.SOLUTION: The exhaust purification system 1 includes: the NOx adsorption catalyst 42 that is disposed in an exhaust pipe 4 and catches an emitted NOx; a plasma reactor 43 for oxidizing the emitted NOx flowing into the NOx adsorption catalyst 42; the fuel reformer 5 for generating a reformed gas including hydrogen by a reforming catalyst from fuel and air; a glow plug for heating reforming catalyst; and an ECU7 for driving the plasma reactor 43 at the start of an engine and driving the glow plug and starting to heat the reforming catalyst while starting to oxidizing the emitted NOx of the engine 2.

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine. Specifically, the present invention relates to an exhaust gas purification system for an internal combustion engine that includes a NOx trapping catalyst that traps NOx in the exhaust gas of the internal combustion engine.

  The exhaust discharged from the internal combustion engine contains NOx. As a technique for adsorbing NOx contained in the exhaust gas and purifying the exhaust gas, a technique for providing a NOx adsorption catalyst containing alkali metal, alkaline earth metal, platinum and the like disposed in the exhaust passage has been proposed. . This NOx adsorption catalyst has a problem of lowering NOx purification performance at low temperatures, and various techniques have been proposed to solve this problem.

For example, in Patent Document 1, paying attention to the characteristic that NO ₂ is better adsorbed to the NOx adsorption catalyst than NO, a plasma generator that oxidizes NO in the exhaust and generates NO ₂ is provided upstream of the NOx adsorption catalyst. A technique for improving the purification performance of a NOx adsorption catalyst is shown.

  NOx adsorption catalysts are also known to exhibit good adsorption performance from low temperatures in a hydrogen atmosphere. As a technique for supplying hydrogen into exhaust gas, a fuel reformer that reforms fuel of an internal combustion engine to generate hydrogen has been proposed (see Patent Document 2).

Japanese Patent Laid-Open No. 11-324652 JP 2009-196837 A

  As described above, although it is known that the performance of the NOx adsorption catalyst can be improved by using a plasma generator and a fuel reformer, an exhaust purification system combining these two devices has not been proposed in the past. In addition, the optimal control procedure has not been deeply studied.

  It is an object of the present invention to provide an exhaust purification system having an improved NOx purification performance at a low temperature immediately after starting an internal combustion engine with a plasma generator and a fuel reformer in an exhaust purification system equipped with a NOx trapping catalyst. To do.

  In order to achieve the above object, the present invention is provided in an exhaust passage (for example, an exhaust pipe 4 to be described later) of an internal combustion engine (for example, an engine 2 to be described later) and captures NOx in the exhaust (for example, to be described later). An exhaust gas purification system for an internal combustion engine (for example, an exhaust gas purification system 1 described later) is provided. The exhaust purification system includes a plasma generating means (for example, a plasma reactor 43 described later) that oxidizes NOx in exhaust flowing into the NOx trapping catalyst, and a reforming catalyst (for example, a reforming catalyst 52 described later) from fuel and air. ) To generate a reformed gas containing hydrogen, and supply the generated gas into the exhaust gas flowing into the NOx trapping catalyst (for example, a fuel reformer 5 described later), and the reforming catalyst And heating means (for example, a glow plug 55 described later), and at the start of the internal combustion engine, the plasma generation means is driven to start oxidation of NOx in the exhaust gas of the internal combustion engine, and the heating means is driven. And a control means (for example, ECU 7 described later) for starting the heating of the reforming catalyst.

In the present invention, a NOx trapping catalyst for trapping NOx in the exhaust is provided in the exhaust passage, and plasma generating means for oxidizing NOx in the exhaust flowing into the NOx trapping catalyst, and hydrogen containing in the exhaust flowing into the NOx trapping catalyst are provided. And a fuel reformer for supplying the reformed gas. Although the majority of the NOx in the exhaust immediately below the internal combustion engine is NO, the plasma generation means, by generating the oxidized NO ₂ to NO in the exhaust gas flowing into the NOx trap catalyst, NOx immediately after internal combustion engine startup The purification performance of the capture catalyst can be improved. Also, the purification performance of the NOx trapping catalyst immediately after starting the internal combustion engine is improved by supplying the hydrogen-containing reformed gas generated by the fuel reformer to the exhaust passage and making the NOx trapping catalyst coexist with hydrogen. Can do.
Particularly in the present invention, when starting the internal combustion engine, the plasma generating means is driven to start oxidation of NOx in the exhaust gas, and the heating means is driven to start heating the reforming catalyst. Thus, after the start of the internal combustion engine, while the reforming catalyst is heated, the ratio of NO ₂ in the NOx in the exhaust flowing into the NOx trapping catalyst can be increased. The reduction in the NOx purification rate of the NOx trapping catalyst can be suppressed. Therefore, after the start of the internal combustion engine, the temperature of the reforming catalyst reaches its activation temperature and the reforming gas can be generated by the fuel reformer. A temporary decrease in the NOx purification rate can be suppressed.

  In this case, it further comprises reformer temperature acquisition means (for example, a reforming catalyst temperature sensor 93 and ECU 7 described later) for acquiring the temperature of the fuel reformer, and the control means is based on the acquired temperature, It is preferable to start supplying fuel and air to the reforming catalyst.

  In the present invention, the temperature of the fuel reformer is acquired, and the supply of fuel and air to the reforming catalyst is started based on this temperature. For example, the reforming catalyst has not reached its activation temperature. Thus, it is possible to avoid the problem that the fuel is supplied and the unburned fuel flows into the exhaust passage.

In this case, the NOx trapping catalyst preferably supports at least Ag.
In the present invention, by using the NOx trapping catalyst supporting at least Ag, it is possible to improve the NOx trapping performance of the NOx trapping catalyst at a low temperature such as immediately after starting the internal combustion engine. In particular, the NOx trapping performance in the presence of hydrogen can be improved.

It is a figure which shows the structure of the engine which concerns on one Embodiment of this invention, and its exhaust gas purification system. It is a figure which shows the relationship between the NOx purification rate in the non-coexistence of hydrogen, and temperature of the NOx adsorption catalyst which concerns on the said embodiment. It is a figure which shows the relationship between the NOx purification rate in the coexistence of hydrogen, and temperature of the NOx adsorption catalyst which concerns on the said embodiment. It is a figure which compares the relationship between the NOx purification rate of the NOx adsorption catalyst which concerns on the said embodiment, and temperature by coexistence with hydrogen and non-coexistence. It is a figure which shows the density | concentration for every component of NOx in the exhaust_gas | exhaustion of the downstream of the plasma reactor which concerns on the said embodiment. It is sectional drawing which shows the structure of the fuel reformer which concerns on the said embodiment. It is a flowchart which shows the control procedure of the fuel reformer and plasma reactor which concern on the said embodiment. It is a figure which shows the hydrogenation area | region which concerns on the said embodiment. It is a time chart which shows the example of control of the fuel reformer and plasma reactor which concern on the said embodiment.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic diagram showing a configuration of an internal combustion engine (hereinafter referred to as “engine”) 2 according to the present embodiment and an exhaust purification system 1 that purifies the exhaust thereof. The engine 2 is a diesel engine that directly injects fuel into the combustion chamber of each cylinder 21. The fuel injection amount from the injector provided for each cylinder 21 of the engine 2 is set by an electronic control unit (hereinafter referred to as “ECU”) 7 described later. Further, the valve opening time of the injector is controlled by a drive signal from the ECU 7 so that a set fuel injection amount can be obtained.

  The engine 2 is provided with an intake pipe 3 through which intake air flows, an exhaust pipe 4 through which exhaust flows, and a supercharger 6 that pumps intake air into the intake pipe 3. The intake pipe 3 is connected to the intake port of each cylinder 21 of the engine 2 through a plurality of branch portions of the intake manifold 31. The exhaust pipe 4 is connected to the exhaust port of each cylinder 21 of the engine 2 through a plurality of branch portions of the exhaust manifold 41. The supercharger 6 includes a turbine that is driven by kinetic energy of exhaust gas that flows through the exhaust pipe 4, and a compressor that is rotationally driven by the turbine and pressurizes intake air in the intake pipe 3. A throttle valve 32 for controlling the intake air amount of the engine 2 is provided on the upstream side of the intake pipe 3. The throttle valve 32 is connected to the ECU 7 via an actuator, and its opening degree is electromagnetically controlled by the ECU 7.

  The exhaust pipe 4 is provided with a plasma reactor 43 as a plasma generation unit and a NOx adsorption catalyst 42 as a NOx trapping catalyst in order from the upstream side. A reformed gas supply passage 59 for supplying hydrogen-containing reformed gas generated by a fuel reformer 5 described later into the exhaust pipe 4 is connected to the upstream side of the plasma reactor 43 in the exhaust pipe 4. ing.

  The NOx adsorption catalyst 42 purifies the exhaust gas by oxidizing and capturing NOx in the exhaust gas. Here, “capturing” in the present invention means including any of adsorption, absorption, and occlusion. The NOx adsorption catalyst 42 is a catalyst supporting Ag as an active species. More specifically, the NOx adsorption catalyst 42 is a catalyst comprising at least one oxide selected from the group consisting of alumina, zirconia, and ceria in addition to Ag. The NOx adsorption catalyst 42 having such a composition oxidizes and captures NOx from a low temperature region of 200 ° C. or lower, for example.

Ag contained in the NOx adsorption catalyst 42 is in a reduced silver state in the presence of hydrogen (see the following formula (1)). Reduced silver has a higher ability to oxidize and adsorb NOx than the state of metallic silver or silver oxide. Specifically, the reduced silver donates electrons to oxygen, and the oxygen that is donated with electrons oxidizes NOx in the exhaust gas, and the oxidized NOx is captured by alumina or the like as NO ₃ ⁻ . For this reason, even at a low temperature of 200 ° C. or lower, NOx (NO and NO ₂ ) in the exhaust can be oxidized and adsorbed (see the following formulas (2) and (3)). In the following formula, Ag (*) represents reduced silver, and (ad.) Represents adsorption to the NOx adsorption catalyst 42.
Formula (1): AgO + H ₂ → Ag (*) + H ₂ + O ₂
Formula (2): NO + O ₂ + Ag (*) → NO ₃ (ad.) + Ag (*)
Formula (3): 2NO ₂ + O ₂ + Ag (*) → 2NO ₃ (ad.) + Ag (*)

The NOx purification performance in the low temperature region (200 ° C. or lower) of the NOx adsorption catalyst 42 using Ag as an active species as described above will be described with reference to FIGS.
FIG. 2 is a graph showing the relationship between the NOx purification rate of the NOx adsorption catalyst and the temperature in the absence of hydrogen. 2, the broken line shows a case where the NOx in the exhaust gas only NO, a solid line indicates the case where the NOx in the exhaust gas only in NO _2. At this time, the hydrogen concentration in the exhaust gas was set to 0 [ppm], and the oxygen concentration was set to 10 [volume%].

As indicated by the broken line, the purification rate for NOx composed only of NO is substantially zero. That is, when the NOx adsorption catalyst is in a low temperature region of 200 ° C. or lower, NO in the exhaust gas is hardly adsorbed by the NOx adsorption catalyst. On the other hand, as shown by the solid line, when NOx in the exhaust gas is composed of only NO ₂ , the NOx adsorption catalyst exhibits significant NOx purification performance.
As described above, according to the NOx adsorption catalyst, the NOx purification rate is obtained by changing the main component of NOx in the exhaust gas to NO ₂ even in a low temperature region of 200 ° C. or less and in the absence of hydrogen. Can be high.

FIG. 3 is a graph showing the relationship between the NOx purification rate of the NOx adsorption catalyst and the temperature in the presence of hydrogen. In FIG. 3, the broken line indicates a case where NOx in the exhaust is composed of only NO, and the solid line indicates a case where NOx in the exhaust is composed of NO ₂ and NO of the same volume. At this time, the hydrogen concentration in the exhaust gas was set to 5000 [ppm], and the oxygen concentration was set to 10 [volume%].
As can be seen from a comparison between FIG. 3 and FIG. 2 described above, when hydrogen is added to the exhaust, the NOx purification performance by the NOx adsorption catalyst in a low temperature region of 200 ° C. or lower is improved regardless of the NOx component. More specifically, when NOx in the exhaust is composed of only NO, the NOx purification rate is almost zero over the entire temperature range of 200 ° C. or less in the absence of hydrogen, whereas in the presence of hydrogen, It shows a NOx purification rate close to 100% from around 130 ° C. Further, in addition to the addition of hydrogen, when the proportion of NO ₂ in the NOx in the exhaust gas is further increased, as shown by the solid line, significant NOx purification performance is exhibited from 50 ° C. or lower.
As described above, according to the NOx adsorption catalyst, the NOx purification rate can be increased by adding hydrogen to the exhaust gas even in a low temperature region of 200 ° C. or lower. By increasing the proportion of NO ₂ among the components of the upper NOx, it is possible to further increase the NOx purification rate.

FIG. 4 is a diagram comparing the relationship between the NOx purification rate of the NOx adsorption catalyst and the temperature in the presence and absence of hydrogen. In FIG. 4, the broken line shows the case where hydrogen is not added to the exhaust gas, and the solid line shows the case where 5000 ppm of hydrogen is added to the exhaust gas. Incidentally, the oxygen concentration in the exhaust gas at this time is 10 [vol%], and constitute a NOx only in NO _2.
As shown in FIG. 4, by configuring NOx in the exhaust only with NO ₂ , it can be purified with a NOx adsorption catalyst even at 200 ° C. or lower, but in addition to this, by adding hydrogen, Furthermore, the NOx purification rate can be improved.

Returning to FIG. 1, the plasma reactor 43 generates plasma when energized, thereby oxidizing NOx in the exhaust gas flowing through the exhaust pipe 4. By providing such a plasma reactor 43 on the upstream side of the NOx adsorption catalyst 42, the NOx in the exhaust gas flowing into the NOx adsorption catalyst 42 is oxidized, the amount of NO that is difficult to adsorb at low temperatures is reduced, and NO ₂ that is easy to adsorb. Increase the amount. As the plasma reactor 43, known ones such as a corona discharge type, a pulse discharge type, and a barrier discharge type can be applied.

FIG. 5 is a diagram comparing the concentration of each NOx component (NO and NO ₂ ) in the exhaust downstream of the plasma reactor, that is, in the exhaust flowing into the NOx adsorption catalyst, when not energized and when energized. As shown on the left side in FIG. 5, the exhaust when the plasma reactor is not energized, that is, the exhaust immediately below the engine 2 contains much more NO than NO ₂ . On the other hand, by energizing the plasma reactor to generate plasma, almost all NO in the exhaust gas can be oxidized and NO ₂ can be generated as shown on the right side in FIG.

  Returning to FIG. 1, the fuel reformer 5 includes a reformer body 51 including a reforming catalyst 52, and a raw material supply device 56 that supplies the reforming catalyst 52 with a raw material composed of fuel and air. , Including.

  The raw material supply device 56 mixes the fuel stored in the fuel tank 23 and the air supplied by the compressor 24 at a predetermined ratio to produce a raw material, and supplies this to the reformer body 51. The raw material supply device 56 includes an air valve 57 that controls the amount of air supplied to the reformer main body 51 and a fuel valve 58 that controls the amount of fuel supplied to the reformer main body 51. Composed. The air valve 57 and the fuel valve 58 are connected to the ECU 7 via actuators (not shown), respectively, and the amount of air supplied to the reformer main body 51, the amount of fuel, and the amount of air relative to the amount of fuel. The ratio is controlled by the ECU 7.

FIG. 6 is a cross-sectional view showing the configuration of the reformer body 51.
The reformer body 51 includes a cylindrical reforming catalyst 52, a cylindrical casing 53 that accommodates the reforming catalyst 52, and an injection that injects a fuel / air mixture into the reforming catalyst 52 in the casing 53. The apparatus 54 includes a glow plug 55 provided at the center of the reforming catalyst 52.

The injection device 54 mixes the fuel and air supplied from the raw material supply device 56 and injects the atomized fuel from the upper end side of the reforming catalyst 52 toward the center.
The glow plug 55 is provided to face the injection device 54 so that the heat generating portion is located at the center of the reforming catalyst 52. The glow plug 55 generates heat when energized, and heats the reforming catalyst 52 from the center side.

  The reforming catalyst 52 includes at least one metal catalyst component selected from the group consisting of rhodium, platinum, palladium, nickel, and cobalt, and at least one oxidation selected from the group consisting of ceria, zirconia, alumina, and titania. Or a composite oxide based on these. The reforming catalyst 52 reforms the atomized fuel injected from the injection device 54 by a partial oxidation reaction to generate a reformed gas containing a reducing gas such as hydrogen, carbon monoxide, and light hydrocarbons. To do. The generated reformed gas is supplied to the upstream side of the plasma reactor 43 in the exhaust pipe 4 via the reformed gas supply passage 59 formed in the casing 53 (see FIG. 1 described above).

  Returning to FIG. 1, the ECU 7 is connected with a reforming catalyst temperature sensor 93, a crank angle position sensor 94, an accelerator opening sensor 95, an ignition switch 96, and the like. The reforming catalyst temperature sensor 93 detects the temperature of the reforming catalyst 52 of the fuel reformer 5 and transmits a signal substantially proportional to the detected value to the ECU 7. The ECU 7 can acquire the temperature of the reforming catalyst 52 based on the output from the reforming catalyst temperature sensor 93. The crank angle position sensor 94 transmits a pulse signal indicating the crank angle of the engine 2 to the ECU 7. The accelerator opening sensor 95 detects the opening of the accelerator pedal of the vehicle and transmits a signal substantially proportional to the detected value to the ECU 7. The ignition switch 96 is provided in a driver's seat of a vehicle (not shown), and transmits a signal for instructing starting or stopping of the engine to the ECU 7. Here, the rotational speed of the engine 2 indicating the operating state of the engine 2 is calculated by the ECU 7 based on the pulse signal transmitted from the crank angle position sensor 94, and the generated torque of the engine 2 is calculated based on the fuel injection amount. Is calculated by The fuel injection amount is calculated by the ECU 7 based on the output of the accelerator opening sensor 95.

  The ECU 7 shapes an input signal waveform from various sensors, corrects a voltage level to a predetermined level, converts an analog signal value into a digital signal value, and a central processing unit (hereinafter referred to as a central processing unit). "CPU"). In addition, the ECU 7 includes a storage circuit that stores various calculation programs executed by the CPU, calculation results, and the like, and an output circuit that outputs control signals to the injector, the fuel reformer 5, the plasma reactor 43, and the like. .

Hereinafter, the procedure for controlling the fuel reformer and the plasma reactor by the ECU 7 will be described with reference to FIGS.
FIG. 7 is a flowchart showing a control procedure of the fuel reformer and the plasma reactor. A series of processing shown in this flowchart is executed by the ECU 7 in response to detection of engine start by the ignition switch.

  In S1, it is determined whether or not the operating state of the engine belongs to a predetermined hydrogen addition region. Here, the hydrogen addition region refers to a region of the engine operating state where it can be determined that it is necessary to improve the purification performance of the NOx adsorption catalyst by supplying the hydrogen-containing reformed gas generated by the fuel reformer. . In this embodiment, the operating state of the engine is defined based on two parameters, the generated torque and the engine speed. In this case, the hydrogen addition region is defined as a low torque region where the engine exhaust temperature tends to be low as shown in FIG. More specifically, the hydrogen addition region is defined as a region where the generated torque is lower than the torque determination line defined according to the engine speed.

  If the determination in S1 is YES and the engine operating state belongs to the hydrogen addition region, the process proceeds to S2, and it is determined whether or not the reforming catalyst is in an activated state. This discrimination is performed by discriminating whether or not the temperature of the reforming catalyst acquired based on the output of the reforming catalyst temperature sensor is higher than the activation temperature of the reforming catalyst as described above.

  When the determination of S2 is NO, that is, when the temperature of the reforming catalyst has not reached its activation temperature, such as when the engine is started, the glow plug is energized (see S3) and the reforming catalyst is heated. Then, the plasma reactor is energized (see S4), and the NOx in the exhaust gas flowing into the NOx adsorption catalyst is oxidized.

  On the other hand, if the determination in S2 is YES and the temperature of the reforming catalyst has reached the activation temperature, energization to the glow plug is stopped (see S5), and fuel and air are supplied to the reforming catalyst. As a result, the reformed gas is generated (see S6), and the current supply to the plasma reactor is stopped (see S7).

  On the other hand, if the determination in S1 is NO and the operating state of the engine does not belong to the hydrogen addition region, it is determined that it is not necessary to supply hydrogen to the NOx adsorption catalyst, and the process proceeds to S8. In S8, the supply of fuel and air to the reforming catalyst is stopped or restricted, the supply of reformed gas to the NOx adsorption catalyst is stopped, and the energization to the plasma reactor is stopped (see S7).

FIG. 9 is a time chart showing a control example of the fuel reformer and the plasma reactor according to the flowchart.
First, in response to the ignition being turned on at time t0, a series of processes shown in the flowchart is started. At this time, it is determined that the operating state of the engine belongs to the hydrogenation region (see S1), and it is further determined that the temperature of the reforming catalyst is lower than the activation temperature (see S2). Energization is started (see S3). Thereby, the temperature of the reforming catalyst starts to rise rapidly. At this time, energization of the glow plug is started and energization of the plasma reactor is also started (see S4). Thus, it oxidizes NO in the exhaust gas flowing into the NOx adsorption catalyst to produce an NO _2. As shown in FIG. 2, immediately after the engine is started and the NOx adsorption catalyst is at a low temperature, NO ₂ is better adsorbed to the NOx adsorption catalyst than NO, so that the reformer cannot be supplied by the fuel reformer. A decrease in the NOx purification rate of the NOx adsorption catalyst can be prevented.

Next, in response to the determination that the temperature of the reforming catalyst exceeds its activation temperature at time t1 (see S3), the energization to the glow plug is stopped (see S5), and the fuel to the reforming catalyst is determined. Then, the supply of air is started (see S6). Then, the hydrogen concentration of the exhaust gas flowing into the NOx adsorption catalyst starts to increase. Thus, by supplying the hydrogen-containing reformed gas to the exhaust gas and making the NOx adsorption catalyst coexist with hydrogen, as shown in FIG. 3, both NO and NO ₂ are favorably adsorbed by the NOx adsorption catalyst. Become. For this reason, it is determined that NOx can be sufficiently purified by the NOx adsorption catalyst without oxidizing NO in exhaust gas and generating NO ₂ in the plasma reactor, and energization to the plasma reactor is stopped (see S7).

  It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.

  In the above embodiment, the exhaust purification system in which the plasma reactor 43 and the NOx adsorption catalyst 42 are provided in the exhaust pipe 4 has been described as an example, but the present invention is not limited to this. A NOx purification catalyst that reduces NOx may be further provided on the downstream side of the NOx adsorption catalyst 42. Thereby, the NOx adsorbed by the NOx adsorption catalyst can be appropriately reduced by the downstream NOx purification catalyst, so that the exhaust gas can be continuously purified.

  Moreover, in the said embodiment, although the temperature of the reforming catalyst 52 was acquired directly based on the output of the reforming catalyst temperature sensor 93, it is not restricted to this. For example, the temperature of the reforming catalyst 52 can be indirectly acquired based on the internal resistance value of the glow plug.

  Further, in the above embodiment, the reformed gas generated by the fuel reformer 5 is supplied to the upstream side of the plasma reactor 43 in the exhaust pipe 4, but the position where the reformed gas is supplied is the NOx adsorption catalyst 42. It is not limited to this as long as it is upstream. For example, the exhaust pipe 4 may be supplied between the plasma reactor 43 and the NOx adsorption catalyst 42.

In the above embodiment, when the reformed gas is supplied by the fuel reformer in S7, the plasma reactor is turned off in the subsequent S8. However, the present invention is not limited to this. As described with reference to FIGS. 2 to 4, the purification rate of the low-temperature NOx adsorption catalyst can be further improved by oxidizing NO into NO ₂ and adding hydrogen in the plasma reactor. Therefore, the plasma reactor may be turned on while supplying the reformed gas from the fuel reformer.

DESCRIPTION OF SYMBOLS 1 ... Exhaust purification system 2 ... Engine (internal combustion engine)
4 ... Exhaust pipe (exhaust passage)
42 ... NOx adsorption catalyst (NOx trapping catalyst)
43 ... Plasma reactor (plasma generating means)
5 ... Fuel reformer 52 ... Reforming catalyst 55 ... Glow plug (heating means)
7 ... ECU (control means, reformer temperature acquisition means)
93 ... Reforming catalyst temperature sensor (reformer temperature acquisition means)

Claims (3)

An exhaust purification system for an internal combustion engine provided with an NOx trapping catalyst that is provided in an exhaust passage of the internal combustion engine and traps NOx in the exhaust,
Plasma generating means for oxidizing NOx in the exhaust gas flowing into the NOx trapping catalyst;
A fuel reformer that generates a reformed gas containing hydrogen from a fuel and air with a reforming catalyst, and supplies the generated gas into the exhaust gas flowing into the NOx trapping catalyst;
Heating means for heating the reforming catalyst;
A control means for driving the plasma generating means to start oxidation of NOx in the exhaust gas of the internal combustion engine and driving the heating means to start heating the reforming catalyst when starting the internal combustion engine; An exhaust gas purification system for an internal combustion engine. Further comprising reformer temperature acquisition means for acquiring the temperature of the fuel reformer,
2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the control unit starts supplying fuel and air to the reforming catalyst based on the acquired temperature.   The exhaust purification system for an internal combustion engine according to claim 1 or 2, wherein the NOx trapping catalyst carries at least Ag.

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